LifeCell™ Corporation - University of Delaware
4/13/2020 BMEG450: Senior Design
University of Delaware
A NOVEL TOOL FOR REMOVAL OF HUMAN ADIP OSE TISSUE
Team Cutting Edge
Brandon Boles- BMEG
Audrey Guyer- BMEG
Ryan Mitchell- BMEG
Krunal Parikh- BMEG
Matthew Ringer- BMEG
Sponsor:
LifeCell™ Corporation
Brian Tamedl
Amanda Palmer
César Tapia
Advisor:
Anita Singh, PhD.
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TABLE OF CONTENTS
BMEG450: Senior Design
University of Delaware
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University of Delaware
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INTRODUCTION
Background and Significance
BMEG450: Senior Design
University of Delaware
LifeCell™ Corporation processes donated human skin into allografts for further use by hospitals and reconstructive physicians. Before the donated skin is further processed, technicians remove the adipose tissue from the dermal layer using a scalpel and forceps. The current method of fat removal is associated with a variety of issues including worker injury and damage to the dermal layer. The motivation of this project is to mitigate those issues in order to improve worker safety and promote the company’s profitability through a more uniform allograft product.
Project Scope
The scope of this project is to develop a functional prototype that will remove adipose tissue from the dermal layer of donated human skin while also promoting technician safety and increasing functionality over the current process.
Wants and Constraints
The wants and constraints were generated to meet the demands of the engineering support team and technicians at LifeCell
™
in order to improve the existing method of removing adipose tissue without hindering current production or safety requirements. o Safety: The risk of harm through glove puncture and repetitive use injuries for the technicians should be lower than the existing method. o Functionality: The device should effectively remove all adipose tissue without damaging the dermal layer of donor tissue. o Cost-efficiency: Device should optimize high durability with low cost.
Design Metrics
Metric
Technician
Incidents
Technician fatigue
Visual inspection, fat removal
Visual inspection, dermal damage
Want/Constraint Description
Safety
Safety
Functionality
Functionality
The device should pose no risk of user harm
The device should minimize the risk of repetitive use injuries
The device should be effective in fat removal
The device should not damage the dermal layer of tissue
Target Value
0 technician incidents
50% reduction in worker fatigue
100% fat removal from the dermal tissue
80% reduction in tissue damage
Reference
Industry standard
Comparison to current method; target value supplied by LifeCell™
LifeCell™ product standard
Comparison to current method; target value supplied by LifeCell™
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Cost of handle
Cost of blade
Cost-efficient
Cost-efficient
BMEG450: Senior Design
University of Delaware
The design should minimize cost while maintaining functionality
The design should minimize cost while maintaining functionality
Less than $20 if disposable OR less than $200 if reusable
Less than $10 per donor lot
Target values supplied by
LifeCell™
Target value supplied by LifeCell™
CONCEPT GENERATION & SELECTION
Benchmarking
The current system LifeCell™ uses to separate the hypodermis from the dermis of the donated tissue lot involves the use of a scalpel blade and forceps. The forceps are used to secure the lot tissue while the scalpel blade separates the two layers with a swiping cutting motion. This technique leads to worker injury through glove puncture incidents and repetitive use injuries. The adipose tissue also varies in thickness, and the interface between the dermal layer and the adipose tissue layer is often uneven. As a result, mechanical damage to the dermal layer is undesirable but common.
A major competitor product currently on the market is the Amalgatome® SK, as shown in Figure
1. This device provides an ergonomic handle, allows for cutting at a variety of angles, reduces overall cutting time, and uses an electronic cutting blade to remove the fat layer. In order to create an efficient and competitive device, the same key features will be incorporated into the proposed concept in order to mitigate or eliminate the issues of worker injury and damage to the dermal layer.
Figure 1. The Amalgatome® SK is an existing competitor product with a circular powered blade.
