Preparation And Properties Of Magnesium Oxide Nanoparticles/Poly L-lactic Acid Composites In Medicine

Poly-L-lactic acid (PLLA) is a kind of biodegradable polylactic acid polymer with highinitial strength and good biocompatibility for commercial bone graft material, and the devicehas been used in non-load-bearing bone repair. But it has many disadvantages, such as itsdegradation intermediates exhibite acidity, cell affinity and capacity is weak, insufficientmechanical strength, especially the effects of uncontrollable urge caused by the degradationlimit its widespread clinical application.Nano magnesia (MgO-NPs) is dissolved gradually inbody fluids and release Mg2+ions and OH-ions, the pH of the body fluid increased.This studycombined both the advantages of MgO-NPs and PLLA; we prepared PLLA/MgO compositesby using chemical methods to regulate the degradation,cell toxicity and mechanical propertiesof PLLA through the reinforcement which is modified MgO-NPs(m-MgO-NPs). We obtainedthe biodegradable fracture fixed composite which meet the requirements of the clinical use,and explored the dispersion and interface binding between PLLA matrix and modifiedMgO-NPs. Finally we obtained the following conclusions:(1) We modified MgO-NPs with racemic malic acid-low molecular weight polylactic acidcopolymer under vacuum and145℃for8.5hours. The chemical reactions of carboxylgroup (-COOH), the Mg-O bond of MgO and the surface hydroxyl group(-OH) adsorbedby MgO-NPs occurred in the process of modification;MgO-NPs was modified byaluminate coupling agent under80℃, the amount of aluminate coupling agent was1wt%,chemical bondings occurred between hydrophilic groups of aluminate coupling agent andMgO-NPs.(2) The m-MgO-NPs/PLLA composites were prepared by solution co-blended process. Thereaction between the carboxyl group (-COOH) of copolymer and the hydroxyl group (-OH)of PLLA improved the dispersion and surface bonding between MgO-NPs and PLLAmatrix.(3) The crystallization of the PLLA was improved by the significant heterogeneous nucleationof m-MgO-NPs along with grain refinement. The tensile strength of the composite filmsincreased significantly with the increasing of m-MgO-NPs amount and the elongation atbreak decreased. The degradation process of PLLA was regulated by m-MgO-NPs in vitroexperiments.(4) The hydrophilicity of PLLA composite was improved by m-MgO-NPs. The results ofMTT assay showed that: the cytotoxicity of composite material decreased with theaddition of m-MgO-NPs. The cytotoxicity of pure PLLA and0.5wt%m-MgO-NPs/PLLAcomposite material was level one, when the added amount of m-MgO-NPs reached1wt%,the cytotoxicity of composite material was level0. Along with the extension of culturetime, the cell survival rate increased gradually and over100%, indicating that them-MgO-NPs owned effect of cell proliferation promoting.