3D Printing Silk Fibroin/Polyacrylamide Triple-Network Composite Hydrogels with Stretchability, Conductivity, and Strain-Sensing Ability as Bionic Electronic Skins

Electronic skins have received increasing attention due to their great application potential in wearable electronics. Meanwhile, tremendous efforts are still needed for the fabrication of multifunctional composite hydrogels with complex structures for electronic skins via simple methods. In this work, a novel three-dimensional (3D) printing composite hydrogel with stretchability, conductivity, and strain-sensing ability is produced using a one-step photocuring method to achieve a dual-signal response of the electronic skin. The composite hydrogel exhibits a triple-network structure composed of silk microfibers (SMF), regenerated silk fibroin (RSF), and polyacrylamide (PAM). The establishment of triple networks is based on the electrostatic interaction between SMF and RSF, as well as the chemically cross-linked RSF and PAM. Thanks to its specific structure and components, the composite hydrogel possesses enhanced mechanical properties (elastic modulus of 140 kPa, compressive stress of 21 MPa, and compression modulus of 600 kPa) and 3D printability while retaining stretchability and flexibility. The interaction between negatively charged SMF and cations in phosphate-buffered saline endows the composite hydrogel with good conductivity and strain-sensing ability after immersion in a low-concentration (10 mM) salt solution. Moreover, the 3D printing composite hydrogel scaffold successfully realizes real-time monitoring. Therefore, the proposed hydrogel-based ionic sensor is promising for skin tissue engineering, real-time monitoring, soft robotics, and human–machine interfaces

One-Step Approach to Prepare Transparent Conductive Regenerated Silk Fibroin/PEDOT:PSS Films for Electroactive Cell Culture

Silk fibroin (SF)-based electroactive biomaterials with favorable electroconductive property and transparency have great potential applications for cell culture and tissue engineering. Poly­(3,4-ethylenedioxythiophene)-poly­(styrenesulfonate) (PEDOT:PSS) is an excellent candidate as a conductive component, which has been widely used in the field of bioelectronics; however, it is hard to be directly coated onto the surface of regenerated SF (RSF) materials with good stability under a cell culture environment. In this study, a one-step facile PEDOT:PSS modification approach for RSF films based on a suitable post-treatment process of RSF was developed. PEDOT:PSS was successfully embedded and fixed into the shallow surface of an RSF film, forming a tightly conjunct conductive layer on the film surface based on the conformation transition of RSF during the post-treatment process. The conductive layer demonstrated a PSS-rich surface and a PEDOT-rich bulk structure and showed excellent stability under a cell culture environment. More specifically, the robust RSF/PEDOT:PSS film achieved in the post-treatment formula with 70% ethanol proportion possessed best comprehensive properties such as a sheet resistance of 3.833 × 103 Ω/square, a conductivity of 1.003 S/cm, and transmittance over 80% at maximum in the visible range. This kind of electroactive biomaterial also showed good electrochemical stability and degradable properties. Moreover, pheochromocytoma-derived cell line (PC12) cells were cultured on the RSF/PEDOT:PSS film, and an effective electrical stimulation cell response was demonstrated. The facile preparation strategy and the good electroconductive property and transparency make this RSF/PEDOT:PSS film an ideal candidate for neuronal tissue engineering and further for biomedical applications

Strong Silk Fibers Containing Cellulose Nanofibers Generated by a Bioinspired Microfluidic Chip

As spider silks have extraordinary mechanical properties, the design of high-performance artificial silk fibers has been one of the focuses in the field of biomimetic fibers. Cellulose nanofibers (CNFs) have considerable potential being an effective reinforcing agent in biocompatible composites because of their high aspect ratio, good stiffness of the crystalline regions, and biocompatibility. In this study, regenerated silk fibroin (RSF)/CNF hybrid fibers were dry-spun through a microfluidic chip, which mimicked the shape of spider’s major ampullate gland. The results showed that the presence of CNF can substantially enhance the mechanical properties of RSF. In specific, the breaking strength of the RSF/CNF fibers with 0.1 wt % CNF was increased to 486 ± 106 MPa with a maximum value of 686 MPa, significantly higher than that of silk fibers from silkworm. The enhancement could be attributed to higher orientation of crystalline and mesophase contents, higher crystallinity, and hydrogen bonds linked between RSF and CNF. This study outlined a simple and environmentally friendly pathway to generate artificial silks with high-performance properties

