Sterility Definition the state in which the probability

Sterility • Definition: the state in which the probability of any one bacterial endospore surviving is 10 or lower • Minimizes bacterial contamination • Reduces likelihood for infection • Can alter the material surface and bulk structure • Shelf Aging-- Post Sterilization --Manufacturing issues-what is the best sterilization method? What is shelf life for the device?

Pre-Surgical Implant Life

Sterilization Schemes • • • Eto Gas Steam Autoclaving E-beam radiation Gamma Radiation

Gamma Radiation • • • Advantages: deeply penetrating no residuals no post-sterilization treatment crosslinking- good for wear resistance • Disadvantages: • chain cleavage, loss of molecular weight and higher crystallinity • embrittlement

Oxygen aids in high reactivity towards free radical generation in radiation sterilization schemes • • R --g --> R. } initiation R. --O 2 --> RO 2. } propagation RO 2. --RH-> RO 2 H + R. } RO 2 H --RH-> RO. +. OH } chain branching RO. --RH-> ROH + R. }. OH --RH-> H O + R. 2 RO 2 H, RO 2. , R. -----> scission and crosslinking 2 RO 2. ----> RO 2 R + O 2} termination Increased crystallinity and density Increased oxidation levels Loss of fatigue, fracture and wear properties

Crystallinity and Density Evolution 60 50 40 30 % Crystallinity 20 10 0 Nonsterile Sterile

Remedies and Current Trends • Sterilization with Et. O and gas plasma • 5 year mandate shelf life • Gamma radiation in inert atmosphere, oxygen barrier