Design of Remote Endoscopic
Suturing Device
By
Prasanga D. Hiniduma Lokuge
Bachelor of Science in Chemical Engineering
Massachusetts Institute of Technology
Class of 2000
Submitted to the Department of Mechanical Engineering
in Partial Fulfillment of the Requirements for the Degree of
Master of Science in Mechanical Engineering
at the
Massachusetts Institute of Technology
MASSACHUSETTS INSTITUTE
OF TECHNOLOGY
June 2003
JUL 0 8 2003
LIBRARIES
©2003 Massachusetts Institute of Technology
All rights reserved
Signature of Author...................................................
Departmenvof Mecl anical Engineering
June 23, 2003
C ertified by ..........................................
Ernesto E.3re
Adjunct Professor of Mechanical Engineering
Thesis Supervisor
Accepted by..............................
.........................
Ain A. Sonin
Students
on
Graduate
Chairman, Departments Committee
BARKER
I
To
Amma
& Daddy
and
tfhe fire that burns in us afl..
2
Acknowledgements
In every person's life there comes an Oscar moment when they can look back on an
achievement and thank the people that helped them get there. This is one of my Oscar
moments.
The two years I have spent on this thesis have been nothing if not eventful. I have met
several folks along the way, some of whom were mere passersby and others who have
walked with me a distance. Some have unintentionally contributed to my personal
development while others have invested a significant amount of time to help me get to
where I am today.
Thank you...
To Professor Rohan Abeyaratne for convincing me to give graduate school a chance; and
to John Zentgraf and Betsy Mueller of the Guidant Corporation and Dean Colbert of the
GSO for taking a chance on me. Their generous fellowships enabled me to pursue this
Masters' degree.
To Professor Blanco, my advisor who willingly took me under his wing two years ago.
For his acamedic lessons as well as the lessons in life. For teaching me to accept failure
and to learn from it. For instilling in me the pursuit of excellence. For the many
discussions we have had ranging from the design of aeroplanes to the meaning of life. It
is not often a student comes across a teacher who believes and dedicates his life toward a
more holistic education of his students. Professor Blanco is a pioneer in his field of
design. I continue to be in awe of the magic and accuracy in his hands that can easily
defeat even the best computer software when it comes to renderings and engineering
drawings. And I will also have the highest respect and admiration for the way he happily
accepts and solves a design challenge making the process look so simple and fun. I
consider myself very fortunate to have learned from him.
To Mark Belanger, one of the funniest and best instructors and mentors I've met at MIT.
I've learned some of my most important engineering skills and best come-back lines from
him and I'm absolutely positive this thesis would not have been complete had it not been
for his contribution to it. In addition, a big thank you to my other friends in the LMP Dave, Gerry and Pat who helped ease the stress during those final days, and always put a
smile on my face, whether I wanted it or not! "There's no freak in French fries, guys!"
To Peter Morley and the gang at Central Machine for the many brainstorming sessions
we had. To Leslie Regan and Marie Pommet for always getting me out of trouble! To
Jamy Drouillard and Amy Smith for introducing me to the magic of digital photography!
3
To my spiritual guide Ayya Gotami for helping me calm my monkey mind. For tirelessly
trying to instill in me the importance of self-discipline and impulse control, for wanting
only the best for me and for the sincerity with which she has guided me. To Gosaka who
in his own magical way has taught me more about life and the important things that
matter, than I could have read in a dozen books. To Eriko for the many laughs and chats
we've shared in so little a time in her new Jaguar. To Amorn, Suchada, Sang Arun and
Achara Panh for their emotional support from a distance and all the good food throughout
this time.
To Lynn Roberson for walking by my side the past 5 years. For always making the time
to listen, for her timely advice, for helping me listen to my own voice speak, for teaching
me to honor the great feminine in me and for guiding me to reclaim my once surrendered
fire.
To Sanith for helping me make the decision to stay back in Cambridge, and for showing
me the importance of trust between friends.
My thanks also to the many potholes along the way - the mistakes I've made and learned
from, the interesting people I've encountered, the tough times that have never lasted but
always left their mark and life's little miracles that were timely and much appreciated.
And to my Family......
To Shuti, Sudu and Aiya - thanks for the comic relief! For being there for me in ways
that only sisters and brothers could; and of course for putting up with the thesis-driven
mood swings this past year! Aiya- welcome to our family! Sudu - I'm proud of you!!
And finally, to the two most important people in my life: amma and daddy - thank you
for the love, the genuine good wishes, the prayers, the sacrifices and the daily phone
calls! I love you!
4
Abstract
Many surgical procedures require incisions to be made on the target organ and the body
cavity. In order to avoid infection, and to guide the body's wound healing process after
surgery, it is necessary to perform accurate ligation and closure of these open wounds.
Extensive research shows that suturing and knotting are considered some of the most
time-consuming tasks of surgery, taking between 3.5-6 minutes for each single stitch.
With advances in medical technology, most operations today are carried out through
minimally invasive techniques that eliminate the large incisions on the body cavity. This
makes a surgeon's task even harder. This thesis proposes a design for a new endoscopic
suturing device which can be controlled remotely with single hand operability. The
design introduces a novel two-way sliding latch mounted on the shank of a 1550 needle.
This latch allows the deposition of a secure locked stitch along the defect. The needle is
actuated by the push of a trigger on a pistol grip handle. The actuation mechanism is
simple and robust requiring very few parts, and containing minimal moving parts within
the device. A large scale prototype of scale 1.5 the actual size was built and tested on test
specimen. The prototype functioned well and proved the mechanics and strengthened the
overall design concept.
5
Table of Contents
Page()
I A cknow ledgem ents
..............................................................
II A bstract
..........................................................
1.0 Chapter 1: Introduction
1.1 Minimally Invasive Surgery
..................................................
1.2 Minimally Invasive Suturing
.................................................
.........................................................
1.3 Analysis of Problem
9
10
12
2.0 Chapter 2: Wound Closure in Mammals
2.1 Definition of a wound
.........................................................
2.2 Surgical Wound Closure ..........................................................
2.3 Wound Closure Techniques and Devices
..............................
2.4 Limitations of Current Techniques and Devices ..............................
14
14
15
20
3
5
3.0 Chapter 3: Concept Generation and Product Development
22
................................................
3.1 Design Constraints
23
..........................................
3.2 Concept Generation and Prototyping
3.3 Experimental Observation and Evolution of Concepts ........................ 23
3.3.1 Design Concept 1: New Continuous Circular Motion (CCM)
23
device .........................................
3.3.2 Design Concept 2: CCM with altered orientation of needle ....... 31
3.3.3 Design Concept 3: Double Chain Stitch with hooked needle.......32
3.3.3.1 Design 3b: Hook with Closing Wire ......................... 36
3.3.3.2 Design 3c: Hook curved into Needle ......................... 37
3.3.3.3 Design 3d: Curved Hook on Outer Face of Needle ...... 39
....... 41
3.3.3.4 Design 3e: Needle with Two-way Sliding Latch
43
3.3.4 Arc Angle of Needle ................................................
4.0 Final Design Concept and Product Development
4.1 Elements required for a Working Device .......................................
4.2 First Large Scale Prototype of Overall Device ..............................
4.2.1 Further Modification ................................................
4.3 Testing of First Prototype ..........................................................
4.4 Second Large Scale Prototype
....................................................
.................................................
4.5 Testing of Second Prototype
............................................................
4.6 Features of D evice
............................................
4.7 Future Work
4.8 Emerging Wound Closure Technology .......................................
4.8.1 Integration of other areas of science and engineering to enhance
...............................
current biomechanical methods
4.8.1.1 The Biochemical Dimension ..............................
4.8.1.2 The Bioelectrical Dimension ..............................
.........................
4.8.1.3 Modification of Existing Devices
..
4 .9 T he Future ..........................................................................
5.0 R eferences............................................................................
45
47
50
52
52
56
63
64
65
66
66
67
67
67
69
6
List of Figures
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Page ()
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
Diagrammatic representation of a Laparoscopy ................................. 10
11
Endoscopic suturing
.............................................................
13
.......................................................
The Endo-Stitch@ at work.
Schematic of the three different wound healing processes
............... 15
...... 16
Methods of suturing distinguished by pattern and depth of closure
18
Mechanical working of a staple ...................................................
................................. 20
The Two modes of Adhesive Application
............... 24
Initial Blanco-Mead Continuous Circular Motion concept
Conceptual Representation of altered Blanco-Mead Design: Design
. . .. 25
C on cept 1 .......................................................................
26
..............................
Figure 10.0 Main components of the sewing mechanism
...... 27
Figure 11.0 Pictorial representation of Continuous Circular motion of needle
28
..........................................
Figure 12.0 Photograph of large-scale prototype
.28
Figure 13.0 First needle built for Design Concept 1
29
Figure 14.0 C C M Proof of C oncept ............................................................
Figure 15.0 Attempts to solve the challenge of topology of thread ........................ 30
31
...............
Figure 16.0 Altered Orientation of needle ................
Figure 17.0 Double Chain stitch suture device conceived by Professor Ernesto
. . .. 32
.......................................................................
B lan co
33
...................................................
Figure 18.0 Rendering of overall device
........................ 34
Figure 19.0 Sketch showing driving components of the needle
34
...................................................
Figure 20.0 New 180-degree arc needle
35
..........................................
Figure 21.0 Rendition of workings of the needle
36
Figure 22.0 Photograph of the first needle ................................................
37
..........................................
Figure 23.0 Design of a hook with closing wire
37
............................................................
Figure 24.0 C urved hook needle
...................... 38
Figure 25.0 3-D topological feature ignored in 2-D sketches
Figure 26.0 Mounted setup of needle with hook on inner surface ..................... 39
39
........................
Figure 27.0 New curved hook on outer face of needle
Figure 28.0 Photograph of needle prototype with hook on the outer face of
40
..........................................
the needle
Figure 29.0 The Topology challenge in Round 2 of suturing.................................40
............................... 41
Figure 30.0 Sketch of needle with proposed sliding latch
41
.......................................
Figure 31.0 Working of the sliding latch feature
............... 42
Figure 32.0 The solution - curved needle with a two-way sliding latch
43
...................................................
Figure 33.0 Detailed working of the latch
Figure 34.0 Relation between arc angle and depth of penetration ...................... 44
46
.......................................
Figure 35.0 Expected movement of the needle
47
............................................................................
Figure 36.0 Pulley
48
Figure 37.0 Adjustable thread holder ..........................................................
48
Figure 38.0 Workings of the trigger ............................................................
Figure 39.0 Illustration showing trigger-needle interaction ................................. 49
49
.......................................
Figure 40.0 Photograph of first version of handle
50
.................................................
Figure 41.0 Overall Prototype assembly
7
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
42.0 Redesigned Trigger Mechanism .................................................
..........................................................
43.0 Redesigned handle
..............................
