Sericin Film Research Articles

Silk Sericin Films from Concentrated Aqueous Solutions: Processing Routes, Structure, and Properties

Silk Sericin Films from Concentrated Aqueous Solutions: Processing Routes, Structure, and Properties

Enhancing Healing of Infected Wounds with Glycerin‐Modified Sodium Alginate/Silk Sericin Composite Film Functionalized with Polygonatum sibiricum Polysaccharide‐Capped Silver Nanoparticles

AbstractA sodium alginate/silk sericin (SA/SS) film was modified with glycerin (GI) and Polygonatum sibiricum polysaccharide@silver nanoparticles (PSP@AgNPs) to create a SA/SS/GI/PSP@AgNP composite film with antibacterial and antioxidant properties. The physicochemical properties of the SA/SS/GI/PSP@AgNP composite film were analyzed, and its cytocompatibility, antioxidant activity, and antibacterial properties were investigated. The optimum conditions for the preparation of the SA/SS/GI/PSP@AgNP composite film were 2 % SA, 2 % SS, 20 % GI, and 40 μg/mL of PSP@AgNPs. The addition of GI improved the surface smoothness of the composite films, while the presence of PSP@AgNPs did not significantly alter it. Spectroscopic characterization demonstrated that GI and PSP@AgNPs were physically bound to SA/SS. Approximately 53 % of the PSP@AgNP was released from the SA/SS/GI/PSP@AgNP composite film over 24 h of soaking in aqueous solution. The resulting leaching solution did not cause hemolysis or cytotoxicity, indicating its biocompatibility. Additionally, the SA/SS/GI/PSP@AgNP composite film exhibited strong antioxidant and antibacterial properties, and it promoted healing of mouse wounds infected with Staphylococcus aureus.

Effect of rheological behaviors of polyacrylonitrile grafted sericin solution on film structure and mechanical properties

Sericin protein possesses excellent biocompatibility, antioxidation, and processability. Nevertheless, manufacturing large quantities of strong and tough pure regenerated sericin materials remains a significant challenge. Herein, we design a lightweight structural sericin film with high ductility by combining radical chain polymerization reaction and liquid-solid phase inversion method. The resulting polyacrylonitrile grafted sericin films exhibit the ability to switch between high strength and high toughness effortlessly, the maximum tensile strength and Young's modulus values are 21.92 ± 1.51 MPa and 8.14 ± 0.09 MPa, respectively, while the elongation at break and toughness reaches up to 344.10 ± 35.40 % and 10.84 ± 1.02 MJ·m−3, respectively. Our findings suggest that incorporating sericin into regenerated films contributes to the transformation of their mechanical properties through influencing the entanglement of molecular chains within polymerized solutions. Structural analyses conducted using infrared spectroscopy and X-ray diffraction confirm that sericin modulates the mechanical properties by affecting the transition of condensed matter conformation. This work presents a convenient yet effective strategy for simultaneously addressing the recycling of sericin as well as producing regenerated protein-based films that hold potential applications in biomedical, wearable, or food packaging.

Bioactive self-assembling silk fibroin–sericin films for skin tissue engineering

The quest for an ideal wound dressing material has been a strong motivation for researchers to explore novel biomaterials for this purpose. Such explorations have led to the extensive use of silk fibroin (SF) as a suitable polymer for several applications over the years. Unfortunately, another major silk protein—sericin has not received its due attention yet in spite of having favorable biological properties. In this study, we report an approach of blending SF and silk sericin (SS) without the usage of chemical crosslinkers is made possible by the usage of formic acid which evaporates to induce β-sheets formation to form cytocompatible films. Raman spectroscopy confirms the presence of SF/SS components in blend and formation of β-sheet in films. In situ, gelation kinetics studies were conducted to understand the change in gelation properties with addition of sericin into SF. Methyl thiazolyl tetrazolium and live/dead assays were performed to study cellular attachment, viability and proliferation on SF/SS films. The antibacterial properties of SF/SS films were tested using Gram-negative and Gram-positive bacteria. The re-structured SF/SS films were stable, transparent, show good mechanical properties, antibacterial activity and cytocompatibility, therefore can serve as suitable biomaterial candidates for skin regeneration applications.

