Using polyvinyl alcohol-ionic hydrogels containing a wound healing agent to manage wounds in different environments.

OBJECTIVE: To explore the effects of pH on properties of polyvinyl alcohol (PVA)-ionic hydrogels containing wound healing promoters. METHOD: PVA was combined with a natural wound healing promoter (silk sericin (SS)), and an anionic agent (eosin (ES)) or cationic agent (methylene blue (MB)), and made into hydrogels. Properties of the hydrogels and behaviour at different pHs were investigated. RESULTS: The density and gel fraction of PVA/SS-ES hydrogel and PVA/SS-MB hydrogel were considerably lower compared with hydrogel without SS. The swelling ratio and degradation of the hydrogels increased with increasing SS concentration in all pH solutions. The influence of SS in interrupting long-chain PVA molecules was confirmed based on changes in Fourier-transform infrared spectroscopy (FTIR). The SS released from the gels was found to interact with the ionic agent and influenced the release profile of the ionic agent. Surprisingly, the anionic agent in PVA/SS-ES hydrogel showed 70% release in high pH solution whereas the cationic agent in PVA/SS-MB hydrogel showed 86% release in low pH solution. Moreover, the active agent could accumulate on the skin layer and had a positive effect on a specific wound area. CONCLUSION: Based on the results obtained in this study, it is suggested to use anionic hydrogels containing wound healing promoter for wounds at high pH and cationic hydrogels containing wound healing promoter for wounds with low pH. Ability to improve wound healing using a natural healing agent combined with ionic agents and controlling the pH of hydrogels will help in developing quick and low-cost treatment for wounds.

Sericin-Based Poly(Vinyl) Alcohol Relieves Plaque and Epidermal Lesions in Psoriasis; a Chance for Dressing Development in a Specific Area.

The noncontagious immune-mediated skin disease known as psoriasis is regarded as a chronic skin condition with a 0.09-11.4% global prevalence. The main obstacle to the eradication of the disease continues to be insufficient treatment options. Sericin, a natural biopolymer from Bombyx mori cocoons, can improve skin conditions via its immunomodulatory effect. Many external therapeutic methods are currently used to treat psoriasis, but sericin-based hydrogel is not yet used to treat plaques of eczema. Through the use of an imiquimod rat model, this study sought to identify the physical and chemical characteristics of a silk sericin-based poly(vinyl) alcohol (SS/PVA) hydrogel and assess both its therapeutic and toxic effects on psoriasis. The cytokines, chemokines, and genes involved in the pathogenesis of psoriasis were investigated, focusing on the immuno-pathological relationships. We discovered that the SS/PVA had a stable fabrication and proper release. Additionally, the anti-inflammatory, antioxidant, and anti-apoptotic properties of SS/PVA reduced the severity of psoriasis in both gross and microscopic skin lesions. This was demonstrated by a decrease in the epidermal histopathology score, upregulation of nuclear factor erythroid 2-related factor 2 and interleukin (IL)-10, and a decrease in the expression of tumor necrosis factor (TNF)-α and IL-20. Moreover, the genes S100a7a and S100a14 were downregulated. Additionally, in rats given the SS/PVA treatment, blood urea nitrogen, creatinine, and serum glutamic oxaloacetic transaminase levels were within normal limits. Our findings indicate that SS/PVA is safe and may be potentiated to treat psoriasis in a variety of forms and locations of plaque because of its physical, chemical, and biological characteristics.

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.

The characteristics of bacterial nanocellulose gel releasing silk sericin for facial treatment.

