Final Paper - Research



Vanderbilt University

Department of Biomedical Engineering

ThermalFuse Suture

Team Members:

Katie Good

Emily Schaefer

Advisor:

Bruce Beyer, M.D.

Paul King, Ph.D.

Date of Submission:

April 24, 2007

Table of Contents

Abstract 2

Introduction 3

Problem Statement 4

Literature Review 4

Patent Search 5

Methodology 5

Results and Discussion 11

I. Data Analysis 11

II. Safety, Health, and Risk Analysis 12

III. Economic and Market Consideration 14

Conclusion 15

Recommendations 16

I. Future Direction 16

II. Ethical Issues and Regulations 17

References 17

Appendices 20

Abstract

Our advisor, Dr. Bruce Beyer, a surgeon of Obstetrics and Gynecology at Vanderbilt University Medical Center, desired an alternative suturing method which only requires movement orthogonal to the wound. He believes the new method would be especially beneficial in the training environment and would result in reduced patient rehospitalization because the sutures would be more secure. The newly developed suturing method would affect many women, 1.2 million women give birth by cesarean section per year1 and 600,000 women have hysterectomies each year2. Several closure procedures were identified and eliminated. The twist tie method, however, fit all of the criteria and allowed us to use suture material already developed and commonly used in the operating room. The twist tie method closes by thermally fusing the suture material to itself with a hair straightener. The Vicryl sutures fused together and held strong, however, we were unable to fuse the Dexon sutures. Both the 0-gauge and 2-0 gauge Vicryl sutures fused at 92.22°C had a tensile stress (241.811 N, 58.908 N, respectively) comparable to the tied sutures (207.744 N, 63.375 N, respectively) of the same gauge. Both the 0-gauge and 2-0 gauge Vicryl sutures fused at 73.89°C had a lower tensile stress (186.255 N, 19.945 N, respectively) than the sutures fused at 92.22°C or the tied sutures. These results show that applying heat to the Vicryl sutures did not compromise the integrity of the material. The results also indicate that the strength of the fused suture at the 92.22oC temperature is comparable to the tied suture of the same gauge. Since the suture strengths are comparable, there is promise for development of this closure method for sealing pedicles and closing tissue in cesarean sections and hysterectomies. The next step was to develop a heating element that is more conducive within an operating room. The device needs to be sterilizable and waterproof. Several design ideas were considered when developing the heating element. Our prototype heating element, which employed the same principle as the hair straightener, was developed using coiled stainless-steel wire as a thermally conductive heat source. Gold plated aluminum heating surfaces were attached to a modified hemostat and contained the coiled stainless-steel wires. Future work still needs to be done on the heating element design for the safety.

Introduction

It takes time and practice for surgeons to become proficient at what they do. This is especially true when tying sutures to seal pedicles and close wounds in deep cavities. Our advisor, Dr. Bruce Beyer, a surgeon and assistant professor of Obstetrics and Gynecology at Vanderbilt University Medical Center, noticed that less experienced surgeons have greater difficulty in properly tying sutures in confined areas common to gynecological surgeries.

Deep cavity medical procedures, specifically cesarean sections and hysterectomies, restrict a surgeon's ability to properly maneuver when performing tasks such as suturing. Traditional suture tying requires lateral movement in order to suitably secure the knot and ensure the suture will not loosen. Dr. Beyer desired an alternative suturing method which only requires movement orthogonal to the wound. He believes the new method would be especially beneficial in the training environment and would result in reduced patient rehospitalization because the sutures would be more secure. Dr. Beyer does not want to replace all types of sutures, but believes an alternative design has specific applications for surgeries which involve joining together thick tissues or tying off pedicles, which can occur during a cesarean section or in a hysterectomy. The newly developed suturing method would affect many women, 1.2 million women give birth by cesarean section per year1 and 600,000 women have hysterectomies each year2. Women who receive cesarean sections are 2.3 times more likely to result in rehospitalization due to wound complications and infection3 than those who have natural births. In a study comparing abdominal and vaginal hysterectomies, 14.9% of a group of 82 women, who had abdominal hysterectomies, were rehospitalized. The number of rehospitalization cases due to these procedures could be greatly reduced with a new suturing technique providing a more secure and reliable closure method, which would reduce the incidence of wound opening, infection, and internal hemorrhaging. The average hospitalization costs for a cesarean section is approximately $7,1864 and $3,0815 for a hysterectomy. Additional costs for rehospitalization are burdensome for patients.

