Silk fibroin (herein referred to as silk) is a broadly applicable biologically-derived polymer with customizable mechanical properties and limited foreign body response <i>in vivo</i>. The primary structure of silk mainly comprises non-reactive amino acids, including alanine and glycine, rendering it challenging to modify via traditional synthetic approaches. Previously reported methods to chemically modify the side chains on silk are limited to introducing functional groups to target specific interactions with biomolecules (e.g., cell attachment, protein adsorption). Functionalization strategies that minimize interactions with biomolecules are equally important for implantable device applications, such as preventing bacterial colonization or cell attachment of certain areas of the implant. Such modifications are seldom reported, and the few reports that exist employ spray coating or other physical modifications of solid silk constructs. Because these strategies modify an already formed solid material, they cannot be used to create constructs with homogenous chemistry, nor can be used to pattern specific construct regions – two features that are desirable when creating an implantable biomaterial.<br/><br/>We report a new synthetic approach to chemically-modify silk side chains with fluorocarbon chains. First, the carboxylic acid content of the silk is enhanced via modification of primary alcohol groups on serine, tyrosine, and threonine residues. Carboxylic acids are then conjugated to ethylene diamine via carbodiimide coupling, resulting in enhanced primary amine content. Finally, a hypervalent iodonium salt containing a fluorocarbon component is added to the silk, where fluorocarbon chains are covalently bound to primary amines via an F-capping reaction. Chemically-modified silks are readily soluble in the organic solvent hexafluoroisopropanol, and thus, can easily be cast into films or used to coat existing solid structures. In this talk, we will discuss the versatility of this modification strategy by utilizing hypervalent iodonium salts with varying fluorocarbon chain length. We will present how wettability and surface chemistry change when different fluorocarbon chain lengths are conjugated to silk. Additionally, we will present proof-of-concept performance testing that illustrates the interactions of modified silk materials with biological systems.

Functionalizing silk fibroin with fluorocarbons via F-capping chemistry to create multiuse inks

2019 Spring National Meeting

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