Tippawan Siritientong

Potential applications of silk sericin, a natural protein from textile industry by-products

Silk is composed of two major proteins, fibroin (fibrous protein) and sericin (globular, gumming protein). Fibroin has been used in textile manufacturing and for several biomaterial applications, whereas sericin is considered a waste material in the textile industry. Sericin has recently been found to activate the proliferation of several cell-lines and has also shown various biological activities. Sericin can form a gel by itself; however, after mixing with other polymers and cross-linking it can form a film or a scaffold with good characteristics that can be used in the cosmetic and pharmaceutical industries. Sericin is proven to cause no immunological responses, which has resulted in a more acceptable material for biological applications.

Formulation and characterization of silk sericin–PVA scaffold crosslinked with genipin

A porous-three-dimensional scaffold shows several advantages in terms of tissue engineering since it can provide a framework for cells to attach, proliferate and form an extracellular matrix. Sericin, a by-product from the silk industry, can form a three-dimensional scaffold with PVA after freeze-drying but has a fragile structure. Glycerin (as a plasticizer) and genipin (a crosslinking agent) are necessary to make a strong and stable matrix. Our objective was to investigate the properties of a three-dimensional silk sericin and PVA scaffold with and without glycerin and genipin at various concentrations. SEM showed that adding glycerin into scaffold gave better uniformity and porosity. Smaller pore sizes and better uniformity were found as the concentration of genipin in the scaffold increased. The results of FTIR indicated that glycerin retained a high moisture content and had a major effect at 3286 cm(-1), indicating the presence of water molecule in the matrix structure. Adding genipin into the scaffold resulted in a higher degree of crosslinking or fewer free ∈-amino groups, as shown by the decrease in the stretching (=C-H) peak and absorption peaks around 1370-1650 cm(-1), respectively. The sericin/PVA scaffold had a low water sorption capacity, but adding glycerin significantly increased this property. Genipin further enhanced the moisture absorption capacity of the scaffold and extended the time taken to reach equilibrium. After immersing the sericin/PVA scaffold into purified water, the scaffold completely dissolved within an hour, whereas the scaffolds containing glycerin or glycerin with 0.1% genipin swelled 8 and 11 times, respectively, compared with the initial stage after 6h of immersion. In terms of mechanical properties, the sericin/PVA/glycerin scaffold exhibited a similar compressive strength to the scaffold with a high genipin concentration, whereas a low concentration of genipin softened and reduced the compressive strength of the scaffold. A small amount of sericin was released from the scaffold and a higher concentration of genipin, resulting in less protein leaching compared to non-crosslinked sericin/PVA. The fraction of protein released from the sericin/PVA/glycerin scaffold was about 4%, with values of about 1 and 0.04% in the case of scaffolds with 0.01 and 0.1% genipin, respectively. All results indicated that the composition of the scaffolds had a significant effect on their physical properties, and that can easily be tuned to obtain scaffolds suitable for biological applications.

Sericin cream reduces pruritus in hemodialysis patients: a randomized, double-blind, placebo-controlled experimental study

BackgroundUremic pruritus (UP) is a significant complication in ESRD patients and substantially impairs their quality of life. UP is considered to be a skin manifestation of chronic inflammation. Because sericin can suppress the release of pro-inflammatory cytokines, the purpose of this study was to investigate the short-term safety and efficacy of sericin cream for treating UP in hemodialysis patients.MethodsThis study used a double-blind design to investigate the effects of random topical administration of sericin cream and cream base (placebo) on either the right or left extremities of hemodialysis patients for 6 weeks. Skin hydration, irritation and pigmentation were evaluated every 2 weeks using Skin Diagnostic SD27. The visual analog scale for itching was also evaluated every 2 weeks, and the Kidney Disease Quality of Life Short Form was performed on the day of each patient’s enrollment and after 6 weeks of treatment.ResultsFifty dialysis patients were enrolled, 47 of which completed the study. The hydration of the skin of the patients’ extremities increased significantly after administration of sericin cream; significant differences were found between sericin treatment and control after 6 weeks of treatment (p = 0.041 for arms and p = 0.022 for legs, respectively). Moreover, a significant difference was also found in skin irritation between the two treatments (p = 0.013 for arms and p = 0.027 for legs, respectively). At the end of the study, the skin pigmentation level was significantly reduced on both the arms (p = 0.032) and legs (p = 0.021) of the sericin-treated side compared with the side treated with cream base. The mean itching score decreased significantly from moderate to severe at the time of enrollment to mild pruritus after 6 weeks of treatment (p = 0.002). A better quality of life was found in all domains tested although statistically significant differences before and after treatment was found only in the patients’ pain scores, the effect of kidney disease on daily life, sleep quality and symptoms or problems related to kidney disease.ConclusionsWe conclude that sericin cream has a high potential for reducing UP in hemodialysis patients.The trial registration number of this study is ISRCTN16019033; its public title is “sericin cream reduces pruritus in hemodialysis patients”.

