Keratoprosthesis Research Articles

Moldable Crystalline α-Chitin Hydrogel with Toughness and Transparency toward Ocular Applications

A N-acetylated chitosan hydrogel was investigated for ocular applications. One of the drawbacks in the original hydrogel protocol, poor moldability, was circumvented by optimizing the addition of the acetylating agent, acetic acid anhydride (Ac2O), at −10 °C. This simple but significant optimization realized the preparation of N-acetylated chitosan hydrogels with a wider variety of parameters such as higher chitosan concentration and molecular weight, the use of a more benign solvent (ethanol replaced methanol), and the arbitral shapes ranging from microbeads and contact lenses to bulky blocks that could be gripped. The prepared N-acetylated chitosan hydrogels exhibited high transparency and integrity given the nanofibrous network made of highly crystalline α-chitin. Furthermore, the gel retained a regenerable character: an oven-dried gel was reswollen by emersion in an acid bath. These previously unnoticed advantages and the innate high biocompatibility of chitosan and chitin elevate N-acetylated chitosan hydrogel as a next-generation bio-derived soft material for ocular applications such as contact lenses, artificial corneas, and drug delivery vehicles.

Grafting with chondroitin sulfate on poly(vinyl alcohol) to improve antifouling property

Poly(vinyl alcohol) (PVA) hydrogels become muddy while used in artificial corneas. To enhance the antifouling property of PVA hydrogels, a PVA hydrogel was grafted with chondroitin sulfate (CdS) through a two-step reaction in this work. The surface chemical compositions, surface morphology and thermal property of the hydrogel were characterized by attenuated total reflectance FTIR, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy and thermogravimetric analysis. It was confirmed that CdS was successfully grafted onto the surface of the PVA hydrogel through a two-step method. After grafting with p(GMA-CdS) (GMA: glycidyl methacrylate), both the thermal and mechanical properties of the PVA hydrogel became weaker and the PVA hydrogel became hydrophilic. The biocompatibility of the PVA-g-p(GMA-CdS) hydrogel could be considered as non-cytotoxic according to ISO 10993-5:2009. The antifouling property of the PVA-g-p(GMA-CdS) hydrogel, namely its anti-protein adsorption and anti-cell adhesion, was significantly improved due to surface hydration, steric exclusion effect and charge surface. The anti-protein adsorption of the PVA-g-p(GMA-CdS) hydrogel increased by about 33·48% in comparison with that of the PVA hydrogel and the anti-cell adhesion increased by about 67·92%. Overall, the PVA-g-p(GMA-CdS) hydrogel is an ideal biomaterial candidate for artificial corneas.

Histopathological Study of an Explanted Novel Artificial Corneal Device

To report the first histopathological examination of an explanted KeraKlear keratoprosthesis device and surrounding host corneal tissue 1 year after transplantation. An explanted KeraKlear artificial cornea was evaluated by histopathology to assess for tissue integration and corneal remolding. Histopathological examination revealed collagenous ingrowth between the anterior and posterior corneal stromal lamellae through the holes in the device skirt. Hematoxylin and eosin stain (H&E), periodic acid Schiff (PAS), and Masson trichrome stains demonstrated no significant inflammation, vascularization, or edema. The KeraKlear artificial corneal device seems to be a biocompatible alternative to donor corneal tissues for visual rehabilitation for suitable patients.

The First Study Investigating the Clinical Outcomes of Boston Keratoprosthesis Type I Implantation in Indonesia