44.0 Redesigned handle before polished finish
45.0 N eedle
...........................................................................
. ...
46.0 Pulley
........................................................................
47.0 Pulley and needle assembled together ........................................
..................................................................
48.0 Thread holder
.........................................................
49.0 Cable cross section
...............................
50.0 Photograph of second prototype assembly
.......................................
51.0 SolidWorks rendition of final device
52.0 Expected mechanisms with new setup .......................................
..............................
53.0 Challenge of missing thread within track
54.0 Large scale experimental set up to investigate needle-thread
. . ..
..............................................................
interaction
55.0 Angle formed by thread from facilitating pick up by Needle ...............
56.0 Needle-thread interaction during the various stages of a single suture ......
...............
57.0 Final thread layout showing suture pattern on test specimen
.................................................
58.0 Final functioning prototype
.................................
59.0 Representation of device as used in surgery
60.0 Sketch showing device at work ................................................
51
51
52
53
53
53
54
54
55
55
56
57
58
59
59
61
62
62
60
8
Chapter 1.0: Introduction
All surgical procedures ranging from appendectomies to gall bladder operations to
cholecystectomies require incisions to be made on the target organ and the body cavity.
In order to avoid infection, and to guide the body's wound healing process after surgery,
it is necessary to perform accurate ligation' and closure of these open wounds. Extensive
research carried out by researchers at Simon Fraser University in Canada, shows that
suturing and knotting are considered some of the most time-consuming tasks of surgery,
taking between 3.5-6 minutes for each single stitchl.Wound closure methods that exist
currently range from sutures and staples to ligating clips and adhesives. With advances in
medical technology, most of the above operations are today carried out through
minimally invasive techniques that eliminate the large incisions on the body cavity.
However, this advantage also serves as a hidden disadvantage to the surgeon, who now
has to operate through tiny pencil-sized holes on the body cavity. There is therefore a
rising need for smaller, smarter suturing, stapling and other ligating devices, that will
allow a larger range of motion and more degrees of freedom to move within the body
cavity. These devices should be designed for hard to reach locations that would in an
open surgery have been quite simple.
The aim of this thesis therefore, is to design and prototype an improved automated
endoscopic suturing device that will facilitate the task of the surgeon. In order to achieve
a working device, research has been carried out on existing suturing devices in the market
and much of the design features address the mechanical and functional needs of the
surgical procedure and the ergonomic comforts of the surgeon.
1.1 Minimally Invasive Surgery
Minimally invasive surgery, also known as endoscopic surgery, is a surgical operation
wherein a surgeon makes minute incisions on a patient's body, and inserts pencil-sized
instruments in cannulae placed through them. This type of keyhole surgery does away
with the need to place large incisions in the patient's body, to reach the targeted organs.
The surgeon makes use of a fiber optic camera, called a scope and employs several long,
thin rigid instruments to do the job of his hands. Recovery after a minimally invasive
procedure is very rapid; on the scale of days as opposed to weeks in open surgeries.
Three incisions are usually made in the patient. The first incision, a blind one, is carried
out using a trocar. The scope is then inserted through this portal, enabling the surgeon to
see what is being done after this. Two other incisions are made to house the surgical
instrumentation, as shown below:
9
Figure 1.0 Diagrammatic representation of a laparoscopy 2. Source: Ballantyne, Leahy, Modlin:
Techniques of Laparoscopic Surgery
Minimally invasive surgery specific to the abdominal cavity is known as laparoscopic
surgery. That specific to the joints is known as arthroscopic surgery.
Advantages
-
of endoscopic surgery over open surgery:
Less pain, less strain on the patient
Faster recovery
Small injuries (aesthetic reasons)
Economic gain (shorter illness time)
A few of the challenges in laparoscopic and any minimally invasive surgery for that
matter are-:
-
-
-
-
The absence of depth perception and difficult hand-eye coordination-minimally
invasive surgery requires that the surgeon think and act three dimensionally while
looking at a two dimensional image on the screen. Also the surgeon stands the risk
of being optically deceived if he does have an optimal appreciation of instrument
location i.e. working toward the scope, yields a reversed image on the screen, which
is why working ahead of the camera is advised.
Restricted mobility- apart from the restrictions placed on the surgeon by the length
of the instrument, the field of access is described by a cone with the apex of the cone
being the trocar at the fascial level.
No tactileperception - it is hard for the surgeon to sense how tight or how loose a
suture may be on the tissue.
Placement of Trocars - it is important to note that the insertion of the first trocar into
the cavity is a blind act for the surgeon, and has in many cases, led to the death of
the patient due to accidental incisions of delicate organs within the body resulting in
hemorrhage. The placement of the two other trocars is less challenging, once the
scope is in, and allows for accurate visualization of the ensuing processes. Their
placement however with respect to each other matters. If they are placed too close to
each other, or at an incorrect angle, the result will either be an interesting "sword
fight" or an inability to accurately secure the knot in suturing.
Suturing - the limitations faced here are a result of limitations of the instruments.
10
i-
-sposm.'o- - - - , -
-
! !
.-
-
1.2 Minimally Invasive Suturing 2
This is a process whereby the defect tissues are apposed using a miniscule needle that is
passed through a pencil-sized cannula, into the body cavity. The needle is remotely
controlled from outside the body cavity. There are a wide variety of needle holders and
several needle types available for laparoscopic suturing techniques. Generally, one of
three needle types is used: an atraumatic straight needle, the ski needle, and the standard
semiconductor curved needle. The needle is manipulated in varying ways, dependent on
the device. Current devices enable several varying techniques based on a common
principle that guides a straight or curved needle across the defect to be sutured and then
grasps it on the other side either with a passive needle holder or a guiding pathway
integrated into the device. Most devices do not incorporate a knotting mechanism. The
suture material is often manipulated intracorporeally by the surgeon. These knots can be
placed either extracorporeally,wherein throws are placed outside the cavity and then
brought down to the operative field by a knot pusher or intracorporeallywhere throws of
the knot are placed directly at the operative site using laparoscopic instrumentation.
There are three techniques for the formation of secure intracorporeal knots including the
standard microsurgical square knot, the internal twist knot and the Dundee internal knot.
Figure 2.0 Endoscopic suturing
2.Source:
Ballantyne, Leahy, Modhin: Techniques of
Laparoscopic Surgery
11
1.3 Analysis of Problem'
Research carried out by the team at Simon Frasier University in Canada helps understand
the endoscopic suturing process and its challenges better. Their results are based on a
motion/time study of the actual surgery and a survey of 78 surgeons. The team studied in
detail, the subtasks involved in manual laparoscopic suturing.
Table 1.0: Duration of suturing subtasks in laparoscopyl
Subtasks
1- Position needle
2- Bite tissue
3- Pull needle through
4- Re-position needle
5- Re-bite tissue
6- Re-pull needle th
7- Pull suture through
Total
No. of
movements
3
4
5
4
4
5
4
29
Ave. duration
Novice (seconds)
103
15
25
35
22
23
32
255
Average duration
Expert (seconds)
51
20
17
13
15
13
24
153
Their studies summarized that:
1) almost 50% of the suturing time is spent to capture and orient the needle to a
specific orientation
2) secure the grasp on the needle and penetrate the tissue to some desired orientation,
which takes about 20% of the total time
3) re-capturing the emerging needle from the other side of tissue takes 20% of the
time.
This highlights the challenges of minimally invasive suturing:
- Many of the needle holders do not provide a sufficient grip on the needle,
resulting in swiveling and difficulties maintaining accurate direction of needle
passage.
- Most of these movements require flexible orientation of the tools used which are
hindered by the stiff graspers and the narrow cannulae.
- Knot tying - minimally invasive surgery requires learning several new techniques
for knot tying, a process that has become second nature for most surgeons.
Success in passing the knots to its eventual location depends on the friction of the
suture, thereby limiting the biomaterials that can be used. In addition, constant
tension must be maintained on the free ends of the suture while the pusher is used
to accurately place the knot. Failure to do so can result in too loose a knot or
worse yet, a tear at the site of ligation.
Two devices on the current market have been studied to further understand the current
needs of surgeons. These are the Endo-Stitch@ and the Quik-Stitch®.
Endo Stitch* of the Laparoscopic Training and Resource CenterTM-. The Endo Stitch
needle is 9mm long and 0.9mm wide and sharp on both ends. The suture attaches to the
12
middle of the needle. Tissue can be grasped securely between the jaws of the Endo Stitch
simply by closing the handles of the instrument. The needle and suture can be passed
smoothly through the tissue in the jaws by moving a pivoting flip lever. Pressing the jaws
firmly against the lateral walls of defect of any size, at any depth in the defect, causes the
needle and suture to pass easily through. The device provides a running locked stitch, and
produces an intracorporealknot without the need for a knot pusher. This device allows
the suturing process to be carried out single handedly, but requires two hands and a
grasper for the knotting process.
Figure 3.0 (a) Running locked stitch
placed by the Endo-Stitch
Figure 3.0 (b) Intracorporeal knot placed
using grasper
Figure 3.0 The Endo-Stitch® at work. Source: Laparoscopic Training and Resource CenterM
Company Profile(www. fibroid.com/laparoscopicl sutureclose.htm)
Pare Surgical
The Quik-Stitch* Endoscopic Suturing System PARE Surgical, Inc. (Englewood, CO)
uses a 5mm delivery system and a needle driver to allow a surgeon to place a stitch
easily. An applicator contains a suture spool and a pre-tied Roeder knot which is pushed
into place by pulling the suture ends. This is an
extracorporealknot. The device still requires the use
of a grasper to place the thread. However it is the first
suturing device that addresses knot-making and
placement directly. The diagram on the right is cited
from the Pare Surgical Company Website
These case studies and the findings of the Simon
Fraser group indicate the need for a feature that
facilitates single handed capturing and orienting of the needle. The findings also state the
need for an automatic actuation mechanism that will guide the needle through a fixed
trajectory, recapturing it as it emerges, such that the process can be repeated easily.
13
Chapter 2: Wound Closure in Mammals
Since the suturing process is meant to aide the natural wound healing process, it is
important to gain an understanding of wound closure in the adult mammal and in the
process, study how the various wound closure mechanisms work. This Chapter is
dedicated to this task.
2.0 Definition of a wound
A wound is an injury or defect that occurs at an anatomical site. This could range from an
abrasion or blister on the skin, to an ulcer in the alimentary canal, to a puncture in an
internal organ. They can be generated by accidental environmental stimuli, or can be
planted in bodies deliberately by a surgeon in order to accomplish a more important
surgical task. This thesis focuses on the latter, termed surgical defects and assumes a
basic knowledge of the wound healing process in mammals.
