Hyaluronan Modulates the Biomechanical Properties of the Cornea

Recent Advances in Degradable Biomedical Polymers for Prevention, Diagnosis and Treatment of Diseases

Biomedical polymers play a key role in preventing, diagnosing, and treating diseases, showcasing a wide range of applications. Their unique advantages, such as rich source, good biocompatibility, and excellent modifiability, make them ideal biomaterials for drug delivery, biomedical imaging, and tissue engineering. However, conventional biomedical polymers suffer from poor degradation in vivo, increasing the risks of bioaccumulation and potential toxicity. To address these issues, degradable biomedical polymers can serve as an alternative strategy in biomedicine. Degradable biomedical polymers can efficiently relieve bioaccumulation in vivo and effectively reduce patient burden in disease management. This review comprehensively introduces the classification and properties of biomedical polymers and the recent research progress of degradable biomedical polymers in various diseases. Through an in-depth analysis of their classification, properties, and applications, we aim to provide strong guidance for promoting basic research and clinical translation of degradable biomedical polymers.

Biomolecule-based hydrogels as delivery systems for limbal stem cell transplantation: A review

Limbal stem cell deficiency (LSCD) is a complex disease of the cornea resulting from dysfunction and/or loss of limbal stem cells (LSCs) and their niche. Most patients with LSCD cannot be treated by conventional corneal transplants because the donor tissue lacks the LSCs necessary for corneal epithelial regeneration. Successful treatment of LSCD depends on effective stem cell transplantation to the ocular surface for replenishment of the LSC reservoir. Thus, stem cell therapies employing carrier substrates for LSCs have been widely explored. Hydrogel biomaterials have many favorable characteristics, including hydrophilicity, flexibility, cytocompatibility, and optical properties suitable for the transplantation of LSCs. Therefore, due to these properties, along with the necessary signals for stem cell proliferation and differentiation, hydrogels are ideal carrier substrates for LSCD treatment. This review summarizes the use of different medical-type hydrogels in LSC transplantation from 2001 to 2024. First, a brief background of LSCD is provided. Then, studies that employed various hydrogel scaffolds as LSC carriers are highlighted to provide a multimodal strategic reference for LSCD treatment. Finally, an analysis of prospective future developments and challenges in the field of hydrogels as LSC carriers for treating LSCD is presented.

Hyaluronate Protects From Benzalkonium Chloride-Induced Ocular Surface Toxicity

Purpose

The purpose of this study was to investigate the effect of sodium hyaluronate (SH) on benzalkonium chloride (BAK)-induced toxicity in the ocular surface epithelium and corneal nerves.

Methods

Ocular surface epithelial cells from Balb/c mice were cultured with 0.1% to 0.4% SH and 0.001% to 0.01% BAK and their metabolic activity, viability, and wound repair capacity were assessed in vitro. Following a controlled corneal wound, re-epithelialization and recovery of epithelial barrier function and mechanosensitivity were measured in Balb/c mice treated with 0.4% SH 3 times/day and 0.01% BAK twice daily for 3 weeks. Nerve morphology was assessed by confocal microscopy of corneal whole mounts.

Results

Whereas BAK exposure reduced metabolic activity, viability, and wound repair ability of ocular epithelial cells in vitro, pretreatment with SH ameliorated BAK toxicity in a concentration-dependent manner. The highest SH concentration partially reversed the effects of 0.01% BAK in vitro and increased the corneal healing rate of BAK-exposed mice. Although all corneal wounds closed after 4 days, continuous SH treatment improved corneal barrier dysfunction 18 days after wounding and accelerated the recovery of corneal mechanical sensitivity to baseline levels in BAK-exposed mice. SH treatment also increased corneal nerve density in the wounded area after 3 weeks.

Conclusions

SH mitigates BAK-associated ocular epithelial and neurotoxicity in a concentration-dependent manner.

Translational Relevance

Commercially available, high-concentration SH formulations may have added benefits in treating BAK-associated ocular surface toxicity.

In Situ UNIversal Orthogonal Network (UNION) Bioink Deposition for Direct Delivery of Corneal Stromal Stem Cells to Corneal Wounds

The scarcity of human donor corneal graft tissue worldwide available for corneal transplantation necessitates the development of alternative therapeutic strategies for treating patients with corneal blindness. Corneal stromal stem cells (CSSCs) have the potential to address this global shortage by allowing a single donor cornea to treat multiple patients. To directly deliver CSSCs to corneal defects within an engineered biomatrix, we developed a UNIversal Orthogonal Network (UNION) collagen bioink that crosslinks in situ with a bioorthogonal, covalent chemistry. This cell-gel therapy is optically transparent, stable against contraction forces exerted by CSSCs, and permissive to the efficient growth of corneal epithelial cells. Furthermore, CSSCs remain viable within the UNION collagen gel precursor solution under standard storage and transportation conditions. This approach promoted corneal transparency and re-epithelialization in a rabbit anterior lamellar keratoplasty model, indicating that the UNION collagen bioink serves effectively as an in situ -forming, suture-free therapy for delivering CSSCs to corneal wounds. TEASER. Corneal stem cells are delivered within chemically crosslinked collagen as a transparent, regenerative biomaterial therapy.

