Preparation And Properties Research Of Biodegradable Magnesium/Polylactic Acid Composites

Ploylactic acid (PLA) is new kind of fully biodegradable and plant sources polymer, it can be degraded and absorbed completely in the human body,and its biocompatibility has been approved by the U.S. Food and Drug Administration (FDA). It has a great use in clinical currently.For its good biodegradability, it let the patients avoid the pain from the secondary surgery and reduce the operation risk of failure, but it also has some defect to be bone fixation material. For example, the degradation products of PLA is acidic,lack of bone bonding force,short of biological activity. so it is a research hotspot to modified PLA and make it to be a better biomedical material in currently.Magnesium has good bioactivity and biocompatibility, it can also completely degraded and absorbed in the human body. The degradation product is alkaline. Magnesium element is one of essential microelement in the human body. Add a few magnesium powders in the PLA substrate, in order to counteract the acidity of the degradation of PLA and improve the biological activity of the PLA substrate. In this work, the industrial level PLA was used to composite with magnesium powder in order to judge feasibility of the experiment. During the process of the experiment, we found that the binding force between magnesium and PLA matrix is not strong; the p H value of the degradation is high in the early days. So the fluoride treatment was used to the magnesium powder, then composite with the PLA in order to improve the Mg/PLLA composite. After successfully verify the feasibility of the experiment, the medical PLA was used to composite with magnesium and fluoride magnesium powder respectively. The comprehensive study was carried on the materials, the results are as follows:1) Magnesium powder as well as fluoride treatment magnesium powder was well-distributed in the matrix of the composite materials. Smooth surface of the composite material was obtained, and magnesium particles scatter in the PLA matrix with good bonding strength. 2) PLA composite materials with magnesium powder/fluoride treatment magnesium powder get a fine mechanical property which is available for orthopedic application although less than the PLA’s. The tensile strength of magnesium/Fluoride treatment magnesium powder added PLA were far better than those HA added PLA. fluoride treatment powder gets a better bonding strength than untreated magnesium powder with PLA matrix.3) Mixing of magnesium/fluoride treatment magnesium powder with PLA lead to heterogeneous nucleation while cooling, which results in the speeding up of the crystallizations and the higher crystallinity.4) Acidity while PLA degradation was reduced (pH7.2-7.7) via adding3%～5%magnesium powders because that Mg can react with H2O with the OH" releasing.5) Bioactivity was significantly improved, which was proved by the result of the degradation in SBF, via mixing magnesium/fluoride treatment magnesium powder with PLA.6) Addition of magnesium/fluoride treatment magnesium powder into PLA performs a well cytocompatibility.7) In summary, PLA with addition of3%～5%Mg/fluoride treatment Mg powder performs best whatever mechanical properties/thermal properties/degradation behavior as well as cytocompatibility, and the PLA with fluoride treatment Mg powder seems like a little bit better than that PLA with Mg powder’s.