ePTFE Implants Research Articles

A Comparative Analysis of Expanded Polytetrafluoroethylene and Small Intestinal Submucosa—Implications for Patch Repair in Ventral Herniorrhaphy

Small intestinal submucosa and expanded polytetrafluoroethylene are commonly used as adjuncts to repair in ventral herniorrhaphy. Despite their overlapping indications, the physical characteristics of the two materials are quite distinct. This study compares the in vivo properties of two bioprosthetic products, small intestinal submucosa (SiS Gold; Cook Biotech, West Lafayette, IN) and lyophilized small intestinal submucosa (LyoSiS; Cook Biotech), with expanded polytetrafluoroethylene (ePTFE; W.L. Gore and Associates, Flagstaff, AZ). Six pigs underwent placement of duplicate samples of each material (SiS Gold, LyoSiS, and ePTFE) within the abdomen as peritoneal onlays (total of six samples per pig). Gross characteristics were evaluated and random samples harvested for histological analysis at 8 wk following implantation. The percentage of contraction was determined by comparing pre-implant to post-implant area. Neovascularity (percent area blood vessels, %A(bv)) was quantitatively assessed by immunohistochemical staining with an endothelial marker, CD-31 antibody. Sites of active collagen deposition were identified and distinguished from pre-existing collagen using a pro-collagen antibody to characterize tissue incorporation and remodeling. Compared with the original area of 22.75 cm(2), significant contraction was observed in SiS Gold, LyoSiS, and ePTFE at 8 wk (post-implant area; 7.6 cm(2), 5.7 cm(2), and 11.2 cm(2) respectively, P < 0.0001). The post-implant areas represent contraction of 67% for SiS Gold, 75% for LyoSiS, and 51% for ePTFE. The ePTFE implants experienced significantly less contraction than both the SiS Gold and LyoSiS implants (P = 0.002). No statistical difference in contraction was noted when SiS was compared with LyoSiS. Compared to SiS Gold, LyoSiS had a higher density of capillary ingrowth (2.7% A(bv)versus 2.2% A(bv), P = 0.01). As expected, vascular ingrowth was absent from the ePTFE samples. Qualitative analysis with pro-collagen antibody revealed new collagen deposition within the lamellar matrix of both SiS Gold and LyoSiS. In contrast, a similar analysis of ePTFE demonstrated a pattern of collagen encapsulation compared with the tissue infiltration and incorporation observed with SIS grafts. The host response to ePTFE, SiS Gold and LyoSiS differs at 8 wk following implantation; SiS Gold and LyoSiS undergo tissue ingrowth and remodeling whereas ePTFE undergoes little or no incorporation or morphological change. The physical properties of the materials differ as well; SiS Gold, and LyoSiS experience significantly more contraction than ePTFE. Future comparative analysis may help determine which characteristic, contraction or incorporation, contributes more to long-term success in the patch repair of ventral hernia.

Peritoneal Effects of Prosthetic Meshes Used to Repair Abdominal Wall Defects: Monitoring Adhesions by Sequential Laparoscopy

The prosthetic materials currently used to repair abdominal wall defects sometimes have to be placed in contact with the visceral peritoneum. This interface is often a site of complications such as intestinal obstruction or fistulas due to adhesions. The aim of this study was to follow the process of adhesion formation in several prosthetic materials by sequential laparoscopy. Defects (7 x 5 cm) were created in the abdominal wall of 30 New Zealand White rabbits and repaired using Surgipro polypropylene mesh (PP), Ultrapro monocryl-prolene mesh (UP), Dual Mesh expanded polytetrafluoroethylene (ePTFE), Composix (PP-ePTFE), Parietex Composite (polyester with collagen-polyethylene glycol-glycerol coating [PO-gl]), or PL-PU99 (PP-polyurethane) patches fixed to the edges of the defect by running polypropylene suture. Adhesions to the implants were laparoscopically determined at 3, 7, and 14 days after surgery. Percentage adhesion scores were significantly lower for ePTFE, PP-ePTFE, PO-gl, and PP-PU, compared to PP or UP. No differences were observed in adhesion scores recorded at 3, 7, and 14 days postimplant. Reticular prostheses were infiltrated by disorganized scar tissue with fibers concentric to the mesh filaments. In contrast, ePTFE implants were encapsulated by organized tissue, with fibers running parallel to the surface of biomaterial. All three composites achieved good recipient tissue integration and a homogeneous, organized, and well-vascularized neoperitoneum. At 14 days postimplant, laminar prostheses and composites showed similar results in terms of adhesion formation and integration within host tissue. Our findings suggest that both the composite prostheses and the laminar ePTFE performed very well in terms of reduced adhesion formation at the peritoneal interface.

