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research-article2015
SRIXXX10.1177/1553350615579728Surgical InnovationYousefian et al
Original Article
LigLAP: Encirclement and Ligation of Vessels in Laparoscopic Surgery: A Double-Layer Suture Sealing Approach
Surgical Innovation 1–9 © The Author(s) 2015 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1553350615579728 sri.sagepub.com
Reza Yousefian, MS1, Paul Jones, BSME1, Michael A. Kia, DO2, and Mehrdad Hosseini Zadeh, PhD1
Abstract This article proposes a potential automatic ligation (LigLAP) method to occlude vessels and ducts in several laparoscopic surgical procedures. Currently, stapling devices are widely used for this purpose. However, there are some complications associated with stapling devices, including biliary leak and tissue damage. In this article, we examine the feasibility of an alternative method that uses a double-layer suture to encircle and occlude a vessel. A heating element melts the outer layer of the suture at the cross-point of the suture to create a seal. Several electromechanical mechanisms have been proposed to carry out this ligation process. In addition, some parts have been prototyped for experimental verification and visualization. Several double-layered sutures have been created, and their tensile strength and sealing capabilities have been measured. Moreover, a simple leakage experiment has been performed to verify experimentally the idea of using the double-layer suture. The results show that the new suture and the thermal sealing method provide the required strength to occlude balloons filled with water. Although the results suggest that the proposed method and the double-layer suture may be used in surgical ligation processes, much more rigorous testing of leakage is required. Keywords minimally invasive surgery, ligation process, automatic suturing, welding
Introduction Minimally invasive surgeries (MISs) are the procedures of choice in comparison to open surgeries. These surgeries allow surgeons to complete surgery operations through small incisions on the body. The size of incisions is restricted to avoid undue loss of blood and eschew manipulation of tissues. Hence, the body’s response to the surgery is with a reduced immune activation and catabolism.1-3 There are several advantages for MIS, such as shorter hospital stays and recovery periods, less scarring, less injury to tissue, and more postoperative comfort.4-7 Therefore, the use of laparoscopic surgeries has increased and is preferred in possible operations. For instance, laparoscopic cholecystectomy has replaced open cholecystectomy since it was first reported8 in 1987 and is one of the most frequently performed laparoscopic operations.9,10 The occlusion of the vessels/ducts is required in many surgeries such as cholecystectomy, renal surgery, and the resection of rectal cancer, to name a few. Several studies have assessed the feasibilities of laparoscopic methods to occlude vessels.11-18 In contrast to the occlusion process in
open surgeries, most of these methods do not use sutures to surround a vessel and tighten the suture to occlude vessels/ ducts. For example, laparoscopic stapling devices are frequently used as a method of duct closure and vessel occlusion in laparoscopic surgeries.19 Technical failures and dangers of stapling devices have been reported when the staples are not closed securely.20 In addition, bile leak is a known postoperative problem that could be caused by dislodgment and migration of the clips as well as bile duct necrosis.21-23 Moreover, a relatively large space behind the duct and/or vessel is required when using stapling devices. Other problems include vascular and duct injury, bleeding from the liver bed, and bile leak.24-26 Furthermore, in some cases, for example in the presence of chronic inflammation, laparoscopic cholecystectomy using stapling devices 1
Kettering University, Flint, MI, USA Department of Surgery, Michigan State University (McLaren Regional medical center), Flint, MI, USA 2
Corresponding Author: Reza Yousefian, Electrical and Computer Engineering Department, Kettering University, 1700 University Ave, Flint, MI 48504, USA. Email: [email protected]
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Figure 1. A. The proposed device. B. Expanded view of the device: 1, bottom jaw; 2, top jaw; 3, heating element; 4, movable cam; 5, cutting mechanism; 6, locking mechanism; and 7, shaft.
is difficult and dangerous.27 The traditional response to these difficult cases is conversion to open surgery. Similar to open surgery ligation techniques, sutures are preferred to occlude vessels/ducts in several intracorporeal laparoscopic ligation techniques using current laparoscopic surgery devices.21,22,28 However, these methods and devices do not provide automatic suturing to easily ligate and occlude vessels/ducts during the laparoscopic procedures. In one attempt, Egan29 has proposed a procedure of suturing to close an opening and claimed that the method can occlude vessels/ducts in which the suture is threaded through a channel to make a loop. The suture thread would be secured using an anvil and cut to create a closed loop with overlapping ends. After cutting, the suture ends would be melted together to form a weld. This method may work to close openings. However, it may fail to occlude vessels/ducts because the suture is not tightened while forming the weld. To the best of our knowledge, no experimental verification procedure has examined the Egan method to occlude vessels/ducts. Similar to the Egan method, our method (LigLAP) forms a weld in an automatic suturing procedure. However, in the proposed method, the weld is created while the suture is tightened and the vessel is occluded. In this method, the suture would be looped around the vessel/duct and tightened to occlude the vessel/duct. Then, the heating element melts the cross-point of the suture to form the weld. A new double-layer suture with 2 melting temperatures has been created to be used in a potential ligation procedure. The 2 layers of the suture are the following: (1) an inner layer with higher melting point temperature, which provides strength to the suture and keeps the suture intact during the melting process, and (2) an outer layer with a relatively lower melting temperature that will be melted and create the weld. In all, 7 samples of the suture are extruded, and 2 experiments have been conducted to measure key properties of the sutures, including melting
temperatures and tensile strengths. A leakage experiment has also been conducted to examine use of the doublelayer suture and the thermal sealing method in the occlusion of elastic balloons filled with water.