BACKGROUND: Recently, naturally derived facial masks with beneficial biological properties have received increasing interest. In this study, silk sericin-releasing bacterial nanocellulose gel was developed to be applied as a bioactive mask for facial treatment. RESULTS: The silk sericin-releasing bacterial nanocellulose gel produced at a pH of 4.5 had an ultrafine and extremely pure fiber network structure. The mechanical properties and moisture absorption ability of the gel were improved, compared to those of the commercially available paper mask. Silk sericin could be control-released from the gel. A peel test with porcine skin showed that the gel was less adhesive than the commercially available paper mask, which would be removed from the face more easily without pain. The in vitro cytotoxicity test showed that the gel was not toxic to L929 mouse fibroblast and HaCaT human keratinocyte cells. Furthermore, when implanted subcutaneously and evaluated according to ISO10993-6 standard, the gel was not irritant to tissue. CONCLUSION: The silk sericin-releasing bacterial nanocellulose gel had appropriate physical and biological properties and safety for the facial treatment application.

Epidermis of Cereus hildmannianus as a biomimetic scaffold for tissue engineering.

A thin plastic-like film separated from the epidermis of Cereus hildmannianus has excellent tensile strength, resistance to water and high antimicrobial activity and supports the growth of mouse fibroblast cells. Cactuses are one of the most under explored plant species with high potential for food, materials, pharmaceutical and other applications. Although studies have shown the ability of cactuses to be used for food, as a source for fibers, as reinforcement for composites and other applications, the role of individual layers and their properties has been studied to a limited extent. In this paper, a thin translucent layer was separated from the epidermis of C. hildmannianus and studied for its composition, structure and properties. The layer is composed of about 73% cellulose and 2% lignin and morphologically, shows surface with uneven and serrated edges. Films with length of up to 36 cm, strength of 6.8 MPa and elongation of 2.5% could be peeled from the cactus suggesting their suitability for food packaging and other applications. X-ray diffraction patterns and FTIR spectrums indicated that the films are similar to that of cellulose and major thermal degradation occurred above 280°C. Compared to standards, the cactus films showed about 41% and 44% inhibition against gram positive and gram negative bacteria and 67% inhibition of the common fungal strain (A. niger). Films showed high stability in water and to common chemicals. When used as substrates for mouse fibroblast cell growth, no cytotoxicity was observed and the cactus peel supported the attachment and proliferation of cells demonstrating potential to be used as a biomaterial for tissue engineering applications.

Sericin coated thin polymeric films reduce keratinocyte proliferation via the mTOR pathway and epidermal inflammation through IL17 signaling in psoriasis rat model.

Therapeutic treatment forms can play significant roles in resolving psoriatic plaques or promoting wound repair in psoriatic skin. Considering the biocompatibility, mechanical strength, flexibility, and adhesive properties of silk fibroin sheets/films, it is useful to combine them with anti-psoriatic agents and healing stimulants, notably silk sericin. Here, we evaluate the curative properties of sericin-coated thin polymeric films (ScF) fabricated from silk fibroin, using an imiquimod-induced psoriasis rat model. The film biocompatibility and psoriatic wound improvement capacity was assessed. A proteomics study was performed to understand the disease resolving mechanisms. Skin-implantation study exhibited the non-irritation property of ScF films, which alleviate eczema histopathology. Immunohistochemical and gene expression revealed the depletion of ß-defensin, caspase-3 and -9, TNF-α, CCL-20, IL-1ß, IL-17, TGF-ß, and Wnt expressions and S100a14 mRNA level. The proteomics study suggested that ScF diminish keratinocyte proliferation via the mTOR pathway by downregulating mTOR protein, corresponding to the modulation of TNF-α, Wnt, and IL-1ß levels, leading to the enhancement of anti-inflammatory environment by IL-17 downregulation. Hematology data demonstrated the safety of using these biomaterials, which provide a potential therapeutic-option for psoriasis treatment due to desirable effects, especially anti-proliferation and anti-inflammation, functioning via the mTOR pathway and control of IL-17 signaling.

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.

Evaluating efficacy and safety of the topical silicone gel containing onion extract in the treatment of post-cesarean surgical scars.

