Improved tissue ingrowth and anchorage of expanded polytetrafluoroethylene by perforation: an experimental study in the rat

Polymer Hernia Repair Materials: Adapting to Patient Needs and Surgical Techniques

Biomaterials and their applications are perhaps among the most dynamic areas of research within the field of biomedicine. Any advance in this topic translates to an improved quality of life for recipient patients. One application of a biomaterial is the repair of an abdominal wall defect whether congenital or acquired. In the great majority of cases requiring surgery, the defect takes the form of a hernia. Over the past few years, biomaterials designed with this purpose in mind have been gradually evolving in parallel with new developments in the different surgical techniques. In consequence, the classic polymer prosthetic materials have been the starting point for structural modifications or new prototypes that have always strived to accommodate patients’ needs. This evolving process has pursued both improvements in the wound repair process depending on the implant interface in the host and in the material’s mechanical properties at the repair site. This last factor is important considering that this site—the abdominal wall—is a dynamic structure subjected to considerable mechanical demands. This review aims to provide a narrative overview of the different biomaterials that have been gradually introduced over the years, along with their modifications as new surgical techniques have unfolded.

Surgical perspectives regarding application of biomaterials for the management of large congenital diaphragmatic hernia defects

This review focuses on the surgical viewpoints on patch repairs in neonates with large congenital diaphragmatic hernia defects. The main focus  is on the various biomaterials that have been employed to date with regard to their source of origins, degradation properties as well as tissue integration characteristics. Further focus  is on the present knowledge on patch integration when biomaterials are placed in the diaphragmatic defect. The review will also look at the present evidence on the biomechanical characteristics of the most commonly used biomaterials and compares these materials to diaphragmatic tissue to offer more  insight on the present practice of patch repairs in large defects. Since tissue engineering and regenerative medicine has offered another dimension to diaphragmatic replacement, a detailed overview of this technology will be undertaken with regard to cell sourcing, scaffolds, in vitro versus in vivo implants as well as quality of tissue produced, to explore the limitations and the feasibility facing the scientific community in its clinical implementation of skeletal muscle-engineered tissue beyond laboratory research for diaphragmatic replacement.

* The New Zealand White Rabbit as a Model for Preclinical Studies Addressing Tissue Repair at the Level of the Abdominal Wall

In this report, we review the use of the New Zealand White rabbit as the experimental animal for several models of abdominal wall repair. For the repair of an abdominal wall defect, such as a hernia in clinical practice, multiple types of prosthetic material exist. Before their marketing, each of these biomaterials needs to be tested in a preclinical setting to confirm its biocompatibility and appropriate behavior at the different tissue interfaces. For preclinical trials, we have always used the New Zealand White rabbit as the model owing to its ease of handling and suitable size. This size allows for laparoscopic studies designed to follow the behavior in real time of a biomaterial implanted at the peritoneal interface, a delicate interface that often gives rise to complications in human practice. The size of the rabbit also offers a sufficiently large number of implant samples to be harvested for a complete battery of tests at several time points postimplant. In this review, we first describe the models established and then provide the results obtained so far using these models to test the different types of biomaterial. We end our review with a discussion of the clinical implications of these results.

The persistent challenge of parastomal herniation: a review of the literature and future developments

AIM

The aim of this review article was to outline current evidence relating to the treatment and prevention of parastomal herniation with a view to guide surgeons dealing with patients potentially affected by this complication.

METHOD

Medline and PubMed databases were searched using the keywords 'parastomal hernia/herniation', 'stoma hernia/herniation' and 'stoma complications'. Evidence was obtained from randomized and non-randomized studies. Case reports and articles not written in English were excluded. Qualitative assessment of all included studies was performed using the Oxford Centre for Evidence-Based Medicine 2011 levels of evidence.

