Silk Fibroin as a Functional Biomaterial for Drug and Gene Delivery

Current status and prospects of gelatin and its derivatives in oncological applications: Review

Treating cancer remains challenging due to the substantial side effects and unfavourable pharmacokinetic characteristics of antineoplastic medications, despite the progress made in comprehending the properties and actions of tumour cells in recent years. The advancement of biomaterials, such as stents, implants, personalised drug delivery systems, tailored grafts, cell sheets, and other transplantable materials, has brought about a significant transformation in healthcare and medicine in recent years. Gelatin is a very adaptable natural polymer that finds extensive application in healthcare-related industries owing to its favourable characteristics, including biocompatibility, biodegradability, affordability, and the presence of accessible chemical groups. Gelatin is used as a biomaterial in the biomedical sector for the creation of drug delivery systems (DDSs) since it may be applied to various synthetic procedures. Gelatin nanoparticles (NPs) have been extensively employed as carriers for drugs and genes, specifically targeting diseased tissues such as cancer, tuberculosis, and HIV infection, as well as treating vasospasm and restenosis. This is mostly due to their biocompatibility and ability to degrade naturally. Gelatins possess a diverse array of potential applications that require more elucidation. This review focuses on the use of gelatin and its derivatives in the diagnosis and treatment of cancer. The advancement of biomaterials and bioreactors, coupled with the increasing understanding of emerging applications for biomaterials, has enabled progress in enhancing the efficacy of tumour treatment.

Curcumin-shellac nanoparticle-loaded GelMA/SilMA hydrogel for colorectal cancer therapy

In this study, a novel approach was employed to develop a therapeutic system for colorectal cancer treatment. Specifically, a GelMA/SilMA hydrogel loaded with curcumin-shellac nanoparticles (Cur@Lac NPs) was created. A microfluidic swirl mixer was utilized to formulate stable Cur@Lac NPs, ensuring their consistent and effective encapsulation. The pH-specific release of curcumin from the NPs demonstrated their potential for colon cancer treatment. By carefully regulating the ratio of GelMA (gelatin methacrylate) and SilMA (silk fibroin methacrylate), a GelMA/SilMA dual network hydrogel was generated, offering controlled release and degradation capabilities. The incorporation of SilMA notably enhanced the mechanical properties of the dual network matrix, improving compression resistance and mitigating deformation. This mechanical improvement is crucial for maintaining the structural integrity of the hydrogel during in vivo applications. In comparison to the direct incubation of curcumin, the strategy of encapsulating curcumin into NPs and embedding them within the GelMA/SilMA hydrogel resulted in more controlled release mechanisms. This controlled release was achieved through the disintegration of the NPs and the swelling and degradation of the hydrogel matrix. The encapsulating strategy also demonstrated enhanced cellular uptake of curcumin, leveraging the advantages of both NPs and in-situ hydrogel injection. This combination ensures a more efficient and sustained delivery of the therapeutic agent directly to the tumor site. Overall, this approach holds significant promise as a smart drug delivery system, potentially improving the efficacy of colorectal cancer treatments by providing targeted, controlled, and sustained drug release with enhanced mechanical stability and biocompatibility.

Dry and wet wrinkling of a silk fibroin biopolymer by a shape-memory material with insight into mechanical effects on secondary structures in the silk network

Surface wrinkling provides an approach to modify the surfaces of biomedical devices to better mimic features of the extracellular matrix and guide cell attachment, proliferation, and differentiation. Biopolymer wrinkling on active materials holds promise but is poorly explored. Here we report a mechanically actuated assembly process to generate uniaxial micro-and nanosized silk fibroin (SF) wrinkles on a thermo-responsive shape-memory polymer (SMP) substrate, with wrinkling demonstrated under both dry and hydrated (cell compatible) conditions. By systematically investigating the influence of SMP programmed strain magnitude, film thickness, and aqueous media on wrinkle stability and morphology, we reveal how to control the wrinkle sizes on the micron and sub-micron length scale. Furthermore, as a parameter fundamental to SMPs, we demonstrate that the temperature during the recovery process can also affect the wrinkle characteristics and the secondary structures in the silk network. We find that with increasing SMP programmed strain magnitude, silk wrinkled topographies with increasing wavelengths and amplitudes are achieved. Furthermore, silk wrinkling is found to increase β-sheet content, with spectroscopic analysis suggesting that the effect may be due primarily to tensile (e.g., Poisson effect and high-curvature wrinkle) loading modes in the SF, despite the compressive bulk deformation (uniaxial contraction) used to produce wrinkles. Silk wrinkles fabricated from sufficiently thick films (roughly 250 nm) persist after 24 h in cell culture medium. Using a fibroblast cell line, analysis of cellular response to the wrinkled topographies reveals high viability and attachment. These findings demonstrate use of wrinkled SF films under physiologically relevant conditions and suggest the potential for biopolymer wrinkles on biomaterials surfaces to find application in cell mechanobiology, wound healing, and tissue engineering.

Spider minor ampullate silk protein nanoparticles: an effective protein delivery system capable of enhancing systemic immune responses

Spider silk proteins (spidroins) are particularly attractive due to their excellent biocompatibility. Spider can produce up to seven different types of spidroins, each with unique properties and functions. Spider minor ampullate silk protein (MiSp) might be particularly interesting for biomedical applications, as the constituent silk is mechanically strong and does not super-contract in water, attributed to its amino acid composition. In this study, we evaluate the potential of recombinant nanoparticles derived from Araneus ventricosus MiSp as a protein delivery carrier. The MiSp-based nanoparticles were able to serve as an effective delivery system, achieving nearly 100% efficiency in loading the model protein lysozyme, and displayed a sustained release profile at physiological pH. These nanoparticles could significantly improve the delivery efficacy of the model proteins through different administration routes. Furthermore, nanoparticles loaded with model protein antigen lysozyme after subcutaneous or intramuscular administration could enhance antigen-specific immune responses in mouse models, through a mechanism involving antigen-depot effects at the injection site, long-term antigen persistence, and efficient uptake by dendritic cells as well as internalization by lymph nodes. These findings highlight the transnational potential of MiSp-based nanoparticle system for protein drug and vaccine delivery.

