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Study Of Constructing The Bioactive Graded Coating On Titanium Implant Material

Posted on:2006-09-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q CengFull Text:PDF
GTID:1104360155473696Subject:Oral and clinical medicine
Abstract/Summary:PDF Full Text Request
Titanium metal and its alloys have been widely used as orthopedic and dental implants for their superior mechanical properties and good biocompatibility. However, Titanium is bioinert materials, the responses of bone to them are non-specific and the processes of osseointegration need long time. To achieve controlled desired biological responses, induce specific responses of tissue and cell, and accelerate of normal bone healing, a multiple-function bioactive graded coating in the paper was constructed on the surface of commercially pure titanium (cpTi) by activating the oxide layer using the chemical treatments and then binding the collagen, chitosan and rhBMP-2 to the oxide layer with biochemical methods.There are four major parts in this research. 1. The activation of the titanium oxide layer by chemical treatmentTo improve the amount of OH functional groups and its bioactivity, titanium metal was chemically treated with alkali treatment and sequent hot water aging. The surface morphology, chemical composition and crystal structure were used to characterize the titanium surfaces by SEM, XRD and XPS, and their bioactivity was evaluated. The results showed that aging in hot water apparently unchanged the porous network structure prepared by immersion in an aqueous solution of 5 M NaOH at 80℃ for 24 h,, and the surface titanium oxide was predominantly anatase. The treatment with a H2O2/HCl solution at 80℃ for 30 min followed by hot water aging also produced an anatase titania gel layer on the specimen surface, but the pores were sparse and the intensity of the anatase peak was relatively weak. After chemical treatment and sequent aging in hot water the amount of surface OH groups (acidic or basic OH group) was increased. The immersion test in the ACS or DMEM solution showed that calcium phosphate can deposit onto the modified titanium surface. The modified titanium surface promoted the prolifation of the osteoblasts. These results indicate that the chemical treatment (especially NaOH) and sequent hot water immersion improve the bioactivity of titanium. On the other hand, a high OH group concentration is very important as functional groups for the apatite nucleation or biochemical modification via an organometallic interface of immobilizing biomolecules.2. The study of the self-assembly adsorption and covalent attachment of collagen on titanium oxide layerThe self-assembly adsorption of collagen on two titanium surface and immobilization of collagen on the oxide layer ware investigated. The resultsshowed at the low concentration collagen was adsorbed in a simple means. By increasing the concentration, the adsorbed amount was improved and collagen reorganized into a net- like pattern on the modified titanium surface and into an interleaving structure on pure titanium. These indicated collagen had the self-assembly property, which was related with collagen concentration and titanium surface character. An intermediary aminoalkylsilane spacer molecule was then covalently linked to the oxide layer, followed by the covalent binding of collagen to the free terminal NH2 groups using by coupling of carbodiimide (EDC). Surface analyses following coating procedures consisted of XPS, SEM, and AFM. The results verified the occurrence of the grating of collagen. The surface amount of the collagen grafted on the oxide surface was determined by the Bradford method. The stability of the collagen layer was studied by incubating the collagen-coated titanium in PBS buffer saline. The surface density of the collagen decreased very slightly after the incubation, indicating the good stability of the coated collagen layer.3. Construction of the extracellular matrix-like layer on titanium surfaceThe compound of collagen and chitosan was immobilized on the titanium oxide in the means of covalent grafting and adsorption coating using aminoalkylsilane and EDC as coupling agents. The rhBMP-2 was grafted to the organic layer by the coupling of EDC and then the extracellular matrix-like layer was constructed. The released dosed of rhBMP-2 from coating in the PBS buffer saline was analyzed by Liquid Chromatograph and the release profile of rhBMP-2 was scaled. Results showed that rhBMP-2 had released slowly and lastingly during the soaking period, especially by coupling process.It indicated the extracellular matrix-like layer acted not only as scaffold but also carriers of rhBMP-2.4. Effect of the biooactive graded layer of titanium surface on the biological and functional characteristics of osteoblastic cellPrimary rat cells were isolated from the SD rat calvarial bone and cultured on four kinds of Ti-based implant surfaces in vitro. Cell attachment (30, 60, 120), spreading (cell skeleton actin analysis), cell proliferation (MTT test) and differentiation (ALP activity, calcium-containing in the extracellula matrix) were evaluated. The results showed that two groups of Ti/col and Ti/ECM-like could accelerate the early adhesion and spreading on the titanium surface. These two groups surfaces promoted osteoblasts proliferation and made them grow in a multilayer means. The modified titanium surfaces increased the ALP activity and calcium-containing, especially Ti/ECM-like group. The results indicated the graded layer had the good compatibility and adhesion, spreading, proliferation and differentiation of osteoblasts were improed.This research explored that on the titanium implant surface the possibility and the biological effects of construction of a graded bioactive layer, which contained growth factors and would play different poles during process of osseointegration and bone remodeling. Biochemical methods in this study were a promising surface modification method for Ti-based dental implants.
Keywords/Search Tags:biochemical modification, titanium oxide layer, collagen, chitosan, rhBMP-2, osteoblast
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