Fabrication and characterization of biomaterial film from gland silk of muga and eri silkworms

Cephalopod inspired self-healing protein foams for oil-water separation

Cephalopods are remarkable creatures, captivating scientists with their advanced neurophysiology, complex behavior, and miraculously effective camouflage. Research into cephalopods has led to many discoveries in neuroscience, cell biology, and materials science. Specifically, squids provide us with remarkable self-healing Squid Ring Teeth protein, which is applied herein to extend the life span of foams. Despite the advantages of porosity in surface science applications, porosity impairs mechanical properties by making materials more prone to structural damage -which traditional polymeric foams also suffer from. Drawing inspiration from Squid Ring Teeth, we developed self-healing tandem repeat proteins to overcome these challenges. By leveraging porosity and self-healing properties inspired by Squid Ring Teeth, we created bioengineered protein foams with high separation capacity (5.1 g g-1) and efficiency (≈94%). The foams healed entirely within minutes which regained over 100% strength after repair. These advances promise applications for efficient continuous water treatment through durable filter cartridges.

Physical Transient Photoresistive Variable Memory Based on Graphene Quantum Dots

Biomaterials have attracted attention as a major material for biodegradable and transient electronic devices. In this work, biocompatible gelatin-doped graphene quantum dot films are reported as active layer switching memories with good electrical properties and physical transient properties. Such nonvolatile memory devices have write-once-read-many electrical properties and a concentrated distribution of low-resistance and high-resistance states. It provides a solution for the current obstacle of resistive memory storage and computing integration. Based on the sensitivity of the device to ultraviolet light, the "OR gate" logic operation is completed. Furthermore, the active layer can be dissolved in deionized water within 15 min, and the gelatin substrate-based device can be destroyed immediately in water, indicating the potential biodegradation and physical transient properties of our fabricated device. Biocompatible memory devices are environmentally friendly, sustainable for safe storage, and low-cost, making them ideal for storage applications.

High-Strength Collagen-Based Composite Films Regulated by Water-Soluble Recombinant Spider Silk Proteins and Water Annealing

Spider silk has attracted extensive attention in the development of high-performance tissue engineering materials because of its excellent physical properties, biocompatibility, and biodegradability. Although high-molecular-weight recombinant spider silk proteins can be obtained through metabolic engineering of host bacteria, the solubility of the recombinant protein products is always poor. Strong denaturants and organic solvents have thus had to be exploited for their dissolution, and this seriously limits the applications of recombinant spider silk protein-based composite biomaterials. Herein, through adjusting the temperature, ionic strength, and denaturation time during the refolding process, we successfully prepared water-soluble recombinant spider major ampullate spidroin 1 (sMaSp1) with different repeat modules (24mer, 48mer, 72mer, and 96mer). Then, MaSp1 was introduced into the collagen matrix for fabricating MaSp1-collagen composite films. The introduction of spider silk proteins was demonstrated to clearly alter the internal structure of the composite films and improve the mechanical properties of the collagen-based films and turn the opaque protein films into transparency ones. More interestingly, the composite film prepared with sMaSp1 exhibited better performance in mechanical strength and cell adhesion compared to that prepared with water-insoluble MaSp1 (pMaSp1), which might be attributed to the effect of the initial dissolved state of MaSp1 on the microstructure of composite films. Additionally, the molecular weight of MaSp1 was also shown to significantly influence the mechanical strength (enhanced to 1.1- to 2.3-fold) and cell adhesion of composite films, and 72mer of sMaSp1 showed the best physical properties with good bioactivity. This study provides a method to produce recombinant spider silk protein with excellent water solubility, making it possible to utilize this protein under environmentally benign, mild conditions. This paves the way for the application of recombinant spider silk proteins in the development of diverse composite biomaterials.