Characterization and functional properties of novel nanocomposite sericin-based films incorporated with sericin nanoparticles

Sericin is an interesting protein that can be formed into sericin films for biomedical and food applications. Moreover, sericin can be prepared as sericin nanoparticles (SNs) and incorporated to enhance the film barrier properties. The SNs had a size of 407 nm, as verified by dynamic light scattering. To improve the mechanical properties of sericin films, pectin was added at different ratios of sericin:pectin (w:w) (3:0, 3:1, 3:2, and 3:3). Additionally, various amounts of SNs (0, 5, and 10%) were incorporated to form nanocomposite sericin-based films. The addition of pectin and SNs led to lower solubility and higher water vapor permeability than sericin film alone. The Fourier-transform infrared results showed that the interaction between sericin and pectin molecules increased the tensile strength of the films. Furthermore, the differential scanning calorimetry results indicated that adding pectin to sericin films increased the melting temperature, resulting in improved thermal stability of the composite films. However, higher pectin content reduced the total phenolic content and antioxidant activity. Nonetheless, SNs incorporation helped increase the antioxidant activity of composite films. Thus, the nanocomposite sericin-based films could be an alternative for food packaging materials or biomedical applications.

Factors affecting sericin hydrolysis and application of sericin hydrolysate in sericin films.

Sericin is a natural protein and a by-product obtained from silk processing. To enhance the antioxidant properties of sericin, sericin hydrolysis was studied. The solvent effects (distilled water, citric acid and hydrochloric acid) and hydrolysis methods (heat treatment (water bath) and mild ultrasonic treatment at 20%, 40% or 60% amplitude) were investigated on the properties of sericin hydrolysate (SH). Furthermore, solvent effects (distilled water and 15% ethanol) were examined for the properties of the sericin films incorporated with selected SH. The SH samples from acid hydrolysis and the ultrasonic method had a darkened visual appearance. However, the degree of hydrolysis and antioxidant activity of SH increased with ultrasonic-assisted acid hydrolysis. The molecular weight (MW) of sericin was notably reduced. As expected, hydrochloric acid hydrolysis resulted in a lower MW for the SH than from citric acid. Thus, SH from hydrochloric acid and 20% amplitude in the ultrasonic method were selected to produce a sericin film. As revealed, using distilled water as a general solvent provided films with lower solubility and water vapor permeability but higher tensile strength. Furthermore, the addition of SH enhanced the antioxidant properties of its hydrolysate as a novel protein packaging film material for various applications.

Antioxidant and UV-blocking glucose-crosslinked sericin films with enhanced structural integrity

The utilization of sericin should be expanded to increase the availability of silkworm silk. However, the poor mechanical properties and susceptibility to moisture of sericin have continuously restricted its use. In this study, a facile crosslinked sericin film was prepared using a glucose-induced Maillard reaction, and the physicochemical properties and antioxidant functionality of the crosslinking reaction were investigated. The glucose-induced Maillard reaction can be conducted in an environmentally friendly manner through a simple heat treatment of sericin at 90 °C, and the degree of crosslinking can be adjusted by controlling the amount of added glucose. The glucose-induced Maillard reaction improves the mechanical properties of the sericin film, reduces its vulnerability in a moist environment, and provides UV protection and improved antioxidant activity.

Effect of cross-linkable bacterial cellulose nanocrystals on the physicochemical properties of silk sericin films

The manufacture of eco-friendly cocoon silk-derived sericin films increases the availability of sericulture resources and the interest in expanding the range of the potential applications of sericin-based materials. However, the brittleness and weak tensile properties of sericin and its vulnerability to moist environments have limited its use. To overcome these two shortcomings of sericin, a functionalized bacterial cellulose-derived nanocrystal (average diameter: 25.4 nm) capable of physical strengthening and chemical crosslinking on existing sericin films was prepared. The improvement of the optical, physicochemical, and mechanical properties of the sericin film was observed through the dialdehyde bacterial cellulose nanocrystals (D-CNCs) incorporated into the silk sericin (SS) matrix. The physical reinforcing effect of the D-CNCs on the SS films enhances the mechanical properties of the films. Simultaneously, the chemical crosslinking reaction of D-CNCs develops the ultraviolet-blocking, water-resistant, and antioxidant properties of the films. The simultaneous fabrication, physical reinforcement, and chemical crosslinking of the SS/D-CNCs biocomposite film produced using an aqueous solution will provide information on the functionalization and performance improvement of water-soluble biopolymeric materials, especially hydrophilic protein resources.