Another competitor product is the Zimmer® Electric Dermatome Skin Grafting System, as depicted in Figure 2. Although this product is used to harvest skin grafts from living patients, there are a few elements that may translate well to concept proposals for the scope of this project.
The device incorporates a rechargeable battery located in the handle of this device, which is removed before the device is placed in the autoclave. The handle also comes with a knob to adjust the height of the blade, allowing the production of various graft thickness.
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University of Delaware
Figure 2. The Zimmer® Electric Dermatome involves the use of a mechanized blade to harvest skin grafts from live patients.
Preliminary Concepts
Based on the gathered benchmarking data, three preliminary concepts were proposed to the sponsor in order to promote increased technician safety and dermal protection. Concepts A, B, and C are outlined as follows.
Concept A
The first preliminary concept is an automated device with a curved cylindrical handle and a disposable rectangular blade with curved edges. A thin, plastic bumper piece is attached to the device under the blade to protect the dermis from mechanical damage as the adipose tissue is removed. This bumper piece will provide a guiding surface for the technician as he or she removes the adipose tissue. Along the handle, there is a trigger mechanism that initiates a continuous horizontal blade motion to begin cutting. The blade is intended to cut at 4,500-5,500 cycles per minute. This value was obtained for the Zimmer® Electric Dermatome product, which performs a similar function in cutting human tissue, and will work as a starting point for our design. See Figure 3 for a sketch of concept A.
Figure 3. Concept A integrates a thin, plastic bumper piece with an automated blade.
Concept B
The second preliminary concept is an automated device with a straight handle. A rounded bumper is located flush with the scalpel blade, allowing the technician guide the blade laterally along the dermal layer. The bumper aims to offer protection against mechanical damage to the dermal layer. The motor and blade will also cycle at 4,500 to 5,500 revolutions per minute, as previously described for concept A. See Figure 4 for a preliminary sketch of concept B.
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University of Delaware
Figure 4. Concept B integrates a rounded protective bumper with an automated blade.
Concept C
The third preliminary concept is an automated device with a cylindrical handle. An adjustableheight bumper is connected underneath a disposable rectangular blade by a two screw system.
The adipose tissue is removed using a lateral motion of the handle, and the blade will cycle at a perpendicular angle to the handle motion at approximately 4,500 to 5,500 cycles per minute, as previously explained for concepts A and B. See Figure 5 for a preliminary sketch of concept C.
Figure 5. Concept C integrates an adjustable height bumper with an automated blade.
Concept Selection
The final concept was selected after speaking with the sponsor and prioritizing concepts A, B, and C using the design metrics. Concept A will best meet LifeCell™ Corporation’s needs with a few minor modifications to the handle, as depicted in Figure 6. Notably, the handle was enlarged and the blade head will have an adjustable angle to promote ergonomics in both the seated workstation and new cleanroom suites available at the LifeCell™ facility (see Appendix A). The forward driven motion of the handle paired with the lateral blade motion is proven technology used in electric shavers and other cutting applications. The smooth, longitudinal motion provided by this concept improves user safety over the current lateral, swiping motion. This longitudinal motion not only helps eliminate puncture incidents, but it also allows technicians to use larger muscle groups in the back to prevent repetitive use injuries over the long-term. See
Appendix B for information about the proposed motor, Appendix C for the prioritized ranking table used in the selection of concept A, and Appendix D for the updated timeline and path forward for further prototyping and design validation.
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University of Delaware
Figure 6. Final concept selection for the fat removal tool
FINAL DESIGN
Overview
The fat removal device prototype incorporates an ergonomic handle with a translational blade motion that achieves the separation of the adipose tissue from the dermis. The motor rotates at
9.000 revolutions per minute and is supplied by a 3.2 V rechargeable battery. A standard razor blade is used and is easily removed from the pin clamping system between tissue lots and upon dulling. The blade rests on the 1/16” bumper, which protects the dermal layer. A toggle safety switch and pressure activated trigger mechanism power the device while minimizing the risk of puncture injury to the technicians. See Figure 7 for a rendering of the final design.
