Tuning the conformation and mechanical properties of silk fibroin hydrogels

Innovative approaches in bioadhesive design: A comprehensive review of crosslinking methods and mechanical performance

In biomedical applications, bioadhesives have become a game-changer, offering novel approaches to tissue engineering, surgical adhesion, and wound healing. This comprehensive review paper provides a thorough analysis of bioadhesives and their categorization according to application site and crosslinking process, bonding efficacy, and mechanical characteristics. The use of bioadhesives to stop bleeding and seal leaks is also covered in the review. The article delves into the various crosslinking techniques used in bioadhesives, including chemical, physical, and hybrid approaches. It emphasizes on how these mechanisms control the adhesive's elasticity, durability, and structural integrity. In addition, the review looks at the mechanical strength of bioadhesives, taking important characteristics like shear strength, toughness, elasticity, and tensile strength into account. It is highlighted how important bioadhesives are to the life sciences because they drive innovation and interdisciplinary cooperation, address present healthcare issues, and create new avenues for therapeutic development. The paper also explores some vital characteristics of bioadhesives that, when strategically combined with one another, improve their efficacy and usefulness in a variety of surgical and medical applications. The analysis concludes by examining nature-inspired adhesives, including those based on geckos, mussels, and tannic acid, and their unique bonding mechanisms and potential for use in advanced biomedical applications.

Influence of material format and surface chemistry for the sustained delivery and efficacy of silk drug delivery systems in vivo

Silk fibroin materials are promising for use in controlled drug delivery in the field of tissue engineering and biomedical applications thanks to silk's generally established biocompatibility and tunable properties for implants and drug storage. Several factors must be considered in the materials design, including material format, drug properties and release kinetics, and the activity and stability of the drug after release. While numerous reviews described silk-based DDS that demonstrated controllable in vitro release, success in vivo has been limited, especially in some material formats. This review therefore aims to provide insight into the current material format and functionalization strategies to maximize in vivo performance by describing the in vivo activity of recently developed silk drug delivery systems. The review also aims to provide a fresh perspective on the suitable format and functionalization strategies for a target biomedical application. Based on the release behavior of drugs in various material formats, silk films, foams, and microneedles were better suited to serve as scaffolds for cell regeneration and improved recovery rate for biomedical applications involving wound healing and tissue engineering. Gels and particles could be incorporated within the films and foams but the purpose would be to serve as additional physical barriers towards drug diffusion in these types of application. For drugs or therapeutics that target internal organs (i.e. brain, liver, intestines, etc.), gels and particles were mainly used due to their size. In the event that the material format selection based on the target application does not contribute a lot to the prolonged release of drugs or therapeutic agents, hybrid functionalization strategies were adapted to make the surface chemistry of the material more responsive to the environmental stimuli for a more tunable silk DDS.

Silk Fibroin Methacrylation: Chemical Synthesis to Biomechanical Optimization in Tissue Engineering

In recent years, a major focus in the field of tissue engineering has been the search for a suitable biomaterial for clinical applications. Researchers have sought to optimize natural, synthetic, and hybrid options, with an aim to enhance biological, chemical, physical, and mechanical properties. In the past decade, silk fibroin has emerged as a promising approach due to its suitable properties. Specifically, the chemical modification of silk fibroin with methacrylate agents, namely glycidyl methacrylate, methacrylic anhydride, and gelatin methacryloyl, confers the material with improved biophysical properties. This review presents an in-depth overview of silk fibroin's structure and suitable properties, silk fibroin methacrylate synthesis and characterization techniques, and applications of silk fibroin in bone and cartilage, skin, and nerve tissue engineering. Challenges include a limited understanding of methacrylate agents on specific cell types, which can be addressed by further in vivo investigations utilizing biomaterial compounds to confer tissue-specific needs. We conclude with our perspective of the present limitations and future trends of the methacrylated SF platform.

Construction of Cells-Membrane-Cells Living Complexes for Cartilage Repair by Enhancing the Structural Stability of Fibrous Membranes

3D cartilage tissue engineering scaffolds with stable structures are crucial for promoting cartilage tissue growth and repair. However, limited research attention is given to the effects of 3D cells-membrane-cells sandwich-like living complexes with enhanced structural stability for cartilage repair. In this study, silk fibroin/graphene oxide@kartogenin (SF/GO@KGN) fibrous membranes with improved structural stability are developed through the regulation of the crystallinity, and living complexes are constructed for cartilage repair using rat bone marrow stromal cells (rBMSCs) and the SF/GO@KGN fibrous membranes. Results show that the physicochemical properties of the SF/GO@KGN fibrous membranes, including morphology, tensile strength, swelling ratio, degradation, and KGN release rate are greatly influenced by the crystallinity of the fibrous membranes. The enhanced structural stability of the fibrous membranes promotes the adhesion, proliferation, and chondrogenic differentiation of rBMSCs on the surface of the fibrous membranes, as well as the deposition of the cartilage's extracellular matrix (ECM). Animal experiments demonstrate that sandwich-like cells-membrane-cells living complexes with high structural stability significantly promote early cartilage formation and ECM deposition. This study not only provides a facile and effective strategy for cartilage regeneration and repair but also provides new insights for designing and preparing other tissue engineering scaffolds.

Silk fibroin: An innovative protein macromolecule-based hydrogel/ scaffold revolutionizing breast cancer treatment and diagnosis - Mechanisms, advancements, and targeting capabilities

Breast cancer (BC) is recognized as the most typical cancer diagnosed in women globally, posing significant public health challenges. Several protein-based biological macromolecules have been investigated for drug delivery in BC treatment due to biological and tunable mechanical properties. Silk fibroin (SF)-based hydrogel/scaffold is gaining attraction in BC therapy. The functionalization of SF with folic acid or antibodies enables targeted delivery to BC cells that overexpress folate receptors. In this context, this perspective article explored the potential biological activity, targeting capacity, functionalization, and drug carrier abilities of SF-based hydrogel for BC therapy. In addition, the article exclusively delves into the potential molecular pathways of SF-based hydrogel/ scaffolds for targeted therapy in BC. The article also summarizes the perspectives on the diagnosis abilities of SF-based hydrogel/ scaffolds in BC treatment, making it the first instance of such perspective literature. This insightful literature presents practical guidance for researchers, clinicians, and scientists eager to investigate the innovative biological applications and targeting potential of SF-based hydrogels and scaffolds in advancing breast cancer treatments.

Nano-structured antibiofilm coatings based on recombinant resilin

The applications of responsive biomaterials for tuning cell-surface interactions have been recently explored due to their unique switchable characteristics. However, rational design of surfaces using suitable biomacromolecules to attain optimal physicochemical performance, biocompatibility, cell adhesion and anti-fouling properties is quite challenging. Resilin-mimetic polypeptides (RMPs) are intrinsically disordered biomacromolecules that exhibit multi-stimuli responsive behaviour, including reversible dual-phase thermal behaviour forming self-assembled nano- to microstructures. However, there is a limited understanding of the effect of morphological features of RMP-based nanostructures, and their influence on surface properties. Therefore, in this study, a family of responsive RMP-based nanostructured coatings (nano-coacervates, nanogels and nano-bioconjugates) are fabricated to investigate their various surface properties that influence cell-surface interactions. The effects of their physicochemical properties, such as conformation, packing density, charge, roughness, and stiffness, are investigated using atomic force microscopy, neutron scattering and reflectometry techniques. Biocompatibility and microbiological testing show that these nanostructured switchable responsive coatings can be applied to a wide range of substrates to modulate biofilm formation and attribute antimicrobial characteristics. The developed nanocoatings have the potential to find applications in many areas, including implantable medical devices, and drug delivery.

