Monocyte-derived macrophages are critical in the host-foreign body response to biomaterials and have been studied extensively in various culture conditions in vitro, such as medium supplemented with fetal bovine serum (FBS) or autologous human serum (AHS). Since monocyte maturation into macrophages is highly plastic and may vary considerably depending on the surface, isolation procedures and in vitro culture conditions, we hypothesize that variations in protein adsorption and serum type will greatly impact monocyte behavior in a surface-dependent manner. The impact of xenoproteins on monocyte-surface interactions has not been well studied methodically and the use of AHS rather than FBS for macrophage-biomaterials studies in vitro is far from universal. The commonly used reference materials - tissue culture polystyrene (TCPS), polyethylene glycol (PEG) and polydimethylsiloxane (PDMS) - were employed in this study and we found a 3-fold higher adherent monocyte density on TCPS when AHS was used vs. FBS-supplemented medium. On PEG hydrogels, an 8- to 10-fold higher adhesion density was observed when AHS was employed vs. FBS, while on PDMS no difference in adhesion density was observed between the two sera conditions. Additionally, the presence of lipopolysaccharide abrogated the serum-dependent effect on cell adhesion on TCPS. Significantly different variations in protein release were observed between the serum conditions on these surfaces; in particular, there was a 100-fold higher concentration of growth-related oncogene for the AHS condition on PDMS even though the adhesion levels were comparable between the two serum conditions. These results emphasize the combined impact of the surface type and FBS xenoproteins in mediating the observed monocyte response to biomaterials in vitro.
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