Silk fibroin (SF) as a natural biopolymer has become a popular material for biomedical applications due to its minimal immunogenicity, tunable biodegradability, and high biocompatibility. Nowadays, various techniques have been developed for the applications of SF in bioengineering. Most of the literature reviews focus on the SF-based biomaterials and their different forms of applications such as films, hydrogels, and scaffolds. SF is also valuable as a coating on other substrate materials for biomedicine; however, there are few reviews related to SF-coated biomaterials. Thus, in this review, we focused on the surface modification of biomaterials using SF coatings, demonstrated their various preparation methods on substrate materials, and introduced the latest procedures. The diverse applications of SF coatings for biomedicine are discussed, including bone, ligament, skin, mucosa, and nerve regeneration, and dental implant surface modification. SF coating is conducive to inducing cell adhesion and migration, promoting hydroxyapatite (HA) deposition and matrix mineralization, and inhibiting the Notch signaling pathway, making it a promising strategy for bone regeneration. In addition, SF-coated composite scaffolds can be considered prospective candidates for ligament regeneration after injury. SF coating has been proven to enhance the mechanical properties of the substrate material, and render integral stability to the dressing material during the regeneration of skin and mucosa. Moreover, SF coating is a potential strategy to accelerate nerve regeneration due to its dielectric properties, mechanical flexibility, and angiogenesis promotion effect. In addition, SF coating is an effective and popular means for dental implant surface modification to promote osteogenesis around implants made of different materials. Thus, this review can be of great benefit for further improvements in SF-coated biomaterials, and will undoubtedly contribute to clinical transformation in the future.
Biocompatible Materials/chemistry* ; Silk/chemistry* ; Fibroins/pharmacology* ; Dental Implants ; Osteogenesis ; Tissue Scaffolds/chemistry* ; Tissue Engineering/methods*

OBJECTIVES: To design and prepare silk fibroin/hyaluronic acid composite hydrogel. METHODS: The thiol modified silk fibroin and the double-bond modified hyaluronic acid were rapidly cured into gels through thiol-ene click polymerization under ultraviolet light condition. The grafting rate of modified silk fibroin and hyaluronic acid was characterized by ¹H NMR spectroscopy; the gel point and the internal microstructure of hydrogels were characterized by rheological test and scanning electron microscopy; the mechanical properties were characterized by compression test; the swelling rate and degradation rate were determined by mass method. The hydrogel was co-cultured with the cells, the cytotoxicity was measured by the lactate dehydrogenase method, the cell adhesion was measured by the float count method, and the cell growth and differentiation on the surface of the gel were observed by scanning electron microscope and fluorescence microscope. RESULTS: The functional group substitution degrees of modified silk fibroin and hyaluronic acid were 17.99% and 48.03%, respectively. The prepared silk fibroin/hyaluronic acid composite hydrogel had a gel point of 40-60 s and had a porous structure inside the gel. The compressive strength was as high as 450 kPa and it would not break after ten cycles. The water absorption capacity of the composite hydrogel was 4-10 times of its own weight. Degradation experiments showed that the hydrogel was biodegradable, and the degradation rate reached 28%-42% after 35 d. The cell biology experiments showed that the cytotoxicity of the composite gel was low, the cell adhesion was good, and the growth and differentiation of the cells on the surface of the gel were good. CONCLUSIONS The photocurable silk fibroin/hyaluronic acid composite hydrogel can form a gel quickly, and has excellent mechanical properties, adjustable swelling rate and degradation degree, good biocompatibility, so it has promising application prospects in biomedicine.
Fibroins/chemistry* ; Hydrogels/chemistry* ; Hyaluronic Acid/chemistry* ; Biocompatible Materials/chemistry* ; Click Chemistry ; Sulfhydryl Compounds ; Silk/chemistry*

