Human acellular dermal matrix for ventral hernia repair reduces morbidity in transplant patients.

PURPOSE: Organ transplantation is widely accepted as the treatment of choice for native organ failure. Due to required immunosuppression, however, organ recipients are prone to wound infections, incisional hernias, and fascial dehiscence. These complications are especially dangerous in this patient population, as they can compromise the survival of the transplanted organ. Various methods have been employed to repair ventral and incisional hernias in these patients. These include primary repair, synthetic mesh, biologic mesh, tensor fascia lata grafts (TFL), component separation, flaps from the thighs, or a combination of these. The goal of this study was to review the experience at our institution with ventral hernia repair in transplant patients and to compare outcomes of the various repair techniques. METHODS: Patients with liver, renal, or pancreas transplants requiring immunosuppression who underwent a ventral or incisional hernia repair at the University of Maryland from 2000-2005 were reviewed retrospectively. Factors examined include type and location of hernia, type of repair, post operative infection, hernia recurrence, reoperation, mesh removal, and length of follow up. Complication rates were compared using odds ratio and chi-square. RESULTS: A total of 104 patients met the criteria with a mean length of follow up of 26 months. Of these, 34 patients had repair with human acellular dermal matrix (HADM), 26 had synthetic mesh, 25 had primary repair, and 9 had TFL. Rates of wound infection in these groups were 15, 65, 8, and 11% respectively (χ (2) = 28, P < 0.001). Rates of recurrence were 24, 77, 36, and 11% respectively (χ (2) = 22, P < 0.001). The rate of mesh removal with HADM and synthetic mesh were 12 and 69%, respectively (χ (2) = 14, P < 0.001). When comparing HADM and synthetic mesh, the odds ratio for wound infection is 11 (95% CI 3.2-38) and for mesh removal is 8.7 (95% CI 2.6-28). CONCLUSION: When repairing ventral or incisional hernias in immunosuppressed transplant patients, HADM provides significantly reduced morbidity from reduced rates of infection, recurrence, and need for operative removal of mesh.

Effect of suture material on tensile strength and complication rate in abdominal fascial defects repaired with acellular dermal matrix.

BACKGROUND: Repair of ventral hernias represents a challenging problem for surgeons. AlloDerm (LifeCell, Branchburg, NJ, USA), an acellular dermal matrix (ADM) product derived from cadaveric human skin, has gained in popularity in the management of abdominal hernias because of its ability to support neovascularization and therefore resist infection. Surgeons have traditionally used nonabsorbable suture when using ADM in this setting, perhaps because of concerns regarding wound strength. This study was undertaken to examine the influence of suture material on wound breaking strength and complication rates in abdominal wall defects closed with ADM. METHODS: Full-thickness abdominal defects were created in athymic rats and immediately repaired with an ADM interposition graft using either interrupted Prolene or Maxon suture. Complications were recorded over time and the animals were sacrificed at 1 month intervals. The abdominal repair complex was harvested and wound strength was measured using a tensiometer. RESULTS: There were no hernias in any of the groups. There were also no cases of major adhesions to the AlloDerm. Two rats in the Prolene group developed a stitch extrusion through the ventral skin. Wound breaking strength increased significantly from the second to third month after surgery in both suture groups (p=0.0000, LSD test). The breaking strength of the abdominal fascia-ADM complex increased over the course of the experiment in both test groups, but no significant difference was found between the groups at any time point (p=0.3157). At 3 months, the breaking strength of the Prolene group and Maxon group was nearly identical (27.1 N +/- SD 7.4 and 29.7 N +/- SD 9.6, respectively). CONCLUSIONS: We were unable to identify a significant difference in breaking strength at the interface between ADM and normal, native fascia when using permanent versus resorbable sutures.

Ventral hernia repair using allogenic acellular dermal matrix in a swine model.

BACKGROUND: This study was designed to assess the long-term efficacy of allogenic acellular dermal matrix (ADM) used as an interpositional graft for ventral hernia repair in a swine model. METHODS: We created 12x4-cm full-thickness abdominal wall defects in 22 Yucatan miniature pigs. The defect was repaired with either two 6x4-cm pieces of AlloDerm (acellular dermal matrix processed from pig skin in order to avoid a xenogenic response, LifeCell Corporation, Branchburg, NJ USA) (n = 12), or expanded polytetrafluoroethylene mesh (ePTFE) (Gore-Tex, W.L. Gore & Associates, Inc., Newark, DE USA) (n = 10). In six pigs, a separate 3-cm fascial incision was made, which was then suture repaired as a control for tensiometry testing. The surgical sites were evaluated at either 3 months or 9 months for the presence of a hernia, stretching of the implant, adhesions, vascularity, and biomechanical strength. RESULTS: Two hernias occurred in both the ADM and the ePTFE groups. There was minimal stretching of the implants and minimal adhesions in both groups. Fluorescein testing and histology indicated vascular ingrowth into the ADM. There was no statistical difference between the mean breaking strengths of the ADM-fascial interface (106.5 N +/- SD 40.1), the interface between two pieces of ADM (149.1 N +/- SD 76.7), and the primary fascial repair (108.1 N +/- SD 20.9) at 9 months. The ADM-fascial interface had a significantly higher breaking strength than that of the ePTFE-fascia interface (66.1 N +/- SD 30.1) (P = 0.017, t-test, P = 0.043 Wilcoxon rank sum test). CONCLUSIONS: In this study, we were unable to demonstrate a difference between ADM and ePTFE in their ability to repair ventral hernias at 9 months in a swine model. The ADM additionally supports vascular ingrowth and exhibits increased breaking strength at the fascia-implant interface.

