Programmable Matrix‐Filler Interactions in Bio‐Inspired Polymer Nanocomposites

ABSTRACT Biological nanocomposites, such as spider silk and bamboo, employ sacrificial dynamic interactions across multiple length scales to build hierarchical structures with tunable and robust mechanics. Inspired by these systems, we programmed non‐covalent matrix‐filler interactions within an active polymer–peptide hybrid to achieve mechanically‐ and architecturally‐tunable nanocomposites. Self‐assembling poly(β‐benzyl‐ l ‐aspartate) (PBLA) blocks are grafted onto cellulose nanocrystals (CNCs) and incorporated into a non‐chain extended peptide−polyurea (PPU) hybrid, in which ordered PBLA blocks, coupled to a hydrophobic poly(dimethylsiloxane) (PDMS) block, direct matrix‐filler interactions to the soft domain. This design enables control of the self‐assembled morphology and mechanical performance. We explore PPU/CNC self‐assembly as a function of CNC surface chemistry by comparing peptide‐grafted and non‐grafted CNCs. Incorporation of peptide‐grafted CNCs redirects interactions to the PBLA blocks within the PPU. At 5 wt% CNC content, urea ordering is maintained, and dynamic peptide–matrix interactions lead to a pseudo‐dual network, preserving elastic modulus with enhanced extensibility (∼300% vs. 175%) and toughness (0.54 vs. 0.21 MJ/m 3 ) relative to the PPU. Hysteresis and fractography experiments reveal improved stress transfer and energy storage through targeted PBLA interactions. Overall, this work demonstrates how this active‐matrix strategy can program assembly pathways in scalable polymer nanocomposites for applications ranging from coatings to biomedicine.