Functional modification of silk fibroin from silkworms and its application to medical biomaterials: A review

Silk fibroin (SF) from the silkworm Bombyx mori is a fibrous protein identified as a widely suitable biomaterial due to its biocompatibility, tunable degradation, and mechanical strength. Various modifications of SF protein can give SF fibers new properties and functions, broadening their applications in textile and biomedical industries. A diverse array of functional modifications on various forms of SF has been reported. In order to provide researchers with a more systematic understanding of the types of functional modifications of SF protein, as well as the corresponding applications, we comprehensively review the different types of functional modifications, including transgenic modification, modifications with chemical groups or biologically active substance, cross-linking and copolymerization without chemical reactions, their specific modification methods and applications. Furthermore, recent applications of SF in various medical biomaterials are briefly discussed.

Self-assembled silk fibroin cross-linked with genipin supplements microbial carbonate precipitation in building material

The process of microbially induced carbonate precipitation (MICP) is known to effectively improve engineering properties of building materials and so does silk fibroin (SF). Thus, in this study, an attempt was taken to see the improvement in sand, that is, basic building material coupled with MICP and SF. Urease producing Bacillus megaterium was utilized for MICP in Nutri-Calci medium. To improve the strength of SF itself in bacterial solution, it was cross-linked with genipin at the optimized concentration of 3.12 mg/mL. The Fourier transform infrared (FTIR) spectra confirmed the crosslinking of SF with genipin in bacterial solution. In order to understand how such cross-linking can improve engineering properties, sand moulds of 50 mm3 dimension were prepared that resulted in 35% and 55% more compressive strength than the one prepared with bacterial solution with SF and bacterial solution only, respectively with higher calcite content in former one. The FTIR, SEM, x-ray powder diffraction spectrometry and x-ray photoelectron spectroscopy analyses confirmed higher biomineral precipitation in bacterial solution coupled with genipin cross-linked SF. As the process of MICP is proven to replace cement partially from concrete without negatively influence mechanical properties, SF cross-linked with genipin can provide additional significance in developing low-carbon cement-based composites.

Improved Physiochemical Properties of Chitosan@PCL Nerve Conduits by Natural Molecule Crosslinking

Nerve conduits may represent a valuable alternative to autograft for the regeneration of long-gap damages. However, no NCs have currently reached market approval for the regeneration of limiting gap lesions, which still represents the very bottleneck of this technology. In recent years, a strong effort has been made to envision an engineered graft to tackle this issue. In our recent work, we presented a novel design of porous/3D-printed chitosan/poly-ε-caprolactone conduits, coupling freeze drying and additive manufacturing technologies to yield conduits with good structural properties. In this work, we studied genipin crosslinking as strategy to improve the physiochemical properties of our conduit. Genipin is a natural molecule with very low toxicity that has been used to crosslink chitosan porous matrix by binding the primary amino group of chitosan chains. Our characterization evidenced a stabilizing effect of genipin crosslinking towards the chitosan matrix, with reported modified porosity and ameliorated mechanical properties. Given the reported results, this method has the potential to improve the performance of our conduits for the regeneration of long-gap nerve injuries.

Biomimetic Electrospun Self-Assembling Peptide Scaffolds for Neural Stem Cell Transplantation in Neural Tissue Engineering

Spinal cord regeneration using stem cell transplantation is a promising strategy for regenerative therapy. Stem cells transplanted onto scaffolds that can mimic natural extracellular matrix (ECM) have the potential to significantly improve outcomes. In this study, we strived to develop a cell carrier by culturing neural stem cells (NSCs) onto electrospun 2D and 3D constructs made up of specific crosslinked functionalized self-assembling peptides (SAPs) featuring enhanced biomimetic and biomechanical properties. Morphology, architecture, and secondary structures of electrospun scaffolds in the solid-state and electrospinning solution were studied step by step. Morphological studies showed the benefit of mixed peptides and surfactants as additives to form thinner, uniform, and defect-free fibers. It has been observed that β-sheet conformation as evidence of self-assembling has been predominant throughout the process except for the electrospinning solution. In vitro NSCs seeded on electrospun SAP scaffolds in 2D and 3D conditions displayed desirable proliferation, viability, and differentiation in comparison to the gold standard. In vivo biocompatibility assay confirmed the permissibility of implanted fibrous channels by foreign body reaction. The results of this study demonstrated that fibrous 2D/3D electrospun SAP scaffolds, when shaped as micro-channels, can be suitable to support NSC transplantation for regeneration following spinal cord injury.

Biomass carbon mining to develop nature-inspired materials for a circular economy

A transition from a linear to a circular economy is the only alternative to reduce current pressures in natural resources. Our society must redefine our material sources, rethink our supply chains, improve our waste management, and redesign materials and products. Valorizing extensively available biomass wastes, as new carbon mines, and developing biobased materials that mimic nature's efficiency and wasteless procedures are the most promising avenues to achieve technical solutions for the global challenges ahead. Advances in materials processing, and characterization, as well as the rise of artificial intelligence, and machine learning, are supporting this transition to a new materials' mining. Location, cultural, and social aspects are also factors to consider. This perspective discusses new alternatives for carbon mining in biomass wastes, the valorization of biomass using available processing techniques, and the implementation of computational modeling, artificial intelligence, and machine learning to accelerate material's development and process engineering.