RESULTS

The search revealed a total of 228 publications of which 115 fulfilled the selection criteria. Stoma formation through the rectus muscle is complicated by parastomal herniation in up to 50% of cases. There is no conclusive evidence that alternative techniques (e.g. extraperitoneal, lateral rectus abdominis positioned stoma) are superior. Open and laparoscopic parastomal hernia repair have similar recurrence rates up to 50%. The 'Sugarbaker' technique appears to be superior to the 'keyhole' technique when a laparoscopic approach is used. Prophylactic mesh reinforcement of the stoma trephine appears to reduce the herniation rate to approximately 15% and is accompanied by a decrease in symptomatic hernias requiring repair without any difference in stoma-related morbidity.

CONCLUSION

Large prospective controlled trials are required to compare surgical techniques of stoma formation in reducing the incidence of parastomal herniation. Despite limited evidence, routine prophylactic mesh reinforcement of the stoma trephine should be offered to all patients undergoing permanent stoma formation.

The long-term behavior of lightweight and heavyweight meshes used to repair abdominal wall defects is determined by the host tissue repair process provoked by the mesh

BACKGROUND

Although heavyweight (HW) or lightweight (LW) polypropylene (PP) meshes are widely used for hernia repair, other alternatives have recently appeared. They have the same large-pore structure yet are composed of polytetrafluoroethylene (PTFE). This study compares the long-term (3 and 6 months) behavior of meshes of different pore size (HW compared with LW) and composition (PP compared with PTFE).

METHODS

Partial defects were created in the lateral wall of the abdomen in New Zealand White rabbits and then repaired by the use of a HW or LW PP mesh or a new monofilament, large-pore PTFE mesh (Infinit). At 90 and 180 days after implantation, tissue incorporation, gene and protein expression of neocollagens (reverse transcription-polymerase chain reaction/immunofluorescence), macrophage response (immunohistochemistry), and biomechanical strength were determined. Shrinkage was measured at 90 days.

RESULTS

All three meshes induced good host tissue ingrowth, yet the macrophage response was significantly greater in the PTFE implants (P < .05). Collagen 1/3 mRNA levels failed to vary at 90 days yet in the longer term, the LW meshes showed the reduced genetic expression of both collagens (P < .05) accompanied by increased neocollagen deposition, indicating more efficient mRNA translation. After 90-180 days of implant, tensile strengths and elastic modulus values were similar for all 3 implants (P > .05).

CONCLUSION

Host collagen deposition is mesh pore size dependent whereas the macrophage response induced is composition dependent with a greater response shown by PTFE. In the long term, macroporous meshes show comparable biomechanical behavior regardless of their pore size or composition.

Laparoscopic parastomal hernia repair using a keyhole technique results in a high recurrence rate

INTRODUCTION

Parastomal herniation is a common complication of stoma formation, and its operative treatment is notoriously difficult. Recently we have reported the promising short-term results of a keyhole technique in which a Gore-Tex Dual Mesh with a central keyhole is laparoscopically fashioned around the bowel to close the hernia. In the long-term, recurrence is one of the major issues in hernia repair, therefore, this aspect was prospectively investigated.

METHODS

Since 2002, a total of 55 consecutive patients (27 men; median age, 63 years) with a symptomatic primary (n = 45) or recurrent parastomal hernia (n = 10) were electively operated using this technique. Patients were invited to the outpatient clinic on a regular basis and were examined for the occurrence of a recurrent hernia. At the last visit, all patients were asked to complete a short questionnaire.

RESULTS

Median follow-up (98%) was 36 (range, 12-72) months. During follow-up a recurrent parastomal hernia was diagnosed in 20 patients (37%). Three recurrences were asymptomatic and were treated conservatively. The other 17 patients (85%) developed mild-to-severe symptoms necessitating redo-surgery in 9 (45%) patients. Surprisingly, satisfaction with the procedure was high among patients (89%), even in the presence of a recurrence. Patients who reported unsatisfactory results belonged mainly to the group in whom the initial laparoscopic approach had to be converted to an open procedure.