Preparing the functional biomaterial with osteogenic bioactivities by incorporating annealing pretreated silk fiber and iron oxide nanoparticles

Silk fiber (SF), a kind of bio-fiber from biomass protein fibers with biocompatibility and mechanical properties, has been widely utilized in biomedical engineering. However, SF-based bio-scaffolds often encounter challenges in promoting osteogenesis within bone tissue engineering (BTE) applications. In this study, SF-based composites were constructed via the solution casting method in the presence of IONPs (SFFC-IONPs), followed by annealing-induced self-assembly to form magnetic SF annealing films (SFFCA-IONPs). Three types of IONPs loaded SF films (SFFCA-50, SFFCA-100, and SFFCA-200) were prepared by altering the feeding IONPs (50 μg/mL, 100 μg/mL, and 200 μg/mL). Results demonstrated that SFFC films primarily exhibited random coil structures and were water-soluble, while SFFCA films demonstrated the formation of silk II structures and became water-insoluble. The incorporation of IONPs significantly enhanced the porosity, mechanical strength, and thermal stability of the SFFCA films. Furthermore, the SFFCA-IONPs films not only exhibited excellent biocompatibility but also demonstrated enhanced osteo-inductive properties, as evidenced by increased alkaline phosphatase (ALP) activity, enhanced mineralized nodule formation, and upregulation of osteogenic gene expression. This study presents a promising bio-based material with significant potential for use as a scaffold in BTE applications.

A review on recent progress in polysaccharide/protein hydrogels in winter sports: Classification, synthesis routes, and application

In today's world, emerging materials play prominent roles in competitive sport applications. Among them, hydrogels gained increasing attention in winter sports applications owing to their unique advantages, such as flexibility, conductivity, and adhesion. However, traditional hydrogels prepared by synthetic routes from petroleum materials lose performance at freezing temperatures below zero degrees, limiting their direct use in winter sports. The emergence of natural polymer materials has brought new opportunities for winter sports. Polysaccharide or protein (polysaccharides/proteins) hydrogels obtained from biomass resources are renewable and abundant, especially when taking into consideration the depletion of resources and environmental pollution in contemporary society. The development and utilization of polysaccharide/protein hydrogels may contribute to solving the resource shortage problem. In this paper, the latest research dealing with natural polymer hydrogels for winter sports applications is reviewed. In the first section, recent research trends of hydrogel classification and crosslinking methods are summarized. The performance advantages and specific applications of polysaccharide/protein hydrogels in winter sports are then discussed, with the application scope covering index monitoring, event violation detection, protective equipment, rehabilitation, and venues. Finally, the practical challenges faced by polysaccharide/protein hydrogels in winter sports are prospected along with the innovation and optimization design routes, such as the introduction of natural crosslinking agents and bionic structures. These insights aim to provide a reference for the development of advanced materials for winter sports applications.

Advancements in Injectable Hydrogels for Controlled Insulin Delivery: A Comprehensive Review of the Design, Properties and Therapeutic Applications for Diabetes and Its Complications

Glycemic management in diabetes patients remains heavily reliant on multiple daily insulin injections, which often leads to poor patient compliance and an elevated risk of hypoglycemia. To overcome these limitations, injectable hydrogels capable of encapsulating insulin within polymeric networks have emerged as a promising alternative. Ideally, a single injection can form an in situ depot that allows prolonged glycemic control and lower injection frequency. This review summarizes recent advances in injectable hydrogels for controlled insulin delivery, focusing on the polymer sources, crosslinking strategies, and stimuli-responsive release mechanisms. Synthetic polymers such as PEG, PNIPAM, and Pluronics dominate the current research due to their highly tunable properties, whereas naturally derived polysaccharides and proteins generally require further modifications for enhanced functionality. The crosslinking types, ranging from relatively weak physical interactions (hydrogen bonds, hydrophobic interactions, etc.) to dynamic covalent bonds with higher binding strength (e.g., Schiff base, phenylboronate ester), significantly influence the shear-thinning behavior and stimuli-responsiveness of hydrogel systems. Hydrogels' responsiveness to temperature, glucose, pH, and reactive oxygen species has enabled more precise insulin release, offering new options for improved diabetic management. Beyond glycemic regulation, this review also explores insulin-loaded hydrogels for treating complications. Despite the progress, challenges such as burst release, long-term biocompatibility, and scalability remain. Future research should focus on optimizing hydrogel design, supported by robust and comprehensive data.

Designing Silk Biomaterials toward Better Future Healthcare: The Development and Application of Silk-Based Implantable Electronic Devices in Clinical Diagnosis and Therapy

Implantable medical electronic devices (IMEDs) have attracted great attention and shown versatility for solving clinical problems ranging from real-time monitoring of physiological/ pathological states to electrical stimulation therapy and from monitoring brain cell activity to deep brain stimulation. The ongoing challenge is to select appropriate materials in target device configuration for biomedical applications. Currently, silk-based biomaterials have been developed for the design of diagnostic and therapeutic electronic devices due to their excellent properties and abundant active sites in the structure. Herein, the aim is to summarize the structural characteristics, physicochemical properties, and bioactivities of natural silk biomaterials as well as their derived materials, with a particular focus on the silk-based implantable biomedical electronic devices, such as implantable devices for invasive brain-computer interfaces, neural recording, and in vivo electrostimulation. In addition, future opportunities and challenges are also envisioned, hoping to spark the interests of researchers in interdisciplinary fields such as biomaterials, clinical medicine, and electronics.

Electrically Conductive Injectable Silk/PEDOT: PSS Hydrogel for Enhanced Neural Network Formation

With no effective treatments for functional recovery after injury, spinal cord injury (SCI) remains one of the unresolved healthcare challenges. Human induced pluripotent stem cell (hiPSC) transplantation is a versatile patient-specific regenerative approach for functional recovery after SCI. Injectable electroconductive hydrogel (ECH) can further enhance the cell transplantation efficacy through a minimally invasive manner as well as recapitulate the native bioelectrical microenvironment of neural tissue. Given these considerations, we report a novel ECH prepared through self-assembly facilitated in situ gelation of natural silk fibroin (SF) derived from mulberry Bombyx mori silk and electrically conductive PEDOT:PSS. PEDOT:PSS was pre-stabilized to prevent the potential delamination of its hydrophilic PSS chain under aqueous environment using 3% (v/v) (3-glycidyloxypropyl)trimethoxysilane (GoPS) and 3% (w/v) poly(ethylene glycol)diglycidyl ether (PeGDE). The resultant ECH formulations are easily injectable with standard hand force with flow point below 100 Pa and good shear-thinning properties. The ECH formulations with unmodified and GoPS-modified PEDOT:PSS, that is, SF/PEDOT and SF/PEDOTGoP maintain comparable elastic modulus to spinal cord (~10-60 kPa) under physiological condition, indicating their flexibility. The GoPS-modified ECHs also display improved structural recoverability (~70%-90%) as compared to the unmodified versions of the ECHs (~30%-80%), as indicated by the three interval time thixotropy (3ITT) test. Additionally, these ECHs possess electrical conductivity in the range of ~0.2-1.2 S/m comparable to spinal cord (1-10 S/m), indicating their ability to mimic native bioelectrical environment. Approximately 80% or more cell survival was observed when hiPSC-derived cortical neurons and astrocytes were encapsulated within these ECHs. These ECHs support the maturation of cortical neurons when embedded for 7 days, fostering the development of a complex, interconnected network of long axonal processes and promoting synaptogenesis. These results underline the potential of silk ECHs in cell transplantation therapy for spinal cord regeneration.