Precisely Printable Silk Fibroin/Carboxymethyl Cellulose/Alginate Bioink for 3D Printing

Three-dimensional (3D) bioprinting opens up many possibilities for tissue engineering, thanks to its ability to create a three-dimensional environment for cells like an extracellular matrix. However, the use of natural polymers such as silk fibroin in 3D bioprinting faces obstacles such as having a limited printability due to the low viscosity of such solutions. This study addresses these gaps by developing highly viscous, stable, and biocompatible silk fibroin-based inks. The addition of 2% carboxymethyl cellulose sodium and 1% sodium alginate to an aqueous solution containing 2.5 to 5% silk fibroin significantly improves the printability, stability, and mechanical properties of the printed scaffolds. It has been demonstrated that the more silk fibroin there is in bioinks, the higher their printability. To stabilize silk fibroin scaffolds in an aqueous environment, the printed structures must be treated with methanol or ethanol, ensuring the transition from the silk fibroin's amorphous phase to beta sheets. The developed bioinks that are based on silk fibroin, alginate, and carboxymethyl cellulose demonstrate an ease of printing and a high printing quality, and have a sufficiently good biocompatibility with respect to mesenchymal stromal cells. The printed scaffolds have satisfactory mechanical characteristics. The resulting 3D-printing bioink composition can be used to create tissue-like structures.

Piezoelectric dressings for advanced wound healing

The treatment of chronic refractory wounds poses significant challenges and threats to both human society and the economy. Existing research studies demonstrate that electrical stimulation fosters cell proliferation and migration and promotes the production of cytokines that expedites the wound healing process. Presently, clinical settings utilize electrical stimulation devices for wound treatment, but these devices often present issues such as limited portability and the necessity for frequent recharging. A cutting-edge wound dressing employing the piezoelectric effect could transform mechanical energy into electrical energy, thereby providing continuous electrical stimulation and accelerating wound healing, effectively addressing these concerns. This review primarily reviews the selection of piezoelectric materials and their application in wound dressing design, offering a succinct overview of these materials and their underlying mechanisms. This study also provides a perspective on the current limitations of piezoelectric wound dressings and the future development of multifunctional dressings harnessing the piezoelectric effect.

Therapeutic Potential Evaluation of Silk Sericin Stabilized Fisetin to Ulcerative Colitis

Ulcerative colitis is a chronic inflammatory bowel disease with a high recurrence rate. Natural phytochemical compounds are increasingly being considered as preventative and supportive treatments for this condition. However, the poor water solubility and stability of many of these compounds limit their effectiveness in vivo. To address this issue, fisetin (FT), a natural phytochemical with poor solubility, is stabilized using silk sericin (SS) to create a composite (SS/FT). The therapeutic potential of the SS/FT on ulcerative colitis is extensively investigated, and the results showed that it effectively alleviated the body weight loss and colon length shortening induced by dextran sulfate sodium. Notably, SS/FT downregulated the immune response, decreased colonic histopathological lesions, and reduced the cGAS/STING signal activation. This suggests that SS/FT may offer a promising therapy for treating ulcerative colitis.

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

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

Silk Bioprotein as a Novel Surgical-Site Wound Dressing: A Prospective, Randomized, Single-Blinded, Superiority Clinical Trial

Background

Medical adhesive-related skin injuries (MARSIs) affect about 1.5 million patients annually in the United States. Complications include allergic contact dermatitis, skin blistering, skin tears, and surgical-site infections (SSIs). The authors hypothesize that a natural hypoallergenic silk bioprotein wound dressing will decrease the incidence of MARSI in comparison to a synthetic alternative.

Objectives

This study aimed to assess the efficacy and safety of a silk bioprotein wound dressing compared to the Dermabond Prineo (Ethicon, Inc., Somerville, NJ) skin closure system.

Methods

This prospective, randomized, single-blinded trial studied 25 patients who were dressed with Dermabond Prineo on one side of their body and on the contralateral side with the silk bioprotein dressing after undergoing abdominoplasty or reduction mammaplasty procedures. Data were collected over 5 postoperative visits using photographs and an investigator administered questionnaire to track rash, itch, discomfort, erythema, edema, SSIs, need for pharmaceutical intervention, mechanical injury, removal time, and bathing routines.

Results

Sixty-four percent (16/25) of patients characterized the severity of discomfort as a score of 4 out of 10 or greater on the Dermabond Prineo control side and only 4% (1/25) for the silk-dressing side (P < .001). Fifty-two percent (13/25) had a visible rash of 4 or higher on the Dermabond Prineo side of their incision and 0% (0/25) had a rash on the silk side (P < .001). Fifty-two percent (13/25) required steroids or antibiotics to treat MARSI to Dermabond Prineo and 0% (0/25) required pharmaceutical intervention on the silk side (P < .001).

Conclusions

The use of a silk bioprotein wound dressing significantly reduces the incidence of MARSI throughout the postoperative period.

Level of Evidence 2

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.

A Convergent fabrication of silk fibroin nanoparticles on quercetin loaded metal-organic frameworks for promising nanocarrier of myocardial infraction

The biomacromolecule silk fibroin (SF) may be constructed to promote biomimetic nucleation and nanostructures of inorganic nanomaterials, offering it a promising candidate for use in various biomimetic applications. We combined SF-NPs and ZIF-8-NPs to fabricate new drug vehicles that effectively release the drug. SF nanoparticles (SF-NPs) were assembled into quercetin (QCT), a myocardial drug added to fabricate QSF-NPs. By acting as a template for the ZIF-8 nucleation onto the surface, the QSF-NPs fabricated core-shell-structured nanocomposites (named QSF@Z-NCs) with ZIF-8 as the core-shell and the QSF-NPs. The biocompatibility analysis using the MTT assay revealed that the developed QCT, SF-NPs, and QSF@Z-NCs are not harmful to cardiac myoblast (H9C2) cells. The in vivo model demonstrated that H9C2 cells encouraged cardiomyocyte fibre regeneration in myocardial infarction rats. We fabricated a brand-new technique using H9C2 cells and QSF@Z-NCs that might encourage the healing processes in myocardial ischemia cells. This study's results demonstrate that it successfully treats myocardial injury.

Evaluation and Application of Silk Fibroin Based Biomaterials to Promote Cartilage Regeneration in Osteoarthritis Therapy

Osteoarthritis (OA) is a common joint disease characterized by cartilage damage and degeneration. Traditional treatments such as NSAIDs and joint replacement surgery only relieve pain and do not achieve complete cartilage regeneration. Silk fibroin (SF) biomaterials are novel materials that have been widely studied and applied to cartilage regeneration. By mimicking the fibrous structure and biological activity of collagen, SF biomaterials can promote the proliferation and differentiation of chondrocytes and contribute to the formation of new cartilage tissue. In addition, SF biomaterials have good biocompatibility and biodegradability and can be gradually absorbed and metabolized by the human body. Studies in recent years have shown that SF biomaterials have great potential in treating OA and show good clinical efficacy. Therefore, SF biomaterials are expected to be an effective treatment option for promoting cartilage regeneration and repair in patients with OA. This article provides an overview of the biological characteristics of SF, its role in bone and cartilage injuries, and its prospects in clinical applications to provide new perspectives and references for the field of bone and cartilage repair.

