Wet Spinning of Silk Fibroin-Based Core–Sheath Fibers

Photo-synthesis of sensing silk fibroin fibers with double-network structures

Toughened fibers are highly desirable for a wide range of practical applications, particularly in biomedical and textile industries. Herein, robust silk fibroin fibers with a double-network (DN) structure were successfully fabricated using an in situ photo-polymerization process after swelling. The DN fibers were characterized in terms of morphology, secondary structure, alkali resistance, and tensile properties. These fibers demonstrated remarkable tensile strength in both dry and wet states, along with enhanced alkali resistance, making them highly suitable for demanding environments. Another key advancement in this study is the incorporation of a chromatic biosensor into the DN silk suture, enabling the fibers to undergo a visible blue-to-red color change upon exposure to bacterial strains, both to the naked eye and under a microscope. This color change is essential for bacterial sensing, enabling real-time detection and providing an effective tool for infection monitoring and biosensors in surgical sutures.

Modeling the 3-dimensional structure of the silkworm's spinning apparatus in silk production

The silk-spinning process of the silkworms transforms the liquid silk solution to a solid state under mild conditions, making it an attractive model for bioinspiration However, the precise mechanism behind silk expulsion remains largely unknown. Here we selected the silkworms as representative models to investigate the silk-spinning mechanism. We used serial block-face scanning electron microscopy (SBF-SEM) to reconstruct the three-dimensional structures of the spinnerets in silkworms at various stages and with different gene backgrounds. By comparing the musculature and duct deformation of these spinneret models during the spinning process, we were able to simulate the morphological changes of the spinneret. Based on the results, we proposed three essential factors for silkworm spinning: the pressure generated by the silk gland, the opening duct, and the pulling force generated by head movement. Understanding the silkworm spinning process provides insights into clarify the fluid-ejecting mechanism of a group of animals. Moreover, these findings are helpful to the development of biomimetic spinning device that mimics the push-and-pull dual-force system in silkworms. STATEMENT OF SIGNIFICANCE: The silkworms' spinning system produces fibers under mild conditions, making it an ideal candidate for bioinspiration. However, the mechanism of silk expulsion is unknown, and the three-dimensional structure of the spinneret is still uncertain. In this study, we reconstructed a detailed 3-dimensional model of the spinneret at near-nanometer resolution, and for the first time, we observed the changes that occur before and during the silk-spinning process. Our reconstructed models suggested that silkworms have the ability to control the spinning process by opening or closing the spinning duct. During the continuously spinning period, both the pressure generated by the silk gland and the pulling force resulting from head movement work in tandem to expel the silk solution. We believe that gaining a full understanding of the spinning process steps can advance our ability to spin synthetic fibers with properties comparable to those of native fibers by mimicking the natural spinning process.

Guanidine-containing double-network silks with enhanced tensile and antibacterial property

The bacterial infection of surgical wounds results in prolonged hospitalization and even death of patients, calling for antibacterial function in modern suture products. To tackle this challenge, cationic guanidine-containing copolymer was synthesized, exhibiting antibacterial potency over 5 log reduction against both Gram-positive S. aureus and Gram-negative E. coli. Furthermore, we developed a double-network silk suture by integrating a guanidine-containing copolymer network into the silk fibroin network. This suture exhibited biocidal activity against S. aureus and E. coli, and superior strength compared to the commercial product in both dry and wet conditions. These results may bring general benefits to public health and medical equipment sustainability.

Fabrication of Hydrogel-Based Composite Fibers and Computer Simulation of the Filler Dynamics in the Composite Flow

Fibrous structures with anisotropic fillers as composites have found increasing interest in the field of biofabrication since they can mimic the extracellular matrix of anisotropic tissues such as skeletal muscle or nerve tissue. In the present work, the inclusion of anisotropic fillers in hydrogel-based filaments with an interpenetrating polymeric network (IPN) was evaluated and the dynamics of such fillers in the composite flow were analyzed using computational simulations. In the experimental part, microfabricated rods (200 and 400 μm length, 50 μm width) were used as anisotropic fillers in extrusion of composite filaments using two techniques of wet spinning and 3D printing. Hydrogels such as oxidized alginate (ADA) and methacrylated gelatin (GelMA) were used as matrices. In the computational simulation, a combination of computational fluid dynamics and coarse-grained molecular dynamics was used to study the dynamics of rod-like fillers in the flow field of a syringe. It showed that, during the extrusion process, microrods are far from being well aligned. Instead, many of them tumble on their way through the needle leading to a random orientation in the fiber which was confirmed experimentally.