Material and Methods LigLAP: Automatic Suturing-Occlusion Laparoscopic Procedure The LigLAP method may enable surgeons to occlude vessels automatically using a double-layer suture. This occlusion process may be repeated several times to occlude all required places on the vessel to prevent bleeding. The LigLAP can be used in several surgeries in which vessels must be occluded during the operation, including renal surgery and cholecystectomy. Unlike the stapling devices (currently common devices for this purpose), little space may be required behind the vessel in the LigLAP method. The LigLAP method includes the following 5 main steps: 1. Encircling the vessel with the suture: This is accomplished by the use of a channel created in the jaws of the proposed device. 2. Locking one end of the suture: To address this, we have designed, prototyped, and tested a locking mechanism using a shape memory alloy (SMA) wire. 3. Occluding the vessel by tightening the suture: The suture is pulled while its end is locked in the locking mechanism. During this step, the suture comes out of the channel and starts occluding the vessel. 4. Sealing the suture using a heating element: The heating element has been designed to melt the outer layer of the suture as well as force the suture
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pushed forward, leading to the formation of the cross-point of the suture on the V-shaped heating element; 2 U-shaped channels are made in the wings to facilitate the motion of the suture toward the heating element.
Figure 2. ABS (acrylonitrile butadiene styrene) prototypes of the jaws.
to make a cross-point in front of the heating element. 5. Cutting and releasing the suture: A cutting mechanism has been designed using a SMA actuator. To perform the above steps, several mechanisms have been proposed in the design of a potential laparoscopic surgical device. The design and system overview of the device are shown in Figure 1. Each component of the device is briefly illustrated as follows: Jaws. The bottom and top jaws are presented as components 1 and 2, respectively, in Figure 1B. The top jaw is movable, and the bottom jaw is stationary and provides a fixed point as a reference for a surgeon. Large-scale prototypes of the jaws are made using ABS (acrylonitrile butadiene styrene) and shown in Figure 2. Two important roles of the jaws are (1) to enclose the vessel and (2) to serve as a complete route for the suture to encircle the vessel. There is a semicircular channel, 1 mm in diameter, to provide this route. The curvature of the channel is designed to make a cross-point of the suture possible during the tightening step (step 3). To open/close the top jaw, a cam (labeled 4 in Figure 1) is connected to the tail of the jaw. As shown in Figure 1A, the other side of the cam is in the slot of a movable part, which is also used to move the heating element. The heating element is briefly presented next. Heating Mechanism. As shown in Figure 3, the heating element is placed on a movable mount in the heating mechanism. This enables the element to melt the outer layer of the suture and seal it after tightening (step 4). The design of the movable mount includes the following components. 1. a V-shaped stage for the heating element to be attached to the mount, providing more surface contact between the heating element and the suture; and 2. a pair of wings that force the suture completely out of the channel when the mount is
Locking and Cutting Mechanism. The end of the suture has to be locked (step 2) during the tightening process. Because of the small space available, a SMA-based locking system has been designed, prototyped, and tested.7 In addition, for cutting and releasing the suture (step 5), a similar design to the locking system is proposed, with an additional small blade to cut the suture. The design of the locking mechanism and the experimental setup that includes the locking prototype is shown in Figure 4. The peg of the locking system is initially open and is closed by the contraction of the SMA wire looped through the peg. The prototype was made out of ABS at a larger scale (Figure 4), and a 275-µm nitinol SMA wire was used as the actuator. A torsional spring was also used to provide backward force for the peg and, thus, for the SMA wire. The Joule effect of electric current is used to heat the SMA wire, resulting in its contraction and holding/cutting the suture. In addition, surface material used on the peg and the base of the locking mechanism, where the suture end is held in between, effects the maximum pulling force of the suture. This is because of the difference in surface friction of various materials. Figure 5 presents the results showing the average of maximum pulling force applied to the suture for 6 different materials.7 The biocompatibility and small size of SMA wires are important in biomedical applications, especially in MISs.7,30-32 SMA wires have many advantages, such as suitability for clean room applications, a high ratio of force to volume, a high strain feature, a small size, and the ability to perform without noise emission.7,33 Shaft and Mounting Element. The shaft is designed with an inside mount (movable part), labeled 2 in Figure 6A, to move the heating element forward/backward and to open/ close the top jaw. There are also openings in the top and bottom of the shaft (labeled 1 in Figure 6A), allowing the top jaw to open. All parts of the design, except the bottom jaw, are shown in Figure 7.
Double-Layer Suture The thermal sealing of the suture plays an important role in the LigLAP method. Because the main goal is to create a seal by melting the suture without cutting it, a new double-layer suture with 2 melting temperatures has been developed for the LigLAP process. A single-layer suture cannot be used for this purpose because when the heat is
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Figure 3. The heating element: A. Design of the heating mechanism. B. Position of the heating mechanism in the device.
would be useful for the proposed occlusion process. The details of all preliminary measurements and the final leakage experiment are presented in the following sections. The results of all experiments are described in the Results section.
Figure 4. Design and the experimental setup to examine the locking mechanism: 1, mount; 2, the peg of the locking system; 3, position of torsional spring, which provides enough force to bring back the peg to its initial position.
