Natural polymer-derived photocurable bioadhesive hydrogels for sutureless keratoplasty

Engineered Mesenchymal Stromal Cell Exosomes-Loaded Microneedles Improve Corneal Healing after Chemical Injury

Corneal alkali burns represent a prevalent ophthalmic emergency with the potential to induce blindness. The main contributing mechanisms include excessive inflammation and delayed wound healing. Existing clinical therapies have limitations, promoting the exploration of alternative methods that offer improved efficacy and reduced side effects. Adipose-derived stem cell-exosome (ADSC-Exo) has the potential to sustain immune homeostasis and facilitate tissue regeneration. Nevertheless, natural ADSC-Exo lacks disease specificity and exhibits limited bioavailability on the ocular surface. In this study, we conjugated antitumor necrosis factor-α antibodies (aT) to the surface of ADSC-Exo using matrix metalloproteinase-cleavable peptide chains to create engineered aT-Exo with synergistic effects. In both in vivo and in vitro assessments, aT-Exo demonstrated superior efficacy in mitigating corneal injuries compared to aT alone, unmodified exosomes, or aT simply mixed with exosomes. The cleavable conjugation of aT-Exo notably enhanced wound healing and alleviated inflammation more effectively. Simultaneously, we developed poly(vinyl alcohol) microneedles (MNs) for precise and sustained exosome delivery. The in vivo results showcased the superior therapeutic efficiency of MNs compared with conventional topical administration and subconjunctival injection. Therefore, the bioactive nanodrugs-loaded MNs treatment presents a promising strategy for addressing ocular surface diseases.

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.

Silk fibroin hydrogel adhesive enables sealed-tight reconstruction of meniscus tears

Despite orientationally variant tears of the meniscus, suture repair is the current clinical gold treatment. However, inaccessible tears in company with re-tears susceptibility remain unresolved. To extend meniscal repair tools from the perspective of adhesion and regeneration, we design a dual functional biologic-released bioadhesive (S-PIL10) comprised of methacrylated silk fibroin crosslinked with phenylboronic acid-ionic liquid loading with growth factor TGF-β1, which integrates chemo-mechanical restoration with inner meniscal regeneration. Supramolecular interactions of β-sheets and hydrogen bonds richened by phenylboronic acid-ionic liquid (PIL) result in enhanced wet adhesion, swelling resistance, and anti-fatigue capabilities, compared to neat silk fibroin gel. Besides, elimination of reactive oxygen species (ROS) by S-PIL10 further fortifies localized meniscus tear repair by affecting inflammatory microenvironment with dynamic borate ester bonds, and S-PIL10 continuously releases TGF-β1 for cell recruitment and bridging of defect edge. In vivo rabbit models functionally evidence the seamless and dense reconstruction of torn meniscus, verifying that the concept of meniscus adhesive is feasible and providing a promising revolutionary strategy for preclinical research to repair meniscus tears.

Photocurable and Temperature-Sensitive Bioadhesive Hydrogels for Sutureless Sealing of Full-Thickness Corneal Wounds

Penetrating corneal wounds can cause severe vision impairment and require prompt intervention to restore globe integrity and minimize the risk of infection. Tissue adhesives have emerged as a promising alternative to suturing for mitigating postoperative complications. However, conventional water-soluble adhesives suffer formidable challenges in sealing penetrating corneal wounds due to dilution or loss in a moist environment. Inspired by the robust adhesion of mussels in aquatic conditions, an injectable photocurable bioadhesive hydrogel (referred to as F20HD5) composed of polyether F127 diacrylate and dopamine-modified hyaluronic acid methacrylate is developed for sutureless closure of corneal full-thickness wounds. F20HD5 exhibits high transparency, wound-sealing ability, proper viscosity, biodegradability, and excellent biocompatibility. It allows in situ cross-linking via visible light, thereby providing sufficient mechanical strength and adhesiveness. In vivo, the adhesive hydrogel effectively closed penetrating linear corneal incisions and corneal injuries with minimal tissue loss in rabbits. During the 56-day follow-up, the hydrogel facilitates the repair of the injured corneas, resulting in more symmetrical curvatures and less scarring in distinction to the untreated control. Thus, bioinspired hydrogel holds promise as an effective adhesive for sealing full-thickness corneal wounds.

Bone morphogenetic protein 4 thermosensitive hydrogel inhibits corneal neovascularization by repairing corneal epithelial apical junctional complexes

Corneal neovascularization (CNV) is a heavy attribute of blinding disease changes. Existing medications need numerous infusions and have a limited absorption. Investigating novel drugs with safety, efficacy, and convenience is crucial. In this study, we developed a bone morphogenetic protein 4 (BMP4)-loaded poloxamer-oxidized sodium alginate (F127-OSA) thermosensitive hydrogel. The 14 % F127-OSA hydrogel transformed from sol to gel at 31-32 °C, which might extend the application period on the ocular surface. The hydrogel's porous structure and uniform dispersion made it possible for drugs to release gradually. We used a suture-induced rat CNV model to investigate the mechanism of CNV inhibition by hydrogel. We discovered that F127-OSA hydrogel loaded with BMP4 could significantly reduce the length and area of CNV, relieve corneal edema, and stop aberrant epithelial cell proliferation. The hydrogel's efficacy was superior to that of the common solvent group. Additionally, BMP4 thermosensitive hydrogel repaired ultrastructure, including microvilli, intercellular junctions, and damaged apical junctional complexes (AJCs), suggesting a potential mechanism by which the hydrogel prevented CNV formation. In conclusion, our investigation demonstrates that F127-OSA thermosensitive hydrogel loaded with BMP4 can repair corneal epithelial AJCs and is a promising novel medication for the treatment of CNV.

