Studies on the fabrication of polymer–protein hybrid self-assemblies have aroused great interest over the past years because of a broad range of applications of the materials in drug/protein delivery, biosensors, and enhancement of protein stability. The hybrid assemblies are usually fabricated from polymer–protein bioconjugates, which may suffer from the damages to the protein structures and the loss of functionalities in the synthesis. Herein, we report a simple and efficient approach to the fabrication of vesicle-like structures based on coassembly of homopolymer chains and protein molecules. At room temperature, poly­(N-isopropylacrylamide) (PNIPAM) and bovine serum albumin (BSA) are able to form complexes through hydrophobic interactions in aqueous solution. Upon heating to a temperature above the cloud point of PNIPAM, vesicle-like structures with collapsed PNIPAM in the walls and BSA at the surfaces are formed. The size and membrane thickness of the assemblies can be tuned by the molar ratio of PNIPAM to BSA. The hydrophobic interaction between PNIPAM and BSA plays a key role in the complex formation and self-assembly process. The complexes and assembled structures are analyzed by using micro differential scanning calorimetry, light scattering, and transmission electron microscopy. BSA in the assemblies retains over 90% of its activity, and the protein stability is enhanced because of the hydrophobic interaction between proteins and polymers. This approach allows us to prepare polymer–protein assemblies without bioconjugate synthesis. Meanwhile, possible damages to the protein structures and the loss of bioactivities of proteins can be avoided.

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Synthesis and self-assembly of bioconjugates composed of proteins and synthetic molecules have been widely studied because of the potential applications in medicine, biotechnology, and nanotechnology. One of the challenging research studies in this area is to develop organic solvent-free approaches to the synthesis and self-assembly of amphiphilic bioconjugates. In this research, dialysis-assisted approach, a method based on unimer-aggregate equilibrium, was applied in the coassembly of lysozyme and conjugate of cholesterol and glutathione (Ch-GSH). In phosphate buffer solution, amphiphilic Ch-GSH conjugate self-assembles into vesicles, and the vesicle solution is dialyzed against lysozyme solution. Negatively charged Ch-GSH unimers produced in the unimer-vesicle exchange equilibrium, diffuse across the dialysis membrane and have electrostatic interaction with positively charged lysozyme, resulting in the formation of Ch-GSH-lysozyme bioconjugate. Above a critical concentration, the three-component bioconjugate molecules self-assemble into bioactive vesicles.

Main observation and conclusion Natural biopolymer‐based hydrogels have been extensively studied in recent years due to their excellent biocompatibility. However, the preparation of multi‐functional and tough natural biopolymer‐based hydrogels is still a challenging problem. Herein, a natural biopolymer‐based hydrogel is prepared using gelatin and carboxymethyl chitosan (CMCS) through a one‐step soaking method. The prepared hydrogel without any synthetic polymers and crosslinking agents has a fully physical crosslinking structure. Due to the hydrophobic interaction brought by the Hofmeister effect, the mechanical properties of soaked hydrogels (tensile stress and strain can reach 3.77 MPa and 1082%) are superior to conventional protein hydrogels. In addition, the prepared gelatin/carboxymethyl chitosan (Gel/CMCS) hydrogels exhibit a variety of appealing properties, including good shape memory, fatigue resistance, electrical conductivity, water retention, drug releasing, antibacterial property, and recyclability. This strategy opens up a new horizon to fabricate hydrogels with excellent mechanical properties and multiple functions, which can extend their applications in the biomedicine area and other related fields.

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