Study On Construction Of The Electro-bioactive Coating On The Dental Implant Surface: Use Of Electrically Conductive Polypyrrole (PPy)

In the clinical application of dental implants there are still some problems related to the imperfectness of osseointegration of implants with alveolar bone. How to improve the osseointegration is still a challenge we are facing. The ideal dental implant material will be not only bioactive and biocompatible but also interactive and programmable, and thus capable of seamless communication with surrounding tissues. Specifically, materials that incorporate stimulatory cues, such as electrical signals, can be used to promote cell attachment, proliferation, and differentiation.One of the possible strategies which can lead to the development of a new titanium-based electro-bioactive material consists in the doping of biologically active molecules to the dental implant surface in order to improve osseoinduction and chemical banding of interface between bone and dental implant surface. To this end, polypyrrole(PPy) has been chosen for the following reasons: 1)it has remarkable conductivity; 2)it can be electrodeposited onto metallic materials; 3)as coating material it can be used for metal protection; 4)its biocompatibility with respect to mammalian cells has been tested in recent years; 5)its properties impart the electrochemically controlled release ability.There are three major parts in this research.1. Synthesis and physical chemical properties of the electroactive PPy-coated titanium substratesPPy coatings have been successfully electrosynthesized on the Ti-substrates by constant current method in aqueous media. The cyclic voltammetry demonstrated the intrinsic redox reaction of the PPy-coated titanium substrates and the conductivity of PPy films was measured using a four-point probe technique. Though the analysis of FTIR and XPS, the chemical composition of the PPy coating was detect. Surface roughness was measured by a profilometer, SEM was used to characterize surface morphology, and a goniometer was used to evaluate the contact angle and surface energy of the PPy coating. Lap shear tests and potentialdynamic polarization curve showed that the PPy film could be remarkably adhered to the Ti-substrates and represented efficient coatings against corrosion.The results indicated that the PPy film could be electrosynthesized directly onto metallic implant and still retain remarkable conductivity and intrinsic redox properties. Moreover, the PPy coating not only bonded to the Ti-substrate but also addressed the fundamental issue of protecting the dental implant against corrosion, avoiding the problem of ions release in the surrounding tissue. The surface roughness, contact angle and surface energy values of Ppy-coated titanium substrate varied with the dopants and the electrosynthesis conditions.2. Effect of the electroactive PPy-coated titanium substrates on the biological and functional characteristics of osteoblastic cellsPrimary rat cells were isolated from the SD rat calvarial bone. The osteoblastic phenotype of these cells were confirmed by cell shape microscopy, ALP stain, collagen type I stain and mineralization experimental. A custom-build constant direct microcurrent stimulator, which possesses the function of feedback control of the applied current intensity with a current range(10-100 μ A) and high accuracy(±1μ A),was used in the experiment. With negative controls, osteoblastic cells were cultured on the surfaces of PPy-coated titanium substrate. The Ti needle electrode served as the cathode and the PPy-coated titanium substrate with osteoblastic cells as the anode. Osteoblastic cells attachment, spreading, proliferation activity, osteocalcin secretion, calcium-containing in the extracellularmatrix and mineralization experiment were completed to examine the osteoblasts behavior on the PPy-coated titanium substrates.In conclusion, oseoblasts cultured on the PPy-coated titanium substrates and subjected to an anodic current stimulus through the PPy coating showed a significant increasing adhesion on the material. It could also enhance the c...