Fibroin allergy. IgE mediated hypersensitivity to silk suture materials

Immune response profiles induced by silk-based biomaterials: a journey from 'immunogenicity' towards 'immuno-compatibility

Silk is a widely accepted biomaterial for tissue regeneration owing to its tunable biomechanical properties and ease of chemical modification. However, a number of aspects associated with its clinical use are still debated. Indeed, to achieve clinical success, a biomaterial must favorably interact with host tissues without evoking local or systemic immuno-inflammatory responses. The analysis of immune responses associated with silk under in vitro and in vivo conditions provides useful insights, improving the understanding of the functional characteristics of silk biomaterials and further promoting their clinical application. Silk evokes moderate immune responses upon implantation in vivo, depending on the material structure, fabrication method, degradation time, and implantation in soft or hard tissue sites, which rapidly subside within a few days/weeks. In vitro studies indicate that its immune-stimulatory properties are largely due to inherent protein conformation and differential processing parameters. Strategically controlled levels of immune responses in vivo with marginal immunogenicity of silk-based biomaterials may contribute to matrix remodeling and replacement by native tissue matrix around the implanted site. Therefore, immunomodulatory strategies should be developed to promote the use of silk-based biomaterials as promising candidates for numerous clinical applications.

Material matters: exploring the interplay between natural biomaterials and host immune system

Biomaterials are widely used for various medical purposes, for instance, implants, tissue engineering, medical devices, and drug delivery systems. Natural biomaterials can be obtained from proteins, carbohydrates, and cell-specific sources. However, when these biomaterials are introduced into the body, they trigger an immune response which may lead to rejection and failure of the implanted device or tissue. The immune system recognizes natural biomaterials as foreign substances and triggers the activation of several immune cells, for instance, macrophages, dendritic cells, and T cells. These cells release pro-inflammatory cytokines and chemokines, which recruit other immune cells to the implantation site. The activation of the immune system can lead to an inflammatory response, which can be beneficial or detrimental, depending on the type of natural biomaterial and the extent of the immune response. These biomaterials can also influence the immune response by modulating the behavior of immune cells. For example, biomaterials with specific surface properties, such as charge and hydrophobicity, can affect the activation and differentiation of immune cells. Additionally, biomaterials can be engineered to release immunomodulatory factors, such as anti-inflammatory cytokines, to promote a tolerogenic immune response. In conclusion, the interaction between biomaterials and the body's immune system is an intricate procedure with potential consequences for the effectiveness of therapeutics and medical devices. A better understanding of this interplay can help to design biomaterials that promote favorable immune responses and minimize adverse reactions.

Recent trends using natural polymeric nanofibers as supports for enzyme immobilization and catalysis

All the disciplines of science, especially biotechnology, have given continuous attention to the area of enzyme immobilization. However, the structural support made by material science intervention determines the performance of immobilized enzymes. Studies have proven that nanostructured supports can maintain better catalytic performance and improve immobilization efficiency. The recent trends in the application of nanofibers using natural polymers for enzyme immobilization have been addressed in this review article. A comprehensive survey about the immobilization strategies and their characteristics are highlighted. The natural polymers, e.g., chitin, chitosan, silk fibroin, gelatin, cellulose, and their blends with other synthetic polymers capable of immobilizing enzymes in their 1D nanofibrous form, are discussed. The multiple applications of enzymes immobilized on nanofibers in biocatalysis, biosensors, biofuels, antifouling, regenerative medicine, biomolecule degradation, etc.; some of these are discussed in this review article.

Contact Dermatitis in the Surgical Patient: A Focus on Wound Closure Materials

ABSTRACT

Irritant and allergic contact dermatitis from wound closure materials can occur in patients after surgical procedures. The resulting inflammation from contact dermatitis can compromise wound healing, mimic surgical site infections, and result in wound dehiscence. Components of wound closure material, such as antibiotic coatings, dyes, sterilizing compounds, or the material itself, have been implicated as contact allergens. This article provides the latest overview of the components of 3 major forms of wound closure materials-sutures, staples, and tissue adhesives-associated with contact dermatitis, discusses their cross-reactivity, and provides diagnostic and treatment guidelines.

