Engineering DN hydrogels from regenerated silk fibroin and poly(N-vinylcaprolactam)

Temperature-responsive hydrogel prepared from N-vinyl-ε-caprolactam Pickering emulsions stabilized by cationic cellulose nanocrystals for preservative delivery in food packaging

Hydrogels show potential for application in the anti-corrosion of food preservation packaging. However, hydrogels capable of modulating the release rate kinetics of preservatives under elevated temperature conditions for food preservation packaging remain underexplored. Herein, cationic cellulose nanocrystals (AH-CNCs) were employed as emulsifiers to stabilize N-vinyl-ε-caprolactam (NVCL) and the temperature-responsive hydrogel was fabricated via free radical polymerization. This novel hydrogel enables control the release rate of preservatives by adjusting the addition amount of AH-CNCs under conditions exceeding the lower critical solution temperature (LCST). Below the LCST, increasing AH-CNC contents systematically enhance the swelling rate, concurrently reducing pore size and augmenting the structural stability of the hydrogel matrix. Upon surpassing the LCST, the release rate of preservative salicylaldehyde (SA) can be controlled by tuning the AH-CNCs contents and leveraging electrostatic adsorption between AH-CNCs with positive properties and negatively charged SA. Notably, fruit visualization assays validated that the temperature-responsive hydrogel matrix effectively extends the shelf life of fruits via dual-mode preservative delivery. Consequently, this temperature-responsive hydrogel demonstrates significant potential for practical implementation in smart food preservation packaging applications.

Regeneration of articular cartilage defects: Therapeutic strategies and perspectives

Articular cartilage (AC), a bone-to-bone protective device made of up to 80% water and populated by only one cell type (i.e. chondrocyte), has limited capacity for regeneration and self-repair after being damaged because of its low cell density, alymphatic and avascular nature. Resulting repair of cartilage defects, such as osteoarthritis (OA), is highly challenging in clinical treatment. Fortunately, the development of tissue engineering provides a promising method for growing cells in cartilage regeneration and repair by using hydrogels or the porous scaffolds. In this paper, we review the therapeutic strategies for AC defects, including current treatment methods, engineering/regenerative strategies, recent advances in biomaterials, and present emphasize on the perspectives of gene regulation and therapy of noncoding RNAs (ncRNAs), such as circular RNA (circRNA) and microRNA (miRNA).

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.

3D Bioprinting Technology and Hydrogels Used in the Process

3D bioprinting has gained visibility in regenerative medicine and tissue engineering due to its applicability. Over time, this technology has been optimized and adapted to ensure a better printability of bioinks and biomaterial inks, contributing to developing structures that mimic human anatomy. Therefore, cross-linked polymeric materials, such as hydrogels, have been highly targeted for the elaboration of bioinks, as they guarantee cell proliferation and adhesion. Thus, this short review offers a brief evolution of the 3D bioprinting technology and elucidates the main hydrogels used in the process.

NVCL-Based Hydrogels and Composites for Biomedical Applications: Progress in the Last Ten Years

Hydrogels consist of three-dimensionally crosslinked polymeric chains, are hydrophilic, have the ability to absorb other molecules in their structure and are relatively easy to obtain. However, in order to improve some of their properties, usually mechanical, or to provide them with some physical, chemical or biological characteristics, hydrogels have been synthesized combined with other synthetic or natural polymers, filled with inorganic nanoparticles, metals, and even polymeric nanoparticles, giving rise to composite hydrogels. In general, different types of hydrogels have been synthesized; however, in this review, we refer to those obtained from the thermosensitive polymer poly(N-vinylcaprolactam) (PNVCL) and we focus on the definition, properties, synthesis techniques, nanomaterials used as fillers in composites and mainly applications of PNVCL-based hydrogels in the biomedical area. This type of material has great potential in biomedical applications such as drug delivery systems, tissue engineering, as antimicrobials and in diagnostic and bioimaging.

Polymeric Hydrogels for Controlled Drug Delivery to Treat Arthritis

Rheumatoid arthritis (RA) and osteoarthritis (OA) are disabling musculoskeletal disorders that affect joints and cartilage and may lead to bone degeneration. Conventional delivery of anti-arthritic agents is limited due to short intra-articular half-life and toxicities. Innovations in polymer chemistry have led to advancements in hydrogel technology, offering a versatile drug delivery platform exhibiting tissue-like properties with tunable drug loading and high residence time properties This review discusses the advantages and drawbacks of polymeric materials along with their modifications as well as their applications for fabricating hydrogels loaded with therapeutic agents (small molecule drugs, immunotherapeutic agents, and cells). Emphasis is given to the biological potentialities of hydrogel hybrid systems/micro-and nanotechnology-integrated hydrogels as promising tools. Applications for facile tuning of therapeutic drug loading, maintaining long-term release, and consequently improving therapeutic outcome and patient compliance in arthritis are detailed. This review also suggests the advantages, challenges, and future perspectives of hydrogels loaded with anti-arthritic agents with high therapeutic potential that may alter the landscape of currently available arthritis treatment modalities.

