SummaryThe synthesis of poly(1actic acids) from the cyclic lactides and properties of the polymem prepared have been described. Degradation rates in vitro under homogeneous and heterogeneous conditions have been meaqured. The kinetics of deesterification under homogeneous conditions is second order and an activation energy of 11 Kcal/mol has been calculated. This is comparable to the value found for the hydrolysis of alkyl acetates. A biological in vilro method for determining the degradation of poly(1actic acids) has been described. The method indicates, in accordance with expectations, that poly (dl-lactic acid) degrades at a faster rate than L(+) lactic acid. Initial results of medical evaluation of the polymers in suture, rod, and film form are presented.
An in vivo method is described for screening polymeric materials for biocompatibility. The test is based on grading acute and subacute tissue reactions at 7 and 28 days, respectively, following implantation in rats. The methods is reproducible and reliable. It is designed to provide uniform test criteria for biocompatibility assessment in the early phases of the development of surgical implant materials.
Two substances, one promoting growth (promine) of ascites tumors in mice and the other inhibiting it (retine) have both been found in several tissues, namely, thymus, aorta, muscle, and tendon. In spite of similar solubilities in the solvents used for their extraction, the substances could be roughly separated. The value of the ratio between these substances in the same tissue may be significant.
An in vitro method has been developed for screening of candidate biomaterials in an early phase of their development. The test is based on L-929 mouse fibroblast cultures and their response to powdered polymer samples. It applies microscopic observation for the detection of morphological changes, uses dye exclusion testing for cell viability determination, and utilizes estimation of population doublings as an end point. The test is shown to be reliable and reproducible and is compared to in vivo implantation studies in rats, previously reported.
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