provided to make a seal, the suture will be melted and cut. The suture consists of 2 polymer layers: a core and a coat that is melted to create a seal. The outer layer (coat) has a much lower melting temperature than the core. Therefore, when the heating is provided, the coat will be melted to create the seal, and the core is not melted. Another requirement is that the suture has to be rigid enough to pass the channel in the jaws. Two types of sutures that meet the above requirements have been produced using extrusion machines. In the first type, polyglycolic acid (PGA) core is coated by polyethylene (PE), resulting in a strong PGA core and low melting temperature PE coat. To extrude the second type, a polylactic acid (PLA) core is coated by polycaprolactone (PCL) polymer. The sutures have been made with various diameters, ranging from 0.35 to 1.00 mm. Figure 8 shows a sample of the double-layer suture and its cross-sectional view. After the design and extrusion of the sutures, the key properties of the sutures in regard to the occlusion method need to be measured. The tensile strength, seal creation tension, and melting temperatures are important properties of the sutures. The following tensile and seal experiments have been conducted to provide the required information about important properties of sutures that
Tension Experiment. Because the sutures will be used under tension during the tightening process, the tensile strength is an important factor to be measured. The goal of this experiment was to measure the maximum tensile strength of the sutures with various core sizes. A total of 7 sizes of double-layer PGA/PE sutures were extruded as experimental units, which are presented in Table 1. As shown in Figure 9, the breaking tensile strength of the suture was measured while the 2 ends of the suture were tied to a movable force sensor and a rigid bar. In each trial, the force sensor was slowly moved away from the bar using a fine-tuning knob until the suture was broken. The force at breaking point was noted as the maximum tensile strength of the suture. The measurements were done 5 times for each suture. Seal Strength Experiment. This experiment investigated the strength of the thermal seal for the PLA/PCL suture. This investigation had 2 goals: (1) to find the maximum applied force necessary to break the seal (bond strength) and (2) to measure the effect of tension on the seal strength. In this experiment, the seal strength was measured under 3 tensions. The melting temperature and tension are critical factors in seal formation. To study the effect of tension on seal strength, it is required to form several seals under a temperature that melts only the coat of the suture. To find the temperature, several seals were created at various melting temperatures during a pilot study. The results of the pilot study show that 45°C is the minimum temperature at which the suture coat was melted and the
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Figure 5. Average of maximum pulling force with different surface materials.7
Figure 6. Shaft of the device: A. Shaft of the device with an inside mount. B. Movable support with connecting parts.
Figure 7. All parts of the design except the bottom jaw.
core was intact during the sealing process. As a result, this temperature was used to create the seals in 3 sets of trials. Each set included 3 trials in which a seal was created under a certain tension. The tensions for the 3 sets were 2, 3, and 4 N. Figure 10 depicts the experimental setup to create a seal under a controlled tension; it also measures the seal strength at the breaking point of the
Figure 8. A sample of the double-layer suture and its crosssectional view.
seal. A prototype was made for this experiment to form a cross-point similar to the one in the LigLAP method for seal creation. The suture was looped around a knob on the prototype, and then the 2 ends of the suture were guided in the opposite direction to create the cross-point. Finally, the 2 ends were connected to a force sensor. A controlled pulling force was provided when the seal was created at the cross-point using a soldering iron. To measure the strengths of the experimental units, after 60 s, the force sensor was slowly moved away, and the forces at the seal breaking points were recorded. These are presented in the Results section. Leakage Experiment. The main goal of this experiment was to investigate the effectiveness of the double-layer suture in the potential occlusion process. Water balloons were used to mimic the elasticity of vessels in this experiment. Essentially, we wanted to evaluate whether or not there was any loss of water when water balloons were occluded by the sealed double-layer suture. The results
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Table 1. Seven Sizes of the Sutures.
S1 S2 S3 S4 S5 S6 S7
Material
Diameter (mm)
Core Percentage
Radius of Core (mm)
Thickness of Sheath (mm)
PGA/PE PGA/PE PGA/PE PGA/PE PGA/PE PGA/PE PGA/PE
0.46 0.5 0.52 0.52 0.52 0.68 0.68
PGA, 10% PGA, 60% PGA, 50% PGA, 40% PGA, 30% PGA, 60% PGA, 50%
0.072 0.193 0.183 0.164 0.142 0.263 0.24
0.157 0.057 0.067 0.086 0.108 0.07 0.10
Abbreviations: PGA, polyglycolic acid; PE, polyethylene.
Figure 9. Experimental setup for the suture tension experiment.
Figure 10. Seal strength experiment.
were then compared with that from another group of water balloons occluded by a strong string. A total of 16 water balloons were used as experimental units. The size and initial weight of the balloons were randomly chosen and ranged from 121.209 to 175.329 g. The balloons were divided into 2 groups. The first group included 8 balloons that were occluded by the doublelayer suture. The second group, which was the control group, consisted of the other 8 balloons that were occluded by double-knotted strings. The 0.48-mm PLA/ PCL suture was used in the occlusion of the first 8 balloons. The core radius and the thickness of the coat were 0.108 and 0.132 mm, respectively. A soldering iron was utilized as the heating element to melt the coat of the suture. The suture was tightened around each balloon
until the balloon was fully occluded and then thermally sealed at 45°C using the soldering iron, as shown in Figure 11. The heating time was about 0.5 s. The control balloons were occluded using a strong string. Two tight knots were placed, as depicted in Figure 11, to ensure that there was no leakage. For both groups, the weights of all balloons were measured to determine the loss of water. The initial weights and the weights after 3, 6, 12, 24, 48, 72, and 96 hours were measured using a weighing scale, with 0.001 g accuracy.
Results Tension Experiment For each trial, the final recorded force at breaking was captured. The mean force and standard deviation values across all measurements for each suture were calculated and are presented in Figure 12. Suture number 6 was seen to have the highest tensile strength (15.7 N) among all sutures.
Seal Strength Experiment The maximum forces required for breaking the seals were recorded. The mean force and the standard deviation val-
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Figure 11. A soldering iron is approaching the suture cross-point to form a seal in the left picture. The right-top and rightbottom pictures show the final occluded balloons by the string and the polylactic acid/polycaprolactone (PLA/PCL) suture, respectively.
ues across all measurements for each tension were calculated and are shown in Figure 13.
Leakage Experiment To compare the weights of all water balloons, the weights were normalized because the initial weights of water balloons were different. The mean weight and the standard deviations for each group were calculated across all occluded balloons for the 7 measurements after the starting time, and the results are presented in Figure 14.
Discussion In this article, a potential occlusion method (LigLAP) to address the problems associated with stapling devices has been presented. This method involves a double-layer suture that encircles vessels/ducts. A weld was formed using a heating element while the suture was tightened, and vessels/ducts were occluded. The heating element melted the outer layer of the suture to create the weld. Finally, the end of the suture was cut and released. In addition, several experiments were conducted to measure several properties of the sutures and evaluate the potential functionality and validity of the method. The conclusions are discussed below.