3D Printing of Biocompatible and Antibacterial Silica-Silk-Chitosan-Based Hybrid Aerogel Scaffolds Loaded with Propolis

The aim of this study is to design a therapeutic enhanced three-dimensional (3D) silk fibroin (SF)-based scaffold containing propolis (Ps)-loaded chitosan (CH) nanocarriers. To this aim, we initially synthesized a hybrid gel-based ink by a synergistic sol-gel and self-assembly approach and then processed the resulting gels by microextrusion-based 3D printing followed by supercritical drying to obtain 3D hybrid aerogel scaffolds. Ps was utilized to enhance the final scaffold's bactericidal efficacy and cell responsiveness. For the synthesis of the scaffold, two Ps loading methods (in preprint and postprinting steps) were investigated in order to optimize the Ps drug quantities in the scaffold and maximize the antibacterial properties of scaffold. In the postprinting Ps loading step, the hybrid silica-oxidized SF (SFO)-CH hydrogel ink was 3D printed into a construct with an interconnected porous structure, and then, Ps was loaded into the printed construct. In the preprint loading method, PS was incorporated into the SF and a hydrolyzed silane solution prior to gelation. The morphological studies demonstrate that the addition of Ps encapsulated CH nanoparticles (NPs) into the hydrogel solution improved the porosity of the developed scaffolds. The rheological analysis of the designed gel ink with and without Ps loading and the release kinetics were studied. The antimicrobial results show that the Ps-loaded scaffolds in the postprinting step exhibited superior antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) strains compared to a preprinted Ps-loaded scaffold. Direct and indirect in vitro cytotoxicity tests also confirmed the designed Ps-loaded scaffold biocompatibility toward a mouse fibroblast (L929) cell line. We demonstrated that the scaffold formulated by propolis-loaded chitosan NPs can enhance the migration and proliferation of L929 fibroblast cells. The obtained results prove the promise of the designed 3D printed silica-SFO-CH-Ps scaffolds as a potent 3D scaffold to mediate tissue regeneration but also as an antibacterial highly porous matrix to support wound healing.

Bioprinting of anisotropic functional corneal stroma using mechanically robust multi-material bioink based on decellularized cornea matrix

Corneal scarring is a common cause of blindness, affecting millions globally each year. A huge gap between the demand and supply of donor tissue currently limits corneal transplantation, the only definitive therapy for patients with corneal scarring. To overcome this challenge, researchers have harnessed the efficacy of 3D bioprinting to fabricate artificial corneal stromal constructs. With all the different bioinks available, the decellularized corneal matrix-based bioprinted construct can fulfill the required biological functionality but is limited by the lack of mechanical stiffness. Additionally, from a biophysical standpoint, it is necessary for an ideal corneal substitute to mimic the anisotropy of the cornea from the central optic zone to the surrounding periphery. In this study, we enhanced the mechanical robustness of decellularized cornea matrix (DCM) hydrogel by blending it with another natural polymer, sonicated silk fibroin solution in a defined ratio. Although hybrid hydrogel has an increased complex modulus than DCM hydrogel, it has a lower in vitro degradation rate and increased opaqueness due to the presence of crystalline beta-sheet conformation within the hydrogel. Therefore, we used this multi-material bioink-based approach to fabricate a corneal stromal equivalent where the outer peripheral corneal rim was printed with a mechanically robust polymeric blend of DCM and sonicated silk fibroin and the central optic zone was printed with only DCM. The bioprinted corneal stroma thus maintained its structural integrity and did not break when lifted with forceps. The two different bioinks were encapsulated with human limbus-derived mesenchymal stem cells (hLMSC) individually and 3D bioprinted in different patterns (concentric and parallel) to attain a native-like structure in terms of architecture and transparency. Thus, the bilayer cornea constructs maintained high cell viability and expressed keratocyte core proteins indicating optimal functionality. This approach helped to gain insight into bioprinting corneas with heterogeneous mechanical property without disturbing the structural clarity of the central optic zone.

Preparation of carboxylated-silk nanofibers by the one-pot method of maleic acid hydrolysis

In this study, a maleic acid (MA) hydrolysis one-pot method is proposed to prepare carboxylated silk nanofibers (MA-SNFs). The MA concentration, hydrolysis temperature, and processing time were optimized. Combined with high-pressure homogenization, MA-SNFs with a carboxyl content of 0.617±0.019 mmol/g and length of 333±116 nm were obtained with a yield of 54.90±1.98 % at the optimal conditions: 50 wt% of MA concentration, 110 °C of hydrolysis temperature and 120 min of processing time. The morphology, chemical structure, and crystal structure of raw silk fibroin (SF), acid-hydrolyzed silk fibroin and nanofibers were studied. Furthermore, MA was reused several times with a recovery rate of >94 % and maintained almost the same treatment effect. Finally, due to the presence of carboxyl groups, MA-SNF hydrogels were successfully prepared by an acetic coagulation vapor bath which exhibited excellent self-supporting ability and mechanical properties as well as a more sensitive pH response compared with regenerated silk fibroin solution and other non-carboxylated silk nanofibers. The MA-SNF aerogels had the characteristics of light weight, high strength and porous with cross-linked nanostructures.

Regulating Bacterial Culture through Tailored Silk Inverse Opal Scaffolds

Controlling the growth of microbial consortia is of great significance in the biomedical field. Selective bacterial growth is achieved by fabricating silk inverse opal (SIO) scaffolds with varying pore sizes ranging from 0.3 to 4.5 µm. Pore size significantly influences the growth dynamics of bacteria in both single and mixed-strain cultures. Specially, the SIO-4.5 µm scaffold is observed to be more favorable for cultivating S. aureus, whereas the SIO-0.3 µm scaffold is more suitable for cultivating E. coli and P. aeruginosa. By adjusting the secondary conformation of silk fibroin, the stiffness of the SIO substrate will be altered, which results in the increase of bacteria on the SIO by 16 times compared with that on the silk fibroin film. Manipulating the pore size allows for the adjustment of the S. aureus to P. aeruginosa ratio from 0.8 to 9.3, highlighting the potential of this approach in regulating bacterial culture.

Bioactive silk fibroin hydrogels: Unraveling the potential for biomedical engineering

Silk fibroin (SF) has received special attention from the scientific community due to its noteworthy properties. Its unique chemical structure results in an uncommon combination of macroscopically useful properties, yielding a strong, fine and flexible material which, in addition, presents good biodegradability and better biocompatibility. Therefore, silk fibroin in various formats, appears as an ideal candidate for supporting biomedical applications. In this review, we will focus on the hydrogels obtained from silk fibroin or in combination with it, paying special attention to the synthesis procedures, characterization methodologies and biomedical applications. Tissue engineering and drug-delivery systems are, undoubtedly, the two main areas where silk fibroin hydrogels find their place.

