Non-toxic thermotropic liquid crystals for use with mammalian cells

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Abstract
This paper reports the results of a study that aimed to identify thermotropic liquid crystals that are not toxic to mammalian cells. Mesogenic compounds were mixed to create eight liquid crystalline phases, each with a unique set of functional groups. We investigated the toxicity of each liquid crystalline phase using two mammalian cell lines—3T3 fibroblast and SV-40 transformed human corneal epithelial (HCEC) cells. Using dual fluorescent staining assays based on calcein acetoxymethylester (Calcein-AM) and ethidium homodimer, we measured correspondingly the number of viable and dead cells following immersion of the cells in the liquid crystals. It was found that most of the liquid crystals, such as commonly used 5CB and E7, caused cell death after contact with cells for four hours. However, we identified a class of liquid crystals containing fluorophenyl groups that possess minimal or no toxicity (as indicated by results of assays based on Calcein-AM and ethidium homodimer) to cells. Following immersion in fluorophenyl liquid crystals for four hours, the cells were observed to proliferate in culture medium at rates similar to control cells exposed to phosphate-buffered saline (PBS) for four hours. In contrast, treatment of cells for 24 hours with either PBS or liquid crystals (media containing no nutrients and growth factors) resulted in cell death.