In which year did E Gorter and F Grendel make a breakthrough by examining the surface area of lipids and concluded that the lipid surface surrounding cells must be of two layers?

In 1925, Evert Gorter and François Grendel made a significant discovery in cell biology by examining the surface area of lipids extracted from red blood cells. Their experiments showed that the lipid surface surrounding cells must consist of two layers, which led to the conclusion of the lipid bilayer model. This finding became the foundation for the current understanding of cellular membranes, which are composed of a double layer of lipids with embedded proteins, crucial for various cellular functions.