Silk acid-tyramine hydrogels with rapid gelation properties for 3D cell culture

Silk fibroin (SF) can be enzymatically crosslinked through tyrosine residues to fabricate hydrogels with good biocompatibility and tunable mechanical properties. Using tyramine substitution can increase the phenolic group content to facilitate the gelation kinetics and mechanical properties. In this study, a two-step chemical modification method is demonstrated to synthesize silk acid-tyramine (SA-TA) conjugates with a high phenolic group content (>7 mol%). The SA-TA shows rapid enzyme-catalyzed gelation property where the sol-gel transition takes less than 10 s at 37 °C, allowing cell encapsulation with uniform distribution while maintaining high cell viability (>90 %). Furthermore, the enzyme-catalyzed SA-TA hydrogels show enhanced storage modulus than enzyme-catalyzed SF hydrogels, long-term stability, and good cytocompatibility, indicating their great potential in 3D cell culture. The in vivo implantation study demonstrates that the SA-TA hydrogels are biodegradable with a mild immune response. This implies that SA-TA hydrogels can be applied in various medical applications, such as tissue engineering, cell delivery, and 3D bioprinting. STATEMENT OF SIGNIFICANCE: In this study, a two-step chemical modification method is demonstrated to synthesize silk acid-tyramine (SA-TA) conjugates with a high phenolic group content (>7 mol%). Owing to the increased content of the phenolic group, the SA-TA shows rapid enzyme-catalyzed gelation property where the sol-gel transition takes less than 10 s at 37 °C, allowing cell encapsulation with uniform distribution while maintaining high cell viability (>90 %). Furthermore, the enzyme-catalyzed SA-TA hydrogels show enhanced storage modulus than enzyme-catalyzed SF hydrogels, long-term stability, and good cytocompatibility, indicating their great potential in 3D cell culture. The in vivo implantation study demonstrates that the SA-TA hydrogels are biodegradable with a mild immune response. This implies that SA-TA hydrogels can be applied in various medical applications, such as tissue engineering, cell delivery, and 3D bioprinting.

Oral Administration of Berberine Hydrochloride Based on Chitosan/Carboxymethyl-β-Cyclodextrin Hydrogel

In this study, a novel oral formulation of berberine hydrochloride (BBH) hydrogel was successfully synthesized through physical cross-linking using chitosan (CS) and carboxymethyl-β-cyclodextrin (CMCD). The characterization results confirmed the successful synthesis of the CS/CMCD hydrogel and the subsequent loading of BBH into this composite (CS/CMCD/BBH) was effectively accomplished. The BBH was used as a model drug and the resulting hydrogel demonstrated a sustained drug release profile. In addition to its improved solubility and sustained release characteristics, the hydrogel exhibited excellent antibacterial activity against common pathogens such as Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans). Additionally, in vitro studies indicated that the hydrogel was not cytotoxic to NIH3T3 and HaCaT cells, suggesting its safety for biomedical applications. This lack of cytotoxic effects, combined with the mechanical strength, solubility improvements, and antibacterial properties of the hydrogel, positions the CS/CMCD/BBH hydrogel as a promising candidate for the effective oral delivery of BBH. By addressing the solubility and delivery challenges of BBH, this hydrogel offers a viable solution for the oral administration of BBH, with potential applications in various biomedical fields.

Particulate 3D Hydrogels of Silk Fibroin-Pluronic to Deliver Curcumin for Infection-Free Wound Healing

Skin is the largest protective tissue of the body and is at risk of damage. Hence, the design and development of wound dressing materials is key for tissue repair and regeneration. Although silk fibroin is a known biopolymer in tissue engineering, its degradation rate is not correlated with wound closure rate. To address this disadvantage, we mimicked the hierarchical structure of skin and also provided antibacterial properties; a hydrogel with globular structure consisting of silk fibroin, pluronic F127, and curcumin was developed. In this regard, the effect of pluronic and curcumin on the structural and mechanical properties of the hydrogel was studied. The results showed that curcumin affected the particle size, crystallinity, and ultimate elongation of the hydrogels. In vitro assays confirmed that the hydrogel containing curcumin is not cytotoxic while the diffused curcumin and pluronic provided a considerable bactericidal property against Methicillin-resistant Staphylococcus aureus. Interestingly, presence of pluronic caused more than a 99% reduction in planktonic and adherent bacteria in the curcumin-free hydrogel groups. Moreover, curcumin improved this number further and inhibited bacteria adhesion to prevent biofilm formation. Overall, the developed hydrogel showed the potential to be used for skin tissue regeneration.

Silk Fibroin-Enriched Bioink Promotes Cell Proliferation in 3D-Bioprinted Constructs

Three-dimensional (3D) bioprinting technology enables the controlled deposition of cells and biomaterials (i.e., bioink) to easily create complex 3D biological microenvironments. Silk fibroin (SF) has recently emerged as a compelling bioink component due to its advantageous mechanical and biological properties. This study reports on the development and optimization of a novel bioink for extrusion-based 3D bioprinting and compares different bioink formulations based on mixtures of alginate methacrylate (ALMA), gelatin and SF. The rheological parameters of the bioink were investigated to predict printability and stability, and the optimal concentration of SF was selected. The bioink containing a low amount of SF (0.002% w/V) was found to be the best formulation. Light-assisted gelation of ALMA was exploited to obtain the final hydrogel matrix. Rheological analyses showed that SF-enriched hydrogels exhibited greater elasticity than SF-free hydrogels and were more tolerant to temperature fluctuations. Finally, MG-63 cells were successfully bioprinted and their viability and proliferation over time were analyzed. The SF-enriched bioink represents an excellent biomaterial in terms of printability and allows high cell proliferation over a period of up to 3 weeks. These data confirm the possibility of using the selected formulation for the successful bioprinting of cells into extracellular matrix-like microenvironments.

Impact of Silk-Ionomer Encapsulation on Immune Cell Mechanical Properties and Viability

Encapsulation of single cells is a powerful technique used in various fields, such as regenerative medicine, drug delivery, tissue regeneration, cell-based therapies, and biotechnology. It offers a method to protect cells by providing cytocompatible coatings to strengthen cells against mechanical and environmental perturbations. Silk fibroin, derived from the silkworm Bombyx mori, is a promising protein biomaterial for cell encapsulation due to the cytocompatibility and capacity to maintain cell functionality. Here, THP-1 cells, a human leukemia monocytic cell line, were encapsulated with chemically modified silk polyelectrolytes through electrostatic layer-by-layer deposition. The effectiveness of the silk nanocoating was assessed using scanning electron microscopy (SEM) and confocal microscopy and on cell viability and proliferation by Alamar Blue assay and live/dead staining. An analysis of the mechanical properties of the encapsulated cells was conducted using atomic force microscopy nanoindentation to measure elasticity maps and cellular stiffness. After the cells were encapsulated in silk, an increase in their stiffness was observed. Based on this observation, we developed a mechanical predictive model to estimate the variations in stiffness in relation to the thickness of the coating. By tuning the cellular assembly and biomechanics, these encapsulations promote systems that protect cells during biomaterial deposition or processing in general.

Comparative Analysis of Electrospun Silk Fibroin/Chitosan Sandwich-Structured Scaffolds for Osteo Regeneration: Evaluating Mechanical Properties, Biological Performance, and Drug Release

An intensive idea of bone tissue engineering is to design regenerative nanofibrous scaffolds that could afford a natural extracellular matrix (ECM) microenvironment with the ability to induce cell proliferation, biodegradation, sustained drug release, and bioactivity. Even the mechanical properties and orientation of the nanofibers may enhance the performance of the scaffolds. To address this issue, we designed novel sandwich-like hybrid silk fibroin (SF)/silica/poly(vinyl alcohol) (PVA) nanofibers scaffolds. The developed scaffold was further characterized using scanning electron microscopy (SEM), elemental mapping, X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and water/blood contact angle measurements. Owing to the interfacial interaction between the layers of organic (chitosan/silk fibroin) and inorganic (silica) in the nanofibrous scaffold, a biocompatibility study has been made on an osteoblast-like (MG63) cell line, which has significant statistical differences; hemocompatibility and the mechanical profile were evaluated in detail to understand the suitability as a biomaterial. To endow the scaffold biodegradation rate, antibacterial activity, porosity profile, and cephalexin monohydrate (CEM), a drug-loading/drug release study was also performed for all of the nanofibers. This strategy explored superior mechanical strength with higher biomineralization on SF/silica/PVA nanofibers. Eventually, the proposed article compared the observation of monolayered scaffolds with designed sandwich-structured scaffolds for the enhancement of bone regeneration.