Biomedical applications of chitosan/silk fibroin composites: A review

Natural polymers have been used in the biomedical fields for decades, mainly derived from animals and plants with high similarities with biomacromolecules in the human body. As an alkaline polysaccharide, chitosan (CS) attracts much attention in tissue regeneration and drug delivery with favorable biocompatibility, biodegradation, and antibacterial activity. However, to overcome its mechanical properties and degradation behavior drawbacks, a robust fibrous protein-silk fibroin (SF) was introduced to prepare the CS/SF composites. Not only can CS be combined with SF via the amide and hydrogen bond formation, but also their functions are complementary and tunable with the blending ratio. To further improve the performances of CS/SF composites, natural (e.g., hyaluronic acid and collagen) and synthetic biopolymers (e.g., polyvinyl alcohol and hexanone) were incorporated. Also, the CS/SF composites acted as slow-release carriers for inorganic non-metals (e.g., hydroxyapatite and graphene) and metal particles (e.g., silver and magnesium), which could enhance cell functions, facilitate tissue healing, and inhibit bacterial growth. This review presents the state-of-the-art and future perspectives of different biomaterials combined with CS/SF composites as sponges, hydrogels, membranes, particles, and coatings. Emphasis is devoted to the biological potentialities of these hybrid systems, which look rather promising toward a multitude of applications.

Methacrylated Silk Fibroin Additive Manufacturing of Shape Memory Constructs with Possible Application in Bone Regeneration

Methacrylated silk (Sil-MA) is a chemically modified silk fibroin specifically designed to be crosslinkable under UV light, which makes this material applicable in additive manufacturing techniques and allows the prototyping and development of patient-specific 2D or 3D constructs. In this study, we produced a thin grid structure based on crosslinked Sil-MA that can be withdrawn and ejected and that can recover its shape after rehydration. A complete chemical and physical characterization of Sil-MA was first conducted. Additionally, we tested Sil-MA biocompatibility according to the International Standard Organization protocols (ISO 10993) ensuring the possibility of using it in future trials. Sil-MA was also tested to verify its ability to support osteogenesis. Overall, Sil-MA was shown to be biocompatible and osteoconductive. Finally, two different additive manufacturing technologies, a Digital Light Processing (DLP) UV projector and a pneumatic extrusion technique, were used to develop a Sil-MA grid construct. A proof-of-concept of its shape-memory property was provided. Together, our data support the hypothesis that Sil-MA grid constructs can be injectable and applicable in bone regeneration applications.

Enhanced formation of bioactive and strong silk-bioglass hybrid materials through organic-inorganic mutual molecular nucleation induction and templating

Materials based on silk fibroin (SF) are important for many biomedical applications due to their excellent biocompatibility and tunable biodegradability. However, the insufficient mechanical strength and low bioactivity of these materials have limited their applications. For silk hydrogels, slow gelation is also a crucial problem. In this work, a simple approach is developed to address these challenging problems all at once. By mixing SF solution with bioglass (BG) sol, instant gelation of silk is induced, the storage modulus of the hydrogel and the compressive modulus of the aerogel are significantly enhanced. The formation of a complex of SF and tetraethyl orthosilicate (TEOS), either through hydrogen bonding or TEOS condensation on SF, facilitated the aggregation of SF and, on the other hand, created active sites for the condensation of TEOS and BG formation on the surface of silk nanofibrils. The resultant hybrid gels have much higher capacity for biomineralization, indicating their higher bioactivity, compared with the pristine silk gels. This organic (SF)-inorganic (BG) mutual nucleation induction and templating can be used for a general approach to produce bioactive silk materials of various formats not limited to gels and may also inspire the formation of other functional protein-BG hybrid materials.

Electrospun Silk Fibroin/kappa-Carrageenan Hybrid Nanofibers with Enhanced Osteogenic Properties for Bone Regeneration Applications

Simple Summary

Bone tissue engineering has recently been considered as a potential alternative approach to treating patients with bone disorders/defects caused by tumors, trauma, and infection. Scaffolds play a crucial role in the field because they can serve as a template that can provide optimal structural and functional support for cells. In this study, we prepared a series of electrospun silk fibroin/kappa-carrageenan nanofibrous membranes with the aim of mimicking bone extracellular matrix structure and composition and improving the biological properties of silk-fibroin-based nanofibers. Our research found that a combinational approach blending kappa-carrageenan and silk fibroin could enhance the biological properties of the nanostructured scaffold. kappa-carrageenan could also enhance the osteogenic potential and bioactivity properties of silk fibroin nanofibers, while genipin crosslinking preserved the mechanical strength of hybrid nanofibrous mats, indicating that the electrospun hybrid scaffolds could be a potential candidate for bone regeneration applications.

Abstract

In this study, a novel nanofibrous hybrid scaffold based on silk fibroin (SF) and different weight ratios of kappa-carrageenan (k-CG) (1, 3, and 5 mg of k-CG in 1 mL of 12 wt% SF solution) was prepared using electrospinning and genipin (GP) as a crosslinker. The presence of k-CG in SF nanofibers was analyzed and confirmed using Fourier transform infrared spectroscopy (FTIR). In addition, X-ray diffraction (XRD) analysis confirmed that GP could cause SF conformation to shift from random coils or α-helices to β-sheets and thereby facilitate a more crystalline and stable structure. The ultimate tensile strength (UTS) and Young’s modulus of the SF mats were enhanced after crosslinking with GP from 3.91 ± 0.2 MPa to 8.50 ± 0.3 MPa and from 9.17 ± 0.3 MPa to 31.2 ± 1.2 MP, respectively. Notably, while the mean fiber diameter, wettability, and biodegradation rate of the SF nanofibers increased with increasing k-CG content, a decreasing effect was determined in terms of UTS and Young’s modulus. Additionally, better cell viability and proliferation were observed on hybrid scaffolds with the highest k-CG content. Osteogenic differentiation was determined from alkaline phosphatase (ALP) activity and Alizarin Red staining and expression of osteogenic marker genes. To this end, we noticed that k-CG enhanced ALP activity, calcium deposition, and expression of osteogenic genes on the hybrid scaffolds. Overall, hybridization of SF and k-CG can introduce a promising scaffold for bone regeneration; however, more biological evaluations are required.

