De novo engineering of reticular connective tissue in vivo by silk fibroin nonwoven materials

Silk Fibroin Materials: Biomedical Applications and Perspectives

The golden rule in tissue engineering is the creation of a synthetic device that simulates the native tissue, thus leading to the proper restoration of its anatomical and functional integrity, avoiding the limitations related to approaches based on autografts and allografts. The emergence of synthetic biocompatible materials has led to the production of innovative scaffolds that, if combined with cells and/or bioactive molecules, can improve tissue regeneration. In the last decade, silk fibroin (SF) has gained attention as a promising biomaterial in regenerative medicine due to its enhanced bio/cytocompatibility, chemical stability, and mechanical properties. Moreover, the possibility to produce advanced medical tools such as films, fibers, hydrogels, 3D porous scaffolds, non-woven scaffolds, particles or composite materials from a raw aqueous solution emphasizes the versatility of SF. Such devices are capable of meeting the most diverse tissue needs; hence, they represent an innovative clinical solution for the treatment of bone/cartilage, the cardiovascular system, neural, skin, and pancreatic tissue regeneration, as well as for many other biomedical applications. The present narrative review encompasses topics such as (i) the most interesting features of SF-based biomaterials, bare SF's biological nature and structural features, and comprehending the related chemo-physical properties and techniques used to produce the desired formulations of SF; (ii) the different applications of SF-based biomaterials and their related composite structures, discussing their biocompatibility and effectiveness in the medical field. Particularly, applications in regenerative medicine are also analyzed herein to highlight the different therapeutic strategies applied to various body sectors.

Super silkworm cocoons constructed by multi-silkworm larvae: Promising composites with dense structures and excellent mechanical properties

A normal silkworm cocoon (NSC) with a unique nonwoven structure is usually spun by a single silkworm larva. Notably, there is a special Bombyx mori genetic resource that many (three or more) mature larvae tend to collectively spin into one cocoon, which was named "multi-silkworm cocoon" ("MSC"). However, the MSCs display loose structure and poor mechanical properties which limits their further application. In this study, a series of hybrid silkworm cocoons (HMSCs) are obtained by hybridizing "MSC" with a selected commercial silkworm strain successfully. The morphology, microstructures, and mechanical properties of cocoons constructed by one to three silkworm larvae were characterized and compared. The results indicated that about 48.3 % of silkworm larvae could create double and triple cocoons in the F1 generation of the silkworm hybrid, displaying robust fiber networks and dense structures. The mechanical characteristics of the HMSCs, including the tensile, peeling, compression, and needle penetration resistance properties, exceeded those of MSCs, showing significant application potential for high-performance bio-composites. This study provides a practical approach for obtaining silkworm cocoons with controllable structures and mechanical properties to develop and fabricate natural composite and biomimetic materials.

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

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

A comprehensive review of silk-fibroin hydrogels for cell and drug delivery applications in tissue engineering and regenerative medicine

Hydrogel scaffolds hold great promise for developing novel treatment strategies in the field of regenerative medicine. Within this context, silk fibroin (SF) has proven to be a versatile material for a wide range of tissue engineering applications owing to its structural and functional properties. In the present review, we report on the design and fabrication of different forms of SF-based scaffolds for tissue regeneration applications, particularly for skin, bone, and neural tissues. In particular, SF hydrogels have emerged as delivery systems for a wide range of bio-actives. Given the growing interest in the field, this review has a primary focus on the fabrication, characterization, and properties of SF hydrogels. We also discuss their potential for the delivery of drugs, stem cells, genes, peptides, and growth factors, including future directions in the field of SF hydrogel scaffolds.

Human Keratinocytes and Fibroblasts Co-Cultured on Silk Fibroin Scaffolds Exosomally Overrelease Angiogenic and Growth Factors

Objectives: The optimal healing of skin wounds, deep burns, and chronic ulcers is an important clinical problem. Attempts to solve it have been driving the search for skin equivalents based on synthetic or natural polymers. Methods: Consistent with this endeavor, we used regenerated silk fibroin (SF) from Bombyx mori to produce a novel compound scaffold by welding a 3D carded/hydroentangled SF-microfiber-based nonwoven layer (C/H-3D-SFnw; to support dermis engineering) to an electrospun 2D SF nanofiber layer (ESFN; a basal lamina surrogate). Next, we assessed-via scanning electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, mono- and co-cultures of HaCaT keratinocytes and adult human dermal fibroblasts (HDFs), dsDNA assays, exosome isolation, double-antibody arrays, and angiogenesis assays-whether the C/H-3D-SFnws/ESFNs would allow the reconstitution of a functional human skin analog in vitro. Results: Physical analyses proved that the C/H-3D-SFnws/ESFNs met the requirements for human soft-tissue-like implants. dsDNA assays revealed that co-cultures of HaCaTs (on the 2D ESFN surface) and HDFs (inside the 3D C/H-3D-SFnws) grew more intensely than did the respective monocultures. Double-antibody arrays showed that the CD9⁺/CD81⁺ exosomes isolated from the 14-day pooled growth media of HDF and/or HaCaT mono- or co-cultures conveyed 35 distinct angiogenic/growth factors (AGFs). However, versus monocultures' exosomes, HaCaT/HDF co-cultures' exosomes (i) transported larger amounts of 15 AGFs, i.e., PIGF, ANGPT-1, bFGF, Tie-2, Angiogenin, VEGF-A, VEGF-D, TIMP-1/-2, GRO-α/-β/-γ, IL-1β, IL-6, IL-8, MMP-9, and MCP-1, and (ii) significantly more strongly stimulated human dermal microvascular endothelial cells to migrate and assemble tubes/nodes in vitro. Conclusions: Our results showed that both cell-cell and cell-SF interactions boosted the exosomal release of AGFs from HaCaTs/HDFs co-cultured on C/H-3D-SFnws/ESFNs. Hence, such exosomes are an asset for prospective clinical applications as they advance cell growth and neoangiogenesis and consequently graft take and skin healing. Moreover, this new integument analog could be instrumental in preclinical and translational studies on human skin pathophysiology and regeneration.

Preparation of silk fibroin/hyaluronic acid composite hydrogel based on thiol-ene click chemistry

OBJECTIVES

To design and prepare silk fibroin/hyaluronic acid composite hydrogel.

