Biomechanical effects of e-PTFE implant structure on soft tissue implantation stability: a study in the porcine model

Preventing nasal airway collapse with irradiated homologous costal cartilage versus expanded polytetrafluoroethylene: a novel animal model for nasal airway reconstruction

Airway collapse can occur when the forces of inhalation overpower the strength of the nasal lining flap. The authors established an animal model of the reconstructed nasal airway, and examined mechanical properties of tissue composites based on various materials. Twenty-three Sprague-Dawley rats were divided into three experimental groups: control (n = 5), irradiated homologous costal cartilage (IHCC, n = 10), and expanded polytetrafluoroethylene (ePTFE, n = 8). Two dorsal skin flaps represented nasal lining and skin envelope. No framework, an IHCC or ePTFE rim graft was used as framework. At three weeks, changes in the cross-sectional area of the lining flap were measured when negative pressure was applied. En-bloc specimens containing the graft and soft tissue were examined for histological change and tissue ingrowth. Reduction of cross-sectional area with simulated inhalation was 87.74% in the control group, 82.76% (IHCC), and 67.29% (ePTFE). Cross-sectional reduction was significantly less in ePTFE group than control group (p = 0.004) and IHCC group (p = 0.001). The difference was not significant in the control and IHCC groups. There was histologic evidence of tissue ingrowth in the ePTFE group. This novel animal model of nasal airway reconstruction supports the use and potential benefit of using ePTFE for prevention of airway collapse.

Lamination for subdermal implant fixation

Thirty-six aluminum oxide laminated discs were implanted into 12 young rabbits (18 with a 0.5-mm porous layer and 18 with 1 mm) to determine whether implants that are porous only on one side could fixate to subcutaneous tissue. After 3 months, discs were encased within thin pouches (0.02-0.14 mm) of fibrous connective tissue, as would have been expected of a completely porous implant. Solid sides showed no, while the porous sides showed little, attachment to pouches. Forty-seven percentage (17) of the discs had moved 1.4 +/- 0.8 cm beyond the 4.7 + 1 cm they had moved due to normal skin growth, while two others had moved between 6.2 and 6.5 cm beyond this measure. The proportion of 1 mm porous layer discs migrating within subcutaneous tissue was no greater than the proportion of 0.5 mm layer discs migrating (p = 0.15). Porous layer height and disc migration did not affect the attachment strength of pouch to surrounding tissues (68 +/- 23 N, p = 0.34). Pouch thickness, which has been associated to the level of applied forces in other studies, increased with migration distance (p = 0.054). Results indicate that one-sided porous discs are likely easier to retrieve than completely porous ones, but cannot be prevented from migrating in loose tissue of young animals. Data is being used to design subdermal radio frequency devices for endangered marine animals.

[Long-term histological outcome for the larynx after Gore-Tex medialization thyroplasty]

OBJECTIVES

We studied the long-term histological response of the human larynx to Gore-Tex implant and evaluated whether its biocompatibility.

STUDY DESIGN

Retrospective histological study.

METHODS

We conducted medialization laryngoplasty with expanded polytetrafluoroethylene (ePTEE or Gore-Tex) in a patient with vocal-fold paralysis. A strip of Gore-Tex was folded several times and inserted into the pocket preserving the inner perichondrium through a thyroid cartilage window. The patient died 12 months later and we histologically analyzed the larynx.

RESULTS

No evidence was seen of foreign body granuloma, migration, extrusion, or infection. A modest inflammatory response with a fibrous capsule was present around implants. We confirmed the infiltration of abundant collagen and numerous fibroblasts into the microporous implant structure.

CONCLUSION

Histological examination results suggest that Gore-Tex implants are safe and biocompatible with the human larynx. A slight inflammatory response and infiltration of fibrous tissue into the implant itself demonstrated that Gore-Tex implants are immunologically well tolerated.

