Gelation Process and Physicochemical Properties of Thai Silk Fibroin Hydrogels Induced by Various Anionic Surfactants for Controlled Release of Curcumin

In vitro and in vivo investigation of chitosan/silk fibroin injectable interpenetrating network hydrogel with microspheres for cartilage regeneration

Articular cartilage is an avascular and almost acellular tissue with limited self-regenerating capabilities. Although injectable hydrogels have garnered a lot of attention as a promising treatment, a biocompatible hydrogel with adequate mechanical properties is yet to be created. In this study, an interpenetrating network hydrogel comprised of chitosan and silk fibroin was created through electrostatic and hydrophobic bonds, respectively. The polymeric network of the scaffold combined an effective microenvironment for cell activity with enhanced mechanical properties to address the current issues in cartilage scaffolds. Furthermore, microspheres (MS) were utilized for a controlled release of methylprednisolone acetate (MPA), around ~75 % after 35 days. The proposed scaffolds demonstrated great mechanical stability with ~0.047 MPa compressive moduli and ~145 kPa compressive strength. Moreover, the degradation rate of the samples (~45 % after 35 days) was optimized to match neo-cartilage formation. Furthermore, the use of natural biomaterials yielded good biocompatibility with ~76 % chondrocyte viability after 7 days. According to gross observation after 12 weeks the defect site of the treated groups was filled with minimally discernible boundary. These results were confirmed by histopathology assays were the treated groups showed higher chondrocyte count and collagen type II expression.

Manipulating supramolecular gels with surfactants: Interfacial and non-interfacial mechanisms

Gel is a class of self-supporting soft materials with applications in many fields. Fast, controllable gelation, micro/nano structure and suitable rheological properties are essential considerations for the design of gels for specific applications. Many methods can be used to control these parameters, among which the additive approach is convenient as it is a simple physical mixing process with significant advantages, such as avoidance of pH change and external energy fields (ultrasound, UV light and others). Although surfactants are widely used to control the formation of many materials, particularly nanomaterials, their effects on gelation are less known. This review summarizes the studies that utilized different surfactants to control the formation, structure, and properties of molecular and silk fibroin gels. The mechanisms of surfactants, which are interfacial and non-interfacial effects, are classified and discussed. Knowledge and technical gaps are identified, and perspectives for further research are outlined. This review is expected to inspire increasing research interest in using surfactants for designing/fabricating gels with desirable formation kinetics, structure, properties and functionalities.

Accelerated Simple Preparation of Curcumin-Loaded Silk Fibroin/Hyaluronic Acid Hydrogels for Biomedical Applications

The development of new biomaterials from natural fibres in the field of biomedicine have attracted great interest in recent years. One of the most studied fibres has been silk fibroin produced by the Bombyx mori worm, due to its excellent mechanical properties and its biodegradability and bioavailability. Among the different biomaterials that can be prepared from silk fibroin, hydrogels have attracted considerable attention due to their potential use in different fields, such as scaffolding, cell therapy and biomedical application. Hydrogels are essentially a three-dimensional network of flexible polymer chains that absorb considerable amounts of water and can be loaded with drugs and/or cells inside to be used in a wide variety of applications. Here we present a simple sonication process for the preparation of curcumin-hyaluronic acid-silk fibroin hydrogels. Different grades of hydrogels were prepared by controlling the relative amounts of their components. The hydrogels were physically and morphologically characterised by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM) and their biological activity was tested in terms of cell viability in a fibroblast cell line.

Robust Silk Protein Hydrogels Made by a Facile One-Step Method and Their Multiple Applications

Silk fibroin is a natural polymer that has various material forms and wide applications. Hydrogel is one of the most attractive silk materials because of its hydrophilicity, biocompatibility, and flexibility. However, its applications are still quite limited because they have a complicated preparation process and/or low mechanical strength. Herein, a simple way to prepare tough silk fibroin hydrogels via a solvent-exchange method is introduced. The degummed silk fiber was directly dissolved in a calcium chloride/formic acid solution and then water was used to replace the solvent. The silk fibroin hydrogel that was obtained using this facile method exhibited even better mechanical properties than most silk fibroin hydrogels that have been reported in the literature. Also, the silk fibroin hydrogel maintained biocompatibility that was as good as that prepared via other methods. Finally, the possibility of using this regenerated silk fibroin hydrogel as a multi-functional platform (such as a catalyst carrier, photothermal agent, and underwater adhesive) has been discussed. Therefore, such a natural, sustainable, robust, and good biocompatible silk fibroin hydrogel that is prepared by an improved method may have great potential for further applications.