Nanofiber Systems as Herbal Bioactive Compounds Carriers: Current Applications in Healthcare

Nanofibers have emerged as a potential novel platform due to their physicochemical properties for healthcare applications. Nanofibers’ advantages rely on their high specific surface-area-to-volume and highly porous mesh. Their peculiar assembly allows cell accommodation, nutrient infiltration, gas exchange, waste excretion, high drug release rate, and stable structure. This review provided comprehensive information on the design and development of natural-based polymer nanofibers with the incorporation of herbal medicines for the treatment of common diseases and their in vivo studies. Natural and synthetic polymers have been widely used for the fabrication of nanofibers capable of mimicking extracellular matrix structure. Among them, natural polymers are preferred because of their biocompatibility, biodegradability, and similarity with extracellular matrix proteins. Herbal bioactive compounds from natural extracts have raised special interest due to their prominent beneficial properties in healthcare. Nanofiber properties allow these systems to serve as bioactive compound carriers to generate functional matrices with antimicrobial, anti-inflammatory, antioxidant, antiseptic, anti-viral, and other properties which have been studied in vitro and in vivo, mostly to prove their wound healing capacity and anti-inflammation properties.

Fabrication of Mesoporous Silica Nanoparticle-Incorporated Coaxial Nanofiber for Evaluating the In Vitro Osteogenic Potential

The most important role of tissue engineering is to develop a biomaterial with a property that mimics the extracellular matrix (ECM) by enhancing the lineage-specific proliferation and differentiation with favorable regeneration property to aid in new tissue formation. Thus, to develop an ideal scaffold for bone repair, we have fabricated a composite nanofiber by the coaxial electrospinning technique. The coaxial electrospun nanofiber contains the core layer, consisting of polyvinyl alcohol (PVA) blended with oregano extract and mesoporous silica nanoparticles (PVA-OE-MSNPs), and the shell layer, consisting of poly-ε-caprolactone blended with collagen and hydroxyapatite (PCL-collagen-HAP). We evaluated the physicochemical properties of the nanofibers using X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). In vitro biocompatibility, cell adhesion, cell viability, and osteogenic potential were evaluated by 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenlytetrazolium bromide (MTT), calcein AM, and alkaline phosphatase (ALP) activity and Alizarin Red staining in NIH 3T3/MG-63 cells. The results showed that the nanoparticle-incorporated coaxial nanofiber was observed with bead-free, continuous, and uniform fiber morphology with a mean diameter in the range of 310 ± 125 nm. From the biochemical studies, it is observed that the incorporation of nanofiber with HAP and MSNPs shows good swelling property with ideal porosity, biodegradation, and enhanced biomineralization property. In vitro results showed that the scaffolds with nanoparticles have higher cell adhesion, cell viability, ALP activity, and mineralization potential. Thus, the fabricated nanofiber could be an appropriate implantable biomaterial for bone tissue engineering.

In Situ Prevascularization Strategy with Three-Dimensional Porous Conduits for Neural Tissue Engineering

Neovascularization is crucial for peripheral nerve regeneration and long-term functional restoration. Previous studies have emphasized strategies that enhance axonal repair over vascularization. Here, we describe the development and application of an in situ prevascularization strategy that uses 3D porous nerve guidance conduits (NGCs) to achieve angiogenesis-mediated neural regeneration. The optimal porosity of the NGC is a critical feature for achieving neovascularization and nerve growth patency. Hollow silk fibroin/poly(l-lactic acid-co-ε-caprolactone) NGCs with 3D sponge-like walls were fabricated using electrospinning and freeze-drying. In vitro results showed that 3D porous NGC favored cell biocompatibility had neuroregeneration potential and, most importantly, had angiogenic activity. Results from our mechanistic studies suggest that activation of HIF-1α signaling might be associated with this process. We also tested in situ prevascularized 3D porous NGCs in vivo by transplanting them into a 10 mm rat sciatic nerve defect model with the aim of regenerating the severed nerve. The prevascularized 3D porous NGCs greatly enhanced intraneural angiogenesis, resulting in demonstrable neurogenesis. Eight weeks after transplantation, the performance of the prevascularized 3D NGCs was similar to that of traditional autografts in terms of improved anatomical structure, morphology, and neural function. In conclusion, combining a reasonably fabricated 3D-pore conduit structure with in situ prevascularization promoted functional nerve regeneration, suggesting an alternative strategy for achieving functional recovery after peripheral nerve trauma.