Problem Statement

Our advisor asked us to design a suturing method which would be less cumbersome for deep cavity procedures such as hysterectomies and cesarean sections. An alternative suturing method which only requires movement orthogonal to the wound or pedicle is desirable. Dr. Beyer believes a new method would be especially beneficial in the training environment and would result in reduced patient rehospitalization because the sutures would be more secure. Our aim is not to replace all types of sutures or suturing methods, but believe an alternative design has specific applications for surgeries which involve joining together thick tissues or tying off pedicles in deep cavities.

Literature Review

There exists a wide variety of methods for closing tissue, most of which have been adapted from everyday closure methods. Some examples of surgical closure methods adapted from commonplace closure methods include tied sutures, staples, tissue adhesives6,7 and adhesive paper-tape. These methods have been previously studied,8,9,10 but are not all appropriate for all applications. For example, tissue adhesives are only used for small low-tension skin wounds and would not be appropriate for sealing a pedicle or sub-dermal wounds.11 A broad review of surgical procedures and tools has been done for obstetric and gynecological applications,11 which provided insight into the current surgical methods. By evaluating the current methods, we were able to identify more specific design criteria for an improved suturing technique.

Patent Search

In conducting a patent search we found a patent for a device which fuses the tail ends of the suture knot to ensure that the knot does not slip12. However, this device does not have a pinching mechanism and is only proposed for sealing the ends of a traditionally tied suture together. The method proposed in the patent still entails tying traditional sutures and does not solve the current problem of not having enough room to tie a secure suture. This device may, however, be useful in procedures where there is adequate room to tie proper sutures and where fusing the ends would act as an added measure to ensure the suture did not loosen.

A device which actually operates on a similar principle to a zip-tie is the Wiseband, produced by Wisebands Ltd.13 However, this device is not intended for internal suturing and is only approved for use prior to surgery for closure of tissue-deficit skin wounds. It operates by applying unidirectional tension to a flat plastic band (5 mm wide and 50 cm long) attached to a metal surgical needle.14 The plastic band is only temporarily left in the skin and is removed upon completion of surgery. While the mechanical operation of this device might prove useful for a future design of a suturing system, this device itself has an entirely different intended purpose.

Methodology

Dr. Beyer proposed the idea of a suturing technique with the same mechanics as a cable zip-tie. He favored the clicking mechanism, which prevents a cable tie from loosening and avoided any lateral movement when closing. From his initial idea, several design goals and criteria were established. The suture needed to be bioabsorbable, have an tensile strength (80- 100N) and degradation rate (3-4 weeks) comparable to suture materials currently used for these specific gynecological procedures, utilize unidirectional tension, and maintain suture integrity while providing a simple closure method for the surgeon. Several closure procedures were identified and eliminated. The "Problem Formulation and Brainstorming" section of Innovation Workbench (Appendix A) aided in establishing design constraints and modifications to the traditional suture method. Cable zip-tie and other similar closure methods such a trash bag tie (Figure 1) were explored initially. However, feasibility issues arose when attempting to develop a suture which would use "teeth" as a closure method. To meet the absorption criteria we needed to use an absorbable material, but the materials that fit our design criteria do not have the structural properties necessary to maintain such a mechanical closure. These designs would need to be formed by injection molding and were out of the price range provided. The approach altered to incorporate similar characteristics using products already available. The final two ideas considered were a beaded model (Figure 2, a) and a twist tie model (Figure 2, b), per Dr. King's suggestion. The beaded model maintains the clicking mechanism of the zip-tie, but with beads instead of teeth. The beads would actually be a more favorable design for a suture because it would not have sharp edges. In order to keep the loop that slides over the beads in place, the loop would have to consist of a shrinkable material and treated to lock it in place. Once again the manufacturing method prevented further development, as it was established that either 3-D printing or injection molding would be needed for this process. The twist tie method, however, fit all of the criteria and allowed us to use suture material already developed and commonly used in the operating room. The twist tie method closes by thermally fusing the suture material together after twisting the two ends of the suture.