Silk fibroin, a natural fibrin, is a suitable matrix biomaterial for wound repair due to its unique properties such as good biocompatibility, tunable biodegradation and mechanical properties, low host inflammatory response, low cost, ease of fabrication, etc. Silk fibroin can be used alone or in combination with other materials to construct various dressings including scaffolds, hydrogels, films, smart mats, and microneedles, which can meet the needs of different wound repair and regulate the wound repair process. Thus, the application research of silk fibroin in skin tissue engineering has increased dramatically. Compared with other natural materials, silk fibroin promotes tissue regeneration and wound repair by improving cell proliferation, migration, and differentiation behavior at different stages, showing unique advantages in different dimensions. Based on the development of silk fibroin wound repair materials in the recent years, this review focuses on the mechanism and application prospect of silk fibroin and its composite materials in wound repair.
Fibroins/metabolism* ; Biocompatible Materials/therapeutic use* ; Tissue Engineering ; Hydrogels ; Fibrin ; Tissue Scaffolds

Extracellular matrix (ECM) stiffness is closely related to the physiological and pathological states of breast tissue. The current study was aimed to investigate the effect of silk fibroin/collagen composite hydrogels with adjustable matrix stiffness on the growth and phenotype of normal breast epithelial cells. In this study, the enzymatic reaction of horseradish peroxidase (HRP) with hydrogen peroxide (H₂O₂) was used to change the degree of cross-linking of the silk fibroin solution. The rotational rheometer was used to characterize the composite hydrogel's biomechanical properties. Human normal mammary epithelial cell line MCF-10A were inoculated into composite hydrogels with various stiffness (19.10-4 932.36 Pa) to construct a three dimensional (3D) culture system of mammary epithelial cells. The CCK-8 assay was applied to detect the cell proliferation rate and active states in each group. Hematoxylin-Eosin (HE) staining and whole-mount magenta staining were used for histological evaluation of cell morphology and distribution. The results showed that with the increase of matrix stiffness, MCF-10A cells exhibited inhibited proliferation rate, decreased formation of acinus structures and increased branching structures. Meanwhile, with the increase of matrix stiffness, the polarity of MCF-10A cells was impeded. And the increase of matrix stiffness up-regulated the expression levels of mmp-2, mmp-3, and mmp-9 in MCF-10A cells. Among the genes related to epithelial-mesenchymal transition (EMT), the expression level of the epithelial marker gene E-cadherin was significantly down-regulated, while the interstitial cell marker gene Vimentin was up-regulated, and the expression levels of Snail, Wnt5b and Integrin β1 in the Wnt pathway were up-regulated. These results suggest that the silk fibroin/collagen composite hydrogels with adjustable matrix stiffness regulates the proliferation and the phenotype of MCF-10A cells. The effects of increased matrix stiffness may be closely related to the changes of the polar structures and function of MCF-10A cells, as well as the occurrence of ECM-remodeling and EMT.
Collagen/metabolism* ; Epithelial Cells/metabolism* ; Fibroins/pharmacology* ; Humans ; Hydrogels/metabolism* ; Hydrogen Peroxide ; Phenotype

Silk fibroin has the characteristics of good biocompatibility, mechanical properties, degradation performance and easy shaping, which makes silk fibroin become the focus of biomedical material preparation and research, and has received extensive attention. This article reviews the prior art methods of silk fibroin degumming, dissolution and regeneration processing. The specific applications of silk fibroin materials in the field of biomedical materials are reviewed, and the application prospects of silk fibroin in the field of biomedical materials are prospected.
Biocompatible Materials ; Fibroins

BACKGROUND: Recently, carbon fibers have been utilized to develop a depth-type microelectrode array for chronic neural recording. Since the diameter of carbon fibers is smaller than the conventional electrodes made of metal wires or microfabricated silicon, the carbon fiber electrodes showed an improved capability for chronic neural recording with less tissue damages. However, the carbon fiber based microelectrodes have a limitation of short insertion depth due to a low stiffness. METHODS: We proposed a carbon fiber based microelectrode array embedded with a mechanical support structure to facilitate the penetration into the deeper brain. The support is made of biodegradable silk fibroin to reduce the reactive tissue responses. The 4-channel carbon fiber based microelectrode arrays were fabricated and accessed in terms of electrochemical impedance, recording capability for 1-month implantation in rat hippocampi. The electrodes with tungsten supports were fabricated and tested as a control group. Immunohistochemical analysis was performed to identify the reactive glial responses. RESULTS: The carbon fiber based electrode arrays with silk supports showed about 2-fold impedance increase 2 weeks after implantation while the number of active electrodes decreased simultaneously. However, after 1 month, the electrode impedance decreased back to its initial value and the percentage of active electrodes also increased above 70%. Immunohistochemical staining clearly showed that the electrodes with silk supports induced less reactive glial responses than that with tungsten supports. CONCLUSION: The proposed carbon fiber based microelectrode array is expected to be used for long-term in vivo neural recording from deep brain regions with the minimized reactive tissue response.
Animals ; Brain ; Carbon ; Electric Impedance ; Electrodes ; Fibroins ; Microelectrodes* ; Rats ; Silicon ; Silk* ; Tungsten