Long-term treatment for lipoatrophy associated or not with HIV infection using ePTFE implants and polyacrylamide gel

HIV-related lipoatrophy (HIVLA) is notable for its increasing incidence, multiple etiologies, relatively low morbidity, apparently irreversible effects, and unequivocal clinical features. The underlying cause of HIVLA is still controversial, but there is an increasing demand for correction. We describe a treatment approach using soft malar implants and polyacrylamide gel injections, separately or in combination. Expanded polytetrafluoroethylene (GORE-SAM, W.L. Gore & Associates, Flagstaff, AZ) malar implants were used for augmentation of the most sunken areas below the eye. They were placed subperiosteally and more medially than conventional implants. After trying sheets and custom-made implants, preshaped GORE-Tex SAM implants are now used systematically. Polyacrylamide gel (Eutrophill, Lab Procytech, Martillac, France) injections were performed continuously and evenly from one side to the other in the deepest part of the sunken area at the subcutaneous level only. A total of 85 consecutive patients were treated using implants alone in 8 cases, injections alone in 65 cases, and both implants and injections in 12 cases. The few adverse effects included 3 cases of chronic inflammation (dental conflict) after placement of sheets and custom-made implants; no such cases occurred using preshaped implants. Some very light bulges developed after polyacrylamide injections, which usually disappeared after a few months. Mean follow-up was 16 months for injections and 29 months for implants. Combination treatment using implants in sunken areas near the bone and fillers in soft tissue areas offers a balanced trade-off between benefits and risks and provides excellent long-term and natural results, as well as notable psychological benefits.

Who Is Still Using Expanded Polytetrafluoroethylene?

Expanded polytetrafluoroethylene (ePTFE) is a permanent, solid implant that has been used for facial soft tissue augmentation. The implants are generally used in the lower third of the face for filling lips, nasolabial folds, and deeper facial lines. Many physicians have noted complications with this use. To determine physician satisfaction trends for ePTFE. METHODS. A physician satisfaction survey was sent out in February 2000. Information regarding perceived patient and physician satisfaction regarding favored sites for the use of augmentation with ePTFE, the quantity used, and revision rates was assessed. A second survey was mailed in July 2003 to the same physicians to gain information regarding long-term satisfaction with ePTFE. The results from the first survey revealed that 10 of 12 physicians perceived that their patients were satisfied with ePTFE implants in all locations with the exception of the lips. There was a wide variation in the number of cases of ePTFE performed per year among the different physicians. Reported revision rates varied from less than 1 to 100% in the lips. The majority of the physicians found that removal of the implant was easy. The results from the second survey in 2003 revealed that 100% of the physicians were disappointed with these products. Physicians' assessments of their patients' satisfaction revealed that one-third were mildly disappointed and two-thirds were satisfied. Revision rates in all cases were increased between the first and second survey. A subjective patient satisfaction survey was not done during either of these time periods. New procedures are often quickly embraced by both physicians and patients. It is crucial that we reevaluate and report long-term experience and satisfaction. Although this informal survey has limitations, it appears that some physicians are less satisfied with ePTFE as a soft tissue implant. Larger studies including objective measurements delineating the degree of improvement and subjective patient satisfaction would be welcomed.

