Poly-L-lysine/poly-L-glutamic acid-based layer-by-layer self-assembled multilayer film for nitric oxide gas delivery

Nitric oxide (NO) gas is an endogenously produced radical gas involved in numerous physiological and pathological processes in the human body and shows potential for biomedical applications. Numerous studies have attempted to develop an NO-releasing platform in the past few decades. To take advantage of exogenous NO gas delivery, controlling the total concentration and release profile are the most important factors. To develop a controlled NO-releasing system, we used the poly-L-lysine (PLL) and poly-L-glutamic acid (PGA) because of their high biocompatibility in biomedical applications. We constructed (PLL/PGA)_n multilayer thin films using the layer-by-layer self-assembly technique. We then synthesized the N-diazeniumdiolate, a proton-responsive NO donor, into the polypeptide multilayer film in a high-pressure reaction under NO gas. We investigated the film growth profile by quartz crystal microbalance and thickness measurements and determined the film surface morphology by scanning electron microscopy and atomic force microscopy. By comparing films with different thicknesses, we confirmed NO donor formation by UV–vis and Fourier-transform infrared spectroscopy. We also determined the release profiles of each film using a real-time NO analysis machine (NOA280i).