Tunable thermal diffusivity of silk protein assemblies based on their structural control and photo-induced chemical cross-linking

Silk, which has excellent mechanical properties and is lightweight, serves as a structural material in natural systems. However, the structural and functional applications of silk in artificial systems have been limited due to the difficulty in controlling its properties. In this study, we demonstrate the tunable thermal diffusivity of silk-based assemblies (films) based on secondary structural control and subsequent cross-linking. We found that the thermal diffusivity of the silk film is increased by the formation of β-sheet structures and dityrosine between Tyr residues adjacent to the β-sheet structures. Our results demonstrate the applicability of silk proteins as material components for thermally conductive biopolymer-based materials.

A novel ternary magnetic nanobiocomposite based on tragacanth-silk fibroin hydrogel for hyperthermia and biological properties

This study involves the development of a new nanocomposite material for use in biological applications. The nanocomposite was based on tragacanth hydrogel (TG), which was formed through cross-linking of Ca2+ ions with TG polymer chains. The utilization of TG hydrogel and silk fibroin as natural compounds has enhanced the biocompatibility, biodegradability, adhesion, and cell growth properties of the nanobiocomposite. This advancement makes the nanobiocomposite suitable for various biological applications, including drug delivery, wound healing, and tissue engineering. Additionally, Fe3O4 magnetic nanoparticles were synthesized in situ within the nanocomposite to enhance its hyperthermia efficiency. The presence of hydrophilic groups in all components of the nanobiocomposite allowed for good dispersion in water, which is an important factor in increasing the effectiveness of hyperthermia cancer therapy. Hemolysis and 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assays were conducted to evaluate the safety and efficacy of the nanobiocomposite for in-vivo applications. Results showed that even at high concentrations, the nanobiocomposite had minimal hemolytic effects. Finally, the hyperthermia application of the hybrid scaffold was evaluated, with a maximum SAR value of 41.2 W/g measured in the first interval.

An injectable and photocurable methacrylate-silk fibroin/nano-hydroxyapatite hydrogel for bone regeneration through osteoimmunomodulation

Tissue engineering has emerged as a promising approach for addressing bone defects. Most of the traditional 3D printing materials predominantly relying on polymers and ceramics. Although these materials exhibit superior osteogenic effects, their gradual degradation poses a limitation. Digital light processing (DLP) 3D bioprinting that uses natural biomaterials as bioinks has become one of the promising strategies for bone regeneration. In this study, we introduce a hydrogel biomaterial derived from silk fibroin (SF). Notably, we present the novel integration of nano-hydroxyapatite (nHA) into the hydrogel, forming a composite hydrogel that rapidly cross-links upon initiation. Moreover, we demonstrate the loading of nHA through non-covalent bonds in SilMA. In vitro experiments reveal that composite hydrogel scaffolds with 10 % nHA exhibit enhanced osteogenic effects. Transcriptomic analysis indicates that the composite hydrogel promotes bone regeneration by inducing M2 macrophage polarization. Furthermore, rat femoral defect experiments validate the efficacy of SilMA/nHA10 in bone regeneration. This study synthesis of a simple and effective composite hydrogel bioink for bone regeneration, presenting a novel strategy for the future implementation of digital 3D printing technology in bone tissue engineering.

Protein-based microneedles for biomedical applications: A systematic review

Microneedles are minimally-invasive devices with the unique capability of bypassing physiological barriers. Hence, they are widely used for different applications from drug/vaccine delivery to diagnosis and cosmetic fields. Recently, natural biopolymers (particularly carbohydrates and proteins) have garnered attention as safe and biocompatible materials with tailorable features for microneedle construction. Several review articles have dealt with carbohydrate-based microneedles. This review aims to highlight the less-noticed role of proteins through a systematic search strategy based on the PRISMA guideline from international databases of PubMed, Science Direct, Scopus, and Google Scholar. Original English articles with the keyword "microneedle(s)" in their titles along with at least one of the keywords "biopolymers, silk, gelatin, collagen, zein, keratin, fish-scale, mussel, and suckerin" were collected and those in which the proteins undertook a structural role were screened. Then, we focused on the structures and applications of protein-based microneedles. Also, the unique features of some protein biopolymers that make them ideal for microneedle construction (e.g., excellent mechanical strength, self-adhesion, and self-assembly), as well as the challenges associated with them were reviewed. Altogether, the proteins identified so far seem not only promising for the fabrication of "better" microneedles in the future but also inspiring for designing biomimetic structural biopolymers with ideal characteristics.

Optimizing protein delivery rate from silk fibroin hydrogel using silk fibroin-mimetic peptides conjugation

Controlled release of proteins, such as growth factors, from biocompatible silk fibroin (SF) hydrogel is valuable for its use in tissue engineering, drug delivery, and other biological systems. To achieve this, we introduced silk fibroin-mimetic peptides (SFMPs) with the repeating unit (GAGAGS)n. Using green fluorescent protein (GFP) as a model protein, our results showed that SFMPs did not affect the GFP function when conjugated to it. The SFMP-GFP conjugates incorporated into SF hydrogel did not change the gelation time and allowed for controlled release of the GFP. By varying the length of SFMPs, we were able to modulate the release rate, with longer SFMPs resulting in a slower release, both in water at room temperature and PBS at 37 °C. Furthermore, the SF hydrogel with the SFMPs showed greater strength and stiffness. The increased β-sheet fraction of the SF hydrogel, as revealed by FTIR analysis, explained the gel properties and protein release behavior. Our results suggest that the SFMPs effectively control protein release from SF hydrogel, with the potential to enhance its mechanical stability. The ability to modulate release rates by varying the SFMP length will benefit personalized and controlled protein delivery in various systems.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as an insulin carrier in silk fibroin hydrogels for transdermal delivery via iontophoresis

In this study, silk fibroin (SF) was utilized as the starting material to fabricate physically crosslinked hydrogels. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was synthesized and characterized as a drug carrier, with insulin as the model drug. PEDOT:PSS, with a high electrical conductivity of 1666 ± 49 S cm-1, interacted with insulin molecules via electrostatic interaction by replacing the dopant PSS molecules. Insulin-loaded PEDOT:PSS embedded in the SF hydrogel resulted in an increase in the degree of swelling, pore size, and mesh size of the hydrogel. In the in vitro release and release-permeation experiments, the amounts of insulin release and release-permeation were investigated using a modified Franz diffusion cell, under the effects of SF concentrations, electric fields, and pH values. The amounts of insulin release and release-permeation from the pristine SF hydrogel and the PEDOT:PSS/SF hydrogel followed the power laws with the scaling exponents close to 0.5, indicating the Fickian diffusion or the concentration gradient. Under electric fields, with or without PEDOT:PSS used as the drug carrier, the insulin amount and diffusion coefficient were shown to increase with the increasing electric field due to the electro-repulsive forces between the cathode and insulin molecules and SF chains, electroosmosis, and SF matrix swelling. The SF hydrogel and PEDOT:PSS as the drug carrier are demonstrated herein as new components in the transdermal delivery system for the iontophoretically controlled insulin basal release applicable to diabetes patients.

