Metrics & MoreArticle Recommendations CONSPECTUS: Protein thin films (PTFs) with tunable structure and function can offer multiple opportunities in various fields such as surface modification, biomaterials, packaging, optics, electronics, separation, energy, and environmental science. Although nature may offer a variety of examples of high-level control of structure and function, e.g., the S layer of cells, synthetic alternatives for large-area protein-based thin films with fine control over both biological function and material structure are a key challenge, especially when aiming for facile, low-cost, green, and large-scale preparation as well as a further extension of function, such as the encapsulation and release of functional building blocks. Therefore, regarding the structure and function of PTFs, we will first briefly comment on the problems associated with PTF fabrication, and then, regarding the basis of our long-term research on protein-based thin films, we will summarize the new strategies that we have developed in recent years to explore and control the structure and function of PTFs for frontier research and practical applications.Inspired by naturally occurring protein amyloid fibrillization, we proposed the amyloid-like protein aggregation strategy to assemble proteins into supramolecular 2D films with extremely large sizes and enduring interfacial adhesion stability. This approach opened a new window for PTF fabrication in which the spontaneous interfacial 2D aggregation of protein oligomers instead of traditional 1D protofibril elongation directs the assembly of proteins. As a result, the film morphology, thickness, porosity, and function can be tailored by simply tuning the interfacial aggregation pathways.We further modified amyloid-like protein aggregation to develop chemoselective reaction-induced protein aggregation (CRIPA). It is well known that chemoselective reactions have been employed for protein modification. However, the application of such reactions in PTF fabrication has been overlooked. We initiated this new strategy by employing thiol−disulfide exchange reactions. These reactions are chemoselective toward proteins containing specific disulfide bonds with high redox potentials, resulting in amyloid-like aggregation and thin film formation. Functional proteins with immunity to such reactions can be encapsulated in thin films and released on demand without a loss of activity, opening a new avenue for the development of functional PTFs and coatings. Finally, the resultant amyloid-inspired PTFs, as a new type of biomimetic materials, provide a good platform for integration with various biomedical functions. Here, the creation of bioactive surfaces on virtually arbitrary substrates by amyloid-like PTFs will be discussed, highlighting antimicrobial, antifouling, molecular separation, and interfacial biomineralization activities that exceed those of their native protein precursors and synthetic alternatives.

The adhesion and modification of wet surfaces by an interfacial adlayer remain a key challenge in chemistry and materials science. Herein, we report a transparent and biocompatible amyloid-like nanofilm that breaks through the hydration layer of a wet surface and achieves strong adhesion with a hydrogel/tissue surface within 2 s. This process is facilitated by fast amyloid-like protein aggregation at the air/water interface and the resultant exposure of hydrophobic groups. The resultant protein nanofilm adhered to a hydrogel surface presents an adhesion strength that is 20 times higher than the maximum friction force between the upper eyelid and eyeball. In addition, the nanofilm exhibits controllable tunability to encapsulate and release functional molecules without significant activity loss. As a result, therapeutic contact lenses (CLs) could be fabricated by adhering the functionalized nanofilm (carrying drug) on the CL surface. These therapeutic CLs display excellent therapeutic efficacy, showing an increase in cyclosporin A (CsA) bioavailability of at least 82% when compared to the commercial pharmacologic treatment for dry eye syndrome. Thus, this work underlines the finding that the bioinspired amyloid-like aggregation of proteins at interfaces drives instant adhesion onto a wet surface, enabling the active loading and controllable release of functional building blocks.

Proteins have been adopted by natural living organisms to create robust bioadhesive materials, such as biofilms and amyloid plaques formed in microbes and barnacles. In these cases, β-sheet stacking is recognized as a key feature that is closely related to the interfacial adhesion of proteins. Herein, we challenge this well-known recognition by proposing an α-helix-mediated interfacial adhesion model for proteins. By using bovine serum albumin (BSA) as a model protein, it was discovered that the reduction of disulfide bonds in BSA results in random coils from unfolded BSA dragging α-helices to gather at the solid/liquid interface (SLI). The hydrophobic residues in the α-helix then expose and break through the hydration layer of the SLI, followed by the random deposition of hydrophilic and hydrophobic residues to achieve interfacial adhesion. As a result, the first assembled layer is enriched in the α-helix secondary structure, which is then strengthened by intermolecular disulfide bonds and further initiates stepwise layering protein assembly. In this process, β-sheet stacking is transformed from the α-helix in a gradually evolving manner. This finding thus indicates a valuable clue that β-sheetfeaturing amyloid may form after the interfacial adhesion of proteins. Furthermore, the finding of the α-helix-mediated interfacial adhesion model of proteins affords a unique strategy to prepare protein nanofilms with a well-defined layer number, presenting robust and modulable adhesion on various substrates and exhibiting good resistance to acid, alkali, organic solvent, ultrasonic, and adhesive tape peeling.

Polyetheretherketone (PEEK), a widely used implant material, has attracted the attention of scientific researchers because of its bone-matched elastic modulus, radiolucency, and chemical resistance. However, the bioinert chemical properties of PEEK do not promote bone apposition once implanted. In this study, using a phase-transitioned lysozyme (PTL) nanofilm as a sandwiched layer, a robust hydroxyapatite (HAp) coating on PEEK (HAp@PTL@PEEK) is constructed. The PTL nanofilm shows strong adhesion to the PEEK surface and induces biomimetic mineralization to form a compact HAp coating on PEEK in simulated body fluids. This HAp coating not only shares a higher adhesion strength and better stability but can also be applied to implants with complex 3D structures. HAp@PTL@PEEK showed significantly enhanced osteogenic capacity when cultured with rat bone marrow mesenchymal stem cells by promoting initial cell adhesion, proliferation, and osteogenic differentiation in vitro. In vivo evaluations utilizing models of femoral condyle defects and skull defects confirm that the HAp coating substantially augments bone remodeling and osseointegration ability. Compared with the traditional method, our modified method is simpler, more environmentally friendly, and uses less hazardous components. Furthermore, the obtained HAp coating shares a higher adhesion strength to PEEK and a better osteogenic capacity. The study offers a novel method to improve the osseointegration of PEEK-based implants in biointerfaces and tissue engineering.

The excessive and unreasonable use of pesticides has adversely affected the environment and human health. The soil, one of the most critical natural resources supporting human survival and development, accumulates large amounts of pesticide residues. Compared to traditional spectrophotometry analytical methods, nanoparticle-based sensors stand out for their simplicity of operation as well as their high sensitivity and low detection limits. In this review, we focus primarily on the functions that various nanoparticles have and how they can be used to detect various pesticide residues in soil. A detailed discussion was conducted on the properties of nanoparticles, including their color changeability, Raman enhancement, fluorescence enhancement and quenching, and catalysis. We have also systematically reviewed the methodology for detecting insecticides, herbicides, and fungicides in soil by using nanoparticles.