The antigenicity of silk-based biomaterials: sources, influential factors and applications

Silk is an ancient material with essential roles in numerous biomedical applications, such as tissue regeneration and drug delivery, because of its excellent tunable mechanical properties and diverse physical structures. In addition to the necessary functionalities for biomedical applications, another critical factor for materials applied in biology is the appropriate immune interactions with the body. This review focuses on the immune responses of silk-based materials applied in biomedical applications, specifically antigenicity. The factors affecting the antigenicity of silk-based materials are complicated and are related to the composition and structural characteristics of the materials. At the same time, the composition of silk-based materials varies with its species sources, such as silkworms, spiders, honey bees, or engineered recombinant silk. Additionally, different processing methods are used to fabricate different material formats, such as films, hydrogels, scaffolds, particles, and fibers, resulting in different structural characteristics. Furthermore, the resulting body reactions are also different with different degrees of the immune response. Silk protein typically induces a mild immune response, and immunogenicity can play active roles in osteogenesis, angiogenesis, and protection from inflammation. However, there are some rare reports of severe immune responses caused by silk, which can result in an allergic response or tissue necrosis. The source of allergenicity in silk-based materials is currently under-studied and how to regulate and eliminate the overreaction of the immune system is essential for further applications. Overall, the diverse characteristics of silk-based materials mostly show beneficial bioresponses with mild immunogenicity, and the tunable properties make it applicable in immune-related biomedical applications.

Silk biomaterials for vascular tissue engineering applications

Vascular tissue engineering is a rapidly growing field of regenerative medicine, which strives to find innovative solutions for vascular reconstruction. Considering the limited success of synthetic grafts, research impetus in the field is now shifted towards finding biologically active vascular substitutes bestowing in situ growth potential. In this regard, silk biomaterials have shown remarkable potential owing to their favorable inherent biological and mechanical properties. This review provides a comprehensive overview of the progressive development of silk-based small diameter (<6 mm) tissue-engineered vascular grafts (TEVGs), emphasizing their pre-clinical implications. Herein, we first discuss the molecular structure of various mulberry and non-mulberry silkworm silk and identify their favorable properties at the onset of vascular regeneration. The emergence of various state-of-the-art fabrication methodologies for the advancement of silk TEVGs is rationally appraised in terms of their in vivo performance considering the following parameters: ease of handling, long-term patency, resistance to acute thrombosis, stenosis and aneurysm formation, immune reaction, neo-tissue formation, and overall remodeling. Finally, we provide an update on the pre-clinical status of silk-based TEVGs, followed by current challenges and future prospects. STATEMENT OF SIGNIFICANCE: Limited availability of healthy autologous blood vessels to replace their diseased counterpart is concerning and demands other artificial substitutes. Currently available synthetic grafts are not suitable for small diameter blood vessels owing to frequent blockage. Tissue-engineered biological grafts tend to integrate well with the native tissue via remodeling and have lately witnessed remarkable success. Silk fibroin is a natural biomaterial, which has long been used as medical sutures. This review aims to identify several favorable properties of silk enabling vascular regeneration. Furthermore, various methodologies to fabricate tubular grafts are discussed and highlight their performance in animal models. An overview of our understanding to rationally improve the biological activity fostering the clinical success of silk-based grafts is finally discussed.

Histologic evaluation of therapeutic responses in ischemic myocardium elicited by dual growth factor delivery from composite glycosaminoglycan hydrogels

In this project, the ability of dual growth factor-preloaded, silk-reinforced, composite hyaluronic acid-based hydrogels to elicit advantageous histologic responses when secured to ischemic myocardium was evaluated in vivo. Reinforced hydrogels containing both Vascular Endothelial Growth Factor (VEGF) and Platelet-derived Growth Factor (PDGF) were prepared by crosslinking chemically modified hyaluronic acid and heparin with poly(ethylene glycol)-diacrylate around a reinforcing silk mesh. Composite patches were sutured to the ventricular surface of ischemic myocardium in Sprague-Dawley rats, and the resulting angiogenic response was followed for 28 days. The gross appearance of treated hearts showed significantly reduced ischemic area and fibrous deposition compared to untreated control hearts. Histologic evaluation showed growth factor delivery to restore myofiber orientation to pre-surgical levels and to significantly increase elicited microvessel density and maturity by day 28 in infarcted myocardial tissue (p < 0.05). In addition, growth factor delivery reduced cell apoptosis and decreased the density of elicited mast cells and both CD68+ and anti-inflammatory CD163+ macrophages. These findings suggest that HA-based, dual growth factor-loaded hydrogels can successfully induce a series of beneficial responses in ischemic myocardium, and offer the potential for therapeutic improvement of ischemic myocardial remodeling.

