Inspired by the nontrivial and controlled movements of molecular machines, we report an azobenzene‐based molecular shuttle PR2, which can perform light‐gated ion transport across lipid membranes. The amphiphilicity and membrane‐spanning molecular length enable PR2 to insert into the bilayer membrane and efficiently transport K+ (EC50=4.1 μm) through the thermally driven stochastic shuttle motion of the crown ether ring along the axle. The significant difference in shuttling rate between trans‐PR2 and cis‐PR2 induced by molecular isomerization enables a light‐gated ion transport, i.e., ON/OFF in situ regulation of transport activity and single‐channel current. This work represents an example of using a photoswitchable molecular machine to realize gated ion transport, which demonstrates the value of molecular machines functioning in biomembranes.

Peptide-based supramolecular hydrogels have attracted great attention due to their good biocompatibility and biodegradability and have become promising candidates for biomedical applications. The bottom-up self-assembly endows the peptides with a highly ordered secondary structure, which has proven to be an effective strategy to improve the mechanical properties of hydrogels through strong physical interactions and energy dissipation. Inspired by the excellent mechanical properties of spider-silk, which can be attributed to the rich β-sheet crystal formation by the hydrophobic peptide fragment, a hydrophobic peptide (HP) that can form a β-sheet assembly was designed and introduced into a poly­(vinyl alcohol) (PVA) scaffold to improve mechanical properties of hydrogels by the cooperative intermolecular physical interactions. Compared with hydrogels without peptide grafting (P-HP0), the strong β-sheet self-assembly domain endows the hybrid hydrogels (P-HP20, P-HP29, and P-HP37) with high strength and toughness. The fracture tensile strength increased from 0.3 to 2.1 MPa (7 times), the toughness increased from 0.4 to 21.6 MJ m–3 (54 times), and the compressive strength increased from 0.33 to 10.43 MPa (31 times) at 75% strain. Moreover, the hybrid hydrogels are enzymatically degradable due to the dominant contribution of the β-sheet assembly for network cross-linking. Combining the good biocompatibility and sustained drug release of the constructed hydrogels, this hydrophobic β-sheet peptide represents a promising candidate for the rational design of hydrogels for biomedical applications.

Hydrogel actuators, capable of generating reversible deformation in response to external stimulus, are widely considered as new emerging intelligent materials for applications in soft robots, smart sensors, artificial muscles, and so on. Peptide self‐assembly is widely applied in the construction of intelligent hydrogel materials due to their excellent stimulus response. However, hydrogel actuators based on peptide self‐assembly are rarely reported and explored. In this study, a pH‐responsive peptide (MA‐FIID) is designed and introduced into a poly(N‐isopropyl acrylamide) backbone (PNIPAM) to construct bilayer and heterogeneous hydrogel actuators based on the assembly and disassembly of peptide molecules under different pH conditions. These peptide‐containing hydrogel actuators can perform controllable bending, bucking, and complex deformation under pH stimulation. Meanwhile, the Hofmeister effect of PNIPAM hydrogels endows these peptide‐containing hydrogels with enhanced mechanical strength, ionic stimulus response (CaCl2), and excellent shape‐memory property. This work broadens the application of supramolecular self‐assembly in the construction of intelligent hydrogels, and also provides new inspirations for peptide self‐assembly to construct smart materials.

Short peptides that can respond to external stimuli have been considered as the preferred building blocks to construct hydrogels for biomedical applications. In particular, photoresponsive peptides that are capable of triggering the formation of hydrogels upon light irradiation allow the properties of hydrogels to be changed remotely by precise and localized actuation. Here, we used the photochemical reaction of the 2-nitrobenzyl ester group (NB) to develop a facile and versatile strategy for constructing photoactivated peptide hydrogels. The peptides with high aggregation propensity were designed as hydrogelators, which were photocaged by a positively charged dipeptide (KK) to provide strong charge repulsion and prevent self-assembly in water. Light irradiation led to the removal of KK and triggered the self-assembly of peptides and the formation of hydrogel. Light stimulation endows spatial and temporal control, which enables the formation of hydrogel with precisely tunable structure and mechanical properties. Cell culture and behavior study indicated that the optimized photoactivated hydrogel was suitable for 2D and 3D cell culture, and its photocontrollable mechanical strength could regulate the spreading of stem cells on its surface. Therefore, our strategy provides an alternative way to construct photoactivated peptide hydrogels with wide applications in biomedical areas.

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