Enzyme-Based Nitric Oxide (NO) Releasing Surfaces: Nitric Oxide Synthase As a Source of Catalytic NO Release in Polymeric Films and in Electrospun Fibers

Nitric oxide (NO) is a key player at multiple physiologic fronts including the body’s immune response, neurotransmission, and cardiovascular processes. Among other effect on the cardiovascular system, NO is known to counteract platelet aggregation, and therefore has the ability to prevent the thrombosis cascade on the surface of blood-contacting medical implants and vascular grafts. Capitalizing on this property, NO-releasing surfaces have been proposed to counteract thrombosis on the surface of implanted devices or devices used as part of cardiovascular procedures. However, previous proposals using organic or inorganic sources of NO face the challenge that the amount of available NO is finite, which limits the long-term viability of implanted devices. We proposed the use of NOS enzymes, in alternating layer-by-layer thin film architecture, as the catalytic source of NO released using substrates of the NOS reaction in blood or plasma. We will summarize the performance of thin based on polyethyleneimine (PEI) including the effect of fabrication conditions on enzyme and loading and enzyme activity and subsequent effect on counteracting platelet adhesion from platelet-rich plasma. We will also describe and characterize membranes of electrospun fibers embedding nitric oxide synthase as a catalytic source of NO release. The NO-releasing membrane is to be used as a biocompatible platform for medical applications such as support-scaffolds for internal wounds. We will describe the process of formation of these NOS-based NO-releasing fibers. We will discuss the characterization of such material with methods including atomic force microscopy and enzymatic activity assay of encapsulated enzyme by monitoring levels of NO released over time. We will compare and contrast the results of PEI-based thin films with embedded NOS enzyme and electrospun fibers with encapsulated NOS.