Stimulated Endothelial Cell Adhesion and Angiogenesis with Laminin-5 Modification of Expanded Polytetrafluoroethylene

Biomedical implants often exhibit poor clinical performance due to the formation of a periimplant avascular fibrous capsule. Surface modification of synthetic materials has been evaluated to accelerate the formation of functional microcirculation in association with implants. The current study used a flow-mediated protein deposition system to modify expanded polytetrafluoroethylene (ePTFE) with a laminin-5-rich conditioned growth medium and with medium from which laminin-5 had been selectively removed. An in vitro model of endothelial cell adherence determined that laminin-5 modification resulted in significantly increased adhesion of human microvessel endothelial cells to ePTFE. In vivo studies evaluating the periimplant vascular response to laminin-5-treated samples indicated that absorption of laminin-5-rich conditioned medium supported accelerated neovascularization of ePTFE implants. A flow system designed to treat porous implant materials facilitates laminin-5 modification of commercially available ePTFE, resulting in increased endothelial cell adhesion in vitro and increased vascularization in vivo.

A Prospective Study of Tubed ePTFE Lip Implants: An Objective Evaluation of Efficacy, Hardness, and Length

Introduction: Previous studies of expanded polytetrafluoroethylene (ePTFE) soft tissue implants using subjective measurements have indicated problems with implant hardening, contraction, and loss of efficacy over time. However, clinical studies using objective measures have not yet been published in the evaluation of these implants. This study aims to evaluate lip ePTFE implants prospectively with objective evaluation of changes in implant hardness and length, lip projection, and vermilion show over time. Methods: Patients with atrophic lips were enrolled in this study. Thin-walled tubes of ePTFE were implanted into upper or lower lips. Lip projection and vermilion show were measured using lateral digital images and digital software. Lip hardness was measured using a durometer, a hand-held device designed to register the hardness of various substances using a spring-loaded indentor. All measurements were completed preoperatively and postoperatively at days 15, 30, 90, and 180. Preoperative measurements served as control data. All measurements from preoperative and additional time-point values were compared using at test. Results: A total of 19 implants were placed in 10 patients. One implant was removed due to patient dissatisfaction with overprojection, another was removed for acute infection. One implant/patient was lost to follow-up. Durometer scores of the lip increased nearly fourfold, which indicates an increase in hardness over time (P &lt; .001). Gains in lip projection peaked at 2 mm by 3 months postoperatively and returned to within 1 mm of baseline by 6 months. No implant shortening occurred. Discussion: Tubular ePTFE implants were safe and resulted in modest gains in lip projection over 6 months. However, these implants lost initial gains in projection and hardened over time, with loss of vermilion show in some cases. These changes over time may be due to a process similar to the capsular contracture commonly seen with breast implants.

A new ePTFE soft tissue implant for natural-looking augmentation of lips and wrinkles.

Expanded polytetrafluoroethylene (ePTFE) implants have been used for augmentation of thinning lips and wrinkles due to aging for more than 10 years. The aesthetic results have often been excellent, but complications such as infection, extrusion, migration, shrinkage, and hardening have occurred in some patients. To assess short-term results and complications in patients undergoing augmentation of the lips, nasolabial folds, and marionette lines with a newly designed ePTFE implant. Thirty patients received 60 Advanta ePTFE implants for augmentation of the lips, nasolabial folds, or marionette lines. All patients received a natural-looking augmentation following 3-4 days of noticeable swelling. The only significant complications involved two upper lip implants that were removed for suspected infection. In a preliminary series, Advanta ePTFE implants provided effective, natural-looking augmentation of the lips and nasolabial folds with minimal complications.