Characterization and Toxicity Evaluation of Broiler Skin Elastin for Potential Functional Biomaterial in Tissue Engineering

Broiler skin, a by-product of poultry processing, has been proven to contain essential elastin, a high-value protein with many applications. The present study reported the extraction of water-soluble elastin from broiler skin by using sodium chloride (NaCl), sodium hydroxide (NaOH), and oxalic acid treatment before freeze-drying. Chemical characterization such as protein and fat content, Fourier-transform infrared (FTIR) spectroscopy, amino acid composition and thermal gravimetric analysis (TGA) were performed and compared with commercial elastin from bovine neck ligament. The resultant elastin’s toxicity was analyzed using an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium assay and primary skin irritation test. Results showed a high quality of the extracted-elastin with the presence of a high amount of proline (6.55 ± 0.40%) and glycine (9.65 ± 0.44%), low amount of hydroxyproline (0.80 ± 0.32%), methionine (2.04 ± 0.05%), and histidine (1.81 ± 0.05%) together with calculated 0.56 isoleucine/leucine ratio. FTIR analysis showed the presence of typical peaks of amide A, B, I, and II for protein with high denaturation temperature around 322.9 °C. The non-toxic effect of the extracted elastin was observed at a concentration lower than 0.5 mg/mL. Therefore, water-soluble elastin powder extracted from broiler skin can be an alternative source of elastin as a biomaterial for tissue engineering applications.

Accelerating skin barrier repair using novel bioactive magnesium-doped nanofibers of non-mulberry silk fibroin during wound healing

Novel magnesium doped non-mulberry silk fibroin nanofibers with ability to enhance skin barrier function were successfully fabricated using electrospinning technique for wound healing applications. Magnesium nanoparticles incorporated in the electrospun nanofibers releases Mg2+ ions at the site of implementation. The effect of Mg2+ is of considerable concern in wound healing due to its skin barrier repair ability and its role in blood coagulation. The physicochemical characterization of the scaffold was investigated by determining the morphology and secondary structure confirmation. The effects of Mg2+ ions in silk fibroin microenvironment have been evaluated using SEM, XRD, and FTIR to confirm the incorporation of magnesium in the film. The aim of this study is to see the effect of doped Mg on the structural, physical, and biological properties of non-mulberry silk fibroin (NSF) film. The magnesium doped nanofibrous film exhibited enhanced mechanical property, satisfactory blood clotting ability, and good in vitro degradability. This silk fibroin-based film mimicking extracellular matrix for skin regeneration were constructed using electrospinning technique. The wound healing efficiency of prepared nanofibers were evaluated in full-thickness wound models of rat. The Mg doped silk fibroin film exhibited faster wound healing activity (14 days) among all experimental group. The study indicates the potential of magnesium-doped silk /PVA film as skin substitute film.

Structure and Functions of Cocoons Constructed by Eri Silkworm

Eri silkworm cocoons (E cocoons) are natural composite biopolymers formed by continuous twin silk filaments (fibroin) bonded by sericin. As a kind of wild species, E cocoons have characteristics different from those of Bombyx mori cocoons (B cocoons). E cocoons have an obvious multilayer (5–9 layers) structure with an eclosion hole at one end and several air gaps between the layers, which can be classified into three categories—cocoon coat, cocoon layer, and cocoon lining—with varying performance indexes. There is a significant secondary fracture phenomenon during the tensile process, which is attributed to the high modulus of the cocoon lining and its dense structure. Air gaps provide cocoons with distinct multistage moisture transmission processes, which form a good moisture buffer effect. Temperature change inside cocoons is evidently slower than that outside, which indicates that cocoons also have an obvious temperature damping capability. The eclosion hole does not have much effect on heat preservation of E cocoons. The high sericin content of the cocoon coat, as well as the excellent ultraviolet absorption and antimicrobial abilities of sericin, allows E cocoons to effectively prevent ultraviolet rays and microorganisms from invading pupae. The ultraviolet protection factor (UPF) of the E cocoon before and after degumming were found to be 17.8% and 9.7%, respectively, which were higher than those of the B cocoon (15.3% and 4.4%, respectively), indicating that sericin has a great impact on anti-UV performance. In the cocoon structure, the outer layer of the cocoon has 50% higher content than the inner layer, and the E cocoon shows stronger protection ability than the B cocoon. Understanding the relationship between the structure, property, and function of E cocoons will provide bioinspiration and methods for designing new composites.

