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This study was designed to evaluate the behavior of a new composite polypropylene-polyurethane (PL-PU99) when placed in direct contact with the visceral peritoneum during the repair of an abdominal wall defect. Full-thickness abdominal wall defects (7 x 5 cm) were created in 36 anaesthetized white New Zealand rabbits. The defects were repaired with polypropylene prostheses or PL-PU99 prostheses (comprised of PL and a polyurethane sheet glued to the PL with acrylic adhesive) to establish two study groups (n = 18 each). Animals were sacrified 14, 30, or 90 days after implantation and prosthesis/surrounding tissue specimens were subjected to light and electron microscopy and morphometric analysis of the newly formed peritoneum. Immunohistochemical analysis was performed using the rabbit specific monoclonal antibody RAM-11. The biomechanical strength of the implants was also assessed. Firm adhesions were detected in the PL implants, whereas adhesions were practically non-existent in the PL-PU99 implants. The surface area covered by adhesions was greater (p < 0.01) in the PL group (7.36 vs. 0.11 cm2). The neoperitoneum formed after the implantation of a PL prosthesis was disorganized in structure, whereas that formed at the interface with the PL-PU99 prosthesis was structurally similar to the host peritoneum. The excellent performance of the PL-PU99 prosthesis shown in this study warrants further investigation into its use for the repair of abdominal wall defects when the prosthetic patch needs to be placed in contact with the intestinal loops.

The present study compared the performance of three composite prostheses used to repair abdominal wall defects in rabbits. Two of them [Parietex Compositereg (PC) and Composixreg (CS)] are commonly used in clinical practice and one was designed by the present team (PL-PU99). At 14 and 90 days postimplant, specimens were obtained for morphological, macrophage response (RAM-11) and morphometric and biomechanical analysis. The prosthetic area covered by adhesions was significantly greater (p < 0.05) in the CS group (6.83 plus minus 2.31 cm(2)) than in PC (0.11 +/- 0.02 cm(2)) or PL-PU99 (0.10 +/- 0.07 cm(2)). At 14 days, it was observed a homogeneous, organized, well-vascularized neoperitoneum that was significantly thicker (p < 0.05) in PL-PU99. Except in the CS implants, this layer was covered by a continuous mesothelium. All three composites achieved good recipient tissue integration. Highest macrophage levels were recorded at 14 days with significantly higher values in the PL-PU99 prosthesis. Biomechanical strength was significantly greater (p < 0.05) in CS at two weeks postimplant, but it was similar at 90 days. These findings suggest that the three composites show ideal integration with host tissue, along with similar biomechanical strength at 90 days, and significantly higher adhesion formation is induced by the CS prosthesis, possibly due to incomplete mesothelialization of the lower prosthetic surface., (Copyright 2002 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 63: 182--190, 2002; DOI 10.002/jbm.10123)

Poor mechanical properties of biological tissue are known to cause wear, leading to the failure of cardiac bioprostheses made of calf pericardium. Different chemical agents such as sodium dodecyl sulfate (SDS) are presently being tested as possible inhibitors of the calcification process. The objective of this report was to determine the mechanical behavior of calf pericardium treated with SDS for 24 h and the influence of the suture on the mechanical properties of the tissue. Forty-eight samples were tested: 24 subjected to a standard treatment with glutaraldehyde (12 sewn with 4/0 silk suture thread) and 24 incubated with SDS for 24 h (12 sewn with the same suture thread). Each sutured and non-sutured sample was cut into two strips to yield paired samples. All were subjected to tensile stress to breaking point. The mean stress at breaking point in the non-sutured series treated with glutaraldehyde alone was 16.42 and 13.85 MPa depending on the region of the pericardium, while in the sutured samples subjected to glutaraldehyde the mean stress was 7.50 and 7.63 MPa, respectively, differences which were statistically significant (p = 0.03 and p = 0.003, respectively) when the means for non-sutured samples from equivalent regions treated with glutaraldehyde were compared. The stress at breaking point was lower in the SDS-treated series, ranging between 2.60 and 3.56 MPa. The mathematical functions that govern the stress/strain or deformation were obtained. In the series of pericardium treated with SDS, deformations of 10% were produced with stresses of under 0.4 MPa, an outcome that is intolerable from the constructive point of view. We established a regression model that enabled us to determine the mechanical behavior of a sutured sample by testing a contiguous piece of tissue, with a high correlation coefficient (r \gt 0.99). We consider this finding to be of interest in the selection of pericardium for use in the construction of leaflets for cardiac bioprostheses., (Copyright 2000 Kluwer Academic Publishers)