TNP-470 Reduces Collagen and Macrophage Accumulation in Expanded Polytetrafluoroethylene Tube Implants

Background. TNP-470 is a potent angiogenic inhibitor that has been demonstrated to decrease the rate of cutaneous wound healing. This study investigated the effect that TNP-470 has upon collagen growth and macrophage infiltration into expanded polytetrafluoroethylene (e-PTFE) tube implants.Methods. e-PTFE tubes (1.0 cm in length) were implanted into the dorsum of male Swiss–Webster mice (8–10 weeks old). TNP-470 was administered subcutaneously in doses of 0.5, 1.0, or 5.0 mg/kg for determination of hydroxyproline accumulation on day 18 after implantation. Additionally, TNP-470 was administered at 5.0 mg/kg for determination of macrophage infiltration on days 4, 8, 13, and 18 after implantation.Results. Administration of TNP-470 at doses of 1.0 and 5.0 mg/kg on days 0, 2, and 4 significantly (P < 0.05) decreased hydroxyproline accumulation in e-PTFE implants on day 18 after implantation. Administration of 0.5 mg/kg of TNP-470 yielded no significant difference vs the vehicle control (P < 0.81). Additionally, administration of TNP-470 at 5.0 mg/kg on days 0, 2, and 4 significantly (P < 0.05) decreased macrophage infiltration into e-PTFE implants on day 4 after implantation. There was also a significantly (P < 0.05) increased percentage of macrophages in the e-PTFE implants on day 13 after wounding. No significant differences were observed between the experimental and control groups on days 8 and 18.Conclusions. Administration of TNP-470 significantly decreases hydroxyproline accumulation in e-PTFE implants. These data suggest that while TNP-470 is administered, macrophage infiltration is impaired; however, upon discontinuing administration, macrophage infiltration increases. Possible mechanisms to account for these findings are discussed.

Tubular e-PTFE implants in glottal and neoglottal insufficiency: tolerance and stability in an animal model.

The aim of our research is to develop a laryngeal tissue augmentation technique that will be useful in treating glottal and neoglottal insufficiency. In a previous study the feasibility of insertion of tubular expanded poly-tetrafluoroethylene (e-PTFE) tissue implants into the larynx of a porcine model was demonstrated. In this paper we report the clinical, endoscopic, computed tomography (CT) and magnetic resonance image (MRI) and histopathological follow-up findings. These results demonstrate host tolerance of the implant over the period of study (six months) with little tissue reactivity to tubular e-PTFE implants in the porcine model. The tubular shape of the implant enhances stabilization by the rapid and complete host tissue penetration of the implant's interstices, making tubular e-PTFE a potentially useful soft tissue augmentation material for laryngeal incompetence.

Ultrastructural alterations of polytetrafluoroethylene prostheses implanted in abdominal wall provoked by infection: clinical and experimental study.

Infection of an expanded polytetrafluoroethylene (ePTFE) prosthesis after implant is a major drawback of its use in current clinical practice. The aim of the present study was to compare the behavior of such prostheses implanted into New Zealand rabbits with that of prostheses infected after clinical implant. Experimental implants of ePTFE Soft Tissue Patch were performed to repair defects (7 x 5 cm) created in the abdominal wall of 10 rabbits. Prior to implant the prostheses were contaminated with Staphylococcus aureus. Five animals implanted with noncontaminated ePTFE prostheses served as controls. All the animals were sacrificed at 30 days after implant. For the clinical study, specimens were taken from three ePTFE implants that had been found to be infected after intervention. The clinical and experimental implant specimens were processed for light microscopy and scanning electron microscopy. Macroscopic and microscopic examination of experimental and clinical implants revealed alterations to the ePTFE structure, such as areas of fragmentation, fracture lines, and detachment of fine layers of ePTFE that harbored numerous Staphylococcus colonies. Neoformed tissue around contaminated implants was arranged more loosely, and on occasion large spaces between fibers gave rise to an "unknitted" appearance with respect to the control implants. It may be concluded that microporous ePTFE prostheses show similar behavior following experimental or clinical implant in the presence of infection. Irreversible changes to the structure of the prosthesis are produced owing to colonization of the biomaterial by microorganisms, which in most cases necessitates total replacement of the prosthesis.

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 (7 × 5 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.

