Photolithographic Masking Method to Chemically Pattern Silk Film Surfaces

Using a Functional Wool Keratin Photoresist to Build Iridescent and Fluorescent 3D Micro-Pattern for Dual-Mode Optical Anti-Counterfeiting

The construction of bio-nanostructures plays a critical role in the advancement of applications across bioelectronics, bio-optical devices, and biomedicine. Among various fabrication techniques, soft lithography emerges as an efficient and scalable method for producing high-quality intricate surface micropatterns. Herein, a mild and aqueous approach is developed to endow biocompatible wool keratin (WK) with photoresponsiveness; and utilize the gold nanoclusters (AuNCs) incorporated functional bio-photoresist to build iridescent and fluorescent micrometer-scale patterns for dual-mode optical anti-counterfeiting. Specifically, the chemical modification of WK is achieved by using glycidyl methacrylate under mild conditions. And then, the modified WK can function as a green bio-photoresist, which can be cross-linked via UV light-initiated radical polymerization. By combining soft lithography, both positive and negative 3D WK micro-patterns with stability, biocompatibility, and controlled degradability can be facilely fabricated. Notably, the obtained periodic microstructures exhibit typical iridescent behavior with an excellent diffraction efficiency. Interestingly, by using WK as both a reductant and a stabilizer, the AuNCs functional WK resist with significant fluorescence response can be in situ generated. More importantly, through the skillful combination of iridescent micro-patterns and fluorescence, the WK/AuNCs-based hybrid micro-patterns can be further used for dual-mode optical anti-counterfeiting, which can significantly enhance information storage and encryption security.

Achieving Biofunctional Micropatterns via Protein-Based Aqueous Photoresists with Tailored Functionalities

Photolithography is the most widely used micropatterning technique at the micro- and nanoscale in device fabrication. However, traditional photoresists used in photolithography are typically nonaqueous-based toxic substances that require harsh conditions for processing, limiting the development of biofunctional and biocompatible micropatterns. In this study, a protein-based aqueous photoresist derived from chemically modified silk fibroin named SAMA, capable of achieving high-resolution micropatterning (<1.2 µm) while retaining good biocompatibility, is presented. The entire fabrication process, including spin-coating, development, and lift-off, employs solely SAMA and water, eliminating the need for toxic reagents and elevated temperature. Notably, the SAMA photoresist allows covalent conjugation of biofunctional molecules, such as enzymes and nucleic acids, while preserving their bioactivity during micropatterning. This innovative approach enables the high-throughput generation of bioactive micropatterns for various applications such as biosynthesis, diagnostics, and biosensors.

Using reduced sericin as a green resist for precise pattern fabrication via water-based lithography

The use of toxic resists and complex procedures has impeded the resolution and quality of micro/nanofabrication on virtually arbitrary substrates via photolithography. To fabricate a precise and high-resolution pattern, a sericin nanofilm-based coating was developed by reducing disulfide bonds and subsequently assembling sericin protein. Upon exposure to ultraviolet (UV) light, intermolecular amide bonds in sericin are cleaved through the action of a reducing agent, allowing the reduced sericin (rSer) coating to exhibit the functional ability to generate diverse geometric micro/nanopatterns through photomask-governed photolithography. The rSer film serves as a platform for the encapsulation of fluorescent molecules, enabling fluorescent micropatterns applicable in anti-counterfeiting and encryption. In addition, the patterned rSer nanofilms support biocompatible cell proliferation. With their excellent chemical stability, high-resolution geometric patterns can be transferred onto silicon substrates through chemical etching, resulting in periodic chemical etching patterns that display structural colours. Inspired by the micro/nanostructures of lotus leaves, elliptical microstructures exhibit superhydrophobic behaviour, highlighting the versatility of the rSer film for applications in semiconductors, anti-counterfeiting, smart displays, and superhydrophobic coatings.