Development of Thermoplastic Polyurethane Films for the Replacement of Corneal Endothelial Function of Transparency Maintenance

Endothelial keratoplasty is the main surgical procedure for treating corneal endothelial dysfunction (CED), which is limited by the global shortage of donor corneas. Herein, we developed and evaluated the modified thermoplastic polyurethane (M-TPU) films with gelatin-glycidyl methacrylate to replace the corneal endothelial function and maintain corneal transparency. The films displayed comparable light transmission characteristics with normal corneas and clinically favorable mechanical properties for surgical manipulation. After surface modification, the hydrophilicity and biocompatibility of M-TPU films were significantly improved. In the rabbit CED model, the M-TPU implants exhibited firm adhesion to the exposed stromal surface. The rabbit corneal transparency and thickness could be restored completely within 1 week of M-TPU film implantation. There was no significant inflammatory reaction and immune rejection during the follow-up of 1 month. Proteomic analysis suggested that the complement inhibition, the increase of mineral absorption, and the decrease of P53 apoptosis signaling pathway and lysine degradation might be beneficial in maintaining the corneal transparency. Overall, our study demonstrated the potential of M-TPU films as artificial implants for the replacement of corneal endothelial function to restore corneal thickness and transparency.

A Versatile Hydrogel with Antibacterial and Sequential Drug-Releasing Capability for the Programmable Healing of Infectious Keratitis

Hydrogels have attracted tremendous attention as favorable corneal substitutes for treating severe infectious keratitis (IK). However, current hydrogel-based corneal substitutes were majorly designed to promote the single stage of corneal regeneration, which falls short in meeting the clinical management needs of severe IK including the multiple phases of corneal wound healing. Herein, we introduce a versatile hybrid hydrogel (SQPV) composed of silk fibroin and chitosan, which exhibits spatiotemporal properties for drug release. The SQPV is fabricated by incorporating verteporfin-loaded poly(lactic-co-glycolic)-polyethylene glycol-o-nitrobenzene micelles into a hydrogel network, which is formed from methacrylate silk fibroin and glycidyl methacrylate functionalized quaternized chitosan containing polydeoxyribonucleotide. This double network approach results in a material with exceptional anti-inflammatory, antibacterial, and proliferative stimulation and tissue remodeling regulation capabilities. Furthermore, SQPV showcases mechanical strength and transparency akin to those of native cornea. Extensive in vitro and in vivo studies validate SQPV's ability to effectively eliminate residual bacteria, mitigate inflammation, foster regeneration of corneal epithelium and stroma, prevent corneal scarring, and ultimately expedite wound healing. In summary, the SF/CS-based hybrid hydrogel may represent a promising substitute for comprehensive corneal repair and regeneration in severe IK.

Preparation of chitosan/citral forward osmosis membrane via Schiff base reaction with enhanced anti-bacterial properties

In this study, hydrogels generated by the Schiff base reaction between citral and chitosan (CS) were used for the first time to improve the anti-bacterial property of forward osmosis (FO) membranes. The composite membranes were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Water contact angle (WCA), Zeta potential and confocal laser scanning microscopic (CLSM). In the FO filtration experiment, the membrane performance of TFC-1 with 1 M sodium chloride solution as the draw solution and deionized water as the feed solution was the best, with the water flux of 25.54 ± 0.7 L m-2 h-1 and the reverse salt flux of 4.7 ± 0.4 g m-2 h-1. Although the hydrogel coating produced a certain hydraulic resistance, the flux of the modified membrane was only reduced by about 8%, compared with the unmodified membrane. However, the anti-bacterial property (Pseudomonas aeruginosa) and anti-fouling properties (bovine serum protein and lysozyme protein) of the modified membranes were improved, showing good antibacterial properties (99%) and flux recovery rate (over 90%). The modified method has the advantages of easy access to raw materials, simple operation and no risk of secondary pollution, which can effectively reduce the cost of chemical cleaning and extend the service life of the membrane. The modification of membrane by chitosan-based hydrogel is a promising option in the field of membrane anti-bacteria.

Bioadhesives with Antimicrobial Properties

Bioadhesives with antimicrobial properties enable easier and safer treatment of wounds as compared to the traditional methods such as suturing and stapling. Composed of natural or synthetic polymers, these bioadhesives seal wounds and facilitate healing while preventing infections through the activity of locally released antimicrobial drugs, nanocomponents, or inherently antimicrobial polers. Although many different materials and strategies are employed to develop antimicrobial bioadhesives, the design of these biomaterials necessitates a prudent approach as achieving all the required properties including optimal adhesive and cohesive properties, biocompatibility, and antimicrobial activity can be challenging. Designing antimicrobial bioadhesives with tunable physical, chemical, and biological properties will shed light on the path for future advancement of bioadhesives with antimicrobial properties. In this review, the requirements and commonly used strategies for developing bioadhesives with antimicrobial properties are discussed. In particular, different methods for their synthesis and their experimental and clinical applications on a variety of organs are reviewed. Advances in the design of bioadhesives with antimicrobial properties will pave the way for a better management of wounds to increase positive clinical outcomes.