Introduction and Objective: Boston keratoprosthesis (Boston KPro) is an artificial cornea (collar button design) for a severely damaged cornea that is not suitable for penetrating keratoplasty (PKP). One main advantage of Boston KPro type I is there is no need to perform tarsoraphy. There were no previous studies investigating the clinical outcome of Boston KPro implantation in Indonesia, therefore we aimed to investigate the visual outcomes, device retention, and complications following Boston KPro type 1 keratoprosthesis.
 Case Presentation: This study was a case series of 11 patients conducted at Jakarta Eye Center with 18 months follow up period. The inclusion criteria were patients with severe corneal diseases that are not amenable for PKP. We found that VA baseline were LP (±72.72%) and HM (27.27%) (mean VA baseline=2.51±0.14 logMAR or equal to HM – LP VA) which significantly improved to 1.09 ± 0.69 logMAR (equal to 6/60 Snellen, ±36.3% were near normal vision based on WHO criteria), p=0.007. Two cases (±16.7%) were still HM because of implant explantation with corneal melting. There were 80.5% retention rates at final follow-up and other complications were retroprosthetic membrane formation (26.7%), elevated IOP (13.9%), and sterile corneal stromal necrosis (17.8%).There was no endophtalmitis found in this study.
 Conclusion: Boston K-Pro type 1 is a recommended option for patients with multiple corneal graft failure. It provides promising visual outcome with good retention rates. The number of Boston K-Pro type 1 implantations should be increased to counterbalance the corneal blindness burden in Indonesia.

Active loading graphite/hydroxyapatite into the stable hydroxyethyl cellulose scaffold nanofibers for artificial cornea application

The design of biocompatible porous scaffolds that encourage cell adhesion for corneal tissue engineering applications continues to be challenging. In addition to porous hydrogels, nanofibers that can simulate the extracellular matrix structure for cell adhesion would be beneficial. Graphite and nano-hydroxyapatite (nHA) are two bioactive materials that have been used to improve cell adhesion in scaffolds for corneal tissue engineering. In this study, nanofibers were fabricated from hydroxyethyl cellulose and polyvinyl alcohol (PVA) and cross-linked by glutaraldehyde bound to graphite and nano-hydroxyapatite. This scaffold surrounded a transparent hydrogel core from PVA that was cross-linked by freeze-thawing cycles. The chemical and mechanical evaluations demonstrated that nanofibers met the requirements as a scaffold for corneal tissue engineering. The results showed that when the concentration of nHA was approximately 1.66 wt%, the morphology of human epithelial cells did not change, and clot formation occurred around the scaffold during the 1-week in vivo implantation.

The Current Status of Infant Keratoprosthesis

The concepts of pediatric keratoprosthesis (KPro) and more recently infant keratoprosthesis are relatively new. Our first case was performed in 2003..

Osteo-odonto keratoprosthesis in Egypt: a case series

Purpose The aim of this study was to evaluate the preliminary results of osteo-odonto keratoprosthesis (OOKP) performed in Alexandria Main University Hospital, Alexandria, Egypt in eyes with end-stage cicatrizing conjunctivitis.Patients and methods OOKP surgery was done in two stages. Stage 1 included preparation of the globe, buccal mucous membrane harvesting, and preparation of osteo-odonto alveolar lamina with the cemented optical cylinder. The prepared lamina was then placed in the submuscular space for 2–3 months. In stage 2, the lamina–optical cylinder complex was implanted under the buccal mucous membrane and the posterior part of the optical cylinder was placed in a central corneal opening to act as an artificial cornea, transmitting image to the retina.Results Six eyes with end-stage ocular surface disease were included in this study. Anatomical success, in the form of retention of the prosthesis, was achieved in five eyes. The procedure failed in one eye due to unhealthy canines with a small amount of bone in the lamina. Functional success, defined as restoration of vision, was achieved in four eyes. Visual improvement was not attained in one eye (in addition to the eye with anatomical failure) due to optic atrophy despite good retention of the device.Conclusion OOKP is a promising procedure to regain vision in severe cases of end-stage corneal blindness, unsuitable for cadaveric corneal grafts. Proper selection of cases is crucial to achieve the best anatomical and functional results.

A Foldable Nonpenetrating Keratoprosthesis: Medium to Long-Term Clinical Results in Patients with Corneal Blindness due to Noninflammatory Anterior Cornea Disease.

