3D printed biomimetic epithelium/stroma bilayer hydrogel implant for corneal regeneration

Mineralized cellulose nanofibers reinforced bioactive hydrogel remodels the osteogenic and angiogenic microenvironment for enhancing bone regeneration

Slow osteogenesis and insufficient vascularization remain significant challenges in achieving effective bone repair and functional restoration with tissue-engineered scaffolds. Herein, a novel mineralized nanofibers reinforced bioactive hydrogel was designed to enhance bone regeneration inspired from the structural and functional properties of the bone tissue extracellular matrix (ECM). This bioactive hydrogel integrated enzymatically mineralized TEMPO-oxidized bacterial cellulose (m-TOBC) nanofibers and mesoporous silica nanoparticles (MSNs) loaded with the angiogenic drug dimethyloxalylglycine (DMOG) into gelatin methacryloyl (GelMA). The m-TOBC nanofibers achieved one stone, three birds: improving the printability of GelMA ink, mechanical properties, and osteoconduction of the hydrogel. The incorporation of MSNs loaded with DMOG fostered an angiogenic microenvironment through the release of DMOG. Results indicated that the bioactive hydrogel significantly enhanced in vitro mineralized matrix deposition and osteoblastic alkaline phosphatase expression. Additionally, the bioactive hydrogel had good ability to promote angiogenesis in terms of enhanced endothelial cell migration, tube formation, and upregulated angiogenic genes expression levels. In a critical-sized rat cranial defect model, the bioactive hydrogel significantly enhanced bone regeneration. Overall, this research offered a promising strategy to design nanofibers enhanced hydrogel to remodel osteogenic and angiogenic microenvironment for enhancing bone repair.

Highly transparent and elastic acellular swim bladder with potential application in cornea implantation

Corneal injury is the leading cause of blindness worldwide, and corneal transplantation remains a critical clinical treatment for restoring vision. However, the shortage of corneal donors greatly limits the application of this therapy. Although some biological corneal scaffolds such as collagen hydrogels and decellularized amniotic membranes, have emerged in recent years, their clinical efficacy is unsatisfactory because of poor tissue integration caused by the difficult suturing required and poor biomechanical properties of the scaffolds. To address these shortcomings, a decellularized swim bladder corneal scaffold was developed in this research. Specifically, using a freezing and thawing process, with 0.5% sodium deoxycholate and nuclease, the natural elastin fibers were preserved during the decellularization process, which enhanced the elastic properties of the scaffold. Dehydration and cross-linking increased the light transmittance of the decellularized swim bladder to 93.1 ± 0.8%, which was slightly higher than that of human corneas. Furthermore, cross-linking further improved the mechanical properties of the scaffolds (circumferential fracture tensile stress, elastic modulus and suture strength were 25.66 ± 4.42 MPa, 184.43 ± 23.27 MPa and 123.5 ± 2.69 gf, respectively), which were far superior to most previously reported biocorneal scaffolds reported so far. In addition, decellularized swim bladder collagen matrix scaffolds (SBCMs) supported the proliferation and adhesion of rabbit corneal epithelial cells (RCECs) and rabbit corneal stromal cells (RCSCs). Subcutaneous implantation experiments revealed that the scaffolds had a lower acute inflammatory response and better anti-degradation ability than human amniotic membranes used clinically. In summary, SBCMs have good biocompatibility, high light transmittance and excellent biomechanical properties, and can be used in the future to develop a novel generation of artificial corneas.

Plant Polyphenol-Based Injectable Hydrogels: Advances and Biomedical Applications

Plant polyphenol-based hydrogels, known for their biocompatibility and adhesive properties, have emerged as promising materials in biomedical applications. These hydrogels leverage the catechol group's ability to form stable bonds in moist environments, similar to mussel adhesive proteins. This review provides a comprehensive overview of their synthesis, adhesion mechanisms, and applications, particularly in wound healing, tissue regeneration, and drug delivery. However, challenges related to in vivo stability and long-term biocompatibility remain critical barriers to clinical translation. Future research should focus on enhancing the bioactivity, biocompatibility, and scalability of these hydrogels, while addressing concerns related to toxicity, immune responses, and large-scale manufacturing. Advances in artificial intelligence-assisted screening and 3D/4D bioprinting are expected to accelerate their development and clinical translation. Furthermore, the integration of biomimetic designs and responsive functionalities, such as pH or temperature sensitivity, holds promise for further improving their therapeutic efficacy. In conclusion, the development of multifunctional plant polyphenol-based hydrogels represents a promising frontier in advancing personalized medicine and minimally invasive treatments.

Novel Biomimetic Collagen-Based Corneal Repair Material Achieved via a "Killing Two Birds with One Stone" Strategy Using Carboxymethyl-β-Cyclodextrin

Collagen, as the principal structural component of the cornea, has emerged as a promising biomaterial for artificial corneal owing to its excellent biocompatibility and degradability. However, the mechanical properties of current collagen membrane cannot match the requirements of artificial corneal materials. Inspired by the hierarchical lamellar organization of native corneal stromal collagen, a biomimetic collagen-based corneal repair material was designed via a "killing two birds with one stone" strategy. In this strategy, carboxymethyl-β-cyclodextrin (CM-β-CD) was incorporated into the collagen, serving dual functions: regulating the in vitro self-assembly process of collagen molecules and establishing multiple covalent cross-linking sites within the network. Concurrently, controlled external shear forces were applied to induce anisotropic alignment of collagen fibers, effectively replicating the highly organized structural hierarchy characteristic of native corneal stromal tissue. The resulting membrane exhibited a 67% enhancement in tensile strength (0.52 MPa) compared to pure collagen membranes. Notably, in vivo lamellar keratoplasty evaluations revealed accelerated tissue regeneration, achieving complete re-epithelialization within 14 days versus 28 days for controls. These findings establish the material's potential as an advanced artificial corneal for tissue engineering applications.

