Methods for stepwise deposition of silk fibroin coatings

Abstract

The invention provides a method for the controlled assembly of layered silk fibroin coatings using aqueous silk fibroin material. The methods described herein can be used to coat substrates of any material, shape, or size. Importantly, the described methods enable control of the biomaterial surface chemistry, thickness, morphology and structure using layered thin film coatings, or bulk coatings. Furthermore, the methods can be performed in all water and do not require intensive chemical processing enabling controlled entrapment of labile molecules such as, drugs, cytokines, and even cells or viruses to generate functional coatings that can be used in a variety of applications.

What is claimed is: 
     
         1 . A method for preparing a silk fibroin biomaterial coating on a substrate comprising:
 a. contacting a substrate with an aqueous silk fibroin solution such that the solution forms a first layer upon the substrate; and   b. dehydrating said first layer by exposure of the layer to a flow of dehydrating gas.   
     
     
         2 . The method of  claim 1 , further comprising step (c), step (d) and step (e):
 c. contacting the dehydrated first layer with a silk fibroin solution such that the solution forms a second layer upon the dehydrated first layer;   d. dehydrating said second layer by exposure of the second layer to a flow of dehydrating gas;   e. repeating steps (c) and (d) until the desired numbers of layers are deposited upon the substrate resulting in a layered coating on said substrate.   
     
     
         3 . The method of  claim 2 , wherein each layer is washed in water prior to dehydrating. 
     
     
         4 . The method of  claim 3 , wherein the water further comprises methanol or a solution, treatment or material that induces loss of water from the coating. 
     
     
         5 . The method of  claim 2 , wherein thickness of at least one layer is from about 1 to about 12 nm or from about 50 nm to about 5,000 nm 
     
     
         6 . The method of  claim 1 , wherein thickness of the layer is from about 1 to about 12 nm or from about 50 nm to about 5,000 nm. 
     
     
         7 . The method of  claim 1 , wherein the silk fibroin biomaterial coating has a uniform distribution of a granule morphology. 
     
     
         8 . The method of  claim 1 , wherein the dehydrating gas is nitrogen gas (N 2 ) or hot air. 
     
     
         9 . The method of  claim 1 , wherein the thickness of each deposited layer is controlled by:
 (i) controlling the concentration of salt in the silk fibroin solution used to form the layer, wherein the concentration of salt is increased in order to favor deposition of silk fibroin onto said substrate or onto the dehydrated layer when said substrate or said dehydrated layer is hydrophobic, and wherein the concentration of salt is decreased in order to favor deposition of silk fibroin onto said substrate or onto the dehydrated layer when said substrate or said dehydrated layer is hydrophilic;   (ii) controlling the concentration of fibroin in the silk fibroin solution used to form the layer, such that the concentration of fibroin in the silk fibroin solution is increased to favor deposition of silk fibroin onto said substrate or onto the dehydrated layer;   (iii) controlling the pH of the silk fibroin solution used to form the layer, such that when the substrate is a negatively charged substrate, the pH of the silk fibroin solution is lowered in order to favor deposition of the silk fibroin onto said substrate or onto the dehydrated layer; and when the substrate is a positively charged substrate, the pH of the silk fibroin solution is increased in order to favor deposition of the silk fibroin onto said substrate or onto the dehydrated layer; or   (iv) controlling the ratio of methanol to water used in washing each layer prior to dehydrating each layer, wherein a higher methanol content favors deposition of the silk fibroin onto said substrate or onto the dehydrated layer.   
     
     
         10 . The method of  claim 1 , wherein the substrate is a plastic, wood, glass, ceramic, leather, cloth, synthetic, or metal object. 
     
     
         11 . The method of  claim 1 , wherein the substrate is a biomedical device, a biomaterial, biosensor, a tissue engineering scaffold, a stent, a suture, a mesh, a plate, a screw, a catheter, a tubing, a gel, or a 3D porous scaffold. 
     
     
         12 . The method of  claim 1 , wherein the silk fibroin solution further comprises a bioactive agent. 
     
     
         13 . The method of  claim 12 , wherein the bioactive agent is a cell, a virus, a metal, or a therapeutic agent. 
     
     
         14 . The method of  claim 13 , wherein the bioactive agent is a therapeutic agent selected from the group consisting of a protein, a peptide, a nucleic acid, a peptide nucleic acid (PNA), an aptamer, an antibody, and a small molecule. 
     
     
         15 . The method of  claim 12 , wherein the bioactive agent is selected from the group consisting of an antiproliferative agent, an antineoplastic agent, an antiinflammatory agent, an antiplatelet agent, an anticoagulant agent, an antifibrin agent, an antithrombin agent, an antimitotic agent, an antibiotic agent, and an antioxidant. 
     
     
         16 . The method of  claim 12 , further comprising contacting the substrate with an aqueous silk fibroin solution containing no added bioactive material. 
     
     
         17 . A coated substrate as produced by the method of  claim 1 . 
     
     
         18 . A formulation for controlled release of a therapeutic agent, wherein the composition comprises a coated substrate of  claim 12 . 
     
     
         19 . The pharmaceutical formulation of  claim 18 , wherein the therapeutic agent is selected from the group consisting of a protein, a peptide, a nucleic acid, a peptide nucleic acid (PNA), an aptamer, an antibody, and a small molecule. 
     
     
         20 . The pharmaceutical formulation of  claim 18 , wherein the therapeutic agent is selected from the group consisting of an antiproliferative agent, an antineoplastic agent, an antiinflammatory agent, an antiplatelet agent, an anticoagulant agent, an antifibrin agent, an antithrombin agent, an antimitotic agent, an antibiotic agent, and an antioxidant.