OBJECTIVE: To explore the effect of lentivirus-mediated BMP-2 overexpression plasmid transfection into bone marrow mesenchymal stem cells and silk fibroin scaffold on osteoblast transformation. METHODS: The lentivirus BMP-2 overexpression vector was constructed, bone marrow mesenchymal stem cells were cultured, and the combined culture system of nuclear scaffolds was constructed. Alizarin red staining and alkaline phosphatase staining were used to detect the osteogenic transformation of bone marrow mesenchymal stem cells in vitro. Ten New Zealand white rabbits, weighing 3.2 to 4.5 kg(averaging 3.9 kg), aged (2.89±0.45) years old, were selected to construct the rabbit tibial defect model by drilling a conical tibial defect (5 mm in length, 2 mm in width and 3 mm in depth) with an oral drill. The repair of the tibial defect in the animal model was observed by HE staining. The experimental group was implanted with silk fibroin scaffold + BMP-2 overexpression vector bone marrow mesenchymal stem cell complex, while the negative control group was implanted with silk fibroin scaffold+non-transfected bone marrow mesenchymal stem cell complex. RESULTS: Compared with the control group(silk fibroin scaffold+non-transfected bone marrow mesenchymal stem cells), the number of adherent cells on the surface of the scaffold in the experimental group(silk fibroin scaffold+transfected BMP-2 overexpression vector BMP-2 complex) increased significantly. Compared with the control group, the ECM secretion in the experimental group increased significantly. EDX analysis showed that the content of calcium ion was 0.22% in the control group and 0.86% in the experimental group, which showed that the ability of inducing calcium ion formation in the experimental group was stronger than that in the control group. Alizarin red staining of calcium nodules showed that there was no obvious change in the naked eye of the control group, and a small amount of calcium nodules could be seen under the microscope. In the experimental group, obvious red area staining was observed by naked eye, and a large number of calcium nodules were observed by microscopy. The results of alkaline phosphatase staining showed that there was no obvious change in the naked eye of the control group, and no obvious change in the microscopic observation. In the experimental group, purple area staining was observed by naked eyes, and ALP staining was strongly positive by microscopy. The combined culture system of silk fibroin scaffold and bone marrow mesenchymal stem cells can repair cartilage defects. The repair effect of BMP-2 bone marrow mesenchymal stem cells after transfection is obviously better than that of non-transfection group. HE staining showed that inflammatory cells decreased and scaffolds disappeared slightly in the control group. In the experimental group, inflammatory cells were significantly reduced, scaffolds disappeared and angiogenesis was observed. CONCLUSIONS Lentivirus-mediated BMP-2 overexpression plasmid can promote BMSC to differentiate into osteocytes and secrete more extracellular matrix containing Ca²⁺ to promote bone defect repair.
Animals ; Bone Marrow Cells ; Bone Morphogenetic Protein 2 ; Cells, Cultured ; Fibroins ; Lentivirus ; Mesenchymal Stem Cells ; Osteoblasts ; Osteogenesis ; Plasmids ; Rabbits ; Transfection