Crosslinking strategies for silk fibroin hydrogels: promising biomedical materials

Due to their strong biomimetic potential, silk fibroin (SF) hydrogels are impressive candidates for tissue engineering, due to their tunable mechanical properties, biocompatibility, low immunotoxicity, controllable biodegradability, and a remarkable capacity for biomaterial modification and the realization of a specific molecular structure. The fundamental chemical and physical structure of SF allows its structure to be altered using various crosslinking strategies. The established crosslinking methods enable the formation of three-dimensional (3D) networks under physiological conditions. There are different chemical and physical crosslinking mechanisms available for the generation of SF hydrogels (SFHs). These methods, either chemical or physical, change the structure of SF and improve its mechanical stability, although each method has its advantages and disadvantages. While chemical crosslinking agents guarantee the mechanical strength of SFH through the generation of covalent bonds, they could cause some toxicity, and their usage is not compatible with a cell-friendly technology. On the other hand, physical crosslinking approaches have been implemented in the absence of chemical solvents by the induction of β-sheet conformation in the SF structure. Unfortunately, it is not easy to control the shape and properties of SFHs when using this method. The current review discusses the different crosslinking mechanisms of SFH in detail, in order to support the development of engineered SFHs for biomedical applications.

Safety Assessment of Silk Protein Ingredients as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) reviewed the safety of Hydrolyzed Silk and 9 other silk protein ingredients, which function primarily as skin and hair conditioning agents and bulking agents in cosmetic products. The Panel reviewed relevant data relating to the safety of these ingredients and concluded that 8 ingredients are safe in the present practices of use and concentration in cosmetics, as described in this safety assessment, but that the available data are insufficient for determining the safety of 2 silk protein ingredients in cosmetic products, MEA-Hydrolyzed Silk and Silkworm Cocoon Extract.

Silk Fibroin-Based Materials for Catalyst Immobilization

Silk fibroin is a widely and commercially available natural protein derived from silkworm cocoons. Thanks to its unique amino acid composition and structure, which lead to localized nanoscale pockets with limited but sufficient hydration for protein interaction and stabilization, silk fibroin has been studied in the field of enzyme immobilization. Results of these studies have demonstrated that silk fibroin offers an important platform for covalent and noncovalent immobilization of enzymes through serving as a stabilization matrix/support with high retention of the biological activity of the enzymes of interest. In the hope of providing suggestions for potential future research directions, this review has been written to briefly introduce and summarize key advances in silk fibroin-based materials for immobilization of both enzymes/biocatalysts (including alkaline phosphatase, β-glucosidase, glucose oxidase, lipase, urease, uricase, horseradish peroxidase, catalase, xanthine oxidase, tyrosinase, acetylcholinesterase, neutral protease, α-chymotrypsin, amylase, organophosphorus hydrolase, β-galactosidase, carbonic anhydrase, laccase, zymolyase, phenylalanine ammonia-lyase, thymidine kinase, and several others) and non-enzymatic catalysts (such as Au, Pd, Fe, α-Fe2O3, Fe3O4, TiO2, Pt, ZnO, CuO, Cu2O, Mn3O4, and MnO2).

Silk fibroin safety in the eye: a review that highlights a concern

The biomedical use of silk as a suture dates back to antiquity. Fibroin is the structural element that determines the strength of silk and here we consider the safety of fibroin in its role in ophthalmology. The high mechanical strength of silk meant sufficiently thin threads could be made for eye microsurgery, but such usage was all but superseded by synthetic polymer sutures, primarily because silk in its entirety was more inflammatory. Significant immunological response can normally be avoided by careful manufacturing to provide high purity fibroin, and it has been utilised in this form for tissue engineering an array of fibre and film substrata deployed in research with cells of the eye. Films of fibroin can also be made transparent, which is a required property in the visual pathway. Transparent layers of corneal epithelial, stromal and endothelial cells have all been demonstrated with maintenance of phenotype, as have constructs supporting retinal cells. Fibroin has a lack of demonstrable infectious agent transfer, an ability to be sterilised and prepared with minimal contamination, long-term predictable degradation and low direct cytotoxicity. However, there remains a known ability to be involved in amyloid formation and potential amyloidosis which, without further examination, is enough to currently question whether fibroin should be employed in the eye given its innervation into the brain.

Mites, caterpillars and moths

Besides conditions such as scabies and hypersensitivity to house dust mites, other diseases caused by mites and caterpillars tend to be more uncommon in everyday practice. Nevertheless, there is a broad spectrum of medically relevant disorders associated with these arthropods. Mites may act as parasites that infect or colonize the skin (e.g., scabies, pseudoscabies, demodicosis) or they may pierce the host's skin and feed on tissue fluid and blood (trombiculosis). In the latter case, they also play a role as vectors transmitting Orientia tsutsugamushi, the pathogen that causes Tsutsugamushi fever. In addition to house dust mites, storage mites, too, are characterized by their allergenic potential. The terms erucism and lepidopterism are used for the various diseases caused by caterpillars and moths. Both terms are not used consistently. With respect to pathogenesis, various mechanisms have been described, including type I and type IV hypersensitivity as well as irritant and toxin-induced reactions. In Germany, skin reactions following exposure to the hairs of oak processionary caterpillars are particularly common. Extracutaneous manifestations including nausea, vomiting, hemorrhage, arthropathy or even life-threatening reactions have been reported in association with certain exotic species. Some species act as parasites by feeding on blood or tears. As natural silk can cause immediate and delayed-type hypersensitivity reactions, workers in the silk industry may develop allergic asthma, rhinitis, or conjunctivitis. Consumption of silkworm pupae is associated with the risk of food allergy.