METHODS

The thiol modified silk fibroin and the double-bond modified hyaluronic acid were rapidly cured into gels through thiol-ene click polymerization under ultraviolet light condition. The grafting rate of modified silk fibroin and hyaluronic acid was characterized by 1H NMR spectroscopy; the gel point and the internal microstructure of hydrogels were characterized by rheological test and scanning electron microscopy; the mechanical properties were characterized by compression test; the swelling rate and degradation rate were determined by mass method. The hydrogel was co-cultured with the cells, the cytotoxicity was measured by the lactate dehydrogenase method, the cell adhesion was measured by the float count method, and the cell growth and differentiation on the surface of the gel were observed by scanning electron microscope and fluorescence microscope.

RESULTS

The functional group substitution degrees of modified silk fibroin and hyaluronic acid were 17.99% and 48.03%, respectively. The prepared silk fibroin/hyaluronic acid composite hydrogel had a gel point of 40-60 s and had a porous structure inside the gel. The compressive strength was as high as 450 kPa and it would not break after ten cycles. The water absorption capacity of the composite hydrogel was 4-10 times of its own weight. Degradation experiments showed that the hydrogel was biodegradable, and the degradation rate reached 28%-42% after 35 d. The cell biology experiments showed that the cytotoxicity of the composite gel was low, the cell adhesion was good, and the growth and differentiation of the cells on the surface of the gel were good.

CONCLUSIONS

The photocurable silk fibroin/hyaluronic acid composite hydrogel can form a gel quickly, and has excellent mechanical properties, adjustable swelling rate and degradation degree, good biocompatibility, so it has promising application prospects in biomedicine.

In-vivo evaluation of silk fibroin small-diameter vascular grafts: state of art of preclinical studies and animal models

Autologous vein and artery remains the first choice for vascular grafting procedures in small-diameter vessels such as coronary and lower limb districts. Unfortunately, these vessels are often found to be unsuitable in atherosclerotic patients due to the presence of calcifications or to insufficient size. Synthetic grafts composed of materials such as expanded polytetrafluoroethylene (ePTFE) are frequently employed as second choice, because of their widespread availability and success in the reconstruction of larger arteries. However, ePTFE grafts with small diameter are plagued by poor patency rates due to surface thrombogenicity and intimal hyperplasia, caused by the bioinertness of the synthetic material and aggravated by low flow conditions. Several bioresorbable and biodegradable polymers have been developed and tested to exploit such issues for their potential stimulation to endothelialization and cell infiltration. Among these, silk fibroin (SF) has shown promising pre-clinical results as material for small-diameter vascular grafts (SDVGs) because of its favorable mechanical and biological properties. A putative advantage in graft infection in comparison with synthetic materials is plausible, although it remains to be demonstrated. Our literature review will focus on the performance of SF-SDVGs in vivo, as evaluated by studies performing vascular anastomosis and interposition procedures, within small and large animal models and different arterial districts. Efficiency under conditions that more accurately mime the human body will provide encouraging evidence towards future clinical applications.

A comparative in vitro and in vivo study of porcine- and bovine-derived non-cross-linked collagen membranes

The porcine-derived non-cross-linked collagen membrane Bio-gide® (BG) and the bovine-derived non-cross-linked collagen membrane Heal-all® (HA) were compared to better understand their in vitro biophysical characteristics and in vivo degradation patterns as a reference for clinical applications. It was showed that the porosity, specific surface area, pore volume and pore diameter of BG were larger than those of HA (64.5 ± 5.2% vs. 48.6 ± 6.1%; 18.6 ± 2.8 m² /g vs. 2.3 ± 0.6 m² /g; 0.114 ± 0.002 cm³ /g vs. 0.003 ± 0.001 cm³ /g; 24.4 ± 3.5 nm vs. 7.3 ± 1.7 nm, respectively); the average swelling ratio of BG was higher than that of HA (412.6 ± 41.2% vs. 270.0 ± 2.7%); the tensile strength of both dry and wet HA was higher than those of BG (18.26 ± 3.27 MPa vs. 4.02 ± 1.35 MPa; 2.24 ± 0.21 MPa vs. 0.16 ± 0.02 MPa, respectively); 73% of HA remained after 72 h in collagenase solution, whereas only 8.2% of BG remained. A subcutaneous rat implantation model revealed that, at 3, 7, 14, 28, and 56 days postmembrane implantation, there were more total inflammatory cells, especially more M1 and M2 polarized macrophages and higher M2/M1 ratio in BG than in HA; in addition, the fibrous capsule around BG was also thicker than that around HA. Moreover, concentrations of dozens of cytokines including interleukin-2(IL-2), IL-7, IL-10 and so forth. in BG were higher than those in HA. It is suggested that BG and HA might be suitable for different clinical applications according to their different characteristics.

3D Printing Silk-Based Bioresorbable Piezoelectric Self-Adhesive Holey Structures for In Vivo Monitoring on Soft Tissues

Flexible and biocompatible adhesives with sensing capabilities can be integrated onto human body and organ surfaces, characterized by complex geometries, thus having the potential to sense their physiological stimuli offering monitoring and diagnosis of a wide spectrum of diseases. The challenges in this innovative field are the following: (i) the coupling method between the smart adhesive and the soft human substrates, (ii) the bioresorbable behavior of the material, and (iii) the electrical exchange with the substrate. Here, we introduce a multifunctional composite by mixing silk fibroin, featuring piezoelectric properties, with a soluble plant-derived polyphenol (i.e., chestnut tannin) modified with graphene nanoplatelets. This material behaves as a glue on different substrates and gives rise to high elongation at break, conformability, and adhesive performances to gastrointestinal tissues in a rat model and favors the printability via extrusion-based 3D printing. Exploiting these properties, we designed a bioresorbable 3D printed flexible and self-adhesive piezoelectric device that senses the motility once applied onto a phantom intestine and the hand gesture by signal translation. Experimental results also include the biocompatibility study using gastrointestinal cells. These findings could have applicability in animal model studies, and, thanks to the bioresorbable behavior of the materials, such an adhesive device could be used for monitoring the motility of the gastrointestinal tract and for the diagnosis of motility disorders.