A suture-free, shape self-adaptive and bioactive PEG-Lysozyme implant for Corneal stroma defect repair and rapid vision restoration

Corneal transplantation is a prevailing treatment to repair injured cornea and restore vision but faces the limitation of donor tissue shortage clinically. In addition, suturing-needed transplantation potentially causes postoperative complications. Herein, we design a PEG-Lysozyme injective hydrogel as a suture-free, shape self-adaptive, bioactive implant for corneal stroma defect repair. This implant experiences a sol-gel phase transition via an in situ amidation reaction between 4-arm-PEG-NHS and lysozyme. The physicochemical properties of PEG-Lysozyme can be tuned by the components ratio, which confers the implant mimetic corneal modulus and provides tissue adhesion to endure increased intraocular pressure. In vitro tests prove that the implant is beneficial to Human corneal epithelial cells growth and migration due to the bioactivity of lysozyme. Rabbit lamellar keratoplasty experiment demonstrates that the hydrogel can be filled into defect to form a shape-adaptive implant adhered to native stroma. The implant promotes epithelialization and stroma integrity, recovering the topology of injured cornea to normal. A newly established animal forging behavior test prove a rapid visual restoration of rabbits when use implant in a suture free manner. In general, this work provides a promising preclinical practice by applicating a self-curing, shape self-adaptive and bioactive PEG-Lysozyme implant for suture-free stroma repair.

Human cornea-derived extracellular matrix hydrogel for prevention of post-traumatic corneal scarring: A translational approach

Corneal scarring and opacification are a significant cause of blindness affecting millions worldwide. The current standard of care for corneal blindness is corneal transplantation, which suffers from several drawbacks. One alternative approach that has shown promise is the use of xenogeneic corneal extracellular matrix (ECM), but its clinical applicability is challenging due to safety concerns. This study reports the innovative use of human cornea-derived ECM to prevent post-traumatic corneal scarring. About 30 - 40% of corneas donated to the eye banks do not meet the standards defined for clinical use and are generally discarded, although they are completely screened for their safety. In this study, human cornea-derived decellularized ECM hydrogel was prepared from the non-transplantation grade human cadaveric corneas obtained from an accredited eye-bank. The prepared hydrogel was screened for its efficacy against corneal opacification following an injury in an animal model. Our in vivo study revealed that, the control collagen-treated group developed corneal opacification, while the prophylactic application of human cornea-derived hydrogel effectively prevented corneal scarring and opacification. The human hydrogel-treated corneas were indistinguishable from healthy corneas and comparable to those treated with the xenogeneic bovine corneal hydrogel. We also demonstrated that the application of the hydrogel retained the biological milieu including cell behavior, protein components, optical properties, curvature, and nerve regeneration by remodeling the corneal wound after injury. The hydrogel application is also sutureless, resulting in faster corneal healing. We envision that this human cornea-derived ECM-based hydrogel has potential clinical application in preventing scarring from corneal wounding. STATEMENT OF SIGNIFICANCE: There are significant challenges surrounding corneal regeneration after injury due to extensive scarring. Although there is substantial research on corneal regeneration, much of it uses synthetic materials with chemical cross-linking methods or xenogeneic tissue-based material devices which have to undergo exhaustive safety analysis before clinical trials. Herein, we demonstrate the potential application of a human corneal extracellular matrix hydrogel without any additional materials for scarless corneal tissue regeneration, and a method to reduce the wasting of donated allogenic corneal tissue from eye banks. We found no difference in efficacy between the usage of human tissues compared to xenogeneic sources. This may help ease clinical translation and can be used topically without sutures as an outpatient procedure.

The effect of GelDex-S58 hydrogel on anti-conjunctival scarring after glaucoma filtration surgery

Excessive scarring is the main cause of surgical failure in glaucoma filtration surgery. S58 has been shown to have an excellent antifibrotic effect but its duration of action is not sufficient to achieve the desired antiscarring effect. In this study, a light-cured bioadhesive hydrogel composed of GelMA and oxidized dextran (ODex), namely, GelDex, was used to load S58 (GelDex-S58). The microscopic morphology of GelDex-S58 appeared to be a porous structure with good slow-release properties and suitable degradation time. Cell Counting Kit-8, cell scratch and transwell assays showed that GelDex-S58 significantly reduced TGF-β-induced fibroblast proliferation, increased migration and invasion ability. In in vivo studies, GelDex-S58 treatment prolonged follicular retention, reduced mean intraocular pressure, and significantly reduced collagen deposition and α-SMA expression levels in the conjunctival tissue compared to treatment with S58 alone. In conclusion, GelDex-S58 could reduce scar formation after glaucoma filtration surgery.

ECM-Like Adhesive Hydrogel for the Regeneration of Large Corneal Stromal Defects

The repair of large-diameter corneal stroma defects is a major clinical problem. Although some studies have attempted to use hydrogels to repair corneal damage, most of these hydrogels can only be used for focal stromal defects that are ≤3.5 mm in diameter due to poor hydrogel adhesion. Here, a photocurable adhesive hydrogel that mimics the extracellular matrix (ECM) with regard to composition for repairing 6 mm-diameter corneal stromal defects in rabbits is investigated. This ECM-like adhesive can be rapidly cured after light exposure, with high light transmittance and good mechanical properties. More importantly, this hydrogel maintains the viability and adhesion of cornea-derived cells and promotes their migration in vitro in 2D and 3D culture environments. Proteomics analysis confirms that the hydrogel promotes cell proliferation and ECM synthesis. Furthermore, in rabbit corneal stromal defect repair experiments, it is proven by histological and proteomic analysis that this hydrogel can effectively promote corneal stroma repair, reduce scar formation, and increase corneal stromal-neural regeneration at the six months follow-up. This work demonstrates the great application of ECM-like adhesive hydrogels for the regeneration of large-diameter corneal defects.