3D Printable Soy/Silk Hybrid Hydrogels for Tissue Engineering Applications

The development of protein-based 3D printable hydrogel systems with tunable structure and properties is a critical challenge in contemporary biomedicine. Particularly, 3D printing of modular hydrogels comprising different types of protein tertiary structure, such as globular and fibrous, has not yet been achieved. Here we report the extrusion-based 3D printing of hybrid hydrogels photochemically co-cross-linked between globular soy protein isolate (SPI) and fibrous silk fibroin (SF) for the first time. The hierarchical structure and organization of pristine SPI and SF, and 1:3 (SPI/SF) hybrid inks under various shear stress were investigated using in situ rheology combined with small-/ultra-small-angle neutron scattering (Rheo-SANS/USANS). The hybrid ink exhibited an isotropic mass fractal structure that was stable between tested shear rates of 0.1 and 100 s^-1 (near printing shear). The kinetics of sol-gel transition during the photo-cross-linking reaction and the micromechanical properties of fabricated hydrogels were investigated using photorheology and atomic force microscopy, where the hybrid hydrogels exhibited tunable storage and Young's moduli in the range of 13-29 and 214-811 kPa, respectively. The cross-link density and printing accuracy of hybrid hydrogels and inks were observed to increase with the increase in SF content. The 3D printed hybrid hydrogels exhibited a micropore size larger than that of solution casted hydrogels; where the 3D printed 1:3 (SPI/SF) hybrid hydrogel showed a pore size about 7.6 times higher than that of the casted hydrogel. Moreover, the fabricated hybrid hydrogels exhibit good mouse fibroblast cell attachment, viability, and proliferation, demonstrating their potential for tissue engineering applications.

Functional silk fibroin hydrogels: preparation, properties and applications

Over the past decade, the hydrogels prepared from silk fibroin have received immense research attention due to the advantages of safe nature, biocompatibility, controllable degradation and capability to combine with other materials. They have broad application prospects in biomedicine and other fields. However, the traditional silk protein hydrogels have a simple network structure and single functionality, thus, leading to poor adaptability towards complex application environments. As a result, the application fields and development have been significantly restricted. However, the development of functional silk protein hydrogels has provided the opportunities to overcome the limitations of the silk protein hydrogels. In recent years, the functional design of the silk protein hydrogels and their potential applications have attracted the attention of scholars worldwide. Nevertheless, a comprehensive review on functional silk protein hydrogels is missing so far. In order to gain an in-depth understanding of the development status of the functional silk protein hydrogels, this article reviews the current status of the preparation, properties and application of the functional silk protein hydrogels. The article first briefly introduces the current cross-linking methods (including physical and chemical cross-linking), principles, advantages and limitations of the silk protein hydrogels. Subsequently, the types of functional silk protein hydrogels (e.g., high strength, injectable, self-healing, adhesive, conductive, environmental stimuli-responsive, 3D printable, etc.) and design principles for functional implementation have been introduced. Next, based on the advantages of the various functional aspects of the silk protein hydrogels, the applications of these hydrogels in the biomedical field (tissue engineering, sustained drug release, wound repair, adhesives, etc.) and bioelectronics are reviewed. Finally, the development prospects and challenges associated with silk protein functional hydrogels have been analyzed. It is hoped that this study will contribute towards the future innovation of the silk protein hydrogels by promoting the rational design of new mechanisms and successful realization of the target applications.

Silk fibroins in multiscale dimensions for diverse applications

Silk biomaterials in different forms such as particles, coatings and their assemblies, represent unique type of materials in multiple scales and dimensions. Herein, we provide an overview of multi-scale silk fibroin materials including silk particles, silk coatings and silk assemblies, each of which represents a unique type of material with wide range of applications. They feature tunable structures and mechanical properties with excellent biocompatibility, which are essentially required for various biomedical and drug delivery applications. The review focuses on bringing a new perspective on the utilization of regenerated silk fibroins in modern biomedicine by beginning with the fabrication of silk in multiscale dimensions and their state-of-the-art applications in various biomedical and bioelectronic fields. It covers the fundamentals of processing silk fibroins in multi-dimensions (sizes and shapes) with a specific emphasis on its structural tunability at various length scales (nano-micro) by using the latest fabrication methods/mechanisms and advanced fabrication technologies, followed by their recent applications in diverse fields of biomedicine.