In vitro biocompatibility and biomechanics study of novel, Microscopy Aided Designed and ManufacturEd (MADAME) materials emulating natural tissue weaves and their intrinsic gradients

This study conducted biomechanical and biocompatibility tests of textiles and textile composites, created using recursive logic to emulate the properties of natural tissue weaves and their intrinsic mechanical stiffness gradients. Two sets of samples were created, first to test feasibility on textile samples designed as periosteum substitutes with elastane fibers mimicking periosteum's endogenous elastin and nylon fibers substituting for collagen, and then on composites comprising other combinations of suture materials before and after sterilization. In the first part, the bulk tensile mechanical stiffness of elastane-nylon textiles were tuned through respective fiber composition and orientation, i.e., aligned with and orthogonal to loading direction. Cell culture biocompatibility studies revealed no significant differences in proliferation rates of embryonic murine stem cells seeded on textiles compared to collagen membrane controls. Until the 15th day of culture, cells were rarely observed in direct contact with the elastane fibers, similar to previous observations with elastomeric sheets used in periosteum substitute implants. In the second part of the study textile samples were created from FDA-approved medical sutures comprising silk, expanded polytetrafluoroethylene, and polybutester. Biocompatibility and mechanical stiffness were assessed as a function of sterilization/disinfection mode (steam, ethylene oxide, and serial disinfection with ethanol). Cell proliferation rates did not differ significantly from controls, except for silk-suture containing textiles, which showed bacterial contamination and no viable cells after 15 days' culture for all sterilization methods. Sterilization had mixed (mostly not significant) effects on textile stiffness, except for the case of polybutester suture-based textiles that showed a significant increase in stiffness with ethylene oxide sterilization. In general, all textile combinations exhibited significantly higher stiffness than periosteum. Textiles comprising medical sutures of different stiffnesses arranged in engineered patterns offer a novel means to achieve mechanical gradients in medical device materials, emulating those of nature's own.

Efficiency of resveratrol-loaded sericin nanoparticles: Promising bionanocarriers for drug delivery

Sericin protein nanoparticles are a biocompatible, bio-viable class of nanocarriers gaining prominence in drug delivery system. This research aimed to investigate the suitability fabrication of silk protein (SP) nanoparticles for loading with resveratrol (RSV) via a solventless precipitation technique. The addition of 0.5% (w/v) pluronic surfactant proved optimal for SP nanoparticle fabrication, with obtained nanoparticles being spherical, mono-dispersed and having mean size of approximately 200-400 nm. All exhibited negative surface charges, the extent of which being dependent on the SP concentration, and were non-toxic to normal skin fibroblasts (CRL-2522). Loading of RSV, a promising which poorly soluble multi-targeted anti-oxidative and anti-inflammatory natural polyphenol, into SP nanoparticles proved feasible, with encapsulation levels of 71-75% for 0.6% and 1.0% (w/v) nanoparticle formulations, respectively. Resveratrol-loaded SP nanoparticles strongly inhibited growth of colorectal adenocarcinoma (Caco-2) cells although proved non-cytotoxic to skin fibroblasts, as indicated by cell viability assays. Cellular internalization of SP nanoparticles proved facile and dependent on incubation time; transfection of these carriers, in vitro results indicating sustained release of RSV (over 72 h), and drug solubility enhancements on encapsulation highlight their potential in therapeutic and pharmaceutical applications. Thus, SP nanoparticles is a promising approach to be potential bio-nanocarrier for drug delivery system.

Physico-chemical characterization of Antheraea mylitta silk mats for wound healing applications

In the field of plastic reconstructive surgery, development of new innovative matrices for skin repair is in demand. The ideal biomaterial should promote attachment, proliferation and growth of cells. Additionally, it should degrade in an appropriate time period without releasing harmful substances, not exerting a pathological immune response. The materials used should display optimized mechanical properties to sustain cell growth and limit scaffold contraction. Wound healing is a biological process directed towards restoration of tissue that has suffered an injury. An important phase of wound healing is the generation of a basal epithelium wholly replacing the epidermis of the wound. Wild silk from Antheraea mylitta meets these demands to a large extent. To evaluate the effects of the treatment, Antheraea mylitta and Bombyx mori samples were characterized by SEM-EDX, FT-IR, XRD and TGA-DSC techniques. Preliminary cell growth behavior was carried out by culturing epidermal cells and proliferation was quantified via viability assay. Moreover, Antheraea mylitta possesses excellent cell-adhesive capability, effectively promoting cell attachment and proliferation. Antheraea mylitta serves as a delivery vehicle for cells. With all these unique features, it is expected that Antheraea mylitta mat will have wide utility in the areas of tissue engineering and regenerative medicine.