Surgical defects can be of different kinds: incisions on the skin surface for implantation
of percutaneous tubing in kidney dialysis, excisions of the dysfunctional or damaged part
of an organ - as in the liver or the spleen, deep incisions of the musculoskeleton in open
heart surgeries which involve a complete opening of the thoracic segment (a sternotomy),
wounds caused during organ transplants - kidney, liver, heart, and incisions made during
a Caesarian Section
An open defect or wound, whether intentionally or unintentionally generated, can lead to
an uncontrollable loss of blood in the case of an internal organ (hemorrhaging), or even to
the loss of tissue fluid leading to potential water and metabolite imbalances in the
organism. The other dangerous threat of an open wound is the risk of infection and
contamination that follows. To avoid any of the above, a wound needs to be surgically
closed so as to help it heal.
2.1 Surgical wound closure
Post surgical wound closure can be of three types based on the gravity of the defect that
was initially created.
1. Primary Intent: an incision or a puncture heals by primary intent if the freshly
cut edges of the tissue can be juxtaposed together. What results is a harmonious
joining of epithelial and connective tissue on one side of the defect to the
epithelial and connective tissue on the other side of the defect. This is the most
rapid form of healing.
2. Secondary Intent: This refers to the strategy of allowing wounds to heal on their
own without surgical closure. In this case, a layer of granulation tissue forms over
the injured surface and an epidermal layer develops over time, replacing the
granulation tissue from the edges inward. This is a slower form of healing than
primary intent.
14
3.
Tertiary Intent: This is also known as delayed primary closure and refers to the
approach of cleansing the initial wound, and following up with wound closure
after about 72 hours. This is used with contaminated wounds, which if left open,
would result in unacceptable cosmetic results.
-
Figure 4(a) Healing by
Primary Intention
-4
Figure 4(b) Healing by
Secondary Intention
_Ic
- -
~
I
-
49-
- -4
Figure 4(c) Healing by
Third Intention
Figure 4.0 Schematic of the three different wound healing processes3
2.2 Wound Closure techniques and devices
For a clearer understanding of the medical devices used in this field, it is worthwhile
mentioning in brief, the various types of wound closure techniques and devices that are in
use today, and their classifying characteristics. This section attempts to summarize in
brief, the work that has already been carried out by Chu, Fraunhofer and Greisler in their
published book: Wound Closure Biomaterials and Devices - an excellent compilation of
the state-of-the-art technology in use today, and its historical origins.
Wound Closure devices used today, can be divided into four categories
4. Suture: this is a biomechanical method of wound closure used to repair damaged
tissues, cut vessels and surgical incisions. By definition, a suture is a thread that
either approximates or maintains tissues until the natural healing process has
15
provided a sufficient level of wound strength. It is then knotted to hold the suture
in place. It may also be used to compress blood vessels in order to stop bleeding 4.
There are different methods of stitching depending on the pattern and the depth of
closure.
X4
Simple Suture
Locked Simple
Running Suture
Vertical Mattress
Suture
Intracuticular
Running Suture
Horizontal Mattress
Suture
Half-Buried
Mattress Suture
Wound Closure
With Tape
Figure 5.0 Methods of suturing distinguished by pattern and depth of closure5 . Drawings by
Dr. D. LeberMD
The basic idea behind the suturing device is similar to that of an everyday sewing
machine, in that it runs a thread through the two edges of a material in order to join
the edges together. The important components of a suturing device are the surgical
needle and the suturing biomaterial (thread). The surgical needle, to which the suture
is attached, has the primary function of introducing the suture through the tissues to
be brought into apposition. Ideally, the needle has no role in wound healing, but
inappropriate needle selection can prolong the operating time and even damage tissue
integrity leading to such complications as tissue necrosis, wound dehiscence,
6,7
bleeding, leakage of anastomoses and poor tissue apposition'.
Sutures can be classified into one of two groups: absorbable and non absorbable.
Absorbable sutures are temporary due to their ability to be "absorbed" or decomposed by
the natural reaction of the body to foreign substances. They can be formulated to have
varying degradation rates, in order to control their length of stay within the body. They
can be either natural or synthetic.
Nonabsorbable sutures are those that are not dissolved or decomposed by the body's
natural action. Some examples of these are surgical silk, surgical cotton, surgical steel,
16
nylon, polypropylene and Polyethylene Terephthalate 6
Sutures can also be manufactured with a wide variety of parameters. In addition to
varying degradation rates, sutures can be monofilament or many filaments twisted
together, spun together or braided. They can also be dyed or coated.
Table 2.0: Classification characteristics of surgical needles 7
Characteristics
Description
Needle Dimensions The size of the needle is determined by four dimensions:
* Length: distance measured along needle from attachment end
to the point
* Chord: linear distance between needle point and attachment
* Radius: distance from center of circle to body of needle
* Diameter: thickness of wire from which needle is fabricated
These can be of three types:
Needle - Suture
Attachment
*
Closed- eye: similar to the household sewing needle
* French (split or spring) eye: is slitted from inside the eye
toward the distal end of the needle, the slit contains ridges to
hold the suture in place
* Swaged (eyeless): wherein suture is bonded to the needle to
form a continuous unit. There are three types: channel swage,
drilled swage and laser-drilled swage.
This is the part of the needle that is grasped by the needle holder during
Needle Body
suturing procedures. There are various types and their use depends on
the suture-needle combination that best suits the clinical requirements of
the procedure: Straight, half curved, Compound Curved
Needle Points
Surgical needles points are of three types:
* Blunt: have rounded tip and an oval cross section, used for
blunt dissection
" Tapered: sharp tip and an oval cross section, not used to cut
tissue, instead, to effect passage through a variety of tissues
that are less resistant to penetration
" Cutting needles: have sharpened points and edges to permit
Needle Acuity
This measure of sharpness is determined by several factors: composition
of the wire, wire physical properties, diameter of the wire, design of the
needle, type of needle point, manufacturing process, needle surface
passage through tissue that is tough or resistant to penetration
finish
Needle
Biomechanics
Needle Holders
These measure the resistance to bending and needle ductility
These are used by the surgeon to hold the needle as it is inserted through
tissue, providing clear field of operation and reducing risk of injury.
Primary requirement therefore is ability to grasp the needle and permit
accurate and precise manipulation of needle with field. There are
different types of holders based on design factors - length, width, profile
d surface.
The performance of suture materials depends on their four general characteristics physical/mechanical, handling, biocompatibility and biodegradation.
17
Staple: This a biomechanical method that allows for accurate apposition with minimal
tension, similar to suturing .It consists of metallic segments that are carefully embedded
across the surface of a wound, so as to hold the two edges of the wound together, until
natural apposition occurs. The staple is folded or bent into a B-shape by means of an
anvil. The leg length of the staple must be long enough to completely penetrate the tissue
to be apposed. Larger staples are generally required for thicker tissue such as the gastric
wall, and smaller ones can be applied to surgeries of the cornea.
Figure 6.0 Mechanical working of a staple8
Staples are used today in human and veterinary gynecological, cardiovascular,
gastrointestinal, esophagal, pulmonary and opthalmological surgery. Their main
advantage over suturing is that they can be manipulated single handedly by a surgeon,
without the use of a grasper, as required in many suturing devices. An inherent
disadvantage however, of stapling is the need to evert the wound edges6 . Since the staple
must penetrate all layers of the tissue being stapled, stapling of thick, inflamed or
edematous tissues may be contraindicated. Also, in the use of staples on bone and
be a minimum clearance of 4 to 6.5 mm between the skin and the
viscera, there needs to
6' 9"10
structures
underlying
Advantages of Stapling: - Faster than traditional suturing
- Reduces tissue trauma by minimizing tissue handling
Ligating clip: This is similar to a staple in that it is also used to forcibly bring about
wound closure. It works in a manner very similar to a staple, wherein a metal wire is bent
into shape holding two edges of tissue together. It is applied to the body using a clip
applier.
Clips are primarily used in lumen occlusion within a vessel or a tubular organ, until
permanent closure occurs naturally. They are also used to ensure hemostasis during
general operations, and are mostly not maintained in place for extended periods of time.
Over the years, they have also increasingly been used in ligation of vessels in
gynecological and urological procedures such as female sterilization (tubule ligation),
prevention of pulmonary emboli by ligation of the inferior vena cava, in
cholecystectomies (surgery of the gall bladder) for ligating cystic ducts and arteries, and
also in the closure of surface wounds.
18
There are two types of Ligating Clips:
Metallic: these are typically plastic or silicone coated titanium strips, coated stainless
steel springs or plastic systems using spring closure. Metal and metal-plastic ligating
clips are easy to use, stable, insoluble and provide secure ligation, but they possess
certain disadvantages. They can induce inflammatory responses and are radio-opaque,
causing problems in radiological, CT, and MRI examinations. As a result, although
they are used vastly in primary skin closure, their use has phased out in favor of
nonmetallic and biodegradable polymeric ligating clips for internal or buried use6 .
Polymeric: these are the most favored among the ligating clips, in that theycounteract
most of the inherent disadvantages of their metallic predecessors -i.e. they are relatively
biocompatible, and rarely set off immunological responses6 .
Advantages of Ligating Clips:
-
Non-toxic
Biocompatible
-
Can be used on many different types of tissues without causing responses
Quick and convenient
-
Adhesives: This is a biochemical method of wound closure wherein the edges of the
wound are held together by glue. This is most often a compound which when placed in
between the edges of the wound, polymerizes to form a strong bond. Similar to the
manner in which suturing and stapling devices are modifications of normal everyday
objects like sewing machines and office staplers, surgical adhesives are a knock off of the
garden-variety glue. These adhesives are widely applied in surgery, not only as tissue
adhesives but also as hemostatic agents and sealants, although their bonding strength may
not be high enough for a secure closure. They however, have to satisfy a few
requirements before they can be used in a surgical context. They need to be sterilizable,
non-toxic, rapidly curable under wet, physiological conditions such as that in the body,
have adequate viscosity during application and of course, be reasonably priced. Once
applied to the tissues, they need to be able to strongly bond in the presence of the
moisture without retarding the wound healing process, while providing a biostable union
until wound closure occurs. There are thus two ideal modes of adhesive application to
ensure that the adhesive layer does not form a delaying barrier to the normal cell
migration that occurs during wound healing. The two modes are:
Spot adhesion6 : wherein the adhesive is spotted onto the region between the tissues, and
therefore does not delay wound healing. However, it does require a strong adhesive
capability in the adhesive.
19
Sheet-aidedadhesion6 : this may cause insufficient adhesion, because of only one-sided
adhesion.
Fig 7(a). Spot adhesion
Fig 7(b) Sheet-aided adhesion
Figure 7.0 The Two modes of Adhesive Application.
Contrary to most sutures, tissue adhesives must always be resorbed in the body to that the
two edges of the wound can eventually meet and be physically reunited for a complete
wound healing. Because of this biodegradation requirement, it is essential that the
biodegradation products of cured tissue adhesive are not toxic. Curing of the adhesive can
occur through polymerization, chemical cross linking, or solvent evaporation at ambient
temperature. The cured adhesive also needs to be tough and yet pliable.