Tension Experiment According to this preliminary result, the double-layer suture demonstrated good strength, and the core size would be an effective variable on the tensile strength. For example, suture number 6, which has the highest core radius of 0.263 mm among all sutures, also has the highest strength.
Seal Strength Experiment In this preliminary experiment, the maximum recorded force (around 5 N) was observed to break the seal that was created under a tension of 2 N. The trend of collected data suggests that a lower tension at seal creation results in greater seal strength. However, it may be that as a result of the small number of observations, the data do not show a significant difference between any of the 2 seal strengths under different tensions. Further investigations are required to substantiate the findings. The minimum melting temperature at which the suture coat would be melted to create a weld is 45°C. This temperature, which has been used during the sealing process, is higher than the body temperature. Therefore, the suture would not be melted without a heating element inside body.
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Figure 14. The normalized mean weight of water balloons and standard deviations. Abbreviation: PLA/PCL, polylactic acid/polycaprolactone.
Figure 12. The mean value and standard deviation for the tensile strength of each suture.
Figure 13. Seal strength of sutures and standard deviations under various tensions while creating the seal.
Leakage Experiment The results showed that there was no significant difference between both groups, and a similar small weight loss was observed for both groups. In addition, an unpaired t test did not show a statistically significant difference between the small weight losses in the 2 groups. The associated probability value (P = .4877) to this test is much larger than the rejection level of .05. It seems that the very minute amount of mass loss (about 2%) for both groups was a result of the evaporation and molecular diffusion of vapor through the membrane of the balloons, suggesting that liquid leakage was not responsible. The measurements in the above experiments provide estimations for the seal creation tension and melting temperatures in a sealing process with a double-layer suture. However, further investigations should be conducted to study the effects of factors such as liquid pressure and suture tension precisely, using experimental units that better model the elasticity of vessels.
In this study, leakage was tested but with limitations in the experimental setup using water balloons and a double-layer suture. In practice, the leakage of a vessel/duct is a serious event, carrying with it significant morbidity and mortality. Therefore, much more rigorous testing of leakage is required to extend the method to occlude vessels/ducts in actual laparoscopic surgery. Future work could also include the study of seal length and a comparison of the single-point seal with a length of seal (larger than single point). In addition, it would be useful to study different materials as the layers of the suture. These potential studies would help improve the LigLAP method. Author Contributions RY has conducted the research and he is the main author of this paper. PJ helped in conducting the experiments. Dr. Kia and Dr. Zadeh co-supervised the research project and helped in proofreading of the paper.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Partial financial support was provided by MSK LLC, a Michigan limited liability company.
References 1. Kapiteijn E, Marijnen CAM, Colenbrander AC, et al. Local recurrence in patients with rectal cancer diagnosed between 1988 and 1992: a population-based study in the west Netherlands. Eur J Surg Oncol. 1998;24:528-535. 2. Heald RJ, Husband EM, Ryall RDH. The mesorectum in rectal cancer surgery: the clue to pelvic recurrence?. Br J Surg. 1982;69:613-616.
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Yousefian et al 3. Vittimberga FJ Jr, Foley DP, Meyers WC, Callery MP. Laparoscopic surgery and the systemic immune response. Ann Surg. 1988;227:326. 4. Johansson M. Management of acute cholecystitis in the laparoscopic era: results of a prospective, randomized clinical trial. J Gastrointest Surg. 2003;7:642-645. 5. Tanović H, Mesihović R. Differences in the postoperative course and treatment in patients after laparoscopic and standard cholecystectomy. Medicinski Arhiv. 2002;57:219-222. 6. Fuchs KH. Minimally invasive surgery. Endoscopy. 2002; 34:154-159. 7. Yousefian R, Kia MA, Zadeh MH. On the design of shape memory alloy locking mechanism: a novel solution for laparoscopic ligation process. World Acad Sci Eng Technol. 2013;78:1644-1647. 8. Gollan JL, Bulkley GB, Diehl AM, et al. Gallstones and laparoscopic cholecystectomy. JAMA. 1993;269:1018-1024. 9. Champault G, Cazacu F, Taffinder N. Serious trocar accidents in laparoscopic surgery: a French survey of 103,852 operations. Surg Laparosc Endosc Percutan Tech. 1996;6:367-370. 10. Bencini L, Boffi B, Farsi M, Sanchez LJ, Scatizzi M, Moretti R. Laparoscopic cholecystectomy: retrospective comparative evaluation of titanium versus absorbable clips. J Laparoendosc Adv Surg Tech. 2003;13:93-98. 11. Beldi G, Glättli A. Laparoscopic subtotal cholecystec tomy for severe cholecystitis. Surg Endosc. 2003;17: 1437-1439. 12. Yu T, Wu SD, Su Y, Kong J, Yu H, Fan Y. Laparoscopic subtotal cholecystectomy as an alternative procedure designed to prevent bile duct injury: experience of a hospital in northern China. Surg Today. 2009;39:510-513. 13. Philips JAE, Lawes DA, Cook AJ, et al. The use of laparoscopic subtotal cholecystectomy for complicated cholelithiasis. Surg Endosc. 2008;22:1697-1700. 14. Sinha I, Smith ML, Safranek P, Dehn T, Booth M. Laparoscopic subtotal cholecystectomy without cystic duct ligation. Br J Surg. 2007;94:1527-1529. 15. Chowbey PK, Sharma A, Khullar R, Mann V, Baijal M, Vashistha A. Laparoscopic subtotal cholecystectomy: a review of 56 procedures. J Laparoendosc Adv Surg Tech A. 2000;10:31-34. 16. Michalowski K, Bornman PC, Krige JEJ, Gallagher PJ, Terblanche J. Laparoscopic subtotal cholecystectomy in patients with complicated acute cholecystitis or fibrosis. Br J Surg. 1998;85:904-906. 17. Gupta A, Agarwal PN, Kant R, Malik V. Evaluation of fundus-first laparoscopic cholecystectomy. JSLS. 2004;8: 255.
