Visible light-crosslinkable tyramine-conjugated alginate-based microgel bioink for multiple cell-laden 3D artificial organ

Visible light-induced simultaneous bioactive amorphous calcium phosphate mineralization and in situ crosslinking of coacervate-based injectable underwater adhesive hydrogels for enhanced bone regeneration

The field of bone tissue engineering is vital due to increasing bone disorders and limitations of traditional grafts. Injectable hydrogels offer minimally invasive solutions but often lack mechanical integrity and biological functionality, including osteoinductive capacity and structural stability under physiological conditions. To address these issues, we propose a coacervate-based injectable adhesive hydrogel that utilizes the dual functionality of in situ photocrosslinking and osteoinductive amorphous calcium phosphate formation, both of which are activated simultaneously by visible light irradiation. The developed hydrogel formulation integrated a photoreactive agent with calcium ions and phosphonodiol in a matrix of tyramine-conjugated alginate and RGD peptide-fused bioengineered mussel adhesive protein, promoting rapid setting, robust underwater adhesion, and bioactive mineral deposition. The hydrogel also exhibited superior mechanical properties, including enhanced underwater tissue adhesive strength and compressive resistance. In vivo evaluation using a rat femoral tunnel defect model confirmed the efficacy of the developed adhesive hydrogel in facilitating easy application to irregularly shaped defects through injection, rapid bone regeneration without the addition of bone grafts, and integration within the defect sites. This injectable adhesive hydrogel system holds significant potential for advancing bone tissue engineering, providing a versatile, efficient, and biologically favorable alternative to conventional bone repair methodologies.

Microgel-Based Smart Materials: How Do You Design a Microgel?

Microgels, which are submicrometer- to micrometer-sized hydrogels, have been investigated for more than four decades and are now widely applied in modern advanced smart materials. The "smartness" of microgel-based materials is attributed to their material composition, cross-linking strategy, and responsiveness to stimuli. These characteristics are inherently influenced and constrained by the fabrication method, which, in turn, affects the properties of the resulting microgel particles. While numerous studies have reported on the applications of microgels, the translation of fundamental research findings into practical applications remains limited. For example, while recent research in biomedical applications has focused on controlled and smart drug release based on novel environmentally responsive mechanisms, this Review highlights that the responsiveness still requires further refinement in terms of selectivity and precision. Moreover, the variety of drugs that can be used remains limited, and as this Review clarifies, microgel-based materials frequently do not possess adequate biocompatibility for biomedical applications. This Review initially summarizes the relationship between microgel synthesis techniques and their resulting properties. Furthermore, we observe that recent reports on the applications of microgels fall primarily into the categories of sensing, separation, biomedical applications, and additive manufacturing. These reports highlight recent advances in microgel applications; however, several challenges specific to each application area still need to be addressed. For instance, improving sensitivity and selectivity is a key concern in the sensing field. This Review identifies these challenges and proposes future directions for the advancement of microgel-based smart materials.

Bioprinting of mesenchymal stem cells in low concentration gelatin methacryloyl/alginate blends without ionic crosslinking of alginate

Bioprinting allows for the fabrication of tissue-like constructs by precise architecture and positioning of the bioactive hydrogels with living cells. This study was performed to determine the effect of very low concentrations of alginate (0.1, 0.3, and 0.5% w/v) on bioprinting of bone marrow mesenchymal stem cells (BMSC) in gelatin methacryloyl (GelMA; 5% w/v)/alginate blend. Furthermore, while GelMA was photocrosslinked in all bioprinted constructs, the effect of crosslinking alginate with calcium chloride on the physical and biological characteristics of the constructs was investigated. The inclusion of low-concentration alginate improved the viscosity and printability of the formulation as well as the compressive modulus of the hydrogels, particularly when ionically crosslinked with calcium chloride, compared with the group in that alginate was not crosslinked. However, the stability and degradability of 3D printed scaffolds that were only photocrosslinked were comparable to those that were additionally crosslinked with calcium chloride. Noteworthily, ionic crosslinking of alginate deteriorated the viability of BMSC. Morphology and growth of BMSC were improved by adding a low alginate concentration; however, ionic crosslinking of alginate affected these factors adversely. The findings of this study underscore the significance of carefully evaluating the crosslinking strategy used in conjunction with cell-laden GelMA/alginate hydrogel to achieve balanced physical and biological properties as well as less complicated post-bioprinting processing.