Adhesives have been known to incite acute inflammation and chronic foreign body giant
cell reactions. However, the high demand from surgeons for good tissue adhesives, due to
their relatively easy manipulation, should fuel the research for safer, better technologies.
2.3 Limitations of current techniques of wound closure
Even though medicine has come a long way from the strips of hyde that were originally
used to heal wounds, there are several disadvantages to current wound closure
technologies that arise from our inability to comprehend and overcome the body's natural
immune responses. These are:
Scarformation: wound closure devices in conjunction with the extra cellular matrix
analogues that exist today, for example the Dermis Regeneration template
(DRT)"(Yannas, 2001) have succeeded in reducing wound contraction and scar
formation to a certain extent, by providing a biodegradable scaffold within the dermis to
induce regeneration. However, this is still not sufficient to cause complete regeneration of
the wounded region. Surgical incisions today (save for the minute incisions made in
minimally invasive surgery) that are sutured, stapled or ligated leave behind scars.
Loss of tissuefunction: Even though research has enabled induced regeneration to a
certain extent, there still lies the problem of the tissue or organ losing its original function
due to the scar tissue that forms. DRT unfortunately cannot regenerate sweat glands etc.
Tissue reaction to biomaterial:All wound closure devices come into direct contact with
the body at some point in the process. This may be the suturing thread of a suture device,
a metallic staple, a ligating clip or a chemical adhesive that bonds with the moisture in
the body to bring about apposition of the wound edges. These biomaterials are recognized
as "foreign particles" by the immune system, which in turn starts a "foreign body
20
reaction", in addition to its response to the original tissue injury caused by surgical
incision. The tissue reaction starts with inflammation and then proceeds through the steps
of wound healing. Acute and chronic inflammation result and the foreign body is coated
with macrophages and "foreign body giant cells", which will lead to formation of
granulation tissue and then fibrosis leading to a fibrous encapsulation. The gravity of this
latter process is a direct function of the biomaterial, its surface properties and the
regenerative capacity of the cells in the surrounding tissue (Grubb, 1998, 1999, 2000).
Cosmetic outcome: none of the techniques available to surgeons today can completely
eliminate the formation of scar on the surface of the wound. This is particularly
emphasized in plastic surgery of the face.
Involvement of more than one type of tissue in a wound: this results in various degrees of
healing, and varying requirements for handling during the process of wound closure that
are specific to each tissue type. Current techniques cannot yet combat this challenge.
Suture needles and material for example are selected on the basis of the dominating tissue
type, or the most sensitive tissue type in the target organ. This results in insufficient
attention to the other tissues, leading most probably to tissue reaction to the biomaterial.
21
Chapter 3: Concept Generation and
Product Development
With a deeper understanding of the physiology of the wound, wound closure and the
current techniques used for the procedure, we were now in a better position to set about
designing our device.
What follows is a detailed account of the Concept Generation phase, wherein a multitude
of ideas were introduced and tested. Design is an evolutionary process. This design has
been no exception. The device has gone through several iterations as each working
concept has been tested, prototyped and proved ineffective. Very successful ideas in the
two-dimensional world of paper have turned out to be disappointingly unfeasible in the
three-dimensional world of reality. Kinetics and moving parts are hard to envision in the
mind's eye, and it's even harder if they are clouded by a biased "expectation". Often,
only the successes of a design process make it to the final report. Failures make their exit
early on. I have chosen to describe the uncensored path I have traveled; of ignoring the
failures, getting disillusioned by the failures, accepting the failures, coming to terms with
them, learning from them, and moving forward. The pursuit of excellence is a valuable
life's lesson Professor Blanco has instilled in me; it is as important if not more, than the
design skills he's taught me, and I wish therefore to share it with other hopeful designers
who read this.
3.1 Design Constraints
Research of prior art and research in the field helped outline the desired features required
of a remote endoscopic suturing device, which became the design constraints that needed
to be met. There were both functional and structural demands on the device: These were
as follows:
Functionally,there was a need for:
a feature that facilitates capturing and orienting of the needle.
an automatic actuation mechanism that will guide the needle through a fixed trajectory,
recapturing it as it emerges, such that the process can start over.
a device that allows suturing on multiple layers.
a device that allows continuous suturing along a defect.
a device that can be operated extracorporeally or remotely.
Structurally, the device needed to:
be no more than 1cm in diameter.
be about 1 foot long
be operable with a single hand
be ergonomically designed.
have minimal parts and minimal joints inside the body cavity
be cordless or battery operated.
22
These constraints gave the following body for the device:
An automated 1 cm wide probe that allows continuous stitching and is actuatedremotely
using a pistolgrip handle via a triggermechanism.
3.2 Concept Generation and Prototyping
Overall Strategy
With the design constraints laid down, several concepts were generated. Each concept
was analyzed in detail. Sketches were drawn to visualize the concept. Prototypes were
built to further test the kinematics of concepts or ideas that worked well in theory. The
prototypes were enlarged sizes of the miniature device. This enabled a careful study of
the kinetics and mechanics involved and also served as a proof of concept for the
functionalities being tested, while at the same time avoiding the problems involved in
miniaturization, such as:
- the need for high precision machining and fabrication which exceeds the available
machine shop resources'
- the need for miniature special parts'.
In instances where the prototyped failed, challenges were noted, and the concept
improved.
3.3 Experimental Observation and Evolution of Concepts
What follows is a detailed chronological account of all the concepts and series of
experimental observations via prototypes that led to the final design.
3.3.1. Design Concept 1: New Continuous Circular Motion (CCM) device
The design worked on initially was conceived by my advisor Professor Ernesto E. Blanco
and John Mead of the John Mead Corporation in 1992. The concept introduced a novel
technique of passing a curved needle through a guided and fixed trajectory. This
immediately addressed the two key design characteristics for the design mentioned in
Section 3.1 .The concept served as the predecessor to all the initial design ideas and is
shown in figure 8.0
The Blanco-Mead concept uses a 270 degree curved needle bearing entrapments on its
body. The needle is encased in a groove within the cannula. This constrains the needle
and guarantees a fixed trajectory. A long hook extending toward the entrapments of the
needle is attached to a centrally located shaft. When the shaft is rotated, it rotates the
hook which latches on the entrapments and in doing so, drives the needle. The needle
rotates continuously in a fixed circular motion along its groove. This feature is termed
Continuous CircularMotion (CCM). The concrete placement of the hook and the
flattened nature of the device-defect interface, prevent the hook from crossing over the
defect. This limits the hook to a 180 degree movement range. Figure 8.0 pictorially
23
describes this challenge. When the hook reaches point B it is rotated back to point A
where it will repeat the process of guiding the needle. It thus alternates between pulling
the needle by its head and pushing it by its tail to complete one revolution of the needle.
Meanwhile, the shaft undergoes three movements per suture:
1) Movement 1: To move hook from position A to position B to pull head of needle.
2) Movement 2: To return hook to position A
3) Movement 3: To move hook from position A to position B to push tail of needle
Though the concept of the fixed trajectory seemed serendipitous, the intricate three-stepmovement of the shaft per suture was considered cumbersome and required more thought
and concentration to operate than a
surgeon can afford to give. The design
also required that the user rotate a
.
3
handle in order to drive the needle
thereby dismissing the one-handed
requirement that was highlighted in
the design constraints. Efforts were
made first to counter the three step
movement of the handle since this was
the most concerning.
The needle design in Design Concept
1 was altered such that it enabled
continuous circular motion around the
device. This allowed a single 360
degree rotation of the central shaft to
guide the needle through one round of
suturing. Additional design features
were added that allowed a hook to
drive the new needle. Design Concept
1 is discussed below.
I
Ll?~
/,
/
r
T4
f ,
Figure 8.0 Initial Blanco-Mead Continuous
Circular Motion concept. Dated 1992
24
Figure 9.0 shows a conceptual representation of the altered Blanco-Mead Design. The
tube A represents the pencil-sized body of the probe. It is shown flat on the bottom,
indicating the location of the probe that sits parallel to the targeted defect. The needle B
rests in a groove within this tube. A central shaft C runs through the tube providing a
connection between the remote operator and the needle within. A housing D mounted on
the shaft contains a hook E aligned coplanar with the needle. Entrapments on the needle
A
B
F
E
D
Figure 9.0 Conceptual Representation of altered Blanco-Mead Design: Design Concept 1
allow the hook to latch onto them, in turn driving the needle. A ledge F at the bottom of
the tube enables a CAM action that gently discontinues the circular motion of the hook
and guides it over the defect. Since the extremely small size of the actual device would
make any testing and redesign challenging, the initial device was dimensioned for a
large-scale prototype. Figure 10.0 lists a detailed description of the individual parts of the
suturing portion of the device.
25
~..j,.Lb,-
. ........
.IIIIII
i....
....
Needle: is a 2700 arc with nodes close to the head and the
tail of the needle. These nodes serve as entrapmentsfor the
hook, which latches onto them, in turn driving the needle. It
was proposedto have a swaged endfor the thread, butfor
the means of a prototype, the threadwas initially glued to
the eye of the needle and later to a groove on the inner
surface of the needle.
Housing: is an aluminum casingthat serves to connect
the shaft to the hook. It is spring loaded to enable the
CAM activated-motion of the hook. It is also constrained
by two springs in the verticaldirection (not shown in
figure)
Ledge: guides the hook in a horizontal trajectory as it
reaches the bottom of the tube. This prevents the hook
from contacting the skin that lays flush with the bottom of
the tube.
Hook: is a cylindricalrod that isflattened at one end and
bent to form a hook. It is inserted into the housing
through a hole drilledon the latter'ssurface. It is held in
place using a set screw.
Shaft: is a cylindricalrod that is milled on one end to
accommodate the housing such that the outerface of the
latter remains flush with the outer diameter of the shaft
40 '40
Figure 10.0 Main components of the sewing mechanism
26
The shaft is rotated to move the hook round the circumference of the tube, and in the
process drives the needle through one revolution. Graspers would need to be used to
manipulate the tissue. Figure 11.0 shows a pictorial cross-sectional simulation of one
round of suturing.
Figure 11.0 Pictorial representation of Continuous Circular motion of needle
Since the needle rotating mechanism was considered the most crucial part of the device,
the actuation of the rotation, thread manipulation, knotting mechanism and ergonomics of
the device were not focused on until a solid needle mechanism was decided upon.
Prototype I
The first prototype built to test Concept 1 had an external tube diameter of 3 inches (a
scale factor of 7 times the original size). The lexan tube was milled to get the appropriate
features. Aluminum was used for all metal parts. The housing was milled on a CNC
milling machine. The shaft and the grooves for the E-clips on it were turned on a lathe.