PURPOSE:To report the medium to long-term safety and performance outcomes of the KeraKlear nonpenetrating artificial cornea (KeraKlear) as the primary procedure in patients with corneal blindness due to noninflammatory anterior cornea disease.METHODS:Fifteen patients with corneal blindness (preoperative visual acuity [VA] of ≥20/200) due to a non-inflammatory anterior corneal condition were included in this prospective, single-center study. Preoperative diagnoses included corneal scars, keratoconus, and corneal dystrophies. Diseased corneas were implanted with the KeraKlear (KeraMed Inc., Irvine, California, USA) by a single surgeon (JMV) using a femtosecond laser to create all incisions. Participants were followed up with for as long as 64 months. Uncorrected Snellen VA and postoperative complications were recorded.RESULTS:The average age at the time of surgery was 49.6 years old and 67% of patients were female. The patients experienced an average improvement in uncorrected Snellen VA of 7.6 lines (−1.17 logMAR). Average uncorrected vision at the last visit was 20/100 (0.73 logMAR), and median uncorrected vision at the last visit was 20/70 (0.54 logMAR). One patient experienced extrusion of the KeraKlear due to infection. There were no cases of glaucoma, retroprosthetic membrane, or endophthalmitis, the three most common complications of penetrating keratoprostheses (KPro).CONCLUSIONS:Medium and long-term outcomes of the KeraKlear indicate that this device is a viable alternative to corneal transplantation as a primary procedure in patients with non-inflammatory causes of corneal blindness, especially when corneal tissue is not available. The KeraKlear does not penetrate into the anterior chamber, and therefore, is less susceptible to the most common complications of penetrating KPro including endophthalmitis, glaucoma, and retroprosthetic membrane. The KeraKlear also has a comparable or improved adverse event rate compared to penetrating keratoplasty.

Poly(methyl methacrylate): Covalent Functionalization of PMMA Surface with L‐3,4‐Dihydroxyphenylalanine (L‐DOPA) to Enhance its Biocompatibility and Adhesion to Corneal Tissue (Adv. Mater. Interfaces 1/2020)

Poly(methyl methacrylate) (PMMA) surface is covalently functionalized with L-3,4-dihydroxyphenylalanine (L-DOPA) to form stable coating that significantly improves the biocompatibility of the PMMA. L-DOPA-functionalized PMMA also preserves the phenotypic characteristics of corneal fibroblast, supporting cellular adhesion, proliferation, and migration, which may lead to better biointegration of the Boston keratoprosthesis, the most commonly implanted artificial cornea for patients with severe corneal diseases. More details can be found in article number 1900767 by James Chodosh, Miguel Gonzalez-Andrades, and co-workers.

Рецензия на монографию д-ра мед. наук, профессора С. А. Якименко «Кератопротезирование»

Рецензия на монографию д-ра мед. наук, профессора С. А. Якименко «Кератопротезирование»

Synthesis and Characterization of Collagen-Chitosan-Sodium Hyaluronates as Artificial Cornea

As reported by Riset Kesehatan Dasar, Indonesia facing a serious problem of blindness with 966.326 cases of 2 million population in 2013. Gold standard such as keratoplasty couldn’t completely heal corneal injury due to the recipient’s rejection and limited donor. In order to overcome those concerns, artificial corneal tissue needs to be developed to produce an artificial cornea which is biocompatible, supports corneal function, and applicable. This research was conducted to provide an initial description of Collagen – Chitosan - Natrium Hyaluronate (Col-Chi-NaHA) as an artificial cornea through FTIR analysis, hydrophilicity and water absorption measurement. The artificial cornea was synthesized by forming ratio of collagen 20% w/v and chitosan 10% w/v, both solutions were dissolved in 0,1 M and 0,6 M acetic acid separately. Into the mixed solution, NaHA was dripped slowly with variation of 0%, 0,3%, and 0,6%. The homogenous solution was cast and heated for 24 hours at 35°C. The dry membranes were neutralized to obtain a pH around 7. From the analysis known that all of the characteristic bands of Col-Chi-NaHA could be observed in obtained membranes. Water absorption measurement demonstrated percentages over 90% on all membranes. The contact angle of obtained membranes was decreased by the addition of NaHA. The results showed that artificial cornea made from Col-Chi-NaHA successfully fabricated has hydrophilic properties to support cellular interaction and provide hydration to keep eye’s clarity and permeability. Therefore, Col-Chi-NaHA could may be a suitable material for the tissue-engineered cornea.

Integrated 3D bioprinting-based geometry-control strategy for fabricating corneal substitutes.

