Adhesion of human monocytes to oxygen- and nitrogen- containing plasma polymers: Effect of surface chemistry and protein adsorption.

The interactions between monocytes and biomaterials can potentially be modulated by controlling the chemical and structural surface properties of biomaterials. The objective of this study was to determine the effect of plasma-deposited functional organic coatings on monocyte adhesion and differentiation into macrophages. Organic coatings with varying oxygen and nitrogen concentration were prepared by low-pressure plasma co-polymerization of binary gas mixtures combining a hydrocarbon (butadiene/ethylene) and a heteroatom-containing gas (carbon dioxide/ammonia) to deposit either oxygen or nitrogen-containing coatings. The deposition parameters controlled the composition of the coatings and, consequently, the surface charge (between 26 mV and -28 mV) and wettability. The adhesion of myeloid leukemia cell lines U937 and NB4 as well as human monocytes to plasma polymerized coatings, was tested using cell culture medium with and without fetal bovine serum. The results showed that the concentration of [-NH2] and [-COOH] on the surface of the plasma polymers, controls the adhesion of U937 and NB4 cell lines to the coatings. Thus, above a certain composition threshold, i.e. [-NH2]=2.6-3.0% and [-COOH]=1.2-1.57 nmol/cm2, the surface facilitates adhesion of both cell lines, irrespective of the culture medium used. Based on qualitative observations the number of monocytes adhering to the coatings was proportional to the concentration of functional groups at the surface of the coatings. The surface plasmon resonance results, in line with cell culture experiments, indicated that the presence of albumin on the surfaces with [-NH2] and [-COOH] above the determined critical concentration may be an indicator of monocyte adhesion to these plasma polymers.