Effect of Silver Sulfadiazine and Metallic Ions on Properties of Thai Silk Fibroin/Gelatin Films for Anti-Bacterial Applications

This study aimed to develop Thai silk fibroin/gelatin (SF/GA) films incorporating various concentrations of silver sulfadiazine (SSD) and to investigate the effects of SSD and metallic ions (Ag(I) and Cu(II)) on chemical conformation of the SF/GA films. We found that the incorporation of SSD in the films changed the conformation of silk fibroin protein by increasing β-sheet content. The same phenomena was also observed with the other 2 metallic ions, Ag(I) and Cu(II), incorporated in the SF/GA films. This effect of metallic ions on the SF conformation transition in the SF/GA films may be similar to the phenomenon occurred during natural spinning process of the Bombyx mori silkworm. The SF/GA films incorporating SSD had therefore more stability, less water-insoluble fraction and extended degradation rate than the SF/GA films without SSD due to the higher content of stable β-sheet conformation. When cultured with L929 mouse fibroblast cells according to ISO 10993 part 5 standard, the SF/GA films incorporating SSD at all concentrations showed no cytotoxicity. The SSD released from the films also showed obvious anti-bacterial activity against Staphylococcus aureus (Gram positive) and Escherichia coli (Gram negative) bacteria. We suggested that the SF/GA films incorporating SSD may be useful for some medical applications in which anti-bacterial effect was required

Characterizations of Poly(vinyl chloride)/Acrylonitrile Styrene Acrylate Blends for Outdoor Applications

Significant enhancement on impact property of poly(vinyl chloride)/acrylonitrile styrene acrylate (PVC/ASA) blends was observed. The effect of ASA content on mechanical characteristics, including impact strength, themomechanical properties, water absorption, and outdoor weathering durability were investigated. The results suggested that the impact strength of the PVC/ASA blends increased drastically at the ASA content of about 30 - 40 wt% and at the ASA content of 50 wt%, the significant high impact strength of up to 77.6 kJ/m2 was obtained. The modulus and strength under tensile and flexural loads of PVC/ASA blends were found to increase with the PVC fraction while glass transition temperature and heat deflection temperature systematically increased with increasing ASA content. The blends are partially miscible in nature as evidenced from the shift of the two glass transition temperatures towards each other in the dynamic mechanical analysis. In addition, ASA fraction in the blends provides improved resistance to UV radiation for the PVC/ASA blend sample under natural weathering. The obtained PVC/ASA blends clearly showed a potential use as high impact plastic products for outdoor application

Osteogenic differentiation of encapsulated cells in dexamethasone-loaded phospholipid-induced silk fibroin hydrogels

The tissue engineering triad comprises the combination of cells, scaffolds and biological factors. Therefore, we prepared cell- and drug-loaded hydrogels using in situ silk fibroin (SF) hydrogels induced by dimyristoyl glycerophosphoglycerol (DMPG). DMPG is reported to induce rapid hydrogel formation by SF, facilitating cell encapsulation in the hydrogel matrix while maintaining high cell viability and proliferative capacity. In addition, DMPG can be used for liposome formulations in entrapping drug molecules. Dexamethasone (Dex) was loaded into the DMPG-induced SF hydrogels together with human osteoblast-like SaOS-2 cells, then the osteogenic differentiation of the entrapped cells was evaluated in vitro and compared to cells cultured under standard conditions. Calcium production by cells cultured in DMPG/Dex-SF hydrogels with Dex-depleted osteogenic medium was equivalent to that of cells cultured in conventional osteogenic medium containing Dex. The extended-release of the entrapped Dex by the hydrogels was able to provide a sufficient drug amount for osteogenic induction. The controlled release of Dex was also advantageous for cell viability even though its dose in the hydrogels was far higher than that in osteogenic medium. The results confirmed the possibility of using DMPGinduced SF hydrogels to enable dual cell and drug encapsulation to fulfil the practical applications of tissue-engineered constructs.This research was partially supported by the Asahi Glass Foundation (grant number: RES_65_530_33_026). CL would like to express gratitude for the Second Century Fund (C2F), Chulalongkorn University, for the support of a post-doctoral fellowship

