Multi-network granular hydrogel with enhanced strength for 3D bioprinting

Enhanced stability of curcumin encapsulated in fish gelatin emulsions combined with γ-Polyglutamic acid

This study examined the rheological properties, interfacial characteristics, particle size, zeta potential, Turbiscan stability index (TSI), morphology, and encapsulation efficiency of curcumin (Cur) loaded fish gelatin (FG) emulsions modified with γ-polyglutamic acid (γ-PGA). The results showed that adding γ-PGA significantly increased curcumin encapsulation efficiency. At 0.3 mg/mL, FG emulsions had an encapsulation efficiency of 80.14 %, while FG-γ-PGA emulsions reached 90.35 %. The FG-γ-PGA emulsions also showed enhanced stability and resistance to phase separation, remaining stable for seven days, compared to three days for FG emulsions. After 24 h, the TSI of FG emulsions with 0.6 mg/mL Cur was 2.46, significantly higher than the 0.55 TSI for FG-γ-PGA emulsions at the same concentration. FG-γ-PGA emulsions had smaller droplet sizes, and analysis of interfacial characteristics, particle size, and zeta potential indicated better system stability than FG emulsions. These improved properties of FG-γ-PGA emulsions highlight their potential as efficient carriers for curcumin. Overall, the favorable characteristics of FG-γ-PGA emulsions suggest promising applications in the food industry, especially for developing functional foods with extended shelf life and enhanced nutritional benefits.

Methods to achieve tissue-mimetic physicochemical properties in hydrogels for regenerative medicine and tissue engineering

Hydrogels are water-swollen polymeric matrices with properties that are remarkably similar in function to the extracellular matrix. For example, the polymer matrix provides structural support and adhesion sites for cells in much of the same way as the fibers of the extracellular matrix. In addition, depending on the polymer used, bioactive sites on the polymer may provide signals to initiate certain cell behavior. However, despite their potential as biomaterials for tissue engineering and regenerative medicine applications, fabricating hydrogels that truly mimic the physicochemical properties of the extracellular matrix to physiologically-relevant values is a challenge. Recent efforts in the field have sought to improve the physicochemical properties of hydrogels using advanced materials science and engineering methods. In this review, we highlight some of the most promising methods, including crosslinking strategies and manufacturing approaches such as 3D bioprinting and granular hydrogels. We also provide a brief perspective on the future outlook of this field and how these methods may lead to the clinical translation of hydrogel biomaterials for tissue engineering and regenerative medicine applications.

Analysis of the adhesive secreting cells of Arion subfuscus: insights into the role of microgels in a tough, fast-setting hydrogel glue

The slug Arion subfuscus produces a tough, highly adhesive defensive secretion. This secretion is a flexible hydrogel that is toughened by a double network mechanism. While synthetic double network gels typically require extensive time to prepare, this slug creates a tough gel in seconds. To gain insight into how the glue forms a double-network hydrogel so rapidly, the secretory apparatus of this slug was analyzed. The goal was to determine how the major components of the glue were distributed and mixed. Most of the glue comes from two types of large unicellular glands; one secretes polyanionic polysaccharides in small, membrane-bound packets, the other secretes proteins that appear to form a cross-linked network. The latter gland shows distinct regions where cross-linking appears to be occurring. These regions are darker, more homogeneous and appear more solid than the rest of the secretory material. The enzyme catalase is highly abundant in these regions, as are basic proteins. These results suggest that a rapid oxidation event occurs in this protein-containing gland, triggering cross-linking before the glue is released. The cross-linked microgels would then join together after secretion to form a granular hydrogel. The polysaccharide-filled packets would be mixed and interspersed among these microgels and may contribute to joining them together. This is an unexpected and highly effective way to form a tough gel rapidly.