Customized surface adhesive and wettability properties of conformal electronic devices

Conformal and body-adaptive electronics have revolutionized the way we interact with technology, ushering in a new era of wearable devices that can seamlessly integrate with our daily lives. However, the inherent mismatch between artificially synthesized materials and biological tissues (caused by irregular skin fold, skin hair, sweat, and skin grease) needs to be addressed, which can be realized using body-adaptive electronics by rational design of their surface adhesive and wettability properties. Over the past few decades, various approaches have been developed to enhance the conformability and adaptability of bioelectronics by (i) increasing flexibility and reducing device thickness, (ii) improving the adhesion and wettability between bioelectronics and biological interfaces, and (iii) refining the integration process with biological systems. Successful development of a conformal and body-adaptive electronic device requires comprehensive consideration of all three aspects. This review starts with the design strategies of conformal electronics with different surface adhesive and wettability properties. A series of conformal and body-adaptive electronics used in the human body under both dry and wet conditions are systematically discussed. Finally, the current challenges and critical perspectives are summarized, focusing on promising directions such as telemedicine, mobile health, point-of-care diagnostics, and human-machine interface applications.

Silk fibroin catheter with stable bioinspired inner-surfaces for inhibition of bioadhesion

Biofilm formation on indwelling medical devices such as catheters and ventilators due to the adhesion of bacteria poses significant challenges in healthcare. Surface modification with micro- and nano-structures offers a promising strategy to prevent bioadhesion and is safer than surface chemical modification approaches. Here, catheters were prepared using silk fibroin (SF) hydrogels and an infusion molding method, with the inner surface featuring a micropapillae structure inspired by lotus leaves (SF-CMP). After phenylethanol (PEA) fumigation treatment, the resulting catheters (SF-CMP PEA) displayed improved swelling resistance and mechanical properties compared to methanol-treated catheters (SF-CMP MeOH). PEA was more efficient than methanol in controlling the size, distribution, and content of silk crystalline β-sheet blocks and thus the swelling and mechanical properties. Moreover, the micro-papillae structure on SF-CMP PEA remained stable over 35 days in solution, in contrast to SF-CMP MeOH, which lasted <7 days. SF-CMP PEA exhibited repellent effects against E. coli and S. aureusin vitro, and low cytotoxicity to the endothelial cells cultured on the unpatterned surface. Additionally, subcutaneous implantation studies showed reduced inflammation around the micropatterned samples compared to controls with a plain, unpatterned surface. The unique properties of SF-based materials, including tunable structures, biocompatibility, degradation, and drug-loading capability make them an attractive material for anti-bioadhesion in applications ranging from indwelling medical devices to tissue engineering scaffolds.

Recent progress in silk fibroin-based flexible electronics

With the rapid development of the Internet of Things (IoT) and the emergence of 5G, traditional silicon-based electronics no longer fully meet market demands such as nonplanar application scenarios due to mechanical mismatch. This provides unprecedented opportunities for flexible electronics that bypass the physical rigidity through the introduction of flexible materials. In recent decades, biological materials with outstanding biocompatibility and biodegradability, which are considered some of the most promising candidates for next-generation flexible electronics, have received increasing attention, e.g., silk fibroin, cellulose, pectin, chitosan, and melanin. Among them, silk fibroin presents greater superiorities in biocompatibility and biodegradability, and moreover, it also possesses a variety of attractive properties, such as adjustable water solubility, remarkable optical transmittance, high mechanical robustness, light weight, and ease of processing, which are partially or even completely lacking in other biological materials. Therefore, silk fibroin has been widely used as fundamental components for the construction of biocompatible flexible electronics, particularly for wearable and implantable devices. Furthermore, in recent years, more attention has been paid to the investigation of the functional characteristics of silk fibroin, such as the dielectric properties, piezoelectric properties, strong ability to lose electrons, and sensitivity to environmental variables. Here, this paper not only reviews the preparation technologies for various forms of silk fibroin and the recent progress in the use of silk fibroin as a fundamental material but also focuses on the recent advanced works in which silk fibroin serves as functional components. Additionally, the challenges and future development of silk fibroin-based flexible electronics are summarized. (1) This review focuses on silk fibroin serving as active functional components to construct flexible electronics. (2) Recent representative reports on flexible electronic devices that applied silk fibroin as fundamental supporting components are summarized. (3) This review summarizes the current typical silk fibroin-based materials and the corresponding advanced preparation technologies. (4) The current challenges and future development of silk fibroin-based flexible electronic devices are analyzed.

