The object of this study was to analyse the physical and chemical properties of synthetic anterior cruciate ligaments (ACL) after in vivo application Tubular ACL prostheses (SEM®) made of poly(ethylencterephthalate) (PET) fibre were explanted from patients after different implantation times. Part of the material was used for histological observations, while the other part was subjected to physico-chemical tests, including analysis of tensile properties, differential scanning calorimetry and gel permeation chromatography. The results were compared with those obtained from the virgin prosthesis. Tensile analysis showed the reduction of the rigidity with implantation time. Differential scanning calorimetry measurements revealed an increase of the crystallinity. Moreover, during a second scan a reduction of the 'cold crystallization peak' intensity was noted, suggesting the presence of low molecular weight materials. This enhances the tendency of the materials to crystallize during the heating scan. Gel permeation chromatography analysis demonstrated an increase of the dispersity due to the degradation of low molecular weight components. Both observations comfirmed that the material undergoes degradation and the results obtained are characteristic of the first stage of the hydrolysis of the amorphous phase in PET materials. Results to date show that PET commercial ligaments are degraded in the body environment. This reduces the performance of the prosthesis, affecting the knee joint mobility leading to further surgical operation.
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