Fabrication and properties of keratoses/sericin blend films

Blend films of keratoses and sericin were prepared using water as a common solvent and glycerol as a plasticizer. An aqueous solution of keratoses extracted from wool via oxidation using peracetic acid was added with different amounts of sericin from silk degumming and blended along with glycerol to obtain films by solution casting method. All the different concentrations of keratoses/silk sericin (KOx/SS) films are observed to be in intact condition. Blend films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, thermal analysis, water uptake and tensile behavior. Only the cast films of 100% keratoses show a smooth surface indicating good miscibility between keratoses and plasticizer, while increasing the amount of sericin the film surface becomes rough. Fourier transform infrared analysis pointed out that the polymers have no covalent interaction with each other. The addition of glycerol to 100% sericin films strongly decreases their thermal stability changing their secondary structure as shown by FT-IR and thermal analysis. A similar behavior was not seen in keratoses. Sericin plasticized film with glycerol shows low mechanical properties, but the addition of 10% of keratoses to the blend strongly enhances the tensile strength of cast films, while the addition of small amounts sericin to keratoses slightly increases its water uptake.

Strong, conductive aramid fiber functionalized by graphene

The surface modification of aramid fibers is an essential and potent approach to manipulate and improve fiber properties. Biogenic fibers are in stark contrast, as exemplified by the case of natural silk fibers. This high-performance fiber features a surface functionalization as a thin sericin film enwraps it for improving the mechanical properties of silks. Inspired by this unique sheath structure of biogenic silk, we improved the performance of aramid fibers by exploiting a coating composed of reduced graphene oxide nanosheets that self-assemble on the fiber surface guided by hydrogen bonding and π-π stacking interactions. The graphene functionalized aramid fibers show a remarkable 1 GPa improvement in tensile strength. Moreover, the functionalized aramid fiber also shows high electrical conductivity which preserved 99% of its conductivity even after 100 cycles. Our approach provides a universal strategy for improving the performance of the fiber via surface functionalization by graphene nanosheets.

Effect of Electrospun Silk Fibroin–Silk Sericin Films on Macrophage Polarization and Vascularization

Biomaterial implantation is followed by an inflammatory cascade dominated by the macrophages, which polarized to the proinflammation M1 phenotype or prohealing M2 phenotype. Generally, silk sericin (SS) is considered to be of high immunogenicity associated with native silk fibers. The blends of silk fibroin (SF) and SS in different mass ratios might elicit different host immune responses and induce macrophage phenotype switch. The objective of this study was to assess the effects of electrospun SF-SS fibrous films with different mass ratios (10:0, 9:1, 8:2, and 7:3) on the macrophage phenotypes and explore the optimal ratio of SF and SS for angiogenesis. Our results indicated that the macrophages were activated by the addition of SS. When the mass ratio of SF and SS reached 7:3, the film displayed the highest degree of vascularization. The macrophages were induced to secrete more M1 and M2 cytokines accompanying with high M2/M1 ratio. Taken together, this study provided a perspective to promote neovascularization by modulating appropriate host response and macrophage phenotypes in tissue engineering field.