Comprehensive review of the state-of-the-art in corneal 3D bioprinting, including regulatory aspects

The global shortage of corneal transplants has spurred an urgency in the quest for efficient treatments. This systematic review not only provides a concise overview of the current landscape of corneal morphology, physiology, diseases, and conventional treatments but crucially delves into the forefront of tissue engineering for corneal regeneration. Emphasizing cellular and acellular components, bioprinting techniques, and pertinent biological assays, it explores optimization strategies for manufacturing and cost-effectiveness. To bridge the gap between research and industrial production, the review outlines the essential regulatory strategy required in Europe, encompassing relevant directives, frameworks, and governing bodies. This comprehensive regulatory framework spans the entire process, from procuring initial components to marketing and subsequent product surveillance. In a pivotal shift towards the future, the review culminates by highlighting the latest advancements in this sector, particularly the integration of tissue therapy with artificial intelligence. This synergy promises substantial optimization of the overall process, paving the way for unprecedented breakthroughs in corneal regeneration. In essence, this review not only elucidates the current state of corneal treatments and tissue engineering but also outlines regulatory pathways and anticipates the transformative impact of artificial intelligence, providing a comprehensive guide for researchers, practitioners, and policymakers in the field.

Advances in Polysaccharide-Based Microneedle Systems for the Treatment of Ocular Diseases

The eye, a complex organ isolated from the systemic circulation, presents significant drug delivery challenges owing to its protective mechanisms, such as the blood-retinal barrier and corneal impermeability. Conventional drug administration methods often fail to sustain therapeutic levels and may compromise patient safety and compliance. Polysaccharide-based microneedles (PSMNs) have emerged as a transformative solution for ophthalmic drug delivery. However, a comprehensive review of PSMNs in ophthalmology has not been published to date. In this review, we critically examine the synergy between polysaccharide chemistry and microneedle technology for enhancing ocular drug delivery. We provide a thorough analysis of PSMNs, summarizing the design principles, fabrication processes, and challenges addressed during fabrication, including improving patient comfort and compliance. We also describe recent advances and the performance of various PSMNs in both research and clinical scenarios. Finally, we review the current regulatory frameworks and market barriers that are relevant to the clinical and commercial advancement of PSMNs and provide a final perspective on this research area.

A mosquito proboscis-inspired cambered microneedle patch for ophthalmic regional anaesthesia

INTRODUCTION

One of the methods for pain management involves the use of local anesthesia, which numbs sensations in specific body regions while maintaining consciousness.

OBJECTIVES

Considering the certain limitations (e.g., pain, the requirement of skilled professionals, or slow passive diffusion) of conventional delivery methods of local anesthetics, developing alternative strategies that offer minimally invasive yet therapeutically effective delivery systems is of great concern for ophthalmic regional anesthesia.

METHODS AND RESULTS

In this study, a rapidly dissolving cambered microneedle (MNs) patch, composed of poly(vinylpyrrolidone) (PVP) and hyaluronic acid (HA) and served as a delivery system for lidocaine (Lido) in local anesthesia, was developed taking inspiration from the mosquito proboscis's ability to extract blood unnoticed. The lidocaine-containing MNs patch (MNs@Lido) consisted of 25 microneedles with a four-pronged cone structure (height: 500 μm, base width: 275 μm), arranged in a concentric circle pattern on the patch, and displays excellent dissolubility for effective drug delivery of Lido. After confirming good cytocompatibility, MNs@Lido was found to possess adequate rigidity to penetrate the cornea without causing any subsequent injury, and the created corneal pinhole channels completely self-healed within 24 h. Interestingly, MNs@Lido exhibited effective analgesic effects for local anesthesia on both heel skin and eyeball, with the sustained anesthetic effect lasting for at least 30 min.

CONCLUSIONS

These findings indicate that the mosquito proboscis-inspired cambered MNs patch provides rapid and painless local anesthesia, overcoming the limitations of conventional delivery methods of local anesthetics, thus opening up new possibilities in the treatment of ophthalmic diseases.