The shortage of donor corneas is a severe global issue, and hence the development of corneal alternatives is imperative and urgent. Although attempts to produce artificial cornea substitutes by tissue engineering have made some positive progress, many problems remain that hamper their clinical application worldwide. For example, the curvature of tissue-engineered cornea substitutes cannot be designed to fit the bulbus oculi of patients. To overcome these limitations, in this paper, we present a novel integrated three-dimensional (3D) bioprinting-based cornea substitute fabrication strategy to realize design, customized fabrication, and evaluation of multi-layer hollow structures with complicated surfaces. The key rationale for this method is to combine digital light processing (DLP) and extrusion bioprinting into an integrated 3D cornea bioprinting system. A designable and personalized corneal substitute was designed based on mathematical modelling and a computer tomography scan of a natural cornea. The printed corneal substitute was evaluated based on biomechanical analysis, weight, structural integrity, and fit. The results revealed that the fabrication of high water content and highly transparent curved films with geometric features designed according to the natural human cornea can be achieved using a rapid, simple, and low-cost manufacturing process with a high repetition rate and quality. This study demonstrated the feasibility of customized design, analysis, and fabrication of a corneal substitute. The programmability of this method opens up the possibility of producing substitutes for other cornea-like shell structures with different scale and geometry features, such as the glomerulus, atrium, and oophoron.

Covalent Functionalization of PMMA Surface with L‐3,4‐Dihydroxyphenylalanine (L‐DOPA) to Enhance its Biocompatibility and Adhesion to Corneal Tissue

AbstractThe Boston keratoprosthesis (B‐KPro) is globally the most commonly implanted artificial cornea for patients with severe corneal diseases, particularly those with multiple allograft failures. Despite providing a good visual recovery, the poor adhesion between the poly(methyl methacrylate) (PMMA)‐made stem and the donor tissue poses a challenge, impacting the clinical outcome of the B‐KPro. Using single‐molecule covalent bonding, PMMA surface is functionalized with l‐3,4‐dihydroxyphenylalanine (l‐DOPA) and its chemical, optical, mechanical, and biological properties are studied. The functionalization process significantly improves biocompatibility of PMMA, without affecting its optical and mechanical properties. Human corneal fibroblasts (HCF) and human corneal epithelial cells (HCEp) seeded on l‐DOPA surface both exhibit greater confluency and metabolic rate compared to those of PMMA during 7‐day cell culture. Moreover, HCF cultured on l‐DOPA demonstrates a higher expression of ALDH3A1, Ki67, Integrin 1, and FAK with no expression of α‐SMA, compared to those of PMMA, which instead show greater expression of α‐SMA. These suggest that l‐DOPA surface fosters cellular adhesion, proliferation, and migration, without adversely impacting the phenotype of the cells. This study offers an inexpensive and efficient tactic to modify the surface of materials with l‐DOPA to achieve the optimal biocompatibility and biointegration of medical devices.

Successful development and clinical translation of a novel anterior lamellar artificial cornea.

Blindness due to corneal diseases is a common pathology affecting up to 23 million individuals worldwide. The tissue‐engineered anterior human cornea, which is currently being tested in a Phase I/II clinical trial to treat severe corneal trophic ulcers with preliminary good feasibility and safety results. This bioartificial cornea is based on a nanostructured fibrin–agarose biomaterial containing human allogeneic stromal keratocytes and cornea epithelial cells, mimicking the human native anterior cornea in terms of optical, mechanical, and biological behavior. This product is manufactured as a clinical‐grade tissue engineering product, fulfilling European requirements and regulations. The clinical translation process included several phases: an initial in vitro and in vivo preclinical research plan, including preclinical advice from the Spanish Medicines Agency followed by additional preclinical development, the adaptation of the biofabrication protocols to a good manufacturing practice manufacturing process, including all quality controls required, and the design of an advanced therapy clinical trial. The experimental development and successful translation of advanced therapy medicinal products for clinical application has to overcome many obstacles, especially when undertaken by academia or SMEs. We expect that our experience and research strategy may help future researchers to efficiently transfer their preclinical results into the clinical settings.

Second harmonic generation imaging reveals asymmetry in the rotational helicity of collagen lamellae in chicken corneas.

