The primary goal of this proposal is to develop novel dental nanocomposite materials using hydroxyapatite nanocrystals and biopolymers containing two motifs identified by natural and artificial evolution processes. Elastin polymers conjugated with hydroxyapatite (HAP) specific peptides will be synthesized using bacterial biosynthetic methods. Elastin is a biopolymer that is native to the extra cellular matrix of connective tissues, and is known to possess both strength and elasticity. Hydroxyapatite specific peptide (HSP) motif has been previously identified by us through a directed evolution process (combinatorial phage display). HSP has been shown to bind to HAP surface, and to nucleate the HAP crystals through a biomineralization process. Bacterial biosynthetic methods will be used to synthesize hydroxyapatite specific peptide conjugated with elastin biopolymer. This biopolymer will have a precisely controlled and defined chemical composition. Physical properties and functions can be encoded in the amino acid sequences of the biopolymers. Dental composite materials will be developed through a biomineralization process on the proposed biopolymers or through the blending of the proposed biopolymers with monodisperse HAP nanocrystals which will be synthesized separately. The resulting composite structures will have a low viscosity and will be able to form and retain a desired shape at room temperature. Through additional chemical modification of the biopolymer using methacrylate anhydride, the polymer will have the ability to cross-link through light exposure or chemical treatment and to form solid composite resins. The proposed dental nanocomposite materials with HSP motifs will improve adhesive bonding to dentin and enamel surfaces, durability, toughness, biocompatibility, and aesthetic appearance. There are many advantages of the proposed dental composite materials: Controlled biosynthesis allows the tuning of both the physical and biological properties of biopolymers by changing their chemical composition or molecular weight. HSP motif conjugated with target biopolymer can control the nucleation process of the hydroxyapatite crystals. Elastic properties of the elastin polymer can be controlled by small modification of the repeating units, pH, ionic strength, and cross-linkages. The proposed biopolymer can be programmed to transform from the highly soluble homogeneous solution state at room temperature (25?C) into ordered nanocomposite materials at physiological temperature (38 ?C). Successful completion of the proposed research will provide novel dental composite materials with desired physical and biological properties. The resulting dental composite materials can be applied to dental practice without modification of the current instrumentation. The resulting nanocomposite materials will possess improved adhesive bonding to dentin and enamel surfaces, durability, toughness, biocompatibility, and aesthetic appearance. To our knowledge, the proposed research is a novel approach to the design of functional materials through the conjugation of natural and directed evolution products.
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