An Integrally Formed Janus Hydrogel for Robust Wet-Tissue Adhesive and Anti-Postoperative Adhesion

Facile fabrication of asymmetrically adhesive hydrogel with robust wet tissue adhesion simultaneously with effective anti-postoperative adhesion still remains a great challenge. In this work, an integrally formed Janus hydrogel is facilely fabricated in one step by controlling the interfacial distribution of free carboxyl groups on the two sides of hydrogels. At a lower stirring speed, the generated bigger sized emulsion droplets mainly occupy the top surface of hydrogel, which effectively hinders the exposition of carboxyl groups on the top surface, driving them to be more distributed on the bottom surface, ultimately resulting in the poor adhesion of top surface but robust adhesion of bottom surface to various wet tissue even underwater. The difference in adhesive strength achieves as high as 20 times between the two surfaces. In vivo rabbit experiment outcomes clearly validate that the bottom surface of hydrogel firmly adheres to the stomach defect, and the other opposite surface can efficiently address the postoperative adhesion problem. Besides, this hydrogel exhibits superior mechanical toughness and conductivity which has been used as a highly adhesive strain sensor to real-time monitor the beating heart in vivo. This simple yet effective strategy provides a much more feasible approach for creating Janus hydrogels bioadhesives.

Direct 3D Bioprinting of Tough and Antifatigue Cell-Laden Constructs Enabled by a Self-Healing Hydrogel Bioink

Three-dimensional (3D) extrusion bioprinting has emerged as one of the most promising biofabrication technologies for preparing biomimetic tissue-like constructs. The successful construction of cell-laden constructs majorly relies on the development of proper bioinks with excellent printability and cytocompatibility. Bioinks based on gelatin methacryloyl (GelMA) have been widely explored due to the excellent biocompatibility and biodegradability and the presence of the arginine-glycine-aspartic acid (RGD) sequences for cell adhesion. However, such bioinks usually require low-temperature or ionic cross-linking systems to solidify the extruded hydrogel structures, which results in complex processes and limitations to certain applications. Moreover, many current hydrogel-based bioinks, even after chemical cross-linking, hardly possess the required strength to resist the mechanical loads during the implantation procedure. Herein, we report a self-healing hydrogel bioink based on GelMA and oxidized dextran (OD) for the direct printing of tough and fatigue-resistant cell-laden constructs at room temperature without any template or cross-linking agents. Enabled by dynamic Schiff base chemistry, the mixed GelMA/OD solution showed the characteristics of a dynamic hydrogel with shear-thinning and self-supporting behavior, which allows bridging the 5 mm gap and efficient direct bioprinting of complex constructs with high shape fidelity. After photo-cross-linking, the resulting tissue constructs exhibited excellent low cell damage, high cell viability, and enhanced mechanical strength. Moreover, the GelMA/OD construct could resist up to 95% compressive deformation without any breakage and was able to maintain 80% of the original Young's modulus during long-term loading (50 cycles). It is believed that our GelMA/OD bioink would expand the potential of GelMA-based bioinks in applications such as tissue engineering and pharmaceutical screening.

Dual-light defined in situ oral mucosal lesion therapy through a mode switchable anti-bacterial and anti-inflammatory mucoadhesive hydrogel

Oral mucosal ulcer is the most prevalent oral mucosal lesion, affecting the quality of life. Due to the moist and highly dynamic oral lining, the existing oral mucoadhesives are unable to serially address the challenges of residency, hemorrhage, bacterial infection and inflammatory reaction. Herein, a dual-light defined oral mucoadhesive (ZPTA-G/HMA) was proposed, with a methacrylate gelatin-methacrylate hyaluronic acid (GelMA-HAMA, G/HMA) double network hydrogel as a matrix, tannic acid (TA) as a high content anchor moiety provider for the moist oral mucosa, and polydopamine modified zinc oxide (ZnO@PDA, ZP) as a photocatalytic antibacterial substance. This platform had good adhesive and hemostatic properties both in vitro and in vivo. Under 520 nm green light (GL) irradiation, ZPTA-G/HMA would anchor to the wet mucosa surface by crosslinking and exert broad-spectrum antibacterial ability (even including Candida albicans) by in situ producing reactive oxygen species (ROS). Moreover, under 808 nm near-infrared (NIR) irradiation, the increased release of TA combined with the photothermal effect of ZP endowed ZPTA-G/HMA with enhanced anti-inflammatory and pro-healing performance. Collectively, ZPTA-G/HMA could be switched by light sources to achieve the dual-mode real-time adjustment of in situ anti-bacterial function and controlled anti-inflammation, combined with ideal mucosal residence, thus promising in developing personalized sequential strategies for varied oral mucosal lesions.

In Situ Formation of Injectable Gelatin Methacryloyl (GelMA) Hydrogels for Effective Intraocular Delivery of Triamcinolone Acetonide

A novel drug delivery system designed for intraocular injection, gelatin methacryloyl (GelMA), has attracted much attention due to its sustained-release character and low cytotoxicity. We aimed to explore the sustained drug effect of GelMA hydrogels coupled with triamcinolone acetonide (TA) after injection into the vitreous cavity. The GelMA hydrogel formulations were characterized using scanning electron microscopy, swelling measurements, biodegradation, and release studies. The biological safety effect of GelMA on human retinal pigment epithelial cells and retinal conditions was verified by in vitro and in vivo experiments. The hydrogel exhibited a low swelling ratio, resistance to enzymatic degradation, and excellent biocompatibility. The swelling properties and in vitro biodegradation characteristics were related to the gel concentration. Rapid gel formation was observed after injection, and the in vitro release study confirmed that TA-hydrogels have slower and more prolonged release kinetics than TA suspensions. In vivo fundus imaging, optical coherence tomography measurements of retinal and choroid thickness, and immunohistochemistry did not reveal any apparent abnormalities of retinal or anterior chamber angle, and ERG indicated that the hydrogel had no impact on retinal function. The GelMA hydrogel implantable intraocular device exhibited an extended duration, in situ polymerization, and support cell viability, making it an attractive, safe, and well-controlled platform for treating the posterior segment diseases of the eye.

