Ming Zhong Li

Preparation of Sericin Film and its Cytocompatibility

Bombyx mori Sericin films were prepared with PEG-DE as cross linking agent. The main physical properties, structure characteristics, cytotoxicity and cell proliferation of sericin films were measured and analyzed. The result showed that sericin films prepared by cast method containing 30-40% of PEG-DE, showed good mechanical properties. PEG-DE caused the changes of the condensed structure of sericin films. The films prepared from sericin extracted both from silk-gland and cocoon shell showed good cytocompatibility. Silk sericin films with PEG-DE had no obvious cytotoxicity to cells.

Neovascularization of Porous Silk Fibroin Films(PSFFs) as Dermis Substitutes Implanted in Rats

Neovascularization in biomaterials plays a key role in wound healing. In this paper, porous silk fibroin films (PSFFs) whose structure was optimized, as dermis substitutes, were implanted in the back skin of rats for recovery of dermis loss. Results showed that a thin layer of loose connective tissue had formed at the interface between PSFFs and subcutaneous tissues, in which abundant blood vessels could be observed at 24 h after surgery. Whereafter the newly formed connective tissue thickened and the number of microvessels in the tissue increased. Furthermore, a few microvessels could be seen in PSFFs at day 5, most of which were capillaries. By day 10, the density of microvessels in PSFFs increased to a peak while the percentage of capillary decreased. At day 23, both the density of microvessels and the percentage of capillary was almost equal to those of normal tissues. In summary, wound healing with PSFFs as dermis substitutes is the neovascularization process of PSFFs. The process includes three major steps: (1) new formation and growth of loose connective tissue into the pores of PSFFs, (2) proliferation and migration of fibroblasts and endothelial cells, and (3) formation of functional microvessels and their networks.

Genotoxic Potential of Regenerated Silk Fibroin Films by Different Cross-Linking Mode

Emerging studies have showed that silk fibroin might be as a naturally occurring degradable biomaterial for tissue engineering with unique mechanical properties, biocompatib ility and processability. To optimize the formation of the regenerated silk fibroin film, in thi s study, we examined the genotoxic potential of the regenerated silk fibroin films by differe nt cross-linking mode with micronucleus and the single cell gel electrophoresis (comet) assa y. The data showed that MNF in group PC and group SD showed significantly no differenc e with blank group (P>0.05), and no evident comet tails were observed. However, the resul t of EC group was significantly different from the control group(P<0.01). Taken together, R SFFs in group PC and group SD have no evident genotoxicity, which is better than group EC.

Study on Silk I Porous 3-D Scaffolds

A series of porous silk fibroin materials were prepared by freezing fibroin aqueous solution at –18 °C for 10 days. The process required no freeze-drying, chemical cross-linking, or the aid of other polymeric materials. X-ray powder diffraction patterns from the porous silk materials displayed features of crystal of metastable silk I polymorph. By adjusting the preparation conditions, silk I porous materials with average pore diameter of 30-240 μm and porosity of 70 -95 % can be prepared. The silk I porous materials were embedded in hypodermis on the dorsal surface of SD white rats, resulting that all rats survived with good general condition, and silk I porous materials were degraded and absorbed mostly in 6 weeks.

Study on Silk Fibroin Gelation: Effect of Polyalcohol

The Bombyx mori silk fibroin gel with three dimensional structures is an important form to be developed for tissue engineering materials. In this paper, silk fibroin gels were prepared with adding polyalcohol into silk fibroin solution. The gel structure was analyzed by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The results demonstrated that when adding more than 100% of polyalcohol, both of glycerol and polyethylene glycol 400 (PEG400) can accelerate the gelation process markedly. With the increase of the percentage of PEG400 and glycerol, it promoted silk fibroin molecules to cluster rapidly and inhibit silk fibroin molecules transforming from the random coil or α-helix to β-sheet in a ratio of 900% especially. Silk fibroin gels containing 100% of polyalcohol had more uniform morphology and the pores distributed uniformly.