Comparative Study of Silk Fibroin-Based Hydrogels and Their Potential as Material for 3-Dimensional (3D) Printing

Three-dimensional (3D) printing is regarded as a critical technology in material engineering for biomedical applications. From a previous report, silk fibroin (SF) has been used as a biomaterial for tissue engineering due to its biocompatibility, biodegradability, non-toxicity and robust mechanical properties which provide a potential as material for 3D-printing. In this study, SF-based hydrogels with different formulations and SF concentrations (1-3%wt) were prepared by natural gelation (SF/self-gelled), sodium tetradecyl sulfate-induced (SF/STS) and dimyristoyl glycerophosphorylglycerol-induced (SF/DMPG). From the results, 2%wt SF-based (2SF) hydrogels showed suitable properties for extrusion, such as storage modulus, shear-thinning behavior and degree of structure recovery. The 4-layer box structure of all 2SF-based hydrogel formulations could be printed without structural collapse. In addition, the mechanical stability of printed structures after three-step post-treatment was investigated. The printed structure of 2SF/STS and 2SF/DMPG hydrogels exhibited high stability with high degree of structure recovery as 70.4% and 53.7%, respectively, compared to 2SF/self-gelled construct as 38.9%. The 2SF/STS and 2SF/DMPG hydrogels showed a great potential to use as material for 3D-printing due to its rheological properties, printability and structure stability.

Interpenetrated biosurfactant-silk fibroin networks - a SANS study

Silk fibroin (SF) based hydrogels have been exploited for years for their inherent biocompatibility and favorable mechanical properties which makes them interesting for biotechnology applications. In this study we investigate silk based composite hydrogels where pH-sensitive, anionic biosurfactant assemblies (sophorolipids SL-C18 : 1 and SL-C18 : 0), are employed to improve the present properties of SF. Results suggest that the presence of SL surfactant assemblies leads to faster gelling of SF by accelerating the refolding from random coil to β-sheet as shown by infrared and UV-visible spectroscopy. Small angle neutron scattering (SANS) including contrast matching studies show that SF and SL assemblies coexist in a fibrillary network that is, in the case of SL-C18 : 0, interpenetrating. The resulting overall network structure in composite gels is slightly more affected by SL-C18 : 1 than by SL-C18 : 0, whereas the structure of both SF and surfactant assemblies remains unchanged. No disassembly of SL surfactant structures is observed, which gives a new perspective on SF-surfactant interactions. The hydrophobic effect within SF is favored in the presence of SL, leading to faster refolding of SF into β-sheet conformation. The presented composite gels, being an interpenetrating network of which one compound (SL-C18 : 0) can be tweaked by pH, open an interesting option towards improved workability and stimuli responsive mechanical properties of SF based hydrogels with possible applications in controlled cell culture and tissue engineering or drug delivery. The presented SANS analysis approach has the potential to be expanded to other protein-surfactant systems and composite hydrogels.

Crosslinking strategies for silk fibroin hydrogels: promising biomedical materials

Due to their strong biomimetic potential, silk fibroin (SF) hydrogels are impressive candidates for tissue engineering, due to their tunable mechanical properties, biocompatibility, low immunotoxicity, controllable biodegradability, and a remarkable capacity for biomaterial modification and the realization of a specific molecular structure. The fundamental chemical and physical structure of SF allows its structure to be altered using various crosslinking strategies. The established crosslinking methods enable the formation of three-dimensional (3D) networks under physiological conditions. There are different chemical and physical crosslinking mechanisms available for the generation of SF hydrogels (SFHs). These methods, either chemical or physical, change the structure of SF and improve its mechanical stability, although each method has its advantages and disadvantages. While chemical crosslinking agents guarantee the mechanical strength of SFH through the generation of covalent bonds, they could cause some toxicity, and their usage is not compatible with a cell-friendly technology. On the other hand, physical crosslinking approaches have been implemented in the absence of chemical solvents by the induction of β-sheet conformation in the SF structure. Unfortunately, it is not easy to control the shape and properties of SFHs when using this method. The current review discusses the different crosslinking mechanisms of SFH in detail, in order to support the development of engineered SFHs for biomedical applications.

Exploring the Gelation Mechanisms and Cytocompatibility of Gold (III)-Mediated Regenerated and Thiolated Silk Fibroin Hydrogels

Accelerating the gelation of silk fibroin (SF) solution from several days or weeks to minutes or few hours is critical for several applications (e.g., cell encapsulation, bio-ink for 3D printing, and injectable controlled release). In this study, the rapid gelation of SF induced by a gold salt (Au3+) as well as the cytocompatibility of Au3+-mediated SF hydrogels are reported. The gelation behaviors and mechanisms of regenerated SF and thiolated SF (tSF) were compared. Hydrogels can be obtained immediately after mixing or within three days depending on the types of silk proteins used and amount of Au3+. Au3+-mediated SF and tSF hydrogels showed different color appearances. The color of Au-SF hydrogels was purple-red, whereas the Au-tSF hydrogels maintained their initial solution color, indicating different gelation mechanisms. The reduction of Au3+ by amino groups and further reduction to Au by tyrosine present in SF, resulting in a dityrosine bonding and Au nanoparticles (NPs) production, are proposed as underlying mechanisms of Au-SF gel formation. Thiol groups of the tSF reduced Au3+ to Au+ and formed a disulfide bond, before a formation of Au+-S bonds. Protons generated during the reactions between Au3+ and SF or tSF led to a decrease of the local pH, which affected the chain aggregation of the SF, and induced the conformational transition of SF protein to beta sheet. The cytocompatibility of the Au-SF and tSF hydrogels was demonstrated by culturing with a L929 cell line, indicating that the developed hydrogels can be promising 3D matrices for different biomedical applications.