Applications of hydrogel materials in different types of corneal wounds

Severe corneal injury can lead to a decrease in light transmission and even blindness. Currently, corneal transplantation has been applied as the primary treatment for corneal blindness; however, the worldwide shortage of suitable corneal donor tissue means that a large proportion of patients have no access to corneal transplants. This situation has contributed to the rapid development of various corneal substitutes. The development and optimization of novel hydrogels that aim to replace partial or full-thickness pathological corneas have advanced in the last decade. Meanwhile, with the help of 3D bioprinting technology, hydrogel materials can be molded to a refined and controllable shape, attracting many scientists to the field of corneal reconstruction research. Although hydrogels are not yet available as a substitute for traditional clinical methods of corneal diseases, their rapid development makes us confident that they will be in the near future. We summarize the application of hydrogel materials for various types of corneal injuries frequently encountered in clinical practice, especially focusing on animal experiments and preclinical studies. Finally, we discuss the development and achievements of 3D bioprinting in the treatment of corneal injury.

A "T.E.S.T." hydrogel bioadhesive assisted by corneal cross-linking for in situ sutureless corneal repair

Corneal transplantation is an effective clinical treatment for corneal diseases, which, however, is limited by donor corneas. It is of great clinical value to develop bioadhesive corneal patches with functions of "Transparency" and "Epithelium & Stroma generation", as well as "Suturelessness" and "Toughness". To simultaneously meet the "T.E.S.T." requirements, a light-curable hydrogel is designed based on methacryloylated gelatin (GelMA), Pluronic F127 diacrylate (F127DA) & Aldehyded Pluronic F127 (AF127) co-assembled bi-functional micelles and collagen type I (COL I), combined with clinically applied corneal cross-linking (CXL) technology for repairing damaged cornea. The patch formed after 5 min of ultraviolet irradiation possesses transparent, highly tough, and strongly bio-adhesive performance. Multiple cross-linking makes the patch withstand deformation near 600% and exhibit a burst pressure larger than 400 mmHg, significantly higher than normal intraocular pressure (10-21 mmHg). Besides, the slower degradation than GelMA-F127DA&AF127 hydrogel without COL I makes hydrogel patch stable on stromal beds in vivo, supporting the regrowth of corneal epithelium and stroma. The hydrogel patch can replace deep corneal stromal defects and well bio-integrate into the corneal tissue in rabbit models within 4 weeks, showing great potential in surgeries for keratoconus and other corneal diseases by combining with CXL.

Dual-crosslinked regenerative hydrogel for sutureless long-term repair of corneal defect

Corneal transplantation is the most effective clinical treatment for corneal defects, but it requires precise size of donor corneas, surgical sutures, and overcoming other technical challenges. Postoperative patients may suffer graft rejection and complications caused by sutures. Ophthalmic glues that can long-term integrate with the corneal tissue and effectively repair the focal corneal damage are highly desirable. Herein, a hybrid hydrogel consisting of porcine decellularized corneal stroma matrix (pDCSM) and methacrylated hyaluronic acid (HAMA) was developed through a non-competitive dual-crosslinking process. It can be directly filled into corneal defects with various shapes. More importantly, through formation of interpenetrating network and stable amide bonds between the hydrogel and adjacent tissue, the hydrogel manifested excellent adhesion properties to achieve suture-free repair. Meanwhile, the hybrid hydrogel not only preserved bioactive components from pDCSM, but also exhibited cornea-matching transparency, low swelling ratio, slow degradation, and enhanced mechanical properties, which was capable of withstanding superhigh intraocular pressure. The combinatorial hydrogel greatly improved the poor cell adhesion performance of HAMA, supported the viability, proliferation of corneal cells, and preservation of keratocyte phenotype. In a rabbit corneal stromal defect model, the experimental eyes treated with the hybrid hydrogel remained transparent and adhered intimately to the stroma bed with long-term retention, accelerated corneal re-epithelialization and wound healing. Giving the advantages of high bioactivity, low-cost, and good practicality, the dual-crosslinked hybrid hydrogel served effectively for long-term suture-free treatment and tissue regeneration after corneal defect.

•

Double-network hydrogel contains regenerative decellularized corneal stroma matrix.

•

Suture-free easy operation, high transparency, strong attachment to stroma bed.

•

Long-term retention on corneal defect with excellent force and pressure resistance.

•

Rapid re-epithelialization, minimal scar formation, sustained cornea regeneration.

•

A functional biomaterial-based strategy for in situ corneal wound healing.