Injectable Granular Hydrogels Enable Avidity-Controlled Biotherapeutic Delivery

Protein therapeutics represent a rapidly growing class of pharmaceutical agents that hold great promise for the treatment of various diseases such as cancer and autoimmune dysfunction. Conventional systemic delivery approaches, however, result in off-target drug exposure and a short therapeutic half-life, highlighting the need for more localized and controlled delivery. We have developed an affinity-based protein delivery system that uses guest-host complexation between β-cyclodextrin (CD, host) and adamantane (Ad, guest) to enable sustained localized biomolecule presentation. Hydrogels were formed by the copolymerization of methacrylated CD and methacrylated dextran. Extrusion fragmentation of bulk hydrogels yielded shear-thinning and self-healing granular hydrogels (particle diameter = 32.4 ± 16.4 μm) suitable for minimally invasive delivery and with a high host capacity for the retention of guest-modified proteins. Bovine serum albumin (BSA) was controllably conjugated to Ad via EDC chemistry without affecting the affinity of the Ad moiety for CD (KD = 12.0 ± 1.81 μM; isothermal titration calorimetry). The avidity of Ad-BSA conjugates was directly tunable through the number of guest groups attached, resulting in a fourfold increase in the complex half-life (t1/2 = 5.07 ± 1.23 h, surface plasmon resonance) that enabled a fivefold reduction in protein release at 28 days. Furthermore, we demonstrated that the conjugation of Ad to immunomodulatory cytokines (IL-4, IL-10, and IFNγ) did not detrimentally affect cytokine bioactivity and enabled their sustained release. Our strategy of avidity-controlled delivery of protein-based therapeutics is a promising approach for the sustained local presentation of protein therapeutics and can be applied to numerous biomedical applications.

Emerging granular hydrogel bioinks to improve biological function in bioprinted constructs

Advancements in 3D bioprinting have been hindered by the trade-off between printability and biological functionality. Existing bioinks struggle to meet both requirements simultaneously. However, new types of bioinks composed of densely packed microgels promise to address this challenge. These bioinks possess intrinsic porosity, allowing for cell growth, oxygen and nutrient transport, and better immunomodulatory properties, leading to superior biological functions. In this review, we highlight key trends in the development of these granular bioinks. Using examples, we demonstrate how granular bioinks overcome the trade-off between printability and cell function. Granular bioinks show promise in 3D bioprinting, yet understanding their unique structure-property-function relationships is crucial to fully leverage the transformative capabilities of these new types of bioinks in bioprinting.

3D printed scaffolds based on hyaluronic acid bioinks for tissue engineering: a review

Hyaluronic acid (HA) is widely distributed in human connective tissue, and its unique biological and physicochemical properties and ability to facilitate biological structure repair make it a promising candidate for three-dimensional (3D) bioprinting in the field of tissue regeneration and biomedical engineering. Moreover, HA is an ideal raw material for bioinks in tissue engineering because of its histocompatibility, non-immunogenicity, biodegradability, anti-inflammatory properties, anti-angiogenic properties, and modifiability. Tissue engineering is a multidisciplinary field focusing on in vitro reconstructions of mammalian tissues, such as cartilage tissue engineering, neural tissue engineering, skin tissue engineering, and other areas that require further clinical applications. In this review, we first describe the modification methods, cross-linking methods, and bioprinting strategies for HA and its derivatives as bioinks and then critically discuss the strengths, shortcomings, and feasibility of each method. Subsequently, we reviewed the practical clinical applications and outcomes of HA bioink in 3D bioprinting. Finally, we describe the challenges and opportunities in the development of HA bioink to provide further research references and insights.