Composition and in silico structural analysis of fibroin from liquid silk of non-mulberry silkworm Antheraea assamensis

Silk is spun from the liquid precursor known as liquid silk secreted from the posterior part and stored in the silk gland lumen with occurrence of many momentary events. The liquid silk in the silk gland is transformed to the spun silk fibre. In this study the elucidation of the protein components of liquid silk from the posterior part of the silk gland (PSG) of saturniid silkworm Antheraea assamensis along with its structural characterization has been reported. The 3D model of the N-terminal amorphous portion with some repeat crystalline motifs (19-255) of core protein fibroin has also been constructed. 1D and 2D electrophoresis revealed the homo-dimeric structure of the silk protein. Secondary structure analysis by Circular dichroism, FTIR spectroscopy showed α helical structural component as predominant conformation in the liquid silk. The crystalline structure investigated through X ray diffraction (XRD) analysis also revealed the presence of less ordered amorphous α helical conformation in the liquid silk. The 3D structural model proposed of the residues from 19 to 255 has revealed structural stability throughout the molecular dynamics simulation process. This study will provide the detailed structural information and in silico analysis of the core protein present in the liquid silk of PSG.

Spectroscopic analysis of Muga silk nanoparticles synthesized by microwave method

Muga silk nanoparticles (MSNP) were synthesized using a microwave-assisted radiolysis method. The effect of microwave on the Muga protein secondary structures was analyzed. The evolution of the secondary structure from random coils to the β-sheets was determined by using FTIR, circular dichroism and X-ray diffraction techniques. The results showed that Muga silk fibroin protein contained the primary structure in silk-I state. When the protein was irradiated with microwave, nanoparticle synthesis was possible having silk-II state imparting crystallinity. The silk nanoparticles were characterized by a particle size analyzer and found to be of ~240 nm in size. The optical properties of these nanoparticles were studied by UV-vis. spectroscopy and photoluminescence. For studying thermal properties, differential scanning calorimetry was performed that revealed early glass transition, which could be attributed to the presence of water and proteins. It also revealed that nanoparticles are thermally stable. Such studies are important for understanding more about the MSNP and would be beneficial for their further wide applications.

Novel non-mulberry silk fibroin nanoparticles with enhanced activity as potential candidate in nanocarrier mediated delivery system

Silk fibroin (SF) is well known for its excellent biocompatible properties facilitating its application in the field of biomedical engineering through different biomaterial fabrications in the recent era. Here in this study, novel nanoparticles from non-mulberry SF of Antheraea assamensis were fabricated, characterized and evaluated for its applicability as nanocarrier. Fabricated nanoparticles were initially compared with prevailing SF nanoparticles from Bombyx mori. Fabricated A. assamensis silk fibroin nanoparticles (AA-SFNps) were found to be lesser in size (80-300 nm in diameter) than B. mori silk fibroin nanoparticles (BM-SFNps) (120-500 nm in diameter). When checked for stability, AA-SFNps were found to be more stable than BM-SFNps in biological media. FTIR and XRD studies revealed persistence of structural properties even after fabrication. TGA and DSC studies showed AA-SFNps to be thermally more stable than BM-SFNps without any cytotoxicity (MTT assay). On loading with model drug Doxorubicin hydrochloride (DOX), AA-SFNps exhibited an encapsulation efficiency of 94.47% with 11.81% loading of the anticancer drug. Cumulative release study revealed highest percentage release of DOX (42.1 ± 0.4%) at pH 5.2 on day 7 in comparison to pH 7.4 and 8.0. Sustained release profile of the DOX loaded AA-SFNps (AA-SFNps-DOX) was clearly reflected and it was found to be highly cytotoxic against triple negative MDA-MB-231 cells in comparison to free DOX at different time points. Overall, this study showed the efficacy of the AA-SFNps as a nanocarrier for future drug delivery applications.

