The Effect of Lyophilization on Graft Acceptance in Experimental Xenotransplantation Using Porcine Cornea

Low-temperature vacuum evaporation as a novel dehydration process for the long-term preservation of transplantable human corneal tissue

Globally there is a shortage of available donor corneas with only 1 cornea available for every 70 needed. A large limitation to corneal transplant surgery is access to quality donor tissue due to inadequate eye donation services and infrastructure in many countries, compounded by the fact that there are few available long-term storage solutions for effectively preserving spare donor corneas collected in countries with a surplus. In this study, we describe a novel technology termed low-temperature vacuum evaporation (LTVE) that can effectively dry-preserve surplus donor corneal tissue, allowing it to be stored for approximately 5 years, shipped at room temperature, and stored on hospital shelves before rehydration prior to ophthalmic surgery. The dry-preserved corneas demonstrate equivalent biological characteristics to non-dried donor tissue, with the exception that epithelial and endothelial cells are removed and keratocytes are rendered non-viable and encapsulated within the preserved extracellular matrix. Structure and composition of the dried and rehydrated corneas remained identical to that of non-dried control corneas. Matrix-bound cytokines and growth factors were not affected by the drying and rehydration of the corneas. The ability to preserve human donor corneas using LTVE will have considerable impact on global corneal supply; utilisation of preserved corneas in lamellar keratoplasties, corneal perforations, ulcers, and tectonic support, will allow non-preserved donor tissue to be reserved for where it is truly required.

Corneal xenotransplantation: Where are we standing?

The search for alternatives to allotransplants is driven by the shortage of corneal donors and is demanding because of the limitations of the alternatives. Indeed, current progress in genetically engineered (GE) pigs, the introduction of gene-editing technology by clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9, and advanced immunosuppressants have made xenotransplantation a possible option for a human trial. Porcine corneal xenotransplantation is considered applicable because the eye is regarded as an immune-privileged site. Furthermore, recent non-human primate studies have shown long-term survival of porcine xenotransplants in keratoplasty. Herein, corneal immune privilege is briefly introduced, and xenogeneic reactions are compared with allogeneic reactions in corneal transplantation. This review describes the current knowledge on special issues of xenotransplantation, xenogeneic rejection mechanisms, current immunosuppressive regimens of corneal xenotransplantation, preclinical efficacy and safety data of corneal xenotransplantation, and updates of the regulatory framework to conduct a clinical trial on corneal xenotransplantation. We also discuss barriers that might prevent xenotransplantation from becoming common practice, such as ethical dilemmas, public concerns on xenotransplantation, and the possible risk of xenozoonosis. Given that the legal definition of decellularized porcine cornea (DPC) lies somewhere between a medical device and a xenotransplant, the preclinical efficacy and clinical trial data using DPC are included. The review finally provides perspectives on the current standpoint of corneal xenotransplantation in the fields of regenerative medicine.

α

The xenogeneic decellularized corneal matrix (DCM) was expected to be used in lamellar keratoplasty in clinic as the substitute of allogeneic cornea. After decellularization treatment, the remaining risk of xenograft rejection needed to be assessed. The galactose-α1,3-galactose, as the most abundant and closely rejection-related xenogeneic antigen, should be one of the important factors concerned in immunological evaluation. In this study, residual αGal in the DCM was first determined by an enzyme-linked immunosorbent assay method with qualified accuracy and specificity. Then the DCM was implanted subcutaneously into the α1,3-galactosyltransferase gene-knockout (GTKO) mice, accompanied by the implantation in the wild-type C57BL/6 mice as a comparison. The total serum antibody levels, anti-Gal antibody levels, inflammatory cytokines and ratios of splenic lymphocyte subtypes were detected and the histopathological analysis of implants were performed to systematically evaluate the immune responses. The experimental result showed the fresh porcine corneal matrix samples had (9.90 ± 1.54) × 10¹² αGal epitope per mg while the content of residual αGal in the DCM was (7.90 ± 2.00) × 10¹² epitope per mg. The GTKO mice had similar potential of reaction to immune stimulation to that of wild-type C57BL/6 mice. At 4 weeks after implantation of DCM, in WT mice and GTKO mice there were both innate immunity response to the DCM characterized by macrophage infiltration. But the elevations of anti-Gal IgG level and the percentage of splenic natural killer cells were only detected in GTKO mice. These changes were thought to be pertinent to the residual αGal antigen, which could not be detected in WT mice. No further αGal antibody-mediated cellular immunity and significant changes of serum cytokine contents were found in GTKO mice, which perhaps suggested that the immune reactions to the DCM after 4 weeks of implantation were moderate and had minor effect on the survival of the corneal graft.

Electrical connectors for neural implants: design, state of the art and future challenges of an underestimated component

Technological advances in electrically active implantable devices have increased the complexity of hardware design. In particular, the increasing number of stimulation and recording channels requires innovative approaches for connectors that interface electrodes with the implant circuitry.

OBJECTIVE

This work aims to provide a common theoretical ground for implantable connector development with a focus on neural applications.

