Resumen de An approach to design new coatings for biomedical applications
Amir Abdel Samie El-Hadad
Ti6Al4V alloy is widely used as implants for orthopedic and dental applications because of its superior mechanical properties, excellent corrosion resistance and good biocompatibility. However, it takes long period of several months for Ti6Al4V implants to integrate with the bone tissue due to their bio-inert feature in nature. An innovating and incipient method to solve the above mentioned drawbacks consist of the development of new coatings which could improve both the biological and corrosion protection performance of the Ti6Al4V alloy. Thus, a variety of strategies have been implemented to modify the surface of Ti6Al4V-based implants and enhance bone growth and their initial stability. A common approach is the deposition of bioactive hybrid coatings including inorganic and organic units on the surface of the Ti6Al4V alloy via sol-gel method. The sol–gel route is of great interest as it offers the possibility of tailoring the material properties by variation of the relative composition of the precursors used. The aim of this thesis is focused on the development of new coatings, starting with inorganic hydroxyapatite (HAp) deposited onto Ti6Al4V substrate prepared through solgel route. The effect of thermal treatment temperature on both in-vitro bioactivity and corrosion performance has been studied in simulated body fluid solution (SBF). A complete physical-chemical characterization was done in all the thermally treated coatings obtained. In-vitro tests in SBF were carried out in order to investigate the biological performance of the films. Due to the high temperature required for synthesizing HAp in crystalline form, porous and cracked coatings have been obtained, as a result of the thermal treatments applied to the prepared coatings. Although of these cracks, on the film was produced the precipitation of bone-like apatite after immersion in SBF. These precipitation products lead also to an improvement of the corrosion performance through blocking effect. The corrosion protection of the coating depends on its ability to act as a physical barrier preventing the penetration of corrosive species to reach the metal surface. This fact stimulated us to reach other goals through the preparation of sets of various new organic-inorganic hybrids. These new coatings have been also prepared through sol-gel route. To obtain workable films and their optimum preparation conditions, a new study has been carried out. The aim of this new study has been to optimize the organic– inorganic hybrid preparation method through studying the structural changes which take place during the hydrolysis and condensation processes of a mixture of ?- methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethylorthosilicate (TMOS) in solution after the addition of water and ethanol. FTIR, liquid-state ²?Si and ¹³C nuclear magnetic resonance (NMR) have been applied for this purpose. The results indicated that, the hydrolysis process of the two silane precursors is a time-dependent process and four hours of reaction are required for obtaining workable films. Then, after the results obtained in the first two stages of this PhD thesis, three different organic-inorganic hybrid coatings have been prepared. These coatings have been based on the MAPTMS/TMOS matrix modified with different phosphorous precursors; HAp as solid phosphorus precursor and triethylphosphite (TEP) and dimethylsilylphosphite (DMTSP) as liquid phosphorus precursors. These precursors have been added in different amounts with the aim to obtain new materials of physicalchemical and biological interest. At this level, during investigation, the following four aspects have been taken into account: 1. Evaluation of the effect of the addition of the different phosphorous precursors on the densification of the siloxane network. 2. Physical-chemical characterization of the resulting coatings. 3. Evaluation of the in-vitro osteointegration of the coatings through assays of normal human osteoblast cytotoxicity and adhesion. 4. Evaluation of the corrosion performance of the coatings. The results obtained along this study have shown that, all the prepared coatings are relatively hydrophobic with respect to the un-coated alloy. All the modified films are denser than the control one based on the MAPTMS/TMOS matrix. This fact allows these coatings to act as effective physical barriers against corrosion. The presence of phosphorus precursors results in further cross-linking and at the same time act as binding sites for protein adsorption. The importance of phosphorus in cell division and proliferation make also these coatings bioactive. The coating based on MAPTMS/TMOS/DMTSP showed the best biological performance in terms of cell proliferation and adhesion. Concerning the barrier properties provided by the designed hybrid films, the sol-gel films obtained by the chemical modification of the MAPTMS/TMOS matrix with TEP, showed the best barrier properties when immersed in SBF for 30 days. -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
