Study On The Preparation Of Hybrid Antibacterial Coatings Used On Denture Base

Poly(methyl methacrylate) based resins are widely used in dentistry due to theproperties of low cost, easy processing and good biocompatibility. As an importantpart of artificial denture, the denture base is mainly made of PMMA resin. However,the research results revealed that the wearing of denture could break the ecologicalbalance of the oral cavity. Then some microorganisms such as Candida albicans andStreptococcus mutans would accumulate and grow on the PMMA resin basedappliances and cause oral diseases such as denture stomatitis and secondary caries.The traditional cleaning methods have the disadvantages of short antibiosis time,tedious handling and damaging the surface of the resin. Therefore, improving theantimicrobial activity of the denture materials becomes one of the most importantresearch areas in dentistry.It is well known that silver is widely used in antibacterial materials because of itshigh antibacterial activity and broad antibacterial spectrum. Silver loaded inorganicantibacterial agents are superior in the aspects of safety, durability and heat resistance,compared with the conventional organic antibacterial materials. Ordered mesoporoussilica possesses the advantages of large specific surface area, diversity of morphology,easy functionalization and good biocompatibility, which makes it a good candidate forthe silver carrier material. Commonly, the antibacterial agents are directly doped in thepolymer resin. However, most of the inner antibacterial agents may not play anyantibacterial effect at all. Besides, the excess using of antibacterial agents may affectthe mechanical properties of the resin. According to what has been mentioned above,the using of antibacterial coatings is a preferable strategy for improving the antibacterial activity of the denture base.In this dissertation, we aim at the design and preparation of antibacterial coatingsthat can be used on denture base. Several kinds of silver loaded mesoporous silicaspheres have been prepared and doped in a designed hybrid coating as antibacterialagents to fabricate antibacterial coatings.In chapter1, we made a brief introduction of denture base and the problemsgenerated when using it. Then we reviewed the development and classification ofantibacterial agents, antibacterial coatings and mesoporous materials.In chapter2, we prepared a hybrid coating by mixing a polymer coating solutionand a hybrid silica sol. The polymer coating solution was prepared byco-polymerization of glycidyl methacrylate (GMA), acrylic acid (AA) and methylmethacrylate (MMA). The hybrid silica sol was prepared by co-hydrolysis andco-condensation of γ-glycidyloxypropyltrimethoxysilane (KH560) and tetraethylorthosilicate (TEOS). The polymer could increase the adhesion while the silica solcould increase the hardness of the hybrid coatings. Besides, the epoxy groups on thepolymer chain and silica sol could form linking structure, which could further increasethe hardness of the coatings. A series of hybrid coatings with differentorganic/inorganic component weight ratio were prepared and the hardness, adhesionand resistance to rupture of the coatings were tested. As the amount of TEOS and thesilica sol component increased, the hardness of the coatings increased while theadhesion and resistance of rupture both decreased. Considering the balance of theproperties, we chose the hybrid coating with the KH560/TEOS molar ratio of2/5andthe organic/inorganic components weight ratio of9/1. The hardness of the coatingreached4H and the adhesion reached the highest level according to the test method.On the other hand, to increase the retention force of the resin, we have successfullygrafted PEG molecular on the hybrid coating surface through the reaction between theisocyanate group of HDI and the hydroxyl group of PEG, which was proved by FTIRspectroscopy and water contact angle test. The contact angle of original hybrid coatingis64°. After PEG-1000and PEG-2000were grafted, the contact angle decreased to46°and35°respectively.In chapter3, we prepared pure mesoporous pure silica spheres and studied theinfluence of the factors including the adding method of precursor, the type and theamount of catalysis and the mass ratio of water/ethanol on the size and morphology of the silica spheres. We found that the using of ammonia as catalyst and adding theprecursor by several times are helpful to avoid the formation of aggregation.Increasing the amount of ammonia and the mass ratio of ethanol/water could increasethe size of the silica spheres. Finally, the silica spheres with the size of400nm andgood dispersity were prepared and loaded with AgCl, and then dispersed in the hybridcoating to fabricate antibacterial coatings. The coatings showed high antibacterialactivity. When the weight ratio of the silica spheres reached2%, the reduction rate ofthe fungus was higher than99%. The hardness of the coatings reached4H and theadhesion reached the best level according to the test method.In chapter4, the amino, thiol and sulfonic group functionalized mesoporous silicaspheres were prepared and used as silver carrier. We studied the influence of the typeand amount of organic groups on the structure of the silica spheres and the loadingamount of silver. We found that the thiol-functionalized silica spheres possess moreordered mesopores, higher silver loading amount, but a much lower releasing rate ofsilver ions. The sulfonic group functionalized silica spheres possess a high loadingamount and a high releasing rate of silver ions at the same time. The samples showedthe highest antibacterial activity in the MBC test on Candida albicans were doped inthe hybrid coating with different weight ratio. The as prepared coatings exhibited highantibacterial activity, high hardness and good adhesion to the substrates. The reductionrate of the fungus reached100%when the weight ratio of antibacterial agent reached2%in the coating. The hardness of the coatings reached4H and the adhesion reachedthe best level according to the test method.In chapter5, hollow mesoporous aluminosilica spheres were prepared byalkaline etching method and loaded with silver chloride to used as antibacterial agent.The hollow mesoporous aluminosilica spheres possess radially oriented orderedmesopores and a high loading amount of AgCl (2.75mmol/g). Then the AgCl loadedhollow mesoporous aluminosilica spheres were doped in the hybrid coating withdifferent weight ratio to fabricate antibacterial coatings. The antibacterial activity ofthe coatings was tested against the fungus Candida albicans. As the doping amountincreased to2wt%, the reduction rate of the fungus reached100%. The hardness ofthe coating reached4H and the adhesion reached the best level according to the testmethod.To sum up, all the hybrid antibacterial coatings exhibited high antibacterial activity, high hardness and good adhesion to the PMMA substrate. Thus the coatingsshowed a great potential in the application in denture base.