Genipin crosslinked chitosan/PEO nanofibrous scaffolds exhibiting an improved microenvironment for the regeneration of articular cartilage

Towards optimizing the growth of extracellular matrix to produce repair cartilage for healing articular cartilage (AC) defects in joints, scaffold-based tissue engineering approaches have recently become a focus of clinical research. Scaffold-based approaches by electrospinning aim to support the differentiation of chondrocytes by providing an ultrastructure similar to the fibrillar meshwork in native cartilage. In a first step, we demonstrate how the blending of chitosan with poly(ethylene oxide) (PEO) allows concentrated chitosan solution to become electrospinnable. The chitosan-based scaffolds share the chemical structure and characteristics of glycosaminoglycans, which are important structural components of the cartilage extracellular matrix. Electrospinning produced nanofibrils of ∼100 nm thickness that are closely mimicking the size of collagen fibrils in human AC. The polymer scaffolds were stabilized in physiological conditions and their stiffness was tuned by introducing the biocompatible natural crosslinker genipin. We produced scaffolds that were crosslinked with 1.0% genipin to obtain values of stiffness that were in between the stiffness of the superficial zone human AC of 600 ± 150 kPa and deep zone AC of 1854 ± 483 kPa, whereas the stiffness of 1.5% genipin crosslinked scaffold was similar to the stiffness of deep zone AC. The scaffolds were degradable, which was indicated by changes in the fibril structure and a decrease in the scaffold stiffness after seven months. Histological and immunohistochemical analysis after three weeks of culture with human articular chondrocytes (HACs) showed a cell viability of over 90% on the scaffolds and new extracellular matrix deposited on the scaffolds.

Chitosan grafted/cross-linked with biodegradable polymers: A review

Public perception of polymers has been drastically changed with the improved plastic management at the end of their life. However, it is widely recognised the need of developing biodegradable polymers, as an alternative to traditional petrochemical polymers. Chitosan (CH), a biodegradable biopolymer with excellent physiological and structural properties, together with its immunostimulatory and antibacterial activity, is a good candidate to replace other polymers, mainly in biomedical applications. However, CH has also several drawbacks, which can be solved by chemical modifications to improve some of its characteristics such as solubility, biological activity, and mechanical properties. Many chemical modifications have been studied in the last decade to improve the properties of CH. This review focussed on a critical analysis of the state of the art of chemical modifications by cross-linking and graft polymerization, between CH or CH derivatives and other biodegradable polymers (polysaccharides or proteins, obtained from microorganisms, synthetized from biomonomers, or from petrochemical products). Both techniques offer the option of including a wide variety of functional groups into the CH chain. Thus, enhanced and new properties can be obtained in accordance with the requirements for different applications, such as the release of drugs, the improvement of antimicrobial properties of fabrics, the removal of dyes, or as scaffolds to develop bone tissues.

Pathophysiological Effects of Sulfur Mustard on Skin and its Current Treatments: Possible Application of Phytochemicals

BACKGROUND

Sulfur-(SM) and nitrogen (NM)-based mustards are the mutagenic incapacitating compounds which are widely used in vesicating the chemical warfare and cause toxicity in many organs, especially skin. SM, as a potent vesicating agent, contributes to the destruction of skin in dermis and epidermis layers. The progression of the lesion depends on the concentration of SM and the duration of exposure. Body responses start with pruritus, erythema, edema and xerosis, which lead to the accumulation of immune cells in the target sites and recruitment of mast cells and paracrine-mediated activity. Pro-inflammatory effectors are accumulated in the epidermis, hair follicles, and sebaceous glands resulting in the destruction of the basement membrane beneath the epidermis. There is still no satisfactory countermeasure against SM-induced lesions in clinical therapy, and the symptomatic or supportive treatments are routine management approaches.

OBJECTIVE

The current review highlights the recent progression of herbal medicines application in SM-induced injuries through the illustrative examples and also demonstrates their efficacies, properties and mechanism of actions as therapeutic agents.

CONCLUSION

Phytochemicals and herbal extracts with anti-bacterial, anti-inflammatory and antioxidant properties have been recently shown to hold therapeutic promise against the SM-induced cutaneous complications. The present review discusses the possible application of herbal medicines in the healing of SM-induced injuries.

Thermoresponsive Chitosan/DOPA-Based Hydrogel as an Injectable Therapy Approach for Tissue-Adhesion and Hemostasis

Chitosan (CS) hydrogels are widely used in wound hemostatic agents due to their superior biocompatibility, biodegradability, and hemostatic effect. However, most of them fail to achieve great hemostatic effect because of poor adhesion to bleeding tissues. Also, the conventional implantation surgery of hemostatic hydrogels to internal bleeding wounds may cause secondary trauma to the human body. In this work, catechol-hydroxybutyl chitosan (HBCS-C) has been designed and prepared by grafting hydroxybutyl groups and catechol groups to the CS backbones. The multifunctional HBCS-C hydrogels are fabricated with the properties of thermosensitivity, injectability, tissue-adhesion, biodegradation, biocompatibility, and wound hemostasis. They exhibit excellent liquid-gel transition at different temperatures, through the changes of hydrophilic-hydrophobic interaction and hydrogen bonds generating from hydroxybutyl groups. By the multiple interactions between catechol groups/amino groups and tissues, the biocompatible hydrogels can strongly adhere on the surface of tissue. To further study, the bleeding rat-liver models are made to evaluate the hemostatic effects. After injecting the hydrogel precursor solution into the rat body, the hydrogels are not only formed in situ within 30 s but are also firmly adhered to the bleeding tissues which shows effective hemostasis. The injectability and tissue-adhesion improvement in this study gives a new insight into hemostatic agents, and the multifunctional hydrogels have a great potential in the biomedical application.

