Haiping Zhang

Enhancing effect of glycerol on the tensile properties of Bombyx mori cocoon sericin films.

An environmental physical method described herein was developed to improve the tensile properties of Bombyx mori cocoon sericin films, by using the plasticizer of glycerol, which has a nontoxic effect compared with other chemical crosslinkers. The changes in the tensile characteristics and the structure of glycerolated (0–40 wt% of glycerol) sericin films were investigated. Sericin films, both in dry and wet states, showed enhanced tensile properties, which might be regulated by the addition of different concentrations of glycerol. The introduction of glycerol results in the higher amorphous structure in sericin films as evidenced by analysis of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra, thermogravimetry (TGA) and differential scanning calorimetry (DSC) curves. Scanning Electron Microscopy (SEM) observation revealed that glycerol was homogeneously blended with sericin molecules when its content was 10 wt%, while a small amount of redundant glycerol emerged on the surface of sericin films when its content was increased to 20 wt% or higher. Our results suggest that the introduction of glycerol is a novel nontoxic strategy which can improve the mechanical features of sericin-based materials and subsequently promote the feasibility of its application in tissue engineering.

Preparation of a Silk Fibroin Spongy Wound Dressing and Its Therapeutic Efficiency in Skin Defects

A novel silk fibroin spongy wound dressing (SFSD) incorporated with nano-Ag particles was prepared by coagulating with 1.25–5.0% (v/v) poly(ethylene glycol diglycidyl ether) (PGDE). The mechanical properties, moisture permeability and hygroscopicity of SFSD, and the nano-Ag release behavior from SFSD were evaluated. The results showed that the soft SFSD had satisfying tensile strength and flexibility, as well as excellent moisture permeability and absorption capability of wound exudates. The moisture permeability was 101 g/m2 per h and the water absorption capacity of SFSD was 595.2% and 251.9% of its own weight in dry and wet states, respectively. The nano-Ag in the SFSD was released continuously at a relatively stable rate in PBS resulting in a remarkable antibacterial property. A rabbit model was used to dynamically observe the healing process of full-thickness skin defects. Full-thickness wounds were created on the dorsal side of rabbits, which were covered with SFSD and porcine acellular dermal matrix (PADM) for comparison. The mean healing time of the wounds covered with SFSD was 17.7 ± 2.4 days, significantly shorter than that with PADM. The histological analysis showed that the epidermal cell layer formed with SFSD was very similar to normal skin, suggesting that SFSD may provide a good component for the development of new wound dressings.

Fabrication of a novel blended membrane with chitosan and silk microfibers for wound healing: characterization, in vitro and in vivo studies

Pure chitosan membranes present insufficient mechanical properties and a high swelling ratio, which limits their application in biomedical field. In this study, silk microfibers were obtained by chemical hydrolysis, and a novel type of chitosan/silk microfiber (CS/mSF) blended membrane was reported and its multiple physical properties were evaluated. The mechanical properties were significantly improved after blending silk microfibers with a chitosan matrix, while the swelling ratio was decreased. Observation of the surface microstructures of the blended membranes via scanning electron microscopy showed abundant embedding of mSF into the CS matrix, as well as connections among mSF. In vitro cytocompatibility was also investigated, and the blended membranes exhibited significant cytocompatibility, which was demonstrated by cell proliferation and cell morphology. Furthermore, the in vivo healing effects of the blended membrane as a wound dressing were determined on a full-thickness skin wound model of rats. Animal studies revealed that the membranes containing mSF exhibited increased wound healing efficiency compared with pure CS membranes and treatment without wound dressing. From an examination of histological changes, a higher level of epithelialization and collagen formation was observed with treatment of CS/mSF blended membranes after a 21 day repair period. In conclusion, our results indicated that the blended membranes with CS and mSF might be a potential candidate material for wound healing.