The handle was cut on a water jet and assembled. After several computations, the
prototype proved that the continuous circular motion concept worked well. When driven
by a large handle, the hook was able to drive the needle through a revolution. A
photograph of the prototype is shown in figure 12.0, followed by a photographic proof of
concept of the CCM method in figure 13.0.
27
Figure 12.0 Photograph of large-scale prototype
Figure 13.0 First needle built for
Design Concept 1
28
Figure 14.0 CCM Proof of Concept
Challenges
The prototype however highlighted a feature that had been overlooked and
underestimated in the initial design concept- the topology of the thread. This turned out to
be the biggest challenge of this phase of the project.
Just as manual stitching involves the monotonous yet crucial step of pulling on the thread
such that it pulls taut on the material, a suturing device requires that the thread be pulled
through the skin with each suture. Various methods were tried, but all resulted in a failure
to pull the thread back all the way into body of the tube, without entanglement with the
other components within. An alternative was to pull the thread in the opposite direction
away from the tube, which would not be possible without the introduction of additional
moving joints. In keeping with the aim to keep the design simple, this idea was
abandoned. An inbuilt suture spool located at the tail end of the needle was considered.
This was also abandoned due to the requirement for high quality miniature parts. Other
29
Wem.a..W."
....
....
...
ft
-
- -
-
solutions were attempted to solve the challenge of the entangled thread. Figures 15(a) and
15(b) below illustrate two concepts that were tried:
Figure 15(a) A tube was placed in a slot
within the outer tube to contain the
thread as it is pulled in via a hook. A
simple bent rod was used for a hook.
The tube successfully contained the
thread, however the setup required an
intelligent hook capable of automatic
grasping and releasing the thread.
Figure 15(b) This led to the design of an
intelligent hook as shown. The moving
joints allowed easy opening and closing of
the hook. The prototype proved the
concept however this idea was abandoned
due to the miniature size of the hook that
was required which demanded additional
moving joints. Also shown is a photograph
of the hook.
Figure 15.0 Attempts to solve the challenge of topology of thread
30
a-MM
-
,-,
It was noted that the thread provided the least resistance to pulling, if it were pulled
perpendicular to the axis of the needle, as opposed to the parallel motion it was being
pulled in. This meant that the thread would be pulled perpendicular to the axis of the
tube, i.e outward from the tube and not contained within the tube similar to the idea of
pulling the thread out of the tube, incorporating this idea also required the use of
additional moving parts.
3.3.2. Design Concept 2: CCM with altered orientation of needle
In Design 2, to avoid the issue of moving parts and achieve the perpendicular relationship
between the planes of the needle and the hook, the orientation of the needle was changed
from being parallel to the axis of the tube, to being perpendicular to the axis. This
concept is illustrated in Figure 16.0 below.
Figure 16.0 Altered Orientation of needle - thread pulled perpendicular to axis of needle
This allows a hook to pull the thread perpendicular to its axis, while at the same time,
being encased within the housing of the tube. Simultaneously, a rack and pinion concept
was proposed to address the challenge of the. The assembly would convert a vertical
movement of a surgeon's thumb to the rotational movement required by the needle.
However, before a second prototype was made to test this assembly and design concept 2,
some other ideas were explored. It was felt that the number of parts in the current
prototype was too high and still increasing. Some parts such as the constraining springs
on the housing seemed redundant. The assembly was not very robust. A device with
minimal moving parts is robust, since very little can go wrong.
31
In addition, the nature of the stitches that was produced by this device was questionable.
The continuous single stitches were easy to deposit, but were equally easy to remove.
This is not a characteristic that is desirable in surgery. Surgeons require that the suture be
sturdy in order to hold the apposition together until the tissues adhere naturally. A
stronger, firmer suture was required that did not have an underlying domino effect.
Given all these disadvantages, it was decided that the continuous circular motion needle
may not be the most convenient mechanism and the design process was restarted. This
brought us to Design Concept 3.
3.3.3. Design Concept 3: Double Chain Stitch with hooked 180 degree
needle
Design Concept 3
investigates and builds on
another concept that was
initiated by Professor Blanco
in 1991. This device deposits
a continuous locked double
chain stitch in the defect,
very similar to a sewing
machine. A dated rendering
of the device and its working
mechanism as sketched by
Professor Blanco is shown in
figure 17.0.
7
-
\
A:, 'N-
~Yt)4
((~
j TL ZE-A (E)-5TSTCHE
Figure 17.0 Double Chain stitch
-
-AQJU-Su-r
R
U
-
E
-
suture device conceived by
Professor Ernesto Blanco.
Source: Blanco's notes dated
1991.
32
v7
The device uses a circular needle that is different in function and structure to the needle
described thus far. It does not exhibit a continuous circular motion feature similar to the
Blanco-Mead concept; instead it moves in two half revolutions to complete one suture. It
is different however in that a hook is not required to drive the needle. Also, a simple
pistol grip with a trigger mechanism actuates the needle. The design of the external suture
pool does away with the huge challenge of the topology of the thread. Since the thread is
pulled from a spool as and when it is needed, the entire body of the thread does not need
to be pulled through the defect each time. This also increases safety of the device by
minimizing the amount of material that re-enters the device after contact with the body.
The simplicity of the proposed concept and its remarkably low number of moving parts
rendered it very attractive.
Given the above promising characteristics, design concept 3 aimed to build on the idea
and test the theory. Having rendered an exterior look for the overall device, efforts were
immediately focused on the sewing feature of the device. Figure 18.0 shows an initial
rendering of the overall device.
Figure 18.0 Rendering of overall device
33
Sewing feature of device
The sewing feature of the device consists of a needle mounted on a pulley that is driven
by a stainless steel cable. The cable is attached to a mounted tension spring on one end,
and to the trigger of the handle at the other. A rough setup is illustrated in Figure 19.0.
Figure 19.0 Sketch showing driving components of the needle
The intriguing needle in this device is a 180 degree arc extending toward the center of the
needle. The end of the needle, unlike its two predecessors does not have a groove for
thread attachment. The needle is not permanently attached to the thread. The front end of
the needle is pointed so as to help penetration through the skin. Behind this front end, is a
purposeful hook which forms the basis of the
entire design and determines the success of
the needle and hence the device. Figure 20.0
show s a close up of the needle followed by a
rendition of how the needle works in theory
in Figure 19.0.
Figure 20.0 New 180-degree arc needle.
34
-007f,
. ..................-.-
0
..
--- - -
.
0
49
Figure 21.0 Rendition of workings of the needle (cross section). Also shows
incorporation of thread into the process.
Prototype 3
Before a considerable amount of time was exhausted on prototyping the whole device, it
was decided to build a prototype of the needle first. The needle was cut on a waterjet
similar to its predecessors, and was mounted on a wooden stand. Figure 22.0 shows a
picture of the first needle.
35
I
N
-
-
-
-
-
I
-
--
Figure 22.0 Photograph of the first needle.
The needle worked well in theory and in practice. It was able to successfully move
through low density foam, pick up thread and bring it back to its point of origin. The
sewing process was not carried any further. Challenges however cropped up when
chicken breast was used to simulate skin. It was noted that the hook of the needle
successfully picked up and delivered thread however the sharp retreating hook served as
an open shear and was found to tear the skin.
More alterations were required if the skin were to be protected. Several permutations of
the shape of the hook followed:
3.3.3.1 Design 3b: Hook with Closing Wire
Hook with closing wire: it was decided to cover the shears of the hook by attaching a
wire to the needle. This action is shown in simple terms in figure 23.0 below.
However, this idea was abandoned due to the following reasons:
- the closing wire motion demanded accurate timing synchronized with needle
motion throughout mechanism. This would be challenging when the device were
miniaturized.
- The closing wire also added to the number of moving joints in the body cavity.
This is always an unsafe characteristic.
36
- -
7
, -
-Advg
at
0U-IF
-I
-
1
-~~
-
--
STITCHING SEQUENCE; PARALLEL LAYERS OF RATERIAL
I
Needle
Closing
Empty needle
Neele hooks on
thread below
penetrotes
4
d-i
Wire
clos ing:
ook
re
Wre closes hook
opening and than
retraces
Needle putts
thread across
Need e advarce
pvL ng tflre ac
layers
C1os jng wire
open s hook
Hook is opened Co
a-!low thread 1oop
tc siae .Jwnrd
Needle penetrates
agoln. Previous lOop
s.lides along needle.
Hook catches new
chread section.
hook is closed
by closing wire
Needle retracts asair
pulling threaa tnroau
previous lcp a.
forming the ChanStatrhe lot then
advar::es rune
c
Figure 23.0 Design of a hook with closing wire. Source: Blanco's notes dated 1991
3.3.3.2. Design 3c: Hook curved into
Needle
Concept 3c returned to the initial hook in
design concept 3, with a minor alteration
made to it. The pointed end of the hook was
curved in as shown in figure 24.0, so as to
blunt out the shear effect of the retreating
hook. Point A would now act as a fulcrum
enabling the hook to bend into the needle as
the latter recedes through the skin. This
bending action also ensures that the thread is
carried safely to the other side.
A
Figure 24.0 Curved hook needle
37
.
.
. .
.
.. . .............
. ...
............
Prototype 3c
For prototype 3c, the waterjet method was abandoned since the flat nature of the needle
did not allow forces to be uniformly distributed, and this was not an accurate
representation of how the cylindrically shaped needle would react to stimulating forces in
the real device. Metal wire was annealed and bent to give the appropriate shape. The
hook was tic-welded.
The revised needle was tested by placing it on a mount. Chicken meat was used again.
The needle was successful this time, in receding through the skin without shearing it. The
suturing process was then taken to the next step, and the needle was moved along the
meat specimen to start the next suture. This however was not successful. The placement
of the hook on the inside surface of the needle did not allow it to retain the loop as it
progressed along the specimen. This is required for a chain stitch. This was a feature that
was not obvious in the 2-D sketches.
L
K
I
/p
r
K-
K
K
K
4-
C
Figure 25.0 3-D topological feature that was ignored in 2-D sketches
38
Figure 26.0 Mounted setup of needle with hook on inner surface
3.3.3.3 Design 3d: Curved Hook On Outer Face of Needle
It was deduced that placing the hook on the outer surface of the needle would solve this
problem. The needle was altered to accommodate this feature.
Prototype 3d
A
The hook on the outer face of the needle
did indeed solve the topological
challenge. The loop was retained whilst
the needle moved along the wound to its
next point of penetration. The needle
however still needed to be tugged so as
to release the thread at the appropriate
time. This was considered a minor issue
Figure 27.0 New curved hook on outer face of nee dle
that could be solved easily by a simple
modification of the hook. Further testing of Prototype 3d however showed another grave
concern that again had been overlooked causing a great setback in the design process.
39
Figure 28.0 Photograph of needle prototype with hook on the outer face of the needle
The Challenge
The needle as it stood was able to perform all the functions that were demanded of it.