TGF-β-Based Therapies for Treating Ocular Surface Disorders

The cornea is continuously exposed to injuries, ranging from minor scratches to deep traumas. An effective healing mechanism is crucial for the cornea to restore its structure and function following major and minor insults. Transforming Growth Factor-Beta (TGF-β), a versatile signaling molecule that coordinates various cell responses, has a central role in corneal wound healing. Upon corneal injury, TGF-β is rapidly released into the extracellular environment, triggering cell migration and proliferation, the differentiation of keratocytes into myofibroblasts, and the initiation of the repair process. TGF-β-mediated processes are essential for wound closure; however, excessive levels of TGF-β can lead to fibrosis and scarring, causing impaired vision. Three primary isoforms of TGF-β exist-TGF-β1, TGF-β2, and TGF-β3. Although TGF-β isoforms share many structural and functional similarities, they present distinct roles in corneal regeneration, which adds an additional layer of complexity to understand the role of TGF-β in corneal wound healing. Further, aberrant TGF-β activity has been linked to various corneal pathologies, such as scarring and Peter's Anomaly. Thus, understanding the molecular and cellular mechanisms by which TGF-β1-3 regulate corneal wound healing will enable the development of potential therapeutic interventions targeting the key molecule in this process. Herein, we summarize the multifaceted roles of TGF-β in corneal wound healing, dissecting its mechanisms of action and interactions with other molecules, and outline its role in corneal pathogenesis.

Tumor biomechanical stiffness by magnetic resonance elastography predicts surgical outcomes and identifies biomarkers in vestibular schwannoma and meningioma

Variations in the biomechanical stiffness of brain tumors can not only influence the difficulty of surgical resection but also impact postoperative outcomes. In a prospective, single-blinded study, we utilize pre-operative magnetic resonance elastography (MRE) to predict the stiffness of intracranial tumors intraoperatively and assess the impact of increased tumor stiffness on clinical outcomes following microsurgical resection of vestibular schwannomas (VS) and meningiomas. MRE measurements significantly correlated with intraoperative tumor stiffness and baseline hearing status of VS patients. Additionally, MRE stiffness was elevated in patients that underwent sub-total tumor resection compared to gross total resection and those with worse postoperative facial nerve function. Furthermore, we identify tumor microenvironment biomarkers of increased stiffness, including αSMA + myogenic fibroblasts, CD163 + macrophages, and HABP (hyaluronic acid binding protein). In a human VS cell line, a dose-dependent upregulation of HAS1-3, enzymes responsible for hyaluronan synthesis, was observed following stimulation with TNFα, a proinflammatory cytokine present in VS. Taken together, MRE is an accurate, non-invasive predictor of tumor stiffness in VS and meningiomas. VS with increased stiffness portends worse preoperative hearing and poorer postoperative outcomes. Moreover, inflammation-mediated hyaluronan deposition may lead to increased stiffness.

Endogenous TSG-6 modulates corneal inflammation following chemical injury

PURPOSE

Tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) is upregulated in various pathophysiological contexts, where it has a diverse repertoire of immunoregulatory functions. Herein, we investigated the expression and function of TSG-6 during corneal homeostasis and after injury.

METHODS

Human corneas, eyeballs from BALB/c (TSG-6+/+), TSG-6+/- and TSG-6-/- mice, human immortalized corneal epithelial cells and murine corneal epithelial progenitor cells were prepared for immunostaining and real time PCR analysis of endogenous expression of TSG-6. Mice were subjected to unilateral corneal debridement or alkali burn (AB) injuries and wound healing assessed over time using fluorescein stain, in vivo confocal microscopy and histology.

RESULTS

TSG-6 is endogenously expressed in the human and mouse cornea and established corneal epithelial cell lines and is upregulated after injury. A loss of TSG-6 has no structural and functional effect in the cornea during homeostasis. No differences were noted in the rate of corneal epithelial wound closure between BALB/c, TSG-6+/- and TSG-6-/- mice. TSG-6-/- mice presented decreased inflammatory response within the first 24 h of injury and accelerated corneal wound healing following AB when compared to control mice.

CONCLUSION

TSG-6 is endogenously expressed in the cornea and upregulated after injury where it propagates the inflammatory response following chemical injury.

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.