Behavior of the different implant materials in acute infection and efficacy of antibiotherapy: Experimental study in rats

In this study, we propose a comparison of the behaviors of four different implant materials in case of acute infection: expanded polytetrafluoroethylene (e-PTFE), porous high density polyethylene (PHDPE), silicone, and autogenous cartilage tissue. The efficacy of prophylactic and therapeutic antibiotic therapies was also investigated in a rat model as four groups: group A, acute infection and no antibiotic therapy (n = 24); group B, acute infection and prophylactic antibiotic therapy (n = 24); group C, acute infection and therapeutic antibiotic therapy (n = 24); and control, no infection and no antibiotic therapy (n = 24). All materials with dimensions of approximately 1 x 1 cm(2) diameter were implanted separately under the dorsal skin of rats. Staphylococcus aureus was used as the infectious agent and antibiotic therapy was done with seftriaxone (Desefin, I.M., 20 mg/kg/day). Tissue specimens were obtained on postoperative days 14 and 21. Semiquantitative and qualitative alterations existing in the connective tissue neighboring the implant material (reaction zone-capsule tissue), fixation to the host tissue, cellular ingrowth (interstice qualitatively), and infection signs were assessed either macroscopically or microscopically. In group A, all materials were affected negatively that led to continuous regression in the wound healing process. Fixation of the cartilage to the surrounding tissue was weak compared with other groups. Fibrovascular tissue ingrowth in porous implants was delayed, and no regular capsule formation was observed around silicone implants. In group B, outcomes were similar to control groups. Porous materials showed tissue ingrowth into the pores as good as the control group. Regular capsular tissue formed around the silicone implants and cartilage tissues. In group C, where silicone had been used, wound healing was not as good as in group B and the control group. In the e-PTFE group, the granulation tissue forming through the pores did not show a good quality as the control group, and capsule formation around the material was irregular, leading to insufficient fixation. While the wound healing properties of the PHDPE group were not as good as the control group, there was no difference in terms of fixation to the wound bed. On the other hand, wound healing of the cartilage group was as satisfying as the control group.

Dual Porosity Expanded Polytetrafluoroethylene for Soft-Tissue Augmentation

BACKGROUND

A variety of nondegradable polymers have been evaluated for use as soft-tissue augmentation devices. This study compared a novel dual porosity expanded polytetrafluoroethylene with current, clinically used devices.

METHODS

Studies were performed in a porcine model of soft-tissue healing with both histologic evaluations and determination of biomechanical strength of tissue incorporation. Five different samples of expanded polytetrafluoroethylene were used in this study. Control devices were clinically available soft-tissue augmentation devices manufactured by W. L. Gore and Associates (Newark, Del.). Atrium Medical Corporation (Hudson, NH) manufactured three test devices with modified porosities. A total of 12 animals were used with implant evaluations performed after 1, 3, 6, and 12 months.

RESULTS

Significant differences in tissue incorporation were observed morphologically with the dual porosity material, including reduced inflammation and increased cellular and extracellular matrix incorporation of the material. Significant increases in both angiogenesis (new vessel formation in the peri-implant tissue) and neovascularization (blood vessel penetration into the interstices of the implants) were observed with the dual porosity expanded polytetrafluoroethylene material.

CONCLUSIONS

This novel dual porosity expanded polytetrafluoroethylene is associated with reduced inflammation and more extensive tissue incorporation as compared with the currently available form. These results suggest a dual porosity expanded polytetrafluoroethylene may provide a superior material for soft-tissue augmentation.

Tissue reactions evoked by porous and plane surfaces made out of silicon and titanium

Square-shaped silicon or titanium implants with plane or porous surfaces surrounded by a rim of silicone were implanted in the rat abdominal wall for evaluation of the tissue response after one, six, or 12 weeks. Cell damage was identified as increased membrane permeability using fluorescence microscopy by injection of propidium iodide prior to the killing of the rats. Capsule thickness and immunohistochemical quantification of macrophages were used as a further measure of the foreign-body reaction. There were no significant differences in capsular cell densities for macrophages, total cells (macrophages, fibroblasts, and other cells), or necrotic cells at the different time points for the four surfaces studied. However, significant differences in the kinetics of the response were found between plane surfaces compared with porous ones. Both types of plane surfaces developed a significant increase in capsule thickness over time in contrast to the porous implants. Porous silicon displayed a significant decrease in total cells in the reactive capsule over time. Furthermore, porous silicon and titanium surfaces displayed a significant decrease in total cell numbers at the implant interface between six and 12 weeks. The present study demonstrated that implanted silicon elicited soft-tissue reactions comparable to that of titanium.