Natural Extracellular Matrix Scaffold-Based Hydrogel Corneal Patch with Temperature and Light-Responsiveness for Penetrating Keratoplasty and Sutureless Stromal Defect Repair

Corneal transplantation remains the gold standard for treating corneal blindness; however, it is hampered globally by donor shortages and the complexity of suture-dependent procedures. Tissue-engineered corneas have demonstrated potential as corneal equivalents. Nevertheless, the development of adhesive corneal patches and full-thickness corneal substitutes remains challenging. In this study, a multifunctional hydrogel corneal patch (MHCP) is constructed by integrating a dual-crosslinked hybrid hydrogel with temperature and light responsiveness with a natural extracellular matrix scaffold. When applied to the ocular surface, MHCP spontaneously releases adhesives at body temperature and forms a stable adhesion with the recipient cornea through photocuring. In addition to its inherent mechanical, optical, and ultrastructural characteristics, which are similar to those of the natural stroma, MHCP demonstrates excellent suture resistance, anti-swelling, and anti-degradation properties after curing. MHCP promotes the proliferation and migration of corneal epithelial cells in vitro and maintains the phenotype of corneal stromal cells. In vivo, MHCP maintains graft hydration and restores corneal structural integrity and transparency during penetrating keratoplasty of various sizes and sutureless lamellar keratoplasty. Collectively, given the advantages of native stroma-like characteristics, operation-facilitating multiple functions, and convenient preparation, MHCP is a promising corneal substitute for clinical applications.

An exploration of the ocular mysteries linking nanoparticles to the patho-therapeutic effects against keratitis

Microbial keratitis, a sight-threatening corneal infection, remains a significant global health concern. Conventional therapies using antimicrobial agents often suffers from limitations such as poor drug penetration, side effects, and occurrence of drug resistance, with poor prognosis. Novel treatment techniques, with their unique properties and targeted delivery capabilities, offers a promising solution to overcome these challenges. This review delves into timely update of the state-of-the-art advance therapeutics for keratitis treatment. The diverse microbial origins of keratitis, including viral, bacterial, and fungal infections, exploring their complex pathogenic mechanisms, followed by the drug resistance mechanisms in keratitis pathogens are reviewed briefly. Importantly, the emerging therapeutic techniques for keratitis treatment including piezodynamic therapy, photothermal therapy, photodynamic therapy, nanoenzyme therapy, and metal ion therapy are summarized in this review showcasing their potential to overcome the limitations of traditional treatments. The challenges and future directions for advance therapies and nanotechnology-based approaches are discussed, focusing on safety, targeting strategies, drug resistance, and combination therapies. This review aims to inspire researchers to revolutionize and accelerate the development of functional materials using different therapies for keratitis treatment.

Printability in Multi-material Projection-Based 3-Dimensional Bioprinting

Accurately reconstructing the intricate structure of natural organisms is the long-standing goal of 3-dimensional (3D) bioprinting. Projection-based 3D printing boasts the highest resolution-to-manufacturing time ratio among all 3D-printing technologies, rendering it a highly promising technique in this field. However, achieving standardized, high-fidelity, and high-resolution printing of composite structures using bioinks with diverse mechanical properties remains a marked challenge. The root of this challenge lies in the long-standing neglect of multi-material printability research. Multi-material printing is far from a simple physical assembly of different materials; rather, effective control of material interfaces is a crucial factor that governs print quality. The current research gap in this area substantively hinders the widespread application and rapid development of multi-material projection-based 3D bioprinting. To bridge this critical gap, we developed a multi-material projection-based 3D bioprinter capable of simultaneous printing with 6 materials. Building upon this, we established a fundamental framework for multi-material printability research, encompassing its core logic and essential process specifications. Furthermore, we clarified several critical issues, including the cross-linking behavior of multicomponent bioinks, mechanical mismatch and interface strength in soft-hard composite structures, the penetration behavior of viscous bioinks within hydrogel polymer networks, liquid entrapment and adsorption phenomena in porous heterogeneous structures, and error source analysis along with resolution evaluation in multi-material printing. This study offers a solid theoretical foundation and guidance for the quantitative assessment of multi-material projection-based 3D bioprinting, holding promise to advance the field toward higher precision and the reconstruction of more intricate biological structures.