Structure Water-Solubility Relationship in α-Helix-Rich Films Cast from Aqueous and 1,1,1,3,3,3-Hexafluoro-2-Propanol Solutions of S. c. ricini Silk Fibroin

Silk fibroin (SF) produced by the domesticated wild silkworm, Samia cynthia ricini (S. c. ricini) is attracting increasing interest owing to its unique mechanical properties, biocompatibility, and abundance in nature. However, its utilization is limited, largely due to lack of appropriate processing strategies. Various strategies have been assessed to regenerate cocoon SF, as well as the use of aqueous liquid fibroin (LFaq) prepared by dissolution of silk dope obtained from the silk glands of mature silkworm larvae in water. However, films cast from these fibroin solutions in water or organic solvents are often water-soluble and require post-treatment to render them water-stable. Here, we present a strategy for fabrication of water-stable films from S. c. ricini silk gland fibroin (SGF) without post-treatment. Aqueous ethanol induced gelation of fibroin in the posterior silk glands (PSG), enabling its separation from the rest of the silk gland. When dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), the SGF-gel gave a solution from which a transparent, flexible, and water-insoluble film (SGFHFIP) was cast. Detailed structural characterization of the SGFHFIP as-cast film was carried out and compared to a conventional, water-soluble film cast from LFaq. FTIR and 13C solid-state NMR analyses revealed both cast films to be α-helix-rich. However, gelation of SGF induced by the 40%-EtOH-treatment resulted in an imperfect β-sheet structure. As a result, the SGF-gel was soluble in HFIP, but some β-sheet structural memory remains, and the SGFHFIP as-cast film obtained has some β-sheet content which renders it water-resistant. These results reveal a structure water-solubility relationship in S. c. ricini SF films that may offer useful insights towards tunable fabrication of novel biomaterials. A plausible model of the mechanism that leads to the difference in water resistance of the two kinds of α-helix-rich films is proposed.

Aggregation State of Residual α-Helices and Their Influence on Physical Properties of S. c. ricini Native Fiber

Formation of the α-helical conformation in the poly-l-alanine (PA) sequence regions, subsequent structural transition to β-sheet during natural spinning, and presence of residual α-helices in Samia cynthia ricini (S. c. ricini) native silk fiber have been experimentally proven. However, the aggregation state of the residual α-helices, and their influence on the mechanical deformation behavior in native fiber remain unclear. Here we show that the α-helices form an ordered aggregation state with a hexagonal packing in the aqueous solution, some of which remain during natural spinning. X-ray scattering and differential scanning calorimetry (DSC) analyses revealed occurrence of a structural transition of the residual α-helices to the β-sheet structure, accompanied by disappearance of the plateau region in the force-strain curve, due to heat-treatment at ~220 °C. On the basis of X-ray scattering before and after tensile stretching of S. c. ricini native silk, a direct connection between the plateau region and the α-helix to β-sheet structural transition was confirmed. Our findings demonstrate the importance of the PA sequence regions in fiber structure formation and their influence on the tensile deformation behavior of S. c. ricini silk, features believed to be essentially similar in other saturniid silks. We strongly believe the residual ordered α-helices to be strategically and systematically designed by S. c. ricini silkworms to impart flexibility in native silk fiber. We anticipate that these knowledge forms a basis for fruitful strategies in the design and development of amino acid sequences for artificial silks with desired mechanical properties.

