Evaluation of soft tissue attachments to a novel intra-abdominal prosthetic in a rabbit model.

BACKGROUND: Laparoscopic ventral hernia repair requires placement of an intraperitoneal prosthetic. Composite mesh types have been developed to address the shortcomings of standard meshes. The authors evaluated the host reaction to intraperitoneal placement of a novel composite material. MATERIALS AND METHODS: A comparison of an innovative polypropylene/polylactide composite mesh was made to parietex composite (PCO), Proceed, and DualMesh. Eighteen meshes per group were implanted on intact peritoneum in New Zealand white rabbits. The main outcome measures included the formation of visceral adhesions, adhesion tenacity, tensiometric measurements, and histological analysis. Evaluations of adhesions were made at 1, 4, and 16 weeks using a 2-mm minilaparoscopy. RESULTS: There were no significant differences in the mean adhesion scores between the composite mesh types at week 1 (P = .15) and week 16 (P = .06). At 4 weeks, PCO had significantly fewer adhesions when compared with the other 3 mesh types (P = .02). Adhesion tenacity was also equivalent within the group at 16 weeks (P = .06). Tensiometry and histological analysis revealed no statistically significant differences between the mesh types. CONCLUSIONS: Four different composite mesh types had equivalent intra-abdominal soft tissue attachments in a rabbit model after a 16-week implantation period. PCO demonstrated the lowest mean adhesion score of each mesh type. Each mesh exhibited equivalent stiffness and energy to failure after explantation. The 4 composite mesh types demonstrated the successful formation of a neoperitoneum and comparable host biocompatibility as evidenced by similar degrees of inflammation.

Evaluation of composite mesh for ventral hernia repair.

INTRODUCTION: Composite mesh prostheses incorporate the properties of multiple materials for ventral hernia repair. This study evaluated a polypropylene/ePTFE composite mesh with a novel internal polydioxanone (PDO) absorbable ring. METHODS: Composite mesh was placed intraperitoneally in 16 pigs through an open laparotomy and explanted at 2, 4, 8, and 12 weeks. Intraabdominal adhesions were measured laparoscopically. Host tissue in-growth was assessed histologically and tensiometrically. Degradation of the internal PDO ring component was also measured tensiometrically. Appropriate statistical tests were used, and P ≤.05 indicated significance. RESULTS: No adhesions were formed in 50% of the grafts explanted at 8 weeks and 25% of grafts explanted at 12 weeks. There were significantly more vascular structures at 8 weeks, 73.5 ± 28, compared with 2 weeks, 6.75 ± 2 (P ≤.01). The T-peel force at the mesh-host tissue interface was not significantly different among time points. The absorbable PDO ring underwent complete degradation by 12 weeks. CONCLUSIONS: This composite mesh was associated with minimal intraabdominal adhesions, progressive in-growth of host tissues, and complete degradation of a novel internal PDO ring that aided mesh positioning. This composite hernia mesh showed a favorable performance in a porcine model of open ventral hernia repair.

Collagen-elastin ratio predicts burst pressure of arterial seals created using a bipolar vessel sealing device in a porcine model.

BACKGROUND: Bipolar electrosurgical devices are used to generate rapid and efficient hemostasis in a wide range of surgical procedures. Of the factors that influence seal integrity, vessel (artery) diameter has been considered the most important variable. In this study we hypothesized that the relative ratio of the components that form the seal (collagen and elastin) determine the degree of vessel distensibility and play an equally important role in defining seal strength. METHODS: Porcine carotid, renal, iliac, and femoral arteries were sealed using a bipolar electrosurgical device in vivo. Following removal, arterial diameter was measured and vessels' seals tested for arterial burst pressure (ABPr). Samples were then analyzed histologically and biochemically for collagen and elastin content. RESULTS: Arteries with the highest collagen-elastin ratio (C/E) (renal) consistently demonstrated significantly higher burst pressures than those arteries with lower C/E ratios (iliac and femoral) independent of artery diameter. CONCLUSION: Using arteries of distinct anatomical origin and physiological function, we demonstrate that total collagen content, and more specifically C/E ratio, in porcine arteries is a more accurate predictor of ABPr than vessel size alone.

An evaluation of electrosurgical vessel-sealing devices in biliary tract surgery in a porcine model.