3D Biofabrication of Microporous Hydrogels for Tissue Engineering

Microporous hydrogels have been utilized in an unprecedented manner in the last few decades, combining materials science, biology, and medicine. Their microporous structure makes them suitable for wide applications, especially as cell carriers in tissue engineering and regenerative medicine. Microporous hydrogel scaffolds provide spatial and platform support for cell growth and proliferation, which can promote cell growth, migration, and differentiation, influencing tissue repair and regeneration. This review gives an overview of recent developments in the fabrication techniques and applications of microporous hydrogels. The fabrication of microporous hydrogels can be classified into two distinct categories: fabrication of non-injectable microporous hydrogels including freeze-drying microporous method, two-phase sacrificial strategy, 3D biofabrication technology, etc., and fabrication of injectable microporous hydrogels mainly including microgel assembly. Then, the biomedical applications of microporous hydrogels in cell carriers for tissue engineering, including but not limited to bone regeneration, nerve regeneration, vascular regeneration, and muscle regeneration are emphasized. Additionally, the ongoing and foreseeable applications and current limitations of microporous hydrogels in biomedical engineering are illustrated. Through stimulating innovative ideas, the present review paves new avenues for expanding the application of microporous hydrogels in tissue engineering.

Photocrosslinkable Biomaterials for 3D Bioprinting: Mechanisms, Recent Advances, and Future Prospects

Constructing scaffolds with the desired structures and functions is one of the main goals of tissue engineering. Three-dimensional (3D) bioprinting is a promising technology that enables the personalized fabrication of devices with regulated biological and mechanical characteristics similar to natural tissues/organs. To date, 3D bioprinting has been widely explored for biomedical applications like tissue engineering, drug delivery, drug screening, and in vitro disease model construction. Among different bioinks, photocrosslinkable bioinks have emerged as a powerful choice for the advanced fabrication of 3D devices, with fast crosslinking speed, high resolution, and great print fidelity. The photocrosslinkable biomaterials used for light-based 3D printing play a pivotal role in the fabrication of functional constructs. Herein, this review outlines the general 3D bioprinting approaches related to photocrosslinkable biomaterials, including extrusion-based printing, inkjet printing, stereolithography printing, and laser-assisted printing. Further, the mechanisms, advantages, and limitations of photopolymerization and photoinitiators are discussed. Next, recent advances in natural and synthetic photocrosslinkable biomaterials used for 3D bioprinting are highlighted. Finally, the challenges and future perspectives of photocrosslinkable bioinks and bioprinting approaches are envisaged.

Granular Hydrogels in Biofabrication: Recent Advances and Future Perspectives

Granular hydrogels, which are formed by densely packing microgels, are promising materials for bioprinting due to their extrudability, porosity, and modularity. However, the multidimensional parameter space involved in granular hydrogel design makes material optimization challenging. For example, design inputs such as microgel morphology, packing density, or stiffness can influence multiple rheological properties that govern printability and the behavior of encapsulated cells. This review provides an overview of fabrication methods for granular hydrogels, and then examines how important design inputs can influence material properties associated with printability and cellular responses across multiple scales. Recent applications of granular design principles in bioink engineering are described, including the development of granular support hydrogels for embedded printing. Further, the paper provides an overview of how key physical properties of granular hydrogels can influence cellular responses, highlighting the advantages of granular materials for promoting cell and tissue maturation after the printing process. Finally, potential future directions for advancing the design of granular hydrogels for bioprinting are discussed.

