Nanocomposites of repeat sequence proteins and phyllosilicate clays and their preparation
Inventors
Drummy, Lawrence F. • McAuliffe, Joseph C. • Naik, Rajesh R. • Vaia, Richard A.
Assignees
United States Department of the Air Force
Publication Number
US-8445641-B2
Publication Date
2013-05-21
Expiration Date
2026-08-22
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Abstract
Nanocomposites of repeat sequence protein polymers and phyllosilicates demonstrated improved material properties, for example, improved elasticity, and are useful as suture, tissue scaffolding, and biodegradable composite materials.
Core Innovation
The invention is directed to compositions comprising nanocomposites of a phyllosilicate and one or more repeat sequence protein polymers. One embodiment uses Na+ Montmorillonite (MMT), a smectite clay, combined with a repeat sequence protein polymer derived from silk and elastin termed SELP. The invention also includes chemically modified SELP analogues reacted with succinic anhydride, and phyllosilicates such as attapulgite. Additives like plasticizers or protein crosslinking agents can be incorporated to tailor the nanocomposites.
These nanocomposites are dispersions of phyllosilicate sheets within a protein matrix achieved through interactions between positively charged lysine residues of the protein and negatively charged phyllosilicate sheets. Electrostatic forces dominate long-range interactions, while hydrogen bonding governs local interactions, resulting in exfoliated morphologies or clustering depending on protein charge. The nanocomposites demonstrate altered or improved material properties, including enhanced elasticity and tensile properties, compared to the repeat sequence protein polymer alone.
The problem addressed is that recombinant proteins like SELP often have mechanical properties inferior to natural structural proteins such as silk or elastin. The invention solves the need for improved mechanical and thermal behaviors in such recombinant proteins for in-vivo and industrial applications by forming nanocomposites with phyllosilicates, thereby enhancing material properties like elastic modulus, tensile strength, morphology, and thermal expansion.
Claims Coverage
The patent includes two independent claims covering nanocomposites of repeat sequence protein polymers and phyllosilicates, and methods for making such nanocomposites. The main inventive features relate to the composition, material properties, additives, morphology, and preparation process of these nanocomposites.
Nanocomposite comprising repeat sequence protein polymer and phyllosilicate
A nanocomposite wherein the repeat sequence protein polymer is a silk elastin like protein (SELP) combined with a phyllosilicate selected from montmorillonite, bentonite, hectorite, saponite, beidellite, attapulgite, and stevensite.
Inclusion of additives to tailor properties
The nanocomposite can further comprise a plasticizer, a protein cross linking agent, or both. The plasticizers include adipic acid derivatives, azeic acid derivatives, benzoic acid derivatives, diphenyl derivatives, citric acid derivatives, epoxides, glycolates, isophthalic acid derivatives, maleic acid derivatives, phosphoric acid derivatives, phthalic acid derivatives, polyesters, trimelitates, polyalkylene glycols, polysaccharides, disaccharides, and monosaccharides. Specific examples include polyethylene glycol and trehalose as plasticizers, and glutaraldehyde as a cross linking agent.
Altered material properties of the nanocomposite
The nanocomposite exhibits at least one altered material property compared to the repeat sequence protein polymer alone, such as tensile strength, elastic modulus (with increases of at least 10%), morphology including exfoliated and generally homogeneous morphology, coefficient of thermal expansion (lowered), and altered zeta potential.
Use of the nanocomposite as biomedical or structural material
The nanocomposite is suitable as suture material, tissue scaffold material, or biodegradable structural material.
Method for making nanocomposites
A method includes selecting a repeat sequence protein polymer (SELP), selecting a phyllosilicate, suspending the phyllosilicate in aqueous liquid, mixing the polymer and suspension, optionally adding plasticizers or crosslinking agents, casting the mixture on a surface, and drying to form the nanocomposite.
Specific protein polymer sequences
The repeat sequence protein polymer can be selected from sequence variants corresponding to SEQ ID No:6 through SEQ ID No:12.
The independent claims collectively cover the composition of nanocomposites comprising silk elastin like protein polymers and various phyllosilicates with optional additives that provide improved mechanical and thermal properties, suitable morphologies, and practical applications, as well as the methods for manufacturing these nanocomposites by mixing and drying dispersions.
Stated Advantages
Improved elasticity with elastic modulus values increasing by 10% to 90% over protein alone.
Altered tensile properties including increased tensile strength.
Altered morphology, particularly exfoliated and homogeneous nanocomposite structures.
Improved thermal properties such as decreased coefficient of thermal expansion and increased glass transition temperature.
Retained variable percentages of water or solvent to tailor material properties.
Documented Applications
Use as suture material.
Use as tissue scaffold material.
Use as artificial tissue material.
Use as biodegradable structural materials including industrial materials.
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