Digital light processing 3D bioprinting of biomimetic corneal stroma equivalent using gelatin methacryloyl and oxidized carboxymethylcellulose interpenetrating network hydrogel

Corneal blindness, a leading cause of visual impairment globally, has created a pressing need for alternatives to corneal transplantation due to the severe shortage of donor tissues. In this study, we present a novel interpenetrating network hydrogel composed of gelatin methacryloyl (GelMA) and oxidized carboxymethyl cellulose (OxiCMC) for bioprinting a biomimetic corneal stroma equivalent. We tested different combinations of GelMA and OxiCMC to optimize printability and subsequently evaluated these combinations using rheological studies for gelation and other physical, chemical, and biological properties. Using digital light processing (DLP) bioprinting, with tartrazine as a photoabsorber, we successfully biofabricated three-dimensional constructs with improved shape fidelity, high resolution, and excellent reproducibility. The bioprinted constructs mimic the native corneal stroma's curvature, with central and peripheral thicknesses of 478.9 ± 56.5µm and 864.0 ± 79.3µm, respectively. The dual crosslinking strategy, which combines Schiff base reaction and photocrosslinking, showed an improved compressive modulus (106.3 ± 7.7 kPa) that closely matched that of native tissues (115.3 ± 13.6 kPa), without relying on synthetic polymers, toxic crosslinkers, or nanoparticles. Importantly, the optical transparency of tartrazine-containing corneal constructs was comparable to the native cornea following phosphate-buffered saline washing. Morphological analyses using scanning electron microscopy confirmed the improved porosity, interconnected network, and structural integrity of the GelMA-OxiCMC hydrogel, facilitating better nutrient diffusion and cell viability.In vitrobiological assays demonstrated high cell viability (>93%) and desirable proliferation of human corneal keratocytes within the biofabricated constructs. Our findings indicate that the GelMA-OxiCMC hydrogel system for DLP bioprinting presents a promising alternative for corneal tissue engineering, offering a potential solution to the donor cornea shortage and advancing regenerative medicine for corneal repair.

Biologically inspired bioactive hydrogels for scarless corneal repair

Corneal injury-induced fibrosis occurs because of corneal epithelial basement membrane (EBM) injury and defective regeneration. Corneal fibrosis inhibition and transparency restoration depend on reestablished EBM, where the collagen network provides structural stability and heparan sulfate binds corneal epithelium-derived cytokines to regulate homeostasis. Inspired by this, bioactive hydrogels (Hep@Gel) composed of collagen-derived gelatins and highly anionic heparin were constructed for scarless corneal repair. Hep@Gel resembled the barrier function of the EBM regarding surface-confined binding, long-time sequestration, and progressive degradation of IL-1, TGF-β, and PDGF-BB, which robustly inhibited the apoptosis and myofibroblast transition of keratocytes. Animal models of rabbits and nonhuman primates confirmed that Hep@Gel effectively limited the influx of inflammatory and fibrotic cytokines from the epithelium into the stroma to down-regulate the wound healing cascade, contributing to better vision quality with 73% reduced fibrosis. Hep@Gel offers a solution for preventing corneal injury-induced scarring and substituting for lamellar keratoplasty to remove scarring.

Focus on seed cells: stem cells in 3D bioprinting of corneal grafts

Corneal opacity is one of the leading causes of severe vision impairment. Corneal transplantation is the dominant therapy for irreversible corneal blindness. However, there is a worldwide shortage of donor grafts and consequently an urgent demand for alternatives. Three-dimensional (3D) bioprinting is an innovative additive manufacturing technology for high-resolution distribution of bioink to construct human tissues. The technology has shown great promise in the field of bone, cartilage and skin tissue construction. 3D bioprinting allows precise structural construction and functional cell printing, which makes it possible to print personalized full-thickness or lamellar corneal layers. Seed cells play an important role in producing corneal biological functions. And stem cells are potential seed cells for corneal tissue construction. In this review, the basic anatomy and physiology of the natural human cornea and the grafts for keratoplasties are introduced. Then, the applications of 3D bioprinting techniques and bioinks for corneal tissue construction and their interaction with seed cells are reviewed, and both the application and promising future of stem cells in corneal tissue engineering is discussed. Finally, the development trends requirements and challenges of using stem cells as seed cells in corneal graft construction are summarized, and future development directions are suggested.

Unveiling the versatility of gelatin methacryloyl hydrogels: a comprehensive journey into biomedical applications

Gelatin methacryloyl (GelMA) hydrogels have gained significant recognition as versatile biomaterials in the biomedical domain. GelMA hydrogels emulate vital characteristics of the innate extracellular matrix by integrating cell-adhering and matrix metalloproteinase-responsive peptide motifs. These features enable cellular proliferation and spreading within GelMA-based hydrogel scaffolds. Moreover, GelMA displays flexibility in processing, as it experiences crosslinking when exposed to light irradiation, supporting the development of hydrogels with adjustable mechanical characteristics. The drug delivery landscape has been reshaped by GelMA hydrogels, offering a favorable platform for the controlled and sustained release of therapeutic actives. The tunable physicochemical characteristics of GelMA enable precise modulation of the kinetics of drug release, ensuring optimal therapeutic effectiveness. In tissue engineering, GelMA hydrogels perform an essential role in the design of the scaffold, providing a biomimetic environment conducive to cell adhesion, proliferation, and differentiation. Incorporating GelMA in three-dimensional printing further improves its applicability in drug delivery and developing complicated tissue constructs with spatial precision. Wound healing applications showcase GelMA hydrogels as bioactive dressings, fostering a conducive microenvironment for tissue regeneration. The inherent biocompatibility and tunable mechanical characteristics of GelMA provide its efficiency in the closure of wounds and tissue repair. GelMA hydrogels stand at the forefront of biomedical innovation, offering a versatile platform for addressing diverse challenges in drug delivery, tissue engineering, and wound healing. This review provides a comprehensive overview, fostering an in-depth understanding of GelMA hydrogel's potential impact on progressing biomedical sciences.