Bioinks for bioprinting using plant-derived biomaterials

Three-dimensional (3D) bioprinting has revolutionized tissue engineering by enabling the fabrication of complex and functional human tissues and organs. An essential component of successful 3D bioprinting is the selection of an appropriate bioink capable of supporting cell proliferation and viability. Plant-derived biomaterials, because of their abundance, biocompatibility, and tunable properties, hold promise as bioink sources, thus offering advantages over animal-derived biomaterials, which carry immunogenic concerns. This comprehensive review explores and analyzes the potential of plant-derived biomaterials as bioinks for 3D bioprinting of human tissues. Modification and optimization of these materials to enhance printability and biological functionality are discussed. Furthermore, cancer research and drug testing applications of the use of plant-based biomaterials in bioprinting various human tissues such as bone, cartilage, skin, and vascular tissues are described. Challenges and limitations, including mechanical integrity, cell viability, resolution, and regulatory concerns, along with potential strategies to overcome them, are discussed. Additionally, this review provides insights into the potential use of plant-based decellularized ECM (dECM) as bioinks, future prospects, and emerging trends in the use of plant-derived biomaterials for 3D bioprinting applications. The potential of plant-derived biomaterials as bioinks for 3D bioprinting of human tissues is highlighted herein. However, further research is necessary to optimize their processing, standardize their properties, and evaluate their long-termin vivoperformance. Continued advancements in plant-derived biomaterials have the potential to revolutionize tissue engineering and facilitate the development of functional and regenerative therapies for diverse clinical applications.

Polymer-Based Wound Dressings Loaded with Essential Oil for the Treatment of Wounds: A Review

Wound healing can result in complex problems, and discovering an effective method to improve the healing process is essential. Polymeric biomaterials have structures similar to those identified in the extracellular matrix of the tissue to be regenerated and also avoid chronic inflammation, and immunological reactions. To obtain smart and effective dressings, bioactive agents, such as essential oils, are also used to promote a wide range of biological properties, which can accelerate the healing process. Therefore, we intend to explore advances in the potential for applying hybrid materials in wound healing. For this, fifty scientific articles dated from 2010 to 2023 were investigated using the Web of Science, Scopus, Science Direct, and PubMed databases. The principles of the healing process, use of polymers, type and properties of essential oils and processing techniques, and characteristics of dressings were identified. Thus, the plants Syzygium romanticum or Eugenia caryophyllata, Origanum vulgare, and Cinnamomum zeylanicum present prospects for application in clinical trials due to their proven effects on wound healing and reducing the incidence of inflammatory cells in the site of injury. The antimicrobial effect of essential oils is mainly due to polyphenols and terpenes such as eugenol, cinnamaldehyde, carvacrol, and thymol.

Microgel delivery systems of functional substances for precision nutrition

Microgels delivery system have great potential in functional substances encapsulation, protection, release, precise delivery and nutritional intervention. Microgel is a three-dimensional network structure formed by physical or chemical crosslinking of biopolymers, whose characteristics include dispersion and swelling, stable structure, small volume and high specific surface area, and is a special kind of colloid. In this chapter, the common wall materials for preparing food grade microgels, and the main preparation principles, methods, advantages and disadvantages of microgels loaded with functional substances were firstly reviewed. Then the main characteristics of microgel as delivery system, such as deformability, high encapsulation, stimulus-responsive release and targeted delivery, and its potential benefits in intervening chronic diseases were summarized. Finally, the applications of microgel delivery system for functional substance in the field of precision nutrition were discussed. This chapter will help to design of next-generation advanced targeting microgel delivery system, and realize precision nutrition intervention of food functional substances on body health.

Three-Dimensional Extrusion Printed Urinary Specific Grafts: Mechanistic Insights into Buildability and Biophysical Properties