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1
3
KEY
1.
Ergonomic handle
2.
Safety toggle switch
3.
Push-button
4.
Delrin blade shield
5.
3 pins
6.
Razor blade
7.
Bumper
4,5,6,7
Figure 7. Fat removal device for tissue assessment at LifeCell™ Corporation
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Design Details
BMEG450: Senior Design
University of Delaware
Initial testing of an existing device was completed in order to validate the motor speed and battery voltage for the final design. Based on this testing, as outlined in Appendix F, the motor in the final design will spin at 9,000 revolutions per minute and will be supplied by a 3.2 V battery power source. This motor speed allows for effective cutting while minimizing dermal tearing and splashing of adipose tissue.
The faceplate design was evolved to meet the sponsor’s needs. A pin system was created using benchmarking from razor blade designs such as a safety razor in order to allow for easy blade replacement as necessary due to blade dulling and cleaning between separate donor lots. The bumper was set to 1/16”, and a blade shield made of Delrin was incorporated to protect fat from becoming trapped in the faceplate during use. See Appendix E for additional benchmarking information.
A dual trigger mechanism was incorporated to add a factor of safety in eliminating technician puncture incidents. A toggle ON/OFF switch must first be turned activated (ON) before the push button can be activated by the technician to initiate blade movement.
A standard razor blade was selected for use in the pin system due to its blade width relative to the desired handle dimensions, low cost, ease of availability, and the option for stainless steel.
Most importantly, the pin system aligns with the three holes in a standard razor blade.
Benchmarking information, engineering calculations, and an overview of the testing that was initiated for each component of the final design can be found in Appendix E. A full project budget is found in Appendix F, and the detailed design schematics are found in Appendix G.
User Instructions
Basic Operation
To remove the safety mechanism of the cutting device, the safety switch located on the top of the device must be flipped to the forward (ON) position. When ready to cut, the blade mechanism can be initiated by pressing and holding the trigger button on the bottom of the device.
The device should not be placed down without switching the safety switch to the backward (OFF) position in order to reduce accidental cutting injuries.
Replacing a Blade
To remove and replace a worn blade, flip the safety switch to the OFF position. The two screws located on the bottom faceplate should be removed using the provided screwdriver. The used blade should be immediately discarded in a sharps container.
The new blade is placed in the three pegs and the faceplate is reattached using the screwdriver.
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A new blade should be used as necessary when dulling occurs as well as in between every donor lot.
Cleaning
Flip the safety switch to the OFF position and remove the bottom faceplate using the provided screwdriver. Discard the blade in a sharps container. Rinse any tissue remnants off the device using running water and soak the removable faceplate parts and screwdriver in 10% bleach solution for 20 minutes. Spray the handle using ethanol and wipe thoroughly.
See Appendix H for more detailed user instructions, including background information about human skin to be used as educational material for technicians at LifeCell™ Corporation.
Cost Analysis
The overall cost of the non-autoclavable fat removal prototype developed for the scope of this project is $28.91, as outlined in the project budget in Appendix F, which is above the $20.00 target value supplied by LifeCell™ for a non-autoclavable device. Scaled up to massproduction, the per-unit production cost of the non-autoclavable design is estimated to be lower than the prototype, about $25.00, for an independent contractor such as Team “Cutting Edge,” as outlined in Appendix I. The final cost to LifeCell™ Corporation is subject to confidentiality clauses between the company and their vendors. There is no foreseeable maintenance cost, as the device is meant for single use only.
DESIGN VALIDATION
Failure Analysis
One major mode of failure is damaging the dermal layer while using the blade in the fat removal process. In the current method, a significant amount of dermal tissue is deemed unusable due to mechanical damage caused by the scalpel blade. To address this issue, a 1/16” stainless steel bumper was incorporated into the design to slide along the dermis during defatting to protect the dermis from coming in contact with the blade. The bumper system decreases the likelihood of human error leading to dermal damage.
