Supramolecular host-guest hyaluronic acid hydrogels enhance corneal wound healing through dynamic spatiotemporal effects

Comparative fluorophotometric evaluation of the ocular surface retention time of cross-linked and linear hyaluronic acid ocular eye drops on healthy dogs

PURPOSE

Evaluate and compare the retention time on the canine ocular surface of crosslinked hyaluronic acid (X-HA), linear hyaluronic acid (L-HA) and saline solution using fluorescent compounds (fluorescein sodium salt, Alexa Fluor 488 cadaverine and Alexa Fluor 488 maleimide).

METHODS

0.9% saline solution (SAL) was combined with fluorescein sodium salt. X-HA and L-HA were covalently modified using Alexa Fluor 488 reactive moieties. Eye drops were applied to 70 eyes of 35 dogs that were previously assessed and determined to have a normal ocular surface. Employing a blue light filter (450-490 nm), digital images were captured from instillation to 180 min. Images were analyzed to assess the percent of the total ocular area covered with green fluorescence at various time points.

RESULTS

X-HA exhibited a dual phase behavior: A broad microgel coverage first, followed by accumulation in tear film meniscus and medial canthus in the second phase, remaining in contact with the ocular surface up to 180 min. Coverage with L-HA and SAL eye drops quickly migrated to the tear meniscus. No traces of the fluorescent compounds were observed by 45 min in eyes treated with SAL solution compound and, by 120 min, eyes treated with L-HA.

CONCLUSIONS

X-HA exhibited a significantly increased ocular surface contact time with the ocular surface compared with L-HA and SAL. Not only could this indicate extended lubrication time but also supports the potential use of this compound as a method for topical sustained-release drug application.

In Situ-Forming, Bioorthogonally Cross-linked, Nanocluster-Reinforced Hydrogel for the Regeneration of Corneal Defects

Corneal defects can lead to stromal scarring and vision loss, which is currently only treatable with a cadaveric corneal transplant. Although in situ-forming hydrogels have been shown to foster regeneration of the cornea in the setting of stromal defects, the cross-linking, biomechanical, and compositional parameters that optimize healing have not yet been established. This, Corneal defects are also almost universally inflamed, and their rapid closure without fibrosis are critical to preserving vision. Here, an in situ forming, bioorthogonally cross-linked, nanocluster (NC)-reinforced collagen and hyaluronic acid hydrogel (NCColHA hydrogel) with enhanced structural integrity and both pro-regenerative and anti-inflammatory effects was developed and tested within a corneal defect model in vivo. The NCs serve as bioorthogonal nanocross-linkers, providing higher cross-linking density than polymer-based alternatives. The NCs also serve as delivery vehicles for prednisolone (PRD) and the hepatocyte growth factor (HGF). NCColHA hydrogels rapidly gel within a few minutes upon administration and exhibit robust rheological properties, excellent transparency, and negligible swelling/deswelling behavior. The hydrogel's biocompatibility and capacity to support cell growth were assessed using primary human corneal epithelial cells. Re-epithelialization on the NCColHA hydrogel was clearly observed in rabbit eyes, both ex vivo and in vivo, with expression of normal epithelial biomarkers, including CD44, CK12, CK14, α-SMA, Tuj-1, and ZO-1, and stratified, multilayered morphology. The applied hydrogel maintained its structural integrity for at least 14 days and remodeled into a transparent stroma by 56 days.

Dual fluorescence response of calix[4]arene-1,8-naphthalimide derivatives towards Hg(II) /Cr(VI) and their antimicrobial studies of transparent biofilms with hyaluronic acid

In this study, 4-sulfo-1,8-naphthalimide calixarene of derivatives were prepared (3 and 4) then transparent biofilms of the Ag salts of these compounds were formed in the presence of hyaluronic acid (HA), and antimicrobial properties were investigated. In chemosensor studies, the sensing ability behavior of 3 and 4 towards some cations and anions was investigated by fluorescence spectroscopy. It was observed that the prepared chemosensors show selectivity towards Hg(II) and Cr(VI). Ligand-ion interaction occurs according to the photo-induced electron transfer (PET) mechanism. The stoichiometric ratio was calculated by using Stern-Volmer plot method and binding constant Ksv values were found as 5.2 × 107 M-1 and 5.5 × 107 M-1 for 3-Hg(II) and 4-Hg(II) complexes, respectively and 4.0 × 107 M-1 and 4.3 × 107 M-1 for 3-Cr(VI) and 4-Cr(VI) complexes. The detection limits of the complexes of 3-Hg(II) and 4-Hg(II) are 6.35 × 10-12and 6.81 × 10-12, while those of 3-Cr(VI) and 4-Cr(VI) are 1.41 × 10- 11and 8.37 × 10-12, respectively. As a result of the antimicrobial test performed with these compounds, it was observed that the most effective material was HA-3Ag, which showed a significant antibacterial effect against Sarcina lutea (S. lutea) at a minimum inhibitory concentration (MIC) value of 0.097 mg/mL.