CONCLUSIONS

Based on the results from the present study, which represents one of the largest patient series with the longest follow up available to date, it is concluded that laparoscopic parastomal hernia repair using a keyhole technique has an intolerably high recurrence rate with the currently available meshes. A new mesh with a less pliable central part and without the tendency to shrink is awaited.

Reconstruction of infected complex abdominal wall defects with autogenous pedicled demucosalized small intestinal sheet

BACKGROUND

Synthetic mesh can increase the risk of complications if it is placed directly over viscera or if the site is contaminated. Therefore, the use of bioprosthetic materials has increased rapidly. Neither synthetic nor bioprosthetic mesh is ideal for reconstructing infected complex abdominal wall defects. Our method using an autogenous pedicled demucosalized small intestinal sheet may be an alternative.

METHODS

Forty-one patients with infected, complex abdominal wall defects, with a mean defect size of 108 cm(2), underwent abdominal wall reconstruction using an autogenous, pedicled, demucosalized small intestinal sheet between January 1970 and December 2006. All patients had bowel and enterocutaneous fistulae in the defect. During operation, after resecting fistulae, the mucosa of the longitudinally split small intestine was scraped off with a scalpel to obtain an autogenous, pedicled, demucosalized small intestinal sheet, and then used to bridge the defect in the abdominal wall. A split thickness skin graft was then applied directly onto the demucosalized surface of the split bowel.

RESULTS

The operative procedure was successful in patients. The wounds between the intestinal sheets and abdominal walls healed spontaneously. Four patients developed regeneration of intestinal mucosa in some of the "meshed" skin grafts at 4-5 days postoperatively. The follow-up evaluation was 24 months to 20 years. Abdominal wall herniation, fistula formation, or bowel obstruction did not occur in these patients.

CONCLUSION

Autogenous, pedicled, demucosalized small intestinal sheets can be an effective method for reconstructing infected complex abdominal wall defects.

Reconstruction of the abdominal wall by using a combination of the human acellular dermal matrix implant and an interpositional omentum flap after extensive tumor resection in patients with abdominal wall neoplasm: A preliminary result

AIM: To present our trial using a combination of the human acellular dermal matrix (HADM) implant and an interpositional omentum flap to repair giant abdominal wall defects after extensive tumor resection.

METHODS: Between February and October of 2007, three patients with giant defects of the abdominal wall after extensive tumor resection underwent reconstruction with a combination of HADM and omentum flap. Postoperative morbidities and signs of herniation were monitored.

RESULTS: The abdominal wall reconstruction was successful in these three patients, there was no severe morbidity and no signs of herniation in the follow-up period.

CONCLUSION: The combination of HADM and omentum flap offers a new, safe and effective alternative to traditional forms in the repair of giant abdominal wall defects. Further analysis of the long-term outcome and more cases are needed to assess the reliability of this technique.

Repair of giant midline abdominal wall hernias: "components separation technique" versus prosthetic repair : interim analysis of a randomized controlled trial

Background

Reconstruction of giant midline abdominal wall hernias is difficult, and no data are available to decide which technique should be used. It was the aim of this study to compare the “components separation technique” (CST) versus prosthetic repair with e-PTFE patch (PR).

Method

Patients with giant midline abdominal wall hernias were randomized for CST or PR. Patients underwent operation following standard procedures. Postoperative morbidity was scored on a standard form, and patients were followed for 36 months after operation for recurrent hernia.

Results

Between November 1999 and June 2001, 39 patients were randomized for the study, 19 for CST and 18 for PR. Two patients were excluded perioperatively because of gross contamination of the operative field. No differences were found between the groups at baseline with respect to demographic details, co-morbidity, and size of the defect. There was no in-hospital mortality. Wound complications were found in 10 of 19 patients after CST and 13 of 18 patients after PR. Seroma was found more frequently after PR. In 7 of 18 patients after PR, the prosthesis had to be removed as a consequence of early or late infection. Reherniation occurred in 10 patients after CST and in 4 patients after PR.

