Application of radiation processing in implant technology

Thermal stability of polymer systems destined to biological purposes is of great importance because their durability determines appropriate applications by selecting biopolymers or biologically compatible materials. Some advantages, as for instance, the mechanical properties, would recommend 'classical' polymers as adequate compounds for implant production. The presence of compounds with similar behavior as bones, like hydroxyapatite, increases the level of compatibility between implant and host organ. The goal of this work is the radiation stability assesment of blends consisting of ethylene-propylene terpolymer, hydroxyapatite and stabilizing additives. The radiochemical ageing was selected for primary evaluation of polymer/hydroxyapatite system under drastic degradation conditions. Oxygen uptake method was applied to characterize the kinetic parameters, oxidation induction time and rate of thermal degradation depending on the oxidation environment (air, temperature (180 deg.C) and normal pressure). Tested samples were mixture of EPDM and hydroxyapatite, 90:10 (w/w). Stabilized specimens with antioxidants, Irganox 1010, Irganox 1076, Santonox R and Cyanox 2246 were also studied. The γ dose values were 100, 200 and 300 kGy. Some main aspects can be pointed out: (a) various concentrations of hydroxyapatite (10, 20 and 30%) do not significantly affect either induction periods or rates of oxidation; (b) EPDM/HA samples stabilized with Irganox 1010 have shown the longest oxidation induction times, from 15 to 25 h; (c) thermal resistance of stabilized EPDM/HH samples has ordered the checked antioxidants in the following sequence: Irganox 1010 > Santonox R > Irganox 1076. (authors)