Tissue Engineering for Tracheal Replacement: Strategies and Challenges

The critical feature in trachea replacement is to provide a hollow cylindrical framework that is laterally stable and longitudinally flexible, facilitating cartilage and epithelial tissue formation. Despite advanced techniques and sources of materials used, most inherent challenges are related to the complexity of its anatomy. Limited blood supply leads to insufficient regenerative capacity for cartilage and epithelium. Natural and synthetic scaffolds, different types of cells, and growth factors are part of tissue engineering approaches with varying outcomes. Pre-vascularization remains one of the crucial factors to expedite the regenerative process in tracheal reconstruction. This review discusses the challenges and strategies used in tracheal tissue engineering, focusing on scaffold implantation in clinical and preclinical studies conducted in recent decades.

Proteomic Analysis of Silk Fibroin Reveals Diverse Biological Function of Different Degumming Processing From Different Origin

Silk, as a kind of natural fibrin, has been prepared into various biomaterials due to its excellent biocompatibility and mechanicalness. However, there are some controversies on the biocompatibility of silk fibroin (SF), especially when it coexists with sericin. In this study, two kinds of silk from Jiangsu and Zhejiang were degummed with two concentrations of Na₂CO₃ solution, respectively, to obtain four kinds of silk fibroin. The effects of different degumming treatments on silk fibroin properties were analyzed by means of color reaction, apparent viscosity measurement, and transmission electron microscope and isobaric tags for relative and absolute quantification analyses, and the effects of different silk fibroin membranes on the growth of Schwann cells were evaluated. The results showed that the natural silk from Zhejiang treated with 0.05% Na₂CO₃ solution had a fuller structure, higher apparent viscosity, and better protein composition. While SF obtained by degumming with 0.5% Na₂CO₃ solution was more beneficial to cell adhesion and proliferation due to the thorough removal of sericin. This study may provide important theoretical and experimental bases for the selection of biomaterials for fabricating artificial nerve grafts.

Adult Human Vascular Smooth Muscle Cells on 3D Silk Fibroin Nonwovens Release Exosomes Enriched in Angiogenic and Growth-Promoting Factors

BACKGROUND

Our earlier works showed the quick vascularization of mouse skin grafted Bombyx mori 3D silk fibroin nonwoven scaffolds (3D-SFnws) and the release of exosomes enriched in angiogenic/growth factors (AGFs) from in vitro 3D-SFnws-stuck human dermal fibroblasts (HDFs). Here, we explored whether coronary artery adult human smooth muscle cells (AHSMCs) also release AGFs-enriched exosomes when cultured on 3D-SFnws in vitro.

METHODS

Media with exosome-depleted FBS served for AHSMCs and human endothelial cells (HECs) cultures on 3D-SFnws or polystyrene. Biochemical methods and double-antibody arrays assessed cell growth, metabolism, and intracellular TGF-β and NF-κB signalling pathways activation. AGFs conveyed by CD9+/CD81+ exosomes released from AHSMCs were double-antibody array analysed and their angiogenic power evaluated on HECs in vitro.

RESULTS

AHSMCs grew and consumed D-glucose more intensely and showed a stronger phosphorylation/activation of TAK-1, SMAD-1/-2/-4/-5, ATF-2, c-JUN, ATM, CREB, and an IκBα phosphorylation/inactivation on SFnws vs. polystyrene, consistent overall with a proliferative/secretory phenotype. SFnws-stuck AHSMCs also released exosomes richer in IL-1α/-2/-4/-6/-8; bFGF; GM-CSF; and GRO-α/-β/-γ, which strongly stimulated HECs' growth, migration, and tubes/nodes assembly in vitro.

CONCLUSIONS

Altogether, the intensified AGFs exosomal release from 3D-SFnws-attached AHSMCs and HDFs could advance grafts' colonization, vascularization, and take in vivo-noteworthy assets for prospective clinical applications.

In vitro modelling of the physiological and diseased female reproductive system

The maladies affecting the female reproductive tract (FRT) range from infections to endometriosis to carcinomas. In vitro models of the FRT play an increasingly important role in both basic and translational research, since the anatomy and physiology of the FRT of humans and other primates differ significantly from most of the commonly used animal models, including rodents. Using organoid culture to study the FRT has overcome the longstanding hurdle of maintaining epithelial phenotype in culture.  Both ECM-derived and engineered materials have proved critical for maintaining a physiological phenotype of FRT cells in vitro by providing the requisite 3D environment, ligands, and architecture. Advanced materials have also enabled the systematic study of factors contributing to the invasive metastatic processes. Meanwhile, microphysiological devices make it possible to incorporate physical signals such as flow and cyclic exposure to hormones. Going forward, advanced materials compatible with hormones and optimised to support FRT-derived cells' long-term growth, will play a key role in addressing the diverse array of FRT pathologies and lead to impactful new treatments that support the improvement of women's health. STATEMENT OF SIGNIFICANCE: The female reproductive system is a crucial component of the female anatomy. In addition to enabling reproduction, it has wide ranging influence on tissues throughout the body via endocrine signalling. This intrinsic role in regulating normal female biology makes it susceptible to a variety of female-specific diseases. However, the complexity and human-specific features of the reproductive system make it challenging to study. This has spurred the development of human-relevant in vitro models for helping to decipher the complex issues that can affect the reproductive system, including endometriosis, infection, and cancer. In this Review, we cover the current state of in vitro models for studying the female reproductive system, and the key role biomaterials play in enabling their development.

Stretchable, Bio-Compatible, Antioxidant and Self-Powering Adhesives from Soluble Silk Fibroin and Vegetal Polyphenols Exfoliated Graphite

The development of bio-glues is still a challenging task, regarding adhesion on wet surfaces; often, high performance and adaption to complex geometries need to be combined in one material. Here, we report biocompatible adhesives obtained by blending regenerated silk (RS) with a soluble plant-derived polyphenol (i.e., chestnut tannin) that was also used to exfoliate graphite to obtain graphene-based RS/tannin (G-RS/T) composites. The resultant G-RS/T hybrid material exhibited outstanding stretchability (i.e., 400%) and high shear strength (i.e., 180 kPa), superior to that of commercial bio-glues, and showed sealant properties for tissue approximation. Moreover, we showed how such nanocomposites exhibit electromechanical properties that could potentially be used for the realization of green and eco-friendly piezoelectric devices. Finally, we demonstrate the in vitro glue’s biocompatibility and anti-oxidant properties that enable their utilization in clinical applications.