In order to fuse the suture, a material with a relatively low glass transition temperature was necessary. Materials considered included common suture materials. Dexon, a homopolymer of glycolic acid15, and Vicryl, copolymer made from 90% glycolide and 10% L-lactide with a polyglactin 370 and calcium stearate16 coating were eventually tested. These two suture materials were chosen initially for their tensile strength of 80 – 100N and their degradation rate of 3 – 4 weeks (Figure 3). These materials were considered optimal materials for our design because their glass transition temperature was low enough to fuse together. Table 1 shows the various melting and glass transition temperatures for the polymers used in manufacturing the suture materials used in this experiment. To ensure these assumptions were accurate, suture material was acquired from the Vanderbilt University Medical Center Hospital Supply and tested. Zero and 2-0 gauge braided and coated Vicryl along with 3-0 gauge, braided, uncoated Dexon were purchased. These two suture materials were chosen for their desirable properties; Vicryl and Dexon both degrade rapidly and have a relatively low glass transition and melting temperature.

To test the suture material for its ability to thermally fuse, the suture was wrapped once around a white cylindrical tube, simulating a pedicle or portion of thick tissue, the two ends of the suture material were then clamped together by hemostats, and the suture material was twisted together by twisting the hemostats. Once the twisted part of the suture was flush and secure against the cylinder, heat was applied to the twisted section of the suture as close to the cylinder as possible (Figure 4). For our initial tests the heat supply was provided by a hair straightener. Two different temperature settings were used to find the optimal fusing temperature. These two settings were 7.5, which equates to 73.89°C and 9, which equates to 92.22°C. Higher temperatures were tested, but melted the suture material too quickly.

Experimental trials using the two different suture gauges were conducted. The twisted sutures were clamped in the hair straightener for 40 seconds and then allowed to cool. The Vicryl sutures fused together and held strong, however, we were unable to fuse the Dexon sutures. A possibility for the Dexon not fusing is the absence of an external coating on the suture.

Once we established that the Vicryl sutures could be fused, we needed to test their tensile strength. The fused suture tensile strength needed to be comparable to the tied sutures tensile strength for use in these surgical procedures. If heating the sutures compromised the integrity of the suture material, the fused Vicryl could not be used. To test the tensile strength of the sutures an Instron Tensometer in the Skin Disease Research Core Center (SDRCC) was used. To ensure the strength of the fused sutures was comparable to traditionally tied sutures, Dr. Beyer, an experienced surgeon, tied three Vicryl sutures of each gauge. Each suture was placed between the vacuum activated clamps on the tensometer. The sutures were positioned so that the fused or tied junction was not in either clamp. The Blue Hill software captured and calculated the tensile stress of each suture as the tensometer pulled on opposite ends. The true tensile strength was then calculated according to the cross-sectional area of the suture. Three tests were run for each of the suture gauges, temperatures, and closing methods.

