Effect of Surgical Technique on Corneal Implant Performance

Biomimetic Convex Implant for Corneal Regeneration Through 3D Printing

Blindness caused by corneal damage affects millions of people worldwide, and this number continues to rise. However, rapid epithelization and a stable epithelium process are the two biggest challenges for traditional corneal materials. These processes are related to corneal curvature, which is an important factor in determination of the corneal healing process and epithelial behavior during corneal damage. In this study, smooth 3D-printed convex corneal implants based on gelatin methacrylate and collagen are generated. As epithelium distribution and adhesion vary in different regions of the natural cornea, this work separates the surfaces into four regions and studies how cells sense topological cues on curvature. It is found that rabbit corneal epithelial cells (RCECs) seeded on steeper slope gradient surfaces on convex structures result in more aligned cell organization and tighter cell-substrate adhesion, which can also be verified through finite element simulation and signaling pathway analysis. In vivo transplantation of convex implants result in a better fit with adjacent tissue and stronger cell adhesion than flat implants, thereby accelerating corneal epithelialization and promoting collagen fibers and neural regeneration within 180 days. Taken together, printed convex corneal implants that facilitate corneal regeneration may offer a translational strategy for the treatment of corneal damage.

LiQD Cornea: Pro-regeneration collagen mimetics as patches and alternatives to corneal transplantation

Transplantation with donor corneas is the mainstay for treating corneal blindness, but a severe worldwide shortage necessitates the development of other treatment options. Corneal perforation from infection or inflammation is sealed with cyanoacrylate glue. However, the resulting cytotoxicity requires transplantation. LiQD Cornea is an alternative to conventional corneal transplantation and sealants. It is a cell-free, liquid hydrogel matrix for corneal regeneration, comprising short collagen-like peptides conjugated with polyethylene glycol and mixed with fibrinogen to promote adhesion within tissue defects. Gelation occurs spontaneously at body temperature within 5 min. Light exposure is not required-particularly advantageous because patients with corneal inflammation are typically photophobic. The self-assembling, fully defined, synthetic collagen analog is much less costly than human recombinant collagen and reduces the risk of immune rejection associated with xenogeneic materials. In situ gelation potentially allows for clinical application in outpatient clinics instead of operating theaters, maximizing practicality, and minimizing health care costs.

Development of Transparent Acellular Dermal Matrix as Tissue-Engineered Stroma Substitute for Central Lamellar Keratoplasty

Purpose

To improve the transparency of the acellular dermal matrix (ADM) and investigate the optical, mechanical and histologic properties and biocompatibility of transparent ADM (TADM) in lamellar keratoplasty.

Methods

A stepwise sectioning strategy was applied to determine the transparency distribution of the ADM, and TADM was fabricated accordingly. Transmittance measurements, uniaxial tension testing, and histologic staining were applied to detect its properties. Lamellar keratoplasty was performed in rabbits with TADM, and postoperative evaluations were conducted including the transmittance of the transplant area and histologic staining.

Results

The transmittance of the ADM increased with increasing depth, and TADM was isolated mechanically at the deepest level. There was a significant improvement in the transmittance of the TADM compared with the ADM, and no significant difference in transmittance between dehydrated TADM and cornea was observed. The elastic modulus of TADM was significantly stronger than that of normal cornea (P = 0.004). TADM consisted of dense collagen fibrils, mainly collagen type I, and the collagen fibril diameter and interfibrillar spacing were determined to be larger than corneal stroma. After lamellar keratoplasty in rabbits, the TADM was well integrated with the host cornea, and transparent cornea without neovascularization was observed at 6 months. Re-epithelization was completed at 1 month, and keratocyte repopulation and collagen remodeling were observed in the graft 3 and 6 months after surgery.

Conclusions

This study presents the transparency distribution of the ADM and a method for obtaining TADM, which demonstrates ideal transparency, strong mechanical properties, and satisfactory biocompatibility when applied in lamellar keratoplasty.

Short peptide analogs as alternatives to collagen in pro-regenerative corneal implants

Short collagen-like peptides (CLPs) are being proposed as alternatives to full-length collagen for use in tissue engineering, on their own as soft hydrogels, or conjugated to synthetic polymer for mechanical strength. However, despite intended clinical use, little is known about their safety and efficacy, mechanism of action or degree of similarity to the full-length counterparts they mimic. Here, we show the functional equivalence of a CLP conjugated to polyethylene glycol (CLP-PEG) to full-length recombinant human collagen in vitro and in promoting stable regeneration of corneal tissue and nerves in a pre-clinical mini-pig model. We also show that these peptide analogs exerted their pro-regeneration effects through stimulating extracellular vesicle production by host cells. Our results support future use of CLP-PEG implants for corneal regeneration, suggesting the feasibility of these or similar peptide analogs in clinical application in the eye and other tissues.