Fabrics of Diverse Chemistries Promote the Formation of Giant Vesicles from Phospholipids and Amphiphilic Block Copolymers

Giant vesicles composed of phospholipids and amphiphilic block copolymers are useful for biomimetic drug delivery, for biophysical experiments, and for creating synthetic cells. Here, we report that large numbers of giant unilamellar vesicles (GUVs) can be formed on a broad range of fabrics composed of entangled cylindrical fibers. We show that fabrics woven from fibers of silk, wool, rayon, nylon, polyester, and fiberglass promote the formation of GUVs and giant polymer vesicles (polymersomes) in aqueous solutions. The result extends significantly previous reports on the formation of GUVs on cellulose paper and cotton fabric. Giant vesicles formed on all the fabrics from lipids with various headgroup charges, chains lengths, and chain saturations. Giant vesicles could be formed from multicomponent lipid mixtures, from extracts of plasma membranes, and from amphiphilic diblock and triblock copolymers, in both low ionic strength and high ionic strength solutions. Intriguingly, statistical characterization using a model lipid, 1,2-dioleoyl-sn-glycero-3-phosphocholine, revealed that the majority of the fabrics yielded similar average counts of vesicles. Additionally, the vesicle populations obtained from the different fabrics had similar distributions of sizes. Fabrics are ubiquitous in society in consumer, technical, and biomedical applications. The discovery herein that biomimetic GUVs grow on fabrics opens promising new avenues in vesicle-based smart materials design.

Preparation of silk resins by hot pressing Bombyx mori and Eri silk powders

We investigate the mechanical properties and structure of silk resins as potential alternatives to tortoiseshell for producing eyeglass frames and various ornaments. Silk powders are obtained from Bombyx mori and Eri silk waste fibers before the degumming process. The powders are fabricated into resins via simple hot pressing under a pressure of 31.2 MPa at temperatures in the range 150-180 °C. The results indicate that the B. mori resins have higher micro-Vickers hardness, three-point bending strength, and elastic modulus (66 Hv, 122 MPa, and 8.7 GPa, respectively) compared to the Eri silk resins (58 Hv, 95 MPa, and 8.2 GPa, respectively). The better mechanical properties of the fibroin resins are related directly to longer drying times. The optimum drying conditions are found to be at a temperature of 100 °C under a-vacuum of -0.1 MPa for a time of 7 d. ATR-FTIR and XRD results show how the fibroin structure changes after resinification and drying. The morphology and the distribution size of particle of the silk powders and the fractured surfaces of the resins are analyzed from SEM micrographs. The present findings demonstrate that silk resins are suitable materials for developing useful applications because of their favorable mechanical properties.

Biomaterials for the Delivery of Growth Factors and Other Therapeutic Agents in Tissue Engineering Approaches to Bone Regeneration

Bone fracture followed by delayed or non-union typically requires bone graft intervention. Autologous bone grafts remain the clinical "gold standard". Recently, synthetic bone grafts such as Medtronic's Infuse Bone Graft have opened the possibility to pharmacological and tissue engineering strategies to bone repair following fracture. This clinically-available strategy uses an absorbable collagen sponge as a carrier material for recombinant human bone morphogenetic protein 2 (rhBMP-2) and a similar strategy has been employed by Stryker with BMP-7, also known as osteogenic protein-1 (OP-1). A key advantage to this approach is its "off-the-shelf" nature, but there are clear drawbacks to these products such as edema, inflammation, and ectopic bone growth. While there are clinical challenges associated with a lack of controlled release of rhBMP-2 and OP-1, these are among the first clinical examples to wed understanding of biological principles with biochemical production of proteins and pharmacological principles to promote tissue regeneration (known as regenerative pharmacology). After considering the clinical challenges with such synthetic bone grafts, this review considers the various biomaterial carriers under investigation to promote bone regeneration. This is followed by a survey of the literature where various pharmacological approaches and molecular targets are considered as future strategies to promote more rapid and mature bone regeneration. From the review, it should be clear that pharmacological understanding is a key aspect to developing these strategies.

Antimicrobials tethering on suture surface through a hydrogel: a novel strategy to combat postoperative wound infections

The present study aimed to develop a novel biocompatible suture biomaterial from Eri silk waste to avoid surgical site infections.

