Coating Overflow Removal Tool
Team Vimage (Team #3)
Mario H Gonzalez
George Lao
Vincent Hoang
November 1, 2004
EXECUTIVE SUMMARY
This purpose of this document is to describe why Guidant Corporation needs a
Coating Overflow Removal Tool for Drug Eluting Stents (DES). There is brief
description on what technologies led us to DES’s, which are considered by many
physicians a revolutionary way to treat cardiovascular disease because they are coated by
a drug that suppresses the immune system to avoid the bodies rejection of a foreign
object.. Since DES’s are such a recent technology their manufacturing has not been
mastered. The drug coating overflows onto unintended surfaces, namely the Inner
Diameter (ID) resulting in an unsafe stent. Since unsafe stents cannot be sold the over
flown stents are discarded and scrapped. This inefficient practice will be remedied by a
tool that can remove any coating overflow from the ID. This tool’s scope will be
designed to be implemented into the point were the stent has failed a quality inspection.
From that point the tool will remove any coating overflow in order to pass a re-inspection
for as many cycles until it passes quality inspection. There are several engineering
requirements that have been set by Guidant, the most important being that outer diameter
must not be contacted in any way to avoid any damage to the drug coating where it is
intended to be. A brief description of Team Vimage’s visit to Guidant’s stent plant in
Temecula is discussed at the end of the document.
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Table of Contents
EXECUTIVE SUMMARY ........................................................................................................ I
INTRODUCTION ................................................................................................................... 1
PROBLEM STATEMENT ....................................................................................................... 2
PROBLEM SCOPE ................................................................................................................ 3
ENGINEERING REQUIREMENTS.......................................................................................... 4
PRELIMINARY BUDGET PLAN ............................................................................................ 5
PRELIMINARY PROJECT PLAN ........................................................................................... 6
TEAM VIMAGE’S VISIT TO GUIDANT ................................................................................. 9
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INTRODUCTION
For people who suffer from heart disease a stent can save their lives. Stents were
not the first treatment method for coronary disease. It was not until 1987 that the first
coronary stent was reportedly used, but physicians had been trying to unblock arteries far
before then. The technology that preceded stents is called angioplasty balloons. The
procedure called, balloon dilation, consisted of a small balloon that would be fed through
a main artery, such as the femoral artery, with a catheter to the problem area. Once the
balloon is in place, it is inflated which compresses the plague against the wall of the
artery. This led treatment directly led to stents because without a way to hold the artery
open restenosis, the blockage an artery after corrective surgery, would occur. Stents were
designed to act as a scaffold and hold the artery open after being expanded by a balloon.
Stents have evolved from bare metal stents to today’s standard called Drug Eluting Stents
(DES), which are coated with a drug.
Our sponsor, Guidant, is planning to release a DES in the near future, but has not
been unable to perfect the manufacturing of it. Currently, the drug coating process is
flawed, which results in non-usable stents. At this point, the team has a clear
understanding of the problem, which is described in detail in the following section. Since
there are many ways to solve this problem the team has decided on a scope for the
problem, which helps in narrowing design ideas by distinguishing tasks the design is to
perform. The scope of the problem is closely related to the engineering requirements,
which Guidant has set, because the scope must include any tolerances or constraints that
are put in the engineering requirements. Once the problem is specifically stated the
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report focuses on the scope and engineering requirements, which will then lead into
budget planning followed by task planning.
PROBLEM STATEMENT
The problem occurs during the coating process. The solution can overflow due to
gravity that pulls the drug layer downward and the surface tension of the drug cause it to
creep around and into the Inner Diameter (ID). The amount coating that overflows
depends on the machine accuracy and precision. The coating within the ID is not desired
because it can affect the delivery process of the stent, in which it can damage the inflating
balloon and causes asymmetric expansion of the stent. Also, the overflow can leave a
scratch on the balloon and when the balloon is expanded to upwards of 200 psi that fine
scratch can lead to a rupture in the balloon and put the patient’s life at risk. Due to these
safety concerns, the stents that do have overflow on the ID are scrapped.
The stents that the coating overflow removal tool will be designed for are made
from 316L Stainless steel, with s-type round struts. The stents are laser cut from a block
of stainless steel with the length ranging from 8mm to 28mm and a fixed diameter of 1.63
mm. The stent is polished until required smoothness is achieved. The drug solution,
Everolimus, is then coated on the outer diameter of the stent. This drug is to suppress the
body’s immune system from rejecting the stent. The complete stent is then inspected by
a specialist to make sure the stent satisfies their quality control standards. Sometimes the
stent cannot pass the inspection because the drug coating has overflow to an undesirable
surface area, which is the inner diameter.
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This overflow creates a problem that needs to be solved in order to maximize the
yield produced. It is obvious that an overflow drug coating removal tool is needed to do
this. It has to remove as much of the drug in the inner diameter with the least amount of
damage to the stent. Our problem is to design and engineering such a device that will
solve their problem while meeting their specifications.
PROBLEM SCOPE
Our goal is to design a machine that automatically cleans all the coating from the
ID surface. We have decided that the tool will clean the entire ID rather than specific
spots ID so that way the entire inner surface will have a uniform surface. It is also easier
to clean the entire surface rather and pinpointing where overflow has occurred and then
remove it from the exact site considering how small stents are. The scope of our project
is going to start at the stage right after the stent has been coated has failed inspection and
ends with another inspection. Our sponsor specified that we cannot alter the way they
coat the stents in any way. We do have the option of changing the way the stents are held
during the coating process to minimize the overflow. To avoid complication, our vision
is that an operator has to feed the stent into the machine, and it will automatically remove
all coating from the ID. After an initial “rough” cleaning there will a final cleaning to
remove any lasting residues. Then everything after is out of the scope of our project.