Hydrogel-Forming Microneedles with Applications in Oral Diseases Management

Controlled drug delivery in the oral cavity poses challenges such as bacterial contamination, saliva dilution, and inactivation by salivary enzymes upon ingestion. Microneedles offer a location-specific, minimally invasive, and retentive approach. Hydrogel-forming microneedles (HFMs) have emerged for dental diagnostics and therapeutics. HFMs penetrate the stratum corneum, undergo swelling upon contact, secure attachment, and enable sustained transdermal or transmucosal drug delivery. Commonly employed polymers such as polyvinyl alcohol (PVA) and polyvinyl pyrrolidone are crosslinked with tartaric acid or its derivatives while incorporating therapeutic agents. Microneedle patches provide suture-free and painless drug delivery to keratinized or non-keratinized mucosa, facilitating site-specific treatment and patient compliance. This review comprehensively discusses HFMs' applications in dentistry such as local anesthesia, oral ulcer management, periodontal treatment, etc., encompassing animal experiments, clinical trials, and their fundamental impact and limitations, for example, restricted drug carrying capacity and, until now, a low number of dental clinical trial reports. The review explores the advantages and future perspectives of HFMs for oral drug delivery.

Therapeutic Agent-Loaded Fibrous Scaffolds for Biomedical Applications

Tissue engineering is a sophisticated field that involves the integration of various disciplines, such as clinical medicine, material science, and life science, to repair or regenerate damaged tissues and organs. To achieve the successful regeneration of damaged or diseased tissues, it is necessary to fabricate biomimetic scaffolds that provide structural support to the surrounding cells and tissues. Fibrous scaffolds loaded with therapeutic agents have shown considerable potential in tissue engineering. In this comprehensive review, we examine various methods for fabricating bioactive molecule-loaded fibrous scaffolds, including preparation methods for fibrous scaffolds and drug-loading techniques. Additionally, we delved into the recent biomedical applications of these scaffolds, such as tissue regeneration, inhibition of tumor recurrence, and immunomodulation. The aim of this review is to discuss the latest research trends in fibrous scaffold manufacturing methods, materials, drug-loading methods with parameter information, and therapeutic applications with the goal of contributing to the development of new technologies or improvements to existing ones.

Silk fibroin carriers with sustained release capacity for treating neurological diseases

Neurological diseases such as traumatic brain injury, cerebral ischemia, Parkinson's, and Alzheimer's disease usually occur in the central and peripheral nervous system and result in nervous dysfunction, such as cognitive impairment and motor dysfunction. Long-term clinical intervention is necessary for neurological diseases where neural stem cell transplantation has made substantial progress. However, many risks remain for cell therapy, such as puncture bleeding, postoperative infection, low transplantation success rate, and tumor formation. Sustained drug delivery, which aims to maintain the desired steady-state drug concentrations in plasma or local injection sites, is considered as a feasible option to help overcome side effects and improve the therapeutic efficiency of drugs on neurological diseases. Natural polymers such as silk fibroin have excellent biocompatibility, which can be prepared for various end-use material formats, such as microsphere, gel, coating/film, scaffold/conduit, microneedle, and enables the dynamic release of loaded drugs to achieve a desired therapeutic response. Sustained-release drug delivery systems are based on the mechanism of diffusion and degradation by altering the structures of silk fibroin and drugs, factors, and cells, which can induce nerve recovery and restore the function of the nervous system in a slow and persistent manner. Based on these desirable properties of silk fibroin as a carrier with sustained-release capacity, this paper discusses the role of various forms of silk fibroin-based drug delivery materials in treating neurological diseases in recent years.

Microfluidic Formulation of Curcumin-Loaded Multiresponsive Gelatin Nanoparticles for Anticancer Therapy

Current anticancer research shows that a combination of multiple treatment methods can greatly improve the killing of tumor cells. Using the latest microfluidic swirl mixer technology, combined with chemotherapy and photothermal-ablation therapy, we developed multiresponsive targeted antitumor nanoparticles (NPs) made of folate-functionalized gelatin NPs under 200 nm in size and with encapsulated CuS NPs, Fe₃O₄ NPs, and curcumin (Cur). By exploring gelatin's structure, adjusting its concentration and pH, and fine-tuning the fluid dynamics in the microfluidic device, the best preparation conditions were obtained for gelatin NPs with an average particle size of 90 ± 7 nm. The comparative targeting of the drug delivery system (DDS) was demonstrated on lung adenocarcinoma A549 cells (low level of folate receptors) and breast adenocarcinoma MCF-7 cells (high level of folate receptors). Folic acid helps achieve targeting and accurate delivery of NPs to the MCF-7 tumor cells. The synergistic photothermal ablation and curcumin's anticancer activity are achieved through infrared light irradiation (980 nm), while Fe₃O₄ is guided with an external magnetic field to target gelatin NPs and accelerate the uptake of drugs, thus efficiently killing tumor cells. The method described in this work is simple, easy to repeat, and has great potential to be scaled up for industrial production and subsequent clinical use.

Pharmaceutical characterization of probucol bile acid-lithocholic acid nanoparticles to prevent chronic hearing related and similar cellular oxidative stress pathologies

Background: Sensorineural hearing loss has been associated with oxidative stress. However, an antioxidant that passes effectively through the ear remains elusive. Method: Probucol (PB)-based nanoparticles were formed using a spray-drying encapsulation technique, characterized and tested in vitro. Results: Uniform, spherical nanoparticles were produced. The addition of lithocholic acid to PB formulations did not affect drug content or production yield, but it did modify capsule size, surface tension, electrokinetic stability and drug release. Cell viability, bioenergetics and inflammatory profiles were improved when auditory cells were exposed to PB-based nanoparticles, which showed antioxidant properties (p < 0.05). Conclusion: PB-based nanoparticles can potentially protect the auditory cell line from oxidative stress and could be used in future in vivo studies as a potential new therapeutic agent for sensorineural hearing loss.

Skin mucus metabolomics provides insights into the interplay between diet and wound in gilthead seabream (Sparus aurata)

The molecular processes underlying skin wound healing in several fish species have been elucidated in the last years, however, metabolomic insights are scarce. Here we report the skin mucus metabolome of wounded and non-wounded gilthead seabream (Sparus aurata) fed with silk fibroin microparticles, a functional additive considered to accelerate the wound healing process. The three experimental diets (commercial diet enriched with 0 mg (control), 50 mg or 100 mg of silk fibroin microparticles Kg^-1) were administered for 30 days and thereafter, a skin wound was inflicted. Skin mucus was collected on day 30 of feeding and 7 days post-wounding and subjected to metabolomic analysis by Ultra Performance Liquid Chromatography coupled with a high-resolution quadrupole-orbitrap mass spectrometry. The most enriched metabolite class was amino acids and derivatives, followed by nucleotides, nucleosides and analogues and carbohydrates and their derivatives. Metabolomic profiles revealed that the diet had a more profound effect than wounding in skin mucus. Metabolic pathway analysis of significantly affected metabolites revealed perturbations in the aminoacyl t-RNA biosynthesis in the skin. In particular, skin wound resulted in a decreased methionine level in mucus. Further, silk fibroin supplementation increased methionine level in skin mucus, which correlated with several wound morphometric parameters that characterized the epithelial healing capacity in seabream. The results provided new insight into the physiological consequences of skin wounds and how these processes could be influenced by dietary manipulation.