In Situ Mineralizing Spinning of Strong and Tough Silk Fibers for Optical Waveguides

Biopolymer-based optical waveguides with low-loss light guiding performance and good biocompatibility are highly desired for applications in biomedical photonic devices. Herein, we report the preparation of silk optical fiber waveguides through bioinspired in situ mineralizing spinning, which possess excellent mechanical properties and low light loss. Natural silk fibroin was used as the main precursor for the wet spinning of the regenerated silk fibroin (RSF) fibers. Calcium carbonate nanocrystals (CaCO₃ NCs) were in situ grown in the RSF network and served as nucleation templates for mineralization during the spinning, leading to the formation of strong and tough fibers. CaCO₃ NCs can guide the structure transformation of silk fibroin from random coils to β-sheets, contributing to enhanced mechanical properties. The tensile strength and toughness of the obtained fibers are up to 0.83 ± 0.15 GPa and 181.98 ± 52.42 MJ·m^-3, obviously higher than those of natural silkworm silks and even comparable to spider silks. We further investigated the performance of the fibers as optical waveguides and observed a low light loss of 0.46 dB·cm^-1, which is much lower than natural silk fibers. We believed that these silk-based fibers with excellent mechanical and light propagation properties are promising for applications in biomedical light imaging and therapy.

Stretchable, Environment-Stable, and Knittable Ionic Conducting Fibers Based on Metallogels for Wearable Wide-Range and Durable Strain Sensors

The construction of fibrous ionic conductors and sensors with large stretchability, low-temperature tolerance, and environmental stability is highly desired for practical wearable devices yet is challenging. Herein, metallogels (MOGs) with a rapidly reversible force-stimulated sol-gel transition were employed and encapsulated into a hollow thermoplastic elastomer (TPE) microfiber through a simple coaxial spinning. The resultant MOG@TPE coaxial fiber exhibited a high stretchability (>100%) in a broad temperature range (-50 to 50 °C). The MOG@TPE fibrous strain sensor demonstrated a high-yet-linear working curve, fast response time (<100 ms), highly stable conductivity under large deformation, and excellent cycling stability (>3000 cycles). The MOG@TPE fibrous sensors were demonstrated to be directly attached to the human skin to monitor the real-time movements of large/facet joints of the elbow, wrist, finger, and knee. It is believed that the present work for preparing the stretchable ionic conductive fibers holds great promise for applications in fibrous wearable sensors with broad temperature range, large stretchability, stable conductivity, and high wearing comfort.

Tunable Spun Fiber Constructs in Biomedicine: Influence of Processing Parameters in the Fibers' Architecture

Electrospinning and wet-spinning have been recognized as two of the most efficient and promising techniques for producing polymeric fibrous constructs for a wide range of applications, including optics, electronics, food industry and biomedical applications. They have gained considerable attention in the past few decades because of their unique features and tunable architectures that can mimic desirable biological features, responding more effectively to local demands. In this review, various fiber architectures and configurations, varying from monolayer and core-shell fibers to tri-axial, porous, multilayer, side-by-side and helical fibers, are discussed, highlighting the influence of processing parameters in the final constructs. Additionally, the envisaged biomedical purposes for the examined fiber architectures, mainly focused on drug delivery and tissue engineering applications, are explored at great length.

Isotropic and Anisotropic Scaffolds for Tissue Engineering: Collagen, Conventional, and Textile Fabrication Technologies and Properties

In this review article, tissue engineering and regenerative medicine are briefly explained and the importance of scaffolds is highlighted. Furthermore, the requirements of scaffolds and how they can be fulfilled by using specific biomaterials and fabrication methods are presented. Detailed insight is given into the two biopolymers chitosan and collagen. The fabrication methods are divided into two categories: isotropic and anisotropic scaffold fabrication methods. Processable biomaterials and achievable pore sizes are assigned to each method. In addition, fiber spinning methods and textile fabrication methods used to produce anisotropic scaffolds are described in detail and the advantages of anisotropic scaffolds for tissue engineering and regenerative medicine are highlighted.

Recent applications of electrical, centrifugal, and pressurised emerging technologies for fibrous structure engineering in drug delivery, regenerative medicine and theranostics

Advancements in technology and material development in recent years has led to significant breakthroughs in the remit of fiber engineering. Conventional methods such as wet spinning, melt spinning, phase separation and template synthesis have been reported to develop fibrous structures for an array of applications. However, these methods have limitations with respect to processing conditions (e.g. high processing temperatures, shear stresses) and production (e.g. non-continuous fibers). The materials that can be processed using these methods are also limited, deterring their use in practical applications. Producing fibrous structures on a nanometer scale, in sync with the advancements in nanotechnology is another challenge met by these conventional methods. In this review we aim to present a brief overview of conventional methods of fiber fabrication and focus on the emerging fiber engineering techniques namely electrospinning, centrifugal spinning and pressurised gyration. This review will discuss the fundamental principles and factors governing each fabrication method and converge on the applications of the resulting spun fibers; specifically, in the drug delivery remit and in regenerative medicine.