This scope is advantageous because it is recyclable. If the after the two step cleaning
treatment there is still some overflow found in the re-inspection then the stent can be put
into the coating overflow removal tool.
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ENGINEERING REQUIREMENTS
The requirement posted by our sponsor is very straight forward.
1)
It cannot damage the stent during the coating removal process. Since the stent
will expands 2 to 3 times its diameter after they are implanted, a little scratch
can lead to major failure.
2)
Our final design must be able to work with stents that are 8 mm to 28 mm
long.
3)
Our coating removal process cannot contact the outer surface of the stent. The
coating they use are gummy and sticky even after they are dry. Any contact
will embed impurity on the stent surface. For medical devices, this is
definitely unacceptable.
4)
Most importantly, our coating removal process cannot damage the coating
located at the outer surface. It just destroys the purpose of using a drug eluting
stent over the bare metal stent.
5)
Each operation time must be less than 2 minutes.
6)
The operation should be easily operated by 1 person. Labor intensive
processes will dramatically increase the cost manufacturing of each stent.
There are also some additional requests for our design:
1)
If we are designing a machine that does the coating removal, it should have a
footprint the size of an 8 ½” x 11” paper. Since there is a limited amount of
space in their lab, the size of an additional machine is a very important factor.
2)
If possible, remove all left over coating solution off the inner diameter. Since
the DES is still under development, there are no absolute values of tolerance
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we can or cannot have. During the course of our design process, we will have
to report the estimated possible leftover to Guidant and let them decide the
acceptability of our design.
These two additional requests are not required to be satisfied by our final design, but
our sponsor will be very happy if we can meet these two specifications. We hope to have
as simple of a design as possible to minimize any necessary maintenance. Also, simple
designs are more reliable than very complicated machines and since this machine should
last indefinitely with proper maintenance we feel the simpler is better for its purpose.
PRELIMINARY BUDGET PLAN
With the standard budget of $400 dollars it seems unlikely to be able design and
build a small and precise tool, but Guidant has agreed to provide, within reason, any tools
or special equipment that may be necessary to work with stents to offset any spending.
We have set a rough draft of our project budget by putting a price tag of about $1100
dollars on any donations Guidant will give. By taking into consideration of our limited
time and resource, we will need $1500 dollar for our budget. The $1000 dollars is to be
spending entirely on the manufacturing of the design. This includes buying pre-made
parts such as simple machineries, specialize cutting tools or blades, heating or freezing
equipment, and lastly any special material needed. Considering the fragility of the stent
and it micro-size, or material need to be tough and yet small, so a one-third of the $1000
will be spend in material wise. The one third will be distributing to the machinery cost.
Lastly, the rest will be use for building the supportive structure or outline of the design.
The extra $500 dollar will be emergency money in case any unexpected problem arise
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with our intial design and parameters need to be changed. The allocation is sufficient
because we are aiming to make a simplest machine that will remove the coating only.
Therefore, our budget plan is set within these constraints and yet will try to meet
Guidant’s standard for quality.
PRELIMINARY PROJECT PLAN
Our project plan is divided into three phases; the first is project development,
followed by project design and manufacture and lastly is project testing and analysis. In
the project development phase, which covers the first quarter of school, the goal is to
specify, justify and research the problem we are given by Guidant. Task fo the first
quarter include background research, visiting Guidant, define our problem very
specifically and create a list of potential conceptual design. By the end of this quarter we
will have a clear project definition and requirement, and finalize a conceptual design. At
the beginning of winter quarter, our design and manufacture phase will begin. This
includes, research and development of similar conceptual design, a detail drawing of the
design and production plan for manufacturing the design. The most important goal for
this quarter is to be focus on the design layout, such detail drawing, and get them done by
the end of the quarter. During spring break, we plan to work on some part of the
manufacturing process of our product beside what is being made by the machine shop.
We will assemble the parts during the beginning part of the spring quarter. We have two
major goals for this quarter, one is to test and revised our product and the last is to
analyze our project. The test and revised part will include sample testing and making
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sure it functions properly and if not fixed it. In the analyzing part of the project we will
look for specific requirements that were or was not met by or sponsor and find out why.
The project plan is illustrate in the Gantt chart, which show the amount of time distribute
for specify task.
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Remaining
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Table 1.1 Gantt Chart
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Finalizing Product
Analysis and Feedback
Test and Adjust design
Assemble of Parts
Munafacturing
Design Review Process
Production Planning
Detailed design analysis
Finalize Conceptual Design
Budget Planning
Conceptual Design
Narrow Design Possibilities
Design Brain Storm
Planing and Developement
Problem Definition Report
Background Research
Contact Guidant
TEAM VIMAGE’S VISIT TO GUIDANT
Recently on a trip to Temecula, to visit Guidant’s stent plant our host Mark
Abushabky gave us a brief tour of the facilities. This gave us the opportunity to see the
specific stents that we will be working with and how they are processed. Through glass
we saw the machines used to coat the stents and actually inspections taking place. This is
when we found out that Evirolimus is an immunosuppressant that alters DNA, which is
the main reason we will not be having any contact with the real coated stents. Contrary,
we will be provided with stents that are “dummy” coated for testing purposes. An
interesting procedure that Guidant insisted we do was to sign a confidentiality agreement
in order to protect any confidential material.
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