BACKGROUND: Cesarean section scars are post-surgical problems in women. Many active ingredients have been found to diminish scar formation. Clinical investigations on the onion extract have gained more attention due to its properties, such as improvement of scar appearance and texture. However, published studies evaluating the usefulness of the onion extract in the treatment of scars are controversial. METHODS: The three-month study period followed a prospective, randomized, and double-blinded design. Each enrolled subject's post-cesarean completely sealed wounds were divided into two halves along the closure axis. Each half was randomly assigned to the treatment with either silicone gel containing 5% onion extract or the silicone gel containing vitamin C. All subjects were respectively evaluated at the one, two, and three months of the treatment. RESULTS: After the three-month follow-up, there was a statistically significant difference in scar improvement between before and after treatment. None of statistically significant difference in the Patient and Observer Scar Assessment Scale (POSAS) and Vancouver Scar Scale (VSS) scores and melanin value was found between silicone gel containing 5% onion extract and the control silicone gel. However, the improvement of scar erythema by treatment with the silicone gel containing 5% onion extract was significantly greater than in the control group. No adverse effects were reported in either group.

A review on the synthesis and properties of hydroxyapatite for biomedical applications.

Hydroxyapatite (HA or HAp) is one of the most preferred biomaterials, specifically for bone tissue engineering. HAp is available naturally and is also chemically synthesized. The properties, shape, size and crystalline structure and applications of HAp vary widely depending on the source and extraction methods used. In addition to conventional chemical approaches such as precipitation or sol-gel techniques, newer methods such as microwave synthesis and atomic-layer deposition provide an opportunity to generate HAp with desirable structure and properties. Various methods used for the synthesis of HAp have their own pros and cons. Hence, it is essential to understand the role of specific methods and conditions on the properties and structure of HAps in order to obtain HAp with properties suitable for specific applications. In addition to pure HAp, substantial efforts have been made to dope HAp with various minerals or bioentities to enhance their suitability for medical, environmental remediation and other approaches. In this review, we provide an overview of the various chemical methods used to produce HAp, properties of the HAp produced and its potential applications. Particular focus of this paper is on the co-relation between properties and processes used to synthesis HAp. This review will enable readers to quickly understand the importance of synthesis methods and conditions on the properties of HAp and choose appropriate means to generate HAp with desired properties for specific applications.

Litter to Leaf: The Unexplored Potential of Silk Byproducts.

Silk has remained the most preferred protein fiber since its discovery in 3000 BC. However, the cost, availability, and resources required to rear the silkworms and process silk are imposing considerable constraints on the future of silk. It is often unrealized that apart from the fibers, production and processing of silk are a source for a diverse range of sustainable, biodegradable, and biocompatible polymers. Hence, delineating itself from being the primary source of protein fibers for millenniums, the silk industry worldwide is transitioning into a biobased industry and as a source for pharmaceuticals, biomaterials, cosmetics, food, and energy. Toward this, byproducts (BPs) and co-products (CPs) that are inevitably generated are now being considered to be of immense economic value and could be up to 10 times more valuable than the silk fibers. Here, we elucidate the properties and potential applications of silk BPs and CPs to present the true potential of silkworms and to promote the establishment of silkworm-based bioeconomy and biorefineries.

Inflammatory reaction, clinical efficacy, and safety of bacterial cellulose wound dressing containing silk sericin and polyhexamethylene biguanide for wound treatment.

Bacterial cellulose wound dressings containing silk sericin and PHMB (BCSP) were developed in our previous studies. It had good physical properties, efficacy, and safety. For further use as a medical material, this dressing was investigated for its efficacy and safety in split-thickness skin graft (STSG) donor-site wound treatment compared to Bactigras® (control). Moreover, the inflammatory responses to both dressings were also deeply investigated. For in vivo study, expressions of anti-inflammatory cytokines were intensely considered in the tissue interfacing area. The result showed that IL-4 and TGF-ß from BCSP-treated tissue had advantages over Bactigras®-treated tissue at 14 and 21 days post-implantation. For clinical study, a single-blinded, randomized controlled study was generated. The half of STSG donor site wound was randomly assigned to cover with BCSP or Bactigras®. Twenty-one patients with 32 STSG donor site wounds were enrolled. The results showed that wound-healing time was not significantly different in both dressings. However, wound quality of BCSP was better than Bactigras® at healing time and after 1 month (p < 0.05). The pain scores of BCSP-treated wound were statistically significant lower than Bactigras®-treated wound (p < 0.05). No sign of infection or adverse event was observed after treatment with both dressings. In conclusion, the inflammation responses of the dressing were clearly clarified. The advantages of BCSP were wound-quality improvement, pain reduction, and infection protection without adverse events. It was fit to be used as the alternative treatment of STSG donor site wound.