Fabrication of green composite hand knitted silk mesh reinforced with silk hydrogel

Soft tissue defects like hernia and post-surgical fistula formation can be resolved with modern biomaterials in the form of meshes without post-operative complications. In the present study hand knitted silk meshes were surface coated with regenerated silk fibroin hydrogel and pure natural extracts. Two phytochemicals (Licorice extract (LE) and Bearberry extract (BE)) and the two honeybee products (royal jelly (RJ) and honey (HE)) were incorporated separately to induce antibacterial, anti-inflammatory, and wound healing ability to the silk hydrogel coated knitted silk meshes. Meshes were dip coated with a blend of 4 % silk hydrogel (w/v) and 5 % extracts. Dried modified meshes were characterized using SEM, DMA, GC-MS and FTIR. Antimicrobial testing, in-vitro cytotoxicity, in-vitro wound healing and Q-RT-PCR were also performed. SEM analysis concluded that presence of coating reduced the pore size up to 47.7 % whereas, fiber diameter was increased up to 17.9 % as compared to the control. The presence of coating on the mesh improved the mechanical strength/Young's modulus by 1602.8 %, UTS by 451.7 % and reduced the % strain by 51.12 %. Sustained release of extracts from MHRJ (62.9 % up to 72 h) confirmed that it can induce antibacterial activity against surgical infections. Cytocompatibility testing and gene expression results suggest that out of four variables MHRJ presented best cell viability, % wound closure and expression of wound healing marker genes. In-vivo analyses in rat hernia model were carried out using only MHRJ variant, which also confirmed the non- toxic nature and wound healing characteristics of the modified mesh. The improved cell proliferation and activated wound healing in vitro and in vivo suggested that MHRJ could be a valuable candidate to promote cell infiltration and activate soft tissue and hernia repair as a biomedical implant.

Microfibre-Functionalised Silk Hydrogels

Silk hydrogels have shown potential for tissue engineering applications, but several gaps and challenges, such as a restricted ability to form hydrogels with tuned mechanics and structural features, still limit their utilisation. Here, Bombyx mori and Antheraea mylitta (Tasar) silk microfibres were embedded within self-assembling B. mori silk hydrogels to modify the bulk hydrogel mechanical properties. This approach is particularly attractive because it creates structured silk hydrogels. First, B. mori and Tasar microfibres were prepared with lengths between 250 and 500 μm. Secondary structure analyses showed high beta-sheet contents of 61% and 63% for B. mori and Tasar microfibres, respectively. Mixing either microfibre type, at either 2% or 10% (w/v) concentrations, into 3% (w/v) silk solutions during the solution-gel transition increased the initial stiffness of the resulting silk hydrogels, with the 10% (w/v) addition giving a greater increase. Microfibre addition also altered hydrogel stress relaxation, with the fastest stress relaxation observed with a rank order of 2% (w/v) > 10% (w/v) > unmodified hydrogels for either fibre type, although B. mori fibres showed a greater effect. The resulting data sets are interesting because they suggest that the presence of microfibres provided potential 'flow points' within these hydrogels. Assessment of the biological responses by monitoring cell attachment onto these two-dimensional hydrogel substrates revealed greater numbers of human induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) attached to the hydrogels containing 10% (w/v) B. mori microfibres as well as 2% (w/v) and 10% (w/v) Tasar microfibres at 24 h after seeding. Cytoskeleton staining revealed a more elongated and stretched morphology for the cells growing on hydrogels containing Tasar microfibres. Overall, these findings illustrate that hydrogel stiffness, stress relaxation and the iPSC-MSC responses towards silk hydrogels can be tuned using microfibres.

Evaluation of heat transfer in porous scaffolds under cryogenic treatment: a numerical study

The present work had evaluated the effect of cryogenic treatment (233 K) on the degradation of polymeric biomaterial using a numerical model. The study on effect of cryogenic temperature on mechanical properties of cell-seeded biomaterials is very limited. However, no study had reported material degradation evaluation. Different structures of silk-fibroin-poly-electrolyte complex (SFPEC) scaffolds had been designed by varying hole distance and hole diameter, with reference to existing literature. The size of scaffolds were maintained at 5 [Formula: see text] 5 mm2. Current study evaluates the effect of cryogenic temperature on mechanical properties (corelated to degradation) of scaffold. Six parameters related to scaffold degradation: heat transfer, deformation gradient, stress, strain, strain tensor, and displacement gradient were analyzed for three different cooling rates (- 5 K/min, - 2 K/min, and - 1 K/min). Scaffold degradation had been evaluated in the presence of water and four different concentrations of cryoprotectant solution. Heat distribution at various points (points_base, point_wall and point_core) on the region of interest (ROI) was found similar for different cooling rates of the system. Thermal stress was found developing proportional to cooling rate, which leads to minimal variation in thermal stress over time. Strain tensor was found gradually decreasing due to attenuating response of deformation gradient. In addition to that, dipping down of cryogenic temperature had prohibited the movement of molecules in the crystalline structure which had restricting the displacement gradient. It was found that uniform distribution of desired heat at different cooling rates has the ability to minimize the responses of other scaffold degradation parameters. It was found that the rates of change in stress, strain, and strain tensor were minimal at different concentrations of cryoprotectant. The present study had predicted the degradation behavior of PEC scaffold under cryogenic temperature on the basis of explicit mechanical properties.

Silk wastes and autoclaved degumming as an alternative for a sustainable silk process

Silk degumming is considered the first point in the preparation of silk-based materials since this process could modify the silk fiber and the properties of its related products. This study evaluated the differences in morphology, secondary structure, amino acid content, thermal stability, and mechanical properties of two types of raw materials, defective cocoons (DC) and silk fibrous waste (SW), degummed by chemical (C) and autoclaving (A) methods. Subsequently, silk fibroin films were prepared by dissolving each type of degummed fibers, and thermal and structural films properties were determined. The findings demonstrated that autoclaving is an efficient alternative to remove silk sericin, as the resulting fibers presented improved structural, thermal, and mechanical properties compared to those obtained by the chemical method. For films preparation, autoclave resulted in a good option, but dissolution parameters need to be adjusted for defective cocoons. Furthermore, similarities between the physicochemical properties of fibers and films from both fibrous wastes suggest that SW is a promising raw material for producing fibrous resources and regenerated silk fibroin materials. Overall, these findings suggest new recycling methods for fibrous waste and by-products generated in the silk textile production process.

Advanced Mechanical Testing Technologies at the Cellular Level: The Mechanisms and Application in Tissue Engineering

Mechanics, as a key physical factor which affects cell function and tissue regeneration, is attracting the attention of researchers in the fields of biomaterials, biomechanics, and tissue engineering. The macroscopic mechanical properties of tissue engineering scaffolds have been studied and optimized based on different applications. However, the mechanical properties of the overall scaffold materials are not enough to reveal the mechanical mechanism of the cell-matrix interaction. Hence, the mechanical detection of cell mechanics and cellular-scale microenvironments has become crucial for unraveling the mechanisms which underly cell activities and which are affected by physical factors. This review mainly focuses on the advanced technologies and applications of cell-scale mechanical detection. It summarizes the techniques used in micromechanical performance analysis, including atomic force microscope (AFM), optical tweezer (OT), magnetic tweezer (MT), and traction force microscope (TFM), and analyzes their testing mechanisms. In addition, the application of mechanical testing techniques to cell mechanics and tissue engineering scaffolds, such as hydrogels and porous scaffolds, is summarized and discussed. Finally, it highlights the challenges and prospects of this field. This review is believed to provide valuable insights into micromechanics in tissue engineering.

