Preparation of new natural silk non-woven fabrics by using adhesion characteristics of sericin and their characterization.

Electro-spun regenerated silk webs have been extensively studied for biomedical applications because of the simplicity of their fabrication methods However, the productivity of the electro-spinning process is low for web fabrication and the mechanical properties of the electro-spun silk web are not satisfactory, which restricts its commercialization. In this study, a new silk non-woven fabric was successfully fabricated by wetting and hot press treatments using the excellent binding characteristic of sericin. The effects of the press temperature and residual sericin content on the preparation, structure, and properties of the silk non-woven fabric were examined. A press temperature of 200°C was optimum for obtaining non-woven fabrics with best mechanical properties, without yellowing. The silk non-woven fabric could not be fabricated without sericin, and a minimum of 8% sericin was required to fabricate it. As the sericin content was increased, the strength and Young's modulus of the silk non-woven fabric increased, while the tensile elongation remained constant. Regardless of the press temperature and sericin content, all the silk non-woven fabrics showed good cell viability, comparable to that of the tissue culture plate (TCP) used as a control until 4days, which however decreased compared to that of TCP after 7days.

Fabrication of an ultrafine fish gelatin nanofibrous web from an aqueous solution by electrospinning.

Electrospinning of aqueous gelatin solution obtained from bovine or porcine sources has been difficult to achieve without additional facilities, such as a temperature control oven or heating cover. Gelatin from cold-water fish has low contents of proline (Pro) and hydroxyproline (Hyp) compared with mammalian-derived gelatin. For this reason, the fish-derived gelatin maintains a sol state without showing gelation behavior at room temperature. In the present study, we prepared an ultrafine fish gelatin nanofibrous web by electrospinning from aqueous solutions without any additive polymers or temperature control facilities. The concentration and viscosity of fish gelatin are the most important factor in determining the electrospinnability and fiber diameter. Electrospinning of aqueous fish gelatin has the highest nanofiber productivity compared to other organic solvent systems. Using glutaraldehyde vapor (GTA), the water stability was improved and substantial enhancement was achieved in the mechanical properties. Finally, the cytotoxicity of a fish gelatin nanofibrous scaffold was evaluated based on a cell proliferation study by culturing human dermal fibroblasts (HDFs) compared with a fish gelatin film and nanofibrous mat from mammalian gelatin. The result shows better initial cell attachment and proliferation compared with the fish gelatin film and no significant difference compared with mammalian-derived gelatin nanofibrous mat. We expect that electrospinning of aqueous fish gelatin could be an effective alternative mammalian gelatin source.

Effect of residual sericin on the structural characteristics and properties of regenerated silk films.

Regenerated silk film has been increasingly attracting the research community's attention for biomedical applications due to its good biocompatibility and excellent cyto-compatibility. However, some limitations regarding its mechanical properties, such as brittleness, have restricted the use of silk films for industrial biomedical applications. In this study, regenerated silk films with different residual sericin content were prepared applying controlled degumming conditions to evaluate the effect of sericin content on the structure and properties of the films generated. When the residual sericin content increased to 0.6%, crystallinity index and breaking strength of silk films were increased. Above this value, these parameters then decreased. A 1.5 fold increase of silk film elongation properties was obtained when incorporating 16% sericin. Regardless of sericin content, all regenerated silk films showed excellent cyto-compatibility, comparable to the one obtained with tissue culture plates.

Multi-biofunction of antimicrobial peptide-immobilized silk fibroin nanofiber membrane: Implications for wound healing.

UNLABELLED: An antimicrobial peptide motif (Cys-KR12) originating from human cathelicidin peptide (LL37) was immobilized onto electrospun SF nanofiber membranes using EDC/NHS and thiol-maleimide click chemistry to confer the various bioactivities of LL37 onto the membrane for wound care purposes. Surface characterizations revealed that the immobilization density of Cys-KR12 on SF nanofibers could be precisely controlled with a high reaction yield. The Cys-KR12-immobilized SF nanofiber membrane exhibited antimicrobial activity against four pathogenic bacterial strains (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa) without biofilm formation on the membrane surface. It also facilitated the proliferation of keratinocytes and fibroblasts and promoted the differentiation of keratinocytes with enhanced cell-cell attachment. In addition, immobilized Cys-KR12 significantly suppressed the LPS-induced TNF-α expression of monocytes (Raw264.7) cultured on the membrane. These results suggest that a Cys-KR12-immobilized SF nanofiber membrane, which has multiple biological activities, would be a promising candidate as a wound dressing material. STATEMENT OF SIGNIFICANCE: This research article reports various bioactivities of an antimicrobial peptide on electrospun silk fibroin nanofiber membrane. Recently, human cathelicidin peptide LL37 has been extensively explored as an alternative antibiotic material. It has not only a great antimicrobial activity but also a wide variety of bioactivities which can facilitate wound healing process. Especially, many studies on immobilization of LL37 or its analogues have shown the immobilization technique could improve performance of wound dressing materials or tissue culture matrices. Nevertheless, so far studies have only focused on the bactericidal effect of immobilized peptide on material surface. On the other hand, we tried to evaluate multi-biofunction of immobilized antimicrobial peptide Cys-KR12, which is the shortest peptide motif as an analogue of LL37. We fabricated silk fibroin nanofiber membrane as a model wound dressing by electrospinning and immobilized the antimicrobial peptide. As a result, we confirmed that the immobilized peptide can play multi-role in wound healing process, such as antimicrobial activity, facilitation of cell proliferation and keratinocyte differentiation, and inhibition of inflammatory cytokine expression. These findings have not been reported and can give an inspiration in wound-care application.

Effect of shear viscosity on the preparation of sphere-like silk fibroin microparticles by electrospraying.

Silk fibroin (SF) is known to be a biocompatible material, and different forms of SF are used for various applications. However, the application of SF in particle form is rarely reported, compared to other forms. In this study, SF microparticles with a diameter of approximately 250 µm were prepared by the electrospray method, using 1 M LiCl/DMSO as a solvent. The dissolution time of SF in the CaCl2/CH3CH2OH/H2O solution and the concentration of the SF dope solution affected the final morphology of the microparticles. A long dissolution time and a low SF concentration led to the formation of irregular microparticles, but a short dissolution time and a high concentration produced sphere-like microparticles. The shear viscosity of the SF dope solution was the main parameter that affected the morphology of the SF microparticles. Regardless of the dissolution time in the CaCl2/CH3CH2OH/H2O solution and the concentration of the SF dope solution, the shear viscosity of the dope solution must be higher than 0.33 Pa s to produce sphere-like microparticles. Finally, cell adhesion experiments demonstrated that these SF microparticles show potential for use as cell carriers.