Graphene oxide coated shell-core structured chitosan/PLLA nanofibrous scaffolds for wound dressing

Graphite oxide (GO) and chitosan (CS) nanofibers have aroused intense interest as wound dressing due to their physicochemical, antimicrobial properties and nanotopography. In this study, GO nanosheets were coated on shell (chitosan, CS)-core (L-polylactic acid, PLLA) structured nanofibrous scaffolds to create a synergistic microenvironment for wound healing. Through scanning electron microscopy (SEM) and atomic force microscopy (AFM) tests, results showed that the surface of GO-coated CS/PLLA nanofibers presented corrugated wrinkles and rougher than that of CS/PLLA nanofibers, and the GO nanosheets did not destroy the structure of nanofibers. X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) demonstrated that GO nanosheets were successfully coated on CS/PLLA nanofibrous scaffolds. Furthermore, the coatings of GO nanosheets significantly improved the hydrophilicity of CS/PLLA nanofibrous scaffolds. GO-coated CS/PLLA nanofibrous scaffolds revealed more excellent antimicrobial activity to Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) than that of CS/PLLA nanofibrous scaffolds, meanwhile, they promoted the proliferation of pig iliac endothelial cells (PIECs). Rats wounds covered by GO-coated CS/PLLA nanofibrous scaffolds were healed better than other groups on pathological section. This type of nanofibrous scaffolds with GO nanosheets would possess an excellent potential in wound healing process.

Structure-property of crosslinked chitosan/silica composite films modified by genipin and glutaraldehyde under alkaline conditions

In this study, genipin and glutaraldehyde in varied concentrations were utilized in chitosan crosslinking under alkaline condition. A UV/Vis analysis was used to investigate the molecular structure of genipin and glutaraldehyde in an aqueous alkaline solution. The results showed the formation of glutaraldehyde dimer and polymerized genipin. The FTIR-ATR, SEM, DSC, XRD, mechanical properties, crosslinking degree and swelling ratio of chitosan based films crosslinked by genipin and glutaraldehyde were determined. The results indicated that the hydrogen bonds formed between genipin and chitosan enabled the films crosslinked by genipin (1 and 5 mmol/L) to have a higher degree of crosslinking, but a lower swelling ratio than glutaraldehyde (1 and 5 mmol/L). Genipin enabled the chitosan-based film to possess better mechanical properties and crystallinity than glutaraldehyde. The polymerization of genipin had a substantial effect on the network structure and swelling behavior of chitosan-based films crosslinked by genipin.

Fabrication and characterization of electrospun PLLA/PANI/TSA fibers

Poly(l-lactic acid)/polyaniline/TSA (PLLA/PANI/TSA) fiber mats play a positive role as a tissue scaffold for osteoblast cell proliferation.

Bioresorbable electrospun gelatin/polycaprolactone nanofibrous membrane as a barrier to prevent cardiac postoperative adhesion

Post-cardiac surgical sternal and epicardial adhesions increase the risk and complexity of cardiac re-operative surgeries, which represent a significant challenge for patients with the congenital cardiac disease. Bioresorbable membranes can serve as barriers to prevent postoperative adhesions. Herein, we fabricated a bioresorbable gelatin/polycaprolactone (GT/PCL) composite membrane via electrospinning. The membrane was characterized in terms of morphology, mechanical properties, and biocompatibility. We then evaluated its efficacy as a physical barrier to prevent cardiac operative adhesions in a rabbit model. Our results showed that the membrane had a nanofibrous structure and was sturdy enough to be handled for the surgical procedures. In vitro studies with rabbit cardiac fibroblasts demonstrated that the membrane was biocompatible and inhibited cell infiltration. Further application of the membrane in a rabbit cardiac adhesion model revealed that the membrane was resorbed gradually and effectively resisted the sternal and epicardial adhesions. Interestingly, six months after the operation, the GT/PCL membrane was completely resorbed with simultaneous ingrowth of host cells to form a natural barrier. Collectively, these results indicated that the GT/PCL membrane might be a suitable barrier to prevent sternal and epicardial adhesions and might be utilized as a novel pericardial substitute for cardiac surgery. STATEMENT OF SIGNIFICANCE: Electrospinning is a versatile method to prepare nanofibrous membranes for tissue engineering and regenerative medicine applications. However, with the micro-/nano-scale structure and high porosity, the electrospun membrane might be an excellent candidate as a barrier to prevent postoperative adhesion. Here we prepared an electropun GT/PCL nanofibrous membrane and applied it as a barrier to prevent sternal and epicardial adhesions. Our results showed that the membrane had sufficient mechanical strength, good biocompatibility, and effectively resisted the sternal and epicardial adhesions. What's more, the membrane was bioresorbable and allowed simultaneous ingrowth of host cells to form a natural barrier. We believe that the current will inspire more research on nanomaterials to prevent postoperative adhesion applications.

Influence of fish collagen on viscoelastic properties and sol-gel phase transition of chitosan solutions

The thermosensitive hydrogels are widely used in tissue engineering due to their non-invasive application. Special interest of researchers, due to the specific characteristics of both materials, is aimed at composites of natural origin obtained from chitosan hydrogels combined with collagen. The mechanical properties of the thermosensitive chitosan-fish collagen hydrogels and the sol-gel phase transition parameters were determined by the rotational rheometry measurement techniques. Based on comparison of the obtained storage modulus G' curves, it was found that the addition of collagen negatively affects the mechanical properties of composite scaffolds. The addition of this protein substance decreases their elasticity. Only the smallest concentration (0.25g collagen/1 g chitosan) of collagen improves the mechanical properties of composite hydrogels, from 56 kPa to 61 kPa. Conducted non-isothermal studies allowed to conclude that the addition of collagen causes an increasing temperature of sol-gel phase transition. However, the observed changes are not a monotone function of the biopolymer concentration.

