Processing And Characterization Of Novel Biodegradable And Bioresorbable PLA/Mg Composites For Osteosynthesis

Eliminating the need for permanent implants removal is the driving force that motivates the research on the development of materials suitable for biodegradable implants. If patients are provided with resorbable implants that can be metabolized by the human body once the bone tissue has healed, their well-being together with the saving on expenses for the healthcare system would be incremented.

The aim of this doctoral thesis was to improve and broaden the applications of current bioresorbable materials used in osteosynthesis (Polylactic acid and Mg) by overcoming their main drawbacks. On one hand, the polylactic acid is associated with foreign body reactions, osteolysis and weaker mechanical properties in comparison with permanent metallic devices, which limits its applications to low-load bearing fractures. On the other, Mg and its alloys present a high degradation rate which leads to the formation of dangerous subcutaneous gas bubbles and a pH increment that causes bone damage and osteolysis.  The long-term goal of this thesis focuses on providing solutions that would lead to cheaper and less intrusive orthopaedic surgery.   

Novel biodegradable and bioresorbable composite materials for osteosynthesis devices based on polylactic acid and Mg were designed and developed. For the matrix, poly-L-lactic acid and poly-L,D-lactic acid with a 4.25% of D-lactyl were used. As reinforcement, irregular shape Mg particles and spherical Mg and Mg5Zn particles were used. PLA/Mg composites were fabricated by means of solvent-free common processes used in industry: extrusion/compression and injection moulding at a lab scale and extrusion/compression at a mid-scale.

In the material developed in this thesis, polylactic acid and Mg particles operate in a kind of symbiosis, each covering for the other´s limitations: while Mg improves polylactic acid mechanical properties, and biocompatibility, the polymeric matrix slows down the degradation rate of Mg, preventing high pH and controlling the hydrogen release.

Experimental results provide evidence that novel PLA/Mg composites have a great potential as resorbable and biocompatible biomaterials for applications in osteosynthesis, due to their controllable degradation rate and adequate mechanical properties.