Evaluation of Silk Fibroin/Gellan Gum Hydrogels with Controlled Molecular Weight through Silk Fibroin Hydrolysis for Tissue Engineering Application

Hydrogel is a versatile material that can be manipulated to achieve the desired physicochemical properties, such as stiffness, pore size, and viscoelasticity. Traditionally, these properties have been controlled through parameters such as concentration and pH adjustments. In this study, we focused on exploring the potential of hydrolyzed silk fibroin (HSF) as a molecular weight-modulating agent to control the physicochemical properties of double-composite hydrogels. We developed a synergistic dual-crosslinked hydrogel by combining ionically crosslinked silk fibroin with gellan gum (GG). The hydrolysis of silk fibroin not only enhanced its hydrophilicity but also enabled adjustments in its mechanical properties, including the pore size, initial modulus elasticity, and relaxation time. Moreover, biocompatibility assessments based on cell viability tests confirmed the potential of these hydrogels as biocompatible materials. By highlighting the significance of developing an HSF/GG dual-crosslinked hydrogel, this study contributes to the advancement of novel double-composite hydrogels with remarkable biocompatibility. Overall, our findings demonstrate the capability of controlling the mechanical properties of hydrogels through molecular weight modulation via hydrolysis and highlight the development of a biocompatible HSF/GG dual-crosslinked hydrogel with potential biomedical applications.

Manufacture of Bilayered Composite Hydrogels with Strong, Elastic, and Tough Properties for Osteochondral Repair Applications

Layered composite hydrogels have been considered attractive materials for use in osteochondral repair and regeneration. These hydrogel materials should be mechanically strong, elastic, and tough besides fulfilling some basic requirements such as biocompatibility and biodegradability. A novel type of bilayered composite hydrogel with multi-network structures and well-defined injectability was thus developed for osteochondral tissue engineering using chitosan (CH), hyaluronic acid (HA), silk fibroin (SF), CH nanoparticles (NPs), and amino-functionalized mesoporous bioglass (ABG) NPs. CH was combined with HA and CH NPs to build the chondral phase of the bilayered hydrogel, and CH, SF, and ABG NPs were used together to construct the subchondral phase of the bilayer hydrogel. Rheological measurements showed that the optimally achieved gels assigned to the chondral and subchondral layers had their elastic moduli of around 6.5 and 9.9 kPa, respectively, with elastic modulus/viscous modulus ratios higher than 36, indicating that they behaved like strong gels. Compressive measurements further demonstrated that the bilayered hydrogel with an optimally formulated composition had strong, elastic, and tough characteristics. Cell culture revealed that the bilayered hydrogel had the capacity to support the in-growth of chondrocytes in the chondral phase and osteoblasts in the subchondral phase. Results suggest that the bilayered composite hydrogel can act as an injective biomaterial for osteochondral repair applications.

Polysaccharide-protein microparticles based-scaffolds to recover soft tissue loss in mild periodontitis

Periodontal regeneration is extremely limited and unpredictable due to structural complications, as it requires the simultaneous restoration of different tissues, including cementum, gingiva, bone, and periodontal ligament. In this work, spray-dried microparticles based on green materials (polysaccharides - gums - and a protein - silk fibroin) are proposed to be implanted in the periodontal pocket as 3D scaffolds during non-surgical treatments, to prevent the progression of periodontal disease and to promote the healing in mild periodontitis. Arabic or xanthan gum have been associated to silk fibroin, extracted from Bombyx mori cocoons, and loaded with lysozyme due to its antibacterial properties. The microparticles were prepared by spray-drying and cross-linked by water vapor annealing, inducing the amorphous to semi-crystalline transition of the protein component. The microparticles were characterized in terms of their chemico-physical features (SEM, size distribution, structural characterization - FTIR and SAXS, hydration and degradation properties) and preclinical properties (lysozyme release, antibacterial properties, mucoadhesion, in vitro cells adhesion and proliferation and in vivo safety on a murine incisional wound model). The encouraging preclinical results highlighted that these three-dimensional (3D) microparticles could provide a biocompatible platform able to prevent periodontitis progression and to promote the healing of soft tissues in mild periodontitis.

Biocompatibility of silk methacrylate/gelatin-methacryloyl composite hydrogel and its feasibility as a vascular tissue engineering scaffold

Silk methacrylate (SilMA) has been studied extensively due to its ability to modify Silk fibroin (SF) by increasing the water solubility and enhancing the mechanical properties of SF hydrogels. However, SilMA hydrogels are generally soft with weak mechanical properties. In order to enhance the mechanical properties of hydrogel scaffolds, we used liquid nitrogen to modify SilMA to obtain a novel N₂-SilMA/gelatin-methacryloyl (GelMA) composite hydrogel. N₂-SilMA was successfully detected by Fourier transform infrared (FTIR) spectroscopy and ¹H nuclear magnetic resonance. Scanning electron microscope showed that the composite hydrogel still had certain arrangement characteristics of SF and dense pores which met the necessary conditions for the cell scaffold. The mechanical tests showed that the mechanical properties of SilMA were greatly enhanced after modification at ultra-low temperature. We evaluated its cytocompatibility and biocompatibility, and the results showed that the composite scaffold promoted the growth of cells. Different types of composite hydrogels were injected into ICR mice and the results showed a stable scaffold structure in vivo, suggesting their ability to promote angiogenesis. In conclusion, the N₂-SilMA/GelMA composite hydrogel had better mechanical properties, excellent cytocompatibility, and biological properties compared to the other groups.

An Injectable Enzymatically Crosslinked and Mechanically Tunable Silk Fibroin/Chondroitin Sulfate Chondro‐Inductive Hydrogel

An injectable hybrid hydrogel is synthesized, comprising silk fibroin (SF) and chondroitin sulfate (CS) through di‐tyrosine formation bond of SF chains. CS and SF are reported with excellent biocompatibility as tissue engineering scaffolds. Nonetheless, the rapid degradation rate of pure CS scaffolds presents a challenge to effectively recreate articular cartilage. As CS is one of the cartilage extracellular matrix (ECM) components, it has the potential to enhance the biological activity of SF‐based hydrogel in terms of cartilage repair. Therefore, altering the CS concentrations (i.e., 0 wt%, 0.25 wt%, 0.5 wt%, 1 wt%, and 2 wt%), which are interpenetrated between SF β‐sheets and chains, can potentially adjust the physical, chemical, and mechanical features of these hybrid hydrogels. The formation of β‐sheets by 30 days of immersion in de‐ionized (DI) water can improve the compression strength of the SF/CS hybrid hydrogels in comparison with the same SF/CS hybrid hydrogels in the dried state. Biological investigation and observation depicts proper cell attachment, proliferation and cell viability for C28/I2 cells. Gene expression of sex‐determining region YBox 9 (SOX9), Collagen II α1, and Aggrecan (AGG) exhibits positive C3H10T1/2 growth and expression of cartilage‐specific genes in the 0.25 wt% and 0.5 wt% SF/CS hydrogels.