Resveratrol-Ampicillin Dual-Drug Loaded Polyvinylpyrrolidone/Polyvinyl Alcohol Biomimic Electrospun Nanofiber Enriched with Collagen for Efficient Burn Wound Repair

Background

The healing of burn wounds is a complicated physiological process that involves several stages, including haemostasis, inflammation, proliferation, and remodelling to rebuild the skin and subcutaneous tissue integrity. Recent advancements in nanomaterials, especially nanofibers, have opened a new way for efficient healing of wounds due to burning or other injuries.

Methods

This study aims to develop and characterize collagen-decorated, bilayered electrospun nanofibrous mats composed of PVP and PVA loaded with Resveratrol (RSV) and Ampicillin (AMP) to accelerate burn wound healing and tissue repair.

Results

Nanofibers with smooth surfaces and web-like structures with diameters ranging from 200 to 400 nm were successfully produced by electrospinning. These fibres exhibited excellent in vitro properties, including the ability to absorb wound exudates and undergo biodegradation over a two-week period. Additionally, these nanofibers demonstrated sustained and controlled release of encapsulated Resveratrol (RSV) and Ampicillin (AMP) through in vitro release studies. The zone of inhibition (ZOI) of PVP-PVA-RSV-AMP nanofibers against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was found 31±0.09 mm and 12±0.03, respectively, which was significantly higher as compared to positive control. Similarly, the biofilm study confirmed the significant reduction in the formation of biofilms in nanofiber-treated group against both S. aureus and E. coli. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis proved the encapsulation of RSV and AMP successfully into nanofibers and their compatibility. Haemolysis assay (%) showed no significant haemolysis (less than 5%) in nanofiber-treated groups, confirmed their cytocompatibility with red blood cells (RBCs). Cell viability assay and cell adhesion on HaCaT cells showed increased cell proliferation, indicating its biocompatibility as well as non-toxic properties. Results of the in-vivo experiments on a burn wound model demonstrated potential burn wound healing in rats confirmed by H&E-stained images and also improved the collagen synthesis in nanofibers-treated groups evidenced by Masson-trichrome staining. The ELISA assay clearly indicated the efficient downregulation of TNF-alpha and IL-6 inflammatory biomarkers after treatment with nanofibers on day 10.

Conclusion

The RSV and AMP-loaded nanofiber mats, developed in this study, expedite burn wound healing through their multifaceted approach.

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.

Hydrogels in Cutaneous Wound Healing: Insights into Characterization, Properties, Formulation and Therapeutic Potential

Hydrogels are polymeric materials that possess a set of characteristics meeting various requirements of an ideal wound dressing, making them promising for wound care. These features include, among others, the ability to absorb and retain large amounts of water and the capacity to closely mimic native structures, such as the extracellular matrix, facilitating various cellular processes like proliferation and differentiation. The polymers used in hydrogel formulations exhibit a broad spectrum of properties, allowing them to be classified into two main categories: natural polymers like collagen and chitosan, and synthetic polymers such as polyurethane and polyethylene glycol. This review offers a comprehensive overview and critical analysis of the key polymers that can constitute hydrogels, beginning with a brief contextualization of the polymers. It delves into their function, origin, and chemical structure, highlighting key sources of extraction and obtaining. Additionally, this review encompasses the main intrinsic properties of these polymers and their roles in the wound healing process, accompanied, whenever available, by explanations of the underlying mechanisms of action. It also addresses limitations and describes some studies on the effectiveness of isolated polymers in promoting skin regeneration and wound healing. Subsequently, we briefly discuss some application strategies of hydrogels derived from their intrinsic potential to promote the wound healing process. This can be achieved due to their role in the stimulation of angiogenesis, for example, or through the incorporation of substances like growth factors or drugs, such as antimicrobials, imparting new properties to the hydrogels. In addition to substance incorporation, the potential of hydrogels is also related to their ability to serve as a three-dimensional matrix for cell culture, whether it involves loading cells into the hydrogel or recruiting cells to the wound site, where they proliferate on the scaffold to form new tissue. The latter strategy presupposes the incorporation of biosensors into the hydrogel for real-time monitoring of wound conditions, such as temperature and pH. Future prospects are then ultimately addressed. As far as we are aware, this manuscript represents the first comprehensive approach that brings together and critically analyzes fundamental aspects of both natural and synthetic polymers constituting hydrogels in the context of cutaneous wound healing. It will serve as a foundational point for future studies, aiming to contribute to the development of an effective and environmentally friendly dressing for wounds.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

