Preparation of a Polylactic Acid with Hydroxyapatite Reinforcement Composite

Biodegradable polymers are a prime material choice for temporary biomedical devices due to its ability to degrade into non-toxic products for their use in vivo. However, polylactic acid (PLA) by itself lacks the sufficient strength and stiffness to permit their use as its properties begin to decrease as the polymer degrades. To improve the polymer’s mechanical properties, hydroxyapatite (HA) will be added to the PLA solution to act as reinforcement. The chemical property, glass transition temperature of a polymer, also plays a key role in the mechanical properties of the polymer. PLA’s glass temperature is 130⁰F. A polymer that is cured at a temperature below the glass temperature is found to be brittle. But at a temperature above the glass temperature, the material is found to be ductile. For the intention of using the composite material for a temporary medical device, a material with ductile characteristics is preferred. Preparation of the composite first involved the degradation of the PLA pellets given by the company NatureWorks. 1.50 grams of PLA pellets and dimethylformamide (DMF) are mixed for about 30 minutes at a temperature of 170⁰F to degrade the pellets. Once the pellets are fully dissolved in the solvent, HA was added to the solution. 15 minutes were given for each sample to provide a homogenous mixture. Once mixed the solution was carefully casted onto a glass slide that was set on top of another hot plate pre-heated to a temperature above the glass temperature. The final stage of preparing the composite is obtaining a composite thin film. An amount of HA added to the solution was varied for each test. It was observed that a small amount of HA is preferred due to less formation of bubbles found on the surface as the sample fully cures. Bubbles become stress concentrators, which creates a brittle material