Hypoglycaemic effects of functional tri-peptides from silk in differentiated adipocytes and streptozotocin-induced diabetic mice

BACKGROUND

In this study, the tri-peptides Gly-Glu-Tyr (GEY) and Gly-Tyr-Gly (GYG), identified previously as active compounds from the silk peptide E5K6, significantly stimulated basal and insulin-mediated glucose uptake by 3T3-L1 fibroblasts in a dose-dependent manner.

RESULTS

Synthetic GEY and GYG peptides at a concentration of 500 µmol L(-1) significantly increased glucose transporter type 4 expression by 157% and 239%, respectively. Differentiation of 3T3-L1 cells into adipocytes leads to accumulation of intracellular fat droplets, and GEY and GYG at a concentration of 250 µmol L(-1) suppressed this effect by 72% and 75%, respectively. GYG improved glucose tolerance in steptozotocin (STZ)-induced diabetic mice in a dose-dependent manner.

CONCLUSION

These results suggest that GYG isolated from E5K6 has anti-diabetic potential and silk waste products containing bioactive peptides could be used to the developments of treatments to lower blood glucose.

A Delayed Allergic Reaction to Polypropylene Suture Used in Flexor Tendon Repair: Case Report

We report a patient who developed a delayed hypersensitivity reaction to a polypropylene suture used in flexor pollicis longus repair. We also review the literature and aim to increase the awareness of hand surgeons to the presentation, diagnosis, and management of these rare cases.

Coatings and films made of silk proteins

Silks are a class of proteinaceous materials produced by arthropods for various purposes. Spider dragline silk is known for its outstanding mechanical properties, and it shows high biocompatibility, good biodegradability, and a lack of immunogenicity and allergenicity. The silk produced by the mulberry silkworm B. mori has been used as a textile fiber and in medical devices for a long time. Here, recent progress in the processing of different silk materials into highly tailored isotropic and anisotropic coatings for biomedical applications such as tissue engineering, cell adhesion, and implant coatings as well as for optics and biosensors is reviewed.

The effects of tetracycline-loaded silk fibroin membrane on proliferation and osteogenic potential of mesenchymal stem cells

BACKGROUND

The main objective of this study was to investigate the effect of tetracycline-loaded silk fibroin membranes (TC-SFMs) on the proliferation and the osteogenic differentiation of human mesenchymal stem cells.

MATERIALS AND METHODS

Four groups (0, 1, 5, and 10% concentration) of TC-SFMs were prepared for the experiments. We investigated cumulative tetracycline (TC) release profile for 7 d. Human gingiva-derived mesenchymal stem cells (GMSCs) were isolated from our previous study and seeded to the TC-SFMs. WST-8 assay (Cell Counting Kit-8; SigmaeAldrich Co, St. Louis, MO), staining of Phalloidin-FITC, and scanning electron microscope analyzed the cellular attachment and viability. Staining of Alizarin Red S (Sigma-Aldrich Co.) and osteogenic marker (osteocalcin) analyzed osteogenic differentiation. Additionally, quantitative polymerase chain reaction measured the expression of osteogenic lineage genes, including bone gamma-carboxyglutamic acid protein, bone sialoprotein, runt-related transcription factor 2, and collagen type I α1 according to TC concentration (0.05, 0.1, 0.25, and 0.5 mg/mL).

RESULTS

The release of TC from TC-SFMs plateaued and neared completion in 24 h. Significantly higher viability was noted achieved in 1% and 5% TC-SFMs. The morphology of GMSCs on TC-SFMs at 0% and 1% concentration showed spindle shapes, but cells in 10% TC-SFMs appeared spheroid. During Alizarin Red S staining at 21 d of osteogenic differentiation, calcium and osteocalcin formation were significantly lower in the 10% TC-SFM group than in the 0, 1, and 5 groups. Compared with the control group, bone gamma-carboxyglutamic acid protein showed significantly low expression rate at TC concentration ≥0.05 mg/mL. Bone sialoprotein was low at TC concentration ≥0.1 mg/mL. Likewise, runt-related transcription factor 2 and collagen type I α1 were low at TC concentration of 0.5 mg/mL.