3D printing sequentially strengthening high-strength natural polymer hydrogel bilayer scaffold for cornea regeneration

3D printing of high-strength natural polymer biodegradable hydrogel scaffolds simultaneously resembling the biomechanics of corneal tissue and facilitating tissue regeneration remains a huge challenge due to the inherent brittleness of natural polymer hydrogels and the demanding requirements of printing. Herein, concentrated aqueous solutions of gelatin and carbohydrazide-modified alginate (Gel/Alg-CDH) are blended to form a natural polymer hydrogel ink, where the hydrazides in Alg-CDH are found to form strong hydrogen bonds with the gelatin. The hydrogen-bonding-strengthened Gel/Alg-CDH hydrogel demonstrates an appropriate thickened viscosity and shear thinning for extrusion printing. The strong hydrogen bonds contribute to remarkably increased mechanical properties of Gel/Alg-CDH hydrogel with a maximum elongation of over 400%. In addition, sequentially Ca2+-physical crosslinking and then moderately chemical crosslinking significantly enhance the mechanical properties of Gel/Alg-CDH hydrogels that ultimately exhibit an intriguing J-shaped stress-strain curve (tensile strength of 1.068 MPa and the toughness of 677.6 kJ/m2). The dually crosslinked Gel-Alg-CDH-Ca2+-EDC hydrogels demonstrate a high transparency, physiological swelling stability and rapid enzymatic degradability, as well as suturability. The growth factor and drug-loaded biomimetic bilayer hydrogel scaffold are customized via a multi-nozzle printing system. This bioactive bilayer hydrogel scaffold considerably promotes regeneration of corneal epithelium and stroma and inhibits cornea scarring in rabbit cornea keratoplasty.

Supramolecular hydrogels for wound repair and hemostasis

The unique network characteristics and stimuli responsiveness of supramolecular hydrogels have rendered them highly advantageous in the field of wound dressings, showcasing unprecedented potential. However, there are few reports on a comprehensive review of supramolecular hydrogel dressings for wound repair and hemostasis. This review first introduces the major cross-linking methods for supramolecular hydrogels, which includes hydrogen bonding, electrostatic interactions, hydrophobic interactions, host-guest interactions, metal ligand coordination and some other interactions. Then, we review the advanced materials reported in recent years and then summarize the basic principles of each cross-linking method. Next, we classify the network structures of supramolecular hydrogels before outlining their forming process and propose their potential future directions. Furthermore, we also discuss the raw materials, structural design principles, and material characteristics used to achieve the advanced functions of supramolecular hydrogels, such as antibacterial function, tissue adhesion, substance delivery, anti-inflammatory and antioxidant functions, cell behavior regulation, angiogenesis promotion, hemostasis and other innovative functions in recent years. Finally, the existing problems as well as future development directions of the cross-linking strategy, network design, and functions in wound repair and hemostasis of supramolecular hydrogels are discussed. This review is proposed to stimulate further exploration of supramolecular hydrogels on wound repair and hemostasis by researchers in the future.