18. Turial S, Engel V, Sultan T, Schier F. Closure of the cystic duct during laparoscopic cholecystectomy in children using the LigaSure Vessel Sealing System. World J Surg. 2011;35:212-216. 1 9. Yeh CN, Jan YY, Liu NJ, Yeh TS, Chen MF. EndoGIA for ligation of dilated cystic duct during laparoscopic cholecystectomy: an alternative, novel, and easy method. J Laparoendosc Adv Surg Tech A. 2004;14: 153-157. 20. Belgaumkar AP, Carswell KA, Chang A, Patel AG. The dangers of using stapling devices for cystic duct closure in laparoscopic cholecystectomy. Surg Laparosc Endosc Percutan Tech. 2009;19:194-197. 21. Golash V. An experience with 1000 consecutive cystic duct ligation in laparoscopic cholecystectomy. Surg Laparosc Endosc Percutan Tech. 2008;18:155-156. 22. Saha SK. Ligating the cystic duct in laparoscopic cholecystectomy. Am J Surg. 2000;179:494-496. 23. Ng WT, Kong CK, Lee WM. Migration of three endoclips following laparoscopic cholecystectomy. J R Coll Surg Edinb. 1999;44:200. 24. Shamiyeh A, Wayand W. Laparoscopic cholecystec tomy: early and late complications and their treatment. Langenbecks Arch Surg. 2004;389:164-171. 25. Jones DB, Soper NJ. Complications of laparoscopic cholecystectomy. Annu Rev Med. 1996;47:31-44. 26. Bezzi M, Silecchia G, Orsi F, et al. Complications after laparoscopic cholecystectomy. Surg Endosc. 1995;9:29-36. 27. Cox MR, Wilson TG, Luck AJ, Jeans PL, Padbury RT, Toouli J. Laparoscopic cholecystectomy for acute inflammation of the gallbladder. Ann Surg. 1993;218:630-634. 28. Medina M. Analysis and physics of laparoscopic intracorporeal square-knot tying. JSLS. 2005;9:113. 29. Egan TD, inventor. Automatic suturing and ligating device. US patent 5417700 A. May 23, 1995. 30. Otsuka K, Ren X. Recent developments in the research of shape memory alloys. Intermetallics. 1999;7:511-528. 31. Duerig T, Pelton A, Stöckel D. An overview of nitinol medical applications. Mater Sci Eng. 1999;273:149-160. 32. Kode VRC, Cavusoglu MC. Design and characterization of a novel hybrid actuator using shape memory alloy and dc micromotor for minimally invasive surgery applications. Mechatronics IEEE/ASME Trans. 2007;12:455-464. 33. Fu Y, Du H, Huang W, Zhang S, Hu M. TiNi-based thin films in MEMS applications: a review. Sens Actuators A Phys. 2004;112:395-408.
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research-article2015
SRIXXX10.1177/1553350615579728Surgical InnovationYousefian et al
Original Article
LigLAP: Encirclement and Ligation of Vessels in Laparoscopic Surgery: A Double-Layer Suture Sealing Approach
Surgical Innovation 1–9 © The Author(s) 2015 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1553350615579728 sri.sagepub.com
Reza Yousefian, MS1, Paul Jones, BSME1, Michael A. Kia, DO2, and Mehrdad Hosseini Zadeh, PhD1
Abstract This article proposes a potential automatic ligation (LigLAP) method to occlude vessels and ducts in several laparoscopic surgical procedures. Currently, stapling devices are widely used for this purpose. However, there are some complications associated with stapling devices, including biliary leak and tissue damage. In this article, we examine the feasibility of an alternative method that uses a double-layer suture to encircle and occlude a vessel. A heating element melts the outer layer of the suture at the cross-point of the suture to create a seal. Several electromechanical mechanisms have been proposed to carry out this ligation process. In addition, some parts have been prototyped for experimental verification and visualization. Several double-layered sutures have been created, and their tensile strength and sealing capabilities have been measured. Moreover, a simple leakage experiment has been performed to verify experimentally the idea of using the double-layer suture. The results show that the new suture and the thermal sealing method provide the required strength to occlude balloons filled with water. Although the results suggest that the proposed method and the double-layer suture may be used in surgical ligation processes, much more rigorous testing of leakage is required. Keywords minimally invasive surgery, ligation process, automatic suturing, welding
Introduction Minimally invasive surgeries (MISs) are the procedures of choice in comparison to open surgeries. These surgeries allow surgeons to complete surgery operations through small incisions on the body. The size of incisions is restricted to avoid undue loss of blood and eschew manipulation of tissues. Hence, the body’s response to the surgery is with a reduced immune activation and catabolism.1-3 There are several advantages for MIS, such as shorter hospital stays and recovery periods, less scarring, less injury to tissue, and more postoperative comfort.4-7 Therefore, the use of laparoscopic surgeries has increased and is preferred in possible operations. For instance, laparoscopic cholecystectomy has replaced open cholecystectomy since it was first reported8 in 1987 and is one of the most frequently performed laparoscopic operations.9,10 The occlusion of the vessels/ducts is required in many surgeries such as cholecystectomy, renal surgery, and the resection of rectal cancer, to name a few. Several studies have assessed the feasibilities of laparoscopic methods to occlude vessels.11-18 In contrast to the occlusion process in
open surgeries, most of these methods do not use sutures to surround a vessel and tighten the suture to occlude vessels/ ducts. For example, laparoscopic stapling devices are frequently used as a method of duct closure and vessel occlusion in laparoscopic surgeries.19 Technical failures and dangers of stapling devices have been reported when the staples are not closed securely.20 In addition, bile leak is a known postoperative problem that could be caused by dislodgment and migration of the clips as well as bile duct necrosis.21-23 Moreover, a relatively large space behind the duct and/or vessel is required when using stapling devices. Other problems include vascular and duct injury, bleeding from the liver bed, and bile leak.24-26 Furthermore, in some cases, for example in the presence of chronic inflammation, laparoscopic cholecystectomy using stapling devices 1
Kettering University, Flint, MI, USA Department of Surgery, Michigan State University (McLaren Regional medical center), Flint, MI, USA 2
Corresponding Author: Reza Yousefian, Electrical and Computer Engineering Department, Kettering University, 1700 University Ave, Flint, MI 48504, USA. Email: [email protected]
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Figure 1. A. The proposed device. B. Expanded view of the device: 1, bottom jaw; 2, top jaw; 3, heating element; 4, movable cam; 5, cutting mechanism; 6, locking mechanism; and 7, shaft.