Tolerogenic responses of CD206+, CD83+, FOXP3+, and CTLA-4 to sericin/polyvinyl alcohol/glycerin scaffolds relevant to IL-33 and HSP60 activity.

Silk sericin-releasing (sericin/polyvinyl alcohol (PVA)/glycerin) scaffolds have been designed for wound dressing applications using different fabrication techniques that influence scaffold antigenicity. The immunological tolerance of scaffolds depends on the balance of immunogenic and tolerogenic responses modulated by dendritic cells (DCs). An in vivo skin implantation model was used to compare the tolerogenic effect of sericin/PVA/glycerin scaffolds prepared by freeze-drying versus salt-leaching techniques, using an Allevyn® scaffold as a control. Immunohistochemical and histopathological studies were performed to evaluate tolerogenic DCs (CD206+), immunogenic DCs (CD83+), regulatory T-cells (FOXP3+ and CTLA-4), a proinflammatory cytokine (interleukin 33: IL-33), a stress marker (heat shock protein 60; HSP60), histopathological changes and related inflammatory cells. It was found that both sericin/PVA/glycerin scaffolds were tolerogenic and induced early activated Treg functions, while the Allevyn® scaffold was immunogenic. However, the tolerance of the freeze-dried sericin/PVA/glycerin scaffolds was not as consistent as the salt-leached sericin/PVA/glycerin scaffolds, indicated by the low level of CTLA-4 expression. This was probably due to molecular cross-linking and the morphological and mechanical properties of the freeze-drying technique, which would enhance the immune response. Severe inflammatory responses (including mast cell degranulation and foreign body giant cell accumulation) and histopathological changes (including fat infiltration and fibrosis formation) were mainly found with the Allevyn® scaffold, presumably from its architecture and chemical composition, especially polyurethane. The up-regulation of IL-33 and HSP60 with the Allevyn® scaffold was correlated with the inflammatory and pathological levels. Our findings suggested that salt-leached sericin/PVA/glycerin scaffolds were tolerogenic, induced a low inflammatory response and were appropriate for wound dressing applications.

The safety and efficacy of bacterial nanocellulose wound dressing incorporating sericin and polyhexamethylene biguanide: in vitro, in vivo and clinical studies.

In our previous work, we have attempted to develop a novel bacterial nanocellulose wound dressing which composed of both polyhexamethylene biguanide (PHMB) as an antimicrobial agent and sericin as an accelerative wound healing component. The loading sequence and concentration of PHMB and sericin were optimized to provide the wound dressing with the most effective antimicrobial activity and enhanced collagen production. In this study, further in vitro, in vivo, and clinical studies of this novel wound dressing were performed to evaluate its safety, efficacy, and applicability. For the in vitro cytotoxic test with L929 mouse fibroblast cells, our novel dressing was not toxic to the cells and also promoted cell migration as good as the commercially available dressing, possibly due to the component of sericin released. When implanted subcutaneously in rats, the lower inflammation response was observed for the novel dressing implanted, comparing to the commercially available dressing. This might be that the antimicrobial PHMB component of the novel dressing played a role to reduce infection and inflammation reaction. The clinical trial patch test was performed on the normal skin of healthy volunteers to evaluate the irritation effect of the dressing. Our novel dressing did not irritate the skin of any volunteers, as characterized by the normal levels of erythema and melanin and the absence of edema, papule, vesicle, and bullae. Then, the novel dressing was applied for the treatment of full-thickness wounds in rats. The wounds treated with our novel dressing showed significantly lower percentage of wound size and higher extent of collagen formation mainly due to the activity of sericin. We concluded that our novel bacterial nanocellulose incorporating PHMB and sericin was a safe and efficient wound dressing material for further investigation in the wound healing efficacy in clinic.