Dimethyl sulfoxide (Me SO) supplemented with fetal bovine serum (FBS) is a widely used cryoprotectant combination. However, high concentration of Me SO is toxic to cells, and FBS presents problems related to diseases such as bovine spongiform encephalopathy and viral infections. Silk protein is a kind of natural macromolecule fiber protein with good biocompatibility and hydrophilicity. The aim of this paper is to analyze the cryoprotective mechanism of silk protein as cryoprotectant. Firstly, differential scanning calorimetry (DSC) was used to measure the thermal hysteresis activity (THA) of silk protein. The THA of 10 mg/mL sericin protein was 0.96°C, and the THA of 10% (V/V) fibroin protein was 1.15°C. Then the ice recrystallization inhibition (IRI) of silk protein-PBS solution was observed with cryomicroscope. The cold stage was set at - 7°C, after 40 minutes' incubation, the mean grain size rate (MGSR) of sericin protein and fibroin protein were 28.99% and 3.18%, respectively, which were calculated relative to phosphate buffer saline (PBS) control. It is indicated that sericin and silk fibroin have certain effects of inhibiting recrystallization of ice crystals. Finally, the structure and physicochemical properties of silk protein were analyzed by Fourier transform infrared spectroscopy (FTIR). The results showed that the content of the random coil was 75.62% and the β-sheet structure was 24.38% in the secondary of sericin protein. The content of the β-sheet structure was 56.68%, followed by random coil structure 22.38%, and α-helix 16.84% in the secondary of fibroin protein. The above analysis demonstrates the feasibility of silk fibroin as a cryoprotectant, and provides a new idea for the selection of cryoprotectants in the future.
Animals ; Bombyx ; Calorimetry, Differential Scanning ; Fibroins ; Sericins ; Silk ; Spectroscopy, Fourier Transform Infrared

OBJECTIVE: This study aims to prepare oriented scaffolds derived from a cartilage extracellular matrix (CECM) and silk fibroin (SF) and use to investigate their physicochemical property in cartilage tissue engineering. METHODS: Oriented SF-CECM scaffolds were prepared from 6% mixed slurry (CECM：SF=1：1) through modified temperature gradient-guided thermal-induced phase separation, followed by freeze drying. The SF-CECM scaffolds were evaluated by scanning electron microscopy (SEM) and histological staining analyses and determination of porosity, water absorption, and compressive elastic modulus of the materials. RESULTS: The SEM image showed that the SF-CECM scaffolds contained homogeneous reticular porous structures in the cross-section and vertical tubular structures in the longitudinal sections. Histological staining showed that cells were completely removed, and the hybrid scaffolds retained proteogly can and collagen. The composition of the scaffold was similar to that of natural cartilage. The porosity, water absorption rate, and vertical compressive elastic modulus of the scaffolds were 95.733%±1.010%, 94.309%±1.302%, and (65.40±4.09) kPa, respectively. CONCLUSIONS The fabricated SF-CECM scaffolds exhibit satisfactory physicochemical and biomechanical properties and thus could be an ideal scaffold in cartilage tissue engineering.
Cartilage ; Extracellular Matrix ; Fibroins ; Porosity ; Silk ; Tissue Engineering ; Tissue Scaffolds

The extracellular matrix (ECM) is known to provide instructive cues for cell attachment, proliferation, differentiation, and ultimately tissue regeneration. The use of decellularized ECM scaffolds for regenerative-medicine approaches is rapidly expanding. In this study, cartilage acellular matrix (CAM)-based bioink was developed to fabricate functional biomolecule-containing scaffolds. The CAM provides an adequate cartilage tissue–favorable environment for chondrogenic differentiation of cells. Conventional manufacturing techniques such as salt leaching, solvent casting, gas forming, and freeze drying when applied to CAM-based scaffolds cannot precisely control the scaffold geometry for mimicking tissue shape. As an alternative to the scaffold fabrication methods, 3D printing was recently introduced in the field of tissue engineering. 3D printing may better control the internal microstructure and external appearance because of the computer-assisted construction process. Hence, applications of the 3D printing technology to tissue engineering are rapidly proliferating. Therefore, printable ECM-based bioink should be developed for 3D structure stratification. The aim of this study was to develop printable natural CAM bioink for 3D printing of a tissue of irregular shape. Silk fibroin was chosen to support the printing of the CAM powder because it can be physically cross-linked and its viscosity can be easily controlled. The newly developed CAM-silk bioink was evaluated regarding printability, cell viability, and tissue differentiation. Moreover, we successfully demonstrated 3D printing of a cartilage-shaped scaffold using only this CAM-silk bioink. Future studies should assess the efficacy of in vivo implantation of 3D-printed cartilage-shaped scaffolds.
Cartilage* ; Cell Survival ; Cues ; Extracellular Matrix ; Fibroins ; Freeze Drying ; Printing, Three-Dimensional* ; Regeneration ; Silk ; Tissue Engineering ; Viscosity