Experimental Research On Amine-containing Plasma Modification Of Pure Titanium Implant Surface

Experimental research on amine-containing plasma modification of pure titanium implant surfaceSince Professor Branemark proposed the Osteointegration theory, the direct contact between implant and bone has been regarded as one of the most important standards to evaluate whether the implant is successful or not. Therefore, to conform to this standard, many scholars have put lots of effort on the fundamental and clinical research to get the best healing effect. At present, more attentions are paid to surface modification of dental implants, to get the better biocompatibility on dental implant surface through physical, chemical or biological methods. As a result, the speed of formation of new bone around implant will be accelerated and the connection of implant and bone will be strengthened, which will improve the stability and success rate of implant.Presently the surface modification methods mainly include:the methods to change the roughness of implant surface (for example sand blasting, acid etching, sand blasting+acid etching and so on), surface coating technology (plasma spray coating, sol-gel coating, ion beam assistance deposition, electrical deposition and so on), oxidation treatment (for example anodic oxidation, micro arc oxidation, thermal oxidization and so on), nitriding, alkali or alkali heat treatment, ion implanting, biochemical modification, self-assembling monolayers technology, physical vapor deposition, chemical vapor deposition and so on. Although some methods have been used in clinical work, most of methods above are still in research stage, and there are some problems about them, such as the unstable coating, dissolution, delamination, the release increase of titanium ion, the acid, alkali or electrolyte remaining, the complex operation, the unstable modified surface and the difficult controlled effect. Therefore, it is urgent to seek an effective and easily controlled method to modify the implant surface without high-temperature treatment or stress on interface of implant and coating.Some research indicated that the chemical character of biomaterial surface will influence the adsorption of protein and molecule, such as fibronectn,integrin,ECM,paxillin,actin and so on, and adjust the response of cell on it, deciding the healing response and speed of implant. This experiment is precisely based on this point, to seek a method to improve the adhesion and growth of osteoblast-like cells and accelerate the osteointegration of implant.The amino group is one of organic functional groups of organism. In human body, protein and many carbohydrate compound contain massive amino groups, thus the amino group has the high affinity in the structure with tissue. Moreover, the amino groups could be the locating site of protein and enzyme. Obviously, modification with amino group will improve the biocompatibility of biomaterial.The low temperature discharge plasma, namely the plasma enhanced chemistry vapor deposition (PECVD), means under high energy from discharge the chemical bond of vapor will be broken and recombine on material surface, and develop a functional coating with different chemical composition. This method has following merits:firstly, the radio frequency does not need the electrode in the plasma reaction chamber, which cannot introduce the impurity from the electrode, avoiding the contamination to modified surface; secondly, the modification is conducted at low temperature, which results in no-stress interface between polymer film and Ti; thirdly, low temperature plasma can modify all kinds of shape materials, especially complicated implant surface, with ultra thin, uniform and pinhole-free film, and the film bonding substrate by covalent bond with strong connection; finally, the most important thing is the low temperature plasma modification belongs to dry chemical method, which is easy to operate with well-controlled result, and the repeatability of result is good. At the same time, plasma can sterilize samples while surface modified. In addition, the low-temperature treatment combined with pulse, which introduces duty cycle, will activate some sole organic molecule and do not destroy their basic chemistry function, which result in producing stable, specific and functional surface. This experiment is mainly divided into two parts as followed:The first part:to determine plasma parameters and to analyze the physics and chemistry performance and stability of modified surface with different parameters.The present experiment mainly studied low-temperature plasma polymerization on titanium implant surface and its biological application. Using Heptylamine as monomer, through the radio frequency (RF,13.56 MHz) low temperature plasma, we modified titanium surface with the-NH2 functional group, to improve its biocompatibility. Firstly, to determine the plasma experiment parameter, we modified titanium surface with different plasma parameters, such as the electric discharge power, the discharge time, the electric discharge pattern, the duty cycle and the sample position and so on. We studied the effect of these parameters on the structure, chemical composition and density of functional group of polymer film and the stability of polymer film in pure water and 75% ethanol. The X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurement instruments were used to study the structure, composition, texture, solubility, stability of modified surface.The second part:taking untreated titanium as a control group, to evaluate the biocompatibility in vitro of modified surface with different plasma parameters.The inverted microscope, the fluorescence microscope and scanning electronic microscope were used to investigate the initial adhesion, shape and distribution of osteoblast (SaOs-2) and fibroblast (L929) on modified surface. The cells on samples were automaticlly counted with ImageXpress system. The functional state of actin on different samples dyed with FITC was analyzed with laser scanning confocal microscope, and the shape and adhesion area of SaOs-2 dyed with PKH26 on different modified surface were analyzed. In addition, the effect of different modification on the proliferation of SaOs-2 was statistical analyzed with MTT method.The results indicated as follows:1. Comparing three different plasma discharge modes, the continuous wave discharge produced cross-linked polymer film with the best stability in pure water and 75% ethanol, but the amino groups introduced were least;2. The pulse discharge introduced more amino groups, but the modified surface was unstable, and the polymer film became not continuous with signal of substrate emerging in XPS result after soaking in pure water and 75% ethanol for 30 min;3. The continuous wave coupled pulse mode discharge introduced the most amino groups with better stability in pure water and 75% ethanol, which means this is the optimal mode for modifying titanium with plasma;4. Through the radio frequency low temperature plasma modification with amino groups, the biocompatibility of titanium was improved, facilitating the adhesion, spreading and proliferation of osteoblast. At the same time inhibited the adhesion and growth of fibroblast;5. The cell compatibility of titanium modified with continuous wave coupled pulse mode was the best.On the base of the results above, we can conclude as follows:The biocompatibility of titanium implant modified with amino-containing plasma functionalization was improved significantly, developing the functional surface with bioactivity; in which continuous wave coupled pulse mode was the best condition for modifying titanium with plasma discharge. The radio frequency low temperature plasma modification was practicable to introduce amino group on titanium surface, and as a new method for titanium implant surface modification, it has a broad prospect.