Changing of mechanical properties of Polylactic Acid-based materials during biodegradation

Arthrodesis is a surgical procedure whose aim is to fix an affected joint to compensate for the lost function of the limb. Nowadays, the common materials for these purposes are medical steel and titanium alloys. However, metal alloys have high mechanical characteristics compared to natural bone. This leads to stress shielding at the bone–implant contact. Also, these implants cannot provide joint fixation at a physiological angle for patients under anesthesia.

The current problems can be solved by developing a self-positioning individualized implant made of composite material with shape memory effect. The materials presented in this research are polylactic acid (PLA) filled with bioinert (SiO₂) and bioactive (hydroxyapatite) particles. The mechanical properties of the composites are close to those of natural bone. Also, PLA is a biodegradable material, which means that the implant can gradually dissolve inside the body. This peculiarity leads to changing mechanical properties over time, but also helps to avoid repeated surgery. This research is focused on how different conditions of biodegradation affect the mechanical characteristics of PLA- SiO₂ and PLA-HAp composites.

Composites with 10, 15 and 20% mass of fillers and pure PLA were produced by extrusion. The process of degradation was observed on flat samples (ISO 14125:1998) to determine the flexural properties of the materials. The samples were immersed in phosphate-buffered saline, blood serum and cell solution to compare the differences in biodegradation mechanisms. The samples were kept in solutions at 37℃ for 1, 2, 4 and 8 weeks. Then, they were tested by mass change, surface SEM and three-point bending.

The results demonstrated changes in the degree of crystallinity and a significant decrease in the mechanical properties of the samples during the process of biodegradation. These were caused by the paramount destruction of the amorphous phase of the polymer.

This study was performed with the support of Grant RNF № 24-23-00442.