Injectable hydrogels derived from marine polysaccharides as cell carriers for large corneal epithelial defects

Injectable hydrogels have been employed for sutureless repair of corneal epithelial defects, which can perfectly fit the defect sites and minimize the associated discomfort. However, numerous hydrogels are ineffective in treating large corneal epithelial defects and still suffer from poor biocompatibility or weak applicability when used as cell carriers. Herein, hydroxypropyl chitin/carboxymethyl chitosan (HPCT/CMCS) temperature-sensitive hydrogels are fabricated, and their physicochemical properties and suitability for corneal epithelial repair are investigated. The results demonstrate that HPCT/CMCS hydrogels have excellent temperature sensitivity between 20 and 25 °C and a transparency of over 80 %. Besides, HPCT/CMCS hydrogels can promote cell proliferation and facilitate cell migration of primary rabbit corneal epithelial cells (CEpCs). A rabbit large corneal epithelial defect model (6 mm) is established, and CEpCs are transplanted into defect sites by HPCT/CMCS hydrogels. The results suggest that HPCT/CMCS/CEpCs significantly enhance the repair of large corneal epithelial defects with a healing rate of 99.6 % on day 8, while reducing inflammatory responses and scarring formation. Furthermore, HPCT/CMCS/CEpCs can contribute to the reconstruction of damaged tissues and the recovery of functional capacities. Overall, HPCT/CMCS hydrogels may be a feasible corneal cell carrier material and can provide an alternative approach to large corneal epithelial defects.

Multifunctional and theranostic hydrogels for wound healing acceleration: An emphasis on diabetic-related chronic wounds

Hydrogels represent intricate three-dimensional polymeric structures, renowned for their compatibility with living systems and their ability to naturally degrade. These networks stand as promising and viable foundations for a range of biomedical uses. The practical feasibility of employing hydrogels in clinical trials has been well-demonstrated. Among the prevalent biomedical uses of hydrogels, a significant application arises in the context of wound healing. This intricate progression involves distinct phases of inflammation, proliferation, and remodeling, often triggered by trauma, skin injuries, and various diseases. Metabolic conditions like diabetes have the potential to give rise to persistent wounds, leading to delayed healing processes. This current review consolidates a collection of experiments focused on the utilization of hydrogels to expedite the recovery of wounds. Hydrogels have the capacity to improve the inflammatory conditions at the wound site, and they achieve this by diminishing levels of reactive oxygen species (ROS), thereby exhibiting antioxidant effects. Hydrogels have the potential to enhance the growth of fibroblasts and keratinocytes at the wound site. They also possess the capability to inhibit both Gram-positive and Gram-negative bacteria, effectively managing wounds infected by drug-resistant bacteria. Hydrogels can trigger angiogenesis and neovascularization processes, while also promoting the M2 polarization of macrophages, which in turn mitigates inflammation at the wound site. Intelligent and versatile hydrogels, encompassing features such as pH sensitivity, reactivity to reactive oxygen species (ROS), and responsiveness to light and temperature, have proven advantageous in expediting wound healing. Furthermore, hydrogels synthesized using environmentally friendly methods, characterized by high levels of biocompatibility and biodegradability, hold the potential for enhancing the wound healing process. Hydrogels can facilitate the controlled discharge of bioactive substances. More recently, there has been progress in the creation of conductive hydrogels, which, when subjected to electrical stimulation, contribute to the enhancement of wound healing. Diabetes mellitus, a metabolic disorder, leads to a slowdown in the wound healing process, often resulting in the formation of persistent wounds. Hydrogels have the capability to expedite the healing of diabetic wounds, facilitating the transition from the inflammatory phase to the proliferative stage. The current review sheds light on the biological functionalities of hydrogels, encompassing their role in modulating diverse mechanisms and cell types, including inflammation, oxidative stress, macrophages, and bacteriology. Additionally, this review emphasizes the significance of smart hydrogels with responsiveness to external stimuli, as well as conductive hydrogels for promoting wound healing. Lastly, the discussion delves into the advancement of environmentally friendly hydrogels with high biocompatibility, aimed at accelerating the wound healing process.