Preparation and Evaluation of Bacterial Nanocellulose/Hyaluronic Acid Composite Artificial Cornea for Application of Corneal Transplantation

The treatment for corneal damage requires donor corneal transplantation, but there is a serious scarcity of donor corneas worldwide. In this study, we aimed to design a new artificial cornea with good cytocompatibility, excellent optical properties and suture resistance, and great moisturizing properties. A new bacterial nanocellulose (BNC) membrane with anisotropic mechanical properties and high light transmission was produced in a horizontal rotary drum reactor. However, as a potential material for artificial keratoplasty, the transparency and mechanical properties of the new BNC membrane were not satisfactory. Thus, hyaluronic acid (HA) was introduced in the BNC to synthesize the BNC/HA composite membrane by using 1,4-butanediol diglycidyl ether (BDDE) as the chemical cross-linking agent. The micro-morphology, light transmittance, mechanical properties, water content, moisture retention ability, and cytocompatibility of the composite membranes were further evaluated. HA was fixed in the BNC network by the ether bond, and the composite membrane was found to have excellent light transmittance (up to 95.96%). The composite membrane showed excellent mechanical properties, for instance, its tensile strength exceeded the human normal intraocular pressure (IOP) (1.33-2.80 kPa), the maximum burst pressure was about 130 kPa, 46-97 times that of the normal IOP, and its suture force was close to that of the human amniotic membrane (0.1 N). Based on the three-dimensional network scaffold of BNC and the high water absorption characteristics of HA, the artificial cornea had high water content and high moisture retention ability. The rabbit corneal stromal cells cultured in vitro showed that the artificial cornea substitute had excellent cytocompatibility. BDDE is the most frequently used cross-linker in most HA products in the current cosmetic medicine industry owing to its long-term safety records for over 15 years. Therefore, the BNC/HA composite hydrogel cross-linked with BDDE has great potential in artificial keratoplasty or ocular surface repair.

Smart bioadhesives for wound healing and closure

The high demand for rapid wound healing has spurred the development of multifunctional and smart bioadhesives with strong bioadhesion, antibacterial effect, real-time sensing, wireless communication, and on-demand treatment capabilities. Bioadhesives with bio-inspired structures and chemicals have shown unprecedented adhesion strengths, as well as tunable optical, electrical, and bio-dissolvable properties. Accelerated wound healing has been achieved via directly released antibacterial and growth factors, material or drug-induced host immune responses, and delivery of curative cells. Most recently, the integration of biosensing and treatment modules with wireless units in a closed-loop system yielded smart bioadhesives, allowing real-time sensing of the physiological conditions (e.g., pH, temperature, uric acid, glucose, and cytokine) with iterative feedback for drastically enhanced, stage-specific wound healing by triggering drug delivery and treatment to avoid infection or prolonged inflammation. Despite rapid advances in the burgeoning field, challenges still exist in the design and fabrication of integrated systems, particularly for chronic wounds, presenting significant opportunities for the future development of next-generation smart materials and systems.

•

Rational material engineering of bioadhesives with optimized mechanical and curative properties.

•

Incorporation of biosensing allows real-time and precise evaluation of the healing stage.

•

Closed-loop, smart bioadhesives that integrate wireless sensing and treatment hold great potential for chronic wound healing.

Fabrication of biphasic cartilage-bone integrated scaffolds based on tissue-specific photo-crosslinkable acellular matrix hydrogels

The fabrication of biphasic cartilage-bone integrated scaffolds is an attractive alternative for osteochondral repair but has proven to be extremely challenging. Existing three-dimensional (3D) scaffolds are insufficient to accurately biomimic the biphasic cartilage-bone integrated microenvironment. Currently, photo-crosslinkable hydrogels based on tissue-specific decellularized extracellular matrix (dECM) have been considered as an important technique to fabricate biomimetic scaffolds, but so far there has been no breakthrough in the photo-crosslinkable hydrogel scaffolds with biphasic cartilage-bone biomimetic microenvironment. Here, we report a novel strategy for the preparation of biomimetic cartilage-bone integrated scaffolds based on photo-crosslinkable cartilage/bone-derived dECM hydrogels, which are able to reconstruct biphasic cartilage-bone biomimetic microenvironment. The biphasic cartilage-bone integrated scaffolds provided a 3D microenvironment for osteochondral regeneration. The cartilage biomimetic scaffolds, consisting of cartilage-derived dECM hydrogels, efficiently regulated chondrogenesis of bone marrow mesenchymal stem cells (BMSCs). The bone biomimetic scaffolds, composed of cartilage/bone-derived dECM hydrogels, first regulated chondrogenesis of BMSCs, followed by endochondral ossification over time. Taken together, the biphasic cartilage-bone integrated tissue could be successfully reconstructed by subcutaneous culture based on cartilage-bone bilayered structural design. Furthermore, the biphasic cartilage-bone biomimetic scaffolds (cell-free) achieved satisfactory cartilage-bone integrated regeneration in the osteochondral defects of rabbits’ knee joints.

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

Corneal regeneration has always been a challenge due to its sophisticated structure and undesirable keratocyte-fibroblast transformation. Herein, we propose 3D printing of a biomimetic epithelium/stroma bilayer implant for corneal regeneration. Gelatin methacrylate (GelMA) and long-chain poly(ethylene glycol) diacrylate (PEGDA) are blended to form a two-component ink, which can be printed to different mechanically robust programmed PEGDA-GelMA objects by Digital Light Processing (DLP) printing technology, due to the toughening effect of crystalline crosslinks from long-chain PEGDA on GelMA hydrogel after photo-initiated copolymerization. The printed PEGDA-GelMA hydrogels support cell adhesion, proliferation, migration, meanwhile demonstrating a high light transmittance, and an appropriate swelling degree, nutrient permeation and degradation rate. A bi-layer dome-shaped corneal scaffold consisting of rabbit corneal epithelial cells (rCECs)-laden epithelia layer and rabbit adipose-derived mesenchymal stem cells (rASCs)-laden orthogonally aligned fibrous stroma layer can be printed out with a high fidelity and robustly surgical handling ability. This bi-layer cells-laden corneal scaffold is applied in a rabbit keratoplasty model. The post-operative outcome reveals efficient sealing of corneal defects, re-epithelialization and stromal regeneration. The concerted effects of microstructure of 3D printed corneal scaffold and precisely located cells in epithelia and stroma layer provide an optimal topographical and biological microenvironment for corneal regeneration.