CONCLUSIONS

Within the limits of this study, 1% and 5% TC-SFMs showed higher proliferation and osteogenic potential of GMSCs than 10% TC-SFM. Therefore, the use of 1% to 5% range of TC may be more suitable to silk fibroin membrane for stem cell tissue engineering.

Sericin removal from raw Bombyx mori silk scaffolds of high hierarchical order

Silk fibroin has previously been described as a promising candidate for ligament tissue engineering (TE) approaches. For biocompatibility reasons, silkworm silk requires removal of sericin, which can elicit adverse immune responses in the human body. One disadvantage of the required degumming process is the alteration of the silk fiber structural properties, which can hinder textile engineering of high order hierarchical structures. Therefore, the aim of this study was to find a way to remove sericin from a compact and highly ordered raw silk fiber matrix. The wire rope design of the test model scaffold comprises several levels of geometric hierarchy. Commonly used degumming solutions fail in removing sericin in this wire rope design. Weight loss measurements, picric acid and carmine staining as well as scanning electron microscopy demonstrated that the removal of sericin from the model scaffold of a wire rope design can be achieved through a borate buffer-based system. Furthermore, the borate buffer degummed silks were shown to be nontoxic and did not alter cell proliferation behavior. The possibility to remove sericin after the textile engineering process has taken place eases the production of highly ordered scaffold structures and may expand the use of silk as scaffold material in further TE and regenerative medicine applications.

Nasal tip abscess due to adverse skin reaction to Prolene: an unusual long term complication of rhinoplasty

OBJECTIVES

Allergic reactions to Prolene are rare. This paper reports a nasal tip abscess which developed in a patient with an adverse skin reaction to Prolene after rhinoplasty.

METHODS AND RESULTS

A 26-year-old woman presented with painful, progressive nasal tip swelling and redness. She had undergone septo-rhinoplasty two years previously. She was initially treated with endonasal drainage of the abscess and antibiotics, but a revision rhinoplasty three months later became necessary because of recurrent abscess formation. Intra-operative findings included granulation tissue with pockets of pus and knotted Prolene sutures at the tip-defining points of the lower lateral cartilages. She was patch-tested with Prolene and a cutaneous Prolene suture was placed on her back; an adverse skin reaction was seen for the latter.

CONCLUSION

Use of non-absorbable sutures, such as Prolene, in the subcutaneous layer may be a potential, rare risk factor for adverse skin reactions.

Tissue engineering strategies in ligament regeneration

Ligaments are dense fibrous connective tissues that connect bones to other bones and their injuries are frequently encountered in the clinic. The current clinical approaches in ligament repair and regeneration are limited to autografts, as the gold standard, and allografts. Both of these techniques have their own drawbacks that limit the success in clinical setting; therefore, new strategies are being developed in order to be able to solve the current problems of ligament grafting. Tissue engineering is a novel promising technique that aims to solve these problems, by producing viable artificial ligament substitutes in the laboratory conditions with the potential of transplantation to the patients with a high success rate. Direct cell and/or growth factor injection to the defect site is another current approach aiming to enhance the repair process of the native tissue. This review summarizes the current approaches in ligament tissue engineering strategies including the use of scaffolds, their modification techniques, as well as the use of bioreactors to achieve enhanced regeneration rates, while also discussing the advances in growth factor and cell therapy applications towards obtaining enhanced ligament regeneration.

Novel tripeptides with α-glucosidase inhibitory activity isolated from silk cocoon hydrolysate

Active compounds with antidiabetic potential were isolated from silk peptide E5K6 by consecutive ultrafiltration and gel filtration using Biogel P-2 and RS-HPLC using a YMC-Pack Pro C18 column. The highest α-glucosidase inhibitory activity of silk peptide E5K6 resulted from fractions with MW <1 kDa. The activities of gel-filtered fractions from silk peptide E5K6 of <1 kDa were assayed in vitro, demonstrating that the fourth peak (F4) had the highest α-glucosidase inhibitory activity (IC(50) = 37.1 mg/mL). F4 of silk peptide E5K6 was separated by HPLC into two peaks. Moreover, the purified compounds were identified as Gly-Glu-Tyr (GEY, MW = 367 Da) and Gly-Tyr-Gly (GYG, MW = 295 Da) according to amino acid sequences, and their α-glucosidase inhibitory activities (IC(50)) were 2.7 and 1.5 mg/mL, respectively.