A Sustainable Solution to Skin Diseases: Ecofriendly Transdermal Patches

Skin is the largest epithelial surface of the human body, with a surface area of 2 m2 for the average adult human. Being an external organ, it is susceptible to more than 3000 potential skin diseases, including injury, inflammation, microbial and viral infections, and skin cancer. Due to its nature, it offers a large accessible site for administrating several medications against these diseases. The dermal and transdermal delivery of such medications are often ensured by utilizing dermal/transdermal patches or microneedles made of biocompatible and biodegradable materials. These tools provide controlled delivery of drugs to the site of action in a rapid and therapeutically effective manner with enhanced diffusivity and minimal side effects. Regrettably, they are usually fabricated using synthetic materials with possible harmful environmental effects. Manufacturing such tools using green synthesis routes and raw materials is hence essential for both ecological and economic sustainability. In this review, natural materials including chitosan/chitin, alginate, keratin, gelatin, cellulose, hyaluronic acid, pectin, and collagen utilized in designing ecofriendly patches will be explored. Their implementation in wound healing, skin cancer, inflammations, and infections will be discussed, and the significance of these studies will be evaluated with future perspectives.

Injectable anti-cancer drug loaded silk-based hydrogel for the prevention of cancer recurrence and post-lumpectomy tissue regeneration aiding triple-negative breast cancer therapy

A single system capable of delivering anticancer drugs and growth factors by a minimally invasive approach is in demand for effective treatment of triple-negative breast cancer (TNBC) after lumpectomy. Here, we showcase one such holistic system for TNBC therapy and its assessment via 3D in vitro lumpectomy model, a first of its kind. Firstly, Bombyx mori silk fibroin (BMSF) and Antheraea assamensis silk fibroin (AASF) blended hydrogels were prepared and biophysically characterized. Secondly, a 3D in vitro lumpectomy model was developed using MDA-MB-231 cell line to assess the efficacy of localized delivery of doxorubicin (dox) using injectable hydrogel system in terminating remaining breast cancer after lumpectomy. Additionally, we have also evaluated the adipose tissue regeneration in the lumpectomy region by delivering dexamethasone (dex) using injectable hydrogels. Rheological studies showed that the BMSF/AASF blended hydrogels exhibit viscoelasticity and injectability conducive for minimally invasive application. The developed hydrogels by virtue of its slow and sustained release of dox exerted cytotoxicity towards MDA-MB-231 cells assessed through in vitro studies. Further, dex loaded hydrogel supported adipogenic differentiation of adipose tissue derived stem cells (ADSCs), while the secreted factors were found to aid in vascularization and macrophage polarization. This was confirmed through in vitro angiogenic tube formation assay and macrophage polarization study respectively. The corroborated results vouch for potential application of this injectable hydrogels for localized anticancer drug delivery and aiding in breast reconstruction, post lumpectomy.

Characteristic Evaluation of Recombinant MiSp/Poly(lactic-co-glycolic) Acid (PLGA) Nanofiber Scaffolds as Potential Scaffolds for Bone Tissue Engineering

Biomaterial-based nanofibrous scaffolds are the most effective alternative to bone transplantation therapy. Here, two recombinant minor ampullate spidroins (spider silk proteins), R1SR2 and NR1SR2C, were blended with Poly(lactic-co-glycolic) Acid (PLGA), respectively, to generate nanofiber scaffolds by electrospinning. The N-terminal (N), C-terminal (C), repeating (R1 and R2) and spacer (S) modules were all derived from the minor ampullate spidroins (MiSp). The physical properties and structures of the blended scaffolds were measured by scanning electron microscopy (SEM), water contact angle measurement, Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), and Tensile mechanical testing. The results showed that blending of MiSp (R1SR2 and NR1SR2C) reduced the diameter of nanofibers, increased the porosity and glass transition temperatures of nanofibrous scaffolds, and effectively improved the hydrophilicity and ultimate strain of scaffolds. It is worth noting that the above changes were more significant in the presence of the N- and C-termini of MiSp. In cell culture assays, human bone mesenchymal stem cells (HBMSCs) grown on NR1SR2C/PLGA (20/80) scaffolds displayed markedly enhanced proliferative and adhesive abilities compared with counterparts grown on pure PLGA scaffolds. Jointly, these findings indicated recombinant MiSp/PLGA, particularly NR1SR2C/PLGA (20/80) blend nanofibrous scaffolds, is promising for bone tissue engineering.

Recent Developments of Silk-Based Scaffolds for Tissue Engineering and Regenerative Medicine Applications: A Special Focus on the Advancement of 3D Printing

Regenerative medicine has received potential attention around the globe, with improving cell performances, one of the necessary ideas for the advancements of regenerative medicine. It is crucial to enhance cell performances in the physiological system for drug release studies because the variation in cell environments between in vitro and in vivo develops a loop in drug estimation. On the other hand, tissue engineering is a potential path to integrate cells with scaffold biomaterials and produce growth factors to regenerate organs. Scaffold biomaterials are a prototype for tissue production and perform vital functions in tissue engineering. Silk fibroin is a natural fibrous polymer with significant usage in regenerative medicine because of the growing interest in leftovers for silk biomaterials in tissue engineering. Among various natural biopolymer-based biomaterials, silk fibroin-based biomaterials have attracted significant attention due to their outstanding mechanical properties, biocompatibility, hemocompatibility, and biodegradability for regenerative medicine and scaffold applications. This review article focused on highlighting the recent advancements of 3D printing in silk fibroin scaffold technologies for regenerative medicine and tissue engineering.

Silk Fibroin as an Efficient Biomaterial for Drug Delivery, Gene Therapy, and Wound Healing

Silk fibroin (SF), an organic material obtained from the cocoons of a silkworm Bombyx mori, is used in several applications and has a proven track record in biomedicine owing to its superior compatibility with the human body, superb mechanical characteristics, and its controllable propensity to decay. Due to its robust biocompatibility, less immunogenic, non-toxic, non-carcinogenic, and biodegradable properties, it has been widely used in biological and biomedical fields, including wound healing. The key strategies for building diverse SF-based drug delivery systems are discussed in this review, as well as the most recent ways for developing functionalized SF for controlled or redirected medicines, gene therapy, and wound healing. Understanding the features of SF and the various ways to manipulate its physicochemical and mechanical properties enables the development of more effective drug delivery devices. Drugs are encapsulated in SF-based drug delivery systems to extend their shelf life and control their release, allowing them to travel further across the bloodstream and thus extend their range of operation. Furthermore, due to their tunable properties, SF-based drug delivery systems open up new possibilities for drug delivery, gene therapy, and wound healing.

