Titre de la dissertation: « Development and Design of Bioresorbable PLA-based Composites: From Interfacial Compatibilization to Porous Temporary Bone Implants ».

Résumé de la dissertation: This thesis is dedicated to design poly(lactic acid)/magnesium (PLA/Mg) composite as a biodegradable and bioresorbable bone implant. Despite the good choice of the biomaterials, PLA/Mg surface properties constrained the successful design of implant as they greatly impact the interactions between the implant and the biological medium. To overcome the interfacial compatibilization issue between the hydrophobic matrix and the hydrophilic charges, different strategies have been investigated. In the first step, we proposed the use of an amphiphilic diblock copolymer (PEO-b-PLLA). This surfactant was able to interact with the Mg filler via its hydrophilic part and to the PLA matrix via its hydrophobic part. Consequently, PLA/Mg interfacial adhesion is controlled which is confirmed via SEM and DMA. Interestingly, the WCA is decreased which had a significant effect on the protein adsorption. During the degradation in SBF, HAp, the major component of natural bone, has been formed in bulk which could induce good osteoconductivity. Moreover, the viability test confirmed the suitability of the designed composites for mesenchymal stem cell cultures. This finding showed therefore that these composites could serve as implants for biomedical applications. Despite the positive role of PEO-b-PLLA surfactant, a slight decrease in the mechanical properties is revealed due to the PEO plasticizing effect. Subsequently, In the second step, we proposed a new approach to overcome the aforementioned issue. This strategy consisted of the use of the dopamine instead of the PEO. PLLA-Dopamine polymer was prepared and used as a compatibilizer in the PLA/Mg interface system. Interestingly, in the absence of the plasticizing effect, a prominent increase in the mechanical properties is observed. Added to that, our investigation showed an enhancement of the composite’s bioactivity. Indeed, thanks to the dopamine bioactivity, the Hap is detected not only in bulk of the PLA/Mg composite but also at the surface. Thus, the osteoconductivity is supposed to be enhanced. Finally, following the positive effect of the PLLA-Dopamine compatibilizer, we focused up on the structural requirement of the implant. To do this, an assessment of mechanical behaviors of a designed additively manufactured PLA composite has been elaborated. Firstly, a comparison between conventional and auxetic structures has been performed to study their influence on the compression and impact resistance properties. Subsequently, the light has been shed on the auxetic structure as it showed the best mechanical properties. Indeed, its extraordinary property has great potential in the field of orthopedics. Then, different parameters such as the dimension and the formulation have been tailored to choose the ideal design for PLA-based biodegradable implant.

Promoteur de thèse: Monsieur Jean-Marie Raquez et Mme Rosica Mincheva