In vitro degradation of poly-L-D-lactic acid (PLDLA) pellets and powder used as synthetic alloplasts for bone grafting

The objective of this study was to evaluate the in vitro degradation of pellet and powder forms of a poly-l-d-lactic acid material used to produce plates and screws for orthopedic, oral, and maxillofacial applications. Materials and methods: In order to produce the powder form the as-received pellets were milled in a cryogenic chamber. Particles size distribution (PSD) histograms were developed for both forms. The materials were then characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) before and after immersion in simulated body fluid for 30, 60, and 90 days. Results: SEM showed that for both forms material degradation started after 30 days of immersion in SBF and evolved until 90 days. Degradation started at the amorphous zones of the polymer and exposed of deeper crystalline layers. The pellet and powder samples PSD showed polydispersed patterns with mean diameters of 673.98 μm and 259.55 μm. Thermal onset degradation temperatures were 365.64°C and 360.30°C, and of 363.49°C and 359.83°C before immersion and after 90 days in SBF for the pellet and powder forms, respectively. The Tg's of the pellets and the powder were approximately 61.5°C and 66°C, and their respective endothermic peaks were observed at approximately 125°C and 120°C. The specific heat (c) was approximately 8.5 J/g and 6.2 J/g for the pellet and powder material, respectively. Conclusion: According to the results obtained, cryogenic milling resulted in particle plastic deformation, and alterations in glass transition temperature, melting temperature, and specific heat of the material.