Non-mulberry silk sericin/poly (vinyl alcohol) hydrogel matrices for potential biotechnological applications

This study reports a novel biopolymeric matrix fabricated by chemically cross-linking poly (vinyl alcohol) with silk sericin protein obtained from cocoons of the tropical tasar silkworm Antheraea mylitta. Glutaraldehyde was used as a cross-linking agent with hydrochloric acid acting as an initiator. The matrices were biophysically characterized and the cytocompatibility of the matrices was evaluated for their suitability as biomaterials. The surface morphology was assessed using atomic force microscopy while the changes taking place after cross-linking were confirmed by Fourier transform infrared spectroscopy. The enhanced thermal stability of the constructs was assessed by thermogravimetric and differential scanning calorimetry. Fourier transform infrared spectroscopy analysis showed that sericin was chemically cross-linked with poly (vinyl alcohol) using glutaraldehyde. Silk sericin protein demonstrated a favorable effect on animal cell culture by successfully improving the adhering and spreading of cells on the poorly adhering surface of poly (vinyl alcohol). Confocal microscopy revealed cell spreading and actin filament development in sericin/poly (vinyl alcohol) hydrogel matrices. These findings prove the potential of non-mulberry silk sericin/poly (vinyl alcohol) hydrogel matrices to be used as biocompatible and biopolymeric material for tissue-engineering and biotechnological applications.

Biosynthesis of β-Glucosidase-Silk Fibroin Nanoparticles Conjugates and Enzymatic Characteristics

Silk fibroin derived from Bombyx mori is a biomacromolecular protein with outstanding biocompatibility. When it was dissolved in highly concentrated CaCl2 solution and then the mixture of the protein and salt was subjected to desalting treatments for long time in flowing water, the resulting liquid silk was water-soluble polypeptides with different molecular masses, ranging from 10 to 200 kDa. When the liquid silk were introduced rapidly into acetone, silk protein nanoparticles (SFNs) with a range of 40~120 nm in diameter could be obtained. The crystalline silk nanoparticles could be conjugated with β-glucosidase with cross-linking of reagent glutaraldehyde. In this work, the activity of β-glucosidase-silk fibroin nanoparticles (βG-SFNs) bioconjugates was determined by p-nitrophenyl-β-D-glucoside (p-NPG) as a substrate and the optimal conditions for the biosynthesis of βG-SFNs bioconjugates were investigated. βG-SFN constructs obtained by 5h of covalent cross-linking time at the experimental conditions of 0.25% cross-linking reagent, 37 °C and the proportion of β-glucosidase and SFNs (75 : 100, U/mg) showed 46% of recoveries. Results showed that kinetic parameters of βG-SFNs were the same as for the free β-glucosidase. The optimal pH was 5.0 and the optimal temperature was 60°C. When β-glucosidase was coupled covalently with silk nanoparticles, the thermal stability of βG-SFNs was slightly enhanced as compared with free β-glucosidase. The apparent Km of βG-SFNs (1.41×10-3 mol•L-1) was near five-fold less than that of the free enzyme (7.26×10−3 mol•L-1), this fully shows that after the free enzyme conjugated with silk fibroin nanoparticles, the enzyme affinity with substrate increased. These results fully demonstrated the silk protein nanoparticles were good carriers as bioconjugation or modification of enzymes. Moreover, they had potential values for research and development in food processing and flavor processing agents.

Silk-based delivery systems of bioactive molecules

Silks are biodegradable, biocompatible, self-assembling proteins that can also be tailored via genetic engineering to contain specific chemical features, offering utility for drug and gene delivery. Silkworm silk has been used in biomedical sutures for decades and has recently achieved Food and Drug Administration approval for expanded biomaterials device utility. With the diversity and control of size, structure and chemistry, modified or recombinant silk proteins can be designed and utilized in various biomedical application, such as for the delivery of bioactive molecules. This review focuses on the biosynthesis and applications of silk-based multi-block copolymer systems and related silk protein drug delivery systems. The utility of these systems for the delivery of small molecule drugs, proteins and genes is reviewed.

Advantage of absorbable suture material for pulmonary artery ligation

PURPOSE

The applicability of absorbable materials as ligatures of pulmonary vessels has not been described. The present study compares tissue reactions around sites of pulmonary arteries ligated with absorbable material (Vicryl) and with nonabsorbable material (silk).

METHODS

Beagle dogs underwent thoracotomy and the pulmonary artery branches were ligated with silk or Vicryl under general anesthesia. The ligated arterial tissues were obtained at 4 and 8 weeks after thoracotomy and processed for pathological analysis.

RESULTS

The arteries ligated using Vicryl or silk were clinically completely sealed at 4 weeks after ligation. More inflammation and granuloma were evident at tissues surrounding ligations made with silk than with Vicryl at 8 weeks. Hyperplasia of the arterial intima continued at 8 weeks after ligation with both Vicryl and silk sutures, although some hyperplasia similar to that in nonligated arterial intima appeared at 4 weeks after ligation.