is difficult and dangerous.27 The traditional response to these difficult cases is conversion to open surgery. Similar to open surgery ligation techniques, sutures are preferred to occlude vessels/ducts in several intracorporeal laparoscopic ligation techniques using current laparoscopic surgery devices.21,22,28 However, these methods and devices do not provide automatic suturing to easily ligate and occlude vessels/ducts during the laparoscopic procedures. In one attempt, Egan29 has proposed a procedure of suturing to close an opening and claimed that the method can occlude vessels/ducts in which the suture is threaded through a channel to make a loop. The suture thread would be secured using an anvil and cut to create a closed loop with overlapping ends. After cutting, the suture ends would be melted together to form a weld. This method may work to close openings. However, it may fail to occlude vessels/ducts because the suture is not tightened while forming the weld. To the best of our knowledge, no experimental verification procedure has examined the Egan method to occlude vessels/ducts. Similar to the Egan method, our method (LigLAP) forms a weld in an automatic suturing procedure. However, in the proposed method, the weld is created while the suture is tightened and the vessel is occluded. In this method, the suture would be looped around the vessel/duct and tightened to occlude the vessel/duct. Then, the heating element melts the cross-point of the suture to form the weld. A new double-layer suture with 2 melting temperatures has been created to be used in a potential ligation procedure. The 2 layers of the suture are the following: (1) an inner layer with higher melting point temperature, which provides strength to the suture and keeps the suture intact during the melting process, and (2) an outer layer with a relatively lower melting temperature that will be melted and create the weld. In all, 7 samples of the suture are extruded, and 2 experiments have been conducted to measure key properties of the sutures, including melting
temperatures and tensile strengths. A leakage experiment has also been conducted to examine use of the doublelayer suture and the thermal sealing method in the occlusion of elastic balloons filled with water.
Material and Methods LigLAP: Automatic Suturing-Occlusion Laparoscopic Procedure The LigLAP method may enable surgeons to occlude vessels automatically using a double-layer suture. This occlusion process may be repeated several times to occlude all required places on the vessel to prevent bleeding. The LigLAP can be used in several surgeries in which vessels must be occluded during the operation, including renal surgery and cholecystectomy. Unlike the stapling devices (currently common devices for this purpose), little space may be required behind the vessel in the LigLAP method. The LigLAP method includes the following 5 main steps: 1. Encircling the vessel with the suture: This is accomplished by the use of a channel created in the jaws of the proposed device. 2. Locking one end of the suture: To address this, we have designed, prototyped, and tested a locking mechanism using a shape memory alloy (SMA) wire. 3. Occluding the vessel by tightening the suture: The suture is pulled while its end is locked in the locking mechanism. During this step, the suture comes out of the channel and starts occluding the vessel. 4. Sealing the suture using a heating element: The heating element has been designed to melt the outer layer of the suture as well as force the suture
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pushed forward, leading to the formation of the cross-point of the suture on the V-shaped heating element; 2 U-shaped channels are made in the wings to facilitate the motion of the suture toward the heating element.
Figure 2. ABS (acrylonitrile butadiene styrene) prototypes of the jaws.
to make a cross-point in front of the heating element. 5. Cutting and releasing the suture: A cutting mechanism has been designed using a SMA actuator. To perform the above steps, several mechanisms have been proposed in the design of a potential laparoscopic surgical device. The design and system overview of the device are shown in Figure 1. Each component of the device is briefly illustrated as follows: Jaws. The bottom and top jaws are presented as components 1 and 2, respectively, in Figure 1B. The top jaw is movable, and the bottom jaw is stationary and provides a fixed point as a reference for a surgeon. Large-scale prototypes of the jaws are made using ABS (acrylonitrile butadiene styrene) and shown in Figure 2. Two important roles of the jaws are (1) to enclose the vessel and (2) to serve as a complete route for the suture to encircle the vessel. There is a semicircular channel, 1 mm in diameter, to provide this route. The curvature of the channel is designed to make a cross-point of the suture possible during the tightening step (step 3). To open/close the top jaw, a cam (labeled 4 in Figure 1) is connected to the tail of the jaw. As shown in Figure 1A, the other side of the cam is in the slot of a movable part, which is also used to move the heating element. The heating element is briefly presented next. Heating Mechanism. As shown in Figure 3, the heating element is placed on a movable mount in the heating mechanism. This enables the element to melt the outer layer of the suture and seal it after tightening (step 4). The design of the movable mount includes the following components. 1. a V-shaped stage for the heating element to be attached to the mount, providing more surface contact between the heating element and the suture; and 2. a pair of wings that force the suture completely out of the channel when the mount is
Locking and Cutting Mechanism. The end of the suture has to be locked (step 2) during the tightening process. Because of the small space available, a SMA-based locking system has been designed, prototyped, and tested.7 In addition, for cutting and releasing the suture (step 5), a similar design to the locking system is proposed, with an additional small blade to cut the suture. The design of the locking mechanism and the experimental setup that includes the locking prototype is shown in Figure 4. The peg of the locking system is initially open and is closed by the contraction of the SMA wire looped through the peg. The prototype was made out of ABS at a larger scale (Figure 4), and a 275-µm nitinol SMA wire was used as the actuator. A torsional spring was also used to provide backward force for the peg and, thus, for the SMA wire. The Joule effect of electric current is used to heat the SMA wire, resulting in its contraction and holding/cutting the suture. In addition, surface material used on the peg and the base of the locking mechanism, where the suture end is held in between, effects the maximum pulling force of the suture. This is because of the difference in surface friction of various materials. Figure 5 presents the results showing the average of maximum pulling force applied to the suture for 6 different materials.7 The biocompatibility and small size of SMA wires are important in biomedical applications, especially in MISs.7,30-32 SMA wires have many advantages, such as suitability for clean room applications, a high ratio of force to volume, a high strain feature, a small size, and the ability to perform without noise emission.7,33 Shaft and Mounting Element. The shaft is designed with an inside mount (movable part), labeled 2 in Figure 6A, to move the heating element forward/backward and to open/ close the top jaw. There are also openings in the top and bottom of the shaft (labeled 1 in Figure 6A), allowing the top jaw to open. All parts of the design, except the bottom jaw, are shown in Figure 7.
