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

Abdominal wall hernia repair: from prosthetic meshes to smart materials

Hernia reconstruction is one of the most frequently practiced surgical procedures worldwide. Plastic surgery plays a pivotal role in reestablishing desired abdominal wall structure and function without the drawbacks traditionally associated with general surgery as excessive tension, postoperative pain, poor repair outcomes, and frequent recurrence. Surgical meshes have been the preferential choice for abdominal wall hernia repair to achieve the physical integrity and equivalent components of musculofascial layers. Despite the relevant progress in recent years, there are still unsolved challenges in surgical mesh design and complication settlement. This review provides a systemic summary of the hernia surgical mesh development deeply related to abdominal wall hernia pathology and classification. Commercial meshes, the first-generation prosthetic materials, and the most commonly used repair materials in the clinic are described in detail, addressing constrain side effects and rational strategies to establish characteristics of ideal hernia repair meshes. The engineered prosthetics are defined as a transit to the biomimetic smart hernia repair scaffolds with specific advantages and disadvantages, including hydrogel scaffolds, electrospinning membranes, and three-dimensional patches. Lastly, this review critically outlines the future research direction for successful hernia repair solutions by combing state-of-the-art techniques and materials.

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.

Managing female pelvic floor disorders: a medical device review and appraisal

Pelvic floor disorders (PFDs) will affect most women during their lifetime. Sequelae such as pelvic organ prolapse, stress urinary incontinence, chronic pain and dyspareunia significantly impact overall quality of life. Interventions to manage or eliminate symptoms from PFDs aim to restore support of the pelvic floor. Pessaries have been used to mechanically counteract PFDs for thousands of years, but do not offer a cure. By contrast, surgically implanted grafts or mesh offer patients a more permanent resolution but have been in wide use within the pelvis for less than 30 years. In this perspective review, we provide an overview of the main theories underpinning PFD pathogenesis and the animal models used to investigate it. We highlight the clinical outcomes of mesh and grafts before exploring studies performed to elucidate tissue level effects and bioengineering considerations. Considering recent turmoil surrounding transvaginal mesh, the role of pessaries, an impermanent method, is examined as a means to address patients with PFDs.

Design Strategies and Applications of Biomaterials and Devices for Hernia Repair

Hernia repair is one of the most commonly performed surgical procedures worldwide, with a multi-billion dollar global market. Implant design remains a critical challenge for the successful repair and prevention of recurrent hernias, and despite significant progress, there is no ideal mesh for every surgery. This review summarizes the evolution of prostheses design toward successful hernia repair beginning with a description of the anatomy of the disease and the classifications of hernias. Next, the major milestones in implant design are discussed. Commonly encountered complications and strategies to minimize these adverse effects are described, followed by a thorough description of the implant characteristics necessary for successful repair. Finally, available implants are categorized and their advantages and limitations elucidated, including non-absorbable and absorbable (synthetic and biologically derived) prostheses, composite prostheses, and coated prostheses. This review not only summarizes the state of the art in hernia repair, but also suggests future research directions toward improved hernia repair utilizing novel materials and fabrication methods.

Omentum prevents intestinal adhesions to mesh graft in abdominal infections and serosal defects

BACKGROUND

Many studies have evaluated the use of grafts in the reconstruction of abdominal wall defects. In this study, the effects resulting from the presence or absence of the omentum were evaluated in the setting of infection or serosal defects in the formation of adhesions in abdominal closures using mesh grafts.

METHODS

For this study, 60 Wistar albino rats were divided into six groups. A circular 3.79-cm(2) fascioperitoneal defect was created. After group-specific procedures, defects were reconstructed using polypropylene mesh grafts. In group C (control group), only a mesh graft recontruction was performed, whereas group O (O for omentectomy) underwent an omentectomy plus mesh closure. In group SD (serosal defect group), the cecum was abrased with a brush before mesh closure. Group SDO underwent cecal abrasion plus an omentectomy. In group I (infection group), the intraabdominal space was filled with 1 ml of solution containing 100,000 colony-forming units (CFUs) of Escherichia coli per milliliter. Group IO received the same same amount of E. coli solution plus an omentectomy before mesh closure. After 28 days, the groups were evaluated by intraabdominal and blood cultures, grading of intraabdominal adhesions, graft-organ adhesions, proportion of adhesions to graft size, and histopathologic studies. The results were statistically evaluated using one-way variant analysis and Scheffe's and Fisher's definite chi-square tests.

RESULTS

For the groups in which the greater omentum was preserved, intestinal adhesions to the graft surface were less frequently observed, especially in cases with intraabdominal infections and serosal defects (p < 0.05).