Since the proposed design is battery operated, battery life and cutting efficiency are another prominent concern. Installing a trigger-switch mechanism into the device the conservation of battery life while the device is not being actively used. When the device is not in use, it can safely and easily be placed aside. This integrated trigger-switch mechanism also minimizes the likelihood of technician harm through accidental puncture incidents.
Another mode of failure is tissue building up inside the device and interrupting the mechanical mechanism, with the potential for decreased cutting efficiency. To mitigate this failure, a Delrin tissue guard was installed above the blade mechanism to prevent tissue from entering the body of
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University of Delaware the device. As the blade cuts through tissue, the fat moves to the side or over top the Delrin piece, preventing tissue buildup from hindering the performance.
The fourth major mode of failure is ineffective cutting. This mode was mitigated through benchmarking of similar cutting applications as well as testing and modifications of the various components of the device including the blade, motor and battery specifications, and bumper dimensions.
Testing
Each component of the final design was quantitatively tested for functionality as well as qualitatively evaluated for overall effectiveness.
Cutting functionality o The overall cutting ability of the prototype razor blade was evaluated and compared to the current scalpel method by using both methods to remove adipose tissue from human skin samples. During testing, both methods were used to remove soft yellow fat ranging from approximately 5 mm to 15 cm thick as well as fascia tissue, which is more difficult to remove. Both blades were equally able to cut through the various tissue types and thicknesses. To improve the cutting ability of the prototype, a serrated-edge blade and a rounded-edge blade were further tested based on feedback from the LifeCell™ engineering team and technicians. The chosen serrated-edge blade was determined to be incompatible with the current blade securement system, but the rounded edge was more effective in cutting through the various types of tissue.
Bumper functionality o Based on a visual inspection of the tissue, the number of deep tissue cuts made into the dermal layer was counted. After initial testing, there were 2 deep tissue cuts, representing an area of 2 cm
2
, made into 500 cm
2
of tissue, representing about 0.4% of non-usable product. While this figure does not meet the original metric value of 0%, it does represent an improvement over the current method, where an estimated 2% of the tissue experiences dermal damage. As a result of initial testing, further modifications to the bumper were incorporated and followup testing suggested this change would further decrease the incidence of dermal damage.
Tissue shield functionality o A qualitative analysis of the installed tissue shield determined if any tissue entered the prototype to cause a decrease in effectiveness. After 60 minutes of use in removing various types of tissue, controlling for battery decline and blade dulling, there was no noticeable decline in functionality. The installed Delrin tissue shield effectively funnels fat away from the front of the device, preventing fat from entering the body of the prototype where the motor and battery are housed.
Blade replacement time o The time it takes to replace the blade in the current design was compared against the time for scalpel blade replacement. It took an average of 60 seconds to replace
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University of Delaware the blade in the senior design prototype, as opposed to 30 seconds for the scalpel tool. The engineering support team at LifeCell™ also approved the current prototype design on the basis of overall increased functionality for the senior design prototype over the current scalpel method.
Battery life o To test the battery life, the device was fully charged and used normally in removing adipose tissue until a qualitative decrease in effectiveness was observed. Initial testing by technicians at LifeCell™ showed that the prototype battery effectiveness declined noticeably after about 15-20 minutes of use, whereas the battery was quoted at 45 minutes of continuous use by the company.
Since the average cutting time per donor lot is 45-60 minutes, the battery life of the current design is not adequate for cordless use. To try and improve this aspect of the design, a different model of beard trimmer was tested, which incorporated a
“boost” feature to initiate a faster motor rpm. This feature increased the effectiveness of cutting, and no noticeable decline in battery life was noted for a
40 minute defatting session.
Blade dulling o To test blade dulling, a new blade was installed and used in removing various types of adipose tissue until a qualitative decrease in effectiveness was observed.
Initial testing by technicians at LifeCell™ showed that the prototype blade dulled after 15-20 minutes of use, as compared to about 10-15 minutes of use for the scalpel method. See Appendix J for full details regarding this testing.