Electrospinning of Chitosan-Based Solutions for Tissue Engineering and Regenerative Medicine

Electrospinning has been used for decades to generate nano-fibres via an electrically charged jet of polymer solution. This process is established on a spinning technique, using electrostatic forces to produce fine fibres from polymer solutions. Amongst, the electrospinning of available biopolymers (silk, cellulose, collagen, gelatine and hyaluronic acid), chitosan (CH) has shown a favourable outcome for tissue regeneration applications. The aim of the current review is to assess the current literature about electrospinning chitosan and its composite formulations for creating fibres in combination with other natural polymers to be employed in tissue engineering. In addition, various polymers blended with chitosan for electrospinning have been discussed in terms of their potential biomedical applications. The review shows that evidence exists in support of the favourable properties and biocompatibility of chitosan electrospun composite biomaterials for a range of applications. However, further research and in vivo studies are required to translate these materials from the laboratory to clinical applications.

Could essential oils enhance biopolymers performance for wound healing? A systematic review

BACKGROUND

Millions of people in the world suffer from chronic wounds of different etiologies such as diabetic foot and leg ulcers, without solutions nowadays. Molecules obtained from plants offer an alternative to aid wound healing. Strong evidence about essential oils (EO) anti-inflammatory and antimicrobial properties is thoroughly described in literature and their chemical compositions are well characterized. More recently, EO effects in experimental wounds have begun to be analyzed.

AIM

We aim to summarize the evidence of EO in experimental wounds, and the possibility of combining them with biopolymers commonly used in skin regeneration.

METHODS

Electronic databases such as ScienceDirect, PubMed and Scopus were used to search scientific contributions until March 2017, using relevant keywords. In a first step, literature focusing on EO and/or mono- or sesqui-terpenoids effects in rodent wounds was identified and summarized. In all cases, chemical structures and EO composition were detailed, as well as references to in vitro activities previously determined, e.g. antibacterial, antioxidant or anti-inflammatory. In a second step, scientific literature devoted to combine EO and biopolymers with the focus set on wound healing innovations, was collected and analyzed.

RESULTS

Treatments with EO from species of genders Lavandula, Croton, Blumea, Eucalyptus, Pinus, Cymbopogon, Eucalyptus, Cedrus, Abies, Rosmarinus, Origanum, Salvia and Plectranthus, have shown positive results in rodent wounds. All of these EO were mainly composed by monoterpenoids-thymol, 1,8-cineole, linalool-or monoterpenes, as limonene or pinenes. Experimental wounds in rodents have shown faster closure rate, better collagen deposition and/or enhanced fibroblasts proliferation. In blends with biopolymers, several EO combined with chitosan, alginate, gelatin or collagen, were processed to give active films or nanofibers, with antioxidant, anti-inflammatory or antimicrobial activities. Curiously, all of these works were carried out since 2010.

CONCLUSIONS

There is significant evidence about the effectivity of EO as wound healers. The incorporation of EO into a polymer matrix that contributes to wound healing is still incipient. However, scientific based evidence of the EO incorporation in resorbable polymeric scaffolds was found and analyzed herein. In summary, EO-biopolymer dressings or scaffolds have become promising artifacts regarding wound treatments, especially in chronic wounds, where treating infection and inflammation are still important issues.

Biocompatible Silk Noil-Based Three-Dimensional Carded-Needled Nonwoven Scaffolds Guide the Engineering of Novel Skin Connective Tissue

Retracting hypertrophic scars resulting from healed burn wounds heavily impact on the patients' life quality. Biomaterial scaffolds guiding burned-out skin regeneration could suppress or lessen scar retraction. Here we report a novel silk noil-based three-dimensional (3D) nonwoven scaffold produced by carding and needling with no formic acid exposure, which might improve burn healing. Once wetted, it displays human skin-like physical features and a high biocompatibility. Human keratinocyte-like cervical carcinoma C4-I cells seeded onto the carded-needled nonwovens in vitro quickly adhered to them, grew, and actively metabolized glutamine releasing lactate. As on plastic, they released no proinflammatory IL-1β, although secreting tumor necrosis factor-alpha, an inducer of the autocrine mitogen amphiregulin in such cells. Once grafted into interscapular subcutaneous tissue of mice, carded-needled nonwovens guided the afresh assembly of a connective tissue enveloping the fibroin microfibers and filling the interposed voids within 3 months. Fibroblasts and a few poly- or mononucleated macrophages populated the engineered tissue. Besides, its extracellular matrix contained thin sparse collagen fibrils and a newly formed vascular network whose endothelin-1-expressing endothelial cells grew first on the fibroin microfibrils and later expanded into the intervening matrix. Remarkably, no infiltrates of inflammatory leukocytes and no packed collagen fibers bundles among fibroin microfibers, no fibrous capsules at the grafts periphery, and hence no foreign body response was obtained at the end of 3 months of observation. Therefore, we posit that silk noil-based 3D carded-needled nonwoven scaffolds are tools for translational medicine studies as they could guide connective tissue regeneration at deep burn wounds averting scar retraction with good functional results.

