Bioabsorbable metal-polymer composites of magnesium (Mg)/poly-lactic acid (PLA) can overcome some of the challenges associated with non-degradable metals (Ti, stainless steel, etc.) as well as degradable metals (Mg, Zn, Fe, etc.) and degradable polymers (PLA, PLGA, etc.) in orthopedic implant applications.

This thesis deals with the development of manufacturing process for surface modification of bioabsorbable Mg wires and Mg wires/PLA composites and the detailed characterization of mechanical, degradation and biological performance. Microstructure of cold-drawn Mg wire could be tuned by processing conditions which allowed to tailor its mechanical and corrosion properties. However, wire strength dropped to negligible values in just 24 h of in vitro degradation due to fast and pitting corrosion. To overcome this limitation, a novel and scalable strategy of Continuous Plasma Electrolytic Oxidation (C-PEO) process was developed for seamless surface modification of Mg wires that introduced a protective oxide layer on the surface of Mg wires which improved corrosion resistance and strength retention of wires (100 MPa after 96 h) and favored cells adhesion. Mg and PEO-modified Mg wires were used to manufacture unidirectional and multi-directional Mg/PLA composite laminates by hot compression.

Mechanical, degradation and biological properties of the composites were studied at both constituent and bulk levels. The mechanical response of composites in tension, compression, and in-plane shear was characterized and was found to be dependent on the orientation of wires. Push-out tests revealed that the PEO oxide layer increased the strength and toughness of the interface between the Mg wire and PLA, which was reflected in the high ductility of unidirectional (in longitudinal tension) and quasi-isotropic composites. Interface strength and bulk mechanical properties of composites decreased during in vitro degradation of 42 days.

It was found by 180 days long in vitro degradation study that the presence of Mg wires accelerated the degradation in comparison to pure PLA, while Mg wires were completely corroded, whereas PEO modification suppressed the corrosion of Mg wires. Finally, composites were found to be cytocompatible, and favored proliferation and differentiation of cells. In summary, Mg/PLA composite is a suitable candidate for the next generation of bioabsorbable orthopedic implants, such as fixation plates, as its mechanical properties can be tailored by stacking sequence of Mg wires while at the same time, the degradation rate can be controlled by PEO surface modification of Mg wires.