Definition
Research performed outside a living organism, such as in cell culture, tissue samples or purified-protein assays.
In vitro, Latin for "in glass", describes experiments performed outside a living organism: cell culture, isolated tissues, receptor binding assays, enzyme assays and other cell-free systems. In vitro work offers tight control over variables, high throughput and mechanistic resolution, and it is usually the first stage of peptide research. Its limitation is context: concentrations, exposure times and cellular environments may not reflect those in a whole organism, so results do not translate directly. For peptide studies, practical factors such as counter-ions (TFA), preservatives (benzyl alcohol) and endotoxin contamination can affect in vitro readouts and should be controlled.