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Editors Selection IGR 9-4

Basic Science: Metal alloys and trabecular cells

Comment by Daniel Stamer on:

70831 Interaction of primary human trabecular meshwork cells with metal alloy candidates for microinvasive glaucoma surgery, Wang WW; Watson KA; Dixon SJ et al., Clinical and Experimental Ophthalmology, 2017; 45: 520-528

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Minimally invasive/micro-invasive glaucoma surgery (MIGS) is a relatively new procedure to lower intraocular pressure by artificially increasing conventional outflow. Small metallic shunts/stents are introduced ab interno to bypass the trabecular meshwork (TM) or stent open Schlemm's canal (SC). Currently unknown is the biocompatibility of these devices with conventional outflow cells. Wang and colleagues examined the effects of titanium (polished and sandblasted) and nitinol alloy on viability, morphology, proliferation and secretion of fibronectin from primary cultures of human TM cell strains obtained from a commercial source (ScienCell). Major findings were that the nitinol alloy decreased viability, proliferation and spreading compared to titanium and glass control. In contrast cells cultured on sandblasted titanium displayed the greatest degree of spreading compared to all other surfaces and materials, while cells cultured on polished titanium aligned with surface grooves. Finally, both nitinol and titanium increased fibronectin secretion compared to glass. Clearly, results show that substratum topography and composition impact behavior of commercial human TM cells. For example, the Hydrus is constructed from nitinol, while the iStent has a titanium surface with heparin coating. Interestingly, the present study did not examine effects of heparin coatings on metal surfaces. Regardless, results reported should be interpreted with caution because these commercial TM cells were not characterized by ScienCell or the investigators according to established protocols in the field (Stamer and Clark, 2016). Another limitation is that TM cells were not tested at confluence, a physiological condition for the majority of TM cells in vivo. Finally, an important cell type that interacts with MIGS devices (particularly the Hydrus) is SC, which was not tested. In any case, the present study was the first to address the important issue of biocompatibility in the conventional outflow tract, demonstrating different responses of cells between materials and surfaces. As new devices are developed, it is essential to test materials and coatings to assure better long term surgical outcomes.

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