Double-Layer Suture The thermal sealing of the suture plays an important role in the LigLAP method. Because the main goal is to create a seal by melting the suture without cutting it, a new double-layer suture with 2 melting temperatures has been developed for the LigLAP process. A single-layer suture cannot be used for this purpose because when the heat is
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Figure 3. The heating element: A. Design of the heating mechanism. B. Position of the heating mechanism in the device.
would be useful for the proposed occlusion process. The details of all preliminary measurements and the final leakage experiment are presented in the following sections. The results of all experiments are described in the Results section.
Figure 4. Design and the experimental setup to examine the locking mechanism: 1, mount; 2, the peg of the locking system; 3, position of torsional spring, which provides enough force to bring back the peg to its initial position.
provided to make a seal, the suture will be melted and cut. The suture consists of 2 polymer layers: a core and a coat that is melted to create a seal. The outer layer (coat) has a much lower melting temperature than the core. Therefore, when the heating is provided, the coat will be melted to create the seal, and the core is not melted. Another requirement is that the suture has to be rigid enough to pass the channel in the jaws. Two types of sutures that meet the above requirements have been produced using extrusion machines. In the first type, polyglycolic acid (PGA) core is coated by polyethylene (PE), resulting in a strong PGA core and low melting temperature PE coat. To extrude the second type, a polylactic acid (PLA) core is coated by polycaprolactone (PCL) polymer. The sutures have been made with various diameters, ranging from 0.35 to 1.00 mm. Figure 8 shows a sample of the double-layer suture and its cross-sectional view. After the design and extrusion of the sutures, the key properties of the sutures in regard to the occlusion method need to be measured. The tensile strength, seal creation tension, and melting temperatures are important properties of the sutures. The following tensile and seal experiments have been conducted to provide the required information about important properties of sutures that
Tension Experiment. Because the sutures will be used under tension during the tightening process, the tensile strength is an important factor to be measured. The goal of this experiment was to measure the maximum tensile strength of the sutures with various core sizes. A total of 7 sizes of double-layer PGA/PE sutures were extruded as experimental units, which are presented in Table 1. As shown in Figure 9, the breaking tensile strength of the suture was measured while the 2 ends of the suture were tied to a movable force sensor and a rigid bar. In each trial, the force sensor was slowly moved away from the bar using a fine-tuning knob until the suture was broken. The force at breaking point was noted as the maximum tensile strength of the suture. The measurements were done 5 times for each suture. Seal Strength Experiment. This experiment investigated the strength of the thermal seal for the PLA/PCL suture. This investigation had 2 goals: (1) to find the maximum applied force necessary to break the seal (bond strength) and (2) to measure the effect of tension on the seal strength. In this experiment, the seal strength was measured under 3 tensions. The melting temperature and tension are critical factors in seal formation. To study the effect of tension on seal strength, it is required to form several seals under a temperature that melts only the coat of the suture. To find the temperature, several seals were created at various melting temperatures during a pilot study. The results of the pilot study show that 45°C is the minimum temperature at which the suture coat was melted and the
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Figure 5. Average of maximum pulling force with different surface materials.7
Figure 6. Shaft of the device: A. Shaft of the device with an inside mount. B. Movable support with connecting parts.
Figure 7. All parts of the design except the bottom jaw.
core was intact during the sealing process. As a result, this temperature was used to create the seals in 3 sets of trials. Each set included 3 trials in which a seal was created under a certain tension. The tensions for the 3 sets were 2, 3, and 4 N. Figure 10 depicts the experimental setup to create a seal under a controlled tension; it also measures the seal strength at the breaking point of the
Figure 8. A sample of the double-layer suture and its crosssectional view.
seal. A prototype was made for this experiment to form a cross-point similar to the one in the LigLAP method for seal creation. The suture was looped around a knob on the prototype, and then the 2 ends of the suture were guided in the opposite direction to create the cross-point. Finally, the 2 ends were connected to a force sensor. A controlled pulling force was provided when the seal was created at the cross-point using a soldering iron. To measure the strengths of the experimental units, after 60 s, the force sensor was slowly moved away, and the forces at the seal breaking points were recorded. These are presented in the Results section. Leakage Experiment. The main goal of this experiment was to investigate the effectiveness of the double-layer suture in the potential occlusion process. Water balloons were used to mimic the elasticity of vessels in this experiment. Essentially, we wanted to evaluate whether or not there was any loss of water when water balloons were occluded by the sealed double-layer suture. The results
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Table 1. Seven Sizes of the Sutures.