Development of dual-functional core-shell electrospun mats with controlled release of anti-inflammatory and anti-bacterial agents for the treatment of corneal alkali burn injuries

In this study, a novel dual-drug carrier for the co-administration of an anti-inflammatory and antibiotic agent consisting of core-shell nanofibers for the treatment of cornea alkali burns was designed. The core-shell nanofibers were prepared via coaxial electrospinning of curcumin-loaded silk fibroin as the core and vancomycin-loaded chitosan/polyvinyl alcohol (PVA) as the shell. Electron microscopy (SEM and TEM) images confirmed the preparation of smooth, bead-free, and continuous fibers that formed clear core-shell structures. For further studies, nanofiber mats were cross-linked by heat treatment to avoid rapid disintegration in water and improve both mechanical properties and drug release. The release profile of curcumin and vancomycin indicated an initial burst release, continued by the extended release of both drugs within 72 hours. Rabbit corneal cells demonstrated high rates of proliferation when evaluated using a cell metabolism assay. Finally, the therapeutic efficiency of core/shell nanofibers in healing cornea alkali burn was studied by microscopic and macroscopic observation, fluorescence staining, and hematoxylin-eosin assay on rabbit eyes. The anti-inflammatory activity of fabricated fibers was evaluated by enzyme-linked immunosorbent assay and Immunofluorescence analysis. In conclusion, using a robust array of in vitro and in vivo experiments this study demonstrated the ability of the dual-drug carriers to promote corneal re-epithelialization, minimize inflammation, and inhibit corneal neovascularization. Since these parameters are critical to the healing of corneal wounds from alkali burns, we suggest that this discovery represents a promising future therapeutic agent that warrants further study in humans.

A light-responsive wound dressing hydrogel: Gelatin based self-healing interpenetrated network with metal-ligand interaction by ferric citrate

Interpenetrated network (IPN) hydrogels with desired mechanical properties were prepared based on gelatin. A copolymer of dimethyl aminoethyl methacrylate (DMAEMA) with 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) in gelatin was chemically cross-linked with methylene bis acrylamide (MBA) to form a semi-IPN hydrogel. Also, IPN hydrogel is fabricated from the AMPS-co-DMAEMA and gelatin in the presence of ferric ions with both chemical and physical cross-linkers. According to the compression test, the metal-ligand interaction has a remarkable impact on the mechanical strength of hydrogel. Ferric ions caused a decrease in the pores size confirmed by the SEM images of hydrogels, resulting in preserving its mechanical stability during the swelling test due to a more robust structure of hydrogel. Ferric to ferrous ions reduction is observed under visible light irradiation, which results in a light-sensitive hydrogel with a higher rate of biodegradation compared to semi-IPN hydrogels. MTT assay results implied that the synthesized hydrogels are non-toxic for the L-929 cell line. Also, for more detailed investigations, histological studies are conducted as in vivo tests. With regards to the improvements of mechanical properties harnessed in IPN hydrogels by ferric ions along with the extraordinary self-healing capability, IPNs would be considered an appropriate option for tissue engineering.

Dynamic Hydrogels with Viscoelasticity and Tunable Stiffness for the Regulation of Cell Behavior and Fate

The extracellular matrix (ECM) of natural cells typically exhibits dynamic mechanical properties (viscoelasticity and dynamic stiffness). The viscoelasticity and dynamic stiffness of the ECM play a crucial role in biological processes, such as tissue growth, development, physiology, and disease. Hydrogels with viscoelasticity and dynamic stiffness have recently been used to investigate the regulation of cell behavior and fate. This article first emphasizes the importance of tissue viscoelasticity and dynamic stiffness and provides an overview of characterization techniques at both macro- and microscale. Then, the viscoelastic hydrogels (crosslinked via ion bonding, hydrogen bonding, hydrophobic interactions, and supramolecular interactions) and dynamic stiffness hydrogels (softening, stiffening, and reversible stiffness) with different crosslinking strategies are summarized, along with the significant impact of viscoelasticity and dynamic stiffness on cell spreading, proliferation, migration, and differentiation in two-dimensional (2D) and three-dimensional (3D) cell cultures. Finally, the emerging trends in the development of dynamic mechanical hydrogels are discussed.