Next we needed to develop a heating element which was more appropriate for use in an operating room. The device needs to be sterilizable and waterproof. Several design ideas were considered when developing the heating element. Initially, heated tweezers were desired because they would be ideal for clamping the suture material and use thermal conduction to produce heat. However, we could not purchase the device because it did not have a variable temperature setting and the price was beyond our means. Other current surgical techniques were also explored. Dr. Robert Galloway, a professor of Biomedical Engineering at Vanderbilt University, allowed us to use an electrocautery unit in his lab to test if we could fuse the sutures with direct current. While this method was unsuccessful for fusing the sutures, it was established that the appropriate heating element would need heat the suture through thermal conduction, not through direct current. We realized that we would need to develop our own heating element and could not use an instrument already present in an operating room. Initially, a hair straightener was taken apart and modified by reducing the size of the resistance coils. This technique, however, did not work because shortening the coils reduced the resistance of the device. By reducing the resistance a greater amount of current traveled through the coiled wires, destroying them. Using the same principle as the hair straightener, a new heating element was designed using coiled stainless-steel wire as a thermally conductive heat source. Gold plated aluminum heating surfaces were attached to a modified hemostat and contained the coiled stainless-steel wires (Figure 5). This heating element had a smaller heated surface area than the hair straightener. To provide power to these coiled wires, the two ends of the wires were attached to DC+ and DC- ports of a capacitor. This specific capacitor was a Nippon Chemi – con 50V, 68,000μF capacitor. The DC+ and DC- ports of the capacitor were connected to a bridge rectifier which was then connected to a toroidal transformer. The ACin of the toroidal transformer was plugged into a voltage-variable transformer. More specifically, a Superior Powerstat ® with an input of 120V and a variable output of 0-140V. A full circuit diagram can be seen in Figure 6. The sutures were then fused with the new heating element to determine the correct voltage setting on the variable transformer. The voltage was increased at increments of 5V until a secure suture closure was established. The best voltage for fusing the sutures is approximately 40V. Although our prototype was able to fuse the sutures, it is still not an appropriate device to be used within the operating room. The large capacitor and primitive insulation on the heating pads would not be very safe for a patient or surgeon.

Results and Discussion

I. Data Analysis

As previously described the Dexon sutures did not successfully fuse when exposed to the heating element. The Vicryl sutures, however, did fuse together creating a reliable suture closure method. Since the Dexon sutures did not fuse, further testing and research was conducted using only the Vicryl sutures.

Both the 0-gauge and 2-0 gauge Vicryl sutures fused at 92.22°C had a tensile stress comparable to the tied sutures of the same gauge. Both the 0-gauge and 2-0 gauge Vicryl sutures fused at 73.89°C had a lower tensile stress than the sutures fused at 92.22°C or the tied sutures. The results from the tensometer are summarized in Figure 7. Missing data was a result of the tensometer not functioning properly or the suture slipping out of the clamps. The average tensile strength across all three trials was also calculated and is listed in Table 2.

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The average tensile strength for both the fused 0-gauge sutures and the tied sutures were well above the required 100 N tensile strength. The average tensile strength of the 0-gauge suture fused at 92.22oC was also greater than the average tensile strength of the 0-gauge tied suture.

These results show that applying heat to the Vicryl sutures did not compromise the integrity of the material. The results also indicate that the strength of the fused sutures at the 92.22oC temperature is comparable to the tied suture of the same gauge. Since the suture strengths are comparable, there is promise for development of this closure method for sealing pedicles and closing tissue in cesarean sections and hysterectomies.

II. Safety, Health, and Risk Analysis

The use of Designsafe (Appendix B) helped us to identify and evaluate some of the potential safety concerns that need to be addressed for future development of our suturing method. Since a considerable amount of heat (almost 100oC) must be applied to the twisted sutures to fuse the two ends, there is a concern of possible tissue damage due to radiant heat from the heating element and also from direct contact with the heated plates. We propose to reduce the amount of radiant heat produced by the heating element by (1) minimizing the size of the exposed metal plates, (2) insulating the backside of the heated coils within the metal plate, and (3) enclosing the entire heating element in a thermoplastic (possibly a polycarbonate-ABS blend with a glass transition temperature of 125oC19), which can withstand high temperatures and will contain a majority of the heat. The end tip of the plates should also be covered to avoid direct contact with tissue which could cause damage.