Denucleation promotes neovascularization of ePTFE in vivo

Expanded polytetrafluoroethylene (ePTFE) implants are being increasingly used as vascular prostheses and other devices. However the tissue response associated with this and other polymer implants continues to limit any long-term function. One of the major approaches currently being investigated to improve biocompatibility involves surface modification of the base polymer. In this report, we attempted to alter the healing characteristics of ePTFE by denucleation, a process which removes air trapped within the interstices of the material. Additionally, adsorption of extracellular proteins on the denucleated polymer was also tested. After 5 weeks implanted in subcutaneous and epididymal fat sites of rats, the material was explantcd and the healing around the implant evaluated histologically. We found that in skin implants, denucleation alone resulted in a substantial reduction in the fibrous capsule which has been previously reported for untreated ePTFE, and an increase in blood vessel development around and within the polymer. Absorption of extracellular matrix proteins prior to implantation resulted in a reduced vascularity of the implants compared with denucleation-only implants. Implants in fat tissue, regardless of treatment, showed very little tissue reaction, either in the number of inflammatory cells, development of a fibrous capsule or neovascularization. These results suggest that the presence of air nuclei within porous material may contribute to the inappropriate healing response associated with these polymers. In addition, they confirm earlier reports that healing around implanted polymers is tissue-specific.

Evaluation of Expanded Polytetrafluoroethylene as a Soft-Tissue Filling Substance: An Analysis of Design-Related Implant Behavior Using the Porcine Skin Model

Soft-tissue augmentation using the synthetic nonfluid biomaterial expanded polytetrafluoroethylene (ePTFE) has been supported by number of recent reports citing the favorable characteristics of biocompatibility, soft and natural feel, ease of use, and permanent augmentation. Concern has been expressed about this application for ePTFE material because of the proximity of the implants to the skin surface and potential problems with infection and extrusion. We evaluated the behavior of a series of specific ePTFE implant designs using a long-term subcutaneous augmentation model. By using a porcine model, 466 implants of ePTFE in the form of strips, rolls, or tubes were placed using a percutaneous insertion device subcutaneously over the dorsum and face. The animals were divided into three study groups by length of implantation (3 weeks, control; 6 months, intermediate term; and 12 months, long-term) and en-bloc tissue specimens, including skin, implants, and underlying soft tissue, were harvested for gross and histologic examination. Implants were removed at the earliest sign of infection, exposure, or extrusion and the difficulty of removal was ascertained and recorded. These data reveal that ePTFE material elicits acceptable levels of tissue activity with low extrusion rates over the short and long term supporting its use for soft-tissue augmentation. The data show a clear difference, however, in the host response and behavior of the implants for this application based on shape or design. A statistically significant difference in the low, but measurable, extrusion rates was observed amongst these implant designs. ePTFE tubes showed greater stability and predictable augmentation over other implant designs for soft-tissue augmentation and seem to represent a substantial improvement for this application. (Plast. Reconstr. Surg. 101: 1307, 1998.)

Evaluation of expanded polytetrafluoroethylene as a soft-tissue filling substance: an analysis of design-related implant behavior using the porcine skin model.

Soft-tissue augmentation using the synthetic nonfluid biomaterial expanded polytetrafluoroethylene (ePTFE) has been supported by number of recent reports citing the favorable characteristics of biocompatibility, soft and natural feel, ease of use, and permanent augmentation. Concern has been expressed about this application for ePTFE material because of the proximity of the implants to the skin surface and potential problems with infection and extrusion. We evaluated the behavior of a series of specific ePTFE implant designs using a long-term subcutaneous augmentation model. By using a porcine model, 466 implants of ePTFE in the form of strips, rolls, or tubes were placed using a percutaneous insertion device subcutaneously over the dorsum and face. The animals were divided into three study groups by length of implantation (3 weeks, control; 6 months, intermediate term; and 12 months, long-term) and en-bloc tissue specimens, including skin, implants, and underlying soft tissue, were harvested for gross and histologic examination. Implants were removed at the earliest sign of infection, exposure, or extrusion and the difficulty of removal was ascertained and recorded. These data reveal that ePTFE material elicits acceptable levels of tissue activity with low extrusion rates over the short and long term supporting its use for soft-tissue augmentation. The data show a clear difference, however, in the host response and behavior of the implants for this application based on shape or design. A statistically significant difference in the low, but measurable, extrusion rates was observed amongst these implant designs. ePTFE tubes showed greater stability and predictable augmentation over other implant designs for soft-tissue augmentation and seem to represent a substantial improvement for this application.