Electrical Stimulation and Conductive Polymers as a Powerful Toolbox for Tailoring Cell Behaviour in vitro

Electrical stimulation (ES) is a well-known method for guiding the behaviour of nerve cells in in vitro systems based on the response of these cells to an electric field. From this perspective, understanding how the electrochemical stimulus can be tuned for the design of a desired cell response is of great importance. Most biomedical studies propose the application of an electrical potential to cell culture arrays while examining the cell response regarding viability, morphology, and gene expression. Conversely, various studies failed to evaluate how the fine physicochemical properties of the materials used for cell culture influence the observed behaviours. Among the various materials used for culturing cells under ES, conductive polymers (CPs) are widely used either in pristine form or in addition to other polymers. CPs themselves do not possess the optimal surface for cell compatibility because of their hydrophobic nature, which leads to poor protein adhesion and, hence, poor bioactivity. Therefore, understanding how to tailor the chemical properties on the material surface will determine the obtention of improved ES platforms. Moreover, the structure of the material, either in a thin film or in porous electrospun scaffolds, also affects the biochemical response and needs to be considered. In this review, we examine how materials based on CPs influence cell behaviour under ES, and we compile the various ES setups and physicochemical properties that affect cell behaviour. This review concerns the culture of various cell types, such as neurons, fibroblasts, osteoblasts, and Schwann cells, and it also covers studies on stem cells prone to ES. To understand the mechanistic behaviour of these devices, we also examine studies presenting a more detailed biomolecular level of interaction. This review aims to guide the design of future ES setups regarding the influence of material properties and electrochemical conditions on the behaviour of in vitro cell studies.

Identification and location of sericin in silkworm with anti-sericin antibodies

Sericin, as the main component of silkworm cocoon silk, surrounds and protects the silk fibroin. Sericin is a natural macromolecular protein complex encoded by the genes Ser1, Ser2, and Ser3. At present, there are no available antibodies against sericin that may be used to identify and locate it at the protein level, hindering the study of its secretion mechanism and materials application. Therefore, the development of effective antibodies against sericin is an urgent necessity. To address this problem, we prepared polyclonal antibodies against the Ser1, Ser2 and Ser3 proteins using synthesized peptides for the first time. The specificity of the antibodies was confirmed using dot blot, immunoblotting and mass spectrometry on the hybrid bands of the middle silk gland. The immunoblotting results of anti-sericin antibodies showed that sericin has different molecular weights in different regions of the middle silk gland and strains in the 5th instar. Through immunohistochemistry, anti-sericin antibodies revealed that sericin presented different distributions in the anterior part of the middle silk gland of 872 strain at the 7th day of 5th instar. In addition, the prepared antibodies not only detected intact sericin molecules, but also detected degraded sericin that was dissolved in five different solvents. In summary, this work prepared effective sericin antibodies for silk protein synthesis and secretion research and provides a possible molecular detection method for biological products containing silkworm sericin.

Exosomes of adult human fibroblasts cultured on 3D silk fibroin nonwovens intensely stimulate neoangiogenesis

Background

Bombyx mori silk fibroin is a biomacromolecule that allows the assembly of scaffolds for tissue engineering and regeneration purposes due to its cellular adhesiveness, high biocompatibility and low immunogenicity. Earlier work showed that two types of 3D silk fibroin nonwovens (3D-SFnws) implanted into mouse subcutaneous tissue were promptly vascularized via undefined molecular mechanisms. The present study used nontumorigenic adult human dermal fibroblasts (HDFs) adhering to a third type of 3D-SFnws to assess whether HDFs release exosomes whose contents promote neoangiogenesis.

Methods

Electron microscopy imaging and physical tests defined the features of the novel carded/hydroentangled 3D-SFnws. HDFs were cultured on 3D-SFnws and polystyrene plates in an exosome-depleted medium. DNA amounts and D-glucose consumption revealed the growth and metabolic activities of HDFs on 3D-SFnws. CD9-expressing total exosome fractions were from conditioned media of 3D-SFnws and 2D polystyrene plates HDF cultures. Angiogenic growth factors (AGFs) in equal amounts of the two groups of exosomal proteins were analysed via double-antibody arrays. A tube formation assay using human dermal microvascular endothelial cells (HDMVECs) was used to evaluate the exosomes’ angiogenic power.

Results

The novel features of the 3D-SFnws met the biomechanical requirements typical of human soft tissues. By experimental day 15, 3D-SFnws-adhering HDFs had increased 4.5-fold in numbers and metabolized 5.4-fold more D-glucose than at day 3 in vitro. Compared to polystyrene-stuck HDFs, exosomes from 3D-SFnws-adhering HDFs carried significantly higher amounts of AGFs, such as interleukin (IL)-1α, IL-4 and IL-8; angiopoietin-1 and angiopoietin-2; angiopoietin-1 receptor (or Tie-2); growth-regulated oncogene (GRO)-α, GRO-β and GRO-γ; matrix metalloproteinase-1; tissue inhibitor metalloproteinase-1; and urokinase-type plasminogen activator surface receptor, but lesser amounts of anti-angiogenic tissue inhibitor metalloproteinase-2 and pro-inflammatory monocyte chemoattractant protein-1. At concentrations from 0.62 to 10 μg/ml, the exosomes from 3D-SFnws-cultured HDFs proved their angiogenic power by inducing HDMVECs to form significant amounts of tubes in vitro.

Conclusions

The structural and mechanical properties of carded/hydroentangled 3D-SFnws proved their suitability for tissue engineering and regeneration applications. Consistent with our hypothesis, 3D-SFnws-adhering HDFs released exosomes carrying several AGFs that induced HDMVECs to promptly assemble vascular tubes in vitro. Hence, we posit that once implanted in vivo, the 3D-SFnws/HDFs interactions could promote the vascularization and repair of extended skin wounds due to burns or other noxious agents in human and veterinary clinical settings.