Statement of significance

Although biomaterials comprising full-length recombinant human collagen and extracted animal collagen have been evaluated and used clinically, these macromolecules provide only a limited number of functional groups amenable to chemical modification or crosslinking and are demanding to process. Synthetic, customizable analogs that are functionally equivalent, and can be readily scaled-up are therefore very desirable for pre-clinical to clinical translation. Here, we demonstrate, using cornea regeneration as our test bed, that collagen-like-peptides conjugated to multifunctional polyethylene glycol (CLP-PEG) when grafted into mini-pigs as corneal implants were functionally equivalent to recombinant human collagen-based implants that were successfully tested in patients. We also show for the first time that these materials affected regeneration through stimulation of extracellular vesicle production by endogenous host cells that have migrated into the CLP-PEG scaffolds.

Biomaterials-enabled cornea regeneration in patients at high risk for rejection of donor tissue transplantation

The severe worldwide shortage of donor organs, and severe pathologies placing patients at high risk for rejecting conventional cornea transplantation, have left many corneal blind patients untreated. Following successful pre-clinical evaluation in mini-pigs, we tested a biomaterials-enabled pro-regeneration strategy to restore corneal integrity in an open-label observational study of six patients. Cell-free corneal implants comprising recombinant human collagen and phosphorylcholine were grafted by anterior lamellar keratoplasty into corneas of unilaterally blind patients diagnosed at high-risk for rejecting donor allografts. They were followed-up for a mean of 24 months. Patients with acute disease (ulceration) were relieved of pain and discomfort within 1–2 weeks post-operation. Patients with scarred or ulcerated corneas from severe infection showed better vision improvement, followed by corneas with burns. Corneas with immune or degenerative conditions transplanted for symptom relief only showed no vision improvement overall. However, grafting promoted nerve regeneration as observed by improved touch sensitivity to near normal levels in all patients tested, even for those with little/no sensitivity before treatment. Overall, three out of six patients showed significant vision improvement. Others were sufficiently stabilized to allow follow-on surgery to restore vision. Grafting outcomes in mini-pig corneas were superior to those in human subjects, emphasizing that animal models are only predictive for patients with non-severely pathological corneas; however, for establishing parameters such as stable corneal tissue and nerve regeneration, our pig model is satisfactory. While further testing is merited, we have nevertheless shown that cell-free implants are potentially safe, efficacious options for treating high-risk patients.

A biomaterial implant supports the regeneration of severely damaged corneas in patients at high risk for rejecting conventional transplantation. An international team from Canada, China, India, Sweden, Ukraine and United Kingdom used mini-pigs to confirm the safety of implanting cell-free corneas made from recombinant human collagen and a synthetic lipid, before examining the effects of implantation on human vision in seven patients. The implants were well-tolerated and led to significant vision improvement in patients with damaged corneas due to infection. Furthermore, within two weeks of surgery the implants had relieved pain. Over two years, sensitivity to touch improved, suggesting an ability to promote nerve regeneration. This study supports the use of animal models to test biomaterials designed for medical applications and describes a safe and promising option for treating patients that not treatable by conventional corneal transplantation.

Clinical outcomes of non-torque pattern double running suture technique for optical penetrating keratoplasty

OBJECTIVE

To validate non-torque pattern double running suture technique for optical penetrating keratoplasty compared with traditional suture method.

METHODS

56 patients (56 eyes) undergoing optical penetrating keratoplasty were divided into two groups. The experimental group (28 cases) underwent non-torque pattern double running suture technique, and the control group (28 cases) underwent interrupted suture. All participants were followed up at 2 weeks, 2 months, 6 months, and 1 year postoperatively. The best corrected visual acuity (BCVA), corneal curvature change and astigmatism change were observed and compared between the two groups, and corneal topographer was used to measure refractive change.

RESULTS

BCVA in experimental group was significantly improved (P<0.05); the corneal topographer showed that astigmatism in experimental group was significantly lower than that in control group at the early postoperative phase (P<0.001). Six months later postoperatively, astigmatism gap between the two groups was narrowed, but the differences were still statistically significant (P<0.001). Twelve months later, astigmatism in the experimental group was similar to six months ago, but astigmatism in control group reduced significantly. No significant difference in astigmatism was observed between two groups (P>0.05).

CONCLUSION

Non-torque pattern double running suture technique for optical penetrating keratoplasty can achieve the BCVA at the very early phase, with stable postoperative refractive status. This novel suture method is accurate and safe with elegant appearance.