Neutral Red Uptake

The purpose of the study is to determine the potential biological reactivity of a mammalian cell culture (L929) in response to the medical device extract. The test item is extracted in MEM with 10% FBS for usually 24 h at 37 °C or 72 h at 37 °C (permanent implants or prolonged exposure test items). The cells are allowed to grow to sub-confluency in tissue culture plates and exposed to the medical device extract at 4 (100%, 50%, 25%, 12.5%) concentrations in 6 replicates. The plates are incubated for 24 hours at 37 °C after which the viability is assessed via the incorporation of Neutral Red (NR) by the lysosomes of the live cells. The number of viable cells correlates to the color intensity determined by photometric measurements after dissolving the NR. The medical device is considered non-cytotoxic if the percentage of viable cells is equal to or greater than 70% of the untreated control.