Since the size of the exposed heated metal plates is a concern, a modified design has been proposed in which the plates are half-cylinders. This would not only reduce the surface area of the exposed heated metal, but also decrease the possible incidence of contacting surrounding tissue, thus making the tool more ideal for confined areas. Enclosing and insulating the device would also reduce the potential for electric shock to the patient, surgeon(s), and anyone assisting the surgeon(s) due to exposed or loose wires.

Another safety concern is from electric shock due to the fluidic environment in the body. If any bodily fluids were to get into the device there would be a potential for electric shock to the patient, surgeon(s), or and anyone in contact with the device at the time. To prevent this risk of electrical shock the heating device needs to be completely waterproof. Making the device waterproof could be accomplished by applying epoxy to all the internal joints and connections when the device was constructed.

Since this device would also be non-disposable we must take into consideration methods of sterilization. There are three main methods for sterilizing medical equipment: (1) autoclave or steam under pressure (2) dry heat sterilization and (3) low temperature chemical methods such as, ethylene oxide gas and hydrogen peroxide gas plasma.20 Due to the electrical nature of the device and sensitivity to moisture autoclaving would not be an option. Also because the device would be made out of a plastic material the dry heat sterilization method would not be an option because the plastic might melt. The sterilization method needs to be taken into consideration when choosing materials in the manufacture of the heating device so that would need to be able to withstand the sterilization process.

III. Economic and Market Consideration

The cost to develop the existing heating element and suturing process was relatively low in comparison to other medical devices. The total cost for all the supplies was $290.93. A breakdown of the cost can be seen in Table 3. The actual cost of the heating element would not include the cost of the sutures or the hemostat used to clamp the sutures because they would already be the operating room and included in the cost of surgery. While we do not propose the use of the specific circuit elements or circuitry from hair straightener for the final heating element design, we can expect that the cost for such electrical components to be comparable. The circuitry in the final design for the heating element will have to be very precise and reliable because it needs to meet the Food and Drug Administration (FDA) performance standards.

Although we cannot predict the actual cost for development and production of the final heating element we expect it should be around $500 per unit once the thermoplastic and insulation materials are factored into the cost. Since the device is reusable the cost of sterilization also needs to be considered. As for the potential number of units to be sold, we realize that this would be a new surgical technique tested primarily in teaching hospitals at first. A conservative estimate for the number of initial units sold is 5000, approximately 5 for each of the 1100 teaching hospitals nationwide.21

Competing technologies, which could potentially limit the market size captured by the ThermalFuse Suture, are traditional sutures, the Quik-Stitch laparoscopic technique, and Liga-Clips which are metal surgical clips. However, our device has certain advantages over all these previously mentioned technologies. Traditional sutures tied using conventional knots pose a problem of not being tied securely due to spatial constraints and failing, which could cause internal bleeding leading to a second emergency surgery. The Quik-Stitch is a laparoscopic technique, which takes practice to perfect and may be unfavorable with surgeons who are more comfortable with traditional surgical techniques. Finally, the Liga-Clips are metal and will remain in the body unless removed via a second surgery, where as the ThermalFuse technique uses absorbable sutures which will degrade over time.

Conclusion

The suture closure method developed fit all the design criteria desired by Dr. Beyer. The ThermalFuse suture is bioabsorbable, avoids applying tension laterally, maintains the necessary tensile strength and degradation rate, and provides secure closure method within confined spaces. Using Vicryl sutures, one of the most common suture materials in operating rooms, we have developed a new technique which can be readily available in most hospitals and allows surgeons to easily seal pedicles and close tissue in deep cavities ensuring a secure closure. This method was developed after considering a variety of surgical closure methods including surgical staples, tape, and tissue adhesives. Based on our design criteria and other constraints, we were limited to closure methods which would be applicable in the specific gynecological procedures including cesarean sections and hysterectomies. After using Innovation Workbench and considering suggestions from our advisors, the twist and fuse method was determined to be the most conducive for our project. Once the method was developed, the fused sutures were tested to ensure the physical properties were comparable to tied sutures. The results proved that the fused sutures were as strong as the tied sutures, determined by the resultant tensile strengths; therefore, the fused sutures could be used in similar applications within the body. After determining that the fused sutures are comparable to tied sutures, an attempt was made to create a more surgically appropriate heating element to fuse the sutures. Further work still needs to be completed on the heating element design for the safety of the surgeon and the patient.

