| Recently, polymer/nano-hydroxyapatite (nano-HA) composites are widely used as bone tissue repair materials. However, the poor interfacial properties between polymer and nano-HA often limit the application of such materials in practical applications. Besides, the bacterial infection in surgery also remains a problem. Therefore, it is of great significance to solve these problems for polymer/nano-HA composites.Dopamine modification is one of the common methods for surface modification, and dopamine also has certain reductive ability. Therefore, dopamine was used to modify the surface of nano-HA in this thesis, and then the polydopamine (PDA) coating on the surface of nano-HA was used as reducing agent to reduce silver ions into silver nanoparticles (Ag). Finally, these modified nanoparticles were mixed with poly-L-lactic acid (PLLA) to get PLLA/HA/Ag composite materials. The composites demonstrated good mechanical properties, biocompatibility, as well as good antibacterial properties with the addition of Ag. Details are listed as follows:(1) Hydroxyapatite nano-rods were prepared by co-precipitation, which was kept in water for further use. Then the wet nano-HA was surface modified by dopamine solution (m-HA) and the success coating of PDA was confirmed by various characterizations. The m-HA demonstrated good dispersibility in both chloroform solvent and PLLA/chloroform solution, owing to the swelling feature of PDA coating and its interaction with PLLA chains. Accordingly, PLLA/m-HA composite demonstrated higher mechanical properties than PLLA/nano-HA. Besides, the highest tensile strength was obtained at the amount of 30 wt.%. Due to good dispersibility of m-HA in the PLLA matrix, in comparison with PLLA/nano-HA, PLLA/m-HA could induce the differentiation of bone mesenchymal stromal cells (BMSCs) more efficiently.(2) Taking advantage of the reductive ability of PDA on the surface of m-HA, the Ag-loaded m-HA (m-HA/Ag) was prepared by soaking m-HA in the silver nitrate solution. Then PLLA/m-HA/Ag composite films were prepared by solution casting and the content of HA was fixed at 30 wt.%. The amount of incorporated Ag was controlled by changing the ratio of m-HA and m-HA/Ag. The results showed that the silver reduction process would not affect the dispersibility of m-HA and the mechanical properties of composites. Besides, the biological experiments indicated that PLLA/m-HA/Ag composites had both good biocompatibility and high antibacterial activity. Therefore, PLLA/m-HA/Ag composites had the potential to be bone defect repair materials.In a summary, this study reported a simple method to improve the dispersibility of nano-HA in PLLA matrix and to load antibacterial Ag by using mussel-inspired dopamine modification. Promisingly, the obtained PLLA/m-HA/Ag composites, which displayed good mechanical properties, were expected to serve as dual-functional (i.e. biocompatible and antibacterial) substrates for bone regeneration. |
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