Polyelectrolyte multilayer films: A sponge for insulin?

Considering restrictive diabetes treatments, new insulin administration strategies constitute a huge medical challenge. This study aimed at developing a new support for insulin reservoirs, using polyelectrolyte multilayer films (PEM films), and thus studying this hormone release in a progressive manner. At first, insulin was loaded in (PDADMAC-PAA) _n films, by immerging them for various periods of time (2, 14 and 24 h) in a solution containing this protein. Confocal laser scanning microscopy (CLSM) revealed that insulin-FITC could diffuse inside the film with a bigger concentration in the upper part of the film (after 2 and 14 h in contact with the polypeptide solution), and then in the whole film (after 24 h) from a solution at pH=4.3 (below insulin's isolelectric point). Environmental scanning electron microscopy (ESEM) and CLSM showed that the film swells upon insulin loading. We finally investigated the insulin release by ATR–FTIR spectroscopy. It revealed that a loaded (PDADMAC-PAA) ₁₅ film, immerged in distilled water, showed no measurable insulin release. In contrast, a slow unloading was observed in the presence of a NaCl 0.15 M solution (salinity close to physiological serum). This study could open the route for a new way of insulin delivery.