Biopolymer Matrices Based on Chitosan and Fibroin: A Review Focused on Methods for Studying Surface Properties

For the creation of tissue-engineered structures based on natural biopolymers with the necessary chemical, physical, adhesive, morphological, and regenerative properties, biocompatible materials based on polysaccharides and proteins are used. This work is devoted to a problem of the technology of polymeric materials for biomedical purposes: the creation of biopolymer tissue engineering matrix and the development of a methodology for studying morphology and functional properties of their surface to establish the prospects for using the material for contact with living objects. The conditions for the formation of scaffolds based on composite materials of chitosan and fibroin determine the structure of the material, the thickness and orientation of molecular layers, the surface morphology, and other parameters that affect cell adhesion and growth. The analysis of studies of the morphology and properties of the surface of biopolymer matrices obtained using different methods of molding from solutions of chitosan and fibroin is carried out.

Injectable Desferrioxamine-Laden Silk Nanofiber Hydrogels for Accelerating Diabetic Wound Healing

Dysangiogenesis and chronic inflammation are two critical reasons for diabetic foot ulcers. Desferrioxamine (DFO) was used clinically in the treatment of diabetic foot ulcers by repeated injections because of its capacity to induce vascularization. Biocompatible carriers that release DFO slowly and facilitate healing simultaneously are preferable options to accelerate the healing of diabetic wounds. Here, DFO-laden silk nanofiber hydrogels that provided a sustained release of DFO for more than 40 days were used to treat diabetic wounds. The DFO-laden hydrogels stimulated the healing of diabetic wounds. In vitro cell studies revealed that the DFO-laden hydrogels modulated the migration and gene expression of endothelial cells, and they also tuned the inflammation behavior of macrophages. These results were confirmed in an in vivo diabetic wound model. The DFO-laden hydrogels alleviated dysangiogenesis and chronic inflammation in the diabetic wounds, resulting in a more rapid wound healing and increased collagen deposition. Both in vitro and in vivo studies suggested potential clinical applications of these DFO-laden hydrogels in the treatment of diabetic ulcers.

Novel applications of platelet concentrates in tissue regeneration (Review)

Numerous studies have explored the suitability of biocompatible materials in regenerative medicine. Platelet concentrates are derived from centrifuged blood and are named according to their biological characteristics, such as platelet-rich plasma, platelet-rich fibrin and concentrated growth factor. Platelet concentrates have gained considerable attention in soft and hard tissue engineering. Indeed, multiple components of autologous platelet concentrates, such as growth factors, fibrin matrix and platelets, serve essential roles in wound healing. Current studies are focused on cutting-edge strategies to meet the requirements for tissue restoration by improving the properties of autologous platelet concentrates. In the present review, applications of platelet concentrates for tissue engineering are discussed, presenting a selection of recent advances and novel protocols. In addition, several aspects of these strategies, such as the advantages of lyophilized platelet concentrates and the combination of platelet concentrates with biomaterials, stem cells or drugs are discussed. The present review aims to summarize novel strategies using platelet concentrates to improve the outcomes of wound healing.

3D printing of biomedically relevant polymer materials and biocompatibility

ABSTRACT

Research on polymer materials for additive manufacturing technology in biomedical applications is as promising as it is numerous, but biocompatibility of printable materials still remains a big challenge. Changes occurring during the 3D-printing processes itself may have adverse effects on the compatibility of the completed print. This prospective will put emphasis on the different additives and processes that can have a direct impact on biocompatibility during and after 3D printing of polymer materials.

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.

In vitro assessment of the bioactivities of sericin protein extracted from a bacterial silk-like biopolymer

Sericin is one of the main components of silk proteins, which has numerous biomedical applications because of its antioxidant, anticancer and antimicrobial properties. We recently isolated and characterized a novel silk-like protein named BNES. It is of non-animal origin and is like a bacterial polymeric silk. Sericin is a very popular protein compound that is effective in treating cancerous tumors. The process of extracting it from natural silk produced by silkworms or spiders is both complex and expensive. From the published scientific literature, it has been shown that sericin has not been previously extracted from a bacterial source. In the present study, sericin was extracted from bacteria capable of producing a biopolymer named BNES whose chemical composition is like that of natural silk and its bio-therapeutic effects were evaluated for the first time. The antioxidant activity of BNES measured by DPPH and ABTS assays showed IC₅₀ values of 0.38 and 0.41 mg mL⁻¹, respectively. BNES displayed satisfactory cytotoxic effect against four cancer cell lines, including Huh-7, Caco-2, MCF-7 and A549 cells, with IC₅₀ values in the ranges of ca. 0.62 ± 0.17, 0.72 ± 0.27, 0.76 ± 0.36 and 0.83 ± 0.31 mg mL⁻¹, respectively, after 24 h of treatment and 0.51 ± 0.22, 0.49 ± 0.19, 0.41 ± 0.25 and 0.55 ± 0.38, respectively, after 48 h of treatment, without affecting normal cells (WI38 cells). The antitumor activity of BNES was established to be an apoptosis-dependent mechanism determined via cellular morphology alterations, cell cycle arrest in the sub-G1 phase and nuclear staining with highly fluorescent fragments. The antimicrobial effects of BNES were examined with yeast and Gram-negative and Gram-positive bacteria. The results confirmed its antimicrobial activity against all tested organisms at concentrations of up to 1.33 mg mL⁻¹. The competitive advantage of the bacterial sericin BNES over sericin extracted from spider or silkworm sources is that it can be produced in very large quantities through large-scale bio-fermenters, which reduces the expected cost of production, in addition to having sustainable bacterial production source.

Sericin is one of the main components of silk proteins, which has numerous biomedical applications because of its antioxidant, anticancer and antimicrobial properties.