OBJECTIVES: The purpose of this study was to evaluate two electrosurgical vessel-sealing devices in biliary surgery. METHODS: Porcine common bile ducts (CBDs) were sealed with two electrosurgical devices, an electrothermal bipolar vessel-sealing device (EBVS) and ultrasonic coagulation shears. Acute study animals underwent surgical bile duct sealing followed by immediate burst pressure testing. Chronic study animals were maintained for 1 week postoperatively and then tested. RESULTS: The seal failure rate in the acute study was 50% for both the EBVS device and shears, and 0% for the laparoscopic surgical clip device used as a control. The latter had significantly higher burst pressures (646.2 ± 281.8 mmHg; P = 0.006) than the EBVS device (97.6 ± 86.6 mmHg) and shears (71.7 ± 89.3 mmHg). No significant difference in burst pressures was noted between the EBVS device and shears (97.6 ± 86.6 mmHg vs. 71.7 ± 89.3 mmHg). In the chronic study, obvious bile leaks occurred in one of four pigs (25%) in the EBVS device subgroup and two of four pigs (50%) in the shears subgroup. The average proximal CBD pressure in seven pigs was 16.1 ± 4.1 mmHg. The average chronic burst pressure in the control subgroup was 1088.0 ± 922.6 mmHg. CONCLUSIONS: Given the high rates of failure of the EBVS device and the shears in consistently sealing biliary ducts, we do not recommend their routine use in biliary surgery.

Pushing the envelope in biomaterial research: initial results of prosthetic coating with stem cells in a rat model.

BACKGROUND: Coating prosthetic for hernia repair with a patient's own cells could improve biocompatibility by decreasing inflammation and adhesion formation and by increasing tissue ingrowth and resistance to infection. The objective of this study was to prove the feasibility of prosthetic coating with stem cells and to assess its resistance to adhesion formation when implanted in an animal model. METHODS: Adult Lewis rat bone marrow stem cells were harvested and cultured. Stem cells were then implanted on three different prosthetics. The prosthetic with the best stem cell adherence was implanted intraperitoneally into six adult rats. Untreated prosthetic was implanted in control animals (n = 12). After 2 weeks, intra-abdominal adhesions were graded using an adhesion scoring scale by two surgeons who were blinded to the animal group. Data were analyzed using the Wilcoxon rank-sum test. RESULTS: Stem cells demonstrated the best adherence and growth on polyglactin prosthetics. After implantation, the stem cell-coated polyglactin prosthetic had <25% of its surface area covered with adhesions in five (83%) samples, whereas the control polyglactin group had only one sample (8.3%) with <25% adhesions, and seven of its samples (58.3%) had >50% surface area adhesions (p < 0.05). CONCLUSIONS: The feasibility of hernia prosthetic coating with stem cells was demonstrated. Furthermore, stem-cell coated polyglactin prosthetic exhibited improved biocompatibility by decreasing adhesion formation in an animal model. Further study is needed to determine the factors that promote stem cell adherence to prosthetics and the in vivo prosthetic biomechanics after stem cell coating. This work is underway in our laboratory.

Effect of bacterial exposure on acellular human dermis in a rat ventral hernia model.

BACKGROUND: Effectiveness of acellular human dermis (AHD) as an alternative to synthetic mesh in contaminated fields has been described. Cellular migration after implantation and corresponding strength of attachment is not well documented. Our aim is to correlate AHD vascularization, fibroblast migration, and strength of attachment with presence of inflammatory cells in clean and contaminated fields. MATERIALS AND METHODS: Lewis rats were randomized to a control and three experimental groups. AHD was placed as an onlay over the intact abdominal wall. Experimental groups (n=72) were exposed to Staphylococcus aureus at 1 x 10(4), 1 x 10(5), or 1 x 10(6) by direct application; controls (n=12) were not exposed. At 5 and 28 d, abdominal walls were explanted and tissue ingrowth assessed via tensiometry measuring energy (E) and max stress (MS) at the AHD-tissue interface. Vascularity, fibroblast migration, and inflammatory cell migration were compared using light microscopy. RESULTS: Shear strength reported as energy and max stress were significantly greater at 28 versus 5 d in all experimental groups, remaining unchanged in controls. Plasma cells and histiocytes significantly increased in all groups; macrophages increased in experimental groups only. Vascular ingrowth increased significantly in all groups; fibroblast migration was greater in controls and 1 x 10(6) exposed group only. CONCLUSIONS: Contamination of AHD results in inflammatory cell influx and a surprising increase in shear strength. Interestingly, shear strength does not increase without contamination. Inflammation stimulates vascular ingrowth, but not equally significant fibroblast migration. Longer survivals are required to determine if energy and max stress of controls increase, and fibroblast migration follows vascular ingrowth.

