THE EFFECT OF THERMAL-TREATMENT ON STERILITY, MOLECULAR AND MECHANICAL-PROPERTIES OF VARIOUS POLYLACTIDES .1. POLY(L-LACTIDE)

Resorbable pins for the treatment of osteochondral defects produced by injection-moulding from poly(L-lactide) were subjected to the action of heat at 105-150 degrees C under a low moisture and low oxygen atmos phere for a predetermined time. Standard procedures were used to evalu ate the sterility, mechanical properties, molecular weight, polydisper sity and crystallinity of the heat-treated samples. All of the heat-tr eated samples were sterile after 2 h of exposure to heat. There was a 10% increase in the shearing strength of the samples treated thermally for up to 10 h. This was attributed to the increase in overall crysta llinity and crystal dimensions in the samples which enhanced the propa gation of cracks formed upon testing through areas of high ductility. There was, however, a 20-35% drop in flexural strength which might res ult from the decreased concentration of the amorphous regions in the h eat-treated implants. A 20% increase in molecular weight of the heat-t reated implants was assigned to the transesterification process betwee n the -OH and -COOH groups present initially in the polymer and/or for med due to chain scission upon exposure of the material to heat.