Biomaterial-Based Scaffolds as Antibacterial Suture Materials

Antibacterial scaffolds are highly desirable for the repair and reconstruction of injured soft tissues. However, the direct fabrication of scaffolds with excellent biocompatibility, flexibility, and antibacterial capacity remains a challenge, especially those based on biomaterials. In this study, we report the biomaterial-based antibacterial scaffolds based on regenerated silk fibroin, 2-hydroxypropyltrimethyl ammonium chloride chitosan, and bladder acellular matrix graft by blend and coaxial electrospinning. This approach eliminated the use of organic solvents and inorganic nanoparticles, ensuring greater clinical safety, mimicking physiological extracellular matrix structures, and the required softness for a suture material. Thus, the scaffold obtained in this study exhibited excellent biocompatibility, the required mechanical characteristics, and excellent antibacterial capacity. The rate of bacterial elimination of Staphylococcus aureus and Escherichia coli reached up to 99.5 and 98.3%, respectively. The scaffold design favored cell growth and proliferation and resulted in the significant promotion of repair and reconstruction of the urethra, indicating that it can be an ideal antibacterial suture material for soft tissue restoration

Image_1_Laminin-Coated Electrospun Regenerated Silk Fibroin Mats Promote Neural Progenitor Cell Proliferation, Differentiation, and Survival in vitro.JPEG

Neural progenitor cell (NPC) transplantation is a promising technique for central nervous system (CNS) reconstruction and regeneration. Biomaterial scaffolds, frameworks, and platforms can support NPC proliferation and differentiation in vitro as well as serve as a temporary extracellular matrix after transplantation. However, further applications of biomaterials require improved biological attributes. Silk fibroin (SF), which is produced by Bombyx mori, is a widely used and studied protein polymer for biomaterial application. Here, we prepared aligned and random eletrospun regenerated SF (RSF) scaffolds, and evaluated their impact on the growth of NPCs. First, we isolated NPCs and then cultured them on either laminin-coated RSF mats or conventional laminin-coated coverslips for cell assays. We found that aligned and random RSF led to increases in NPC proliferation of 143.8 ± 13.3% and 156.3 ± 14.7%, respectively, compared to controls. Next, we investigated neuron differentiation and found that the aligned and the random RSF led to increases in increase in neuron differentiation of about 93.2 ± 6.4%, and 3167.1 ± 4.8%, respectively, compared to controls. Furthermore, we measured the survival of NPCs and found that RSF promoted NPC survival, and found there was no difference among those three groups. Finally, signaling pathways in cells cultured on RSF mats were studied for their contributions in neural cell differentiation. Our results indicate that RSF mats provide a functional microenvironment and represent a useful scaffold for the development of new strategies in neural engineering research.</p

Free-Standing Single-Molecule Thick Crystals Consisting of Linear Long-Chain Polymers

Organic two-dimensional (2D) crystals are fundamentally important for development of future devices. Despite that more than a half of man-made products contain polymers, 2D crystals consisting of long linear chains have yet to be explored. Here we report on the fabrication of 2D polyaniline (PANI) crystals via rational electrochemical polymerization followed by liquid-phase exfoliation. The 2D PANI is molecularly thin (∼0.8 nm) and composed of PANI chains with a number-average molecular weight of ∼31 000. The chains are parallel to each other with the benzene rings standing almost vertically to the surface, implying a face-to-face arrangement of the neighboring chains held together by abundant π–π interactions augmented with hydrogen bonds. The 2D PANI can be readily transferred to various solid surfaces and exhibit interesting electrical and optical properties, suggesting that they would be potentially useful in photoelectronic devices and other applications