Chemical Synthesis of Silk-Mimetic Polymers

Silk is a naturally occurring high-performance material that can surpass man-made polymers in toughness and strength. The remarkable mechanical properties of silk result from the primary sequence of silk fibroin, which bears semblance to a linear segmented copolymer with alternating rigid ("crystalline") and flexible ("amorphous") blocks. Silk-mimetic polymers are therefore of great emerging interest, as they can potentially exhibit the advantageous features of natural silk while possessing synthetic flexibility as well as non-natural compositions. This review describes the relationships between primary sequence and material properties in natural silk fibroin and furthermore discusses chemical approaches towards the synthesis of silk-mimetic polymers. In particular, step-growth polymerization, controlled radical polymerization, and copolymerization with naturally derived silk fibroin are presented as strategies for synthesizing silk-mimetic polymers with varying molecular weights and degrees of sequence control. Strategies for improving macromolecular solubility during polymerization are also highlighted. Lastly, the relationships between synthetic approach, supramolecular structure, and bulk material properties are explored in this review, with the aim of providing an informative perspective on the challenges facing chemical synthesis of silk-mimetic polymers with desirable properties.

Three-Layered Silk Fibroin Tubular Scaffold for the Repair and Regeneration of Small Caliber Blood Vessels: From Design to in vivo Pilot Tests

Silk fibroin (SF) is an eligible biomaterial for the development of small caliber vascular grafts for substitution, repair, and regeneration of blood vessels. This study presents the properties of a newly designed multi-layered SF tubular scaffold for vascular grafting (SilkGraf). The wall architecture consists of two electrospun layers (inner and outer) and an intermediate textile layer. The latter was designed to confer high mechanical performance and resistance on the device, while electrospun layers allow enhancing its biomimicry properties and host's tissues integration. In vitro cell interaction studies performed with adult Human Coronary Artery Endothelial Cells (HCAECs), Human Aortic Smooth Muscle Cells (HASMCs), and Human Aortic Adventitial Fibroblasts (HAAFs) demonstrated that the electrospun layers favor cell adhesion, survival, and growth. Once cultured in vitro on the SF scaffold the three cell types showed an active metabolism (consumption of glucose and glutamine, release of lactate), and proliferation for up to 20 days. HAAF cells grown on SF showed a significantly lower synthesis of type I procollagen than on polystyrene, meaning a lower fibrotic effect of the SF substrate. The cytokine and chemokine expression patterns were investigated to evaluate the cells' proliferative and pro-inflammatory attitude. Interestingly, no significant amounts of truly pro-inflammatory cytokines were secreted by any of the three cell types which exhibited a clearly proliferative profile. Good hemocompatibility was observed by complement activation, hemolysis, and hematology assays. Finally, the results of an in vivo preliminary pilot trial on minipig and sheep to assess the functional behavior of implanted SF-based vascular graft identified the sheep as the more apt animal model for next medium-to-long term preclinical trials.

Laminin-Coated Electrospun Regenerated Silk Fibroin Mats Promote Neural Progenitor Cell Proliferation, Differentiation, and Survival in vitro

Neural progenitor cell (NPC) transplantation is a promising technique for central nervous system (CNS) reconstruction and regeneration. Biomaterial scaffolds, frameworks, and platforms can support NPC proliferation and differentiation in vitro as well as serve as a temporary extracellular matrix after transplantation. However, further applications of biomaterials require improved biological attributes. Silk fibroin (SF), which is produced by Bombyx mori, is a widely used and studied protein polymer for biomaterial application. Here, we prepared aligned and random eletrospun regenerated SF (RSF) scaffolds, and evaluated their impact on the growth of NPCs. First, we isolated NPCs and then cultured them on either laminin-coated RSF mats or conventional laminin-coated coverslips for cell assays. We found that aligned and random RSF led to increases in NPC proliferation of 143.8 ± 13.3% and 156.3 ± 14.7%, respectively, compared to controls. Next, we investigated neuron differentiation and found that the aligned and the random RSF led to increases in increase in neuron differentiation of about 93.2 ± 6.4%, and 3167.1 ± 4.8%, respectively, compared to controls. Furthermore, we measured the survival of NPCs and found that RSF promoted NPC survival, and found there was no difference among those three groups. Finally, signaling pathways in cells cultured on RSF mats were studied for their contributions in neural cell differentiation. Our results indicate that RSF mats provide a functional microenvironment and represent a useful scaffold for the development of new strategies in neural engineering research.

SilkBridge™: a novel biomimetic and biocompatible silk-based nerve conduit

Silk fibroin (Bombyx mori) was used to manufacture a nerve conduit (SilkBridge™) characterized by a novel 3D architecture. The wall of the conduit consists of two electrospun layers (inner and outer) and one textile layer (middle), perfectly integrated at the structural and functional level. The manufacturing technology conferred high compression strength on the device, thus meeting clinical requirements for physiological and pathological compressive stresses. In vitro cell interaction studies were performed through direct contact assays with SilkBridge™ using the glial RT4-D6P2T cells, a schwannoma cell line, and a mouse motor neuron NSC-34 cell line. The results revealed that the material is capable of sustaining cell proliferation, that the glial RT4-D6P2T cells increased their density and organized themselves in a glial-like morphology, and that NSC-34 motor neurons exhibited a greater neuritic length with respect to the control substrate. In vivo pilot assays were performed on adult female Wistar rats. A 10 mm long gap in the median nerve was repaired with 12 mm SilkBridge™. At two weeks post-operation several cell types colonized the lumen. Cells and blood vessels were also visible between the different layers of the conduit wall. Moreover, the presence of regenerated myelinated fibers with a thin myelin sheath at the proximal level was observed. Taken together, all these results demonstrated that SilkBridge™ has an optimized balance of biomechanical and biological properties, being able to sustain a perfect cellular colonization of the conduit and the progressive growth of the regenerating nerve fibers.

Proteins in Ionic Liquids: Reactions, Applications, and Futures

Biopolymer processing and handling is greatly facilitated by the use of ionic liquids, given the increased solubility, and in some cases, structural stability imparted to these molecules. Focussing on proteins, we highlight here not just the key drivers behind protein-ionic liquid interactions that facilitate these functionalities, but address relevant current and potential applications of protein-ionic liquid interactions, including areas of future interest.