Physical and biological assessments of the innovative bilayered wound dressing made of silk and gelatin for clinical applications.

The physical and biological assessments of the innovative bilayered wound dressing made of silk and gelatin that we have developed previously were performed to evaluate its efficacy for clinical applications. The absorption ability and dehydration rate of the dressing were assessed using the split-thickness skin graft and leg ulcer wound bed models. The bioactivities of the bilayered wound dressing were evaluated. The bilayered dressing showed continuous absorption rate of wound exudate, providing the suitability for the wound with extended inflammation phase. The dehydration rate of the bilayered dressing was comparable to the commercially available dressing of which the moisture maintenance capability is claimed. The bilayered dressing showed good conformability, as can be seen by the homogeneous distribution pattern of bromophenol blue absorbed. In terms of biological activities, the bilayered dressing was less toxic to skin cells than the commercially available dressing. The bilayered dressing was also shown to promote cell migration and collagen production due to the bioactive protein components. We here concluded that the superior properties of the bilayered dressing over the commercially available dressing were the conformability and biological activities to accelerate the wound healing, while the other properties were comparable to those of commercially available dressing. The data obtained in this study would be very useful for the further evaluation of the bilayered dressing in clinical trial.

Interaction and effectiveness of antimicrobials along with healing-promoting agents in a novel biocellulose wound dressing.

An ideal wound dressing should keep the wound moist, allow oxygen permeation, adsorb wound exudate, accelerate re-epithelialization for wound closure, reduce pain and healing time, and prevent infection. Our novel biocellulose-based wound dressing was composed of three components: 1) biocellulose (BC), intended to create a moist and oxygen-permeated environment with exudate adsorption; 2) silk sericin (SS) known for its enhancement of collagen type I production, which is critical for re-epithelialization; and 3) the antiseptic polyhexamethylene biguanide (PHMB). To deliver an effective BC wound dressing, the interactions between the components (PHMB vs. SS) needed to be thoroughly analyzed. In this study, we investigated important parameters such as the loading sequence, loading concentration, and loading amount of the active compounds to ensure that the BC wound dressing could provide both antimicrobial activity and promote collagen production during healing. The loading sequence of SS and PHMB into BC was critical to maintain PHMB antimicrobial activity; silk sericin needed to be loaded before PHMB to avoid any negative impacts. The minimum PHMB concentration was 0.3% w/v for effective elimination of all tested bacteria (Bacillus subtilis, Staphylococcus aureus, methicillin-resistant S. aureus, Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa). The amounts of SS and PHMB in BC were optimized to ensure that the dressings released the optimal amounts of both SS to enhance fibroblast collagen production and PHMB for effective antimicrobial activity.

A green salt-leaching technique to produce sericin/PVA/glycerin scaffolds with distinguished characteristics for wound-dressing applications.

Sericin/PVA/glycerin scaffolds could be fabricated using the freeze-drying technique; they showed good physical and biological properties and can be applied as wound dressings. However, freeze-drying is an energy- and time-consuming process with a high associated cost. In this study, an alternative, solvent-free, energy- and time-saving, low-cost salt-leaching technique is introduced as a green technology to produce sericin/PVA/glycerin scaffolds. We found that sericin/PVA/glycerin scaffolds were successfully fabricated without any crosslinking using a salt-leaching technique. The salt-leached sericin/PVA/glycerin scaffolds had a porous structure with pore interconnectivity. The sericin in the salt-leached scaffolds had a crystallinity that was as high as that of the freeze-dried scaffolds. Compared to the freeze-dried scaffolds with the same composition, the salt-leached sericin/PVA/glycerin scaffolds has larger pores, a lower Young's modulus, and faster rates of biodegradation and sericin release. When cultured with L929 mouse fibroblast cells, a higher number of cells were found in the salt-leached scaffolds. Furthermore, the salt-leached scaffolds were less adhesive to the wound, which would reduce pain upon removal. Therefore, salt-leached sericin/PVA/glycerin scaffolds with distinguished characteristics were introduced as another choice of wound dressing, and their production process was simpler, more energy efficient, and saved time and money compared to the freeze-dried scaffolds.

