Design and Characterization of Self-Assembling Peptide (SAP)–Polyethylene Glycol (PEG) Multiblock Copolymers (MBCP) Thin Films

Abstract

Self-assembling peptides (SAPs) provide a versatile, biocompatible platform for soft biomaterials, but their application in mechanically robust, processable polymers remains limited. We report a peptide–polyethylene glycol (PEG) multiblock copolymer (MBCP) using the amphipathic β-sheet-forming SAP K(FEFK)2K as a physical cross-linker. Synthesized via copper-free strain-promoted azide–alkyne cycloaddition (SPAAC), the MBCP was solution-cast from water into free-standing films whose properties were governed by the peptide’s ability to form stable β-sheet fibers and aggregates. Films were tough and plastic at room temperature, but elastomeric above PEG’s melting point (>60 °C). At high temperature, a micro- and nano-scale phase-separated morphology emerged, with peptide fiber-rich domains embedded in a soft, amorphous PEG matrix. At room temperature, only microphase separation persisted, while PEG crystallization produced a semicrystalline matrix in which peptide fibers restricted large crystal growth and were likely segregated at crystallite interfaces. Extensive mechanical testing revealed resilient films with shape-recovery behavior.