•

Crystalline microphase of long PEGDA is employed to toughen GelMA hydrogel.

•

A bi-layer dome-shaped robust hydrogel-based biomimetic corneal scaffold is printed.

•

The 3D printed cornea implant can efficiently repair the rabbits' corneal defect.

Natural Dual-Crosslinking Bioadhesive Hydrogel for Corneal Regeneration in Large-Size Defects

Corneal injectable hydrogels represent a promising alternative to alleviate donor shortage and simplify traditional surgeries. However, most hydrogels focus on repairing focal corneal defects (≤3.5 mm) and leave many clinical requirements unmet. Herein, a novel ion-activated bioadhesive hydrogel (IonBAH) is designed and its long-term performance of repairing large corneal defects (6 mm) is evaluated in rabbits for 6 months. The IonBAH is a dual-network hydrogel composed of natural corneal extracellular matrix and peptide-modified alginate, which enables its desirable transparency and biocompatibility, tunable mechanics, and robust adhesion. Moreover, the IonBAH maintains the secretory phenotype of quiescent keratocytes, while preventing their myofibroblastic differentiation in vitro. Upon application in situ, it rapidly seals the 6 mm corneal defect and forms normal curvature through the coverage of a contact lens impregnated with calcium ions. During the 6 months follow-up, the IonBAH promotes rapid regeneration of corneal epithelium, stroma, and nerves with restored transparency, equivalent to the outcome of donor corneal transplantation. In addition, the suitability of IonBAH as an adhesive and patch for various clinical requirements are also evaluated with a pleasing outcome. Collectively, IonBAH may provide a clinically applicable scaffold for corneal surgeries, especially in large defect repair.

Bio-macromolecular design roadmap towards tough bioadhesives

Emerging sutureless wound-closure techniques have led to paradigm shifts in wound management. State-of-the-art biomaterials offer biocompatible and biodegradable platforms enabling high cohesion (toughness) and adhesion for rapid bleeding control as well as robust attachment of implantable devices. Tough bioadhesion stems from the synergistic contributions of cohesive and adhesive interactions. This Review provides a biomacromolecular design roadmap for the development of tough adhesive surgical sealants. We discuss a library of materials and methods to introduce toughness and adhesion to biomaterials. Intrinsically tough and elastic polymers are leveraged primarily by introducing strong but dynamic inter- and intramolecular interactions either through polymer chain design or using crosslink regulating additives. In addition, many efforts have been made to promote underwater adhesion via covalent/noncovalent bonds, or through micro/macro-interlock mechanisms at the tissue interfaces. The materials settings and functional additives for this purpose and the related characterization methods are reviewed. Measurements and reporting needs for fair comparisons of different materials and their properties are discussed. Finally, future directions and further research opportunities for developing tough bioadhesive surgical sealants are highlighted.

Mechanoresponsive Drug Loading System with Tunable Host-Guest Interactions for Ocular Disease Treatment

Conventional administration of eye drops often requires high dosages and/or repetitive treatments to achieve therapeutic efficacy. This is inefficient and may result in side effects or even toxicity. Although many delivery systems of ophthalmic drugs have been reported, most of them work in a fixed format in which both the type and dose of the loaded drugs cannot be changed upon demand. To overcome this limitation, a hybrid double network hydrogel system composed of methacryloyl gelatin, pluronic F127 diacrylate, and β-cyclodextrin-modified oxidized dextran was developed. The hydrogels presented good mechanical strength and biocompatibility. In vitro assessments demonstrated that the hydrogels loaded with commonly used ophthalmic drugs could sustain the drug release for more than 21 days. This hydrogel system exhibited features of mechanoresponsive drug loading, and the capacity of drug loading could be significantly enhanced by macroscopically mechanical compression. Further in vivo evaluation of the drug delivery capacity showed that a dexamethasone-loaded hydrogel as a fornix insert effectively suppressed upregulation of proangiogenic factors and suture-induced corneal neovascularization in rats. This novel hydrogel system represents a promising drug delivery platform, which could potentially improve the treatments of ocular surface and other diseases.

Graded-Three-Dimensional Cell-Encapsulating Hydrogel as a Potential Biologic Scaffold for Disc Tissue Engineering

BACKGROUND

Intervertebral disk (IVD) degeneration, which can cause lower back pain, is a major predisposing factor for disability and can be managed through multiple approaches. However, there is no satisfactory strategy currently available to reconstruct and recover the natural properties of IVDs after degeneration. As tissue engineering develops, scaffolds with embedded cell cultures have proved critical for the successful regeneration of IVDs.

METHODS

In this study, an integrated scaffold for IVD replacement was developed. Through scanning electron microscopy and other mechanical measurements, we characterized the physical properties of different hydrogels. In addition, we simulated the physiological structure of natural IVDs. Nucleus pulposus (NP) cells and annulus fibrosus-derived stem cells (AFSCs) were seeded in gelatin methacrylate (GelMA) hydrogel at different concentrations to evaluate cell viability and matrix expression.