Collagen Gels Crosslinked by Photoactivation of Riboflavin for the Repair and Regeneration of Corneal Defects

Bioengineered corneal tissue is a promising therapeutic modality for the treatment of corneal blindness as a substitute for cadaveric graft tissue. In this study, we fabricated a collagen gel using ultraviolet-A (UV-A) light and riboflavin as a photosensitizer (PhotoCol-RB) as an in situ-forming matrix to fill corneal wounds and create a cohesive interface between the crosslinked gel and adjacent collagen. The PhotoCol-RB gels supported corneal epithelialization and exhibited higher transparency compared to physically crosslinked collagen. We showed that different riboflavin concentrations yielded gels with different mechanical and biological properties. In vitro experiments using human corneal epithelial cells (hCECs) showed that hCECs are able to proliferate on the gel and express corneal cell markers such as cytokeratin 12 (CK12) and tight junctions (ZO-1). Using an ex vivo burst assay, we also showed that the PhotoCol-RB gels are able to seal corneal perforations. Ex vivo organ culture of the gels filling lamellar keratectomy wounds showed that the epithelium that regenerated over the PhotoCol-RB gels formed a multilayer compared to just a double layer for those that grew over physically cross-linked collagen. These gels can be formed either in situ directly on the wound site to conform to the geometry of a defect, or can be preformed and then applied to the corneal wound. Our results indicate that PhotoCol-RB gels merit further investigation as a way to stabilize and repair deep and perforating corneal wounds.

Cell-instructive biomaterials in tissue engineering and regenerative medicine

The field of biomaterials aims to improve regenerative outcomes or scientific understanding for a wide range of tissue types and ailments. Biomaterials can be fabricated from natural or synthetic sources and display a plethora of mechanical, electrical, and geometrical properties dependent on their desired application. To date, most biomaterial systems designed for eventual translation to the clinic rely on soluble signaling moieties, such as growth factors, to elicit a specific cellular response. However, these soluble factors are often limited by high cost, convoluted synthesis, low stability, and difficulty in regulation, making the translation of these biomaterials systems to clinical or commercial applications a long and arduous process. In response to this, significant effort has been dedicated to researching cell-directive biomaterials which can signal for specific cell behavior in the absence of soluble factors. Cells of all tissue types have been shown to be innately in tune with their microenvironment, which is a biological phenomenon that can be exploited by researchers to design materials that direct cell behavior based on their intrinsic characteristics. This review will focus on recent developments in biomaterials that direct cell behavior using biomaterial properties such as charge, peptide presentation, and micro- or nano-geometry. These next generation biomaterials could offer significant strides in the development of clinically relevant medical devices which improve our understanding of the cellular microenvironment and enhance patient care in a variety of ailments.

From crosslinking strategies to biomedical applications of hyaluronic acid-based hydrogels: A review

Hyaluronic acid (HA) is not only a natural anionic polysaccharide with excellent biocompatibility, biodegradability, and moisturizing effect, but also an essential factor that can affect angiogenesis, inflammation, cell behavior, which has a wide range of applications in the biomedical field. Among them, HA-based hydrogels formed by various physical or chemical crosslinking strategies are particularly striking. They not only retain the physiological function of HA, but also have the skeleton function of hydrogel, which further expands the application of HA. However, HA-based natural hydrogels generally have problems such as insufficient mechanical strength and susceptibility to degradation by hyaluronidase, which limits their application to a certain extent. To solve such problems, researchers have prepared a variety of HA-based multifunctional hydrogels with remarkable properties in recent years by adopting various structural modification methods or novel crosslinking strategies, as well as introducing functionally reactive molecules or moieties, which have extended the application scope. This manuscript systematically introduced common crosslinking strategies of HA-based hydrogels and highlighted the development of novel HA-based hydrogels in anticancer drug delivery, cartilage repair, three-dimensional cell culture, skin dressing and other fields. We hope to provide some references for the subsequent development of HA-based hydrogels in the biomedical field.

Structural Strategies for Supramolecular Hydrogels and Their Applications

Supramolecular structures are of great interest due to their applicability in various scientific and industrial fields. The sensible definition of supramolecular molecules is being set by investigators who, because of the different sensitivities of their methods and observational timescales, may have different views on as to what constitutes these supramolecular structures. Furthermore, diverse polymers have been found to offer unique avenues for multifunctional systems with properties in industrial medicine applications. Aspects of this review provide different conceptual strategies to address the molecular design, properties, and potential applications of self-assembly materials and the use of metal coordination as a feasible and useful strategy for constructing complex supramolecular structures. This review also addresses systems that are based on hydrogel chemistry and the enormous opportunities to design specific structures for applications that demand enormous specificity. According to the current research status on supramolecular hydrogels, the central ideas in the present review are classic topics that, however, are and will be of great importance, especially the hydrogels that have substantial potential applications in drug delivery systems, ophthalmic products, adhesive hydrogels, and electrically conductive hydrogels. The potential interest shown in the technology involving supramolecular hydrogels is clear from what we can retrieve from the Web of Science.