Preparation of Silk Fibroin Microspheres

The Bombyx mori silk fibroin microspheres with controllable size were prepared by electrostatic spraying and freeze-drying method. The effects of solution concentration, voltage and flow rate on the sphere size were discussed. The morphology of microspheres was observed by scanning electron microscopy (SEM). The influence of ethanol treatment on the molecular conformation of silk fibroin microspheres was investigated by XRD and FT-IR spectra. The results indicated that the silk fibroin microspheres with diameter in range of 117-363 μm were spherical in shape, and there were plenty of pores both on the surface and in the interior of the microspheres. The sphere size increased with the rising of silk fibroin solution concentration and flow rate, while decreased as the voltage enhanced. The conformation of silk fibroin microspheres changed from random coil to silk II structure after ethanol treatment.

The Use of PEI in the Targeted Gene Delivery of VEGF165 and Ang-1

Poly (ethyleneimine) (PEI) is utilized as the delivery vector for vascular endothelial growth factor (VEGF) 165-angiopoietin-1 (Ang-1) dual gene simultaneous expression plasmid. The influences of PEI/pDNA ratios on the packing effect, cytotoxicity and transfection efficiency are investigated. The result of agarose gel electrophoresis suggesst that pDNA are entrapped into PEI completely when N/P ratio exceeds 3/1. MTT assay demonstrates that the cell viability is over 90% when the PEI/pDNA (w/w) ratios is respectively 1/2, 2/2, 3/3, 4/2 or 5/2. The L929 cells are transfected with PEI/pDNA in vitro, the results show that the fluorescence intensity and transfection efficiency could reach their highest levels when the PEI/pDNA ratio is 3/2. In general, this study provides a novel method for future in vivo transfection investigations.

Ultrasonication-Induced Rapid Gelation of Wild Silkworm Silk Fibroins

Silk fibroin （SF） hydrogels of the wild silkworm species Antheraea pernyi and Antheraea yamamai were obtained from aqueous SF solutions at room temperature. Both A. pernyi and A. yamamai solutions were slow to gelate. Hydrogels of the two species of wild silkworm were obtained rapidly following ultrasonicaton at 400–500 W. The secondary structure of the freeze-dried SF hydrogels was measured by X-ray diffraction and Fourier transform infrared spectroscopy. Ultrasonication did not change the main secondary structure of the hydrogels, but it accelerated the structural transformation of silk fibroin molecules from random coil or α helix to β sheet and reduced the gelation time.

Structure of Antheraea pernyi/Bombyx mori Silk Fibroin Scaffolds

As the tissue engineering scaffolds, the pore structure and condensed structure of silk fibroin scaffolds should be adjusted and controlled. In this study, Antheraea pernyi/Bombyx mori (A. p/B. m) silk fibroin blend scaffolds were prepared by freeze-drying. The influence of blend ratios on the pore structure and condensed structure of the scaffolds was investigated. The results showed that the average pore diameter of the blend scaffolds changed from 56 to 326 μm. Due to the difference of properties and the macromolecules aggregation status of two silk fibroin solutions, the pore diameter, content of α-helix and crystallinity of the scaffolds decreased with the increasing of the proportion of B. m silk fibroin. By adjusting the blend ratios, the pore structure and condensed structure of A. p/B. m silk fibroin blend scaffolds could be controlled.

Preparation of Braided Silk as a Tubular Tissue Engineering Scaffold

Silkworm silk has been recognized as a satisfactory biomaterial for long time due to its exceptional biocompatibility, biodegradability, mechanical properties etc. For example, silk fibers in the form of sutures have been used for centuries. The aim of this study is to discuss the potential usage of silk as the novel biomedical devices, such as blood vessels. In this study, cuit silks prepared from degummed raw silks were twisted as threads with four different yarn linear densities. A specific braiding machine was used to weave those threads into a tube. Subsequently two different groups of silk tubes were prepared. One was treated by ethanol and the other without. Thickness, porosity, mass per unit area of two groups of braided tubes were measured. Its mechanical properties were also studied. The influence of ethanol treatment and various yarn linear densities on its structural and mechanical properties was also studied. Results indicated that structural and mechanical properties of the tubes were significatly changed by the yarn linear densities and ethanol treatment. Conclusively, braided silk tube could be a potential blood vessel tissue engineering scaffold.