|dc.description.abstract||Over 120 million individuals wear contact lenses (CLs) worldwide and compared to non CL wearers, they exhibit a higher risks of eye infection and ocular inflammatory events. As CLs are evolving towards becoming diagnostic and therapeutic devices, there is a growing need for in vitro models that can efficiently assess ocular surface toxicity and biocompatibility of the technologies embedded in CL. Hence, understanding the effects of CLs on the health and integrity of ocular surface is imperative. While there exists some in vitro ocular cell models for the characterization of cellular mechanisms and biocompatibility, many of these are too complex and costly for rapid testing or don’t always allow for a biomaterial to be present. The aim of this thesis was to explore and develop cell culture models that could best mimic some of the interactions between the ocular surface and a biomaterial.
In the first phase of the development of the in vitro model, to investigate the role of the ocular surface geometry on corneal cells and understand how curvature affects cell response, HPV-immortalized corneal epithelial cells (HCEC) were grown on flat and curved surfaces. Next, the effect of artificial tear flow (dynamic conditions) in an in vitro model was assessed. The OcuCell testing platform, an in vitro system which mimics tear flow between an “eyelid” and “eyeball” pieces, was used to determine the role of dynamic conditions when assessing combination of CL and CL cleaning solutions. The Ocucell eye pieces were made of 10% Sylgard 184; the two pieces fit together and permit a CL to be set on the corneal surface of the “eyeball” piece. HCEC were grown to confluence on the outer curved eyeball surface and on the inner concave surface of the eyelid piece and two CL (Etafilcon A and Balafilcon A) were tested in combination with two CL cleaning solutions, ReNu Fresh (a PHMB-based multi-purpose solution) and ClearCare (a hydrogen peroxide based solution). Experiments were performed under static (no flow) and dynamic conditions. Finally, the effect of crosstalk between two different corneal cell populations in an in vitro testing for CL was investigated. A coculture system using HCEC and conjunctival (ICONJ) corneal cells was implemented, where ICONJ cells were grown on a PET transwell insert and HCEC on the well of a tissue culture treated polystyrene plate (TCPS). When cells reached confluency, they were incubated together with the CL combination. Results were compared to CL incubation with single cell population. All experiments were performed for 6 hours and cells were harvested and expression of integrin α3 and β1 was characterized by flow cytometry.
Curvature was shown to have a significant effect on corneal epithelial cells where cells grown on the convex and concave pieces exhibited a significant upregulation in α3 and β1 integrin expression compared to that of the flat surface. Using the OcuCell test platform, downregulation in integrin expression was observed when HCEC were exposed to various CL-solution combinations. The combination BA-ReNu consistently resulted in significant reduction in integrin α3 and β1 when compared to the control lens (lens incubated in PBS), suggesting that the release of MPS components on BA, such as PHMB and borate buffer, affected HCEC. In the mono culture model, no difference was observed with any CL-solution combinations. In the double culture model (where a contact was placed in between the TCPS and insert with same cell population), some downregulation in integrin expression was observed with HCEC but not ICONJ. However, upon co-culture of HCEC with ICONJ, downregulation of integrin expression was observed in all combinations and more significantly so with BA-ReNu.
In this thesis, the effects of curved versus flat surfaces, dynamic versus static conditions, and mono versus co-culture models, were investigated to understand their potential role when assessing CL biocompatibility. Our results highlight how each experimental in vitro model provides different but complementary information about the biocompatibility of the CL and multipurpose cleaning solution combination. The co-culture model also provides in vitro evidence of the crosstalk between cells and how this may impact ocular cell response to a biomaterial. The in vitro models and methodologies explored in this thesis represent news means to test biocompatibility of CLs, and potentially allow for future testing for ophthalmic materials and contact lens technologies in in vitro cell models that are simple and cost effective to allow for fast prototyping and development.||en