A Review of Curcumin and Its Derivatives as Anticancer Agents

Cancer is the second leading cause of death in the world and one of the major public health problems. Despite the great advances in cancer therapy, the incidence and mortality rates of cancer remain high. Therefore, the quest for more efficient and less toxic cancer treatment strategies is still at the forefront of current research. Curcumin, the active ingredient of the Curcuma longa plant, has received great attention over the past two decades as an antioxidant, anti-inflammatory, and anticancer agent. In this review, a summary of the medicinal chemistry and pharmacology of curcumin and its derivatives in regard to anticancer activity, their main mechanisms of action, and cellular targets has been provided based on the literature data from the experimental and clinical evaluation of curcumin in cancer cell lines, animal models, and human subjects. In addition, the recent advances in the drug delivery systems for curcumin delivery to cancer cells have been highlighted.

Magnetic-silk/polyethyleneimine core-shell nanoparticles for targeted gene delivery into human breast cancer cells

The lack of efficient and cost-effective methods for gene delivery has significantly hindered the applications of gene therapy. In this paper, a simple one step and cost effective salting-out method has been explored to fabricate silk-PEI nanoparticles (SPPs) and magnetic-silk/PEI core-shell nanoparticles (MSPPs) for targeted delivery of c-myc antisense oligodeoxynucleotides (ODNs) into MDA-MB-231 breast cancer cells. The size and zeta potential of the particles were controlled by adjusting the amount of silk fibroin in particle synthesis. Lower surface charges and reduced cytotoxicity were achieved for MSPPs compared with PEI coated magnetic nanoparticles (MPPs). Both SPPs and MSPPs were capable of delivering the ODNs into MDA-MB-231 cells and significantly inhibited the cell growth. Through magnetofection, high ODN uptake efficiencies (over 70%) were achieved within 20 min using MSPPs as carriers, exhibiting a significantly enhanced uptake effect compared to the same carriers via non-magnetofection. Both SPPs and MSPPs exhibited a significantly higher inhibition effect against MDA-MB-231 breast cancer cells compared to human dermal fibroblast (HDF) cells. Targeted ODN delivery was achieved using MSPPs with the help of a magnet, making them promising candidates for targeted gene therapy applications.

Universal nanothin silk coatings via controlled spidroin self-assembly

Robust, biocompatible, and facile coatings are promising for improving the in vivo performance of medical implants and devices. Here, we demonstrate the formation of nanothin silk coatings by leveraging the biomimetic self-assembly of eADF4(C16), an amphiphilic recombinant protein based on the Araneus diadematus dragline spidroin ADF4. These coatings result from concurrent adsorption and supramolecular assembly of eADF4(C16) induced by KH2PO4, thereby providing a mild one-pot coating strategy in which the coating rate can be controlled by protein and KH2PO4 concentration. The thickness of the coatings ranges from 2-30 nm depending on the time immersed in the aqueous coating solution. Coatings can be formed on hydrophobic and hydrophilic substrates regardless of surface chemistry and without requiring specialized surface activation. Moreover, coatings appear to be stable through vigorous rinsing and prolonged agitation in water. Grazing incidence wide angle X-ray scattering, single-molecule force spectroscopy, and Congo red staining techniques confirm the formation of β-sheet nanocrystals within the eADF4(C16) coating, which contributes to the cohesive and adhesive stability of the material. Coatings are exceptionally smooth in the dry state and are hydrophilic regardless of substrate hydrophobicity. Under aqueous conditions, nanothin silk coatings exhibit the properties of a hydrogel material.

Preparation of natural amphoteric silk nanofibers by acid hydrolysis

Direct extraction of silk nanofibers (SNs) from natural silk fibers was developed via a low-intensity ultrasonic-assisted sulfuric acid hydrolysis process.

Additive manufacturing of hierarchical injectable scaffolds for tissue engineering

We present a 3D-printing technology allowing free-form fabrication of centimetre-scale injectable structures for minimally invasive delivery. They result from the combination of 3D printing onto a cryogenic substrate and optimisation of carboxymethylcellulose-based cryogel inks. The resulting highly porous and elastic cryogels are biocompatible, and allow for protection of cell viability during compression for injection. Implanted into the murine subcutaneous space, they are colonized with a loose fibrovascular tissue with minimal signs of inflammation and remain encapsulation-free at three months. Finally, we vary local pore size through control of the substrate temperature during cryogenic printing. This enables control over local cell seeding density in vitro and over vascularization density in cell-free scaffolds in vivo. In sum, we address the need for 3D-bioprinting of large, yet injectable and highly biocompatible scaffolds and show modulation of the local response through control over local pore size.

STATEMENT OF SIGNIFICANCE

This work combines the power of 3D additive manufacturing with clinically advantageous minimally invasive delivery. We obtain porous, highly compressible and mechanically rugged structures by optimizing a cryogenic 3D printing process. Only a basic commercial 3D printer and elementary control over reaction rate and freezing are required. The porous hydrogels obtained are capable of withstanding delivery through capillaries up to 50 times smaller than their largest linear dimension, an as yet unprecedented compression ratio. Cells seeded onto the hydrogels are protected during compression. The hydrogel structures further exhibit excellent biocompatibility 3 months after subcutaneous injection into mice. We finally demonstrate that local modulation of pore size grants control over vascularization density in vivo. This provides proof-of-principle that meaningful biological information can be encoded during the 3D printing process, deploying its effect after minimally invasive implantation.

Repair of urethral defects by an adipose mesenchymal stem cell‑porous silk fibroin material

The aim of the present study was to determine whether it was possible to repair urethral defects with a material of adipose mesenchymal stem cells (ADMSCs)-porous silk fibroin (SF). A total of 39 male New Zealand white rabbits were randomly divided into a control group, an SF group and a bromodeoxyuridine (BrdU)-labeled ADMSCs-SF group (SSF group; n=13/group). Defects were made by resecting the posterior urethral wall. The defects in the SF and SSF groups were repaired using SF and BrdU-labeled ADMSCs-SF materials respectively. Then the anterior wall was sutured, and the urethral catheter was retained for 3 weeks following surgery. The catheter was rinsed with nitrofurazone once a day. The cells with positive expressions of factor VIII related antigen (FVIII-RAg), α-smooth muscle actin (α-SMA) and pan-cytokeratin (AE1/AE3) were detected by immunohistochemical assay, and the distributions of BrdU positive cells and macrophages were observed. Urethrography was performed prior to and following surgery. All rabbits had normal urethral morphologies prior to surgery. The incidence rates of postoperative complications in the control, SF and SSF groups were 76.92 (7/13), 23.07 (3/13) and 15.38% (2/13), respectively (P<0.05). The number of positive macrophages in the SSF group was significantly lower than that of the SF group 4 weeks following surgery (P<0.05). In the SSF group, BrdU positive cells were scattered within the SF material following surgery, primarily at the intersection between the SF material and the urethra. The number of FVIII-RAg positive cells in the SSF and SF groups were significantly different (P<0.05), which were also significantly higher than that of control group (P<0.01). The number of α-SMA positive cells in the SSF and SF groups were significantly different (P<0.05), and these values also significantly exceeded those exhibited by the control group (P<0.01). In addition, the SSF and SF groups had positive staining of AE1/AE3. Similar to normal urethral mucosa, the cytoplasm was stained brownish yellow (P<0.05). It is thus feasible to repair urethral defects using ADMSCs-SF material.