Round 1: pierce through skin, pick up thread on other side, bring thread back to point of
origin, form loop with thread, move forward with loop; Round 2: enter through loop to
pierce second spot, pick up thread and bring back thread to point of origin.
Direction of Travel
Latch picks up
both new loop
and old loop
II
\1
II
y.,1
U
I
Defect in
bird's eye
view
Figure 29.0 The Topology challenge in Round 2 of suturing. Source Blanco's notes
40
M
.......
.. ......
-
- 11=
. ......
- --
--
-
The problem arises in the next step. The needle cannot discriminate thread, and on its
way back to the point of origin after round 2, surfaces with not just the loop from round
2, but also the loop form round 1 which lays on the surface to produce the chain stitch.
The challenge is pictorially represented below and leads to Design Concept 3e.
3.3.3.4 Design 3e: Needle with Sliding latch
A latch was placed on the needle which controls the
exposure of the hook on the needle. The latch is
controlled by friction caused due to the
movement of the needle such that a forward
movement of the needle pushes the latch
back, uncovering the hook; a backward
movement of th needle pushes the latch
forward covering the hook thereby addressing
the issue of grabbing unwanted thread. The figure
below shows the needle that was designed and later
prototyped.
e
50
24e~r-
Figure 30.0 Sketch of needle with proposed
sliding latch
D A
r
b
~K~2~Z1~
(
~1~'
i/I
Figure 31.0 Working of the sliding latch feature. The latch is seen to cover the hook on the
return journey
41
-
- ALil -
NAlaw AM i1a 4
-
.-
- -
-
-
..
-
---
-
__
- -
_
____Z_
Prototype 3e
It was extremely challenging to prototype the needle. The body of the needle was made
by bending 3/16" stainless steel metal rod into shape. The head of the needle was turned
on a lathe and the hook shape was sawed. A 3/16" Aluminum rod was used to make the
latch. This was hollowed out with a drill bit to enable the rod to slide easily over the
needle. It was then bent to ensure concentricity with the needle. The tails end of the
needle which was to be attached to the pulley was formed by first hammering the steel
rod into a flat shape using an oxy-acetylene flame. A " hole was then drilled that
allowed it to be held by the mount.
Sliding Latch
Figure 32.0 The solution - curved needle with a two-way sliding latch
42
LU.
.L.
......
........
Direction of Travel
Latch secures new loop, covers needle
hook and pulls new loop safely
throu gh old loop
Cf
A
Latch moves back
down shank of needle,
setting loop free and
leaving it on tho
surface
t
A
I/ A
I
Latch closes
hook on return
journey due to
friction
I
I4
%
A
Figure 33.0 Detailed working of the latch and how it surmounts the challenge placed above.
3.4 Arc Angle of Needle
An important aspect of the needle that was considered was the angle of curvature. It was
deduced that a lower arc angle required a lesser amount of force to rotate it. Analysis into
this feature showed that the arc angle was dependent on the depth of penetration of the
needle into the skin.
Arc Angle ao Depth of Penetration
43
A lower depth of penetration allowed a lower arc angle, as shown in the figure below.
Arbitrary lengths were chosen at this point, since final specifications on the needle had
not been made. The needle was taken to have a diameter of 1 cm. All other calculations
were based on this value. The figure used a scale ratio of 1 inch = 1 cm for simplicity.
41
Arc Angle: 1550
Depth of penetration: 3/8 units
Arc Angle: 1200
Depth of penetration: 1/8 units
Figure 34.0 Relation between arc angle and depth of penetration.
A needle of 155' arc angle was settled on. Since all prototypes and tests until this stage
had proved that the needle was functional and the idea was acceptable, the next phase of
the project was started: designing the needle actuation and incorporating the needle into
the final device.
44
Chapter 4: Final Design Concept and
Product Development
Having determined the final design for the needle, the overall device was designed,
paying particular attention to how the needle would be actuated. In the initial concept
thought of by Professor Blanco, the thread is held in a suture spool placed outside the
body of the cannula. The tension in the thread is controlled by an idler. The needle is
actuated by cables that are connected to a trigger at the handle. Most surgeons prefer the
pistol grip with a trigger mechanism, since it can be operated with a single hand.
4.1 Elements required for a working device
Needle Actuation
Working from the original concept, the needle is actuated by a trigger control via a pair
of stainless steel cables. The cables wrap around a pulley that is concentric with the
needle. The pulley is designed such that grooves on the surface accommodate both the
needle and the cables.
The cables run along the tube such that one end is attached to the trigger which is pivoted
about a point on the handle. The other end is attached to a tension spring that is anchored
on to a stationary surface within the back end of the device. This setup is shown in Fig
19.0 in Chapter 3.
When the trigger is pulled, it pivots about its fulcrum, pulling the cable with it. The
tension spring allows the cable to expand in length comfortably. Once the trigger is
released, the cable is retracted into place by the spring. This single push-release
movement of the trigger carries the needle through the skin and back to its point of
origin. The surgeon will then move the device along the defect and repeat the process. All
the while, the needle retains the loop from the previous suture, and releases it at the
appropriate time. The movement of the needle relative to the defect is pictorially
represented in figure 35.0
45
-JS:7Y71--
(
SPRING UNDER TENSION
4-
(
(
*
*
**
'7
As the trigger is pulled, it pivots about its fulcrum and pulls on the attached cable causing tension in
the spring. The moving cable turns the pulley which in turn drives the needle through the defect.
45
SPRING RELAXED
(~4 'K
*
*
*
(~K
When the trigger is released, the process is reversed. The tension spring relaxes pulling the cable in
the other direction and driving the pulley in reverse. This carries the needle back through its path in
the defect, bringing with it the thread that has just been picked up.
Figure 35.0 Expected movement of the needle
46
Thread Mechanism
With the new design of the needle, it was clear that the placement of the thread and the
tension required in it, were crucial. The thread needed to be placed at a plane that was
parallel to the needle, very close to the tip of the latter. For ease of testing, it was also
preferred that the thread run the full distance radially, of the tube. This required precise xy coordinates in order to mill two holes on the curved surface of the tube that would
house the thread. Needless to say, this was a challenging task. It was thus decided that the
thread be contained in an adjustable holder, wherein one coordinate was fixed, while the
other was mobile.
Trigger Mechanism and Handle
An appropriate trigger mechanism was needed that would allow maximum movement of
the needle with minimal movement of the trigger. This would make for a comfortable
trigger in use. The handle needed to be ergonomically designed for good grip control.
The first large-scale prototype was thus designed, built and assembled to test the
functionality of the needle and the feasibility of the concept thus far.
4.2 First Large-Scale Prototype of overall device
A ratio of 1:2.5 was chosen for the first device prototype. This proved ideal for reasons
already stated in Section 3.2. The design and prototyping of the components including the
processes used are summarized below.
Needle
The needle design remained unchanged from the last working prototype. The prototype
was however made using a 0.030" O.D stainless steel wire. This was bent into a 1.00"
O.D arc using pliers. The latch was made by welding a sheet of thin stainless steel, and
was curved concentric to the needle. A fine toothed saw was used to shape the hook. The
arc of the needle extends into a curve that enables attachment to the pulley.
Pulley
The pulley is a single stock of brass that has been turned
on a lathe. It measures 0.83" in overall length, and 0.5"
and 0.2" in diameter. Two narrow shafts extend from the
pulley. These vertically lock the pulley to the cannula.
Grooves on the pulley allow the 0.015" stainless steel
cable to be comfortably located. A bushing allows the
pulley to move with minimal friction against the surface of
the plastic tube serving as the cannula.
Figure 36.0 Pulley
47
Cable
5x7 0.015" Stainless Steel cable was used.
Spring
A 0.25" inch diameter tension spring was used in the cannula
Adjustable Thread Tensioner
The tensioner was carved out of a lexan sheet to give it a springy
consistency. A set screw was mounted on the side to enable an
exterior control of the placement of the thread. Figure 37.0 shows
the thread holder.
Figure 37.0 Adjustable thread holder
Cannula
Al" I.D. plastic tubing was used as the cannula. It was milled on either side to allow
space for manipulation of the stainless steel cables, which proved to be challenging to
handle. The tube also contains a tapped a 0.25" hole to house a 10-32 set screw on one
side, and a 0.35" hole to house a rubber bushing on the other side.
Trigger
For the purposes of the first prototype, the trigger was designed to produce a movement
ratio of 1:2; a 3/4" push of the trigger was translated to a 1.5" movement of the cables
connected to it. The trigger was made using a %" sheet of ABS that was water jetted.
Grip grooves on the trigger allow for comfortable manipulation.
A compression spring was placed between the
trigger and the handle, so as to spring load the
trigger.
0
0
Figure 38.0 Workings of the trigger
.4
.4
L
48
Figure 39.0 Illustration of trigger-needle interaction
Handle
The handle was designed with
a functional emphasis, as
opposed to concentrating
efforts on ergonomics at the
time. It was made out of a
polymeric material that was
milled on a CNC, to allow for
the linkage movements, and
then contoured using a water
jet. Aluminum dowels on the
inner surface joined the two
halves together.
Figure 40.0 Photograph of first
version of handle
49
Once the handle was made, all components were assembled together to form the overall
prototype.
Figure 41.0 Overall Prototype assembly
4.2.1 Further Modification
Before the prototype was tested, a few additional changes were made to it to make it
more comfortable to use. The trigger was one major feature that needed revamping. The
compression spring demanded a heavy load of about 4-5 lbs in order to push the trigger.
Although this was a small amount, it was still not comfortable if the device was to be
used single-handedly. A new handle was also worked on that was more aesthetically and
ergonomically pleasing.
New Handle and Trigger Mechanism
The redesigned trigger enabled a lesser amount of force to drive the needle, and also used
only one linkage as opposed to its predecessor. The trigger shape was also redesigned for
more comfort during use. A narrow shaft serves as the fulcrum for the trigger. This is
press fit to the trigger and slip fitted to the handle casing, allowing good rotational
movement about the center of the shaft. A tension spring is attached to the trigger to
spring load it. The cable is guided through the casing by an in-built tubing. Overall the
new handle is simpler in design and more comfortable in use. The new handle was 3-D
printed to make a more ergonomically fitting device. The final look was achieved by
using a combination of filler, sanders and paint.
50
. .
.
.
.........
... .....
......
.
. ...........
......
....
. .......
.....
.......................
Figure 42.0 Redesigned Trigger Mechanism
Figure 43.0 Redesigned handle.
51
Figure 44.0 Redesigned handle before polished finish
4.3 Testing of First Prototype
The first prototype was tested on a sheet of foam rubber which simulated skin. The
trigger and handle worked well. Minimal movement of the handle gave a significant
movement of the needle. However, it was noted that even though the scale factor of the
needle and the other components were 2.5 times the actual size, the length of the device
remained the same as the actual device. This gave confusing results when gauging the
force required on the handle to rotate the needle i.e more force was needed and a larger
distance was traveled in order to rotate the bigger needle. This discrepancy in scale ratios
led us to discontinue testing on this prototype and to build a second prototype that was
closer to the actual device in all dimensions.