Freeze–thaw hydrogel fabrication method: basic principles, synthesis parameters, properties, and biomedical applications

Hydrogel is being broadly studied due to their tremendous properties, such as swelling behavior and biocompatibility. Numerous review articles have discussed hydrogel polymer types, hydrogel synthesis methods, hydrogel properties, and hydrogel applications. Hydrogel can be synthesized by physical and chemical cross-linking methods. One type of the physical cross-linking method is freeze-thaw (F–T), which works based on the crystallization process of the precursor solution to form a physical cross-link. To date, there has been no review paper which discusses the F–T technique specifically and comprehensively. Most of the previous review articles that exposed the hydrogel synthesis method usually mentioned the F–T process as a small part of the physical cross-linking method. This review attempts to discuss the F–T hydrogel specifically and comprehensively. In more detail, this review covers the basic principles of hydrogel formation in an F–T way, the parameters that influence hydrogel formation, the properties of the hydrogel, and its application in the biomedical field.

Additively manufactured Bi-functionalized bioceramics for reconstruction of bone tumor defects

Bone tissue exhibits critical factors for metastatic cancer cells and represents an extremely pleasant spot for further growth of tumors. The number of metastatic bone lesions and primary tumors that arise directly from cells comprised in the bone milieu is constantly increasing. Bioceramics have recently received significant attention in bone tissue engineering and local drug delivery applications. Additionally, additive manufacturing of bioceramics offers unprecedented advantages including the possibilities to fill irregular voids after the resection and fabricate patient-specific implants. Herein, we investigated the recent advances in additively manufactured bioceramics and ceramic-based composites that were used in the local bone tumor treatment and reconstruction of bone tumor defects. Furthermore, it has been extensively explained how to bi-functionalize ceramics-based biomaterials and what current limitations impede their clinical application. We have also discussed the importance of further development into ceramic-based biomaterials and molecular biology of bone tumors to: (1) discover new potential therapeutic targets to enhance conventional therapies, (2) local delivering of bio-molecular agents in a customized and "smart" way, and (3) accomplish a complete elimination of tumor cells in order to prevent tumor recurrence formation. We emphasized that by developing the research focus on the introduction of novel 3D-printed bioceramics with unique properties such as stimuli responsiveness, it will be possible to fabricate smart bioceramics that promote bone regeneration while minimizing the side-effects and effectively eradicate bone tumors while promoting bone regeneration. In fact, by combining all these therapeutic strategies and additive manufacturing, it is likely to provide personalized tumor-targeting therapies for cancer patients in the foreseeable future. STATEMENT OF SIGNIFICANCE: To increase the survival rates of cancer patients, different strategies such as surgery, reconstruction, chemotherapy, radiotherapy, etc have proven to be essential. Nonetheless, these therapeutic protocols have reached a plateau in their effectiveness due to limitations including drug resistance, tumor recurrence after surgery, toxic side-effects, and impaired bone regeneration following tumor resection. Hence, novel approaches to specifically and locally attack cancer cells, while also regenerating the damaged bony tissue, have being developed in the past years. This review sheds light to the novel approaches that enhance local bone tumor therapy and reconstruction procedures by combining additive manufacturing of ceramic biomaterials and other polymers, bioactive molecules, nanoparticles to affect bone tumor functions, metabolism, and microenvironment.

Biomimetic Hydroxyapatite Composite Coatings with a Variable Morphology Mediated by Silk Fibroin and Its Derived Peptides Enhance the Bioactivity on Titanium

Various modifications performed on titanium alloy surfaces are shown to improve osteointegration and promote the long-term success of implants. In this work, a bioactive nanostructured hydroxyapatite (HA) composite coating with a variable morphology mediated by silk fibroin (SF) and its derived peptides (Cs) was prepared. Numerous experimental techniques were used to characterize the constructed coatings in terms of morphology, roughness, hydrophilicity, protein adsorption, in vitro biomineralization, and adhesion strength. The mixed protein layer with different contents of SF and Cs exhibited different secondary structures at different temperatures, effectively mediating the electrodeposited HA layer with different characteristics and finally forming proteins/HA composite coatings with versatile morphologies. The addition of Cs significantly improved the hydrophilicity and protein adsorption capacity of the composite coatings, while the electrodeposition of the HA layer effectively enhanced the adhesion between the composite coatings and Ti surface. In the in vitro mineralization experiments, all the composite coatings exhibited excellent apatite formation ability. Moreover, the composite coatings showed excellent cell growth and proliferation activity. Osteogenic induction experiments revealed that the coating could significantly increase the expression of specific osteogenic markers, including ALP, Col-I, Runx-2, and OCN. Overall, the proposed modification of the Ti implant surface by protein/HA coatings had good potential for clinical applications in enhancing bone induction and osteogenic activity of implants.

Biomedical applications of silk and its role for intervertebral disc repair

Intervertebral disc (IVD) degeneration (IDD) is the main contributor to chronic low back pain. To date, the present therapies mainly focus on treating the symptoms caused by IDD rather than addressing the problem itself. For this reason, researchers have searched for a suitable biomaterial to repair and/or regenerate the IVD. A promising candidate to fill this gap is silk, which has already been used as a biomaterial for many years. Therefore, this review aims first to elaborate on the different origins from which silk is harvested, the individual composition, and the characteristics of each silk type. Another goal is to enlighten why silk is so suitable as a biomaterial, discuss its functionalization, and how it could be used for tissue engineering purposes. The second part of this review aims to provide an overview of preclinical studies using silk-based biomaterials to repair the inner region of the IVD, the nucleus pulposus (NP), and the IVD's outer area, the annulus fibrosus (AF). Since the NP and the AF differ fundamentally in their structure, different therapeutic approaches are required. Consequently, silk-containing hydrogels have been used mainly to repair the NP, and silk-based scaffolds have been used for the AF. Although most preclinical studies have shown promising results in IVD-related repair and regeneration, their clinical transition is yet to come.

Silk fibroin hydrogels for biomedical applications

Silk fibroin hydrogels occupy an essential position in the biomedical field due to their remarkable biological properties, excellent mechanical properties, flexible processing properties, as well as abundant sources and low cost. Herein, we introduce the unique structures and physicochemical characteristics of silk fibroin, including mechanical properties, biocompatibility, and biodegradability. Then, various preparation strategies of silk fibroin hydrogels are summarized, which can be divided into physical cross-linking and chemical cross-linking. Emphatically, the applications of silk fibroin hydrogel biomaterials in various biomedical fields, including tissue engineering, drug delivery, and wearable sensors, are systematically summarized. At last, the challenges and future prospects of silk fibroin hydrogels in biomedical applications are discussed.

Enhanced transdermal insulin basal release from silk fibroin (SF) hydrogels via iontophoresis

Insulin is the peptide hormone used to treat the diabetes patient. The hormone is normally taken by injection. The transdermal drug delivery system (TDDS) is an alternative route. The silk fibroin (SF) hydrogels were fabricated via solution casting as the insulin matrix. The release and release-permeation experiments of the insulin loaded SF hydrogels were carried out using a modified Franz-diffusion cell at 37 °C for 36 h, under the effects of SF concentrations, pH, and electric field. The release-permeation mechanism through the pig skin was from the Case-II transport with the constant release rate. The diffusion coefficient (D) increased with decreasing SF concentration due to a larger mesh size, and with increasing electric field due to the electroreplusive forces between the insulin and the SF hydrogels against the negatively-charged electrode, and the induced SF hydrogel expansion. The rate and amount of insulin release-permeation became relatively lower as it required a longer time to generate aqueous pathways through the pig skin. The present SF hydrogels are demonstrated here deliver insulin with the required constant release rate, and the suitable amount within a prescribed duration.