Age related changes in hyaluronan expression leads to Meibomian gland dysfunction

The prevalence of dry eye disease (DED) ranges from ∼5 to 50 % and its associated symptoms decrease productivity and reduce the quality of life. Approximately 85 % of all DED cases are caused by Meibomian gland dysfunction (MGD). As humans and mice age, their Meibomian glands (MGs) undergo age-related changes resulting in age related-MGD (ARMGD). The precise cause of ARMGD remains elusive, which makes developing therapies extremely challenging. We previously demonstrated that a hyaluronan (HA)-rich matrix exists surrounding the MG, regulating MG morphogenesis and homeostasis. Herein, we investigated whether changes to the HA matrix in the MG throughout life contributes towards ARMGD, and whether altering this HA matrix can prevent ARMGD. For such, HA synthase (Has) knockout mice were aged and compared to age matched wild type (wt) mice. MG morphology, lipid production, PPARγ expression, basal cell proliferation, stem cells, presence of atrophic glands and MG dropout were analyzed at 8 weeks, 6 months, 1 year and 2 years of age and correlated with the composition of the HA matrix. We found that as mice age, there is a loss of HA expression in and surrounding the MGs of wt mice, while, in contrast, Has1-/-Has3-/- mice present a significant increase in HA expression through Has2 upregulation. At 1 year, Has1-/-Has3-/- mice present significantly enlarged MGs, compared to age-matched wt mice and compared to all adult mice. Thus, Has1-/-Has3-/- mice continue to develop new glandular tissue as they age, instead of suffering MG atrophy. At 2 years, Has1-/-Has3-/- mice continue to present significantly larger MGs compared to age-matched wt mice. Has1-/-Has3-/- mice present increased lipid production, increased PPARγ expression and an increase in the number of proliferating cells when compared to wt mice at all-time points analyzed. Taken together, our data shows that a loss of the HA matrix surrounding the MG as mice age contributes towards ARMGD, and increasing Has2 expression, and consequently HA levels, prevents ARMGD in mice.

ROS-Mediated Fragmentation Alters the Effects of Hyaluronan on Corneal Epithelial Wound Healing

A buildup of reactive oxygen species (ROS) occurs in virtually all pathological conditions. Hyaluronan (HA) is a major extracellular matrix component and is susceptible to oxidation by reactive oxygen species (ROS), yet the precise chemical structures of oxidized HA products (oxHA) and their physiological properties remain largely unknown. This study characterized the molecular weight (MW), structures, and physiological properties of oxHA. For this, high-molecular-weight HA (HMWHA) was oxidized using increasing molar ratios of hydrogen peroxide (H2O2) or hypochlorous acid (HOCl). ROS lead to the fragmentation of HA, with the oxHA products produced by HOCl exhibiting an altered chemical structure while those produced by H2O2 do not. HMWHA promotes the viability of human corneal epithelial cells (hTCEpi), while low MWHA (LMWHA), ultra-LMWHA (ULMWHA), and most forms of oxHA do not. HMWHA and LMWHA promote hTCEpi proliferation, while ULMWHA and all forms of oxHA do not. LMWHA and some forms of oxHA promote hTCEpi migration, while HMWHA does not. Finally, all native forms of HA and oxHA produced by HOCl promote in vivo corneal wound healing, while oxHA produced by H2O2 does not. Taken together, our results show that HA fragmentation by ROS can alter the physiological activity of HA by altering its MW and structure.

Characterization of the Molecular Weight of Hyaluronan in Eye Products Using a Novel Method of Size Exclusion High-Pressure Liquid Chromatography

Purpose

Hyaluronan (HA) exists in two forms, high molecular weight HA (HMWHA) and low molecular weight HA (LMWHA), which have distinct physiological functions. Therefore it is imperative to know the form of HA within pharmaceutical products, including eye products. This study developed an accurate, sensitive, and quantitative method to characterize the form of HA in eye products. Thereafter, the effects of the HA-containing eye products on corneal wound healing were investigated.

Methods

The MW distributions and concentrations of HA in over the counter eye products were determined by size exclusion chromatography (SEC) high-pressure liquid chromatography (HPLC). The effects of the eye products containing HA on corneal wound healing were characterized both in vitro and in vivo using the scratch assay and the debridement wound model, respectively.

Results

The concentrations and MWs of HA were successfully determined within a range of 0.014 to 0.25 mg/mL using SEC HPLC. The concentrations of HA in the ophthalmic products varied from 0.14 to 4.0 mg/mL and the MWs varied from ∼100 kDa to >2500 kDa. All but one HA-containing eye product had an inhibitory effect on corneal wound healing, whereas pure HA promoted corneal wound healing.

Conclusions

A novel SEC-HPLC method was developed for quantifying and characterizing the MW of HA in eye products. Although HA promoted corneal wound healing, HA-containing eye products inhibited corneal wound healing, likely caused by preservatives.

Translational Relevance

SEC-HPLC could be implemented as a routine method for determining the form of HA in commercially available ophthalmic products.