Tissue response to expanded polytetrafluoroethylene and silicone implants in a rabbit model

BACKGROUND

Expanded polytetrafluoroethylene (ePTFE) and silicone are safe and relatively biocompatible materials.

OBJECTIVE

To compare, using multiple histologic parameters, the tissue response to a standard silicone soft tissue implant with the response to a modified ePTFE implant. The modified form of ePTFE is reinforced with fluorinated ethylene propylene (FEPRePTFE), which provides increased pliability and material integrity.

METHODS

The implants were placed into a subperiosteal pocket over the skull of adult New Zealand white rabbits. At 7, 30, and 90 days after implantation, en bloc tissue specimens, including skin, implants, surrounding soft tissue, and underlying bone were harvested for gross and histologic evaluation.

OUTCOME MEASURES

The tissue response to the implants was assessed with respect to the number of foreign body giant cells present, the thickness of the fibrous capsule, and the general inflammatory response (n = 6 for each implant at each evaluation period).

RESULTS

There were no cases of rejection, extrusion, or infection. The silicone implants elicited a significantly thicker capsule and less neovascularization (P<.05).

CONCLUSION

The FEPRePTFE demonstrated a favorable tissue response when compared with silicone, particularly in regard to capsule thickness and vascular ingrowth.

Mechanical properties of medical grade expanded polytetrafluoroethylene: the effects of internodal distance, density, and displacement rate

Expanded polytetrafluoroethylene (e-PTFE) is used successfully in a multitude of biomedical and clinical applications. The success of this biomaterial is due to its microporous structure that allows biointegration for fixation, as well as overall mechanical integrity. The mechanical properties and degree of tissue ingrowth depend on the microstructure of the expanded polymer foam, yet little is known about the correlation of the internodal distance and other microstructural features with the monotonic tensile properties. Complete structure-property correlation can be used to provide invaluable knowledge for the design of biomedical devices. The purpose of this study was to investigate the monotonic tensile properties of e-PTFE over a range of medically relevant microstructural features and manufacturing parameters. The microstructural and manufacturing parameters considered were internodal distance, linear density, volumetric density, and reduction ratio. Additionally, the effect of displacement rate on mechanical properties was studied. We found that the ultimate stress and strain increased linearly with linear density (R2 = 0.88 and 0.67, respectively). Surprisingly, elastic modulus did not correlate with any parameter measured and only weak correlations were found between all properties and internodal distance. The yield and ultimate stresses increased with increasing displacement rate (R2 = 0.88 and 0.57, respectively). The findings from this study indicate that linear density is a better predictor of mechanical properties than internodal distance and may be the preferred parameter to control when specifying a material for implantation in load bearing situations.

e-PTFE as scleral buckling episcleral implants: an experimental and histopathologic study

To investigate the effects of focal implantation of expanded polytetrafluoroethylene (e-PTFE) episcleral implants (i.e., explants or exoplants) on surrounding ocular tissues, an experimental and histopathological study was performed. Twenty-seven Fauve de Bourgogne rabbits eyes were implanted for a period of 3-11 months with oval-shaped e-PTFE episcleral implants. A newly formed capsule constantly encased the implants. Affected by the only two severe complications observed, 2 eyes had an endocapsular acute inflammation and could not be included in the study. Finally, 25 eyes were studied histopathologically. Neither intrusion nor extrusion of episcleral implants was observed. Other changes were related to implant characteristics. The inner surface of the capsule was often covered with numerous giant cells attesting to a foreign-body granuloma developed against the irregular outline of the episcleral implants. The porosity of the material was closely related to its surface irregularity, and also allowed its colonization by a fibrovascular and inflammatory tissue mainly in its peripheral layers. Under episcleral implants, sclera was both thinned and invaginated. Expanded PTFE hydrophobia was the other factor that might have suscitated granuloma. These microscopic changes are in contrast with an overall good apparent experimental tolerance to the material. However, additional studies on the long term behavior of this material would be helpful.