Facts and myths of antibacterial properties of silk

Silk cocoons provide protection to silkworm from biotic and abiotic hazards during the immobile pupal phase of the lifecycle of silkworms. Protection is particularly important for the wild silk cocoons reared in an open and harsh environment. To understand whether some of the cocoon components resist growth of microorganisms, in vitro studies were performed using gram negative bacteria Escherichia coli (E. coli) to investigate antibacterial properties of silk fiber, silk gum, and calcium oxalate crystals embedded inside some cocoons. The results show that the previously reported antibacterial properties of silk cocoons are actually due to residues of chemicals used to isolate/purify cocoon elements, and properly isolated silk fiber, gum, and embedded crystals free from such residues do not have inherent resistance to E. coli. This study removes the uncertainty created by previous studies over the presence of antibacterial properties of silk cocoons, particularly the silk gum and sericin.

Fabrication and characterization of Eri silk fibers-based sponges for biomedical application

Cocoon-derived semi-domesticated Eri silk fibers still lack exploitation for tissue engineering applications due to their poor solubility using conventional methods. The present work explores the ability to process cocoon fibers of non-mulberry Eri silk (Samia/Philosamia ricini) into sponges through a green approach using ionic liquid (IL)--1-buthyl-imidazolium acetate as a solvent. The formation of β-sheet structures during Eri silk/IL gelation was acquired by exposing the Eri silk/IL gels to a saturated atmosphere composed of two different solvents: (i) isopropanol/ethanol (physical stabilization) and (ii) genipin, a natural crosslinker, dissolved in ethanol (chemical crosslinking). The sponges were then obtained by freeze-drying. This approach promotes the formation of both stable and ordered non-crosslinked Eri silk fibroin matrices. Moreover, genipin-crosslinked silk fibroin sponges presenting high height recovery capacity after compression, high swelling degree and suitable mechanical properties for tissue engineering applications were produced. The incorporation of a model drug--ibuprofen--and the corresponding release study from the loaded sponges demonstrated the potential of using these matrices as effective drug delivery systems. The assessment of the biological performance of ATDC5 chondrocyte-like cells in contact with the developed sponges showed the promotion of cell adhesion and proliferation, as well as extracellular matrix production within 2 weeks of culture. Sponges' intrinsic properties and biological findings open up their potential use for biomedical applications.

STATEMENT OF SIGNIFICANCE

This work addresses the preparation and characterization of non-mulberry cocoon-derived Eri silk sponges. The insolubility of cocoons-derived non-mulberry silkworms impairs their processability and applications in the healthcare field. We used a green approach with ionic liquids to overcome the lack solubility of such silk fibers. The formation of beta-sheet structures into Eri-based sponges was physically and chemically induced. The sponges were obtained by freeze-drying. The developed structures exhibited flexibility to adapt and recover their shapes upon application and subsequent removal of load, high swelling degree, ability to load an anti-inflammatory drug and to promote its sustained release. They promoted in vitro cellular adhesion, proliferation and extracellular matrix production of a chondrocyte-like cell line, opening up their potential application for biomedical applications.

Nanoscale Control of Silks for Nanofibrous Scaffold Formation with Improved Porous Structure

Silk-based porous scaffolds have been used extensively in tissue engineering because of their excellent biocompatibility, tunable biodegradability and robust mechanical properties. Although many silk-based scaffolds have been prepared through freeze-drying, a challenge remains to effectively control porous structures during this process. In the present study silk fibroin with different nanostructures were self-assembled in aqueous solution by repeated drying-dissolving process and then used to improve porous structure formation in lyophilization process. Viscosity, secondary structures and water interactions were also studied to exclude their influence on the formation and control of porous structures. Following nanofiber formation in aqueous solution, silk scaffolds with improved porous structure were directly formed after lyophilization and then stabilized with water or methanol annealing treatments. Compared to silk scaffolds derived from fresh solution, the nanofibrous scaffolds showed significantly better cell compatibility in vitro. Therefore, this nanoscale control of silk offers feasible way to regulate the matrix features including porous structure and nanostructure, which are important in regulating cell and tissue outcomes in tissue engineering and regeneration, and then achieve silk-based scaffolds with improved properties.