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.This article has been prepared with the support of REMIX Project, funded by the European Union’s Horizon 2020 Research and Innovation programme under the Maria Sklodowska-Curie grant agreement N.778078. Chavee Laomeephol acknowledges the PhD grants supported by Chulalongkorn University for “The 100th Anniversary Chulalongkorn University Fund for Doctoral Scholarship” and “The 90th Anniversary Chulalongkorn University Fund (Ratchadaphiseksomphot Endowment Fund)”. Authors also acknowledge the financial support from FCT (Portuguese Foundation for Science and Technology) for the project PTDC/CTM-BIO/4388/2014 - SPARTAN, the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (FEDER) (NORTE-01-0145-FEDER-000023 FROnTHERA) and the NORTE 2020 Structured Project, co funded by Norte2020

Hydrogelation of Regenerated Silk Fibroin via Gamma Irradiation

Gamma irradiation, which is one of the more conventional sterilization methods, was used to induce the hydrogelation of silk fibroin in this study. The physical and chemical characteristics of the irradiation-induced silk fibroin hydrogels were investigated. Silk fibroin solution with a concentration greater than 1 wt% formed hydrogel when irradiated by gamma rays at a dose of 25 or 50 kGy. The hydrogel induced by 50 kGy of radiation was more thermally stable at 80 °C than those induced by 25 kGy of radiation. When compared to the spontaneously formed hydrogels, the irradiated hydrogels contained a greater fraction of random coils and a lower fraction of β-sheets. This finding implies that gelation via gamma irradiation occurs via other processes, in addition to crystalline β–sheet formation, which is a well-established mechanism. Our observation suggests that crosslinking and chain scission via gamma irradiation could occur in parallel with the β–sheet formation. The irradiation-induced hydrogels were obtained when the solution concentration was adequate to support the radiation crosslinking of the silk fibroin chains. This work has, therefore, demonstrated that gamma irradiation can be employed as an alternative method to produce chemical-free, random coil-rich, and sterilized silk fibroin hydrogels for biomedical applications

Thermomechanical and rheological behaviours of waste glass fibre-filled polypropylene composites

The composites between the reinforced glass fibre wastes obtained from surfboard manufacturing industry and polypropylene were developed for value adding and environmental reasons. The thermomechanical and rheological behaviours of the composites were investigated. Glass fibre contents were varied from 5 to 30wt%. The effects of maleic anhydride grafted polypropylene (MA-PP) compatibilizer on the behaviours were also determined. The results revealed that the addition of glass fibre was able to reduce the heat of fusion of the composite. Additionally, the tensile and flexural properties were increased with increasing the glass fibre contents following the rule of mixtures. The addition of MA-PP led to enhance tensile and flexural properties due to the improvement of the adhesion between matrix and glass fibre, which is correlated with morphological observations. From the rheological studies, the apparent flow activation energy revealed that the addition of glass fibre decreased the fluidity of the molten composite materials; however, it could be slightly improved by using MA-PP

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

Crosslinked Silk Fibroin/Gelatin/Hyaluronan Blends as Scaffolds for Cell-Based Tissue Engineering

3D porous scaffolds fabricated from binary and ternary blends of silk fibroin (SF), gelatin (G), and hyaluronan (HA) and crosslinked by the carbodiimide coupling reaction were developed. Water-stable scaffolds can be obtained after crosslinking, and the SFG and SFGHA samples were stable in cell culture medium up to 10 days. The presence of HA in the scaffolds with appropriate crosslinking conditions greatly enhanced the swellability. The microarchitecture of the freeze-dried scaffolds showed high porosity and interconnectivity. In particular, the pore size was significantly larger with an addition of HA. Biological activities of NIH/3T3 fibroblasts seeded on SFG and SFGHA scaffolds revealed that both scaffolds were able to support cell adhesion and proliferation of a 7-day culture. Furthermore, cell penetration into the scaffolds can be observed due to the interconnected porous structure of the scaffolds and the presence of bioactive materials which could attract the cells and support cell functions. The higher cell number was noticed in the SFGHA samples, possibly due to the HA component and the larger pore size which could improve the microenvironment for fibroblast adhesion, proliferation, and motility. The developed scaffolds from ternary blends showed potential in their application as 3D cell culture substrates in fibroblast-based tissue engineering