Programing Performance of Silk Fibroin Superstrong Scaffolds by Mesoscopic Regulation among Hierarchical Structures

3D-Printed Silk Proteins for Bone Tissue Regeneration and Associated Immunomodulation

Current bone repair methods have limitations, prompting the exploration of innovative approaches. Tissue engineering emerges as a promising solution, leveraging biomaterials to craft scaffolds replicating the natural bone environment, facilitating cell growth and differentiation. Among fabrication techniques, three-dimensional (3D) printing stands out for its ability to tailor intricate scaffolds. Silk proteins (SPs), known for their mechanical strength and biocompatibility, are an excellent choice for engineering 3D-printed bone tissue engineering (BTE) scaffolds. This article comprehensively reviews bone biology, 3D printing, and the unique attributes of SPs, specifically detailing criteria for scaffold fabrication such as composition, structure, mechanics, and cellular responses. It examines the structural, mechanical, and biological attributes of SPs, emphasizing their suitability for BTE. Recent studies on diverse 3D printing approaches using SPs-based for BTE are highlighted, alongside advancements in their 3D and four-dimensional (4D) printing and their role in osteo-immunomodulation. Future directions in the use of SPs for 3D printing in BTE are outlined.

Flexible Meso Electronics and Photonics Based on Cocoon Silk and Applications

Flexible electronics, applicable to enlarged health, AI big data medications, etc., have been one of the most important technologies of this century. Due to its particular mechanical properties, biocompatibility, and biodegradability, cocoon silk (or SF, silk fibroin) plays a key role in flexible electronics/photonics. The review begins with an examination of the hierarchical meso network structures of SF materials and introduces the concepts of meso reconstruction, meso doping, and meso hybridization based on the correlation between the structure and performance of silk materials. The SF meso functionalization was developed according to intermolecular nuclear templating. By implementation of the techniques of meso reconstruction and functionalization in the refolding of SF materials, extraordinary performance can be achieved. Relying on this strategy, particularly designed flexible electronic and photonic components can be developed. This review covers the latest ideas and technologies of meso flexible electronics and photonics based on SF materials/meso functionalization. As silk materials are biocompatible and human skin-friendly, SF meso flexible electronic/photonic components can be applied to wearable or implanted devices. These devices are applicable in human physiological signals and activities sensing/monitoring. In the case of human-machine interaction, the devices can be applicable in in-body information transmission, computation, and storage, with the potential for the combination of artificial intelligence and human intelligence.

Silk Fibroin/Wool Keratin Composite Scaffold with Hierarchical Fibrous and Porous Structure

The present study describes a silk microfiber reinforced meniscus scaffold (SMRMS) with hierarchical fibrous and porous structure made from silk fibroin (SF) and wool keratin (WK) using electrospinning and freeze-drying technology. This study focuses on the morphology, secondary structure, mechanical properties, and water absorption properties of the scaffold. The cytotoxicity and biocompatibility of SMRMS are assessed in vivo and in vitro. The scaffold shows hierarchical fibrous and porous structure, hierarchical pore size distribution (ranges from 50 to 650 µm), robust mechanical properties (compression strength can reach at 2.8 MPa), and stable biodegradability. A positive growth condition revealed by in vitro cytotoxicity testing indicates that the scaffold is not hazardous to cells. In vivo assessments of biocompatibility reveal that only a mild inflammatory reaction is present in implanted rat tissue. Meniscal scaffold made of SF/WK composite shows a potential application prospect in the meniscal repair engineering field with its development.

Ultrastretchable Organogel/Silicone Fiber-Helical Sensors for Self-Powered Implantable Ligament Strain Monitoring

Implantable sensors with the abilities of real-time healthcare monitoring and auxiliary training are important for exercise-induced or disease-induced muscle and ligament injuries. However, some of these implantable sensors have some shortcomings, such as requiring an external power supply or poor flexibility and stability. Herein, an organogel/silicone fiber-helical sensor based on a triboelectric nanogenerator (OFS-TENG) is developed for power-free and sutureable implantation ligament strain monitoring. The OFS-TENG with high stability and ultrastretchability is composed of an organogel fiber and a silicone fiber intertwined with a double helix structure. The organogel fiber possesses the merits of rapid preparation (15 s), good transparency (>95%), high stretchability (600%), and favorable stability (over 6 months). The OFS-TENG is successfully implanted on the patellar ligament of the rabbit knee for the real-time monitoring of knee ligament stretch and muscle stress, which is expected to provide a solution for real-time diagnosis of muscle and ligament injuries. The prepared self-powered OFS-TENG can monitor data on human muscles and ligaments in real-time.