Cyclodextrin regulated natural polysaccharide hydrogels for biomedical applications-a review

Cyclodextrin and its derivative (CDs) are natural building blocks for linking with other components to afford functional biomaterials. Hydrogels are polymer network systems that can form hydrophilic three-dimensional network structures through different cross-linking methods and are developing as potential materials in biomedical applications. Natural polysaccharide hydrogels (NPHs) are widely adopted in biomedical field with good biocompatibility, biodegradability, low cytotoxicity, and versatility in emulating natural tissue properties. Compared with conventional NPHs, CD regulated natural polysaccharide hydrogels (CD-NPHs) maintain good biocompatibility, while improving poor mechanical qualities and unpredictable gelation times. Recently, there has been increasing and considerable usage of CD-NPHs while there is still no review comprehensively introducing their construction, classification, and application of these hydrogels from the material point of view regarding biomedical fields. To draw a complete picture of the current and future development of CD-NPHs, we systematically overview the classification of CD-NPHs, and provide a holistic view on the role of CD-NPHs in different biomedical fields, especially in drug delivery, wound dressing, cell encapsulation, and tissue engineering. Moreover, the current challenges and prospects of CD-NPHs are discussed rationally, providing an insight into developing vibrant fields of CD-NPHs-based biomedicine, and facilitating their translation from bench to clinical medicine.

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.

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Double-network hydrogel contains regenerative decellularized corneal stroma matrix.

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

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

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

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

In Situ-forming Collagen Hydrogels Crosslinked by Multifunctional Polyethylene Glycol as a Matrix Therapy for Corneal Defects: 2-Month Follow-up In Vivo

PURPOSE

We recently showed that in situ-forming collagen gels crosslinked through multifunctional polyethylene glycol (PEG) supported corneal epithelialization 7 days after treatment of lamellar keratectomy wounds. In this study, we aimed to evaluate the longer-term regenerative effects of this gel in animals.

METHOD

Corneal wound healing was assessed 60 days after lamellar keratectomy and gel treatment using slitlamp examination, optical coherence tomography (OCT), pachymetry, corneal topography, an ocular response analyzer, and tonometry. The corneas were evaluated for the presence of beta-tubulin, cytokeratin 3, zonula occludens-1, and alpha smooth muscle actin (SMA) markers. Gene expression of aldehyde dehydrogenase 3A1 (ALDH3A1), cluster of differentiation 31, CD163, alpha-SMA, hepatocyte growth factor, and fibroblast growth factor 2 (FGF-2) and protein expression of CD44 and collagen VI were evaluated.

RESULTS

Intraocular pressure, corneal thickness, and hysteresis for the corneas treated with collagen-PEG gels did not significantly change compared with the saline group. However, placido disk topography revealed greater regularity of the central cornea in the gel-treated group compared to the saline group. The gel-treated group exhibited a lower degree of epithelial hyperplasia than the saline group. Immunohistochemical and gene expression analysis showed that the gel-treated corneas exhibited lower alpha-SMA expression compared with the saline group. CD163 and CD44 were found to be elevated in the saline-treated group compared with normal corneas.

CONCLUSIONS

The in situ-forming collagen-PEG gel promoted epithelialization that improved central corneal topography, epithelial layer morphology, and reduced expression of fibrotic and inflammatory biomarkers after 60 days compared to the saline group.

An Overview of the Supramolecular Systems for Gene and Drug Delivery in Tissue Regeneration

Tissue regeneration is a prominent area of research, developing biomaterials aimed to be tunable, mechanistic scaffolds that mimic the physiological environment of the tissue. These biomaterials are projected to effectively possess similar chemical and biological properties, while at the same time are required to be safely and quickly degradable in the body once the desired restoration is achieved. Supramolecular systems composed of reversible, non-covalently connected, self-assembly units that respond to biological stimuli and signal cells have efficiently been developed as preferred biomaterials. Their biocompatibility and the ability to engineer the functionality have led to promising results in regenerative therapy. This review was intended to illuminate those who wish to envisage the niche translational research in regenerative therapy by summarizing the various explored types, chemistry, mechanisms, stimuli receptivity, and other advancements of supramolecular systems.