Development of robust, ultra-smooth, flexible and transparent regenerated silk composite films for bio-integrated electronic device applications

Regenerated Silk Fibroin (RSF) films are considered promising substrate candidates primarily in the field of bio-integrated electronic device applications. The key issues that ought to be addressed to exploit the inherent advantages of silk thin films include enhancing their flexibility and chemical durability. Such films find a plethora of applications, the significant one being conformal, transparent microelectrode arrays. Elevated temperatures that are regularly used in lithographic processes tend to dehydrate RSF films, making them brittle. Furthermore, the solvents/etchants used in typical device fabrication results in the formation of micro-cracks. This paper addressed both these issues by developing composite films and studying the effect of biodegradable additives in enhancing flexibility and chemical durability without compromising on optical transparency and surface smoothness. Through our rigorous experimentation, regenerated silk blended with Polyvinyl Alcohol (Silk/PVA) is identified as the composite for achieving the objectives. Furthermore, the Cyto-compatibility studies suggest that Silk/PVA, along with all other silk composites, have shown above 80% cell viability, as verified using L929 fibroblast cell lines. Going a step further, we demonstrated the successful patterning of 32 channel optically transparent microelectrode array (MEA) pattern, with a minimum feature size of 5 μm above the free-standing and optically transparent Silk/PVA composite film.

Dynamic Porous Pattern through Controlling Noncovalent Interactions in Polyelectrolyte Film for Sequential and Regional Encapsulation

Inspired by nature, many functional surfaces have been developed with special structures in biology, chemistry, and materials. Many research studies have been focused on the preparation of surfaces with static structure. Achieving dynamical manipulation of surface structure is desired but still a great challenge. Herein, a polyelectrolyte film capable of regional and reversible changes in the microporous structure is presented. Our proposal is based on the combination of azobenzene (Azo) π-π stacking and electrostatic interaction, which could be affected respectively by ultraviolet (UV) irradiation and water plasticization, to tune the mobility of polyelectrolyte chains. The porous patterns can be obtained after regional ultraviolet irradiation and acid treatment. Owing to the reversibility of Azo π-π stacking and electrostatic interaction, the patterns can be repeatedly created and erased in the polyelectrolyte film made by layer-by-layer (LbL) self-assembly of poly(ethyleneimine)-azo and poly(acrylic acid). Furthermore, through two rounds of porous pattern formation and erasure, different functional species can be loaded separately and confined regionally within the film, showing potential applications in the functional surface. This work highlights the coordination of two noncovalent interactions in thin films for regional and reversible controlling its structure, opening a window for more in-depth development of functional surfaces.

Rational Design of PMPC/PDMC/PEGDA Hydrogel Micropatterns onto Polylactic Acid with Enhanced Biological Activity

Polylactic acid (PLA) is one of the biodegradable materials that has been used in the areas of surgical healing lines, cancer treatment, and wound healing. However, the application of PLA is still rather limited due to its high hydrophobicity and poor antibacterial activity. In order to enhance the antifouling and antibacterial performances of PLA, here we modified the surface of PLA with various sizes of hydrogel micropatterns in negative or positive mode using plasma treatment, the photomask technique, and UV-graft polymerization. The hydrogel micropatterns consist of poly(ethylene glycol) diacrylate (PEGDA), poly(2-methacryloyloxyethylphosphorylcholine) (PMPC), and poly(methacryloyloxyethyltrimethylammonium chloride) (PDMC). Compared to PLA, the patterned PLA (PLA-PMPC/PDMC/PEGDA) shows obviously enhanced antifouling and antibacterial activities. For PLA-PMPC/PDMC/PEGDA with either positive or negative micropatterns, the antifouling and antibacterial properties are gradually increasing with decreasing the size of micropatterns. Compared with PLA-PMPC/PDMC/PEGDA bearing positive and negative micropatterns in the same size, the PLA-PMPC/PDMC/PEGDA with negative micropatterns exhibits slightly better biological activity and the PLA-PMPC/PDMC/PEGDA with 3 μm negative hydrogel micropatterns shows the best hydrophilicity, antifouling, and antibacterial properties. Combining the in vitro hemolysis assay, cytotoxicity, water absorption test, and degradation test results, it is suggested that the fabrication of hydrogel micropatterns onto the PLA surface could significantly improve biological activities of PLA. We expect that this work would provide a new strategy to potentially develop PLA as a promising wound dressing.