Biocompatibility Evaluations and Biomedical Sensing Applications of Nitric Oxide-Releasing/Generating Polymeric Materials.

Abstract

Nitric oxide (NO) is a potent signaling molecule secreted by healthy vascular endothelial cells (EC) that is capable of inhibiting the activation and adhesion of platelets, preventing inflammation and inducing vasodilation. Polymeric materials that mimic the EC through the continuous release or generation of NO are expected to exhibit enhanced biocompatibility in vivo. In this dissertation research, the biocompatibility of novel NO-releasing/generating materials has been evaluated via both in vitro and in vivo studies. A new in vitro platelet adhesion assay has been designed to quantify platelet adhesion on NO-releasing/generating polymer surfaces via their innate lactate dehydrogenase (LDH) content. Using this assay, it was discovered that continuous NO fluxes of up to 7.05 ×10-10 mol cm-2 min-1 emitted from the polymer surfaces could reduce platelet adhesion by almost 80%. Such an in vitro biocompatibility assay can be employed as a preliminary screening method in the development of new NO-releasing/generating materials. In addition, the first in vivo biocompatibility evaluation of NO-generating polymers was conducted in a porcine artery model for intravascular oxygen sensing catheters. The Cu(I)-catalyzed decomposition of endogenous S-nitrosothiols (RSNOs) generated NO in situ at the polymer/blood interface and offered enhanced biocompatibility to the NO-generating catheters along with more accurate analytical results for intra-arterial measurements of PO2 levels. NO-generating polymers can also be utilized to fabricate electrochemical RSNO sensors based on the amperometric detection of NO generated by the reaction of RSNOs with immobilized catalysts. Unlike conventional methodologies employed to measure labile RSNO, the advantage of the RSNO sensor method is that measurement in whole blood samples is possible and this minimizes sample processing artifacts in RSNO measurements. An electrochemical RSNO sensor with organoselenium crosslinked polyethylenimine (RSePEI) catalyst was used to determine the endogenous RSNO levels in the whole blood of rabbits and pigs, and substantial variations of RSNO levels were found within the same animal species. The photo-decomposition of RSNOs during sample collection was also studied. The results show that complete insulation from external light during the blood sampling step is critical for the accurate determination of endogenous RSNOs.