High tensile strength and optical clarity are unique properties of the cornea. These features are dictated by the three-dimensional architecture of corneal lamellae. Therefore, understanding the microscopic details of the cornea's structural organization may contribute to the development of artificial cornea for the treatment of corneal diseases. In this study, the combination of forward second harmonic generation (SHG) microcopy and fast Fourier-transform based image analysis was used to characterize the depth-dependent superstructure of chicken corneal stroma. Our results show that from the surface, adjacent lamellae of anterior chicken cornea lamella rotate in a counterclockwise direction, and the same rotational helicity is observed in left and right corneas. Furthermore, the overall average rotational pitch of lamellae is 0.92 ± 0.11 degree/µm which persists for 176 ± 14 µm in the anterior stroma. As depth further increased, the rate of lamellar rotation decreases. Upon reaching posterior stroma, lamellar orientation remains constant. Throughout the stroma, collagen lamellae in chicken rotate a total of 169 ± 21 degrees. The lack of lamellar rotation in posterior stroma suggests that packing efficiency cannot be used to explain the helicity of depth-dependent rotation of anterior stroma. In addition, although the right cornea has a higher rotational pitch (0.95 ± 11 vs 0.90 ± 10 degrees/µm) and thinner anterior stroma (173 ± 13 vs 179 ± 14 µm) than the left cornea, the two effects cancel each other out and result in similar total angular rotation of anterior stroma (161 ± 23 and 165 degrees ± 21). Finally, our observation of a total angular rotation of 169 ± 21 degrees shows that within experimental error, chicken cornea lamellae rotate around 180 degrees or half of a complete turn. Additional studies are needed to arrive at an explanation of chicken superstructure in three dimensions.

Heparin-grafted PVA hydrogels: a material for the optical part of artificial cornea

Heparin (Hep) was grafted to a poly(vinyl alcohol) (PVA) hydrogel surface by using the covalent grafting method. The structure of the modified hydrogel was determined from Fourier transform infrared attenuated total reflection and X-ray photoelectron spectroscopy. The thermal stability of the samples was investigated by thermogravimetry–differential thermal analysis. The effects of the concentration of (3-aminopropyl)triethoxysilane (kh550) and Hep on visible light transmittance, moisture content, equilibrium swelling, hydrophilicity and percentage of Hep sodium release of the composite hydrogel were studied. The visible light transmittance of the modified PVA hydrogel was above 94%. The time of swelling equilibrium was about 60 min and the equilibrium swelling ratio ranged from 3·0 to 3·5. The hydrophilicity was enhanced, and the static water contact angle decreased from 41 to 28°. The bioeffects of the PVA–kh550–Hep hydrogel were evaluated by studying cell adhesion and proliferation. During the adhesion assay in vitro, cell adhesion significantly decreased after the interfaces had been modified with Hep. The Cell Counting Kit-8 assay showed that the biocompatibility of the PVA–kh550–Hep hydrogel improved obviously compared to that of pure PVA. The experimental results demonstrated that the PVA–kh550–Hep hydrogel had good stability, bioactivity and biocompatibility, suggesting its potential applications in artificial corneas.

Genipin-crosslinked polyvinyl alcohol/silk fibroin/nano-hydroxyapatite hydrogel for fabrication of artificial cornea scaffolds—a novel approach to corneal tissue engineering