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.

Physico-chemical properties and efficacy of silk fibroin fabric coated with different waxes as wound dressing.

Silk fibroin (SF) has been widely used as a wound dressing material due to its suitable physical and biological characteristics. In this study, a non-adhesive wound dressing which applies to cover the wound surface as an absorbent pad that would absorb wound fluid while accelerate wound healing was developed. The modification of SF fabrics by wax coating was purposed to prepare the non-adhesive wound dressing that is required in order to minimize pain and risk of repeated injury. SF woven fabrics were coated with different types of waxes including shellac wax, beeswax, or carnauba wax. Physical and mechanical properties of the wax-coated SF fabrics were characterized. It was clearly observed that all waxes could be successfully coated on the SF fabrics, possibly due to the hydrophobic interactions between hydrophobic domains of SF and waxes. The wax coating improved tensile modulus and percentage of elongation of the SF fabrics due to the denser structure and the thicker fibers coated. The in vitro degradation study demonstrated that all wax-coated SF fabrics remained up to 90% of their original weights after 7 weeks of incubation in lysozyme solution under physiological conditions. The wax coating did not affect the degradation behavior of the SF fabrics. A peel test of the wax-coated SF fabrics was carried out in the partial- and full-thickness wounds of porcine skin in comparison to that of the commercial wound dressing. Any wax-coated SF fabrics were less adhesive than the control, as confirmed by less number of cells attached and less adhesive force. This might be that the wax-coated SF fabrics showed the hydrophobic property, allowing the loosely adherence to the hydrophilic wound surface. In addition, the in vivo biocompatibility test of the wax-coated SF fabrics was performed in Sprague-Dawley rats with subcutaneous model. The irritation scores indicated that the carnauba wax-coated SF fabric was not irritant while the shellac wax or beeswax-coated SF fabrics were slightly irritant, comparing with the commercial wound dressing. Therefore, SF fabrics coated with waxes, particularly carnauba wax, would be promising choices of non-adhesive wound dressing.

Development of ethyl alcohol-precipitated silk sericin/polyvinyl alcohol scaffolds for accelerated healing of full-thickness wounds.

Silk sericin has been recently reported for its advantageous biological properties to promote wound healing. In this study, we established that the ethyl alcohol (EtOH) could be used to precipitate sericin and form the stable sericin/polyvinyl alcohol (PVA) scaffolds without the crosslinking. The sericin/PVA scaffolds were fabricated via freeze-drying and subsequently precipitating in various concentrations of EtOH. The EtOH-precipitated sericin/PVA scaffolds showed denser structure, higher compressive modulus, but lower water swelling ability than the non-precipitated scaffolds. Sericin could be released from the EtOH-precipitated sericin/PVA scaffolds in a sustained manner. After cultured with L929 mouse fibroblasts, the 70 vol% EtOH-precipitated sericin/PVA scaffolds showed the highest potential to promote cell proliferation. After applied to the full-thickness wounds of rats, the 70 vol% EtOH-precipitated sericin/PVA scaffolds showed significantly higher percentage of wound size reduction and higher extent of type III collagen formation and epithelialization, compared with the control scaffolds without sericin. The accelerated wound healing by the 70 vol% EtOH-precipitated sericin/PVA scaffolds was possibly due to (1) the bioactivity of sericin itself to promote wound healing, (2) the sustained release of precipitated sericin from the scaffolds, and (3) the activation and recruitment of wound healing-macrophages by sericin to the wounds. This finding suggested that the EtOH-precipitated sericin/PVA scaffolds were more effective for the wound healing, comparing with the EtOH-precipitated PVA scaffolds without sericin.

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.