Cross-linking of dialdehyde carboxymethyl cellulose with silk sericin to reinforce sericin film for potential biomedical application

Developing biomaterials based on the natural biomacromolecule silk sericin from Bombyx mori cocoon is of great interest for biomedical application. Dialdehyde carboxymethyl cellulose (DCMC) is derived from periodate oxidation of carboxy- methyl cellulose. Here, we developed a novel strategy of cross-linking of sericin with DCMC via the Schiff’s base reaction. Fourier transform infrared spectroscopy and scanning electron microscopy indicated the formation of Schiff’s base via the blending of sericin and DCMC. The mechanical properties tests suggested the covalent cross-linking effectively enhanced the tensile strength of sericin. The swelling test and water contact angle indicated the DCMC/SS film had excellent hydrophilicity, swellability. Additionally, we demonstrated the DCMC/SS film had excellent blood compatibility, cytocompatibility and promoting cell proliferation activity by the hemolysis ratio analysis, cell adhesion, cells viability and proliferation assays. The prepared DCMC/SS film has shown great promise in biomedical applications such as wound dressing, artificial skin and tissue engineering.

Effect of heat treatment on the structural characteristics and properties of silk sericin film

Recently, silk sericin has attracted attention because of its unique properties as a biomaterial, including its UV resistance, moisturizing effect on skin, and wound-healing effect. Therefore, the preparation of sericin in various forms such as gel, film, fiber, and sponge is studied for cosmetic and biomedical applications, and the effect of the preparation conditions on the structure and properties of sericin forms is examined to maximize its performance. In this study, silk sericin films were prepared under different preparation conditions and heat-treated at high temperatures (100-250℃) to examine the effect of heat treatment on the film structure. The order of the crystallinity index of the untreated sericin film is as follows: F25 (sericin film cast from formic acid) > WE25 (ethanol treated sericin film cast from water at 25℃) > W25 (sericin film cast from water at 25℃) > W100 (sericin film cast from water at 100℃). As the heat-treatment temperature was increased, the color of the sericin films changed gradually from colorless to yellow, brown, and black depending on the temperature. The crystallinity of the sericin film changed after the heat treatment, depending on the preparation condition. Whereas a sericin film cast from formic acid (F25) started to lose its crystallinity at 200℃, thus undergoing the highest loss of crystallinity among the sericin films studied, the rest (W25, WE25, and W100) showed a decrease in crystallinity at 250℃, owing to the disruption of the b-sheet crystallites due to heat.

Effect of molecular weight on the structure and mechanical properties of silk sericin gel, film, and sponge

In this study, the effect of the MW on the structure and properties of sericin film, sponge, and gel was examined. As the MW of sericin increased, the gelation of the sericin aqueous solution was found to be accelerated, and the gel strength, and the gel-sol transition temperature increased. Irrespective of the casting solvent (water and formic acid) and form of sericin (gel, film, or sponge), the crystallization of the sericins was accelerated. The mechanical properties of the sericin sponge were remarkably improved upon increasing the MW of sericin. The MW of sericin almost did not have an effect on the cell toxicity. As the MW of sericin is increased, the sericin sponge becomes denser and its porosity is reduced, leading to a decrease in the swelling ratio. These results indicate that various characteristics of the sericin forms can be modulated by controlling the MW of sericin, with enhanced potential for biomedical and cosmetic applications.

Facile and green fabrication of silk sericin films reinforced with bamboo-derived cellulose nanofibrils

As the interest in the recycling of byproducts and resources derived from agriculture has increased, research on the application of sericin abandoned in the silk industry has been continuously carried out, but there is a limit due to the weak mechanical properties. Recently, nanocellulose has been attracting attention as an optimal reinforcing material to improve the deficient physical properties of natural polymers. In the present study, bamboo-derived cellulose nanofibrils (B-CNFs) were prepared and used as a facile reinforcer to improve the mechanical properties of the sericin film. B-CNF was prepared via simple and eco-friendly ultrasonic treatment and whole bio-nanocomposite film fabrication process conducted under aqueous solution condition. The prepared B-CNF was well distributed into the glycerol-plasticized sericin matrix without agglomeration until 10 wt% B-CNF loading, while agglomerated cellulose nanofibrils appeared after 20 wt% B-CNF loading. This uniform distribution of B-CNF not only greatly improved the properties of the sericin film but also affected the hydrophilic properties of bio-nanocomposite film. Moreover, the prepared B-CNF reinforced bio-nanocomposite films had notable antioxidant activity without any additional antioxidant ingredients. These findings support the potential use of B-CNF reinforced sericin films in active food packaging, drug delivery carriers, and in wound dressing materials. Silk and bamboo-derived natural polymeric raw materials and aqueous solvent-based film manufacturing processes will strongly provide cost efficiency and environmental friendliness and can be a suitable replacement of petroleum-based polymer industry and its related application fields.