A comparison of gastrojejunal anastomoses with or without buttressing in a porcine model.

INTRODUCTION: The addition of staple-line reinforcements on circular anastomoses has not been well studied. We histologically and mechanically analyzed circular- stapled anastomoses with and without bioabsorbable staple-line reinforcement (SeamGuard, W. L. Gore & Associates, Flagstaff, AZ) in a porcine model. METHODS: Gastrojejunal anastomoses were constructed using a #25 EEA Proximate ILS (Ethicon Endo-Surgery, Cincinnati, OH) mechanical stapling device with and without Bioabsorbable SeamGuard (BSG). Gastrojejunal anastomoses were resected acutely and at 1 week, and burst-pressure testing and histological analysis were performed. Standardized grading systems for inflammation, collagen deposition, vascularity, and serosal inflammation were used to compare the two anastomosis types. RESULTS: Acute burst pressures were significantly higher with BSG than with staples alone (1.37 versus 0.39 psi, p=0.0075). Burst pressures at 1 week were significantly lower with BSG than with staples alone (2.24 versus 3.86 psi, p=0.0353); however, both readings were above normal physiologic intestinal pressures. There was no statistical difference in inflammation (13.4 versus 15.6, p=0.073), width of mucosa (3.2 mm versus 3.2 mm, p=0.974), adhesion formation (0 versus 0.5, p=0.575), number of blood vessels (0.5 versus 1.0, p=0.056), or serosal inflammation (2.0 versus 1.0, p=0.27) between the stapled anastomoses and those buttressed with BSG. Stapled-only anastomoses had statistically more collagen (2.0 versus 1.0, p=0.005) than the anastomoses supported with BSG. CONCLUSIONS: The addition of BSG as a staple-line reinforcement acutely improves the burst strength of a circular anastomosis but not at 1 week. At 1 week, a decrease in collagen content with the BSG-buttressed stapled anastomosis was the only difference in the histologic parameters studied with no difference in vascularity, adhesions, or inflammation. The long-term effect of BSG on anastomotic strength or scarring is yet to be determined. The clinical implications may include decreased stricture formation and also decreased strength at anastomoses.

Comparison of blood vessel sealing among new electrosurgical and ultrasonic devices.

BACKGROUND: Bipolar electrosurgical devices and ultrasonic devices are routinely used in open and advanced laparoscopic surgery for hemostasis. New electrosurgical and ultrasonic instruments demonstrate improved quality and efficiency in blood vessel sealing. METHODS: The 5-mm laparoscopic Gyrus PKS Cutting Forceps (PK), Gyrus Plasma Trissector (GP), Harmonic Scalpel (HS), EnSeal Tissue Sealing and Hemostasis System (RX), LigaSure V with LigaSure Vessel Sealing Generator (LS), LigaSure V with Force Triad Generator (FT), and Ligamax 5 Endoscopic Multiple Clip Applier (LM) were tested to compare burst pressure, sealing time, and failure rate. Each device was used to seal 13 small (2-3 mm diameter), 13 medium (4-5 mm diameter), and 13 large (6-7 mm diameter) arteries from euthanized pigs. A p value <0.05 was considered statistically significant. RESULTS: Mean burst pressures were not statistically different for 2-3 mm or 6-7 mm vessels. For 4-5 mm vessels, LS had the highest mean burst pressure recorded. Mean seal times were shorter for every vessel size when FT was compared with LS (p < 0.05). The shortest sealing times for 2-3 mm vessels were recorded for GP. The shortest sealing times for medium and large vessels were observed with FT. The highest percentage failure rate for each vessel size occurred with GP. For 4-5 mm diameter vessels, the failure rate was 48% for GP, 41% for PK, and 22% for HS. For 6-7 mm diameter vessels, the failure rate was 92% for GP, 41% for PK, and 8% for HS. LM and FT had no recorded failures. CONCLUSION: Among the new 5-mm laparoscopic electrosurgical and ultrasonic instruments available for testing, RX, LS, and FT produced the highest mean burst pressures. FT had the shortest mean seal times for medium and large vessels. Minimal or no seal failures occurred with HS, RX, LS, LM, and FT.

Guidelines for power and time variables for microwave ablation in an in vivo porcine kidney.

