The complete absence of systemic and, first and foremost, direct cellular toxicity is the essential requirement for a filler that is implanted in the skin and remains there for 8 months (on average).

For this reason in particular, in order to exclude even the lowest of cytotoxic effects, increasingly sensitive cytotoxicity assays are needed - which means performing in vitro tests using immortalised human keratinocytes as cell line.

Cytotoxicity can be assessed with the MTT test, which relies on mitochondrial activity. The test, originally developed by Mosman in 1983, is simple, accurate and yields reproducible results (Mosman, 1983). The MTT test is based on the principle that, in most viable cells, mitochondrial activity is constant, so an increase or decrease in the number of cells is directly proportional to mitochondrial activity. Viable cells convert MTT tetrazolium salts into formazan crystals, which can be solubilised in dimethyl sulphoxide (DMSO) for homogeneous spectrophotometric measurement. Therefore any change in the number of viable cells can be detected by measuring the optical density of formazan at 570 nm.

NEAUVIA STIMULATE Hydrogel 26 mg of HA with 1 % hydroxyapatite has shown complete absence of cytotoxicity at various concentrations, even ones higher than the normal concentration used for clinical purposes.

NEAUVIA STIMULATE is a "hybrid" filler, new, safe and reversible, which concentrates in a single product both the tissue filling functions of a filler and the collagen production of particle fillers, which already have successfully been on the market for years. The amount of collagen produced by NEAUVIA STIMULATE is comparable to particle fillers, without having the problem of being irreversibile. NEAUVIA STIMULATE is recommended for interventions on hands, cheeks, nasoslabial and jaw area, and the aesthetic corrections last approximately 12 months.

(not available in Canada yet)