In vivo study of meshes implanted over the inguinal ring and external iliac vessels in uncastrated pigs.

The effects of placing a prosthesis directly on the internal inguinal ring and external iliac vessels in inguinal hernia repair are unknown. We compared tissue responses to five prostheses implanted in this position in uncastrated male pigs. Three types of polypropylene and two types of expanded polytetrafluoroethylene (ePTFE) mesh were implanted in 20 pigs (n = 8 for each prosthesis type). Specimens of the implants and surrounding tissue were obtained 30 and 90 days after implantation and assessed histologically. The polypropylene implants had more adhesions, more surface area covered by adhesions, and more tenacious adhesions than did the ePTFE implants. Perivascular cuffing was observed in eight polypropylene and one ePTFE specimen; ossification, necrosis, and testicular venous congestion were seen in polypropylene specimens. Abnormal healing processes after implantation of polypropylene mesh may increase complications of the transabdominal preperitoneal and total extraperitoneal approaches in laparoscopic inguinal hernia repair, whereas the minimal response to ePTFE meshes may make them safer for use in the preperitoneal space.

Influence of ePTFE polymer implant permeability on the rate and density of corneal extracellular matrix synthesis.

Microporous polymers have great potential for the production of corneal keratoprosthetic devices. Keratocytes invade the pores of expanded polytetrafluoroethylene implants (ePTFE) and collagen synthesis occurs. This ePTFE becomes translucent after its implantation in the stroma of rabbit cornea. The rate and density of cell growth within this polymer depends on the implant thickness, pore size, and its placement in the cornea. We have investigated the influence of the polymer permeability on the collagen and protein contents ePTFE implants. Rabbit corneal stroma were implanted with ePTFE disks (6 mm in diameter) by intralamellar keratoplasty. The implanted polymers were removed from the stroma after 3 to 6 months. The collagen and protein contents were determined after pepsin solubilization. The collagen content of the high-permeability implant was 3.7-fold greater than that of the low-permeability implant 3 months after implantation and 2.4-fold greater after 6 months. The total protein content of the high-permeability implant was 2.5-fold greater than that of low-permeability implant at 3 months and was the same after 6 months. The collagen-to-protein ratio was 68% in the high-permeability implants, and thus similar to that of normal corneal stroma. Thus, high polymer permeability increased both the rate and density of the corneal extracellular matrix ingrowth.

Differential healing and neovascularization of ePTFE implants in subcutaneous versus adipose tissue.

The preclinical evaluation of polymer biocompatibility is often performed using animal subcutaneous implant models. The choice of subcutaneous tissue as the implant site is due to a number of factors including simplicity of the surgery involved. Results from subcutaneous implants cannot necessarily be extrapolated to other tissues due to the differences in cellular composition of tissues. We have evaluated and compared the healing characteristics of expanded polytetrafluoroethylene (ePTFE) discs implanted in either subcutaneous tissue or epididymal fat pad tissue in rats. Following 3 and 5 weeks of implantation, the healing characteristics of discs were evaluated histologically with particular emphasis on tissue and polymer neovascularization. Implants placed in subcutaneous tissue exhibited limited formation of new microvascular elements within and directly in contact with the polymer, and the formation of an extensive fibrous capsule. In contrast, ePTFE implanted in the epididymal fat pads of rats exhibited extensive neovascularization of tissue surrounding the polymer, penetration of these microvascular cells into the graft interstices for distances < or = 100 microns and no morphological evidence of a fibrous capsule. The rat epididymal fat pad provides an alternative tissue for polymer healing evaluations. Due to the extensive presence of fat in subcutaneous tissue in humans, we suggest the fat pad model provides a more relevant preclinical evaluation of the healing characteristics of polymers used clinically in anatomic positions which contain significant amounts of fat.