Fabrication and Characterization of Porous Tubular Silk Fibroin Scaffolds

Silk fibroin (SF) has been one of promising resources of biotechnology and biomedical materials due to its unique properties. Here, different sizes of porous tubular scaffolds were fabricated from a SF aqueous solution with the addition of poly(ethylene glycol diglycidyl ether) (PGDE). The scaffolds were generally flexible and transparent at the wet state with a pore size of 81–128 μm and porosity of 90–96%, depending on the concentrations of SF and PGDE. The mechanical properties measurement showed that the tubular SF scaffolds had satisfying tensile and compression properties, especially the excellent deformation–recovery ability. FT-IR spectra indicated that the SF in the tubular scaffolds was in a β-sheet structure, and no PGDE characteristic band was observed, suggesting that the PGDE could be removed from the scaffolds by soaking in deionized water. The cell compatibility of scaffolds was evaluated, and no obvious cytotoxicity to mouse L-929 fibroblasts was detected.

Silk fibroin/sodium alginate composite nano-fibrous scaffold prepared through thermally induced phase-separation (TIPS) method for biomedical applications

To mimic the natural fibrous structure of the tissue extracellular matrix, a nano-fibrous silk fibroin (SF)/sodium alginate (SA) composite scaffold was fabricated by a thermally-induced phase-separation method. The effects of SF/SA ratio on the structure and the porosity of the composite scaffolds were examined. Scanning electron microscopy and porosity results showed that the 5SF/1SA and 3SF/1SA scaffolds possessed an excellent nano-fibrous structure and a porosity of more than 90%. Fourier transform infrared, X-ray diffraction, and differential scanning calorimetry results indicated the physical interaction between SF and SA molecules and their good compatibility in the 5SF/1SA and 3SF/1SA scaffolds, whereas they showed less compatibility in the 1SF/1SA scaffold. Cell culture results showed that MG-63 cells can attach and grow well on the surface of the SF/SA scaffolds. The nano-fibrous SF/SA scaffold can be potentially used in tissue engineering.

Preparation and characterization of a novel spongy hydrogel from aqueous Bombyx mori sericin

Abstract We attempted to obtain a novel spongy hydrogel from aqueous Bombyxmori (B. Mori) sericin by using a freeze-thaw method without any cross-linking reagent. The aqueous sericin solution utilized was extracted from silkworm cocoons by using boiling method, and showed continuous molecular weight distribution mainly from 43 kDa to 212 kDa and even higher. To optimize the conditions for hydrogel preparation, the efficiency of hydrogel transformation from sericin solution were investigated by changing sericin concentration, freezing time, freezing temperature and frozen-thawed repetition. The porous characteristics of sericin hydrogel including the porosity, density and maximal water absorbency were performed by changing freezingn conditions. The pore size and morphology of hydrogels prepared at different concentration and freezing temperatures were observed with SEM. FTIR, XRD and DSC curves indicate that the hydrogel prepared at -20 °C and -80 °C adopt mainly random coil conformation.

Key Characteristics of a Novel Silk Yarn from Fresh Cocoons

We studied the key characteristics of a novel silk yarn reeled from fresh cocoons. Compared with traditional silk yarn, this novel silk yarn displayed better mechanical properties, especially in terms of a higher breaking stress and toughness, and exhibited a different surface morphology. A cross-sectional observation and the sericin content results illustrated that different sericin coatings on the silk yarn reeled from fresh cocoons surface did not improve the mechanical properties. The degumming and tensile testing analysis indicated that degummed silk fibroin of novel silk yarn is able to resist deformation and fracture better than silk fibroin of traditional silk yarn. The FTIR results revealed that the selected techniques is an important contributor to the silk fibroin mechanical properties, because novel technique brought higher percentage beta-sheet structures in novel silk yarn fibroin than traditional silk yarn. The new technique that using novel silk yarn has improved its mechanical properties and it is expected that the silk yarn with superior mechanical properties could be used in fabrics transistors, electrodes and reinforced biomaterials.