CONCLUSIONS

Preservation of the greater omentum reduces the formation of intestinal adhesions, especially in cases with underlying infections and serosal defects in abdominal closures using mesh grafts. This could be beneficial in related clinical situations in lowering the rate of intestinal fistulas, erosions, and obstructions that can be attributed to the formation of adhesions.

Morphological changes in the anterior abdominal wall of rats with peritonitis and implanted synthetic film

Histological study and electron microscopy of the anterior abdominal wall and laparotomy wound closed using a polytetrafluoroethylene film was performed on rats with experimental peritonitis. We studied 4 types of polytetrafluoroethylene films differing in the size of micropores and technology of treatment. The tissue response differed after implantation of various films. A multilayer film with minimum size of pores was optimal to repair the laparotomy wound.

Polymeric meshes for internal sutures with differentiated adhesion on the two sides

The aim of this work is to investigate the effects of different plasma treatments on ePTFE abdominal prostheses with the final goal of obtaining a new prosthesis, made of a single strand of ePTFE, with clearly differentiated adhesion properties on the two sides, which should be able to promote tissue ingrowth on one side and prevent post surgical visceral adhesions on the other. Samples obtained from ePTFE Bard Dulex Meshes have been treated sequentially with three different gases (N(2), O(2) and NH(3)) in order to choose the optimal treatment conditions to improve ePTFE wettability. In particular, no modification was induced by N(2) treatment, while the full treatment after the final ammonia gas resulted in the best suitable candidate. As demonstrated by scanning electron microscopy, AFM analyses and contact angle measurements, ammonia plasma treatment increases ePTFE surface roughness and renders it more hydrophilic, thus promoting adhesion without any alteration of the material's bulk properties. The reported results also evidence the possibility to obtain the maximum wettability with a cheap treatment by optimizing plasma exposure time. As a preliminary cell adhesion study, Swiss 3T3 fibroblasts (mouse, embryo) have been seeded on the treated and untreated materials in order to assess whether there was any difference in terms of cell attachment and spreading. Cells seeded on the ammonia plasma treated material showed a better adhesion and spreading when compared to the untreated material.

Early imaging of integration response to polypropylene mesh in abdominal wall by environmental scanning electron microscopy: comparison of two placement techniques and correlation with tensiometric studies

The repair of incisional hernias has taken advantage of the strength provided by prosthetic mesh grafts, but the best position for inserting the materials has not been conclusively established. Environmental scanning electron microscopy (ESEM) provides imaging of biologic samples with minimal manipulation. We used ESEM for early imaging of the integration response to polypropylene meshes placed in two anatomic positions in the abdominal wall and correlated results with tensiometric studies. Two macroporous polypropylene prostheses were implanted in a rat model--one on the abdominal aponeurotic layer and one on the peritoneal surface--without creating a wall defect. Studies were performed over implantation intervals of 7, 15, and 30 days in strips obtained from the polypropylene fiber-receptor repair tissue interface. Microscopic appearance, tensile strength, percent elongation, and stiffness were evaluated. Meshes implanted on the abdominal aponeurotic layer showed better early tissue incorporation (higher collagen deposition, capillary density, cell accumulation) and increased tensile strength, reflecting tighter anchorage to the abdominal wall. The percent elongation increased from day 7 to day 30 after implantation, mainly in the deep stratum. The ESEM images correlated well with biomechanical results, indicating the potential of this technique as a powerful, effective tool for use in wound-healing studies.

Fibrous tissue ingrowth and attachment to porous tantalum

This study determined the soft tissue attachment strength and extent of ingrowth to a porous tantalum biomaterial. Eight dorsal subcutaneous implants (in two dogs) were evaluated at 4, 8, and 16 weeks. Upon retrieval, all implants were surrounded completely by adherent soft tissue. Implants were harvested with a tissue flap on the cutaneous aspect and peel tested in a servo-hydraulic tensile test machine at a rate of 5 mm/min. Following testing, implants were dehydrated in a solution of basic fuschin, defatted, embedded in methylmethacrylate, and processed for thin-section histology. At 4, 8, and 16 weeks, the attachment strength to porous tantalum was 61, 71, and 89 g/mm respectively. Histologic analysis showed complete tissue ingrowth throughout the porous tantalum implant. Blood vessels were visible at the interface of and within the porous tantalum material. Tissue maturity and vascularity increased with time. The tissue attachment strength to porous tantalum was three- to six-fold greater than was reported in a similar study with porous beads. This study demonstrated that porous tantalum permits rapid ingrowth of vascularized soft tissue, and attains soft tissue attachment strengths greater than with porous beads.

