Preparation of Silk Nanowhisker-Composited Amphoteric Cellulose/Chitin Nanofiber Membranes.

Native biopolymer nanofibers (cellulose, chitin, and silk nanofiber) are one of the most important contributors to the outstanding functions and mechanical properties of natural materials. To enhance the mechanical performance, A great deal of top-down routes have been reported to prepare biopolymers nanofibers/nanowhiskers that retaining their nanostructures. Compared with advances in cellulose and chitin nanofibers/nanowhiskers, it remains difficult for direct downsizing the natural silk fibers into silk nanofibers/nanowhiskers (SNFs/SNWs) because of their high crystallinity and sophisticated structures. In this work, environmentally friendly and recyclable deep eutectic solvents (DESs) were used to direct pretreat and downsize natural silks into silk nanowhiskers with high yield. SNWs with similar diameter (3.1-22 nm for OA/ChCl DES treated SNWs, 2.7-20 nm for CA/ChCl DES treated SNWs) and contour length (329 ± 140 nm for OA/ChCl DES treated SNWs, 365 ± 200 nm for CA/ChCl DES treated SNWs) to individual nanofibers in natural silk fibers were obtained. In addition, the separated DES with a recovery yield of at least 92% could be reused four times to produce SNWs, indicating the possibility of DESs as green solvents for sustainable biopolymer nanomaterial extraction. Based on the inherent amphoteric properties of SNWs, multicompatibility was explored to facilely composite SNWs with various polymers for preparation of coextruded membranes with enhanced performance and endowed the composites with protein-endowed double adsorption properties. Overall, this work demonstrated that the DES pretreatment process is promising for green and low-cost biopolymer nanomaterial extraction and that the SNWs prepared via DES have good prospects as nanoscale materials in the environmental field and in development of smart biomaterials and drug delivery in biomedicine.

Tiny NaOH Assisted Facile Preparation of Silk Nanofibers and Their Nanotube-Compositing Strong, Flexible, and Conductive Films.

Natural silk nanofibers (SNFs) can not only be used as good building blocks for two- or three-dimensional biomaterials but also provide a clue for understanding the theory of structure-function relationships. Nevertheless, it is still difficult to directly extract SNFs from natural silk fibers due to their high crystallinity and recalcitrant complex structures. In the present study, a dilute alkali-assisted separation of high-yield SNFs is proposed. The degummed silk was first treated with a tiny amount of alkali at a mild temperature, followed by high-pressure homogenization. Under the optimized conditions (2% sodium hydroxide, 0 °C, 48 h), SNFs with diameters of 8-42 nm and lengths of 0.9 ± 0.3 µm were prepared with yields higher than 75%, which retained the natural structures at the nanoscale and some inherent properties of silk fibers. Interestingly, SNFs can be used as a stabilizing matrix to assist carbon nanotubes (CNTs) to disperse, aiming to form a uniform and stable CNT/SNF dispersion. Thereafter, a strong and flexible conductive composite film was fabricated with good mechanical properties. The composite film showed good piezoelectric properties and electric thermal response, which has promising application prospects for SNFs, such as in optical devices, nanoelectronics, and biosensors.

Top-down extraction of surface carboxylated-silk nanocrystals and application in hydrogel preparation.

Bionanomaterial based hydrogels originated from natural biopolymer have drawn much attention for advanced applications. However, nanosilk-based hydrogels derived from top-down approaches remain in their infancy. First, nanosilks based on existing methods fail to prepare hydrogels; second, both nanosilk extraction and surface modification remain a challenge due to high crystallinity and sophisticated hierarchical structures. To produce nanosilk-based hydrogels, pretreatment and oxidation are necessary. In this work, pretreatments were conducted first to loosen the sophisticated structures of natural silk fibers, NaClO oxidation was utilized in succession to introduce carboxyl groups onto silk fibroin. Combined with moderate mechanical disintegration, silk nanocrystals with additional carboxyl groups were prepared facilely. Finally, silk nanocrystal-based hydrogels were prepared successfully through gas phase coagulation. An optimization of pretreatment approaches and oxidation conditions was carried out. The morphologies, chemical and crystalline structures of original, pretreated and oxidized silk fibroin as well as nanofibrillated silk were investigated. In addition, the silk nanocrystal-based hydrogel exhibited outstanding mechanical properties compared to those of dissolved and regenerated silk fibroin-based hydrogels. Moreover, silk nanocrystal-based aerogels present highly porous, interconnected, and crisscrossed network nanostructures, which are ideal candidates for tissue regeneration and provide new prospects as porous scaffolds for bioengineering applications.

Magnetism-Actuated Superhydrophobic Flexible Microclaw: From Spatial Microdroplet Maneuvering to Cross-Species Control.

The flexible maneuvering of microliter liquid droplets is significant in both fundamental science and practical applications. However, most current strategies are limited to the rigid locomotion on confined geographies platforms, which greatly hinder their practical uses. Here, we propose a magnetism-actuated superhydrophobic flexible microclaw (MSFM) with hierarchical structures for water droplet manipulation. By virtue of precise femtosecond laser patterning on magnetism-responsive poly(dimethylsiloxane) (PDMS) films doped with carbonyl iron powder, this MSFM without chemical contamination exhibits powerful spatial droplet maneuvering advantages with fast response (<100 ms) and lossless water transport (∼50 cycles) in air. We further performed quantitative analysis of diverse experimental parameters including petal number, length, width, and iron element proportion in MSFM impacting the applicable maneuvering volumes. By coupling the advantages of spatial maneuverability and fast response into this versatile platform, typical unique applications are demonstrated such as programmable coalescence of droplets, collecting debris via droplets, tiny solid manipulation in aqueous severe environments, and harmless living creature control. We envision that this versatile MSFM should provide great potential for applications in microfluidics and cross-species robotics.

Environmentally Adaptive Shape-Morphing Microrobots for Localized Cancer Cell Treatment.

Microrobots have attracted considerable attention due to their extensive applications in microobject manipulation and targeted drug delivery. To realize more complex micro-/nanocargo manipulation (e.g., encapsulation and release) in biological applications, it is highly desirable to endow microrobots with a shape-morphing adaptation to dynamic environments. Here, environmentally adaptive shape-morphing microrobots (SMMRs) have been developed by programmatically encoding different expansion rates in a pH-responsive hydrogel. Due to a combination with magnetic propulsion, a shape-morphing microcrab (SMMC) is able to perform targeted microparticle delivery, including gripping, transporting, and releasing by "opening-closing" of a claw. As a proof-of-concept demonstration, a shape-morphing microfish (SMMF) is designed to encapsulate a drug (doxorubicin (DOX)) by closing its mouth in phosphate-buffered saline (PBS, pH ∼ 7.4) and release the drug by opening its mouth in a slightly acidic solution (pH < 7). Furthermore, localized HeLa cell treatment in an artificial vascular network is realized by "opening-closing" of the SMMF mouth. With the continuous optimization of size, motion control, and imaging technology, these magnetic SMMRs will provide ideal platforms for complex microcargo operations and on-demand drug release.