Research progress of photo-crosslink hydrogels in ophthalmology: A comprehensive review focus on the applications

Hydrogel presents a three-dimensional polymer network with high water content. Over the past decade, hydrogel has developed from static material to intelligent material with controllable response. Various stimuli are involved in the formation of hydrogel network, among which photo-stimulation has attracted wide attention due to the advantages of controllable conditions, which has a good application prospect in the treatment of ophthalmic diseases. This paper reviews the application of photo-crosslink hydrogels in ophthalmology, focusing on the types of photo-crosslink hydrogels and their applications in ophthalmology, including drug delivery, tissue engineering and 3D printing. In addition, the limitations and future prospects of photo-crosslink hydrogels are also provided.

Kuragel: A biomimetic hydrogel scaffold designed to promote corneal regeneration

Cornea-related injuries are the most common cause of blindness worldwide. Transplantation remains the primary approach for addressing corneal blindness, though the demand for donor corneas outmatches the supply by millions. Tissue adhesives employed to seal corneal wounds have shown inefficient healing and incomplete vision restoration. We have developed a biodegradable hydrogel - Kuragel, with the ability to promote corneal regeneration. Functionalized gelatin and hyaluronic acid form photo-crosslinkable hydrogel with transparency and compressive modulus similar to healthy human cornea. Kuragel composition was tuned to achieve sufficient adhesive strength for sutureless integration to host tissue, with minimal swelling post-administration. Studies in the New Zealand rabbit mechanical injury model affecting corneal epithelium and stroma demonstrate that Kuragel efficiently promotes re-epithelialization within 1 month of administration, while stroma and sub-basal nerve plexus regenerate within 3 months. We propose Kuragel as a regenerative treatment for patients suffering from corneal defects including thinning, by restoration of transparency and thickness.

Wet environment-induced adhesion and softening of coenzyme-based polymer elastic patch for treating periodontitis

Periodontitis, a common chronic inflammatory disease caused by pathogenic bacteria, can be treated with diverse biomaterials by loading drugs, cytokines or proteins. However, these biomaterials often show unsatisfactory therapeutic efficiency due to their poor adhesion, short residence time in the wet and dynamic oral cavity and emerging drug resistance. Here we report a wet-responsive methacrylated gelatin (GelMA)-stabilized co-enzyme polymer poly(α-lipoic acid) (PolyLA)-based elastic patch with water-induced adhesion and softening features. In PolyLA-GelMA, the multiple covalent and hydrogen-bonding crosslinking between PolyLA and GelMA prevent PolyLA depolymerization and slow down the dissociation of PolyLA in water, allowing durable adhesion to oral periodontal tissue and continuous release of LA-based bioactive small molecule in periodontitis wound without resorting external drugs. Compared with the undifferentiated adhesion behavior of traditional adhesives, this wet-responsive patch demonstrates a favorable periodontal pocket insertion ability due to its non-adhesion and rigidity in dry environment. In vitro studies reveal that PolyLA-GelMA patch exhibits satisfactory wet tissue adhesion, antibacterial, blood compatibility and ROS scavenging abilities. In the model of rat periodontitis, the PolyLA-GelMA patch inhibits alveolar bone resorption and accelerates the periodontitis healing by regulating the inflammatory microenvironment. This biomacromolecule-stabilized coenzyme polymer patch provides a new option to promote periodontitis treatment.

Hemoadhican-Based Bioabsorbable Hydrogel for Preventing Postoperative Adhesions

Postoperative peritoneal adhesions are a prevalent clinical issue following abdominal and pelvic surgery, frequently resulting in heightened personal and societal health burdens. Traditional biomedical barriers offer limited benefits because of practical challenges for doctors and their incompatibility with laparoscopic surgery. Hydrogel materials, represented by hyaluronic acid gels, are receiving increasing attention. However, existing antiadhesive gels still have limited effectiveness or carry the risk of complications in clinical applications. Herein, we developed a novel hydrogel using polysaccharide hemoadhican (HD) as the base material and polyethylene glycol diglycidyl ether (PEGDE) as the cross-linking agent. The HD hydrogels exhibit appropriate mechanical properties, injectability, and excellent cytocompatibility. We demonstrate resistance to protein adsorption and L929 fibroblast cell adhesion to the HD hydrogel. The biodegradability and efficacy against peritoneal adhesion are further evaluated in C57BL/6 mice. Our results suggest a potential strategy for anti-postoperative tissue adhesion barrier biomaterials.

Biopolymeric corneal lenticules by digital light processing based bioprinting: a dynamic substitute for corneal transplant

Digital light processing (DLP) technology has gained significant attention for its ability to construct intricate structures for various applications in tissue modeling and regeneration. In this study, we aimed to design corneal lenticules using DLP bioprinting technology, utilizing dual network bioinks to mimic the characteristics of the human cornea. The bioink was prepared using methacrylated hyaluronic acid and methacrylated gelatin, where ruthenium salt and sodium persulfate were included for mediating photo-crosslinking while tartrazine was used as a photoabsorber. The bioprinted lenticules were optically transparent (85.45% ± 0.14%), exhibited adhesive strength (58.67 ± 17.5 kPa), and compressive modulus (535.42 ± 29.05 kPa) sufficient for supporting corneal tissue integration and regeneration. Puncture resistance tests and drag force analysis further confirmed the excellent mechanical performance of the lenticules enabling their application as potential corneal implants. Additionally, the lenticules demonstrated outstanding support for re-epithelialization and stromal regeneration when assessed with human corneal stromal cells. We generated implant ready corneal lenticules while optimizing bioink and bioprinting parameters, providing valuable solution for individuals suffering from various corneal defects and waiting for corneal transplants.