Recommendations

I. Future Direction

Future improvements for the heating device are to (1) minimize the size of the metal plates, (2) insulate the backside of the heated coils within the metal plate, and (3) enclose the entire heating element in a thermoplastic material, which can withstand the high temperatures. The end tip of the plates should also be covered to avoid direct contact with tissue which could lead to further damage. We propose to do the above by modifying the shape of the plates from flat rectangles to half-cylinders (Figure 8). This would not only reduce the surface area of the exposed heated metal, but also decrease the possible incidence of contacting surrounding tissue, thus making the tool more ideal for confined areas. We also propose enclosing, insulating, and waterproofing the device to reduce the potential for electric shock to the patient, surgeon(s), and anyone assisting the surgeon(s) due to exposed or loose wires.

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II. Ethical Issues and Regulations

There were no ethical considerations in the development of the suturing method or heating element because the process was not tested on animal or human subjects. However, the suturing process and heating element, which would be considered a Class II medical device by the FDA, would need to meet all the basic Class I standards and comply with performance standards. The safety and efficacy of the heating element and suturing method would also need to be proven via testing in animal and human clinical trials before the process or the device was approved for use.

References

1. Doheny, K. (2006, August 17). C-Section rate at all-time high in U.S.. Retrieved January 23, 2007 from HealthDay News, Web site:

2. Centers for Disease Control and Prevetion (2006, November 16). Women's reproductive health: Hysterectomy. Retrieved January 23, 2007 from Reproductive Health Web site:

3. Shahida, A., (2004). Short and long term complications of abdominal and vaginal hysterectomy for benign disease. Pakistan Armed Forces Medical Journal, 54 (1), 71-75.

4. Cesarean fact sheet. Retrieved January 25, 2007 from ICEA Cesarean Options Committee Web site:

5. Tsaltas, J., Magnus, A., Mamers, P.M., Lawrence, A.S., Lolatgis, N., & Healy, D.L. (1997). Laparoscopic and abdominal hysterectomy: a cost comparison. The Medical Journal of Australia, 166, 205-207.

6. Singer, A.J. & Thode, H.C. (2004). A review of literature on octylcyanoacrylate tissue adhesive. American Journal of Surgery, 187 (2), 238-248.

7. Reece, T.B., Maxey, T.S., & Kron I.L. (2001). A prospectus on tissue adhesives. American Journal of Surgery 182 (2), 40S–44S.

8. Matin, S.F. (2003). Prospective randomized trial of skin adhesive versus sutures for closure of 217 laparoscopic port-site incisions. Journal of the American College of Surgeons, 196 (6), 845-853.

9. Luckraz, H., Rammohana, K.S., Phillipsa, M., & O’Keefe, P.A. (in press). Is adhesive paper-tape closure of video assisted thoracoscopic port-sites safe. European Journal of Cardio-Thoracic Surgery.

10. S. Maartense, S., Bemelman, W.A., Dunker, M.S., de Lint, C., Pierik, E.G.J.M., Busch, O.R.C., & Gouma, D.J. (2002). Randomized study of the effectiveness of closing laparoscopic trocar wounds with octylcyanoacrylate, adhesive papertape or poliglecaprone. British Journal of Surgery, 89 (11), 1370-1375.

11. Singh, S., & Maxwell, D. (2006). Tools of the trade. Best Practice & Research Clinical Obstetrics and Gynaecology, 20 (1), 41–59.