Wool keratin and silk sericin composite films reinforced by molecular network reconstruction

To reinforce the silk sericin (SS, β-sheets rich) film, the mixed solution is engineered by molecular network reconstruction with the increase in the wool keratin (WK, α-helix rich). Silk sericin demonstrates a transformation from random coil to β-sheets structure under the influence of glycerol, while the SS and WK composite films reveal the molecular network crossly linked by hydrogen bonds. It is surprising to see that the microstructure transforms from β-sheet structure to α-helix structure with the increase in wool keratin. Furthermore, the α-helix in SS–WK composite films can transform to β-sheets under stretching. Meanwhile, the hydrogen bonds are broken, which give rise to the slippage of molecular chains, and a better flexibility and strain with the increase in keratin contents. Raising the WK ratio increases the absorbance of ultraviolet radiation. These results make them as biomedical applications with controllable properties.

Preparation and Properties of Glutaraldehyde Cross-Linked Silk Sericin Films

Glutaraldehyde cross-linked silk sericin films were successfully prepared. FTIR was applied to characterize the chemical structure of films. Compared to pure silk sericin, cross-linked silk sericin film with 3% glutaraldehyde was found a new peak at 1620 cm-1 and the peak intensity of cross-linked film decreased markedly, which indicating cross-linking reaction has been occurred. Thermal and swelling behavior of cross-linked films was investigated. The cross-linking reaction increased the thermal decomposition temperature. The swelling ratio of glutaraldehyde cross-linked silk sericin films went up with increasing glutaralehyde loading to 3wt%.

Preparation and properties of silk sericin/cellulose cross-linking films

Silk sericin/cellulose cross-linked films were successfully prepared using glutaraldehyde as cross-linkinger. FTIR was applied to characterize the chemical structure of films. Cross-linked silk sericin film was found the peak intensity of FTIR for cross-linked film decreased markedly compared to pure silk sericin, which indicating cross-linking reaction has been occurred. The increasing value of swelling ratio also indicated the cross-linking has been happened. The cross-linking reaction increased the thermal decomposition temperature.

The role of glycerol and water in flexible silk sericin film

Silk sericin (SS) can be obtained as a byproduct during the silk fiber process, but its application has been limited due to the brittleness of the SS film. To enhance the flexibility of the SS film, glycerol (Glc) has been added as a plasticizer. The addition of Glc enhanced the elongation property of the SS film when the Glc content was 50–70wt% of SS. Glc also induced the structural transition of SS from a random coil structure to a β-sheet structure. The inconsistent increase of elongation and β-sheet structure of the SS/Glc film were explained by the content of moisture in the SS/Glc film. The moisture content of the SS/Glc film increased proportionally when the Glc content was higher than 50wt% of SS, which was the same Glc content range that exhibited the plasticizing effect. Therefore, the plasticizing effect on the SS film may occur not only because of Glc but also because of water. Furthermore, water also contributed to the increase in the β-sheet structure development. Our results suggest that the moisture content in the plasticized protein film may play an important role when the plasticizer has hygroscopic properties.

Preparation, structure, and properties of cellulose nanofibril/silk sericin composite film

Recently, sericin has attracted increasing attention in biomedical and cosmetic research because of its useful properties including acceleration of wound healing, improvement of cell attachment, and inhibition of ultraviolet-B induced apoptosis. However, sericin films have poor mechanical properties, which restricts the application to those fields. In this study, cellulose nanofibril (CNF)/sericin composite films were fabricated by solvent casting, and the effects of ultrasonication time and CNF content on the solution turbidity, molecular conformation, and film mechanical properties of sericin film were examined. As the ultrasonication time increased, the turbidity of the CNF/sericin suspension decreased. Conversely, as the CNF content increased, the turbidity increased. However, b-sheet crystallization and mechanical properties remained almost unchanged by varying the ultrasonication time and CNF content, indicating that CNF is not effective to improve the mechanical properties of sericin films.