Cultured chondrocytes produce injectable tissue-engineered cartilage in hydrogel polymer.

The purpose of this study was to determine if chondrocytes cultured through several subcultures at very low plating density would produce new cartilage matrix after being reimplanted in vivo with or without a hydrogel polymer scaffold. Chondrocytes were initially plated in low-density monolayer culture, grown to confluence, and passaged four times. After each passage cells were suspended in purified porcine fibrinogen and injected into the subcutaneous space of nude mice while simultaneously polymerizing with thrombin to reach a final concentration of 40 million cells/cc. Controls were made by injecting fresh, uncultured cells with fibrin polymer and by injecting the cultured cells in saline (without polymer). All samples were harvested at 6 weeks. When injected in polymer, both fresh cells and cells that had undergone only one passage in culture produced cartilaginous nodules. Cultured cells did not produce cartilage, regardless of length of time spent in culture, when injected without polymer. Cartilage was also not recovered from samples with cells kept in culture for longer than one passage, even when provided with a polymer matrix. All samples harvested were subjected to histological analysis and assayed for total DNA, glycosaminoglycan (GAG), and type II collagen. There was histological evidence of cartilage in the groups that used fresh cells and cultured cells suspended in fibrin polymer that only underwent one passage. No other group contained areas that would be consistent with cartilage histologically. All experimental samples had a higher percent of DNA than native swine cartilage, and there was no statistical difference between the DNA content of the groups containing cultured or fresh cells in fibrin polymer. Whereas the GAG content of native cartilage was 8.39% of dry weight and fresh cells in fibrin polymer was 12.85%, cultured cells in fibrin polymer never exceded the 2.48% noted from first passage cells. In conclusion, this study demonstrates that porcine chondrocytes that have been cultured in monolayer for one passage will produce cartilage in vivo when suspended in fibrin polymer.

Adhesion of tissue-engineered cartilate to native cartilage.

Reconstruction of cartilaginous defects to correct both craniofacial deformities and joint surface irregularities remains a challenging and controversial clinical problem. It has been shown that tissue-engineered cartilage can be produced in a nude mouse model. Before tissue-engineered cartilage is used clinically to fill in joint defects or to reconstruct auricular or nasal cartilaginous defects, it is important to determine whether it will integrate with or adhere to the adjacent native cartilage at the recipient site. The purpose of this study was to determine whether tissue-engineered cartilage would adhere to adjacent cartilage in vivo. Tissue-engineered cartilage was produced using a fibrin glue polymer (80 mg/cc purified porcine fibrinogen polymerized with 50 U/cc bovine thrombin) mixed with fresh swine articular chondrocytes. The polymer/chondrocyte mixture was sandwiched between two 6-mm-diameter discs of fresh articular cartilage. These constructs were surgically inserted into a subcutaneous pocket on the backs of nude mice (n = 15). The constructs were harvested 6 weeks later and assessed histologically, biomechanically, and by electron microscopy. Control samples consisted of cartilage discs held together by fibrin glue alone (no chondrocytes) (n = 10). Histologic evaluation of the experimental constructs revealed a layer of neocartilage between the two native cartilage discs. The neocartilage appeared to fill all irregularities along the surface of the cartilage discs. Safranin-O and toluidine blue staining indicated the presence of glycosaminoglycans and collagen, respectively. Control samples showed no evidence of neocartilage formation. Electron microscopy of the neocartilage revealed the formation of collagen fibers similar in appearance to the normal cartilage matrix in the adjacent native cartilage discs. The interface between the neocartilage and the native cartilage demonstrated neocartilage matrix directly adjacent to the normal cartilage matrix without any gaps or intervening capsule. The mechanical properties of the experimental constructs, as calculated from stress-strain curves, differed significantly from those of the control samples. The mean modulus for the experimental group was 0.74 +/- 0.22 MPa, which was 3.5 times greater than that of the control group (p < 0.0002). The mean tensile strength of the experimental group was 0.064 +/- 0.024 MPa, which was 62.6 times greater than that of the control group (p < 0.0002). The mean failure strain of the experimental group was 0.16 +/- 0.061 percent, which was 4.3 times greater than that of the control group (p < 0.0002). Finally, the mean fracture energy of the experimental group was 0.00049 +/- 0.00032 J, which was 15.6 times greater than that of the control group. Failure occurred in all cases at the interface between neocartilage and native cartilage. This study demonstrated that tissue-engineered cartilage produced using a fibrin-based polymer does adhere to adjacent native cartilage and can be used to join two separate pieces of cartilage in the nude mouse model. Cartilage pieces joined in this way can withstand forces significantly greater than those tolerated by cartilage samplesjoined only by fibrin glue.