Conclusions

Repair of abdominal wall hernias with the component separation technique compares favorably with prosthetic repair. Although the reherniation rate after CST is relatively high, the consequences of wound healing disturbances in the presence of e-PTFE patch are far-reaching, often resulting in loss of the prosthesis.

Interposition of Polyglactin Mesh Does Not Prevent Adhesion Formation Between Viscera and Polypropylene Mesh

BACKGROUND

The use of intra-peritoneal polypropylene mesh (PPM) to repair incisional hernia carries the risk of adhesions and damage to the intra-abdominal viscera. Polyglactin 910 mesh (PGM) is advocated to avoid contact between PPM and the intra-abdominal viscera. An experimental study in rats was performed to determine if interposition of a resorbable prosthesis between the PPM and viscera alters biocompatibility, adhesion formation, and herniation.

MATERIALS AND METHODS

A 2- x 3-cm abdominal wall defect was created in 80 rats. Rats were randomly assigned for repair with 2.5- x 3.5-cm PPM (n = 40) or 2.5- x 3.5-cm PPM plus polyglactin 910 mesh (PPM-PGM) (n = 40). The rats were sacrificed at 1, 2, 3, and 6 months (n = 10), and an autopsy was performed to determine herniation and adhesion rates. Mesh-fascia interface was taken for histology.

RESULTS

In the PPM group, 1 rat died before the end of the experiment, and at 6 months one of the 10 rats had a herniation. In the PPM-PGM group, two rats died before the end of the experiment, and two rats had a herniation after 1 month and three rats after 6 months. At 1, 2, and 3 months the adhesion score in the PPM group (median, 3; range, 2-3) did not differ from the score in the PPM-PGM group (median, 3; range, 2-3). Also, at 6 months the adhesion score in the PPM group (median, 2; range, 2-3) did not differ from the score in the PPM-PGM group (median, 3; range, 2-3). At microscopy a capsule was formed around the PP fibers, which matured over months in the PPM group. In the first month after implantation an inflammatory response was seen. Histology was similar in both groups, although in the early PPM-PGM group the inflammatory response was more evident.

CONCLUSION

Interposition of PGM between PPM and viscera does not alter adhesion formation nor influences herniation rate.

Pelvic, abdominal, and chest wall reconstruction with AlloDerm in patients at increased risk for mesh-related complications

BACKGROUND

The use of polypropylene mesh in the reconstruction of trunk defects increases complication rates when the mesh is placed directly over viscera or the operative site has been irradiated or contaminated with bacteria. An alternative is AlloDerm (decellularized human cadaveric dermis), which becomes vascularized and remodeled into autologous tissue after implantation. When used for fascial reconstruction, AlloDerm forms a strong repair, causes minimal abdominal adhesions, and resists infection.

METHODS

We did a retrospective study of cancer patients at increased risk for mesh-related complications who underwent trunk reconstruction with AlloDerm over a 1-year period. Risk factors included unavoidable placement of mesh directly over the bowel or lung, perioperative irradiation, and/or bacterial contamination of the defect. The indications, defect characteristics, reconstructive techniques, complications, and surgical outcomes were evaluated.

RESULTS

Thirteen patients were included in the study. Indications for reconstruction were oncologic resection, resection of enterocutaneous fistula, and/or ventral hernia repair. Seven patients had bacterial contamination at the operative site and seven patients received perioperative radiation. The mean musculofascial defect size was 435 cm. AlloDerm was placed directly over the bowel or lung in all patients. Nine patients required flap reconstruction, including 14 pedicled and two free flaps. The mean follow-up was 6.4 months. Complications occurred in six patients, however, there were no clinically evident mesh infections, hernias, or bulges.

