Cell viability and inflammatory response in hydrogel sponges implanted in the rabbit cornea

In the quest for the development of a functional keratoprosthesis, the bioc ompatibility of the porous skirt material in the Chirila keratoprosthesis ( KPro) was investigated. The population of live and dead cells within, and t he inflammatory response to, a tissue-integrating poly(2-hydroxyethyl metha crylate) (PHEMA) sponge were studied. Samples of the hydrogel sponge were i mplanted in rabbit corneas and explanted at predetermined time points up to 12 weeks. The explanted sponges were subjected to cell viability assay usi ng two types of fluoroprobes, 5-chloromethylfluorescein diacetate and ethid ium homodimer-l. A semiquantitative analysis was performed to assess the nu mber of dead cells within the sponge and in the area of corneal stroma prox imal to the sponge. Five rabbits were used for each end point (2, 4 and 12 weeks). To investigate the inflammatory response to the sponge, immunocytoc hemistry, using specific antibodies to rabbit macrophages, enzyme histochem istry of chloroacetate esterase (to detect neutrophils) and transmission el ectron microscopy (TEM) were also employed at 24 h, 2, 4 and 12 weeks after implantation. Four weeks after implantation, fewer viable cells were obser ved in the sponge when compared to the 2-week implant. However, the proport ion of viable cells increased dramatically by 12 weeks. The proportion of n onviable cells decreased gradually with time; central sponge contained 34 /- 11% dead cells after 2 weeks, and 15 +/- 4.3 % after 12 weeks. The stain ing of inflammatory cells demonstrated the presence of macrophages and neut rophils up to 12 weeks after implantation. TEM confirmed the presence of th ese cell types and others, including eosinophils and myofibroblasts, as wel l as blood capillaries. The presence of a significant number of viable cell s at each time point and the uniform reduction of the nonviable cell propor tion with time suggests that the sponge is a conducive environment supporti ng a prolific, viable cellular colonization. Dead cells observed in the fir st instance indicate a normal injury pattern. However, the presence of a sm all but significant proportion of invading inflammatory cells 12 weeks afte r implantation confirms a characteristic pattern of wound healing within th e sponges. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.