Handle ergonomics o The forces required to use the senior design prototype were analyzed and compared to Human Factors Design Standards. Electromyography (EMG) data was collected for forearm contraction during the swiping motion of the scalpel method and the pushing method of the senior design prototype. These results showed an increase in period from .65s to 1.55s and a decrease in voltage from
1.65mV to .65mV for the scalpel method and pushing method respectively. The installed trigger button has a 2.1 mm displacement and 0.5 inch diameter, which complies with HFDS standards. See Appendix J for full details regarding this testing.
Validation Results
Overall, testing of the final design demonstrated functionality in removing the soft yellow adipose tissue as well as tougher fascia from the dermal layer of human skin. LifeCell™ technician and engineering team feedback was used to make changes to the prototype in order to increase the performance in terms of the original metrics. Based on these changes, including the incorporation of a narrower, thinner bumper, rounded razor blade edges, and a “boost” feature for the motor and battery interplay, improvements were noted in the areas of cutting functionality, bumper functionality, and battery life.
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CONCLUSIONS
BMEG450: Senior Design
University of Delaware
Design Evaluation
Upon completion of the project, Team Cutting Edge created and tested a functional prototype that is capable of removing adipose tissue and fascia from the dermis of donated human skin while reducing workplace injuries. This device met the minimum requirements of the scope but there is room for improvement. In order to further improve the device and implement it into the
LifeCell™ process, further modifications still need to be made. The overall design performance should be improved through the implementation of a more powerful motor, a multi-finger grip trigger, and any remaining iterations that arise during further testing and validation.
The overall cost of the prototype was $142.48, which exceeded the $20 target value; however, labor represents a large part of the cost ($108), so the design would be closer to the target value for a team with more machine shop experience. Mass production of a future design would also bring the per-unit production cost closer to this target metric.
This device will provide LifeCell™ with deliverables and a path forward to improve upon the concept and eventually incorporate into their fat removal process.
Deliverables
The deliverables provided to the sponsor include the Bill of Materials (see Appendix F) and User
Instructions (see Appendix H) for the current prototype as well as a proposed continuation of prototyping, as outlined in Appendix K.
Path Forward
While a partially functional prototype was realized upon completion of the project, a fully optimized design was not successfully delivered to the sponsor. Based on specific feedback from the technicians and engineering team at LifeCell™, Team Cutting Edge recommends the following items be incorporated, tested, and validated in future prototype generations: a stronger motor,
Team Cutting Edge recommends the efforts of the project be continued since the problems presented at the beginning of the process, including the technician safety and tissue quality concerns, will continue to plague the current production method.
See Appendix K for a more detailed proposed continuation of future prototyping.
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APPENDIX
Appendix A: Ergonomic Handle Specifications
BMEG450: Senior Design
University of Delaware
Ergonomics are an important consideration in reducing worker fatigue. One way to mitigate the problems associated with the current system is to redesign the handle. The type of grip used in the fat-removal is the power-grip, and the dimensions of the handle should be modified to meet ergonomics data. The handle should be cylindrical in shape, and for an average male user it should be 10-15 cm in length and 3-4 cm in diameter to maximize the power and minimize discomfort
1
. To accommodate female users, who have a smaller average hand size, the lower-end values will be selected for the final design.
An angle adjustment system will be explored to promote a neutral wrist alignment for technicians
2
, allowing the device to be used in both the seated environment of the hood space as well as the standing cleanroom suite environment.
Appendix B: Motor Specifications
The proposed design will employ a motor with the following general power and usage parameters based on an existing market product that performs a similar task. The power requirements will be 14.5 V (fully isolated and regulated) with a maximum current of 4.3 A.
The speed of the motor will be approximately 4,500 to 5,500 cycles per minute
3
, as benchmarked for a comparable device that also cuts human tissue using a vibrational blade motion.