The compositional formulations and the optimization of process parameters to fabricate hydrogel scaffolds with urological tissue-mimicking biophysical properties are not yet extensively explored, including a comprehensive assessment of a spectrum of properties, such as mechanical strength, viscoelasticity, antimicrobial property, and cytocompatibility. While addressing this aspect, the present work provides mechanistic insights into process science, to produce shape-fidelity compliant alginate-based biomaterial ink blended with gelatin and synthetic nanocellulose. The composition-dependent pseudoplasticity, viscoelasticity, thixotropy, and gel stability over a longer duration in physiological context have been rationalized in terms of intermolecular hydrogen bonding interactions among the biomaterial ink constituents. By varying the hybrid hydrogel ink composition within a narrow compositional window, the resulting hydrogel closely mimics the natural urological tissue-like properties, including tensile stretchability, compressive strength, and biophysical properties. Based on the printability assessment using a critical analysis of gel strength, we have established the buildability of the acellular hydrogel ink and have been successful in fabricating shape-fidelity compliant urological patches or hollow cylindrical grafts using 3D extrusion printing. Importantly, the new hydrogel formulations with good hydrophilicity, support fibroblast cell proliferation and inhibit the growth of Gram-negative E. coli bacteria. These attributes were rationalized in terms of nanocellulose-induced physicochemical changes on the scaffold surface. Taken together, the present study uncovers the process-science-based understanding of the 3D extrudability of the newly formulated alginate-gelatin-nanocellulose-based hydrogels with urological tissue-specific biophysical, cytocompatibility, and antibacterial properties.

Ionically annealed zwitterionic microgels for bioprinting of cartilaginous constructs

Foreign body response (FBR) is a pervasive problem for biomaterials used in tissue engineering. Zwitterionic hydrogels have emerged as an effective solution to this problem, due to their ultra-low fouling properties, which enable them to effectively inhibit FBRin vivo. However, no versatile zwitterionic bioink that allows for high resolution extrusion bioprinting of tissue implants has thus far been reported. In this work, we introduce a simple, novel method for producing zwitterionic microgel bioink, using alginate methacrylate (AlgMA) as crosslinker and mechanical fragmentation as a microgel fabrication method. Photocrosslinked hydrogels made of zwitterionic carboxybetaine acrylamide (CBAA) and sulfobetaine methacrylate (SBMA) are mechanically fragmented through meshes with aperture diameters of 50 and 90µm to produce microgel bioink. The bioinks made with both microgel sizes showed excellent rheological properties and were used for high-resolution printing of objects with overhanging features without requiring a support structure or support bath. The AlgMA crosslinker has a dual role, allowing for both primary photocrosslinking of the bulk hydrogel as well as secondary ionic crosslinking of produced microgels, to quickly stabilize the printed construct in a calcium bath and to produce a microporous scaffold. Scaffolds showed ∼20% porosity, and they supported viability and chondrogenesis of encapsulated human primary chondrocytes. Finally, a meniscus model was bioprinted, to demonstrate the bioink's versatility at printing large, cell-laden constructs which are stable for furtherin vitroculture to promote cartilaginous tissue production. This easy and scalable strategy of producing zwitterionic microgel bioink for high resolution extrusion bioprinting allows for direct cell encapsulation in a microporous scaffold and has potential forin vivobiocompatibility due to the zwitterionic nature of the bioink.

Hydrogel Microparticles for Bone Regeneration

Hydrogel microparticles (HMPs) stand out as promising entities in the realm of bone tissue regeneration, primarily due to their versatile capabilities in delivering cells and bioactive molecules/drugs. Their significance is underscored by distinct attributes such as injectability, biodegradability, high porosity, and mechanical tunability. These characteristics play a pivotal role in fostering vasculature formation, facilitating mineral deposition, and contributing to the overall regeneration of bone tissue. Fabricated through diverse techniques (batch emulsion, microfluidics, lithography, and electrohydrodynamic spraying), HMPs exhibit multifunctionality, serving as vehicles for drug and cell delivery, providing structural scaffolding, and functioning as bioinks for advanced 3D-printing applications. Distinguishing themselves from other scaffolds like bulk hydrogels, cryogels, foams, meshes, and fibers, HMPs provide a higher surface-area-to-volume ratio, promoting improved interactions with the surrounding tissues and facilitating the efficient delivery of cells and bioactive molecules. Notably, their minimally invasive injectability and modular properties, offering various designs and configurations, contribute to their attractiveness for biomedical applications. This comprehensive review aims to delve into the progressive advancements in HMPs, specifically for bone regeneration. The exploration encompasses synthesis and functionalization techniques, providing an understanding of their diverse applications, as documented in the existing literature. The overarching goal is to shed light on the advantages and potential of HMPs within the field of engineering bone tissue.