Enzymatic Crosslinked Silk Fibroin Hydrogel for Biodegradable Electronic Skin and Pulse Waveform Measurements

The development of a portable, controllable, and environmentally friendly electronic skin (e-skin) is highly desirable; however, it presents a major challenge. Herein, a biocompatible, biodegradable, and easily usable hydrogel was designed and fabricated as e-skin to enable the transmission of information regarding the spatial pressure distribution. Silk fibroin (SF) was used as the hydrogel skeleton, which endowed the hydrogel with intelligent mechanical sensitivity. During its conditioning in weakly acidic media, the density of the enzymatic crosslink increased and a dense network was formed due to the formation of covalent/hydrogen bonds. Additionally, a conductive SF/polyvinyl alcohol (PVA) hybrid film was molded as a flexible electrode after graphite deposition. The above SF sensing unit based on SF hydrogels and SF/PVA hybrid films showed high strain sensitivity (4.78), fast responsiveness (<0.1 s), good cycling stability (≥10,000), excellent biocompatibility, and biodegradability. Importantly, a coplanar 8 × 8 pixel SF-based e-skin array was successfully fabricated and applied for 3D signal transmission of the object. The SF-based e-skin was capable of precisely tracking the changes in the pulse pressure, the movement of the finger joint, and the vibrations of the vocal cord. Therefore, the current findings provide a solid foundation for future studies exploring the next generation of electronic devices.

From Mesoscopic Functionalization of Silk Fibroin to Smart Fiber Devices for Textile Electronics and Photonics

Bombyx mori silk fibers exhibit significant potential for applications in smart textiles, such as fiber sensors, fiber actuators, optical fibers, and energy harvester. Silk fibroin (SF) from B. mori silkworm fibers can be reconstructed/functionalized at the mesoscopic scale during refolding from the solution state into fibers. This facilitates the mesoscopic functionalization by engaging functional seeds in the refolding of unfolded SF molecules. In particular, SF solutions can be self-assembled into regenerated fiber devices by artificial spinning technologies, such as wet spinning, dry spinning, microfluidic spinning, electrospinning, and direct writing. Meso-functionalization manipulates the SF property from the mesoscopic scale, transforming the original silk fibers into smart fiber devices with smart functionalities, such as sensors, actuators, optical fibers, luminous fibers, and energy harvesters. In this review, the progress of mesoscopic structural construction from SF materials to fiber electronics/photonics is comprehensively summarized, along with the spinning technologies and fiber structure characterization methods. The applications, prospects, and challenges of smart silk fibers in textile devices for wearable personalized healthcare, self-propelled exoskeletons, optical and luminous fibers, and sustainable energy harvesters are also discussed.

Reinforcement of Silk Microneedle Patches for Accurate Transdermal Delivery

Microneedles (MNs) have attracted considerable attention in the pharmaceutical field as a minimally invasive delivery alternative to hypodermic needles. Current material systems of MNs have gradually shifted from metals, ceramics, and silicon to polymer in consideration of toughness and drug loading capacity. Silk fibroin (SF) is considered one of the most promising alternatives because it combines the ability to maintain the activity of biomolecules, adjustable mechanical strength, and excellent biocompatibility. However, the strength and hardness of SF MNs need to be carefully optimized to ensure skin epidermis penetration and controlled drug release, which are rarely explored in reported works. Here, the synergistic effect of glutaraldehyde-based cross-linking and water vapor annealing post-treatment is presented as an effective method to promote the formation of SF molecular networks and the mechanical strength of SF MNs. Moreover, the reinforced MN substrate is coated with a drug-loaded SF layer with low crystallinity. The drug release experiments demonstrate the successful controlled release of rhodamine B, horseradish peroxidase, and tetracycline, which suggests the great potential in the application of vaccine, antibiosis, cosmetology, and so forth.

Exploration of Bioengineered Scaffolds Composed of Thermo-Responsive Polymers for Drug Delivery in Wound Healing

Innate and adaptive immune responses lead to wound healing by regulating a complex series of events promoting cellular cross-talk. An inflammatory response is presented with its characteristic clinical symptoms: heat, pain, redness, and swelling. Some smart thermo-responsive polymers like chitosan, polyvinylpyrrolidone, alginate, and poly(ε-caprolactone) can be used to create biocompatible and biodegradable scaffolds. These processed thermo-responsive biomaterials possess 3D architectures similar to human structures, providing physical support for cell growth and tissue regeneration. Furthermore, these structures are used as novel drug delivery systems. Locally heated tumors above the polymer lower the critical solution temperature and can induce its conversion into a hydrophobic form by an entropy-driven process, enhancing drug release. When the thermal stimulus is gone, drug release is reduced due to the swelling of the material. As a result, these systems can contribute to the wound healing process in accelerating tissue healing, avoiding large scar tissue, regulating the inflammatory response, and protecting from bacterial infections. This paper integrates the relevant reported contributions of bioengineered scaffolds composed of smart thermo-responsive polymers for drug delivery applications in wound healing. Therefore, we present a comprehensive review that aims to demonstrate these systems' capacity to provide spatially and temporally controlled release strategies for one or more drugs used in wound healing. In this sense, the novel manufacturing techniques of 3D printing and electrospinning are explored for the tuning of their physicochemical properties to adjust therapies according to patient convenience and reduce drug toxicity and side effects.