Precisely printable and biocompatible silk fibroin bioink for digital light processing 3D printing

Although three-dimensional (3D) bioprinting technology has gained much attention in the field of tissue engineering, there are still several significant engineering challenges to overcome, including lack of bioink with biocompatibility and printability. Here, we show a bioink created from silk fibroin (SF) for digital light processing (DLP) 3D bioprinting in tissue engineering applications. The SF-based bioink (Sil-MA) was produced by a methacrylation process using glycidyl methacrylate (GMA) during the fabrication of SF solution. The mechanical and rheological properties of Sil-MA hydrogel proved to be outstanding in experimental testing and can be modulated by varying the Sil-MA contents. This Sil-MA bioink allowed us to build highly complex organ structures, including the heart, vessel, brain, trachea and ear with excellent structural stability and reliable biocompatibility. Sil-MA bioink is well-suited for use in DLP printing process and could be applied to tissue and organ engineering depending on the specific biological requirements.

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.

Silk-Derived Protein Enhances Corneal Epithelial Migration, Adhesion, and Proliferation

Purpose

The corneal surface is vulnerable to a myriad of traumatic insults including mechanical, chemical, and thermal injuries. The resulting trauma may render the naturally occurring regenerative properties of the cornea incapable of restoring a healthy epithelial surface, and may result in the loss of corneal transparency and vision. Healing of the corneal epithelium requires a complex cascade of biological processes that work to restore the tissue after injury. New therapeutic agents that act on the multiple steps of the corneal wound-healing process would offer a potential for improving patient outcomes. Here, a novel silk fibroin–derived protein (SDP) was studied for potential impacts on wound healing through studying an in vitro model.

Methods

Solubilized SDP, produced from the Bombyx mori silkworm cocoon, was added to human corneal limbal-epithelial (hCLE) cultures to evaluate the material's effects on epithelial cell migration, proliferation, and adhesion through the use of various scratch wound assays and flow chamber studies.

Results

Results indicated that the addition of SDP to culture increased hCLE migration rate by over 50%, and produced an approximate 60% increase in cell proliferation. This resulted in a nearly 30% enhancement of in vitro scratch wound closure time. In addition, cultures treated with SDP experienced increased cell-matrix focal adhesion formation by over 95% when compared to controls.

Conclusions

The addition of SDP to culture media significantly enhanced hCLE cell sheet migration, proliferation, and attachment when compared to untreated controls, and indicates SDP's potential utility as an ophthalmic therapeutic agent.

Magnetic-Silk Core-Shell Nanoparticles as Potential Carriers for Targeted Delivery of Curcumin into Human Breast Cancer Cells

Curcumin is a promising anticancer drug but its applications in cancer therapy are limited due to its poor solubility, short half-life, and low bioavailability. In this article, we present a curcumin loaded magnetic silk fibroin core-shell nanoparticle system for sustained release of curcumin into breast cancer cells. Curcumin loaded magnetic silk fibroin core-shell nanoparticles were fabricated by a simple salting-out method using sodium phosphate with magnetic nanoparticles. The size, zeta potential, encapsulation/loading efficiency, and curcumin release rate were controlled and optimized by regulating silk fibroin concentration, pH value of the phosphate solution, and curcumin usage. Curcumin loaded magnetic silk fibroin core-shell nanoparticles showed enhanced cytotoxicity and higher cellular uptake in the human Caucasian breast adenocarcinoma cell line (MDA-MB-231cells) evidenced by MTT and cellular uptake assays. In addition, silk fibroin nanoparticles and magnetic silk fibroin nanoparticles without curcumin loaded were used as controls. The particles prepared using sodium phosphate showed significantly smaller diameter (90-350 nm) compared with those prepared using potassium phosphate, which possess a diameter range of 500-1200 nm. These smaller particles are superior for biomedical applications since such a size range is particularly desired for cell internalization. In addition, the magnetic cores inside the particles provide the possibility of using an external magnet for cancer targeting.

Self-Crosslinking of Silk Fibroin Using H2O2-Horseradish Peroxidase System and the Characteristics of the Resulting Fibroin Membranes

Silk fibroin has been widely used in biomedical and clinical fields owing to its good biocompatibility. In the present work, self-crosslinking of fibroin molecules was carried out using the hydrogen peroxide (H₂O₂)-horseradish peroxidase system, followed by preparation of the fibroin membranes, aiming at improving the mechanical property of fibroin-based material and expanding its applications. P-Hydroxyphenylacetamide (PHAD), as the model compound of tyrosine residues in fibroins, was used to investigate the possibility of horseradish peroxidase (HRP)-catalyzed crosslinking. The results were characterized by means of 1H NMR and UPLC-TQD. The efficacy of enzymatic crosslinking of silk fibroins was examined by determining the changes in the relative viscosity, amino acid compositions, and SEC chromatogram. The obtained data indicated that H₂O₂-HRP incubation led to PHAD polymerization, and the molecular weight of fibroin proteins was also noticeably increased after the enzymatic treatment. CD and ATR-FTIR spectra revealed that H₂O₂-HRP treatments had an evident impact on the conformational structure of silk fibroins. The mechanical property and thermal behavior for the modified fibroin membrane were noticeably improved compared to the untreated. Meanwhile, the obtained membrane exhibited good biocompatibility according to the cell growth experiment. The present work provides a novel method for preparation of the fibroin-based materials for biomedical applications.