4.4 Second Large Scale Prototype
The second prototype moved closer to the actual size of the device with a scale factor of
approximately 1.5. It contains a 0.025" diameter needle that has an arc diameter of 0.44".
It is encased in a 0.5" lexan tube. The stainless steel cable used is 0.006" in diameter. The
handle is reused from the large scale prototype. Minor alterations were made to the parts
52
to facilitate manufacturing and these have been incorporated in the final design
blueprints. Following is a detailed description of each of the parts and how they were
manufactured.
Needle
The needle design remained unchanged from the last
working prototype. The final needle was made using a
0.025" O.D stainless steel wire. This was bent into a
0.44" O.D arc using pliers. The latch was obtained
from a hypodermic needle, and was curved concentric
to the needle. The hook was achieved by sawing the
shape with a fine-tooth saw. The arc extends into a
curve that enables attachment to the pulley.
Figure 45.0 Needle
Pulley
The pulley is a two-part assembly measuring 0.25" in diameter and spanning a length of
0.4" in length. It was turned on a lathe from a solid shaft of brass. Its two part assembly
facilitates the attachment of the needle. The upper part is
0.1" in length and the lower 0.2". A 4-40 set screw holds
the two parts together whilst sandwiching the needle
between them. A 20 pitch thread on the surface of the lower
part serves as a groove to hold the 0.006" cable that is
wound around the pulley. A shaft of 0.125" diameter and
0.1" in length extrudes from the bottom of the second part.
This is slip fit into a Delrin@ bushing on the cannula which
serves to minimize friction against the surface of the lexan
Figure 46.0 Pulley
tube serving as the cannula and also vertically locks the
pulley to the lower surface of the cannula. The pulley is
vertically locked to the upper surface of the cannula via an altered 10-32 set screw that
extends loosely into a receptacle on the pulley.
Figure 47.0 Pulley and needle assembled together
53
Cannula
The cannula is a 5/8" O.D, %" I.D lexan tube. It is drilled and tapped 0.15" from the edge
of the tube, to accommodate a 10-32 set screw, and drilled on the opposing side to press
fit a Delrin@ bushing of 0.210" O.D. Two 1" long, 0.125" wide slots on the tube enable
facilitate manipulation of the cable.
Thread holder
The miniature size of this device required a mechanism that
held the thread in tension with an error fluctuation of no more
than 0.002". A part was designed that not only locked the
thread in place but that also helped constrain the needle such
that it was not deflected by any external forces encountered
during passage through the skin. Grooves for the thread were
also integrated into the design.
Fig 48.0 Thread holder
Cable
1x7 Stainless steel cable of 0.006" diameter was used. The cable
was attached to the trigger by sandwiching it between a socket
head screw and a nut. A tube guides the cable from the handle
to the cannula where it is follows the grooves on the pulley.
It then attaches to a tension spring which is suspended on 1/16"
metal rod that is press fit into the tube.
Figure 49.0 Cable cross section
Trigger and Handle
These parts have remained unchanged from the large-scale prototype.
All components were assembled to form the overall product show on the next page.
54
Figure 50.0 Photograph of second prototype assembly
Figure 51.0 SolidWorks rendition of final device
Once the assembly was set up, it was prepared for testing the proposed design
mechanism. Until this point, all individual components were tested as they were
designed, but the whole assembly was not. Prior to testing, the expected mechanism of
the needle-thread interaction was outlined in detail as shown below.
55
Figure 52.0 Expected mechanisms with new setup.
4.5 Testing of Second Prototype
The second prototype was tested using a sheet of foam rubber simulating skin. Prior to
incorporation of the thread, the needle showed great promise. It was able to travel
effortlessly through the material to resurface on the other side when actuated by the
trigger. The force required of the handle was negligible. The latch was effective and
responded well to the friction en route. Incorporation of the thread however gave
unexpected results. The expected mechanism was not achieved throughout. In the first
step, the needle was able to capture the thread constrained in the thread holder and carry
the loop over to the other side as shown in Figure 52.0. However, in step two, since both
the needle and the thread holder do not move relative to each other, the needle cannot
advance along the source thread as was originally conceived. Instead the needle continues
to trace its set path. The result is a failure of the needle to grasp the thread since there is
no longer any thread within its track.
56
....
..
....
Needle misses
thread on
second trip
56
a
Figure 53.0 Challenge of missing thread within track.
The source thread needs to be moved each time the needle picks up a loop, such that it is
ready for the next pickup. Due to the miniature nature of the second prototype, further
testing was carried out on a more improved large-scale prototype. Figure 54.0 shows the
experimental set up.
57
Idler with suture spool
Thread
adjustor
Needle
Wooden
mount
Figure 54.0 Large scale experimental set up to investigate needle-thread interaction.
The setup indeed confirmed the problem of the thread. The thread seemed too constrained
by the holder for it to be able to move when needed. Hence, this constraint was alleviated
by the elimination of the lower part of the thread holder such that the tail end of the
thread was set free. This solved the problem. The thread was now free to move so as to
place itself in the path of the needle. This meeting is made possible by the movement of
the skin relative to the needle and the holder. This was serendipitous. The movement
allows the thread from the stitch before, which lies perpendicular to the plane of the
needle, to form an angle that facilitates pick up by the needle on the next stitch. This is
shown in the figure below.
58
..
.......
.-,
- --
-- - -
-
- -
1
-1 -
7 -= _Vd.
Angle allows
thread to be in
path of
needle, for
easy pickup
Ir
Figure 55.0 Angle formed by thread from previous stitch facilitating pick up by needle
Testing of the experimental setup was carried out using chicken meat. The pictures below
show the success of the sliding latch to grasp thread, release thread and discriminate
thread when needed.
Figure 56(a) Needle emerges at point of origin
with loop from other side. New loop passes
through old retained loop.
59
Figure 56(b)Chain stitch is formed by pulling
needle new loop through old loop.
Figure 56(c) Needle moves onto next point of
insertion, retaining the newest loop.
Figure 56.0 showing needle-thread interaction during the various stages of a single suture
60
Locked
Chain
Sitch
Figure 57.0 Final thread layout showing suture pattern on test specimen
This final change was incorporated into the second smaller sized prototype. The
prototype functioned well to give a suture pattern similar to the large scale prototype.
With the quality of parts and the functionalities required of them, it will be possible to
achieve a target cannula diameter of 1 cm or even less. This possibility is enhanced by
the minimal number of small moving parts required for the device. All parts can be easily
machined given the right equipment. This machining was not possible in the realms of
the machine lab, but can be carried out if the device manufacturing is outsourced.
61
i Am-
-,- -- -
- -- -- --- -- -
Fiaure 58.0 Final functionina prototvDe.
Defect
lcm incision
Target organ
into t ody
cavit
r7
Patient Body
inflated for
surgery)
Figure 59.0 Representation of device as used in surgery
62
....
..........
........
__ _ ........
.........
..
. . ...
Figure 60.0 Sketch showing device at work
4.6 Features of Device
Several key characteristics were highlighted in Chapter 3, and these formed the basis for
the design of this suturing device. The features of the device have helped achieve these
design constraints namely:
(1) An automatic actuation mechanism to guide the needle through a fixed trajectory,
and also recapture and orienting the needle - this is achieved via the pulley-cable
system; a simple and innovative mechanism using an exceptionally low number
of parts. The curved needle is well grounded in the pulley which serves as a selfrighting needle ensuring a fixed trajectory. The needle is constrained additionally
by the thread adjuster. The actuation mechanism also allows a quick delivery of
the needle through the tissue minimizing trauma
(2) Good tactile feedback - is achieved by the center port delivery of the device. As
the needle penetrates the tissue, reactant forces are transmitted via the stainless
steel cables to the handle and hence the surgeon. The stainless steel characteristic
minimizes any dampening of the force, signally relatively accurately the entry and
exit through the tissue.
63
(3) Minimal re-entry of parts into device - the needle is the only part that re-enters
the device after interaction with the body tissue. This is a highly important
characteristic to reduce the spread of any infections over the body of the defect.
(4) Minimal re-entry of thread into device - is achieved by a suture spool located
outside the cannula that is fed to the needle as and when it is needed. This
eliminates the whole body of the thread from being pulled through the tissue each
time.
(5) Secure stitch - this is achieved by the interlocking chain stitch brought about by
the manipulation of the thread by the needle.
(6) Allows suturing on multiple layers - achieved by the design of the cannula which
can be made minute and long enough to penetrate the deepest layer of the defect.
The positioning of the needle facilitates this process.
(7) Extracorporeal operation - achieved by the trigger activated mechanism of the
cables and the tension spring. This setup enables the return journey of the needle
after picking up thread to be entirely passive, requiring less effort on the part of
the surgeon.
(8) Disposability - The device is designed to be disposable since this was a feature
that was ranked highly by surgeons. This eliminates need and concern over
sterilization of equipment.
(9) Cost effective - The device is designed for materials such as titanium to be used
for the cannula. However, almost all parts of the device with the exception of the
needle and the cables can be predominantly plastic without the risk of
compromising on performance.
(10)
Easy operative handling - The needle is actuated by placing a force of less
than 0.5 lb on the trigger. The whole device is made of plastic will not weigh
more than 200 gins. This allows a surgeon to use a single hand to hold and
operate the device.
(11)
A wide range of surgical applications - the device can be used for both
endoscopic surgeries as well as for surface wounds.
(12)
No external power source required to operate it - reducing energy as well
as dependability.
(13)
Ergonomical - the handle and the trigger which are the only parts that will
be held by the user, are designed with grip grooves and allow for maximum
comfort of the fingers as well as the often neglected palm of the user despite the
use of ill-fitting gloves.
(14)
Flexibility of parts - The device can use both absorbable and nonabsorbable thread.
4.7 Future Work
The device has been designed to facilitate only the first phase of suturing - passage of
needle through the tissue. Future work can focus on designing a knotting process that will
only require operation with a single hand. This involves a greater knowledge of the
manipulation and topology of the thread. For now, it is possible for a surgeon to use a
gripper to place knots on the tail ends of a suture thread.
64
4.8 Emerging Wound Closure technology
During the past two decades, wound care has made more advances than it had over the
past two thousand years. Four major factors account for this 5 :
* The biologic mechanisms of tissues repair are now being defined on a
biochemical and molecular level
* Financial support for wound healing research has increased markedly because the
social and financial devastation of wounds has come to be appreciated by health
care providers and federal health care funding agencies.
* The medical-industrial complex can envision profit in the discovery of more
efficacious modalities for wound care and hence is supporting wound healing
research.
* Reconstructive surgical techniques have changed drastically in the past two
decades with the advent of muscular and musculataneous flaps as well as
microvascular free-tissue transfers.