Objective: To extend present knowledge of the biomechanical and structural changes which occur in the cryopreserved, rapidly thawed arterial wall., Materials and Methods: Minipig iliac arterial segments were cryopreserved at -196 degrees C in either minimum essential medium or Wisconsin solution. Fresh segments served as the control group. After 1 month, the specimens were rapidly thawed (37 degrees C) and processed for biomechanical, ultrastructural, morphological and immunohistochemical (MMP-1, MMP-2, MMP-3 and MMP-9) analysis. Visualisation of apoptotic cells was performed by TUNEL method. For the mechanical distension analysis, an in vitro circuit was designed., Results: The cryopreserved segments showed a 42% incidence of spontaneous fracture and the appearance of microfractures which affected the endoluminal third of the vessel. An accumulation of liquid in the subelastica was observed. An increased expression of wall-degradative enzymes (mainly MMP-2) was also observed following cryopreservation. No significant differences were detected in the proportional elasticity module or tensile strength of the specimen groups. No differences in mechanical distension were observed between groups after the vessel segments were subjected to the pulsatile circuit flow for 72 h. Cell damage was most intense in the specimens cryopreserved in Wisconsin solution., Conclusions: Cryopreservation in both the solutions employed, followed by rapid thawing, induce changes in the permeability which increase the fragility of the cryopreserved arterial wall. Both increased expression of wall-degradative enzymes and accumulation of liquid may contribute to graft failure after implantation., (Copyright 2000 Harcourt Publishers Ltd.)

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.

Currently one of the most widely used prosthetic materials in the repair of abdominal wall defects, is expanded polytetrafluoroethylene (ePTFE). It has been suggested that its behavior with respect to the reparative process may depend on its structure. The aim of the present study was to evaluate the effect of the structure of 3 ePTFE prostheses on the scarring process in an abdominal-wall-defect experimental model. The prostheses employed were the Soft Tissue Patch (STP) which is laminar in structure, Mycro Mesh (MM) which is multilaminar with perforations, and the Dual Mesh (DM) prosthesis which has one non-porous surface. Abdominal wall defects (7 x 5 cm) were created in 36 New Zealand rabbits and repaired using fragments of STP, MM and DM. Follow-up periods were 14, 30, 60 and 90 days post-implant. At these times prostheses were macroscopically examined for the presence of infection and/or rejection and the formation of adhesions to abdominal viscera. Specimens were also taken for microscopic analysis (optical and scanning electron) and for immunohistochemical analysis using the rabbit macrophage-specific monoclonal antibody RAM-11. Labelled macrophage counts were performed at each follow-up session. No cases of infection or rejection were found. Loose adhesions between prosthesis and underlying viscera were observed in 2 of the STP, 4 of the MM and 2 of the DM implants. STP and DM implants were progressively encapsulated by organized connective tissue on both peritoneal and subcutaneous surfaces. Cellular colonization was observed on both STP surfaces and on the porous surface of the DM although no more than a third of the biomaterial was penetrated by cells in either case. Colonization was very slight at prosthesis anchorage points. MM implants differed only in the formation of connective tissue bridges in perforated areas, and cellular infiltration in interlaminar spaces. Macrophage response was similar in the 3 prostheses with a reduction in RAM-11 labelled cells (p < 0.05) between 14 and 90 days post-implant. We conclude: a) the 3 types of PTFE prosthesis induced low incidence of adhesion formation between biomaterial and viscera; b) integration mechanism of the 3 prostheses were similar and culminated with the encapsulation of the PTFE by the neoformed tissue; c) the macrophage response induced by the 3 prostheses was similar to that of any reparative process in the absence of biomaterial.