Appendix C: Prioritized Ranking Table for Concepts A, B, and C
The following ranking table was used for Concepts A, B, and C. The lowest score indicates the best overall design, Concept A.
Concept A
Safety
1
Functionality
1
Material
1
Costeffectiveness
2
Overall
Score
5
Concept B
Concept C
2
1
2
3
1
1
1
2
6
7
1
2 http://ergonomics.uq.edu.au/eaol/handle.pdf
3 https://www.osha.gov/SLTC/etools/computerworkstations/positions.html
http://www.zimmer.com/content/pdf/en-US/zimmer_electric_dermatome_ifu.pdf
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Appendix D: Updated Timeline
Milestone Tasks
Lead
Person
Phase 3: Detailed Design & Test Plan
Krunal
Matt
Ryan /
Brandon Modeling of Final Design using SolidWorks
Cost Analysis
Design details
Site visit
User Instructions (Honors add-on)
Draft of Phase 3 report to advisor Audrey
Final Phase 3 report to advisor and sponsor Audrey
All
Audrey
Phase 4: Performance Validation & Path Forward
Failure analysis
LifeCell visit -- testing
Validation results
Design Evaluation
Deliverables
Path Forward/Appendices
Draft of Phase 4 report to advisor
Ryan
All
Matt
Brandon
Krunal
Audrey
Audrey
Final Phase 4 report to advisor and sponsor Audrey
University of Delaware
BMEG450: Senior Design
October November December
1 2 3 4 5 1 2 3 4 1 2 3 4
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Appendix E: Final Design Benchmarking
I.
BMEG450: Senior Design
University of Delaware
Motor and battery testing
A first generation prototype, consisting of the Remington HC5350 beard trimmer with a blade glued to the vibrating face plate, was used to test the ability of the design to cut through adipose tissue. Pork belly was used to test the prototype since the dermal-adipose interface is comparable to that in humans and there was no human tissue available to perform testing on at that time. The prototype effectively separated the two layers while lessening mechanical damage to the dermal layer, as compared to side-by-side testing with a static blade. See Figure 8 below for a picture of the first generation prototype.
Figure 8. First generation prototype with a permanently attached stainless steel blade.
II.
Faceplate
In the first generation prototype, adipose tissue from the pork belly was caught in the faceplate, so a wedge-shaped shield was incorporated into the final design above the blade. Based on current LifeCell™ technician expertise, it was determined that the final design should leave behind no more than 1/16” of adipose tissue, as that thickness can be scraped away using a blunt edge, causing no damage to the dermal layer. Three pegs are used to snap the blade in place underneath the wedge-shaped shield. See Figure 9 below for a picture of the second generation prototype.
Figure 9. Second generation faceplate prototype with Delrin blade guard.
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University of Delaware
III.
Dual trigger
There are many benchmarking examples that use safety trigger mechanisms such as guns and heavy machinery, as well as the Zimmer® Dermatome, a piece of surgical equipment used to collect skin grafts. A safety switch must first be deactivated before the push button on the Dermatome can initiate the mechanical motion of the blade. The final design incorporates a similar mechanism: a toggle switch is paired with a push button to help mitigate technician accidents. A push button was purchased and validated by installing it into the circuit of a Wahl
9918-6171 Groomsman Beard and Mustache Trimmer in order to testing the functionality. It was confirmed that the push button initiated blade movement when the safety switch was deactivated, but the push button did not function when the safety switch was activated. The testing prototype is pictured in Figure 10.
Figure 10. Dual trigger validation testing on a Wahl beard trimmer
IV.
Blade
A standard razor blade was selected for use in the clamp system due to its blade width relative to the desired handle dimensions, low cost, ease of availability, and the option for stainless steel. Most importantly, the pin system aligns with the holes in a standard razor blade that are used to secure it in the system.
Appendix F: Project Budget
The overall budget for the project was $1250. Of those funds, only $614.06 was spent. This final expenditure value includes purchases such as pork belly for initial testing and additional beard trimmers that were used in the iterative validation process.