12. Pitt, Duane D. H.; Jobe, Christopher M.; 2003 Methods and apparatus for annealing suture United States Loma Linda University Medical Center (Loma Linda, CA) 6596015

13. Weiss, J. (2000). Suture band tightening device for closing wounds. United States Wisebands Ltd. (Ra'Anana, IL) D433753

14. Barnea, Y., Gur, E., Amir, A., Leshem, D., Zaretski, A., Miller, E., Shafir, R., & Weiss, J. (2006). Delayed primary closure of fasciotomy wounds with Wisebands, a skin- and soft tissue-stretch device. Injury, 37 (6), 561-566.

15. Syneture (2007). Dexon S. Retrieved March 15, 2007 from Web site:

16. Kirsch, A.J., Chang, D.T., Kayton, M.L., Libutti, S.K., Connor, J.P., & Hensle, T.W. (1997). Effects of diode laser welding with dye-enhanced glue on tensile strength of sutures commonly used in urology. Lasers in Surgery and Medicine, 18, 167-170.

17. Bourne, R.B., MD, FRCSC, Bitar, H. MD, Andreae, P.R., BSC, Martin L.M., MB, BS, Finlay, J.B., PhD, & Marquis, F., MD FRCSC (1988). In-vivo comparison of four absorbable sutures: Vicryl, Dexon Plus, Maxon, and PDS. The Canadian Journal of Surgery, 31(1), 43-45.

18. Kuusk, A. (n.d.). Biodegradable materials. Retrieved March 19, 2007 from University of Toledo, Bioengineering Web site:  

19. Quickparts (n.d.). Polycarbonate-ABS blend. Retrieved April 20, 2007 from Web site:

20. Environmental Media Services (n.d.). Cleaning, disinfection, and sterilization of medical equipment. Retrieved April 20, 2007 from Web site:

21. Association of American Medical Colleges (2002, September 24). America's teaching hospitals urge Congress to halt Medicare cuts. Retrieved April 22, 2007 from Web site:

Appendices

Appendix A – Innovation Workbench

Ideation Process

Project Initiation

Innovation Situation Questionnaire

Brief description of the situation

Surgeons experience difficulty in tying traditional sutures in deep cavities or confined areas. Another closure method needs to be developed to allow for the joining of two tissues.

Improve functional efficiency

Detailed description of the situation

The current suture techniques require the application of tension in opposite directions to tighten and close the knot. In confined areas it is more difficult to apply tension in opposite directions; therefore the integrity of the suture is compromised because the surgeon is unable to complete the knot. Due to space constraints, the surgeons hands and tools are too large and are not always capable of completing a knot in tight spaces. A surgical tie is needed that will allow surgeons an alternative method for joining tissue or sealing a pedicle by only requiring tension applied in one direction. For a suture of this nature, space constraints are less of an issue.

Supersystem - System - Subsystems

|[p|Supersystem - The body (specific tissue) |

|ic| |

|] | |

|[p|System - Suture |

|ic| |

|] | |

|[p|Subsystem - Mechanical techniques |

|ic| |

|] | |

Input - Process - Output

|[p|Input - Manipulation of suture material |

|ic| |

|] | |

|[p|Process - Inserting suture, applying tension to suture |

|ic| |

|] | |

|[p|Output - Closure of tissue |

|ic| |

|] | |

Cause - Problem - Effect

|[p|Cause - The current sutures need bidirectional tension |

|ic| |

|] | |

|[p|Problem - Difficult to tie sutures in confined areas |

|ic| |

|] | |

|[p|Effect - Integrity of tissue closure is compromised |

|ic| |

|] | |

Past - Present - Future

|[p|Past - Technology of procedure was not advanced enough to be performed. |

|ic| |

|] | |

|[p|Present - Tissue closed with traditional sutures. |

|ic| |

|] | |

|[p|Future - Ideal suture for each application. |

|ic| |

|] | |

Resources, constraints and limitations

|[p|Resources - materials experts, surgeons, common knowledge about closure procedures |

|ic| |

|] | |

|[p|Constraints & Limitations - Manufacturing the prototype is not within our financial bounds. The specific materials and equipment for |

|ic|production are not available for our use. |

|] | |

Problem Formulation and Brainstorming

|Suture Diagram |

|[pic] |

|  |

11/29/2006 2:56:17 PM.