A Structural Analysis of Proteinaceous Nanotube Cavities and Their Applications in Nanotechnology

Protein nanotubes offer unique properties to the materials science field that allow them to fulfill various functions in drug delivery, biosensors and energy storage. Protein nanotubes are chemically diverse, modular, biodegradable and nontoxic. Furthermore, although the initial design or repurposing of such nanotubes is highly complex, the field has matured to understand underlying chemical and physical properties to a point where applications are successfully being developed. An important feature of a nanotube is its ability to bind ligands via its internal cavities. As ligands of interest vary in size, shape and chemical properties, cavities have to be able to accommodate very specific features. As such, understanding cavities on a structural level is essential for their effective application. The objective of this review is to present the chemical and physical diversity of protein nanotube cavities and highlight their potential applications in materials science, specifically in biotechnology.

Baicalein-loaded silk fibroin peptide nanofibers protect against cisplatin-induced acute kidney injury: fabrication, characterization and mechanism

Silk fibroin (SF) is a natural polymeric biomaterial widely used in the preparation of drug delivery systems. Herein, silk fibroin peptide (SFP) was self-assembled into nanofibers, encapsulated a poorly water-soluble drug baicalein (SFP/BA NFs), and then used to protect against cisplatin-induced acute kidney injury (AKI). Specifically, the SFP/BA NFs significantly enhanced the aqueous dispersity, storage stability, and in vitro antioxidant activity of BA. SFP/BA NFs increased the drug uptake and localization to mitochondria. In vitro results demonstrated that SFP/BA NFs can relieve the cisplatin-induced HK-2 cell damage, and inhibit the cisplatin-induced accumulation of reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) disruption. Mechanism studies demonstrated that SFP/BA NFs may exert nephroprotective effects by inhibiting both the cisplatin-induced DNA damage and the cGAS/STING pathway activation. In vivo results showed that cisplatin treatment resulted in decreased body weight, increased serum creatinine (SCr), and increased blood urea nitrogen (BUN) levels, while SFP/BA NFs reversed the above symptoms. Furthermore, SFP/BA NFs reversed the cisplatin-induced abnormal changes of antioxidant enzymes (e.g., SOD and GSH), and inhibited the cisplatin-induced DNA damage as well as the activation of cGAS/TING. Above all, our results revealed the potential of SFP/BA NFs to protect against cisplatin-induced AKI.

Electrospun Biomimetic Nanofibrous Scaffolds: A Promising Prospect for Bone Tissue Engineering and Regenerative Medicine

Skeletal-related disorders such as arthritis, bone cancer, osteosarcoma, and osteoarthritis are among the most common reasons for mortality in humans at present. Nanostructured scaffolds have been discovered to be more efficient for bone regeneration than macro/micro-sized scaffolds because they sufficiently permit cell adhesion, proliferation, and chemical transformation. Nanofibrous scaffolds mimicking artificial extracellular matrices provide a natural environment for tissue regeneration owing to their large surface area, high porosity, and appreciable drug loading capacity. Here, we review recent progress and possible future prospective electrospun nanofibrous scaffolds for bone tissue engineering. Electrospun nanofibrous scaffolds have demonstrated promising potential in bone tissue regeneration using a variety of nanomaterials. This review focused on the crucial role of electrospun nanofibrous scaffolds in biological applications, including drug/growth factor delivery to bone tissue regeneration. Natural and synthetic polymeric nanofibrous scaffolds are extensively inspected to regenerate bone tissue. We focused mainly on the significant impact of nanofibrous composite scaffolds on cell adhesion and function, and different composites of organic/inorganic nanoparticles with nanofiber scaffolds. This analysis provides an overview of nanofibrous scaffold-based bone regeneration strategies; however, the same concepts can be applied to other organ and tissue regeneration tactics.

Peptide-functionalised magnetic silk nanoparticles produced by a swirl mixer for enhanced anticancer activity of ASC-J9

Silk fibroin is an FDA approved biopolymer for clinical applications with great potential in nanomedicine. However, silk-based nanoformulations are still facing several challenges in processing and drug delivery efficiency (such as reproducibility and targetability), especially in cancer therapy. To address these challenges, robust and controllable production methods are required for generating nanocarriers with desired properties. This study aimed to develop a novel method for the production of peptide-functionalized magnetic silk nanoparticles with higher selectivity for cancer cells for targeted delivery of the hydrophobic anticancer agent ASC-J9. A new microfluidic device with a swirl mixer was designed to fabricate magnetic silk nanoparticles (MSNP) with desired size and narrow size distribution. The surface of MSNPs was functionalized with a cationic amphiphilic anticancer peptide, G(IIKK)₃I-NH₂ (G3), to enhance their selectivity towards cancer cells. The G3-MSNPs increased the cellular uptake and anticancer activity of G3 in HCT 116 colorectal cancer cells compared to free G3. Moreover, the G3-MSNPs exhibited considerably higher cellular uptake and cytotoxicity in HCT 116 colorectal cancer cells compared to normal cells (HDFs). Encapsulating ASC-J9 in G3-MSNPs resulted in augmented anticancer activity compared to free ASC-J9 and non-functionalized ASC-J9 loaded MSNPs within its biological half-life. Hence, functionalizing MSNPs with G3 enabled targeted delivery of ASC-J9 to cancer cells and enhanced its anticancer effect. Functionalization of nanoparticles with anticancer peptides could be regarded as a new strategy for targeted delivery and enhanced efficiency of anticancer drugs. Furthermore, the microfluidic device introduced in this paper offers a robust and reproducible method for fabrication of small sized homogenous nanoparticles.

