Ten-Year Follow-up of Lamellar Keratoplasty Treatment With Acellular Porcine Corneal Stroma: A Case Report

Current Scenario and Future Perspectives of Porcine Corneal Xenotransplantation

ABSTRACT

Corneal diseases represent a significant cause of blindness worldwide, with corneal transplantation being an effective treatment to prevent vision loss. Despite substantial advances in transplantation techniques, the demand for donor corneas exceeds the available supply, particularly in developing countries. Cornea xenotransplantation has emerged as a promising strategy to address the worldwide scarcity, notably using porcine corneas. In addition to the inherent immune privilege of the cornea, the low cost of porcine breeding and the anatomical and physiological similarities between humans and pigs have made porcine corneas a viable alternative. Nonetheless, ethical concerns, specifically the risk of xenozoonotic transmission and the necessity for stringent biosafety measures, remain significant obstacles. Moreover, the success of xenotransplantation is compromised by innate and adaptive immune responses, which requires meticulous consideration and further studies. Despite these challenges, recent breakthroughs have further contributed to reducing immunogenicity while preserving the corneal architecture. Advances in genetic engineering, such as the use of CRISPR-Cas9 to eliminate critical porcine antigens, have shown promise for mitigating immune reactions. Additionally, new immunosuppressive protocols, such as have techniques like decellularization and the use of porcine-derived acellular matrices, have greatly increased graft survival in preclinical models. Future research must focus on refining immunomodulatory strategies and improving graft preparation techniques to ensure the long-term survival and safety of porcine corneal xenotransplantation in clinical trials in humans.

Corneal stromal structure replicating humanized hydrogel patch for sutureless repair of deep anterior-corneal defect

A critical shortage of donor corneas exists worldwide. Hydrogel patches with a biological architecture and functions that simulate those of native corneas have garnered considerable attention. This study introduces a stromal structure replicating corneal patch (SRCP) composed of a decellularized cornea-templated nanotubular skeleton, recombinant human collagen, and methacrylated gelatin, exhibiting a similar ultrastructure and transmittance (above 80 %) to natural cornea. The SRCP is superior to the conventional recombinant human collagen patch in terms of biomechanical properties and resistance to enzymatic degradation. Additionally, SRCP promotes corneal epithelial and stromal cell migration while preventing the trans-differentiation of stromal cells into myofibroblasts. When applied to an ocular surface (37 °C), SRCP releases methacrylated gelatin, which robustly binds SRCP to the corneal stroma after activation by 405 nm light. Compared to gelatin-based photocurable hydrogel, the SRCP better supports the restoration of normal corneal curvature and withstands deformation under an elevated intraocular pressure (100 mmHg). In an in vivo deep anterior-corneal defect model, SRCP facilitated epithelial healing and vision recovery within 2 weeks, maintained graft structural stability, and inhibited stromal scarring at 4 weeks post-operation. The ideal performance of the SRCP makes it a promising humanized corneal equivalent for sutureless clinical applications.

Construction and biocompatibility of penetrating corneal transplant substitute with cross-linked acellular porcine cornea and biopolymer polyurethane

In this study, acellular porcine cornea (APC) was composited with biopolymer polyurethane (PU), in which Polyethylene glycol (PEG) served as porogen, to fabricate a breathable and impermeable barrier and maintain the transparency of APC. To improve the effect of decellularization on the collagen fibrolamella of the APC, structural regularity and stability as well as postoperative corneal edema and melting, crosslinking was taken as an effective way to improve the mechanical properties and anti-enzymatic hydrolysis of APC. Chemical cross-linking in different agents, crosslink concentrations, and reaction times were conducted. The transparency, elastic modulus, oxygen permeability, crosslinking degree, and expansion thickness were examined. Furthermore, the immunogenicity, cytocompatibility, and histocompatibility of the cross-linked APC-PU composite under the optimal crosslinking parameters (GP-0.2 %-3.0, EDC-1.0 %-1.0, GD-0.8 %-0.3) were analyzed. The results showed that the GD-0.8 %-0.3 samples demonstrated cytotoxicity and significant neovascularization during subcutaneous experiments. Moreover, a proliferation membrane was formed on the PU surface in the orthotopic transplantation, suggesting immune rejection. The GP-0.2 %-3.0 group exhibited pronounced edema and delamination in the 4th week, indicating inadequate permeability and incomplete fiber cross-linking. However, the EDC-1.0 %-1.0 group promoted cell adhesion and proliferation, while maintaining graft integrity without degradation upon subcutaneous implantation. No corneal swelling or degradation was observed within 4 weeks post-transplantation. Cross-linking of EDC/NHS is an effective method for fabricating the ideal and functional APC-PU composite for penetrating keratoplasty.