CONCLUSION

Less inflammation and granuloma are caused at arterial tissues around ligations accomplished with absorbable Vicryl than those done with nonabsorbable silk sutures, although both are equally effective. Absorbable sutures might be suitable for ligating pulmonary arteries.

Silk-based gene carriers with cell membrane destabilizing peptides

Complexes of recombinant silk-polylysine molecules with ppTG1 peptide, a lysine-rich cell membrane destabilizing peptide to bind plasmid DNA (pDNA), are designed as less-cytotoxic and highly efficient gene carriers. The peptide destabilizes the cell membrane and promotes gene transfer. Our particular interest is in how ppTG1 enhances transfection efficiency of the silk-based delivery system into human cells. Genetically engineered silk proteins containing polylysine and the monomeric and dimeric ppTG1 sequences are synthesized in Escherichia coli , followed by transfection experiments. The pDNA complexes of silk-polylysine-ppTG1 dimer recombinant proteins prepared at an N/P 2 (the ratio of number of amines/phosphates from pDNA) shows the highest transfection efficiency into human embryonic kidney (HEK) cells, the level of which is comparable to the transfection reagent Lipofectamine 2000. The assemblies show a globular morphology with an average hydrodynamic diameter of 99 nm and almost no β-sheet structure. Additionally, the silk-based pDNA complexes demonstrate excellent DNase resistance as well as efficient release of the pDNA by enzymes that degrade silk proteins. Also, comparison with β-sheet induced silk-based pDNA complexes indicates that the β-sheet structure content of the silk sequence of the pDNA complexes controls the enzymatic degradation rate of the complexes and, hence, can regulate the release profile of genes from the complexes. The bioengineered silk-based gene delivery vehicles containing cell membrane destabilizing peptides are therefore concluded to have potential for a less-toxic and controlled-release gene delivery system.

Silk Fibroin Based Porous Materials

Silk from the Bombyx mori silkworm is a protein-based fiber. Bombyx mori silk fibroin (SF) is one of the most important candidates for biomedical porous material based on its superior machinability, biocompatibility, biodegradation, bioresorbability, and so on. In this paper, we have reviewed the key features of SF. Moreover we have focused on the morphous, technical processing, and biocompatibility of SF porous materials, followed by the application research. Finally, we provide a perspective the potential and problems of SF porous materials.

Advancing Towards a Tissue-engineered Tympanic Membrane: Silk Fibroin as a Substratum for Growing Human Eardrum Keratinocytes

Human tympanic membrane cells (hTMCs), harvested from tympanic membrane (TM) explants, were grown in culture and then seeded on membranes prepared from silkworm (Bombyx mori) silk fibroin (BMSF) and on tissue-culture plastic membranes (PET). Fibroin was isolated from silk cast into membranes with a thickness of 10—15 μm. The hTMCs were cultured on both materials for 15 days in a serum-containing culture medium. The cells grown on both substrata were subjected to nuclear staining (DAPI) and counted. Further, the cultures were immunostained for a number of protein markers related to the epithelial/keratinocyte phenotype and cell adhesion complexes. The BMSF membranes supported levels of hTMC growth higher than that observed on the PET membranes. The immunofluorochemical analysis indicated unequivocally that BMSF is a more suitable substratum than PET with respect to the growth patterns, proliferation, and cell—cell contact and adhesion. BMSF appear as a promising substratum in the tissue-engineered constructs for the replacement of TM in case of nonhealing perforations.

Usefulness of absorbable sutures in preventing surgical site infection in hepatectomy

We evaluated the usefulness of synthetic absorbable sutures (Vicryl) in preventing surgical site infection (SSI) after hepatectomy. A rat model of 60% partial hepatectomy was used. Bleeding from the cut surface of the liver was controlled by using two suture types: silk and Vicryl. In the Vicryl group, the lesser omentum was slightly adherent to the cut surface of the liver, while in the silk group, the suture remained, and severe adhesions were found. The number of Staphylococcus aureus was significantly larger in the silk group. We compared a group of patients (n = 125) who underwent hepatectomy using silk with one (n = 188) using Vicryl. The respective incidences of SSI and infection on the cut surface of the liver in the Vicryl group (3.2, 1.6%) were significantly lower than in the silk group (11.2, 8.8%). In accordance with the results of multivariate analysis, duration of operation, use of silk sutures and the complication of bile leakage were selected as independent factors. The risk of SSI in the silk group was 3.4 times that in the Vicryl group. The use of synthetic absorbable sutures, instead of silk sutures, in all the procedures of hepatectomy contributed significantly to the prevention of SSI.