Find an alternative way to obtain Apply tension to tighten knot that offers the following: provides or enhances Room to apply tension does not cause Not enough room to apply tension does not require Tie the knot.

Resolve the contradiction: The useful Apply tension to tighten knot should provides Room to apply tension and avoids Not enough room to apply tension.

Find a way to eliminate, reduce, or prevent Not enough room to apply tension in order to avoid Knot is not tightened under the conditions of Apply tension to tighten knot.

Find a way to eliminate, reduce, or prevent Knot is not tightened in order to avoid Tissue not sealed under the conditions of Not enough room to apply tension.

Find a way to eliminate, reduce, or prevent Tissue not sealed under the conditions of Knot is not tightened.

Find an alternative way to obtain Knot is tightened that offers the following: provides or enhances Tissue is sealed does not require Room to apply tension.

Find an alternative way to obtain Tissue is sealed that does not require Knot is tightened.

Develop Concepts

Closure methods:

|[p|Zip tie |

|ic| |

|] | |

|[p|Tying suture in a noose |

|ic| |

|] | |

|[p|Trash bag tie |

|ic| |

|] | |

|[p|Clothing tag |

|ic| |

|] | |

|[p|Twist tie |

|ic| |

|] | |

Evaluate Results

Taking the concept of a twist tie and using it to develop a suture closure method. Using the thermal properties of Vicryl sutures we were able fuse the material together in a similar fashion to a twist tie. We were able to eliminate the need for a mechanical stabilizer in the suture by fusing the two ends together. The end product was a secure suture that could be closed using unidirectional tension.

Appendix B – Designsafe

[pic]

[pic][pic]

[pic][pic][pic]

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[pic]

(a)

[pic]

(b)

Figure 2: (a) Beaded approach (b) Twist tie approach.

[pic]

Figure 3: Tensile strength data for 0-gauge sutures.17

|Polymer |Glass Transition (oC) |Melting Temperature (oC) |

|Poly(glycolic acid) |35 |210 |

|L -Poly(lactic acid) |54 |170 |

Table 1: Data of materials used in manufacturing suture material.18

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Figure 4: (Top) Hair straightener clamping the twisted suture. (Bottom) Fused Vicryl suture.

[pic]

Figure 6: Circuitry for modified heating element.

[pic]

Figure 5: Modified heating element.

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Figure 1: Trash bag tie considered for "teeth" clicking mechanism.

[pic]

[pic]

Figure 7: (Top) Tensometer results for the 0-gauge Vicryl sutures. (Bottom) Tensometer results for the 2-0 gauge Vicryl Sutures.

|Gauge |Heat Setting |Temperature (oC) |Average Tensile Strength (N) |

|0 |7.5 |73.89 |186.255 |

|0 |9 |92.22 |241.811 |

|0 |Tied |N/A |207.744 |

|2 |7.5 |73.89 |19.945 |

|2 |9 |92.22 |58.908 |

|2 |Tied |N/A |63.375 |

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h[+ÔhÃO& hÃO&6?hÞhÃO&6?Table 2: Average tensile strength (N) at break for all trials.

|Hemostat to clamp suture |$21.00 |

|Hemostat for heating element |$20.00 |

|Hair straightener |$21.84 |

|Sutures |$66.30 |

|Circuit elements |$150.00 |

|Plastic Dip |$11.79 |

|TOTAL |$290.93 |

Table 3: Cost for suture method and heating element.

[pic]

Figure 8: Future design prototype for heating element.

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