Random lasing from structurally-modulated silk fibroin nanofibers

Structural arrangement and dimension play vital roles in wave transport and amplification as they can restrict the volume explored by the waves. However, it is challenging to systematically investigate the interplay among structural, optical, and mechanical properties, in part because of limited experimental platforms that modulate the structural arrangement in a continuous manner. We present light amplification action in Rhodamine B doped silk fibroin (SF) nanofibrous scaffolds and its modulation via the control of the alignment or directionality of SF nanofibers through an electrospinning procedure. Random lasing features of such scaffolds are examined as a function of structural arrangement of the SF nanofibers, and optical-structural-mechanical relationships of the SF-based structures are examined. As SF nanofibers are aligned parallel undergoing a transition from three to quasi-two dimension, light amplification features (e.g., lasing threshold and output power) enhanced, which also strongly correlated with mechanical characteristics (i.e., Young’s moduli) of the scaffolds. We confirm such optical characteristics using quasi-mode analyses based on the finite element method. We further demonstrate non-contact, in situ measurement of alternations in lasing features of the scaffolds while the specimens are under tensile loads. These results may highlight potential utility of the scaffolds as a flexible and biocompatible sensor.

Simulation of ECM with Silk and Chitosan Nanocomposite Materials

Extracellular matrix (ECM) is a system used to model the design of biomaterial matrices for tissue regeneration. Various biomaterial systems have been developed to mimic the composition or microstructure of the ECM. However, emulating multiple facets of the ECM in these systems remains a challenge. Here, a new strategy is reported which addresses this need by using silk fibroin and chitosan (CS) nanocomposite materials. Silk fibroin was first assembled into ECM-mimetic nanofibers in water and then blended with CS to introduce the nanostructural cues. Then the ratios of silk fibroin and CS were optimized to imitate the protein and glycosaminoglycan compositions. These biomaterial scaffolds had suitable compositions, hierarchical nano-to-micro structures, and appropriate mechanical properties to promote cell proliferation in vitro, and vascularization and tissue regeneration in vivo. Compared to previous silk-based scaffolds, these scaffolds achieved improvements in biocompatibility, suggesting promising applications in the future in tissue regeneration.

Non-immunogenic, porous and antibacterial chitosan and Antheraea mylitta silk sericin hydrogels as potential dermal substitute

Limitation of existing grafts including restricted donor site, risks of immune reactions, infectious diseases and high cost alarms the growing need of natural, cost effective and functional graft as the dermal substitute. We fabricate stable (>6 weeks) and porous (57.23-75.22μm) yet flexible (in variable pH) matrices using Antheraea mylitta sericin crosslinked with well known biocompatible polysaccharide chitosan by natural crosslinker (genipin) without using any harsh chemical. The fabricated matrices are characterized in terms of chemical modifications (Fourier transform infrared spectroscopy), crystallinity (X-ray diffraction), swelling, degradability and thermal stability. The hydrogels show good adhesion, migration, proliferation and viability of human dermal fibroblasts. The matrices cause no significant immune response of inflammatory cytokines (TNF-α and IL-1β) and hemolysis of human blood. These also retain their intrinsic antioxidant (196.1±17.7μM Fe (II)/mg) and antibacterial (8-15mm zone of inhibition) properties. These results indicate their potential as a cost effective and antibacterial dermal substitute.

Electrospinning of Cross-Linked Magnetic Chitosan Nanofibers for Protein Release

A poly(vinylalcohol) (PVA) electrospun/magnetic/chitosan nanocomposite fibrous cross-linked network was fabricated using in situ cross-linking electrospinning technique and used for bovine serum albumin (BSA) loading and release applications. Sodium tripolyphosphate (TPP) and glutaraldehyde (GA) were used as cross-linkers which modified magnetic-Fe3O4 chitosan as Fe3O4/CS/TPP and Fe3O4/CS/GA, respectively. BSA was used as a model protein drugs which was encapsulated to form Fe3O4/CS/TPP/BSA and Fe3O4/CS/GA/BSA nanoparticles. The composites were electrospun with PVA to form nanofibers. Nanofibers were characterized by field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The characterization results suggest that Fe3O4 nanoparticles with average size of 45 nm were successfully bound on the surface of chitosan. The cross-linked nanofibers were found to contain uniformly dispersed Fe3O4 nanoparticles. The size and morphology of the nanofibers network was controlled by varying the cross-linker type. FTIR data show that these two polymers have intermolecular interactions. The sample with TPP cross-linker showed an enhancement of the controlled release properties of BSA during 30-h experimental investigation. Graphical Abstract ᅟ.

Novel hydroxybutyl chitosan nanoparticles for siRNA delivery targeting tissue factor inhibits proliferation and induces apoptosis in human vascular smooth muscle cells

Chitosan, a polysaccharide isolated from shrimp and other crustacean shells, has been widely investigated for DNA and siRNA delivery. Despite substantial effort having been made to improve chitosan as a non-viral gene delivery vector, the application is severely limited by its poor solubility under physiological conditions. Hydroxybutyl chitosan (HBC), a modified chitosan, is soluble under neutral conditions. Tissue factor (TF) is involved in the pathogenesis of cardiovascular diseases by promoting thrombus formation and inducing the migration and proliferation of vascular smooth muscle cells. Targeting TF is an attractive therapeutic strategy for cardiovascular diseases. In the present study, the use of HBC for the transfer of TF-siRNAs into human umbilical vein smooth muscle cells (HUVSMCs) was investigated, and the effects of TF knockdown on cell proliferation and apoptosis were examined. HBC/siRNA nanoparticles were produced by mixing HBC and siRNA solutions with the assistance of tripolyphosphate buffer. The transfection efficiency with these nanoparticles was 74±2.5%, which was determined using a fluorescence-labeled siRNA under fluorescence microscopy. The delivery of HBC/TF-siRNA resulted in reductions in the production of cellular and soluble TF protein in HUVMSCs, which were measured using western blotting and enzyme-linked immunosorbent assay, respectively. TF knockdown led to inhibited cell proliferation, as assessed using a Cell Counting Kit-8 assay, and increased cell apoptosis, determined using Annexin V-fluorescein isothiocyanate staining. These findings suggested that HBC may be a promising vector for siRNA delivery, and that in vivo HBC/siRNA nanoparticle delivery targeting TF may be a potential option for the treatment of cardiovascular diseases, which warrants further investigation.