Silk Fibroin Hydrogel Reinforced With Magnetic Nanoparticles as an Intelligent Drug Delivery System for Sustained Drug Release

Due to the well-known biocompatibility, tunable biodegradability, and mechanical properties, silk fibroin hydrogel is an exciting material for localized drug delivery systems to decrease the therapy cost, decrease the negative side effects, and increase the efficiency of chemotherapy. However, the lack of remote stimuli response and active drug release behavior has yet to be analyzed comparatively. In this study, we developed magnetic silk fibroin (SF) hydrogel samples through the facile blending method, loaded with doxorubicin hydrochloride (DOX) and incorporated with different concentrations of iron oxide nanoparticles (IONPs), to investigate the presumable ability of controlled and sustained drug release under the various external magnetic field (EMF). The morphology and rheological properties of SF hydrogel and magnetic SF hydrogel were compared through FESEM images and rheometer analysis. Here, we demonstrated that adding magnetic nanoparticles (MNPs) into SFH decreased the complex viscosity and provided a denser porosity with a bigger pore size matrix structure, which allowed the drug to be released faster in the absence of an EMF. Release kinetic studies show that magnetic SF hydrogel could achieve controlled release of DOX in the presence of an EMF. Furthermore, the drug release from magnetic SF hydrogel decreased in the presence of a static magnetic field (SMF) and an alternating magnetic field (AMF), and the release rate decreased even more with the higher MNPs concentration and magnetic field strength. Subsequently, Wilms’ tumor and human fibroblast cells were cultured with almost the same concentration of DOX released in different periods, and cell viability was investigated using MTT assay. MTT results indicated that the Wilms’ tumor cells were more resistant to DOX than the human fibroblasts, and the IC50 values were calculated at 1.82 ± 0.001 and 2.73 ± 0.004 (μg/ml) for human fibroblasts and Wilms’ tumor cells, respectively. Wilms’ tumor cells showed drug resistance in a higher DOX concentration, indicating the importance of controlled drug delivery. These findings suggest that the developed magnetic SFH loaded with DOX holds excellent potential for intelligent drug delivery systems with noninvasive injection and remotely controlled abilities.

Silk Fibroin as a Bioink - A Thematic Review of Functionalization Strategies for Bioprinting Applications

Bioprinting is an emerging tissue engineering technique that has attracted the attention of researchers around the world, for its ability to create tissue constructs that recapitulate physiological function. While the technique has been receiving hype, there are still limitations to the use of bioprinting in practical applications, much of which is due to inappropriate bioink design that is unable to recapitulate complex tissue architecture. Silk fibroin (SF) is an exciting and promising bioink candidate that has been increasingly popular in bioprinting applications because of its processability, biodegradability, and biocompatibility properties. However, due to its lack of optimum gelation properties, functionalization strategies need to be employed so that SF can be effectively used in bioprinting applications. These functionalization strategies are processing methods which allow SF to be compatible with specific bioprinting techniques. Previous literature reviews of SF as a bioink mainly focus on discussing different methods to functionalize SF as a bioink, while a comprehensive review on categorizing SF functional methods according to their potential applications is missing. This paper seeks to discuss and compartmentalize the different strategies used to functionalize SF for bioprinting and categorize the strategies for each bioprinting method (namely, inkjet, extrusion, and light-based bioprinting). By compartmentalizing the various strategies for each printing method, the paper illustrates how each strategy is better suited for a target tissue application. The paper will also discuss applications of SF bioinks in regenerating various tissue types and the challenges and future trends that SF can take in its role as a bioink material.

Fluorescent Hybrid Material Based on Natural Spider Silk and Carbon Dots for Bioapplication

Since the outcome of an operation largely depends on the quality of wound healing, it is one of the most challenging stages in surgery. Today, wound closure is mostly undertaken by means of a surgical suture. Good surgical sutures are biocompatible and biodegradable and possess excellent mechanical properties. Preferably, these sutures demonstrate optical activity for bacteria detection as there is a risk of surgical site infections. In this study, a solution, which fulfills all the requirements for manufacturing a multifunctional hybrid material, is proposed. In this work, a method for the in situ modification of spider silk with fluorescent carbon dots has been developed. The basic concept is the use of silk fibers as both the main framework for tissue regeneration and a carbon source during carbon dot synthesis. The resulting hybrid material exhibits strong photoluminescence in the red region of the spectrum (590 nm) when irradiated with blue light (480 nm). The proposed approach potentially allows for simultaneous wound closure and pathogen detection.

Optimizing the Surface Structural and Morphological Properties of Silk Thin Films via Ultra-Short Laser Texturing for Creation of Muscle Cell Matrix Model

Temporary scaffolds that mimic the extracellular matrix’s structure and provide a stable substratum for the natural growth of cells are an innovative trend in the field of tissue engineering. The aim of this study is to obtain and design porous 2D fibroin-based cell matrices by femtosecond laser-induced microstructuring for future applications in muscle tissue engineering. Ultra-fast laser treatment is a non-contact method, which generates controlled porosity—the creation of micro/nanostructures on the surface of the biopolymer that can strongly affect cell behavior, while the control over its surface characteristics has the potential of directing the growth of future muscle tissue in the desired direction. The laser structured 2D thin film matrices from silk were characterized by means of SEM, EDX, AFM, FTIR, Micro-Raman, XRD, and 3D-roughness analyses. A WCA evaluation and initial experiments with murine C2C12 myoblasts cells were also performed. The results show that by varying the laser parameters, a different structuring degree can be achieved through the initial lifting and ejection of the material around the area of laser interaction to generate porous channels with varying widths and depths. The proper optimization of the applied laser parameters can significantly improve the bioactive properties of the investigated 2D model of a muscle cell matrix.

Preparation and Characterization of Natural Silk Fibroin Hydrogel for Protein Drug Delivery

In recent years, hydrogels have been widely used as drug carriers, especially in the area of protein delivery. The natural silk fibroin produced from cocoons of the Bombyx mori silkworm possesses excellent biocompatibility, significant bioactivity, and biodegradability. Therefore, silk fibroin-based hydrogels are arousing widespread interest in biomedical research. In this study, a process for extracting natural silk fibroin from raw silk textile yarns was established, and three aqueous solutions of silk fibroin with different molecular weight distributions were successfully prepared by controlling the degumming time. Silk fibroin was dispersed in the aqueous solution as “spherical” aggregate particles, and the smaller particles continuously accumulated into large particles. Finally, a silk fibroin hydrogel network was formed. A rheological analysis showed that as the concentration of the silk fibroin hydrogel increased its storage modulus increased significantly. The degradation behavior of silk fibroin hydrogel in different media verified its excellent stability, and the prepared silk fibroin hydrogel had good biocompatibility and an excellent drug-loading capacity. After the protein model drug BSA was loaded, the cumulative drug release within 12 h reached 80%. We hope that these investigations will promote the potential utilities of silk fibroin hydrogels in clinical medicine.

Dietary administration of silk microparticles improves the epidermal and dermal regeneration after a skin wounding in gilthead seabream (Sparus aurata L.)

