An overview of current techniques for ocular toxicity testing

Given the hazardous nature of many materials and substances, ocular toxicity testing is required to evaluate the dangers associated with these substances after their exposure to the eye. Historically, animal tests such as the Draize test were exclusively used to determine the level of ocular toxicity by applying a test substance to a live rabbit’s eye and evaluating the biological response. In recent years, legislation in many developed countries has been introduced to try to reduce animal testing and promote alternative techniques. These techniques include ex vivo tests on deceased animal tissue, computational models that use algorithms to apply existing data to new chemicals and in vitro assays based on two dimensional (2D) and three dimensional (3D) cell culture models. Here we provide a comprehensive overview of the latest advances in ocular toxicity testing techniques, and discuss the regulatory framework used to evaluate their suitability

Dextran preserves native corneal structure during decellularization

Corneal decellularization has become an increasingly popular technique for generating scaffolds for corneal regeneration. Most decellularization procedures result in tissue swelling, thus limiting their application. Here, the use of a polysaccharide, dextran, to reduce swelling and conserve the native corneal structure during decellularization was investigated. Corneas were treated with 1% Triton X-100, 0.5% sodium dodecyl sulfate, and nucleases under constant rotation followed by extensive washing. To reduce swelling, decellularization solutions were supplemented with 5% dextran either throughout the whole decellularization process or during the washing cycles only. Quantitative analysis of DNA content showed a 96% reduction after decellularization regardless of the addition of dextran. Dextran resulted in a significant reduction in swelling from 3.85 ± 0.43 nm without to 1.94 ± 0.29-2.01 ± 0.37 nm (p 0.05. Dextran can counteract the detrimental effects of decellularizing agents on the biomechanical properties of the tissue resulting in similar compressive moduli (mean before decellularization: 5.40 ± 1.18 kPa; mean after decellularization with dextran: 5.64 ± 1.34 kPa, p > 0.05). Cells remained viable in the presence of decellularized scaffolds. The findings of this study indicate that dextran not only prevents significant corneal swelling during decellularization but also enhances the maintenance of the native corneal ultrastructure

Characterizing the role of dextran in the decellularization of porcine corneas [Abstract]

Characterizing the role of dextran in the decellularization of porcine corneas [Abstract

Mechanical characterization of hydrogels and its implications for cellular activities

Mechanical characterization of hydrogels and its implications for cellular activitie

Chemical and topographical effects on cell differentiation and matrix elasticity in a corneal stromal layer model

Control and maintenance of the keratocyte phenotype is vital to developing in vitro tissue engineered strategies for corneal repair. In this study the influence of topographical and chemical cues on the mechanical, phenotypical and genotypical behaviour of adult human derived corneal stromal (AHDCS) cells in three dimensional (3D) multi-layered organised constructs is examined. Topographical cues are provided via multiple aligned electrospun nanofiber meshes, which are arranged orthogonally throughout the constructs and are capable of aligning individual cells and permitting cell migration between the layers. The influence of chemical cues is examined using different supplements in culture media. A non-destructive indentation technique and optical coherence tomography are used to determine the matrix elasiticity (elastic modulus) and dimensional changes, respectively. These measurements were indicative of changes in cell phenotype from contractile fibroblasts to quiescent keratocytes over the duration of the experiment and corroborated by qPCR. Constructs containing nanofibers have a higher initial modulus, reduced contraction and organised cell orientation compared to those without nanofibers. Cell-seeded constructs cultured in serum-containing media increased in modulus throughout the culture period and underwent significantly more contraction than constructs cultured in serum-free and insulin-containing media. This implies that the growth factors present in serum promote a fibroblast-like phenotype; qPCR data further validates these observations. These results indicate that the synergistic effect of nanofibers and serum-free media plus insulin supplementation provide the most suitable topographical and chemical environment for reverting corneal fibroblasts to a keratocyte phenotype in a 3D construct

Influence of cell number and collagen concentration on the mechanical behaviour of collagen hydrogel constructs [Abstracts]

Influence of cell number and collagen concentration on the mechanical behaviour of collagen hydrogel constructs [Abstracts

Ultrastructural maintenance of decellularized corneas using dextran [abstract]

PURPOSE. Corneal decellularization has emerged as a promising alternative to traditional tissue-engineering strategies for the creation of corneal replacements for transplantation. However, decellularization methods can lead to swelling of the cornea, limiting its potential use as a scaffold. In this study, we propose the use of a complex polysaccharide, dextran, to reduce this swelling and maintain the native dimensions and architecture of the cornea. METHODS. Porcine corneal buttons were treated with Triton X-100, SDS and nucleases under constant rotation followed by a washing step. To prevent corneal swelling, the decellularization solution was supplemented with dextran. This solution was added to one group throughout the decellularization process and to a second group during the washing cycle. The resulting acellular scaffolds were systematically evaluated by histological and biochemical analyses, in addition, the ultrastructure of the cornea was examined by transmission electron microscopy (TEM). RESULTS. Results demonstrated that the combination of detergents and nucleases effectively removed the majority of cellular material from the cornea. Furthermore, the addition of dextran prevented significant swelling when used throughout the protocol or only during the washing process. After soaking in glycerol a degree of transparency was returned to all decellularized corneas suggesting maintenance of the extracellular matrix. However, TEM analysis confirmed that dextran must be present throughout the decellularization process to preserve the native ultrastructure of the cornea. CONCLUSIONS. The findings of this study indicate that the addition of dextran to the decellularization process not only prevents significant corneal swelling but also enhances the maintenance of the native ultrastructure of the cornea

Controlling corneal stromal cell phenotype via chemical cues [Abstract]

Controlling corneal stromal cell phenotype via chemical cues [Abstract