Design of artificial corneal scaffolds substitute is crucial for replacement of impaired cornea. In this paper, porous polyvinyl alcohol/silk fibroin/nano-hydroxyapatite (PVA/SF/n-HA) composite hydrogel was prepared via the genipin (GP) cross-linking, the pore diameter of the hydrogel ranged from 8.138 nm and 90.269 nm, and the physical and physiological function of hydrogel were investigated. The resulting hydrogel exhibited favourable physical properties. With the GP content increasing, the structural regularity of PVA/SF/n-HA composite hydrogel was enhanced and the thermal stability was improved. The moisture content was slightly decreased and generally maintained at approximately 70%. The tensile strength was heightened up to 0.64 MPa, while the breaking elongation was decreased slightly. Moreover, the biofunction was investigated. The in vitro degradation test demonstrated that with the addition of GP, the stability of the composite hydrogels in protease XIV solution was promoted and the three-dimensional porosity structure of composite hydrogels was maintained as ever. And the human corneal fibroblasts (HCFs) were employed to examine the cells cytotoxicity of the PVA/SF/n-HA composite hydrogels with different GP content by CCK-8 assay. Based on confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM), HCFs had individually commendable adhesion and proliferation on PVA/n-HA/SF composite hydrogel. HCFs proliferated and grew into the pores of composite hydrogel. The results of biocompatibility experiments of composite hydrogel suggested that it was no acute toxicity, in vitro cytotoxicity was 0 or 1 grade. Overall, results from this paper, PVA/n-HA/SF composite hydrogel was a qualified medical material which conformed to the national standard, could be a promising alternative for artificial cornea scaffold material—a novel approach to corneal tissue engineering.

Nanocellulose isolation characterization and applications: a journey from non-remedial to biomedical claims

Cellulose is a renewable, biodegradable, ecofriendly and sustainable biomaterial. Global market of nanocellulose is comprehensively very high due to its utility. Extraction of nanocellulose from bacteria and plant results in different morphology and size of nanocellulose. Biocompatibility, mechanical strength, biofabrication, crystallinity, high surface area per unit mass, hydrophilicity, porosity, transparency and non-toxicity of bacterial cellulose make it more attractive. The extravagant nanoscaled three-dimensional network of cellulosic structures possess extraordinary properties for biomedical application, evidencing its usage in skin therapy, cardiovascular implants, cartilage meniscus implants, tissue engineering, bone tissue and neural implants, wound care products, drug delivery agents, tablet modification, tissue engineered urinary conduits, and synthesis of artificial cornea. Hence due to potential benefits associated with nanocellulose effective and efficient techniques are required for the isolation of nanocellulose that should be economical, ecofriendly and non-toxic.

PVA Hydrogel Functionalization via PET-RAFT Grafting with Glycidyl Methacrylate and Immobilization with 2-Hydroxypropyltrimethyl Ammonium Chloride Chitosan via Ring-Open Reaction

To solve the biofouling problem of polyvinyl alcohol (PVA) hydrogel as the artificial cornea, glycidyl methacrylate (GMA) and 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC) were grafted on the surface of PVA hydrogel via a new method of photoinduced electron transfer—reversible addition fragmentation chain transfer (PET-RAFT) polymerization and ring-open reaction. Both attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscope (SEM), and thermogravimetric analysis (TGA) confirmed that GMA and HACC were successfully grafted on the surface of PVA hydrogel. A series of experiments to test the hydrophilicity of PVA hydrogel showed that it became hydrophobic due to the introduction of hydrophobic groups after grafting with GMA and HACC. In addition, cytotoxicity in vitro of PVA-g-p(GMA-HACC) hydrogel could be considered as not cytotoxicity according to ISO 10993-5: 2009. The anti-fouling property of hydrogel decreased after grafting with GMA due to the hydrophobic surface, while increased after grafting with HACC due to the steric repulsion of p(GMA-HACC) polymer brush. It’s no doubt that PET-RAFT was a feasible and reliable surface modification method which could be used in many biomolecules due to the excellent advantages.

Hydrophilic modification on polyvinyl alcohol membrane by hyaluronic acid

PVA was dissolved in mixed solvent (DMSO and water) and followed by several freeze-thaw cycles in a mold to produce PVA membrane. Surface modification of PVA membranes by HA molecules was investigated to improve the hydrophilicity of the membrane surface thereby reducing adsorption of the proteins onto the membrane. The surface composition, water contact angle, optical and mechanical properties, surface morphology, cell compatibility and protein adhesion were systematically investigated. ATR-FTIR spectra, XPS, SEM and AFM indicated that PVA membranes were successfully modified by grafting of the HA. The modified membranes showed increased hydrophilicity and cytocompatibility, decreased surface roughness and mechanical properties, and suppressed cell and protein adhesion compared to the pristine membrane. In general, the achievement of the HA coating with anti-adhesive property can potentially be widely used on surface modification of artificial cornea and other biomedical implants.