Preparation strategy of hydrogel microsphere and its application in skin repair

In recent years, hydrogel microsphere has attracted much attention due to its great potential in the field of skin repair. This paper reviewed the recent progress in the preparation strategy of hydrogel microsphere and its application in skin repair. In this review, several preparation methods of hydrogel microsphere were summarized in detail. In addition, the related research progress of hydrogel microspheres for skin repair was reviewed, and focused on the application of bioactive microspheres, antibacterial microspheres, hemostatic microspheres, and hydrogel microspheres as delivery platforms (hydrogel microspheres as a microcarrier of drugs, bioactive factors, or cells) in the field of skin repair. Finally, the limitations and future prospects of the development of hydrogel microspheres and its application in the field of skin repair were presented. It is hoped that this review can provide a valuable reference for the development of the preparation strategy of hydrogel microspheres and promote the application of hydrogel microspheres in skin repair.

Advances in Gelatin Bioinks to Optimize Bioprinted Cell Functions

Gelatin is a widely utilized bioprinting biomaterial due to its cell-adhesive and enzymatically cleavable properties, which improve cell adhesion and growth. Gelatin is often covalently cross-linked to stabilize bioprinted structures, yet the covalently cross-linked matrix is unable to recapitulate the dynamic microenvironment of the natural extracellular matrix (ECM), thereby limiting the functions of bioprinted cells. To some extent, a double network bioink can provide a more ECM-mimetic, bioprinted niche for cell growth. More recently, gelatin matrices are being designed using reversible cross-linking methods that can emulate the dynamic mechanical properties of the ECM. This review analyzes the progress in developing gelatin bioink formulations for 3D cell culture, and critically analyzes the bioprinting and cross-linking techniques, with a focus on strategies to optimize the functions of bioprinted cells. This review discusses new cross-linking chemistries that recapitulate the viscoelastic, stress-relaxing microenvironment of the ECM, and enable advanced cell functions, yet are less explored in engineering the gelatin bioink. Finally, this work presents the perspective on the areas of future research and argues that the next generation of gelatin bioinks should be designed by considering cell-matrix interactions, and bioprinted constructs should be validated against currently established 3D cell culture standards to achieve improved therapeutic outcomes.

3D Bioprinted Chitosan-Based Hydrogel Scaffolds in Tissue Engineering and Localised Drug Delivery

Bioprinting is an emerging technology with various applications in developing functional tissue constructs for the replacement of harmed or damaged tissues and simultaneously controlled drug delivery systems (DDSs) for the administration of several active substances, such as growth factors, proteins, and drug molecules. It is a novel approach that provides high reproducibility and precise control over the fabricated constructs in an automated way. An ideal bioink should possess proper mechanical, rheological, and biological properties essential to ensure proper function. Chitosan is a promising natural-derived polysaccharide to be used as ink because of its attractive properties, such as biodegradability, biocompatibility, low cost, and non-immunogenicity. This review focuses on 3D bioprinting technology for the preparation of chitosan-based hydrogel scaffolds for the regeneration of tissues delivering either cells or active substances to promote restoration.

In Situ Transformation of Electrospun Nanofibers into Nanofiber-Reinforced Hydrogels

Nanofiber-reinforced hydrogels have recently gained attention in biomedical engineering. Such three-dimensional scaffolds show the mechanical strength and toughness of fibers while benefiting from the cooling and absorbing properties of hydrogels as well as a large pore size, potentially aiding cell migration. While many of such systems are prepared by complicated processes where fibers are produced separately to later be embedded in a hydrogel, we here provide proof of concept for a one-step solution. In more detail, we produced core-shell nanofibers from the natural proteins zein and gelatin by coaxial electrospinning. Upon hydration, the nanofibers were capable of directly transforming into a nanofiber-reinforced hydrogel, where the nanofibrous structure was retained by the zein core, while the gelatin-based shell turned into a hydrogel matrix. Our nanofiber-hydrogel composite showed swelling to ~800% of its original volume and water uptake of up to ~2500% in weight. The physical integrity of the nanofiber-reinforced hydrogel was found to be significantly improved in comparison to a hydrogel system without nanofibers. Additionally, tetracycline hydrochloride was incorporated into the fibers as an antimicrobial agent, and antimicrobial activity against Staphylococcus aureus and Escherichia coli was confirmed.