Biodegradation and mechanical properties of hydroxyapatite/poly-DL-lactide composites for fracture fixation

The biodegradation and mechanical properties of self-designed hydroxyapatite / poly-DL-lactide (HA/PDLLA) compositites were investigated in vitro and invio. In vitro, the specimens of HA/PDLLA and unfilled PDLLA with similar molecular weights were immersed in phosphate-buffered saline. Ageing of the various devices were monitored by measuring molecular weight, water absorption, weight loss; PH, mechanical strengths and microstructural changes. The follow-up times were 2,4,6,8, 10 and 12 weeks. In vivo, a transverse transcondylar osteotomy of the distal femur was fixed with a HA/PDLLA rod (diameter, 4. 5mm; length, 30 similar to 40mm). The follow-up times were 3,6 and 12 weeks. Roentgenographic, histologic, and biomechanical studies were carried out. The results show that the HA/PDLLA composities have higher mechanical strength and slower degradation than that of the unfilled PDLLA and that of all osteotomies unite within six weeks without delay. Consequently, the HA/PDLLA composites possess sufficient mechanical strength for the fixation of cancellous osteotomies.