APPROACH

Aspects and experiences from several disciplines are compiled from an engineering perspective to discuss the state of the art of connector solutions. Whenever available, we also present general design guidelines.

MAIN RESULTS

Degradation mechanisms, material stability and design rules in terms of biocompatibility and biostability are introduced. Considering contact physics, we address the design and characterization of the contact zone and review contaminants, wear and contact degradation. For high-channel counts and body-like environments, insulation can be even more crucial than the electrical connection itself. Therefore, we also introduce the requirements for electrical insulation to prevent signal loss and distortion and discuss its impact on the practical implementation.

SIGNIFICANCE

A final review is dedicated to the state of the art connector concepts, their mechanical setup, electrical performance and the interface to other implant components. We conclude with an outlook for possible approaches for the future generations of implants.

In vitro characterization of electrochemically compacted collagen matrices for corneal applications

Loss of vision due to corneal disease is a significant problem worldwide. Transplantation of donor corneas is a viable treatment option but limitations such as short supply and immune-related complications call for alternative options for the treatment of corneal disease. A tissue engineering-based approach using a collagen scaffold is a promising alternative to develop a bioengineered cornea that mimics the functionality of native cornea. In this study, an electrochemical compaction method was employed to synthesize highly dense and transparent collagen matrices. We hypothesized that chemical crosslinking of electrochemically compacted collagen (ECC) matrices will maintain transparency, improve stability, and enhance the mechanical properties of the matrices to the level of native cornea. Further, we hypothesized that keratocyte cell viability and proliferation will be maintained on crosslinked ECC matrices. The results indicated that uncrosslinked and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-N-hydroxysuccinimide (EDC-NHS) crosslinked ECC matrices were highly transparent with light transmission measurements comparable to native cornea. Stability tests showed that while the uncrosslinked ECC matrices degraded within 6 h when treated with collagenase, EDC-NHS or genipin crosslinking significantly improved the stability of ECC matrices (192 h for EDC-NHS and 256 h for genipin). Results from the mechanical tests showed that both EDC-NHS and genipin crosslinking significantly improved the strength and modulus of ECC matrices. Cell culture studies showed that keratocyte cell viability and proliferation are maintained on EDC-NHS crosslinked ECC matrices. Overall, results from this study suggest that ECC matrices have the potential to be developed as a functional biomaterial for corneal repair and regeneration.

Deep anterior lamellar keratoplasty using acellular corneal tissue for prevention of allograft rejection in high-risk corneas

PURPOSE

To determine whether deep anterior lamellar keratoplasty (DALK) using acellular glycerol-cryopreserved corneal tissue (GCCT) could prevent allograft rejection in high-risk corneas.

DESIGN

Prospective, randomized, comparative study.

METHODS

SETTINGS

The Eye Hospital, Wenzhou Medical College, Zhejiang, China.

STUDY POPULATION

All patients with herpes simplex virus keratitis, bacterial keratitis, fungal keratitis, or ocular burn, who were eligible as per study design, were invited to participate.

OBSERVATION PROCEDURES

According to randomized block design, all patients received either GCCT or fresh corneal tissue (FCT) during DALK. Best-corrected visual acuity (BCVA), slit-lamp microscopy, and in vivo confocal microscopy examinations at 1 week and 1, 3, 6, 12, and 24 months after surgery were analyzed. Kaplan-Meier survival analysis was used to evaluate graft survival rate.

MAIN OUTCOME MEASURES

Therapeutic success, 2-year rejection-free graft survival rate and 2-year graft survival rate, in vivo confocal microscopy results, BCVA, and endothelial cell density.

RESULTS

Postoperative BCVA of 20/40 or better at the last follow-up visit was achieved in 57.6% (19/33) of eyes in the GCCT group and in 54.8% (17/31) of the FCT group. No graft rejection occurred in the GCCT group, while in the FCT group 10 episodes of stromal rejection developed in 7 eyes. Overall, the rejection-free graft survival rate at 2 years was significantly higher in the GCCT group as compared with the FCT group (100.0%, 78.8% respectively, P = .006).

CONCLUSIONS

Deep anterior lamellar keratoplasty using acellular glycerol-preserved cornea could prevent allograft rejection and promote graft survival rate in high-risk corneas.

Artificial organs 2010: a year in review

In this Editor's Review, articles published in 2010 are organized by category and briefly summarized. As the official journal of The International Federation for Artificial Organs, The International Faculty for Artificial Organs, and the International Society for Rotary Blood Pumps, Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level."Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide such meaningful suggestions to the author's work whether eventually accepted or rejected and especially to those whose native tongue is not English. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, Wiley-Blackwell, for their expert attention and support in the production and marketing of Artificial Organs. In this Editor's Review, that historically has been widely received by our readership, we aim to provide a brief reflection of the currently available worldwide knowledge that is intended to advance and better human life while providing insight for continued application of technologies and methods of organ Replacement, Recovery, and Regeneration. We look forward to recording further advances in the coming years.