Effect of relaparotomy through previously integrated polypropylene and polytetrafluoroethylene experimental implants in the abdominal wall

BACKGROUND

The appearance of new pathologies affecting abdominal organs after implant of a prosthesis to repair an abdominal wall defect may necessitate reintervention. The aim of this study was to compare the behavior of two types of biomaterial widely used in clinical practice, polypropylene (PL) and polytetrafluoroethylene (ePTFE), after a second laparotomy involving the implant. The behavior, in terms of tensile resistance and integration with tissues, of intact prostheses was compared to that of prostheses subjected to opening and repair.

METHODS

A defect (7x5 cm) involving all tissue layers was created in the anterior abdominal wall of 24 male New Zealand rabbits. These defects were repaired with a reticular, macroporous PL mesh (Marlex, Bard Card., Madrid, Spain) or a laminar, micro/macroporous ePTFE prosthesis (Mycro Mesh, W.L. Gore, Flagstaff, AZ) of similar size to the defect. Four study groups were established: Intact PL/Intact ePTFE (n = 6 each): animals implanted with a PL or ePTFE prosthesis and sacrificed 90 days after implant; Repaired PL/Repaired ePTFE (n = 6 each): animals implanted with a PL or ePTFE prosthesis subjected to midlongitudinal relaparotomy through the center of the prosthesis 90 days postimplant, followed by repair with continuous polypropylene 4/0 suture. Animals in repaired groups were sacrificed 90 days after the second intervention. Specimens comprised of prosthesis and neoformed tissue were subjected to light and scanning electron microscopy. In addition, 2 cm-wide strips, consisting of the prosthesis and anchorage tissue, were subjected to biomechanical analysis using an Instron tensiometer (Instron, Canton, MA). The results obtained were statistically compared using the Mann-Whitney U-test.

RESULTS

The intact PL implants were fully infiltrated by dense, disorganized, well-vascularized scar tissue with fibers concentric to the mesh monofilaments. The appearance of the repaired PL prostheses was similar, with establishment of neoformed tissue in repaired areas of the prosthesis such that both cut edges of the prosthesis were joined together. In contrast, intact ePTFE prostheses were encapsulated by organized tissue with fibers running parallel to the surface of the biomaterial. Repaired ePTFE prostheses including sutured areas were similarly encapsulated. But the edges of the sutured middle area did not fuse. Tensile resistance values of intact and repaired PL prostheses were similar (intact, mean, 34.78 Newtons; repaired, mean, 34.74N, p>0.001). Tensile resistance values of intact ePTFE implants were significantly different to those of the repaired ePTFE prostheses (intact, mean, 22.64N; repaired, mean, 17.21N, p<0.001). Breakage of both types of PL specimen strips was restricted to recipient tissue while breakage of intact ePTFE specimens occurred in the areas of anchorage to the abdominal wall. Rupture of repaired ePTFE specimens took place in the sutured central areas of the prostheses.

CONCLUSIONS

We conclude that relaparotomy through an existing PL prosthesis previously integrated with the abdominal wall does not affect the tissue integration process or the tensile resistance of the implant. When the relaparotomy involves an ePTFE prosthesis, however, although the repair process itself is unaffected, significant loss in tensile strength is incurred. In addition, relaparotomy through both types of biomaterial is likely to result in the neoformation of adhesions in the areas of the prosthesis subjected to opening and repair but, in general, the number of adhesions formed in the presence of intact or repaired polypropylene implants was larger than that observed with the use of ePTFE.

The use of biomaterials in the repair of abdominal wall defects: a comparative study between polypropylene meshes (Marlex) and a new polytetrafluoroethylene prosthesis (Dual Mesh)

In this study we compared the behaviour of the non-porous on one side ePTFE Dual Mesh prosthesis and the macroporous polypropylene mesh Marlex in the repair of abdominal wall defects in rabbits. We evaluated the degree of integration with recipient tissue, biological tolerance, adhesion formation with viscera and the biomechanical resistance of the repair zone. Our results showed good biological tolerance of both prostheses and a high degree of adhesion formation in Marlex implants. In animals with Dual Mesh implants, only loose adhesions were seen. Marlex implants induced the presence of disorganized scar tissue, while the Dual Mesh prostheses were encapsulated by organized tissue. The macrophage response was similar in both decreasing with time. The resistance to traction was higher when the reparation was done with polypropylene. We concluded that the structure of the prosthesis determines its degree of integration and the resistance to traction of the repaired zone.