Natural cross-linker-stabilized acellular porcine corneal stroma for lamellar keratoplasty

Self-assembled sodium alginate polymannuronate nanoparticles for synergistic treatment of ophthalmic infection and inflammation: Preparation optimization and in vitro/vivo evaluation

Frequent administrations are often needed during the treatment of ocular diseases due to the low bioavailability of the existing eye drops owing to inadequate corneal penetration and rapid drug washout. Herein, sodium alginate polymannuronate (SA) nanocarriers were developed using ionic gelation method that can provide better bioavailability through mucoadhesivity and sustained drug release by binding to the ocular mucus layer. This study disproves the common belief that only the G block of SA participates in the crosslinking reaction during ionic gelation. Self-assembly capability due to the linear flexible structure of the M block, better biocompatibility than G block along with the feasibility of controlling physicochemical characteristics postulate a high potential for designing efficient ocular drug delivery systems. Initially, four crosslinkers of varied concentrations were investigated. Taguchi design of experiment revealed the statistically significant effect of the crosslinker type and concentration on the particle size and stability. The best combination was detected by analyzing the particle size and zeta potential values that showed the desired microstructural properties for ocular barrier penetration. The desired combination was SA-Ca-1 that had particle size within the optimal corneal penetration range, that is 10-200 nm (135 nm). The drug carriers demonstrated excellent entrapment efficiency (∼89 % for Ciprofloxacin and ∼96 % for Dexamethasone) along with a sustained and simultaneous release of dual drug for at least 2 days. The nanoparticles also showed biocompatibility (4 ± 0.6 % hemolysis) and high mucoadhesivity (73 ± 2 % for 0.25 g) which was validated by molecular docking analysis. The prepared formulation was able to reduce the scleral inflammation of the rabbit uveitis models significantly within 3 days. Thus, the eye drop showed remarkable potential for efficient drug delivery leading to faster recovery.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

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.

Evolution of biomimetic ECM scaffolds from decellularized tissue matrix for tissue engineering: A comprehensive review

Tissue engineering is essentially a technique for imitating nature. Natural tissues are made up of three parts: extracellular matrix (ECM), signaling systems, and cells. Therefore, biomimetic ECM scaffold is one of the best candidates for tissue engineering scaffolds. Among the many scaffold materials of biomimetic ECM structure, decellularized ECM scaffolds (dECMs) obtained from natural ECM after acellular treatment stand out because of their inherent natural components and microenvironment. First, an overview of the family of dECMs is provided. The principle, mechanism, advances, and shortfalls of various decellularization technologies, including physical, chemical, and biochemical methods are then critically discussed. Subsequently, a comprehensive review is provided on recent advances in the versatile applications of dECMs including but not limited to decellularized small intestinal submucosa, dermal matrix, amniotic matrix, tendon, vessel, bladder, heart valves. And detailed examples are also drawn from scientific research and practical work. Furthermore, we outline the underlying development directions of dECMs from the perspective that tissue engineering scaffolds play an important role as an important foothold and fulcrum at the intersection of materials and medicine. As scaffolds that have already found diverse applications, dECMs will continue to present both challenges and exciting opportunities for regenerative medicine and tissue engineering.

Preparation and Evaluation of Starch Hydrogel/Contact Lens Composites as Epigallocatechin Gallate Delivery Systems for Inhibition of Bacterial Adhesion

Microbial infections caused by wearing contact lenses has become a major health problem, so the design and development of antibacterial contact lenses has attracted widespread attention. To safely and effectively inhibit bacterial adhesion of contact lenses, we have facilely prepared epigallocatechin gallate (EGCG) loaded starch hydrogel/contact lens composites by in-situ free radical polymerization of the mixture containing 2-hydroxylethyl methacrylate, methacrylic acid and ethylene glycol dimethacrylate. The adequate transmittance of the resulting contact lenses was characterized by ultraviolet-visible spectrophotometry, and their satisfactory stability was examined using differential scanning calorimetry and thermogravimetric analysis. Whereafter, cytotoxicity and degradation experiments were performed to investigate the biocompatibility and degradability of the contact lenses. The results showed the nontoxicity and good degradability of the composites. Besides, the capacity of the contact lenses for in vitro release of EGCG was also evaluated, and the results showed that the EGCG in these contact lenses can be sustainably released for at least 14 days. Further bacterial adhesion assay suggested that the EGCG loaded starch hydrogel/contact lenses could significantly reduce the adhesion of Pseudomonas aeruginosa compared to the control. The EGCG loaded starch hydrogel/contact lens composites provide a potential intervention strategy for preventing ocular microbial infections and inhibiting bacterial keratitis.

Gelatin hydrogel/contact lens composites as rutin delivery systems for promoting corneal wound healing

Corneal wound healing is a highly regulated biological process that is of importance for reducing the risk of blinding corneal infections and inflammations. Traditional eye drop was the main approach for promoting corneal wound healing. However, its low bioavailability required a high therapeutic concentration, which can lead to ocular or even systemic side effects. To develop a safe and effective method for treating corneal injury, we fabricated rutin-encapsulated gelatin hydrogel/contact lens composites by dual crosslinking reactions including in situ free radical polymerization and carboxymethyl cellulose/N-hydroxysulfosuccinimide crosslinking. In vitro drug release results evidenced that rutin in the composites could be sustainedly released for up to 14 days. In addition, biocompatibility assay indicated nontoxicity of the composites. Finally, the effect of rutin-encapsulated composites on the healing of the corneal injury in rabbits was investigated. The injury was basically cured in corneas using rutin-encapsulated composites (healing rate, 98.3% ± 0.7%) at 48 h post-operation, while the damage was still present in corneas using the composite (healing rate, 87.0% ± 4.5%). Further proteomics analysis revealed that corneal wound healing may be promoted by the ERK/MAPK and PI3K/AKT signal pathways. These results inform a potential intervention strategy to facilitate corneal wound healing in humans.

Effective elastic modulus of an intact cornea related to indentation behavior: A comparison between the Hertz model and Johnson-Kendall-Roberts model

In this study, a macro-indentation test on the submillimeter scale was performed to analyze the indentation behavior of an intact cornea under physiological pressures. The Hertz and Johnson-Kendall-Roberts (JKR) models were employed to solve the elastic modulus (E) of the intact cornea. The relevant detailed analysis showed that the JKR model, which accounted for the contribution from the adhesion energy, could be used to obtain the E values that were more than two-folds of those obtained from the Hertz model, which only considered the external force. Compared with the uniaxial tension test in vitro, unlike the elastic Hertz-model, the E values under physiological pressures that were obtained with the JKR model were between the lower and upper limits of corneal material. This phenomenon indicated that the JKR model could be used to obtain reasonably effective E values of an intact cornea under physiological pressures.