Bioprintable tough hydrogels for tissue engineering applications

Bioprinting is an advanced fabrication approach to engineer complex living structures as the conventional fabrication methods are incapable of integrating structural and biological complexities. It offers the versatility of printing different cell incorporated hydrogels (bioink) layer by layer; offering control over spatial resolution and cell distribution to mimic native tissue architectures. However, the bioprinting of tough hydrogels involve additional complexities, such as employing complex crosslinking or reinforcing mechanisms during printing and pre/post printing cellular activities. Solving this complexity requires attention from engineering, material science and cell biology perspectives. In this review, we discuss different types of bioprinting techniques with focus on current state-of-the-art in bioink formulations and pivotal characteristics of bioinks for tough hydrogel printing. We discuss the scope of transition from 3D to 4D bioprinting and some of the advanced characterization techniques for in-depth understanding of the 3D printing process from the microstructural perspective, along with few specific applications and conclude with the future perspectives in biofabrication of hydrogels for tissue engineering applications.

In situ-forming, mechanically resilient hydrogels for cell delivery

Injectable, in situ-forming hydrogels can improve cell delivery in tissue engineering applications by facilitating minimally invasive delivery to irregular defect sites and improving cell retention and survival. Tissues targeted for cell delivery often undergo diverse mechanical loading including high stress, high strain, and repetitive loading conditions. This review focuses on the development of hydrogel systems that meet the requirements of mechanical resiliency, cytocompatibility, and injectability for such applications. First, we describe the most important design considerations for maintaining the viability and function of encapsulated cells, for reproducing the target tissue morphology, and for achieving degradation profiles that facilitate tissue replacement. Models describing the relationships between hydrogel structure and mechanical properties are described, focusing on design principles necessary for producing mechanically resilient hydrogels. The advantages and limitations of current strategies for preparing cytocompatible, injectable, and mechanically resilient hydrogels are reviewed, including double networks, nanocomposites, and high molecular weight amphiphilic copolymer networks. Finally, challenges and opportunities are outlined to guide future research in this developing field.

Natural Polymer-Based Hydrogels with Enhanced Mechanical Performances: Preparation, Structure, and Property

Hydrogels based on natural polymers have bright application prospects in biomedical fields due to their outstanding biocompatibility and biodegradability. However, the poor mechanical performances of pure natural polymer-based hydrogels greatly limit their application prospects. Recently, a variety of strategies has been applied to prepare natural polymer-based hydrogels with enhanced mechanical properties, which generally exhibit stiffening, strengthening, and stretchable behaviors. This article summarizes the recent progress of natural polymer-based hydrogels with enhanced mechanical properties. From a structure point of view, four kinds of hydrogel are reviewed; double network hydrogels, nanocomposite hydrogels, click chemistry-based hydrogels, and supramolecular hydrogels. For each typical hydrogel, its preparation, structure, and mechanical performance are introduced in detail. At the end of this article, the current challenges and future prospects of hydrogels based on natural polymers are discussed and it is pointed out that 3D printing may offer a new platform for the development of natural polymer-based hydrogels.

Conductive regenerated silk-fibroin-based hydrogels with integrated high mechanical performances

Strong and tough RSF-based hydrogels that could be used as a strain sensor, a touch screen pen and an electronic skin were developed.

Tough Photocrosslinked Silk Fibroin/Graphene Oxide Nanocomposite Hydrogels

The development of protein-based hydrogels for tissue engineering applications is often limited by their mechanical properties. Herein, we present the facile fabrication of tough regenerated silk fibroin (RSF)/graphene oxide (GO) nanocomposite hydrogels by a photochemical cross-linking method. The RSF/GO composite hydrogels demonstrated soft and adhesive properties during initial stages of photocrosslinking (<2 min), which is not observed for the pristine RSF hydrogel, and rendered a tough and nonadhesive hydrogel upon complete cross-linking (10 min). The composite hydrogels exhibited superior tensile mechanical properties, increased β-sheet content, and decreased chain mobility compared to that of the pristine RSF hydrogels. The composite hydrogels demonstrated Young's modulus as high as ∼8 MPa, which is significantly higher than native cartilage (∼1.5 MPa), and tensile toughness as high as ∼2.4 MJ/m³, which is greater than that of electroactive polymer muscles and at par with RSF/GO composite membranes fabricated by layer-by-layer assembly. Small-angle scattering study reveals the hierarchical structure of photocrosslinked RSF hydrogels to comprise randomly distributed water-poor (hydrophobic) and water-rich (hydrophilic) regions at the nanoscale, whereas water pores and channels exhibiting fractal-like characteristics at the microscale. The size of hydrophobic domain (containing β-sheets) was observed to increase slightly with GO incorporation and/or alcohol post-treatment, whereas the size of the hydrophilic domain (intersheet distance containing random coils) was observed to increase significantly, which influences/affects water uptake capacity, cross-link density, and mechanical properties of hydrogels. The presented results have implications for both fundamental understanding of the structure-property relationship of RSF-based hydrogels and their technological applications.

Effects of magnesium silicate on the mechanical properties, biocompatibility, bioactivity, degradability, and osteogenesis of poly(butylene succinate)-based composite scaffolds for bone repair

The m-MS/PBSu scaffolds, with a hierarchical porous structure, could promote cell proliferation in vitro and bone regeneration in vivo.