Evaluation of biomechanical properties of expanded-polytetrafluoroethylene(TM) soft tissue patch after dorsal implantation in the rat to mimic TMJ lateral reconstruction

Clinically, Gore-Tex Expanded-Polytetrafluoroethylene(TM) (E-PTFE(TM)) has been used to reconstruct the lateral temporomandibular joint (TMJ) ligament . The purpose of this study was to assess changes in the biomechanical prop erties of implanted E-PTFE(TM) over time with respect to tissue infiltratio n. Ninety-six specimens of implants were divided into four groups. Group A was the experimental group. Thirty-six autoclave-sterilized specimens were subcutaneously implanted into the backs of 36 rats. The rats were randomly sacrificed at 2 (n = 12), 7 (n = 12) and 12 (n = 12) weeks. The implants we re tested for mechanical properties including maximal stress, strain and Yo ung's modulus of elasticity (E) using the servo-hydraulic material testing system (MTS). Group B was the in vitro control group. Thirty-six specimens were placed in tissue culture media at 37 degreesC for a time period equiva lent to the experimental group to simulate the effect of a moist, warm envi ronment on biomechanical properties. Group C was the temperature and pressu re control group. Twelve specimens were autoclave-sterilized to determine t he changes of tensile strength under high temperature and pressure. Control group D (no treatment) was tested to determine the initial tensile strengt h. The results showed significantly larger maximal stress as well as an inc rease in E and smaller maximal strain in experimental group A than in contr ol groups B, C and D. There was no significant difference among control gro ups B, C and D. Histological examination of implants at 12 weeks demonstrat ed that 0.2-0.3 mm of 1-mm thick implants were occupied by connective tissu e from each side. It may be concluded that E-PTFE(TM) implants become stron ger and less flexible after implantation in vivo.