Surface Modification Of Maxillofacial Silicone Elastomer By Parylene Coating

Silicone elastomer has been internationally recognized to be the first choice of material to repair oral and maxillofacial defects due to its excellent biocompatibility, chemical stability and good mechanical properties. There are many types of silicone elastomers at present, and the most performances close to or reach the ideal value. Bacterials stick to silicone elastomer easily because the surface of silicone elastomer is porous and it will cause denture stomatitis and other infects of patients. Silicone elastomer also has poor surface wettability, which will cause friction of mucosa and make patient discomfort. These deficiencies are all problems of silicone elastomer should be solved.Parylene has excellent moisture resistance, anti-mildew, anti-bacterial, bioinert, biocompatible, and without toxicity or irritant. It can be used on the surface of mental, glass, resin, plastic, rubber, ceramic, paper and many kinds of materials. It has been widely used in aviation, aerospace, defense, microelectronics, semiconductor, medical, heritage conservation and other fields. It has been considered to be the the highest standard of protective coating on electronic components, medical components, rubber products and metal parts.This is the first time that Parylene coating is used in surface modification of oral biomaterials. Its feasibility is evalued by various performance tests. This research provides new method to surface modification of oral biomaterial, and also provides basis to futher researchs.1. Type choice of Parylene which used in surface modification of silicone elastomer.We observe the cross-section of specimens after three types Parylene coating by SEM. It is found that the combination between Parylene N and silicone elastomer is better than Parylene C or Parylene D. Befor Parylene coating, the surface of silicone elastomer is porous. After Parylene coating, it is dense, and there are scattered globular protuberance on the surface but without any holes. We also test the roughness of silicone elastomer. Results show that the roughness of silicone elastomer after Parylene coating is lower than before Parylene coating.2. Research on bacterial adhesion to silicone elastomer before and after Parylene coating.This part is mainly about Candida albicans and Streptococcus mutans. We use several methods to test the adhesion of Candida albicans and Streptococcus mutans to silicone elastomer and resin before and after Parylene coating. Cells count assay shows that Parylene can reduce Candida albicans and Streptococcus mutans adhesion to silicone elastomer and resin. XTT reduction assay is used to quantify the viable cells in biofilm. We found that XTT absorbance readings ofsilicone elastomer and resin after Parylene coating decreased significantly compared before Parylene coating. SEM results show that hyphal forms of Candida albicans were scarcely observed on the surface of silicone elastomer after Parylene coating. Streptococcus mutans are loosely attached to the surfaces of silicone elastomers A2186 and lucitone 199 resin, with significantly decreased biomass and fewer extracellular matrixes visualized. It means that Parylene has the ability of anti-bacterial biofilm formation. CLSM results show that Parylene can reduce bacterial adhesion to the suface of material, but it is not bactericidal.3. Research on color stability of silicone elastomer before and after Parylene coating.We use three types of common cleaning: 75% alcohol, 0.0125%NaClO, distilled water and four types of exogenous dyes which is daily frequently contacted: red wine, coffee, tea, and cola. By testing and analysising the color values of specimens before and after the experiment, the color stability of silicone elastomer before and after Parylene coating with the influence of the seven liquids above is got. Results show that with the effect of three cleaing and four exogenous dyes Parylene can increase the color stability of silicone elastomer A-2186 and ZY-1.4. Research on suface wettability of silicone elastomer before and after Parylene coating.We use four liquids (water, glycerol, formamide and diiodomethane) with dfferent polar, and test their contact angles on the surface of silicone elastomer. After that the surface free energies of the specimens and their polar and disperse components were calculated from contact angle measurements. Results show that Parylene can reduce the contact angle between the four liquids and silicone elastomer. The surface free energy of silicone elastomer and their polar and disperse components all increase after Parylene coating.5. Research on mechanical property of silicone elastomer before and after Parylene coating.We test the tear strength, tensile strength, elongation, permanent deformation rate and Shore hardness of silicone elastomer before and after Parylene coating to evaluate the influence of Parylene on the mechanical property of silicone elastomer. Results show that the tear strength, tensile strength, elongation and Shore hardness of silicone elastomer increase in ideal value range after Parylene coating. The permanent deformation rate of silicone elastomer doesn't change much after Parylene coating.6. Research on water absorption and solution of silicone elastomer before and after Parylene coating.We test the water absorption and solution of silicone elastomer before and after Parylene coating by weight method. Results show that before Parylene coating, the water absorption of silicone elastomer increases with the time passing by. After Parylene coating, the water absorption of silicone elastomer doesn't increase much after 4 weeks. Before Parylene coating, the solution of silicone elastomer increases with the time passing by. After Parylene coating, the solution of silicone elastomer doesn't increase much after 4 weeks.Through the six parts above, we can conclude that Parylene coating technique can be used in the surface modification of silicone elastomer. It can reduce bacterial adhesion to silicone elastomer and its water absorbtion. It also improves the color stability and wettability of silicone elastomer. In a word, Parylene coating can significantly improve the performance of silicone elastomer.