PURPOSE: Microwave technology provides an emerging thermal ablation technique for solid organ tumors. We propose guidelines and recommend optimal time and power for use. METHODS: Microwave ablations using a VivaWave Microwave Ablation System (Valleylab, Boulder, CO) were performed in vivo in a porcine kidney model. The independent variables were power (20, 30, 40, 45, 50, 60 W) and time (2, 4, 6, 8, 10, 15, 20 min) with the outcome variable diameter of ablation. Following ablations, kidneys were procured for gross and histological evaluation. Analysis of variance (ANOVA) was used followed by Tukey tests when appropriate. A P value of <0.05 was considered statistically significant. RESULTS: In 308 total ablations, a minimum of 7 ablations were performed in 35 of 42 power and time variables (83%). The outcome variable, ablation diameter, was affected significantly by time, power, and time/power interaction (P < 0.0001). For each time point, a one-way ANOVA showed an overall significant difference in ablation size X wattage (P < 0.0001). Tukey tests showed that, at each time point, ablation sizes at 45, 50, and 60 W were not significantly different. After determining that 45 W was optimal, a one-way ANOVA showed an overall significant difference in ablation sizes for time points at 45 W (P < 0.0001). Tukey tests showed that, at 45 W, ablation sizes at 10 min were significantly larger than ablation sizes at 8, 6, 4, and 2 min. CONCLUSIONS: We propose guidelines for use of a novel microwave ablation system and recommend use at 45 W for 10 min.

The effect of preoperative corticosteroids on peritoneal macrophage function after laparoscopic and open abdominal surgery in a rat model.

BACKGROUND: Peritoneal macrophages play an important role in the immune response after abdominal operations. The stress response after these operations has been associated with impaired phagocytosis by peritoneal macrophages. This study examined the influence of minimally invasive techniques and preoperative corticosteroid administration on postoperative peritoneal macrophage phagocytic activity. METHODS: After IACUC approval, 66 Sprague Dawley rats were randomly divided into 7 groups: baseline animals (B), anesthesia controls (AC), open cecectomy (OC), and laparoscopic cecectomy (LC). Within the AC, OC, and LC groups, half received intraperitoneal (IP) dexamethasone (10 mg/kg) 1 hour before surgery (+S), and the other half received an equal volume of normal saline IP (-S). Animals were observed postoperatively for 24 hours and were then euthanized. Peritoneal macrophages were harvested via intraperitoneal lavage. A phagocytosis assay was performed to calculate the net phagocytosis and percent response to the effector agent. Statistical analysis was performed using analysis of variance and a Student t test between groups. A P value of <.05 was considered significant. RESULTS: Significant differences were observed between groups. The B group had a response rate of 94.2% +/- 56.7%, which was not different from the AC groups (-S, P = .28; +S, P = .16) or the LC-S group (P = .9). The lowest phagocytic activity rate was in the OC-S group with a response rate of 33.8% +/- 28.5%. The highest phagocytic response rates occurred in the AC +S (145.2% +/- 60.2%) and LC +S (198.1% +/- 103.5%). These were not significantly different from each other (P = .3). The LC +S group had a significantly higher percent response than all of the other groups. The phagocytic response rate of the OC +S group was not different from either the AC-S group (P = .07) or the LC-S group (P = .8); however, it was less than the AC +S group (P = .02) and the LC +S group (P = .003). CONCLUSION: Open cecectomy resulted in greater impairment of the phagocytic activity of peritoneal macrophages than laparoscopic cecectomy. The addition of preoperative corticosteroids improved phagocytic activity back to baseline function. The combination of minimally invasive surgical technique and preoperative corticosteroid administration resulted in the greatest postoperative phagocytic function of peritoneal macrophages in a rat model.

Guidelines for power and time variables for microwave ablation in a porcine liver.

The purpose of our study was to provide guidelines for the use of a novel microwave ablation system. Microwave ablations using a 915-MHz system were evaluated in a porcine liver. The independent variables were power and time, with the outcome variable being diameter of ablation. After ablations, livers were procured for measurement and histologic evaluation. Our study consisted of 420 ablations. The outcome variable, ablation diameter, was affected significantly by time, power, and time/power interaction (p<0.0001). For each time point, a one-way analysis of variance (ANOVA) showed an overall significant difference in ablation size X wattage (p<0.0001). Tukey tests at each time point showed ablation sizes at 45, 50, and 60 W were not significantly different. After it was determined that 45 W was optimal, a one-way ANOVA showed an overall significant difference in ablation sizes for time points at 45 W (p<0.0001). Tukey tests revealed that at 45 W, ablation sizes at 10, 15, and 20 min were not statistically different. We propose guidelines for diameters based on different time and power variables and recommend 45 W for 10 min to achieve optimal diameters at the shortest time and lowest wattage.