Differential healing and neovascularization of ePTFE implants in subcutaneous versus adipose tissue

The preclinical evaluation of polymer biocompatibility is often performed using animal subcutaneous implant models. The choice of subcutaneous tissue as the implant site is due to a number of factors including simplicity of the surgery involved. Results from subcutaneous implants cannot necessarily be extrapolated to other tissues due to the differences in cellular composition of tissues. We have evaluated and compared the healing characteristics of expanded polytetrafluoroethylene (ePTFE) discs implanted in either subcutaneous tissue or epididymal fat pad tissue in rats. Following 3 and 5 weeks of implantation, the healing characteristics of discs were evaluated histologically with particular emphasis on tissue and polymer neovascularization. Implants placed in subcutaneous tissue exhibited limited formation of new microvascular elements within and directly in contact with the polymer, and the formation of an extensive fibrous capsule. In contrast, ePTFE implanted in the epididymal fat pads of rats exhibited extensive neovascularization of tissue surrounding the polymer, penetration of these microvascular cells into the graft interstices for distances ≤ 100 microns and no morphological evidence of a fibrous capsule. The rat epididymal fat pad provides an alternative tissue for polymer healing evaluations. Due to the extensive presence of fat in subcutaneous tissue in humans, we suggest the fat pad model provides a more relevant preclinical evaluation of the healing characteristics of polymers used clinically in anatomic positions which contain significant amounts of fat. © 1997 John Wiley & Sons, Inc.

Clinical and histologic response of subcutaneous expanded polytetrafluoroethylene (Gore-Tex) and porous high-density polyethylene (Medpor) implants to acute and early infection.

To examine the responses of subcutaneously implanted expanded polytetrafluoroethylene (e-PTFE, Gore-Tex) and porous high-density polyethylene (PHDPE, Medpor) to experimentally induced infection. Sprague-Dawley rats were implanted subcutaneously with either e-PTFE or PHDPE implants. Inocula of Staphylococcus aureus were injected directly over the implants and the wounds were observed for clinical signs of infection. After the animals were killed, the implants were harvested and underwent Histologic examination. Twenty-eight adult male Sprague-Dawley rats weighing 200 to 250 g. A 8-mm diameter, 1-mm-thick implant of either e-PTFE or PHDPE was placed in a subcutaneous pocket over each animal's dorsum. Either at the time of implantation or 14 days afterward, an inoculum of 10(9) colony-forming units of S aureus was injected transcutaneously directly over each implant. The animals were observed for 7 days before being killed. The implants were harvested and examined by both conventional light and scanning electron microscopy, and the degree of capsule reaction, infection, inflammation, and implant degradation was evaluated. Implants inoculated at the time of implantation were more likely to become clinically infected. Results for e-PTFE and PHDPE implants were similar in this group (5 of 5 e-PTFE and 5 of 5 PHDPE implants infected). The PHDPE implants inoculated 14 days after implantation were less likely to become infected (1 of 4 infected) than e-PTFE implants (3 of 4 infected), and were statistically less likely to become infected than PHDPE implants inoculated immediately after implantation (25% vs 100%; P < .02). Histologically, this resistance to infection correlated with increasing fibrovascular ingrowth into the PHDPE implants. The infected PHDPE implant had little to no ingrowth compared with PHDPE control implants. The uninfected e-PTFE implant had evidence of early fibrovascular ingrowth into the peripheral pores of the implant. Because of differences in pore size, PHDPE promotes faster fibrovascular ingrowth. The presence of vascularized host tissue in and around the implant lends stability and resistance to experimentally induced infection. Conservative management of clinical implant infections should be considered if bacterial seeding occurs after substantial fibrovascular ingrowth is present. Future alloplast designs should include pore sizes that will encourage invasion of the implant by host tissue.