Characterization of Silk Fibroin/Chitosan 3D Porous Scaffold and In Vitro Cytology

Bone tissue engineering is a powerful tool to treat bone defects caused by trauma, infection, tumors and other factors. Both silk fibroin (SF) and chitosan (CS) are non-toxic and have good biocompatibility, but are poor biological scaffolds when used alone. In this study, the microscopic structure and related properties of SF/CS composite scaffolds with different component ratios were examined. The scaffold material most suitable for osteoblast growth was determined, and these results offer an experimental basis for the future reconstruction of bone defects. First, via freeze-drying and chemical crosslinking methods, SF/CS composites with different component ratios were prepared and their structure was characterized. Changes in the internal structure of the SF and CS mixture were observed, confirming that the mutual modification between the two components was complete and stable. The internal structure of the composite material was porous and three-dimensional with a porosity above 90%. We next studied the pore size, swelling ratio, water absorption ratio, degradation and in vitro cell proliferation. For the 40% SF-60% CS group, the pore size of the scaffold was suitable for the growth of osteoblasts, and the rate of degradation was steady. This favors the early adhesion, growth and proliferation of MG-63 cells. In addition to good biocompatibility and satisfactory cell affinity, this material promotes the secretion of extracellular matrix materials by osteoblasts. Thus, 40% SF-60% CS is a good material for bone tissue engineering.

Biohybrid Fibro-Porous Vascular Scaffolds: Effect of Crosslinking on Properties

Tubular grafts were fabricated from blends of polycaprolactone (PCL) and poly(glycolide -co-caprolactone) (PGC) polymers and coated with an extracellular matrix containing collagens, laminin, and proteoglycans, but not growth factors (HuBiogel™). Multifunctional scaffolds from polymer blends and membrane proteins provide the necessary biomechanics and biological functions for tissue regeneration. Two crosslinking agents, a natural crosslinker namely genipin (Gp) and a carbodiimide reagent namely 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), were used for further stabilizing the protein matrix and the effect of crosslinking was evaluated for structural, morphological, mechanical properties using SEM, DSC and DMA. SEM images and fiber diameter distribution showed fiber-size between 0.2 µm to 1 µm with the majority of fiber diameters being under 500 nm, indicating upper range of protein fiber-sizes (for example, collagen fibers in extracellular matrix are in 50 to 500 nm diameter range). HB coating did not affect the mechanical properties, but increased its hydrophilicity of the graft. Overall data showed that PCL/PGC blends with 3:1 mass ratio exhibited mechanical properties comparable to those of human native arteries (tensile strength of 1-2 MPa and Young's modulus of <10 MPa). Additionally, the effect of crosslinking on coating stability was investigated to assure the retention of proteins on scaffold for effective cell-matrix interactions.

Preparation and characterization of genipin-cross-linked silk fibroin/chitosan sustained-release microspheres

We report the effects of distinct concentrations of genipin and silk fibroin (SF):chitosan (CS) ratios on the formation of SF–CS composite microspheres. We selected microspheres featuring an SF:CS ratio of 1:1, encapsulated various concentrations of bovine serum albumin (BSA), and then compared their encapsulation efficiency and sustained-release rate with those of pure CS microspheres. We determined that the following five groups of microspheres were highly spherical and featured particle sizes ranging from 70 μm to 147 μm: mass ratio of CS:SF =1:0.5, 0.1 g or 0.5 g genipin; CS:SF =1:1, 0.05 g or 1 g genipin; and CS:SF =1:2, 0.5 g genipin. The microspheres prepared using 1:1 CS:SF ratio and 0.05 g genipin in the presence of 10 mg, 20 mg, and 50 mg of BSA exhibited encapsulation efficiencies of 50.16%±4.32%, 56.58%±3.58%, and 42.19%±7.47%, respectively. Fourier-transform infrared spectroscopy (FTIR) results showed that SF and CS were cross-linked and that the α-helices and random coils of SF were converted into β-sheets. BSA did not chemically react with CS or SF. Moreover, thermal gravimetric analysis (TGA) results showed that the melting point of BSA did not change, which confirmed the FTIR results, and X-ray diffraction results showed that BSA was entrapped in microspheres in a noncrystalline form, which further verified the TGA and FTIR data. The sustained-release microspheres prepared in the presence of 10 mg, 20 mg, and 50 mg of BSA burst release 30.79%±3.43%, 34.41%±4.46%, and 41.75%±0.96% of the entrapped BSA on the 1st day and cumulatively released 75.20%±2.52%, 79.16%±4.31%, and 89.04%±4.68% in 21 days, respectively. The pure CS microspheres prepared in the presence of 10 mg of BSA burst release 39.53%±1.76% of BSA on the 1st day and cumulatively released 83.57%±2.33% of the total encapsulated BSA in 21 days. The SF–CS composite microspheres exhibited higher sustained release than did the pure CS microspheres, and thus these composite microspheres might function as a superior drug carrier.

Fabrication of a novel blended membrane with chitosan and silk microfibers for wound healing: characterization, in vitro and in vivo studies

A novel type of chitosan/silk microfibers blended membrane was fabricated, which could significantly accelerate wound healing efficiency.