Patent ID: 7321022

Claim:
A method of controlling the stability of a film comprising exposing the film to an oxidizing agent or a reducing agent, wherein the film comprises a plurality of layers of polypeptides, wherein adjacent layers are oppositely charged, wherein a first layer comprises a first layer polypeptide and a second layer comprises a second layer polypeptide, wherein the first layer polypeptide is not a homopolymer, is at least 15 amino acid residues long, has a balance of charge at pH 7 greater than or equal to approximately one-half of its total length and comprises a sulfhydryl-containing amino acid residue and one or more first amino acid sequence motifs, wherein each of the first amino acid sequence motifs has a length of 5 to 15 amino acid residues and a balance of charge at pH 7 greater than or equal to approximately one-half of its length; wherein the second layer polypeptide is at least 15 amino acid residues long, and has a balance of charge at pH 7 greater than or equal to approximately one-half of its length and of opposite polarity to that of the first layer polypeptide, and comprises one or more second amino acid sequence motifs, wherein each of the second amino acid sequence motifs has a length of 5 to 15 amino acid residues and a balance of charge at pH 7 greater than or equal to approximately one-half of its length, with the proviso that: 1) the first layer polypeptide comprises two first amino acid sequence motifs that are the same or different and are covalently joined by a glycine linker or a proline linker; or 2) the second layer polypeptide comprises two second amino acid sequence motifs that are the same or different and are covalently joined by a glycine linker or a proline linker.