S1 S2 S3 S4 S5 S6 S7
Material
Diameter (mm)
Core Percentage
Radius of Core (mm)
Thickness of Sheath (mm)
PGA/PE PGA/PE PGA/PE PGA/PE PGA/PE PGA/PE PGA/PE
0.46 0.5 0.52 0.52 0.52 0.68 0.68
PGA, 10% PGA, 60% PGA, 50% PGA, 40% PGA, 30% PGA, 60% PGA, 50%
0.072 0.193 0.183 0.164 0.142 0.263 0.24
0.157 0.057 0.067 0.086 0.108 0.07 0.10
Abbreviations: PGA, polyglycolic acid; PE, polyethylene.
Figure 9. Experimental setup for the suture tension experiment.
Figure 10. Seal strength experiment.
were then compared with that from another group of water balloons occluded by a strong string. A total of 16 water balloons were used as experimental units. The size and initial weight of the balloons were randomly chosen and ranged from 121.209 to 175.329 g. The balloons were divided into 2 groups. The first group included 8 balloons that were occluded by the doublelayer suture. The second group, which was the control group, consisted of the other 8 balloons that were occluded by double-knotted strings. The 0.48-mm PLA/ PCL suture was used in the occlusion of the first 8 balloons. The core radius and the thickness of the coat were 0.108 and 0.132 mm, respectively. A soldering iron was utilized as the heating element to melt the coat of the suture. The suture was tightened around each balloon
until the balloon was fully occluded and then thermally sealed at 45°C using the soldering iron, as shown in Figure 11. The heating time was about 0.5 s. The control balloons were occluded using a strong string. Two tight knots were placed, as depicted in Figure 11, to ensure that there was no leakage. For both groups, the weights of all balloons were measured to determine the loss of water. The initial weights and the weights after 3, 6, 12, 24, 48, 72, and 96 hours were measured using a weighing scale, with 0.001 g accuracy.
Results Tension Experiment For each trial, the final recorded force at breaking was captured. The mean force and standard deviation values across all measurements for each suture were calculated and are presented in Figure 12. Suture number 6 was seen to have the highest tensile strength (15.7 N) among all sutures.
Seal Strength Experiment The maximum forces required for breaking the seals were recorded. The mean force and the standard deviation val-
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Figure 11. A soldering iron is approaching the suture cross-point to form a seal in the left picture. The right-top and rightbottom pictures show the final occluded balloons by the string and the polylactic acid/polycaprolactone (PLA/PCL) suture, respectively.
ues across all measurements for each tension were calculated and are shown in Figure 13.
Leakage Experiment To compare the weights of all water balloons, the weights were normalized because the initial weights of water balloons were different. The mean weight and the standard deviations for each group were calculated across all occluded balloons for the 7 measurements after the starting time, and the results are presented in Figure 14.
Discussion In this article, a potential occlusion method (LigLAP) to address the problems associated with stapling devices has been presented. This method involves a double-layer suture that encircles vessels/ducts. A weld was formed using a heating element while the suture was tightened, and vessels/ducts were occluded. The heating element melted the outer layer of the suture to create the weld. Finally, the end of the suture was cut and released. In addition, several experiments were conducted to measure several properties of the sutures and evaluate the potential functionality and validity of the method. The conclusions are discussed below.
Tension Experiment According to this preliminary result, the double-layer suture demonstrated good strength, and the core size would be an effective variable on the tensile strength. For example, suture number 6, which has the highest core radius of 0.263 mm among all sutures, also has the highest strength.
Seal Strength Experiment In this preliminary experiment, the maximum recorded force (around 5 N) was observed to break the seal that was created under a tension of 2 N. The trend of collected data suggests that a lower tension at seal creation results in greater seal strength. However, it may be that as a result of the small number of observations, the data do not show a significant difference between any of the 2 seal strengths under different tensions. Further investigations are required to substantiate the findings. The minimum melting temperature at which the suture coat would be melted to create a weld is 45°C. This temperature, which has been used during the sealing process, is higher than the body temperature. Therefore, the suture would not be melted without a heating element inside body.
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Figure 14. The normalized mean weight of water balloons and standard deviations. Abbreviation: PLA/PCL, polylactic acid/polycaprolactone.
Figure 12. The mean value and standard deviation for the tensile strength of each suture.
Figure 13. Seal strength of sutures and standard deviations under various tensions while creating the seal.
Leakage Experiment The results showed that there was no significant difference between both groups, and a similar small weight loss was observed for both groups. In addition, an unpaired t test did not show a statistically significant difference between the small weight losses in the 2 groups. The associated probability value (P = .4877) to this test is much larger than the rejection level of .05. It seems that the very minute amount of mass loss (about 2%) for both groups was a result of the evaporation and molecular diffusion of vapor through the membrane of the balloons, suggesting that liquid leakage was not responsible. The measurements in the above experiments provide estimations for the seal creation tension and melting temperatures in a sealing process with a double-layer suture. However, further investigations should be conducted to study the effects of factors such as liquid pressure and suture tension precisely, using experimental units that better model the elasticity of vessels.
In this study, leakage was tested but with limitations in the experimental setup using water balloons and a double-layer suture. In practice, the leakage of a vessel/duct is a serious event, carrying with it significant morbidity and mortality. Therefore, much more rigorous testing of leakage is required to extend the method to occlude vessels/ducts in actual laparoscopic surgery. Future work could also include the study of seal length and a comparison of the single-point seal with a length of seal (larger than single point). In addition, it would be useful to study different materials as the layers of the suture. These potential studies would help improve the LigLAP method. Author Contributions RY has conducted the research and he is the main author of this paper. PJ helped in conducting the experiments. Dr. Kia and Dr. Zadeh co-supervised the research project and helped in proofreading of the paper.
Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Partial financial support was provided by MSK LLC, a Michigan limited liability company.
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