Digital Light Processing 4D Printing of Poloxamer Micelles for Facile Fabrication of Multifunctional Biocompatible Hydrogels as Tailored Wearable Sensors

The lack of both digital light processing (DLP) compatible and biocompatible photopolymers, along with inappropriate material properties required for wearable sensor applications, substantially hinders the employment of DLP 3D printing in the fabrication of multifunctional hydrogels. Herein, we discovered and implemented a photoreactive poloxamer derivative, Pluronic F-127 diacrylate, which overcomes these limitations and is optimized to achieve DLP 3D printed micelle-based hydrogels with high structural complexity, resolution, and precision. In addition, the dehydrated hydrogels exhibit a shape-memory effect and are conformally attached to the geometry of the detection point after rehydration, which implies the 4D printing characteristic of the fabrication process and is beneficial for the storage and application of the device. The excellent cytocompatibility and in vivo biocompatibility further strengthen the potential application of the poloxamer micelle-based hydrogels as a platform for multifunctional wearable systems. After processing them with a lithium chloride (LiCl) solution, multifunctional conductive ionic hydrogels with antifreezing and antiswelling properties along with good transparency and water retention are easily prepared. As capacitive flexible sensors, the DLP 3D printed micelle-based hydrogel devices exhibit excellent sensitivity, cycling stability, and durability in detecting multimodal deformations. Moreover, the DLP 3D printed conductive hydrogels are successfully applied as real-time human motion and tactile sensors with satisfactory sensing performances even in a -20 °C low-temperature environment.

Highly oriented hydrogels for tissue regeneration: design strategies, cellular mechanisms, and biomedical applications

Many human tissues exhibit a highly oriented architecture that confers them with distinct mechanical properties, enabling adaptation to diverse and challenging environments. Hydrogels, with their water-rich "soft and wet" structure, have emerged as promising biomimetic materials in tissue engineering for repairing and replacing damaged tissues and organs. Highly oriented hydrogels can especially emulate the structural orientation found in human tissue, exhibiting unique physiological functions and properties absent in traditional homogeneous isotropic hydrogels. The design and preparation of highly oriented hydrogels involve strategies like including hydrogels with highly oriented nanofillers, polymer-chain networks, void channels, and microfabricated structures. Understanding the specific mechanism of action of how these highly oriented hydrogels affect cell behavior and their biological applications for repairing highly oriented tissues such as the cornea, skin, skeletal muscle, tendon, ligament, cartilage, bone, blood vessels, heart, etc., requires further exploration and generalization. Therefore, this review aims to fill that gap by focusing on the design strategy of highly oriented hydrogels and their application in the field of tissue engineering. Furthermore, we provide a detailed discussion on the application of highly oriented hydrogels in various tissues and organs and the mechanisms through which highly oriented structures influence cell behavior.

Three-dimensional bioprinting in ophthalmic care

Three-dimensional (3D) bioprinting is widely used in ophthalmic clinic, including in diagnosis, surgery, prosthetics, medications, drug development and delivery, and medical education. Articles published in 2011-2022 into bioinks, printing technologies, and bioprinting applications in ophthalmology were reviewed and the strengths and limitations of bioprinting in ophthalmology highlighted. The review highlighted the trade-offs of printing technologies and bioinks in respect to, among others, material type cost, throughput, gelation technique, cell density, cell viability, resolution, and printing speed. There is already widespread ophthalmological application of bioprinting outside clinical settings, including in educational modelling, retinal imaging/visualization techniques and drug design/testing. In clinical settings, bioprinting has already found application in pre-operatory planning. Even so, the findings showed that even with its immense promise, actual translation to clinical applications remains distant, but relatively closer for the corneal (except stromal) tissues, epithelium, endothelium, and conjunctiva, than it was for the retina. This review similarly reflected on the critical on the technical, practical, ethical, and cost barrier to rapid progress of bioprinting in ophthalmology, including accessibility to the most sophisticated bioprinting technologies, choice, and suitability of bioinks, tissue viability and storage conditions. The extant research is encouraging, but more work is clearly required for the push towards clinical translation of research.

Corneal regeneration strategies: From stem cell therapy to tissue engineered stem cell scaffolds

Corneal epithelial defects and excessive wound healing might lead to severe complications. As stem cells can self-renew infinitely, they are a promising solution for regenerating the corneal epithelium and treating severe corneal epithelial injury. The chemical and biophysical properties of biological scaffolds, such as the amniotic membrane, fibrin, and hydrogels, can provide the necessary signals for stem cell proliferation and differentiation. Multiple researchers have conducted investigations on these scaffolds and evaluated them as potential therapeutic interventions for corneal disorders. These studies have identified various inherent benefits and drawbacks associated with these scaffolds. In this study, we provided a comprehensive overview of the history and use of various stem cells in corneal repair. We mainly discussed biological scaffolds that are used in stem cell transplantation and innovative materials that are under investigation.