CONCLUSIONS

AlloDerm successfully can be used in reconstructions for large, complex pelvic, chest, and abdominal wall defects even when placed directly over viscera and when the operative field is irradiated and/or contaminated with bacteria.

Physiologic properties of small intestine submucosa

BACKGROUND

Porcine small intestine submucosa (SiS) has been introduced as a bioprosthesis in herniorrhaphy. This study evaluates in vivo properties of SiS that would affect clinical use.

MATERIALS AND METHODS

Twelve pigs underwent implantation of SiS (perforated and nonperforated) on the peritoneal surface. Gross characteristics were evaluated and random samples harvested for histological study at 2 (n = 6) and 8 (n = 6) weeks. Collagen deposition was determined by polarized microscopy. Neovascularity (percent area blood vessels, %A(bv)) was determined by immunohistochemical staining with a polyclonal CD-31 antibody.

RESULTS

Perforated SiS had a higher density of capillary ingrowth compared with nonperforated at both 2 (5.6%A(bv) versus 1.4%A(bv), P < 0.05) and 8 weeks (6.0%A(bv) versus 1.6%A(bv), P < 0.05). Compared with 2 weeks, 8-week SiS had a larger proportion of incorporation (25% versus 83%, P < 0.05) and new collagen deposition (50% versus 94%, P < 0.05). Significant contraction was observed in SiS 8 weeks after implantation (preimplant area 98 cm2 versus post-implant area 50 cm2, P < 0.05).

CONCLUSION

SiS incorporated well 8 weeks after implantation, with deposition of new collagen. Perforated SiS demonstrated a more rapid and greater amount of neovascularity. The degree of contraction suggests that larger areas of SiS should be selected for herniorrhaphy than would be necessary if synthetic materials were used.

Octylcyanoacrylate Tissue Adhesive as an Alternative to Mechanical Fixation of Expanded Polytetrafluoroethylene Prosthesis

In minimally invasive incisional hernia repair positioning and fixation of the expanded polytetrafluoroethylene (ePTFE) mesh prosthesis on the deep surface of the abdominal wall may be facilitated using tissue adhesives. Octylcyanoacrylate (OCTYL), a new adhesive, forms a strong flexible bond with antimicrobial properties. In a rabbit model for incisional hernia we investigated characteristics of the bond created by OCTYL between ePTFE and abdominal wall musculature. We studied initial bond strength and the postoperative host response to the adhesive over a 6-week period. We compared sutured, stapled, and glued mesh prostheses and examined the tissue-prosthesis interface. The ePTFE mesh was fixed successfully to the abdominal wall with OCTYL and remained tightly attached at 6 weeks. Prostheses fixed with OCTYL and spiral tacks induced few intra-abdominal adhesions compared with sutured mesh. All prostheses were completely reperitonealized at 2 weeks. The force required to displace mesh fixed with sutures and staples was greater than mesh fixed with OCTYL. Analysis of the ePTFE/tissue interface by light and scanning electron microscopy showed host cellular migration into the interstices of the mesh with fixation by tacks and suture, whereas an inflammatory infiltrate was seen on the muscular surface with OCTYL fixation of the mesh.

Abdominal adhesions to prosthetic mesh evaluated by laparoscopy and electron microscopy

BACKGROUND

Most adhesion experiments involve observations at a single time point. We developed a method to evaluate abdominal adhesions to surgical mesh by sequential laparoscopy.

STUDY DESIGN

An abdominal wall defect was created in rats and repaired with polypropylene mesh. Sequential laparoscopic evaluation of adhesion formation was performed in each animal. The percentage of mesh area involved was scored (0% to 100%). At various time intervals animals were sacrificed and samples were obtained for light and scanning electron microscopy.

RESULTS

Adhesions were already present on day 1, increased by day 7, and did not progress thereafter. Mesh surfaces free of adhesions were covered with a confluent mesothelial cell layer, first seen by scanning electron microscopy on day 5 and complete by day 7.

