Study On Surface Modification And Its Biological Properties Of Nano-porous Anodic Alumina

Porous anodic alumina (PAA) is a kind of membrane with highly ordered pore structure,which was fabricated by the method of electrochemical anodization. Recently, PAA has attractedincreasing interest in the field of biomaterials because of its chemical stability,anti-abrasion,anti-corrosion and without toxicity or side effect.The unique feature of PAA is that itpossesses significantly improved specific surface area and carrying capacity for bioactivesubstances, thereby endowing it with particular biological functions.In recent years, numerousstudies have shown that CaO-SiO2bioactive materials have excellent bioactivity andbiodegradability, where it can rapidly induce the bone-like apatite deposition and promote thebone cell proliferation and differentiation. However, infection is unavoidable after transplantation,which would result in transplants loosening, shed off and even operation failure.Copper is anexcellent antibacterial agent. Recent studies have shown that copper ions could promote theproliferation of human bone marrow mesenchymal stem cells (BMSCs) and the expression ofbone-related gene. Thus, to provide PAA with apatite-forming ability, cytocompatibility andantibacterial activity, the ternary system of CaO-SiO2-CuO could loaded into the PAA channelsand achieve CaO-SiO2-CuO/PAA. It will be of great importance in theory significance andmedicinal value.In this study, highly ordered PAA with large-diameter (200nm) was used to prepareCaO-SiO2/PAA and CaO-SiO2-CuO/PAA by sol-gel method with ultrasonic assistance.The in vitroapatite-forming ability of the CaO-SiO2/PAA and CaO-SiO2-CuO/PAA specimens was evaluatedby soaking them in simulated body fluid (SBF). The surface microstructure and chemical propertychanges after soaking in SBF were characterized by field emission scanning electron microscopy(FESEM), X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and Fouriertransform infrared spectroscopy (FTIR). The ionic concentration in the SBF after soaking wasmeasured by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis.Inaddition, osteoblasts in new born rats were inoculated on the surface to evaluate the attachmentand proliferation of the samples. The antibacterial properties of the samples were tested againstgram-positive bacteria of Staphylococcus aureus(S.aureus) and gram-negative bacterium ofEscherichia coli (E. coli).The conclusions are as follows: sol-gel derived bioactive CaO-SiO2and CaO-SiO2-CuO materials were loaded into PAA nano-pores (termed CaO-SiO2/PAA and CaO-SiO2-CuO/PAA) bya sol-dipping method with ultrasonic assistance, which did not destruct the nanostructure of PAA,particularly. In vitro SBF experiments revealed that the CaO-SiO2/PAA and CaO-SiO2-CuO/PAAspecimens dramatically enhanced the apatite-forming ability of PAA in SBF and Ca, Si and Cuions were released from the samples in a sustained and slow manner. Copper ions didn’t weakenthe apatite-forming ability and ion release behavior of CaO-SiO2/PAA. In addition, the newbornrat osteoblasts adhered to PAA, CaO-SiO2/PAA and CaO-SiO2-CuO/PAA surface with normalmorphology after24hours of culture. The proliferation of osteoblasts in newborn rats wasdetermined for up to5days in culture. The result showed that the newborn rat osteoblastsproliferation dramatically compared to PAA. Specifically, E. coli and S. aureus growth wereboth reduced on the CaO-SiO2-CuO/PAA (by86%±4%and88%±2%, respectively) andCaO-SiO2/PAA (by40%±4%and40%±3%, respectively) samples compared to PAA controls after24hours of culture.It has been recognized that the first step of infection is the adhesion of bacteria on implantsinterface. Therefore, implant surface properties are an important part of the development ofantibacterial implants. Wettability has been investigated as an important factor related to bacterialadhesion to surface. So, altering wettability could be a potential tool for increasing antibacterialactivity of the surface. In this study, fluorosilane with low surface energy was used to modify PAA,and expect a kind of hydrophobic surface.The antibacterial properties of the samples were testedagainst S.aureusand E. coli.The conclusions are as follows: the contact angle of PAA was changed from43°±3°to124°±4°after modifying. Antibacterial experiment results showed that, E. coli and S.aureus growth were both reduced on the PTES/PAA (by55%±3%and50%±3%, respectively)samples compared to PAA controls after6hours of culture.In summary, this study demonstrated that the CaO-SiO2-CuO/PAA samples possess goodapatite-forming ability, compatibility to osteoblasts and excellent antibacterial activity causing itto be a promising coating candidate for numerous implant materials and hard tissue repairmaterials for orthopedic.Inaddition,the hydrophobic surface of PTES/PAA also reduced the growthof E. coli and S. aureus.