Photocrosslinked methacrylated natural macromolecular hydrogels for tissue engineering: A review

A hydrogel is a three-dimensional (3D) network structure formed through polymer crosslinking, and these have emerged as a popular research topic in recent years. Hydrogel crosslinking can be classified as physical, chemical, or enzymatic, and photocrosslinking is a branch of chemical crosslinking. Compared with other methods, photocrosslinking can control the hydrogel crosslinking initiation, crosslinking time, and crosslinking strength using light. Owing to these properties, photocrosslinked hydrogels have important research prospects in tissue engineering, in situ gel formation, 3D bioprinting, and drug delivery. Methacrylic anhydride modification is a common method for imparting photocrosslinking properties to polymers, and graft-substituted polymers can be photocrosslinked under UV irradiation. In this review, we first introduce the characteristics of common natural polysaccharide- and protein-based hydrogels and the processes used for methacrylate group modification. Next, we discuss the applications of methacrylated natural hydrogels in tissue engineering. Finally, we summarize and discuss existing methacrylated natural hydrogels in terms of limitations and future developments. We expect that this review will help researchers in this field to better understand the synthesis of methacrylate-modified natural hydrogels and their applications in tissue engineering.

3D bioprinting of corneal decellularized extracellular matrix: GelMA composite hydrogel for corneal stroma engineering

Millions of individuals across the world suffer from corneal stromal diseases that impair vision. Fortunately, three-dimensional (3D) bioprinting technology which has revolutionized the field of regenerative tissue engineering makes it feasible to create personalized corneas. In this study, an artificial cornea with a high degree of precision, smoothness, and programmable curvature was prepared by using digital light processing (DLP) 3D bioprinting in one piece with no support structure, and the construct was then confirmed by optical coherence tomography (OCT). On the basis of this approach, we developed a novel corneal decellularized extracellular matrix/gelatin methacryloyl (CECM-GelMA) bioink that can produce complex microenvironments with highly tunable mechanical properties while retaining high optical transmittance. Furthermore, the composite hydrogel was loaded with human corneal fibroblasts (hCFs), and in vitro experiments showed that the hydrogel maintained high cell viability and expressed core proteins. In vivo tests revealed that the hydrogel might promote epithelial regeneration, keep the matrix aligned, and restore clarity. This demonstrates how crucial a role CECM plays in establishing a favorable environment that encourages the transformation of cell function. Therefore, artificial corneas that can be rapidly customized have a huge potential in the development of in vitro corneal matrix analogs.

Additive Manufacturing and Physicomechanical Characteristics of PEGDA Hydrogels: Recent Advances and Perspective for Tissue Engineering

In this brief review, we discuss the recent advancements in using poly(ethylene glycol) diacrylate (PEGDA) hydrogels for tissue engineering applications. PEGDA hydrogels are highly attractive in biomedical and biotechnology fields due to their soft and hydrated properties that can replicate living tissues. These hydrogels can be manipulated using light, heat, and cross-linkers to achieve desirable functionalities. Unlike previous reviews that focused solely on material design and fabrication of bioactive hydrogels and their cell viability and interactions with the extracellular matrix (ECM), we compare the traditional bulk photo-crosslinking method with the latest three-dimensional (3D) printing of PEGDA hydrogels. We present detailed evidence combining the physical, chemical, bulk, and localized mechanical characteristics, including their composition, fabrication methods, experimental conditions, and reported mechanical properties of bulk and 3D printed PEGDA hydrogels. Furthermore, we highlight the current state of biomedical applications of 3D PEGDA hydrogels in tissue engineering and organ-on-chip devices over the last 20 years. Finally, we delve into the current obstacles and future possibilities in the field of engineering 3D layer-by-layer (LbL) PEGDA hydrogels for tissue engineering and organ-on-chip devices.

Hierarchical hydrogel scaffolds with a clustered and oriented structure

Hydrogel scaffolds play a critical role in tissue engineering due to their hydrophilic network structure and good biocompatibility. Constructing anisotropic scaffolds geometrically similar to injured tissues is conducive to promoting the generation of tissue and organ equivalents, or to guiding and enhancing the regeneration of injured tissues. In this study, we developed polyvinyl alcohol (PVA)/alginate hierarchical hydrogel scaffolds with a clustered and oriented structure using a method that combines directional freezing and drying under stretching. Our hydrogel scaffolds with an adjustable modulus (50 kPa-20 MPa) can match different types of injured tissues. The clustered and oriented structure successfully guided the alignment and orientation of fibroblasts and chondrocytes. This work provides a new idea for constructing hydrogels with hierarchical and anisotropic microstructures, which have promising applications in tissue regeneration.

Digital light processing-based multi-material bioprinting: Processes, applications, and perspectives

In the past decade, three-dimensional (3D) printing technology based on digital light processing (DLP) has developed rapidly and shown application prospects in several fields such as pneumatic robotics, flexible electronics, and tissue engineering. In particular, DLP-based multi-material printing has been capable of constructing heterogeneous 3D structures with characteristic gradients. DLP 3D printing technology has a wide range of applications in the field of bioprinting due to its high precision and mild printing conditions, including functionalized artificial tissues, medical models, and bioreactors. This paper focuses on the development of DLP-based multi-material 3D printing technology and its applications in the field of bioprinting, followed by giving an outlook on future efforts on overcoming the challenges and obstacles of this promising technique.

