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In Situ Construction of Nanostructure on Biomedical Metallic Titanium Implants for Surface Modification and the Research on Its Biological Property

Author: RenNa
Tutor: LiuHong
School: Shandong University
Course: Materials Physics and Chemistry
Keywords: titanium implant surface modification micro/nano-structure osteoblastdifferentiation antibacterial implant
CLC: R318.08
Type: PhD thesis
Year: 2013
Downloads: 266
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Abstract


Biomedical materials are artificial or natural materials, used to replace or revise the lost or diseased biological structure to restore their function. They are closely related with the improvement of the quality of life and longevity of human being. Therefore, this field has drawn more and more attentions. Recently, the progress of material and biological science promote the development of biomaterial. Due to the acceleration of the aging process, the pursuit of human health and longevity, the increase of physical trauma and patients suffering complicate diseases, the demand for biomaterials is tremendous. At present, the increasing number of the repair and replacement surgeries cause pains to the patients, and the increase of the cost. Moreover, the successful rate of the surgery is rather low. Therefore, higher requirements for biological materials are expected.Biomedical metallic titanium (Ti) is widely used for artificial bone, artificial joints, bone screws, dental implants as well as heart valves, vascular stents and other vascular materials, because of their good mechanical property, high corrosion resistance, low elasticity modulus, biocompatibility and simple processing. However, the bionert property of titanium makes it difficult to bind with surrounding tissues and the fibrous tissue would appear during the usage period, which cause thrombus and failure of implants. The mainly available way to resolve the above problems is to form apatite coatings on the surface integrated with host tissues. But a fatal disadvantage is the weak bonding strength between the coatings and the titanium substrate, which makes it easy to fall off. For other physical methods, such as ion implantation, thermal spraying and so on, the cost increased. Another complicate issue for the application of titanium implant is the potential bacterial infection. With the comprehensive disinfection and strictly aseptic operation, the postoperative infection is still a frequent occurrence. Serious infections will prolong hospitalization time, increase the patient’s pains, financial burden and a series of troublesome issues. The main solution for infection is to inject clinically antibiotic, which possess antimicrobial specificity, but this will lead to drug-resistant strains of bacteria after a long-term injection.It’s known that the surface micro-/nanostructure influences cell activity, including cell adhesion, spread, proliferation, differentiation; calcium and magnesium cations play a vital role in bone metabolism; the preconcentration effects of graphene oxide and graphene regulate cell growth and differentiation; silver nanoparticles possess the property of inhibiting bacteria, fungi and viruses, which could be applied in preparing antibacterial implants.Based on the above problems, this paper proposed four topics as below:1. In situ construction of sodium titanate nanostructure on titanium and the biological researchUsing alkali-hydrothermal method, two kinds of sodium titanate nanostructure, nanonetwork and nanotube were constructed through the reaction between metallic titanium and concentrated NaOH; SEM, EDX, HRTEM and Raman confirmed both the sodium titanate nanostructures are monoclinic crystal Na2Ti3O7; the formed nanostructure improved the hydrophilicity of the surface, which is an important factor for affecting cell activity; cell experiments, including cell proliferation, cytoskeleton staining and alkaline phosphatase (ALP) activity demonstrated that sodium titanate nano-network structure promoted cell proliferation and sodium tianate nanotubes and enhanced ALP (the marker of osteogenesis) activity; moreover, the preparation of sodium titanate activates the titanium surface and which is helpful for the following research work.2. Nanostructured titanate with different metal ions on surface of metallic titanium for regulating the fate of rat bone marrow mesenchymal stem cellsNa+-titanate, Mg2+-titanate and Ca2+-titanate nanostructure can be synthesized by a facile method based on a hydrothermal technique and followed by an ion-substitution process. By immersing titanium foil with Na2Ti3O7nanostructured on the surface in MgCl2and CaCl2solution, Na+in titanate can be totally substituted by Mg2+or Ca2+ions. This treatment modified the chemical environment on surface of titanium implants for cell culture, i.e. category and quantity of inorganic cations in titanate nanostructure, which can tune protein adsorption and the fate of mesenchymal stem cells, including adhesion, proliferation and differentiation. Both Mg2+and Ca2+in titanate nanostructure can enhance proliferation and osteogenic differentiation of BMSCs, compared with Na+-titanate nanostructures. Excessive Mg2+and Ca2+in titanate can inhibit cell proliferation and differentiation of BMSCs, yet, after some cations (Mg2+, Ca2+) release into osteogenic inductive medium during cell culture, osteoblastic differentiation could be enhanced. Certainly, Ca2+-titanate has more advantages than Mg2+-titanate in cell differentiation. This facile method of introducing Mg2+and Ca2+into titanate by ion- substitution would be promising in titanium implant design and manufacture.3. A graphene oxide and reduced graphene oxide functionalized Ti implant for improving biological propertyBased on the great significance of graphene and its derivatives in biological applications, graphene oxide (GO) and reduced graphene oxide (rGO) were firstly successfully assembled on titanium foils with sodium titanate nanostructure on the surface to obtain the composite nanostructures. The typical process is through alkylation method using coupling agent to bind GO and sodium titanate nanostructure and then GO was in situ reduce on the surface by hydrazine. Raman, XPS and SEM confirmed the structure and composition of GO and rGO on titanium surface. The modification altered the hydrophilicity of the surface and thus influenced the biological function. Then the protein adsorption and cell experiments demonstrated that functionalized samples, especially GO with a large scale of oxygen-containing groups can concentrate protein and growth factors which are associated with cell activities and promote cell proliferation and differentiation. Because of the great enhancement in cell growth, as well as the hot topic of graphene, the titanium material functionalized with graphene will be promising in the biomedical future.4. In situ construction of a titanate-silver nanoparticle-titanate sandwich nanostructure on a metallic titanium surface for bacteriostatic and biocompatible implantsThe sodium titanate nanonetwork film was first synthesized on the Ti foil surface by the alkaline hydrothermal method. Subsequently, the silver ions substituted for the sodium ions in the layer-structured sodium titanate by immersing sodium titanate into the AgNO3solution. Finally, Ag+ions were reduced to the Ag nanoparticles (AgNPs) in the glucose solution. As a result, a titanate-silver nanoparticle-titanate sandwich nanostructure was successfully in situ constructed on the titanium surface. The size and the amount of AgNPs in the sandwich nanostructure increased with an increase in the concentrations of the silver nitrate and the glucose. Compared with Ag+-titanate samples without reduction, this sandwich nanostructure showed a steady and prolonged release manner of Ag+ions, and thereby improved the bacteriostatic efficacy. An optimal concentration of AgNO3solution for ion-substitution was0.01mM and its bacteriostatic rate was determined as high as99.99%and also it possessed good cytocompatibility. The present work demonstrated a titanate-silver nanoparticle-titanate sandwich nanostructure that has dual functions of antibacterial activity and cytocompatibility. Therefore, the Ti substrate with such a sandwich nanostructure on the surface is a promising implantable biomaterial.

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CLC: > Medicine, health > Basic Medical > Medical science in general > Biomedical Engineering > General issues > Biomaterial
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