Preliminary Characterization of Genipin-Cross-Linked Silk Sericin/Poly(vinyl alcohol) Films as Two-Dimensional Wound Dressings for the Healing of Superficial Wounds

The genipin-cross-linked silk sericin/poly(vinyl alcohol) (PVA) films were developed aiming to be applied as two-dimensional wound dressings for the treatment of superficial wounds. The effects of genipin cross-linking concentration on the physical and biological properties of the films were investigated. The genipin-cross-linked silk sericin/PVA films showed the increased surface density, tensile strength, and percentage of elongation, but decreased percentage of light transmission, water vapor transmission rate, and water swelling, compared to the non-cross-linked films. This explained that the cross-linking bonds between genipin and silk sericin would reduce the mobility of molecular chains within the films, resulting in the more rigid molecular structure. Silk sericin was released from the genipin-cross-linked films in a sustained manner. In addition, either L929 mouse fibroblast or HaCat keratinocyte cells showed high percentage of viability when cultured on the silk sericin/PVA films cross-linked with 0.075 and 0.1% w/v genipin. The in vivo safety test performed according to ISO 10993-6 confirmed that the genipin-cross-linked silk sericin/PVA films were safe for the medical usages. The efficacy of the films for the treatment of superficial skin wounds will be further investigated in vivo and clinically. The genipin-cross-linked silk sericin/PVA films would be promising choices of two-dimensional wound dressings for the treatment of superficial wounds.

Improvement of Physical and Wound Adhesion Properties of Silk Sericin and Polyvinyl Alcohol Dressing Using Glycerin.

OBJECTIVE:This study aimed to use glycerin to improve physical and wound adhesion properties of a wound dressing made of silk sericin and polyvinyl alcohol (PVA). DESIGN:Glycerin of a natural-derived plasticizer was used to modify the properties of silk sericin/PVA scaffolds. Various concentrations of glycerin were mixed with silk sericin and PVA and then fabricated into the scaffolds by a freeze-drying technique. The control study was performed to examine the properties of the silk sericin/PVA scaffolds with and without glycerin. MAIN OUTCOME MEASURES:Physical, mechanical, wound adhesion properties, the release profile of silk sericin, and in vivo safety of the silk sericin/PVA scaffolds with and without glycerin were investigated. MAIN RESULTS:The silk sericin/PVA scaffolds with glycerin exhibited more homogenous structure, less compressive modulus, higher Young modulus and elongation percentage, and a higher degree of crosslinking compared with the scaffold without glycerin. The silk sericin/PVA scaffold with 2% wt/vol glycerin showed more controlled release of silk sericin than the other scaffolds. The sustained release of silk sericin from the scaffold with glycerin would be advantageous for long-term healing of wounds. The silk sericin/PVA scaffold with 2% (wt/vol) glycerin was less adhesive to the wound compared with the scaffold without glycerin. Furthermore, the implantation of silk sericin/PVA scaffolds with 2% (wt/vol) glycerin did not cause any irritation to the tissue. CONCLUSION:The silk sericin/PVA scaffolds with glycerin were introduced as a biocompatible, more flexible, and less adhesive wound dressing than the scaffold without glycerin.