The race is now on to develop wound closure devices and materials that can meet the
challenge of tissue reaction. Efforts are underway to come up with antimicrobial sutures
such as the incorporation of conventional antibiotics - penicillin, sulfonamide onto the
suture surfaces. Also being tried is the incorporation of the silver metal onto the suture.
Antibiotics are also being incorporated into the interior of the suture through mixing of
antibiotics with the suture polymers before spinning into suture fibers. Biomaterials that
can accelerate the wound healing process such as chitin are also being looked into.
Absorbable sutures are being copolymerized so as to improve their biodegradation nature.
Several collagen and hydrogel based adhesives are also being investigated 6
To combat the challenge of minimally invasive surgery, researchers have developed an
automated system that is now in use on an experimental basis in several hospitals around
the country. This is the Da Vinci* robot, which acts as the surgeon's arms and eyes
during the operation. It was born from the same idea that drove the crude automotive and
the aeronautics industry, and is therefore a cousin of the robots used in the NASA Space
Shuttle. It enables surgeons to insert instruments into the body and navigate them like
they were their own hands! The robot has a control counsel and a pair of arms. Two
portals are inserted into the patient to house the robotic arms. The Control counsel has a
mouse control, a camera, a foot pedal and an infra red sensor safety feature that triggers
an automatic stand by action when not in use. The robot has 7 degrees of freedom in its
arm and wrist - that allow a combination of motions of rotation, pitch, insertion, grasp
and yaw. Its arms are 7 mm in diameter. It has an electric scalpel for tissue carving that
can be controlled by the foot pedal. The robot can also filter hand tremor, which can be
indispensable in highly sensitive surgeries like that of the heart. Its wound closure system
is highly specialized in that it uses a curved needle, and allows the surgeon to manipulate
it just as he were sewing and knotting using his own hands. It uses a magnet to retrieve
the needle and a vacuum cleaner to remove any left over thread.
Several new suturing and stapling devices are now being introduced that can be used in
minimally invasive surgeries. Their portal diameters range from 5-12 mm, with long arms
65
that extend into the cavity of the patient and mechanical four bar linkages that enable the
surgeon to control the suturing end within the cavity by movement of the handle
remotely.
" The Surgical Suturing Device developed at Simon Frasier University, Canada in
1998, which consists of a needle that has a circular arc shape that is moved in a
circular path in a guiding frame by friction between the needle and a timing belt.
The timing belt in turn is moved around by a pulley and a pair of bevel gears that
are actuated manually or by a small electric motor. Continuous movement of one
finger can provide the movement, and the surgeon has total control of needle both
in terms of position and range of motion.
" A revolutionizing development in suturing has been introduced by ONUX
Medical, with the advent of their new "Touche" product. This is a 5mm precision
instrument that sutures without needle. Through an ergonomic instrument design,
sutures are created effortlessly, with a multifunctional grasper. It has tissuespecific jaw configurations. The suturing process is a four-step routine - wherein
the tissue is grasped securely, the tissue is sutured by the push of a button, a
gentle twist secures a knot and the suture is then cut1.
4.8.1 Integration of other areas of science and engineering to enhance
current biomechanical methods
Several other dimensions of science and engineering are being looked into, so as to
integrate newer concepts and schools of thought into existing technology, in the quest to
develop better wound closure devices and bring about more optimal healing.
4.8.1.1 The Biochemical Dimension
4
" Microspheres1
: this application of chemical engineering toward wound closure
analyzes the use of a-hydroxyl, PLA, and PGA polymers to locally deliver growth
factors, ground substances (proteoglycans and GAG's) and clotting agents to
wound sites to enhance the process of wound healing and closure.
" Enhanced biomaterials:looks into the use of growth factor-incorporated suturing
material as another possible healing enhancer.
* Combining wound closure techniques: looks at combining the techniques of
sutures and adhesives; i.e. inserting fibrin glue7 before mechanical closure by
sutures, to enhance tissue approximation, and hence speed up and improve wound
closure, both biologically and aesthetically.
" Scaffolds: this builds on existing regeneration template technology, and looks into
using collagen scaffolds"" 5 as biodegradable porous scaffolds to guide ingrowth
of connective tissue and blood vessels and induce regeneration of underlying
tissue via interdigitation, while retaining moisture at the wound surface'
Collagen-GAG matrices have already been investigated by Professor Yannas and
his team at MIT.
* Hydrogels: as wound dressings in an attempt to maintain moisture within the
wound and enable autolytic debridement (slow digestion of dead cells by
endogenous phagocytes and enzymes) of dead tissue.
66
All of the above, are techniques that have very recently been introduced, or are
ideas that are under investigation.
A further possible technique, for which no undergoing investigation has been
heard of, could be a further amalgamation of existing techniques: such as the use
of microsphere-incorporated biodegradable suturing material. With an orientation
such that the microspheres were contained on the outer perimeter of the suture,
enabling them to immediately disperse on contact with the tissue. The underlying
suture material could perhaps be engineered to have a degradation rate
appropriate to the rate of growth of the target tissue. No doubt, suturing with
microsphere-incorporated material will be the challenging aspect of this technique
- perhaps a materials science task?
4.8.1.2 The BioelectricalDimension
-
Polarisationof wound edges: this is a possible technique that could be
carried out to enhance a well-aligned closure of the wound edges 16,17'18
Electricalstimulation: similar to that carried out in physical therapy of
injured muscles in order to enhance blood flow and hence wound healing
within the wound. Wounds possess a lateral voltage gradient across their
edges. This electric field is said to promote the migration of epidermal
cells to close the wound 6 .
4.8.1.3 Modifications to existingdevices
-
-
Improve thermal insulation capabilities of wound closure device: since
this will help to maintain a high temperature (evaporation causes cooling),
ensuring ample oxygen to neutrophils.
Improve moisture retention capabilities of wound closure: there are
several reasons for this:
o Wounds in general possess a lateral voltage gradient across their
edges. This electric field is said to promote the migration of
epidermal cells to close the wound. A moist local wound
environment enables the existence of a bioelectrical force called
the current of injury which could not exist in a dry tissue
environm ent '6,'18.
o A moist site may end up in a less noticeable scar' 7
o A moist environment created by the dressing prevents exposed
neurons in the wound bed from becoming dehydrated. This may
result in less pain",'9
4.9 The Future
Wound Closure has come a long way in the last decade. The future of wound
closure will almost certainly include new technology or new applications of old
technology to enhance the surgeon's ability to heal wounds. With minimally
67
invasive surgery growing to be the "only" approach to surgery, our ability to
perform is currently limited by our inability to obtain information about the
anatomy through minute incisions. Minimally invasive surgery also limits the use
of our other senses. Technology is now giving us tools to obtain that information
formally acquired by our senses. Wound Closure and surgical technology in
general will continue to borrow and adapt more techniques from its cruder
automotive and defense world cousins, drawing a similarity between the body's
immune system and enemy aircraft; and between the surgeon and the fighter pilot.
In this way, perhaps our design and technology to kill, may one day be used to
heal.
We are limited only by our imagination in the development of newer technology
that will further our ability to heal wounds and win this timeless battle between
man and bacteria.
68
Reference
1) Engineering Approaches to Mechanical and Robotic Design for Minimally
Invasive Surgeries, Ali Faraz and Shahram Payandeh; Kluwer Academic
Publishers
2) Ballantyne, Leahy, Modlin: Techniques of LaparoscopicSurgery
3) http://meds.queensu.ca/~pmsp/suturing/sutureworkbook.html
4) United States Pharmacopoiea
5) Schwartz SI, Shires GT, Spencer FC, Daly JM, Fischer JE, Galloway AC (eds);
PrinciplesofSurgery. McGraw-Hill
6) Chu CC, Fraunhofer JAV, Greisler HP: Wound Closure biomaterialsand Devices;
Chapter 3; Surgical Needles; 1997.
7) Wound Closure Manual by Ethicon (J&J)
8) Surgical Stapling Techniques Manual by Ethicon (J&J)
9) Steichen FM, Ravitch MM: "Mechanical Sutures in Surgery", Br. J Surg.,
60,191, 1973
10) Waldron DR, "Skin and Fascia staple closure", Vet.Clin. North America., 24, 413,
1994
11) Yannas IV: Tissue and Organ Regeneration in Adults. Cambridge, Springer, 2001
12) Discovery Health Information
13) Endoscope; October 1995
14) Hollinger J, Biomedical Applications of Synthetic Biodegradable polymers
15) Mian M, Beghe F, Mian E. "Collagen as a pharmacological approach in wound
healing". Jnt J Tiss React 1992;14 Suppl:1-9.
16) Jaffe LF, Vanable JW. "Electrical fields and wound healing". Clinics in
Dermatology,1984;2(3):34-44.
17) Rovee DT et al. Effect of Local Wound Environment on Epidermal Healing. Year
Book Medical Publishers, Chicago, 1972.
18) Nemeth AJ, Eaglstein WH, Taylor JR, et al. "Faster healing and less pain in skin
biopsy sites treated with an occlusive dressing". Archives ofDermatology, Vol
127, November 1991, ppl679-1683.
19) Hedman LA. "Effect of a hydrocolloid dressing on the pain level from abrasions
on the feet during intensive marching". Military Medicine, Vol. 153, April 1988,
ppl88-190.
Other References
1) Mian M, Beghe F, Mian E. "Collagen as a pharmacological approach in wound
healing". Int J Tiss React 1992; 14 Suppl: 1-9.
2) Hutchinson JJ. "Prevalence of wound infection under occlusive dressings, a
collective survey of reported research". Wounds, Vol. 1, 1989;ppl23-133.
3) Hutchinson JJ. "A prospective clinical trial of wound dressings to investigate the
rate of infectionunder occlusion". In Proceedings: Advances in Wound
Management. London, England,MacMillan, 1993, pp 9 3 -96.
4) Hollinger J, Biomedical Applications of Synthetic Biodegradable polymers
69
5) Katz J, Developments in Medical Polymers for Biomaterials; Medical Device &
DiagnosticIndustry; 2001.
6) Steichen FM, Ravitch MM: "Mechanical Sutures in Surgery", Br. J Surg.,
60,191, 1973
7) Waldron DR, "Skin and Fascia staple closure", Vet.Clin. North America., 24, 413,
1994
8) Majno Guido, "The Healing Hand - Man and Wound in the Ancient World",
Harvard University Press, Cambridge, 1977
9) Cushing, H: The control of bleeding in operations of brain tumors with the
description of silver "clips" for the occlusion of vessels inaccessible to the
ligature: Ann. Surg., 54, 1, 1911
10) McKenzie KG: "Some minor modifications of Harvey Cushing's silver slip
outfit" Surg. Gynecol. Obstet., 45, 549, 1927
11) Pavletic MM, Schwartz A, "Stapling Instrumentation" Vet. Clin. North. Am., 24,
247, 1994
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