Artificial Cornea Substitute Based on Hydrogel Skeletons with Natural Stromal Hierarchical Structure and Extracellular Matrix for Sutureless Transplantation

Corneal substitutes with structural and compositional characteristics resembling those of natural corneas have attracted considerable attention. However, biomimicking the complex hierarchical organization of corneal stroma is challenging. In this study, humanized corneal stroma-like adhesive patches (HCSPs) are prepared through a multi-step process. First, polyethylene glycol diacrylate is cast and cured within decellularized porcine cornea (DPC) templates. The DPCs are then enzymatically digested to obtain hydrogel skeletons, which are finally integrated with human corneal extracellular matrix and methacrylate gelatin. HCSPs replicate the ultrastructure, protein components, and optical properties of human corneas and exhibit improved anti-swelling and anti-degradation capabilities compared with conventional DPCs and recombinant human collagen patches. HCSPs can deliver methacrylate gelatin at the ocular surface temperature (37 °C) and achieve stable adhesion to the corneal stroma upon 405 nm light irradiation. Furthermore, HCSPs promote the survival and migration of corneal epithelial and stromal cells while preserving their phenotypes. In rabbit models of lamellar keratoplasty and microperforation repair, HCSPs accelerate epithelial healing, minimize suture-associated complications, and maintain structural stability. These findings suggest that HCSPs are promising donor corneal substitutes for clinical applications.

Different Thicknesses of Acellular Porcine Corneal Stroma on Prognosis of Fungal Corneal Ulcers Treated by Lamellar Keratoplasty: A 5-Year Retrospective Study

PURPOSE

To compare the prognosis and efficacy of acellular porcine corneal stroma (APCS) with different thicknesses for the treatment of fungal corneal ulcers by lamellar keratoplasty (LKP).

METHODS

A total of 52 patients who underwent LKP with APCS for the treatment of fungal corneal ulcers were included in this retrospective study. Patients were divided into 2 groups according to the different thicknesses of APCS (0.30 ± 0.05 mm, L2 group, n = 20; 0.40 ± 0.05 mm, L3 group, n = 32). Observation indicators included best corrected visual acuity, graft transparency, corneal neovascularization, ocular irritation symptoms, corneal epithelial healing time, graft survival, central corneal thickness at 1 year after surgery, and postoperative complications.

RESULTS

Compared with the L3 group, the L2 group had better postoperative best corrected visual acuity and graft transparency ( P < 0.001), less corneal neovascularization ( P < 0.001), and lower incidence of complications ( P < 0.05). There were significant differences in ocular irritation symptoms between the 2 groups ( P < 0.05) at 3 and 6 months postoperatively, which might be related to the higher recurrence rate and graft rejection rate in the L3 group. The comparison of postoperative epithelial healing time also showed significant differences in 2 groups ( P < 0.01). The 1-year survival rate was up to 63.5% in both groups, with no significant difference ( P < 0.05). However, the risk of transplantation was less in the L2 group. Both APCS thicknesses could provide adequate central corneal thickness at 1 year after surgery ( P > 0.05).

CONCLUSIONS

APCS was safe and effective in the treatment of fungal corneal ulcers by LKP. Thinner grafts should be preferred for LKP for fungal corneal ulcers to reduce the risk of grafting.

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

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

Advances in Microgravity Directed Tissue Engineering

Tissue engineering aims to generate functional biological substitutes to repair, sustain, improve, or replace tissue function affected by disease. With the rapid development of space science, the application of simulated microgravity has become an active topic in the field of tissue engineering. There is a growing body of evidence demonstrating that microgravity offers excellent advantages for tissue engineering by modulating cellular morphology, metabolism, secretion, proliferation, and stem cell differentiation. To date, there have been many achievements in constructing bioartificial spheroids, organoids, or tissue analogs with or without scaffolds in vitro under simulated microgravity conditions. Herein, the current status, recent advances, challenges, and prospects of microgravity related to tissue engineering are reviewed. Current simulated-microgravity devices and cutting-edge advances of microgravity for biomaterials-dependent or biomaterials-independent tissue engineering to offer a reference for guiding further exploration of simulated microgravity strategies to produce engineered tissues are summarized and discussed.

Tissue-Engineered Corneal Endothelial Sheets Using Ultrathin Acellular Porcine Corneal Stroma Substrates for Endothelial Keratoplasty

Tissue-engineered cornea endothelial sheets (TECES), created using a biocompatible thin and transparent carrier with corneal endothelial cells, could alleviate the shortage of donor corneas and provide abundant functional endothelial cells. In our previous clinical trials, the effectiveness and safety of the acellular porcine corneal stroma (APCS) applied in lamellar keratoplasty have been confirmed. In this study, we optimized the method to cut APCS into multiple 20 μm ultrathin lamellae by a cryostat microtome and investigated the feasibility of TECES by seeding rabbit corneal endothelial cells (RCECs) on ultrathin APCS. Cell adhesion, proliferation, and functional gene expression of RCECs on tissue-culture plastic and APCS of different thicknesses were compared. The results indicated that ultrathin lamellae were superior in increasing cell viability and maintaining cell functions. Analyzing with histology, electron microscopy, and immunofluorescence, we found that RCECs cultured on 20 μm ultrathin APCS for 5 days grew into a confluent monolayer with a density of 3726 ± 223 cells/mm² and expressed functional biomarkers Na⁺/K⁺-ATPase and zonula occludens. After 14 days, RCECs formed an early stage of Descemet's membrane-like structure by synthesizing collagen IV and laminin. Human corneal endothelial cells were also used to further validate the supportive effect of ultrathin APCS on cells. The resulting constructs were flexible and tough enough to implant into rabbits' anterior chambers through small incisions. TECES adhered to the posterior corneal stroma, and the thickness of cornea gradually reduced to normal after grafting. These results indicate that the ultrathin APCS can serve as a tissue engineering carrier and might be a suitable alternative for endothelial cells expansion in endothelial keratoplasty.