USE OF SUPERCRITICAL-FLUID EXTRACTION AS A METHOD OF CLEANING ANTERIOR CRUCIATE LIGAMENT PROSTHESES - IN-VITRO AND IN-VIVO VALIDATION

The process of supercritical fluid extraction (SFE) using carbon dioxi de as the mobile phase is finding increasing numbers of applications i n a wide variety of industries for the extraction, separation, and cle aning of materials. This study assessed the usefulness of this approac h in removing surface contaminants from a knitted polyester anterior c ruciate ligament (ACL) prosthesis before packaging and sterilizing the product during manufacture. The physical, dimensional, and chemical p roperties of SFE treated compared with commercially scoured control sa mples were characterized using a number of textile test methods: elect ron spectroscopy for chemical analysis, Fourier transform infrared spe ctroscopy, differential scanning calorimetry, and solvent extraction a nalysis. The biocompatibility of the samples was measured in terms of their ability to generate CD18 integrin expression on activated human polymorphonuclear cells, and their inflammatory response when implante d for up to 30 days in the knee joint of rats. SFE treatment was succe ssful in removing most of the nonpolar contaminants from the ACL prost hesis and reducing the amount of residuals to a commercially acceptabl e level. However, some nitrogen containing compounds and polar salts w ere not removed by the SFE process. The results from the biocompatibil ity tests demonstrated that the cleaner SFE treated prosthesis induced significantly lower CD18 expression than the scoured control fabric, and was also associated with a milder inflammatory response and a more rapid rate of healing during the 30 day animal trial. Another effect of SFE processing was to cause the polyester device to shrink and lose porosity because of yarn contraction and modification of the polymer' s microcrystalline structure.