Abstract:

BACKGROUND: The bending strength and elastic modulus of clinical applied metal fixation are 4 and 20 times than that of cortical bone separately. The mechanical properties of the metal cannot change dynamically with bone healing process, so the “stress shielding” emerges and affects the bone healing. Moreover, the metal fixation has to be removed by a second surgery.
OBJECTIVE: To test the mechanical properties of poly-L lactic acid/beta-tricalcium phosphate (PLLA/β-TCP) absorbable fixation materials by in vivo degradation and mechanics experiments.
METHODS: The PLLA/β-TCP were implanted into the right back subcutaneous tissue of 30 New Zealand white rabbits as the experimental group and the PLLA were implanted into the left back subcutaneous tissue as the control group. The rabbits were sacrificed separately at 4, 8, 12, 16, 24 weeks after operation for observation of the mechanical variation of PLLA and PLLA/β-TCP.
RESULTS AND CONCLUSION: The bending strength, shear strength and torsional strength of both PLLA and PLLA/β-TCP decreased with time going on during degradation. The bending strength and shear strength of PLLA/β-TCP were significantly greater than those of PLLA at 12, 16, 24 weeks after operation and at 4, 8, 12, 16, 24 weeks after operation, respectively, (P < 0.05). There was no difference in the torsional strength between the two groups (P > 0.05). The PLLA/β-TCP absorbable materials degrade slower than the pure PLLA. The mechanical strength of PLLA/β-TCP can maintain a longer time to meet the cancellous bone fracture fixation and bone healing requires.