Characteristics of carboxymethyl cellulose/sericin hydrogels and the influence of molecular weight of carboxymethyl cellulose

Carboxymethyl cellulose (CMC),which is a hydrophilic polysaccharide obtained from the carboxymethylation of natural cellulose, has been formulated as hydrogel for various biomedical applications. However, the functional crosslinking agents were required to form the stable CMC hydrogels. In this study, sericin which is a glue-like protein that envelops the fibroin fiber in the silkworm cocoons was introduced to blend with CMC to form a mechanically stable hydrogel without further crosslinking. Furthermore, the effect of molecular weight of CMC on characteristics of the CMC/sericin hydrogels obtained was investigated. We found that the incorporation of sericin in CMC hydrogels enhanced the stability and the hydrogel’s resistance to hydrolysis and enzymatic degradation while the porous structure and swelling abilities of the CMC hydrogels were preserved. The in vitro biodegradation of the CMC/sericin hydrogels and the release of sericin from the hydrogels were evaluated. The biodegradability of the CMC/sericin hydrogels depended on the molecular weight of CMC. The high molecular weight CMC/sericin hydrogels showed the slowest rate of degradation. The slow-degrading high molecular weight CMC/sericin hydrogels resulted in the lowest amount of sericin release while the fast-degrading low and medium molecular weight CMC/sericin hydrogels released high amount of sericin. The high amount of sericin released from the fast-degrading low and medium molecular weight CMC/sericin hydrogels could consequently promote the collagen production of L929 cells. These CMC/sericin hydrogels could be further investigating to be applied as a wound dressing material.

The effects of Bombyx mori silk strain and extraction time on the molecular and biological characteristics of sericin

Sericin was extracted from three strains of Thai Bombyx mori silk cocoons (white shell Chul1/1, greenish shell Chul3/2, and yellow shell Chul4/2) by a high-pressure and high-temperature technique. The characteristics of sericin extracted from different fractions (15, 45, and 60 min extraction process) were compared. No differences in amino acid composition were observed among the three fractions. For all silk strains, sericin extracted from a 15-min process presented the highest molecular weight. The biological potential of the different sericin samples as a bioadditive for 3T3 fibroblast cells was assessed. When comparing sericin extracted from three silk strains, sericin fractions extracted from Chul4/2 improved cell proliferation, while sericin from Chul 1/1 activated Type I collagen production to the highest extent. This study allows the natural variability of sericin obtained from different sources and extraction conditions to be addressed and provides clues for the selection of sericin sources. Graphical abstract Molecular and biological characters of sericin extracted from three strains of Thai Bombyx mori silk cocoons by a high-pressure and high-temperature technique.

A Novel Silk Sericin/Poly (Vinyl Alcohol) Composite Film Crosslinked with Genipin: Fabrication and Characterization for Tissue Engineering Applications

Silk sericin, a gumming protein from silk cocoons, has been a considerable natural protein-based biopolymer for fabrication of desired constructs for potential tissue engineering applications. This study investigated the formulation of a novel biopolymeric silk sericin/poly (vinyl alcohol) film with genipin as crosslinking agent and its physical properties. Silk sericin itself forms a fragile material, adding other polymers such as poly (vinyl alcohol) and glycerin, a plasticizer, resulting in a strong and flexible matrix. The results indicated that at higher concentration of genipin (0.1% w/v), the percentages of crosslinking in sericin/poly (vinyl alcohol) films was significantly higher. The matrices also exhibited higher tensile modulus value and higher elasticity at higher genipin concentration which can be inferred to higher integrity of the structure compared to matrices with genipin at low concentration (0.01% w/v). On the other hand, the reverse patterns were found in percentages of light transmission and the releasing profile of sericin from the composite films. Adding genipin into the matrices resulted in a lower percentage of light transmission indicated the increase in opacity. The releasing profile of sericin from the films showed that high genipin concentrations reduced the peak of protein released and trended to provide the sustain-released profile of protein. These findings indicated that silk sericin film can be formed and the concentrations of crosslinking agents really affect its physical properties.