RESULTS

It was found that different concentrations of GelMA hydrogel can provide a suitable environment for cell survival. However, hydrogels with different mechanical properties influence cell adhesion and extracellular matrix component type I collagen, type II collagen, and aggrecan expression.

CONCLUSION

This tissue-engineered IVD implant had a similar structure and function as the native IVD, with the inner area mimicking the NP tissue and the outer area mimicking the stratified annulus fibrosus tissue. The new integrated scaffold demonstrated a good simulation of disc structure. The preparation of efficient and regeneration-promoting tissue-engineered scaffolds is an important issue that needs to be explored in the future. It is hoped that this work will provide new ideas and methods for the further construction of functional tissue replacement discs.

Sutureless transplantation using a semi-interpenetrating polymer network bioadhesive for ocular surface reconstruction

The conjunctiva covers the largest area of ocular surface and is responsible for tear balance and clear vision. After trauma or surgery, the conjunctiva is prone to scarring and contracture. Transplantation with suture often implies numerous complications, such as inflammation, suture erosion, granuloma. And the suture needs to be removed, which means a secondary trauma. In this study, a (GMO) for sutureless conjunctival transplantation was developed based on a semi-interpenetrating polymer network (sIPN) consisting of gelatin methacrylate (GelMA) and oxidized hyaluronic acid (OHA). The maximum adhesion strength was 157 ± 17 kPa, and the burst pressure was 357 ± 29 kPa, which was 15 times higher than the human intraocular pressure (IOP). GMO bioadhesive hydrogel significantly improved surgical efficiency and secured the collagen scaffold firmly to a rabbit conjunctival defect. The sutureless transplantation approach revealed the promoted tissue repair without scar. In conclusion, GMO bioadhesive may be an attractive alternative to suture for ocular surface reconstruction by avoiding suture-related complications and improving clinical outcome. STATEMENT OF SIGNIFICANCE: Conjunctival tissue is prone to scarring and contracture after trauma, and surgery with sutures often implies numerous complications. In this study, the ocular surface reconstruction was achieved by sutureless transplantation of conjunctival scaffold using bioadhesive hydrogel. The prepared GMO bioadhesive based on the semi-interpenetrating network of gelatin methacrylate (GelMA) and oxidized hyaluronic acid (OHA) had favorable adhesion and mechanical properties. The sutureless transplantation approach significantly improved the operation efficiency, avoided suture-related complications, and promoted the regeneration of conjunctiva. This study highlights the great potential of the sutureless repair strategy for clinical application in ocular surface reconstruction.

Real-Time MRI Monitoring of GelMA-Based Hydrogel-Loaded Kartogenin for In Situ Cartilage Regeneration

The cartilage has poor ability to mount a sufficient healing response. Herein, kartogenin (KGN), an emerging stable non-protein compound with the ability to recruit bone marrow mesenchyme stem cells (BMSCs) to promote chondrogenic differentiation, was grafted onto dopamine-Fe(III) chelating nanoparticles, followed by involving a gelatin- and dextran-based injectable hydrogel to mimic the extracellular matrix to promote cartilage repair. The in vitro results demonstrated that KGN underwent long-term sustained release behavior and availably promoted the deep migration of BMSC cells in yielding hydrogels. Furthermore, in vivo New Zealand white rabbits’ cartilage defect model repairing results showed that cartilage defect obtained significant regeneration post operation in the 12th week, and the defect edge almost disappeared compared to adjacent normal cartilage tissue. Meanwhile, the T2-weighted magnetic resonance imaging (MRI) property resulting from dissociative Fe (III) can significantly monitor the degradation degree of the implanted hydrogels in the defect site. This integrated diagnosis and treatment system gives insight into cartilage regeneration.

Engineered Hemostatic Biomaterials for Sealing Wounds

Hemostatic biomaterials show great promise in wound control for the treatment of uncontrolled bleeding associated with damaged tissues, traumatic wounds, and surgical incisions. A surge of interest has been directed at boosting hemostatic properties of bioactive materials via mechanisms triggering the coagulation cascade. A wide variety of biocompatible and biodegradable materials has been applied to the design of hemostatic platforms for rapid blood coagulation. Recent trends in the design of hemostatic agents emphasize chemical conjugation of charged moieties to biomacromolecules, physical incorporation of blood-coagulating agents in biomaterials systems, and superabsorbing materials in either dry (foams) or wet (hydrogel) states. In addition, tough bioadhesives are emerging for efficient and physical sealing of incisions. In this Review, we highlight the biomacromolecular design approaches adopted to develop hemostatic bioactive materials. We discuss the mechanistic pathways of hemostasis along with the current standard experimental procedures for characterization of the hemostasis efficacy. Finally, we discuss the potential for clinical translation of hemostatic technologies, future trends, and research opportunities for the development of next-generation surgical materials with hemostatic properties for wound management.

Update on Suture Techniques in Corneal Transplantation: A Systematic Review

Effective suturing remains key to achieving successful outcomes in corneal surgery, especially anterior lamellar keratoplasty and full thickness transplantation. Limitations in the technique may result in complications such as wound leak, infection, or high astigmatism post corneal graft. By using a systematic approach, this study reviews articles and conducts content analysis based on update 2020 PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria). The aim of this paper is to summarize the state of the art of corneal suturing techniques for every type of corneal transplant and patient age and also their outcomes regarding astigmatism and complications. Future developments for corneal transplantation will be also discussed. This is important because especially the young surgeon must have knowledge of the implications of every suture performed in order to achieve consistent and predictable post-operative outcomes and also be aware of all the possible complications.