Orthopaedics metallic implants sometime require removal after healing so as to avoid post-operative stress shielding effects. The use of bioresorbable magnesium based alloy is therefore an alternative. However, rapid degradation and hydrogen gas release are the major obstacles. Surface modification can effectively tackle the problem of rapid degradation. A surface treatment using a novel polymer based membrane made of polycaprolactone (PCL) and dichloromethane (DCM) has been recently applied by our team to control the degradation of AZ91 magnesium alloy. This study aims to investigate the in-vitro and in-vivo degradation rates of the treated and untreated magnesium alloys.
Custom-designed polymer membranes with various porosities were deposited on the AZ91 magnesium alloy by spraying process. Simulated body fluid immersion test for 60 days with the temperature controlled at 37℃ was applied to simulate an in-vitro corrosion environment. The concentration of the released ions was analyzed by inductively-coupled plasma mass spectrometry. To evaluate in-vivo degradation, the treated and untreated samples were implanted into the intramedullary cavity of the New Zealand White rabbits for 60 days. The degradation of implanted rods and newly formed bone were monitored and quantified by micro-computed tomography and calculated by CTAn program (Skyscan Company).
The magnesium ions released by untreated samples are about 6 folds higher than the treated at day 60 under in-vitro condition. Gas bubble formation is not found on the treated samples, whereas severe corrosion and gas bubble formation are observed on the untreated. Volume reduction of 0.33% is found on the untreated sample, but not found on the treated. In addition, the volume of newly formed bone is about 10.79 mm3 on the treated sample, which is about 8 folds higher than the untreated.
Both in-vitro and in-vivo studies suggested that the polymer-based membrane can significantly suppress the rapid degradation of magnesium alloy and enhance new bone formation around the material.
Wong HM1, Chu PK2, Luk KDK1, Cheung KMC1, Yeung KWK1
1 Division of Spine Surgery, Department of Orthopaedics and Traumatology, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China
2 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, China