The impact of dietary supplementation with silk fibroin (SF) microparticles on the wound healing process in gilthead seabream (Sparus aurata) skin was studied. A control diet was enriched with different SF levels: 0 (control), 50 (SF50 diet), and 100 (SF100 diet) mg Kg^-1 to form three experimental diets and was fed to seabream for 30 days. Experimental wounds were performed and after 7 days post-wounding (dpw) skin mucus immunity, macroscopic wound closure, and skin regeneration were studied at a microscopic and genetic level. Results indicated that fish fed SF100 did not suffer the decreases in protease and IgM levels observed in the skin mucus of wounded fish fed with the control diet. Macroscopic findings illustrated that dietary SF100 significantly improved the wound closure ratio compared to those reared in the control group. At a microscopic level, changes in the shape of keratocyte cells were evident in the wounded fish. In addition, the intercellular spaces present between epidermal cells and their proliferation in the epidermis, as well as the presence of blood vessels in the dermis were significantly statistically higher in the skin of fish fed the SF100 diet and sampled at 7 dpw compared to those observed in the skin of fish fed the control or SF50 diets. Moreover, regarding the RNA: DNA ratio, statistically significant increases and decreases were observed in fish fed the control and SF100 diet, respectively, in non-wounded and wounded fish. Interestingly, dietary SF100 supplementation improved skin cell proliferation, enhanced the inflammatory phase, and increased the expression of important genes involved in tissue repair and extracellular matrix formation. In conclusion, the SF100 diet can be considered as an appropriate feed additive to improve wound healing in gilthead seabream.

Silk Fibroin-Based Biomaterials for Tissue Engineering Applications

Tissue engineering (TE) involves the combination of cells with scaffolding materials and appropriate growth factors in order to regenerate or replace damaged and degenerated tissues and organs. The scaffold materials serve as templates for tissue formation and play a vital role in TE. Among scaffold materials, silk fibroin (SF), a naturally occurring protein, has attracted great attention in TE applications due to its excellent mechanical properties, biodegradability, biocompatibility, and bio-absorbability. SF is usually dissolved in an aqueous solution and can be easily reconstituted into different forms, including films, mats, hydrogels, and sponges, through various fabrication techniques, including spin coating, electrospinning, freeze drying, and supercritical CO₂-assisted drying. Furthermore, to facilitate the fabrication of more complex SF-based scaffolds, high-precision techniques such as micro-patterning and bio-printing have been explored in recent years. These processes contribute to the diversity of surface area, mean pore size, porosity, and mechanical properties of different silk fibroin scaffolds and can be used in various TE applications to provide appropriate morphological and mechanical properties. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have recently been developed. The typical applications of SF-based scaffolds for TE of bone, cartilage, teeth and mandible tissue, cartilage, skeletal muscle, and vascular tissue are highlighted and discussed followed by a discussion of issues to be addressed in future studies.

Volumetric Scalability of Microfluidic and Semi-Batch Silk Nanoprecipitation Methods

Silk fibroin nanoprecipitation by organic desolvation in semi-batch and microfluidic formats provides promising bottom-up routes for manufacturing narrow polydispersity, spherical silk nanoparticles. The translation of silk nanoparticle production to pilot, clinical, and industrial scales can be aided through insight into the property drifts incited by nanoprecipitation scale-up and the identification of critical process parameters to maintain throughout scaling. Here, we report the reproducibility of silk nanoprecipitation on volumetric scale-up in low-shear, semi-batch systems and estimate the reproducibility of chip parallelization for volumetric scale-up in a high shear, staggered herringbone micromixer. We showed that silk precursor feeds processed in an unstirred semi-batch system (mixing time > 120 s) displayed significant changes in the nanoparticle physicochemical and crystalline properties following a 12-fold increase in volumetric scale between 1.8 and 21.9 mL while the physicochemical properties stayed constant following a further 6-fold increase in scale to 138 mL. The nanoparticle physicochemical properties showed greater reproducibility after a 6-fold volumetric scale-up when using lower mixing times of greater similarity (8.4 s and 29.4 s) with active stirring at 400 rpm, indicating that the bulk mixing time and average shear rate should be maintained during volumetric scale-up. Conversely, microfluidic manufacture showed high between-batch repeatability and between-chip reproducibility across four participants and microfluidic chips, thereby strengthening chip parallelization as a production strategy for silk nanoparticles at pilot, clinical, and industrial scales.

Implantation of injectable SF hydrogel with sustained hydrogen sulfide delivery reduces neuronal pyroptosis and enhances functional recovery after severe intracerebral hemorrhage

Hydrogen sulfide (H₂S), an important endogenous signaling molecule, plays an important neuroprotective role in the central nervous system. However, there is no ideal delivery material or method involving the sustained and controlled release of H₂S for clinical application in brain diseases. Silk fibroin (SF)-based hydrogels have become a potentially promising strategy for local, controlled, sustained drug release in the treatment of various disorders. Here, we show a silk fibroin (SF)-based hydrogel with sustained H₂S delivery (H₂S@SF hydrogel) is effective in treating brain injury through stereotactic orthotopic injection in a severe intracerebral hemorrhage (ICH) mouse model. In this study, we observed H₂S@SF hydrogel sustained H₂S release in vitro and in vivo. The physicochemical properties of H₂S@SF hydrogel were studied using FE-SEM, Raman spectroscopy and Rheological analysis. Treatment with H₂S@SF hydrogel attenuated brain edema, reduced hemorrhage volume and improved the recovery of neurological deficits after severe ICH following stereotactic orthotopic injection. Double immunofluorescent staining also revealed that H₂S@SF hydrogel may reduce cell pyroptosis in the striatum, cortex and hippocampus. However, when using endogenous H₂S production inhibitor AOAA, H₂S@SF hydrogel could not suppress ICH-induced cell pyroptosis. Hence, the therapeutic effect of the H₂S@SF hydrogel may be partly the result of the slow-release of H₂S and/or the effect of the SF hydrogel on the production of endogenous H₂S. Altogether, the results exhibit promising attributes of injectable silk fibroin hydrogel and the utility of H₂S-loaded injectable SF hydrogel as an alternative biomaterial toward brain injury treatment for clinical application.

Silk Hydrogel for Tissue Engineering: A Review

AIM

This review aims to explore the importance of silk hydrogel and its potential in tissue engineering (TE).

BACKGROUND

Tissue engineering is a procedure that incorporates cells into the scaffold materials with suitable growth factors to regenerate injured tissue. For tissue formation in TE, the scaffold material plays a key role. Different forms of silk fibroin (SF), such as films, mats, hydrogels, and sponges, can be easily manufactured when SF is disintegrated into an aqueous solution. High precision procedures such as micropatterning and bioprinting of SF-based scaffolds have been used for enhanced fabrication.

REVIEW RESULTS

In this narrative review, SF physicochemical and mechanical properties have been presented. We have also discussed SF fabrication techniques like electrospinning, spin coating, freeze-drying, and physiochemical cross-linking. The application of SF-based scaffolds for skeletal, tissue, joint, muscle, epidermal, tissue repair, and tympanic membrane regeneration has also been addressed.

CONCLUSION

SF has excellent mechanical properties, tunability, biodegradability, biocompatibility, and bioresorbability.

CLINICAL SIGNIFICANCE

Silk hydrogels are an ideal scaffold matrix material that will significantly impact tissue engineering applications, given the rapid scientific advancements in this field.