Biomimetic Convex Implant for Corneal Regeneration Through 3D Printing

Blindness caused by corneal damage affects millions of people worldwide, and this number continues to rise. However, rapid epithelization and a stable epithelium process are the two biggest challenges for traditional corneal materials. These processes are related to corneal curvature, which is an important factor in determination of the corneal healing process and epithelial behavior during corneal damage. In this study, smooth 3D-printed convex corneal implants based on gelatin methacrylate and collagen are generated. As epithelium distribution and adhesion vary in different regions of the natural cornea, this work separates the surfaces into four regions and studies how cells sense topological cues on curvature. It is found that rabbit corneal epithelial cells (RCECs) seeded on steeper slope gradient surfaces on convex structures result in more aligned cell organization and tighter cell-substrate adhesion, which can also be verified through finite element simulation and signaling pathway analysis. In vivo transplantation of convex implants result in a better fit with adjacent tissue and stronger cell adhesion than flat implants, thereby accelerating corneal epithelialization and promoting collagen fibers and neural regeneration within 180 days. Taken together, printed convex corneal implants that facilitate corneal regeneration may offer a translational strategy for the treatment of corneal damage.

3D printing for personalised medicines: implications for policy and practice

The current healthcare dynamic has shifted from one-size-fits-all to patient-centred care, with our increased understanding of pharmacokinetics and pharmacogenomics demanding a switch to more individualised therapies. As the pharmaceutical industry remains yet to succumb to the push of a technological paradigm shift, pharmacists lack the means to provide completely personalised medicine (PM) to their patients in a safe, affordable, and widely accessible manner. As additive manufacturing technology has already established its strength in producing pharmaceutical formulations, it is necessary to next consider methods by which this technology can create PM accessible from pharmacies. In this article, we reviewed the limitations of current pharmaceutical manufacturing methods for PMs, three-dimensional (3D) printing techniques that are most beneficial for PMs, implications of bringing this technology into pharmacy practice, and implications for policy surrounding 3D printing techniques in the manufacturing of PMs.

Injectable, Hierarchically Degraded Bioactive Scaffold for Bone Regeneration

Bioactive materials play vital roles in the repair of critical bone defects. However, bone tissue engineering and regenerative medicine are still challenged by the need to repair bone defects evenly and completely. In this study, we functionally simulated the natural creeping substitution process of autologous bone repair by constructing an injectable, hierarchically degradable bioactive scaffold with a composite hydrogel, decalcified bone matrix (DBM) particles, and bone morphogenetic protein 2. This composite scaffold exhibited superior mechanical properties. The scaffold promoted cell proliferation and osteogenic differentiation through multiple signaling pathways. The hierarchical degradation rates of the crosslinked hydrogel and DBM particles accelerated tissue ingrowth and bone formation with a naturally woven bone-like structure in vivo. In the rat calvarial critical defect repair model, the composite scaffold provided even and complete repair of the entire defect area while also integrating the new and host bone effectively. Our results indicate that this injectable, hierarchically degradable bioactive scaffold promotes bone regeneration and provides a promising strategy for evenly and completely repairing the bone defects.

Performance of hybrid gelatin-PVA bioinks integrated with genipin through extrusion-based 3D bioprinting: An in vitro evaluation using human dermal fibroblasts

3D bioprinting technology is a well-established and promising advanced fabrication technique that utilizes potential biomaterials as bioinks to replace lost skin and promote new tissue regeneration. Cutaneous regenerative biomaterials are highly commended since they benefit patients with larger wound sizes and irregular wound shapes compared to the painstaking split-skin graft. This study aimed to fabricate biocompatible, biodegradable, and printable bioinks as a cutaneous substitute that leads to newly formed tissue post-transplantation. Briefly, gelatin (GE) and polyvinyl alcohol (PVA) bioinks were prepared in various concentrations (w/v); GE (6% GE: 0% PVA), GPVA3 (6% GE: 3% PVA), and GPVA5 (6% GE: 5% PVA), followed by 0.1% (w/v) genipin (GNP) crosslinking to achieve optimum printability. According to the results, GPVA5_GNP significantly presented at least 590.93 ± 164.7% of swelling ratio capacity and optimal water vapor transmission rate (WVTR), which is <1500 g/m2/h to maintain the moisture of the wound microenvironment. Besides, GPVA5_GNP is also more durable than other hydrogels with the slowest biodegradation rate of 0.018 ± 0.08 mg/h. The increasing amount of PVA improved the rheological properties of the hydrogels, leading the GPVA5_GNP to have the highest viscosity, around 3.0 ± 0.06 Pa.s. It allows a better performance of bioinks printability via extrusion technique. Moreover, the cross-section of the microstructure hydrogels showed the average pore sizes >100 μm with excellent interconnected porosity. X-ray diffraction (XRD) analysis showed that the hydrogels maintain their amorphous properties and were well-distributed through energy dispersive X-ray after crosslinking. Furthermore, there had no substantial functional group changes, as observed by Fourier transform infrared spectroscopy, after the addition of crosslinker. In addition, GPVA hydrogels were biocompatible to the cells, effectively demonstrating >90% of cell viability. In conclusion, GPVA hydrogels crosslinked with GNP, as prospective bioinks, exhibited the superior properties necessary for wound healing treatment.