Injectable tissue-engineered cartilage using a fibrin glue polymer.

The purpose of this study was to demonstrate the feasibility of using a fibrin glue polymer to produce injectable tissue-engineered cartilage and to determine the optimal fibrinogen and chondrocyte concentrations required to produce solid, homogeneous cartilage. The most favorable fibrinogen concentration was determined by measuring the rate of degradation of fibrin glue using varying concentrations of purified porcine fibrinogen. The fibrinogen was mixed with thrombin (50 U/cc in 40 mM calcium chloride) to produce fibrin glue. Swine chondrocytes were then suspended in the fibrinogen before the addition of thrombin. The chondrocyte/polymer constructs were injected into the subcutaneous tissue of nude mice using chondrocyte concentrations of 10, 25, and 40 million chondrocytes/cc of polymer (0.4-cc injections). At 6 and 12 weeks, the neocartilage was harvested and analyzed by histology, mass, glycosaminoglycan content, DNA content, and collagen type II content. Control groups consisted of nude mice injected with fibrin glue alone (without chondrocytes) and a separate group injected with chondrocytes suspended in saline only (40 million cells/cc in saline; 0.4-cc injections). The fibrinogen concentration with the most favorable rate of degradation was 80 mg/cc. Histologic analysis of the neocartilage showed solid, homogeneous cartilage when using 40 million chondrocytes/cc, both at 6 and 12 weeks. The 10 and 25 million chondrocytes/cc samples showed areas of cartilage separated by areas of remnant fibrin glue. The mass of the samples ranged from 0.07 to 0.12 g at 6 weeks and decreased only slightly by week 12. The glycosaminoglycan content ranged from 2.3 to 9.4 percent for all samples; normal cartilage controls had a content of 7.0 percent. DNA content ranged from 0.63 to 1.4 percent for all samples, with normal pig cartilage having a mean DNA content of 0.285 percent. The samples of fibrin glue alone produced no cartilage, and the chondrocytes alone produced neocartilage samples with a significantly smaller mass (0.47 g at 6 weeks and 0.46 g at 12 weeks) when compared with all samples produced from chondrocytes suspended in fibrin glue (p < 0.03). Gel electrophoreses demonstrated the presence of type II collagen in all sample groups. This study demonstrates that fibrin glue is a suitable polymer for the formation of injectable tissue-engineered cartilage in the nude mouse model. Forty million chondrocytes per cc yielded the best quality cartilage at 6 and 12 weeks when analyzed by histology and content of DNA, glycosaminoglycan, and type II collagen.

Transdermal photopolymerized adhesive for seroma prevention.

The purpose of this study was to determine whether or not a synthetic photopolymerized tissue adhesive (polyethylene oxide hydrogel) is useful in seroma prevention using a well established rat mastectomy seroma model. Twenty-three Sprague-Dawley rats received mastectomies. The rats were randomly assigned to either the control group (n = 13) or the experimental group (n = 10). The control animals received 0.2 cc of saline into the wound before closure. The experimental group received either 0.2 cc (n = 5) or 0.4 cc (n = 5) of the polyethylene oxide polymer into their wounds before closure. The experimental animals were placed under an ultraviolet A lamp for 3 minutes to polymerize the adhesive. On postoperative day seven, the resultant seromas were quantified, and wound tissues were harvested for histologic evaluation. The rats in the control group had a mean seroma volume of 3.25 cc (SD = 2.41), whereas the rats treated with polymer had a mean seroma volume of 0.37 cc (SD = 0.51). A Student's t test was performed showing a statistically significant difference between the control and experimental groups (p < 0.005). The volume of polymer used (0.2 cc versus 0.4 cc) did not significantly impact the volume of the resultant seromas. This study demonstrates that photopolymerizable polyethylene oxide hydrogels can be used as a tissue adhesive and that such an adhesive significantly reduces seroma formation in the rat mastectomy model.

Flap perfusion mapping: TRAM flap after abdominal suction-assisted lipectomy.

This technique or its modification (using other dyes) may play a beneficial role in other clinical scenarios where the reconstructive plastic surgeon preoperatively needs to know the integrity of vessels that are too small to image using standard angiographic techniques. In addition, flap perfusion mapping can demonstrate the pattern of skin that is physiologically perfused by the intact vessels. Knowledge of the perfusion characteristics of the tissues to be transferred before surgery may, at the least, alter the design of the tissues to be transferred and, in the extreme case, could affect the nature of the operative choice altogether.