ITEM VENDOR MODEL # COST
Beard trimmer
Blade (10)
Delrin
Pins (3)
Push button
HC5550
Amazon RT00004
McMaster Carr 3962A5
McMaster Carr 97155A109
Reusum C&K TP11
Labor (University of Delaware Colburn Machine Shop)
TOTAL
Remington $27.50
$5.71
$0.10
$0.18
$0.99
$108.00
$142.48
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Appendix G: Detailed Design Schematics
BMEG450: Senior Design
University of Delaware
The final design incorporates a mechanical aspect, in that the rotational motion of a small motor is harnessed by a ball bearing mechanism that initiates translational motion of the cutting blade, as well as an electrical aspect, in that a the motor is in a series circuit with a battery, resistor, toggle safety switch, and pressure-activated push button. The integrated design schematic is found below in Figure 11, while the individual mechanical and electrical schematics are found in
Figures 12 and 13.
Blade
Ball bearing mechanism that converts the rotational motion of the motor into the translational motion of the blade
Electrical circuit with safety trigger, push button, motor, and battery
Figure 11. Integrated mechanical and electrical final design schematic
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University of Delaware
Figure 12. Mechanical schematic for the final design
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Motor: 9,000 rpm
BMEG450: Senior Design
University of Delaware
Toggle safety switch
Push button
Battery: 3.2 V
Figure 13. Circuit diagram for the final design
Appendix H: User Instructions
Human skin is comprised of three layers, the epidermis, dermis, and hypodermis. The primary responsibility of the technicians is to remove the hypodermis, which is comprised primarily of adipose (fat) tissue, from the dermal layer without damaging the dermis. This separation is the first step in processing the donated skin into LifeCell™ allograft products, so a uniform preparation is necessary.
Historically, forceps have been used in conjunction with a medical-grade scalpel using a swiping motion in order to separate the adipose tissue from the dermis. This method is both time consuming and leads to technician injuries through repetitive-use injuries in the wrists as well as puncture incidents due to carelessness. This electronic fat removal tool incorporates factors of safety that mitigate these two primary injury risks through a dual safety toggle-push button mechanism as well as a motorized blade movement that will allow separation of the adipose tissue and the dermal layer to occur more quickly and ergonomically.
Appendix I: Per-unit Production Cost Analysis
The cost of the raw materials for the prototype is $34.48. About 40 units will be used per day at
LifeCell
for an annual usage of approximately 10,000 units. As the number of mass-production units increases, the labor cost per unit will scale down, so it is estimated that the per-unit cost for a disposable device is about $25.00.
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Appendix J: Design Validation Testing, Methodology, and Results
BMEG450: Senior Design
University of Delaware o Technician Survey Results o Based on the performance of the 3 rd
Generation prototype at the LifeCell facility visit on November 21, 2013, three surveys were completed to validate the design performance. This feedback was incorporated into improvements made during the final phase of the project as well as the proposed continuation of work after hand-off to the sponsor. See Figures 13a, 13b, and 13c for scanned copies of the completed surveys. o Particular areas of concern included the power specifications of the Remington
HC5350 motor, the geometry of the faceplate, and the battery life.
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University of Delaware
Figure 13a. Completed feedback survey
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University of Delaware
Figure 13b. Completed feedback survey
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University of Delaware
Figure 13c. Completed feedback survey
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University of Delaware o Handle Ergonomics o Electromyography testing was conducted on Team Cutting Edge member
Matthew Ringer to determine a difference in muscle contraction levels, if any, between the current swiping, lateral motion used by technicians as opposed to the longitudinal pushing/pulling motion proposed for the final design. Surface electrodes were placed on the right forearm, as seen below in Figure 14a, and the output results can be seen in Figure 14b. The left portion of the graph, representing the muscle contraction of the scalpel method, shows a higher frequency and amplitude, meaning stronger, more frequent forearm muscle contraction is associated with the scalpel movement when compared to the prototype movement.
