Evaluation of biomechanical properties of Expanded-Polytetrafluoroethylene™ soft tissue patch after dorsal implantation in the rat to mimic TMJ lateral reconstruction

Clinically, Gore-Tex Expanded-Polytetrafluoroethylene™ (E-PTFE™) has been used to reconstruct the lateral temporomandibular joint (TMJ) ligament. The purpose of this study was to assess changes in the biomechanical properties of implanted E-PTFE™ over time with respect to tissue infiltration. 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 were tested for mechanical properties including maximal stress, strain and Young'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°C for a time period equivalent to the experimental group to simulate the effect of a moist, warm environment on biomechanical properties. Group C was the temperature and pressure control group. Twelve specimens were autoclave-sterilized to determine the changes of tensile strength under high temperature and pressure. Control group D (no treatment) was tested to determine the initial tensile strength. The results showed significantly larger maximal stress as well as an increase in E and smaller maximal strain in experimental group A than in control groups B, C and D. There was no significant difference among control groups B, C and D. Histological examination of implants at 12 weeks demonstrated that 0.2-0.3 mm of 1-mm thick implants were occupied by connective tissue from each side. It may be concluded that E-PTFE™ implants become stronger and less flexible after implantation in vivo.