CONCLUSIONS

Intraabdominal adhesions are best studied by sequential laparoscopy. Adhesions develop within 1 day of prosthesis placement. Adhesion-free surfaces are carpeted with mesothelial cells by day 7 and remain free thereafter, for duration of study.

Experimental assay of a Dual Mesh polytetrafluoroethylene prosthesis (non-porous on one side) in the repair of abdominal wall defects

The porosity of the prosthetic biomaterials used to repair defects in the abdominal wall seems to influence the tissue repair process insofar as tissue integration of the prosthetic material and the formation of adhesions with abdominal viscera are concerned. We studied the behaviour of a new type of polytetrafluoroethylene prosthesis used for the repair of abdominal wall defects. Dual Mesh (DM), which has two different faces; one face has a porosity between 30 and 60 microns, while the other is non-porous. In 20 New Zealand White rabbits, a full-thickness (except skin) 7 cm x 5 cm defect was created in the anterior abdominal wall that was repaired with DM. At 14, 30, 60 and 90 days, samples were obtained and studied by light and scanning electron microscopy. An immunohistochemical study was made with antibody anti-rabbit macrophages (RAM-11). Tensile strength was measured with an Instron tensiometer using 2-cm-wide strips obtained parallel to the shorter axis of the implant. DM induced little tissue adhesion to the material on the visceral peritoneum interface and was surrounded by organized repair tissue. The biomaterial was integrated in the repair tissue on the subcutaneous interface, but not on the peritoneal interface. The macrophage response decreased between days 14 and 90 (P < 0.001). Tensile strength increased significantly (P < 0.05) at every study period. We conclude that the DM prosthesis has little tendency to formation of visceral adhesions, the DM prosthesis was well tolerated by the receptor organism and the tensile strength of the prosthesis/receptor tissue interface increased with time.

Improvement of the tissue integration of a new modified polytetrafluoroethylene prosthesis: Mycro Mesh

We studied the behaviour of the different tissue interfaces formed on a new type of prosthesis used for the repair of abdominal wall defects, Mycro Mesh (W. L. Gore and Ass., Flagstaff, AZ, USA), which consists of perforated layers of polytetrafluoroethylene (PTFE). In 20 New Zealand white rabbits, a full-thickness (except skin) 7 cm x 5 cm defect was created in the anterior abdominal wall. The defects were repaired with a prosthetic implant (Mycro Mesh) that was placed in direct contact with abdominal viscera and subcutaneous tissue. At 14, 30, 60 and 90 d post-implantation, samples were obtained from the tissue interfaces formed between the prosthesis and subcutaneous tissue, visceral peritoneum and receptor tissue, respectively. Samples were studied by optical microscopy and scanning electron microscopy. The immunohistological study was made with RAM-11, a monoclonal antibody specific for rabbit macrophages. Tensile strength was measured with an Instron tensiometer using 2 cm wide strips obtained parallel to the shorter axis of the implant. Strips included the prosthesis and two anchor zones on the receptor tissue. Macroscopically, the prosthesis induced little adhesion formation on the visceral peritoneum interface. Microscopically, an organized neoperitoneum and abundant tissue formed on the subcutaneous interface. In the prosthesis perforations, bridges of tissue linked the peritoneal and subcutaneous sides. The macrophage response decreased significantly in intensity between day 14 and day 90 (Student-Newman-Keuls test, P = 0.01). Tensile strength increased significantly (Wilcoxon test, P < 0.05) at every study period. To conclude: the Mycro Mesh prosthesis proved suitable for implantation in sites where it comes in contact with abdominal viscera and it provided good support for the formation of an organized neoperitoneum; the perforations in the prosthetic material improved implant integration; the macrophage response was not altered by the biomaterial and the tensile strength of the prosthesis increased as scar tissue formation and tissular integration of the prosthesis progressed.