Background: Two types of prosthetic material used for repairing hernial defects of the abdominal wall were compared: Mycro Mesh and Marlex. Mycro Mesh (MM) is a new polytetrafluoroethylene product of layered, microporous structure. Macroscopically, it presents regularly distributed, 2-mm orifices that perforate the biomaterial. Marlex (PL) is a well-known polypropylene mesh product with a macroporous structure., Study Design: In 24 white New Zealand rabbits, a full-thickness (except skin) 5 x 7-cm defect was created in the anterior wall of the abdomen. Defects were repaired with either MM (n = 12) or PL (n = 12) implants and studied at 14, 30, 60, and 90 days after implantation. Samples of the interfaces between prosthesis and subcutaneous tissue, visceral peritoneum, and receptor tissue, respectively, were studied. Samples were processed for optical microscopy and scanning electron microscopy (SEM). An immunohistochemical study was made using RAM-11, a monoclonal antibody specific for rabbit macrophages. The tensile strength of the repairs was made using an Instron tensiometer on 2-cm wide transversal strips that included the prosthesis and its anchor zones to the receptor tissue., Results: The formation of adhesions between the prosthesis and intestine was important with the PL implants but not with the MM implants. Optical microscopy and SEM showed formation of an organized connective tissue surrounding the MM implants. At 90 days, compact bridges of connective tissue linked the tissue on the subcutaneous and peritoneal sides of the prosthesis. The PL implants became integrated into a disorganized, highly vascularized connective tissue. The intensity of the macrophage response was similar in both prostheses and decreased between days 14 and 90 (Student-Newman-Keuls test p = 0.01). The tensile strength of the PL implants was greater than that of the MM implants. At 90 days, the tensile strength of the PL implants was mean equals 33.11 N and of the MM implants, mean equals 22.65 N (Mann-Whitney test p < 0.001)., Conclusions: The tissue integration of the PL and MM implants differed; fewer visceral adhesions formed on MM than on PL; the macrophage reaction was not determinant of the success of failure of either biomaterial; and the tensile strength of the prosthesis-receptor tissue interface was much greater in the PL implants than in the MM implants.

A material subjected to traction stress increases in length; if we maintain the elongation constant, the stress varies over a period of time. This phenomenon has been referred to as relaxation. The purpose of this study was to define a mathematical law that relates the variation in stress to time when elongation remains constant in bovine pericardium. The mathematical function obtained after assaying 34 samples to the point of relaxation, subjected to initial stresses ranging from 0.17-10.07 MPa, responds to the following equation: y = -0.0252 + 0.953 alpha - (0.0165 + 0.015 alpha)lnt, where y is the stress withstood at an instant in time, t, after initial stress alpha. A normogram, validated by assays of up to 6,340 min duration (4.40 days), is presented for graphic calculation, permitting the computation of the loss of stress due to relaxation of this biomaterial, with initial stresses ranging from 1-10 MPa.

Our study of the different biomaterials used in the construction of biological cardiac prostheses has shown it to be of vital importance that the physical properties of the tissue and of the suture that anchors it to the rigid polymeric support are compatible. By means of dynamic tests, we have determined the fatigue curve in sutured bovine pericardial tissue, expressed by the equation log y = 1.27 +/- 0.18 (0.26 +/- 0.05) log t, where y is the initial fatigue stress (MPa) and t is the time (min) it takes to achieve permanent deformation of the tissue. By applying this correction, we determine a set of values for stress-time which, when compared with those obtained with a non-sutured sample, reveal a significant fall in this ratio and, thus, a decrease in the durability. The use of suture threads of lesser elasticity than the pericardium may play an important role in reducing the durability of the bioprosthesis constructed with these materials.

The limited durability of the valve bioprostheses made from calf pericardium is partially due to the calcification of this biomaterial and to mechanical fatigue of the tissue. The object of this study is to determine the harmful effect on the pericardial membrane of cutting caused by the suture thread by showing the different elastic behaviors of the biomaterials employed. This cutting stress is established during the process of molding the valve leaflet, creating a vulnerable point from the very moment of construction, which is an important factor in the limited duration of the bioprosthesis.

Assessment of relaxation (loss of load within a given time) without apparent deformation is a necessary step before durability assay of biomaterials. From results obtained using calf pericardium, the following conclusions were drawn: (a) there is no limit to relaxation for this biomaterials; (b) the lesser the load applied, the greater the relaxation; and (c) the relaxation curve follows the logarithmic function y = K1 - K2 - Int. These findings demonstrate the poor behaviour of the biomaterial at supposedly low loads and suggest that rupture-point load is not a reliable reference to determine the safety coefficient of calf pericardium used in cardiac bioprostheses.