Advances in 3D bioprinting technology for functional corneal reconstruction and regeneration

Corneal transplantation constitutes one of the major treatments in severe cases of corneal diseases. The lack of cornea donors as well as other limitations of corneal transplantation necessitate the development of artificial corneal substitutes. Biosynthetic cornea model using 3D printing technique is promising to generate artificial corneal structure that can resemble the structure of the native human cornea and is applicable for regenerative medicine. Research on bioprinting artificial cornea has raised interest into the wide range of materials and cells that can be utilized as bioinks for optimal clarity, biocompatibility, and tectonic strength. With continued advances in biomaterials science and printing technology, it is believed that bioprinted cornea will eventually achieve a level of clinical functionality and practicality as to replace donated corneal tissues, with their associated limitations such as limited or unsteady supply, and possible infectious disease transmission. Here, we review the literature on bioprinting strategies, 3D corneal modelling, material options, and cellularization strategies in relation to keratoprosthesis design. The progress, limitations and expectations of recent cases of 3D bioprinting of artifial cornea are discussed. An outlook on the rise of 3D bioprinting in corneal reconstruction and regeneration is provided.

3D bioprinting of corneal models: A review of the current state and future outlook

The cornea is the outermost layer of the eye and serves to protect the eye and enable vision by refracting light. The need for cornea organ donors remains high, and the demand for an artificial alternative continues to grow. 3D bioprinting is a promising new method to create artificial organs and tissues. 3D bioprinting offers the precise spatial arrangement of biomaterials and cells to create 3D constructs. As the cornea is an avascular tissue which makes it more attractive for 3D bioprinting, it could be one of the first tissues to be made fully functional via 3D bioprinting. This review discusses the most common 3D bioprinting technologies and biomaterials used for 3D bioprinting corneal models. Additionally, the current state of 3D bioprinted corneal models, especially specific characteristics such as light transmission, biomechanics, and marker expression, and in vivo studies are discussed. Finally, the current challenges and future prospects are presented.

Pt(IV) prodrug initiated microparticles from microfluidics for tumor chemo-, photothermal and photodynamic combination therapy

Multimodal treatment modalities hold great potential for cancer therapy, thus current efforts are focusing on the development of more effective and practical synergistic therapeutic platforms. Herein, we present a novel trans, trans,trans-[Pt(N₃)₂(OH)₂(py)₂] (Pt(IV)) prodrug-initiated hydrogel microparticles (M_ICG-Pt) with indocyanine green (ICG) encapsulation by microfluidics for efficiently synergistic chemo-, photothermal (PTT) and photodynamic therapy (PDT). The employed Pt(IV) could not only serves as an initiator to generate azidyl radical (N₃ ^•) for photo-polymerization of methacrylate gelatin (GelMA) matrix, but also be reduced to high cytotoxic platinum(II) (Pt(II)) species for tumor chemotherapy. The laden ICG with highly photothermal heating ability and intrinsic reactive oxygen species (ROS) productivity endows the M_ICG-Pt with effective PTT/PDT performances upon near-infrared (NIR) light irradiation. In addition, benefiting from the production of oxygen during the photo-activation process of Pt(IV), the PDT efficacy of ICG-laden M_ICG-Pt could be further enhanced. Based on these advantages, we have demonstrated that the M_ICG-Pt could significantly eliminate cancer cells in vitro, and remarkably suppressed the tumor growth in vivo via synergistic chemotherapy, PTT, and PDT. These results indicate that such Pt(IV)-initiated hydrogel microparticles are ideal candidates of multimodal treatment platforms, holding great prospects for cancer therapy.

Mesoporous bioglass capsule composite injectable hydrogels with antibacterial and vascularization promotion properties for chronic wound repair

Building an angiogenesis microenvironment and inhibiting wound infection are of great significance for chronic wound repair. In this paper, polydopamine-encapsulated mesoporous bioglass (MBG@PDA) capsules were constructed to realize the integration of angiogenesis and infection inhibition through the formation of a composite hydrogel with modified hyaluronic acid (HAMA) to promote wound healing. The experiments showed that the composite hydrogel had good adhesion and toughness and promoted the migration of fibroblasts to accelerate the epithelialization process. In addition, in the composite hydrogel, MBG@PDA could release Mg²⁺ to promote the proliferation and migration of vascular endothelial cells for angiogenesis. At the same time, MBG@PDA in the composite hydrogel could facilitate the long-term release of drugs to inhibit the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) for reducing the possibility of wound infection. Finally, the results of in vivo experiments showed that a multifunctional dressing could repair wounds more quickly by promoting angiogenesis and reducing the pathological areas. In summary, the construction of these composite hydrogels can provide a repair method in the wound-repair field.

Progress in Gelatin as Biomaterial for Tissue Engineering

Tissue engineering has become a medical alternative in this society with an ever-increasing lifespan. Advances in the areas of technology and biomaterials have facilitated the use of engineered constructs for medical issues. This review discusses on-going concerns and the latest developments in a widely employed biomaterial in the field of tissue engineering: gelatin. Emerging techniques including 3D bioprinting and gelatin functionalization have demonstrated better mimicking of native tissue by reinforcing gelatin-based systems, among others. This breakthrough facilitates, on the one hand, the manufacturing process when it comes to practicality and cost-effectiveness, which plays a key role in the transition towards clinical application. On the other hand, it can be concluded that gelatin could be considered as one of the promising biomaterials in future trends, in which the focus might be on the detection and diagnosis of diseases rather than treatment.