Effect of D-lactide in PLA for oro-craniofacial surgery

Objectives: Polylactide(PLA) has been utilized to hard tissue fixture for several time. This investigation is to study the effect of D-lactide content in PLA to the characteristics of crystallization, morphology and physical properties of PLA. To shorten the long experimental period needed for hard tissues, accelerated aging method was adopted in the study. Methods: Group A by milling(15D/85L) and Group B by molding injection(5D/95L) those were placed in 57°C shaker(40 rpm) with the bath ratio of 1:20 between bone plates and PBS. Each group has 65 bone plates were produced. The bone plates were taken out the shaker at a time interval and were analyzed according to ASTM F1635-95 standard (2000). Results: The Group A bone plates, containing 15% D-form, had significant weight lost of 54.3% after 12 weeks while Group B bone plates, containing 5% D-form, had weight lost of 23.9% after 26 weeks. Upon strength, the Group A was decreased from 31.10±2.35N to 23.03±3.27N(-25.9%) within one week, while the Group B was slightly increased from 35.38±0.30N to 38.86±2.82N after one week and decreased to 21.75±1.62N(-38.5%) after 3 weeks. Upon molecular weight, the Group A was decreased from 164kDa to 87.90kDa(-46%) after one week while the Group B was decreased from 110kDa to 92.30kDa(-16%). The results shows that the Group B, with lower molecular weight, can maintain the mechanical strength longer and degrade slower than the Group A, with higher molecular weight. Conclusion: Using the accelerated aging method can shorten up to 4-fold of the experimental period and so this method is quite suitable for any hard tissue-related in vitro studies, which require a longer experimental period. Furthermore, higher content of D-form in PLA is susceptible to water invasion due to the morphological alternation and, ultimately, will result in the acceleration of weight loss, decreased strength and molecular weight.