Figure 14a. EMG testing of the lateral and longitudinal arm motions
Figure 14b. EMG test results for the scalpel motion (lower left) and prototype motion
(lower right).
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University of Delaware o Handle Ergonomics o The chosen trigger button has 2.1 mm displacement and 0.5 inch diameter. These values comply with Human Factors Design Standards for button diameter, displacement in single fingered push buttons under standard HFDS 6.1.5.8.1. The button pressing resistance of 1.81 N complies with standards requiring resistance between 1.4 N and 5.6 N for operation.
Appendix K: Proposed Prototyping Continuation
In the allotted project time, an optimized prototype was not successfully delivered to the sponsor.
Based on specific feedback from the technicians and engineering team at LifeCell™, Team
Cutting Edge recommends the following items be incorporated, tested, and validated in future prototype generations. During future validation, it is also recommended that testing occur in a seated position to better simulate the current technician environment.
More Powerful Motor
The proposed motor has higher RPM and torque values compared to the current motor installed in the Remington HC5500 while still employing the same overall dimensions. The prototype should be disassembled, and the old motor replaced with the new one. Modifications of the ballcatching mechanism may be necessary based on the dimensions of the spindle.
ITEM: Mabuchi RS-380 Brushed DC Motor
Vendor: Robot Shop
Power: 6V
Rpm: 18000
Torque: 1.65 oz-in
Cost: $5.99
Another simpler way to validate different motor specifications would be to retrofit a razor blade to horse clippers, since they incorporate a more powerful motor directly off the shelf. Validation testing on human tissue would further isolate more effective motor specifications for incorporation into the optimized final product.
ITEM: Andis 22510
Vendor: Amazon
6000 strokes per minute
Ideal for bridle paths, ears, face and fetlocks
Memory Free NiMH battery
1 hour cordless run time
List Price: $100.00
Lever Actuator Trigger
Based on technician and engineering team feedback, the current push button is unfavorable since it protrudes from the device and requires force be initiated using one finger. A lever actuator trigger is suggested as a future replacement since the force required to push the trigger is distributed throughout the whole hand instead of a single finger. After the proper motor and
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University of Delaware power source are validated, it will likely be necessary to manufacture the outer casing for the handle in order to incorporate a lever actuator trigger.
ITEM: LS Series Standard Snap Action Switches
Vendor: E-switch.com
Life expectancy: 50,000 Cycles Minimum
Mechanical life: 1,000,000 Cycles Typical
Insulation resistance: 100MΩ Min.
Dielectric strength: 1,500VAC for 1 minute
Operating temp: -25°C to 85°C (std)
Altered Tissue Shield
In order to improve the cleaning process as well as the blade replacement time, the next step in the prototyping process should be altering the tissue shield and ball-bearing mechanism. Ideally, the final design should be as simplified as possible such that the various plastic parts are computer modeled into a single piece. At this stage, potential mechanisms for blade securement may be explored such that the blade can be replaced more quickly and safely. One potential suggestion would be the incorporation of a clamp/lever system to replace the current screw system located beneath the bumper.
Removable Battery
Next, a removable, rechargeable battery should be researched, installed, and validated in order to further advance the prototype toward the eventual goal of an autoclavable product. The overall specifications of the battery will depend on the requirements of the validated motor, but consideration should be given to battery life in that the battery should last for the full duration of the fat removal process for a single donor (>60 minutes).
Autoclavable Parts
After all necessary design changes have been incorporated and validated into a fully functional prototype, the next step would be to convert all materials to autoclavable alternatives, likely stainless steel.
Mass Production
Once an autoclavable prototype has been manufactured and validated for all safety and regulatory concerns, the final step for LifeCell ™ would be to hand-off the design for mass production. Considerations should be given to the chosen materials with respect to the difference in upfront cost and maintenance for disposable and autoclavable parts.
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