Chitosan/Silk Fibroin Materials for Biomedical Applications-A Review

This review provides a report on recent advances in the field of chitosan (CTS) and silk fibroin (SF) biopolymer blends as new biomaterials. Chitosan and silk fibroin are widely used to obtain biomaterials. However, the materials based on the blends of these two biopolymers have not been summarized in a review paper yet. As these materials can attract both academic and industrial attention, we propose this review paper to showcase the latest achievements in this area. In this review, the latest literature regarding the preparation and properties of chitosan and silk fibroin and their blends has been reviewed.

A Review on Antibacterial Silk Fibroin-based Biomaterials: Current State and Prospects

Bacterial contamination of biomaterials is a common problem and a serious threat to human health worldwide. Therefore, the development of multifunctional biomaterials that possess antibacterial properties and can resist infection is a continual goal for biomedical applications. Silk fibroin (SF), approved by U.S. Food and Drug Administration (FDA) as a biomaterial, is one of the most widely studied natural polymers for biomedical applications due to its unique mechanical properties, biocompatibility, tunable biodegradation, and versatile material formats. In the last decade, many methods have been employed for the development of antibacterial SF-based biomaterials (SFBs) such as physical loading or chemical functionalization of SFBs with different antibacterial agents and bio-inspired surface modifications. In this review, we first describe the current understanding of the composition and structure-properties relationship of SF as a leading-edge biomaterial. Then we demonstrate the different antibacterial agents and methods implemented for the development of bactericidal SFBs, their mechanisms of action, and different applications. We briefly address their fabrication methods, advantages, and limitations, and finally discuss the emerging technologies and future trends in this research area.

Mixing and flow-induced nanoprecipitation for morphology control of silk fibroin self-assembly

Tuning silk fibroin nanoparticle morphology using nanoprecipitation for bottom-up manufacture is an unexplored field that has the potential to improve particle performance characteristics. The aim of this work was to use both semi-batch bulk mixing and micro-mixing to modulate silk nanoparticle morphology by controlling the supersaturation and shear rate during nanoprecipitation. At flow rates where the shear rate was below the critical shear rate for silk, increasing the concentration of silk in both bulk and micro-mixing processes resulted in particle populations of increased sphericity, lower size, and lower polydispersity index. At high flow rates, where the critical shear rate was exceeded, the increased supersaturation with increasing concentration was counteracted by increased rates of shear-induced assembly. The morphology could be tuned from rod-like to spherical assemblies by increasing supersaturation of the high-shear micro-mixing process, thereby supporting a role for fast mixing in the production of narrow-polydispersity silk nanoparticles. This work provides new insight into the effects of shear during nanoprecipitation and provides a framework for scalable manufacture of spherical and rod-like silk nanoparticles.

Tuning silk fibroin nanoparticle morphology using nanoprecipitation for bottom-up manufacture is an unexplored field that has the potential to improve particle performance characteristics.

The stiffness variability of a silk fibroin scaffold during bone cell proliferation

Complex assessment of gradual changes in scaffold morphology and stiffness is an essential step in bone filler development. Current approach, however, does not reflect long term cell proliferation effect as the mechanical tests are usually conducted on pristine materials without cells or cell influence on material stiffness is evaluated after one time period only. Here, biocompatible silk fibroin (SF) porous scaffolds envisioned for bone defect filling were prepared by dissolving of fibroin fibers, followed by dialysis, freeze-drying and final stabilization. Particular attention was devoted to the influence of bone cell proliferation up to 2 months on the stiffness of the material. The morphology of the material was studied in terms of its inner structure and the overall changes in the surface characteristics due to proliferation of MG 63 bone cell line. The SF scaffold stiffness significantly increased during first month followed by its decline during second month due to bone cell seeding. After 2 months, the SF scaffold was completely colonized, which resulted in a gradual decay of its structure. The length of degradation due to bone cell proliferation and mechanical behavior corresponded to the requirements set for reasonable filler material indicating that porous SF scaffolds comprise a promising biomaterial for bone regeneration.

The Effect of Sterilization on the Characteristics of Silk Fibroin Nanoparticles

In recent years, silk fibroin nanoparticles (SFNs) have been consolidated as drug delivery systems (DDSs) with multiple applications in personalized medicine. The design of a simple, inexpensive, and scalable preparation method is an objective pursued by many research groups. When the objective is to produce nanoparticles suitable for biomedical uses, their sterility is essential. To achieve sufficient control of all the crucial stages in the process and knowledge of their implications for the final characteristics of the nanoparticles, the present work focused on the final stage of sterilization. In this work, the sterilization of SFNs was studied by comparing the effect of different available treatments on the characteristics of the nanoparticles. Two different sterilization methods, gamma irradiation and autoclaving, were tested, and optimal conditions were identified to achieve the sterilization of SFNs by gamma irradiation. The minimum irradiation dose to achieve sterilization of the nanoparticle suspension without changes in the nanoparticle size, polydispersity, or Z-potential was determined to be 5 kiloGrays (kGy). These simple and safe methods were successfully implemented for the sterilization of SFNs in aqueous suspension and facilitate the application of these nanoparticles in medicine.

Enhanced osteogenic effect in reduced BMP-2 doses with siNoggin transfected pre-osteoblasts in 3D silk scaffolds

Bone morphogenetic proteins (BMPs), especially BMP-2, are being increasingly used in bone tissue engineering due to its osteo-inductive effects. Although recombinant human BMP-2 (rhBMP-2) was approved by Food and Drug Administration (FDA) to use for bone repair, its high doses cause undesired side effects. In order to reduce the BMP-2 dose for enhanced osteogenic differentiation, in this study we decided to suppress the synthesis of Noggin protein, the primary antagonist of BMP-2, on the MC3T3-E1 cells using Noggin targeted small interfering RNA (siRNA). Unlike other studies, Noggin siRNA (siNoggin) transfected cells were seeded on silk scaffolds, and osteogenic differentiation was investigated for a long-term period (21 days) with MTT, qPCR, SEM/EDS, and histological analysis. Besides, siNoggin transfected MC3T3-E1 cells were evaluated as a new cell source for tissue engineering studies. It was determined that Nog gene expression was suppressed in the siNoggin group and Ocn gene expression increased 5-fold compared to the control group (*p < 0.05). The osteogenic effect of BMP-2 was clearly observed in siNoggin transfected cells. According to the SEM/EDS analysis, the siNoggin group has mineral structures clustered on cells, which contain intense Ca and P elements. Histological staining showed that the siNoggin group has a more intense mineralized area than that of the control group. In conclusion, this study indicated that Noggin silencing by siRNA induces osteogenic differentiation in reduced BMP-2 doses for scaffold-based bone regeneration. This non-gene integration strategy has as a safe therapeutic potential to enhance tissue regeneration.