Protein adsorption and monocyte activation on germanium nanopyramids

Germanium can form defect-free pyramidal islands on Si(1 0 0)-2×1 with a height of 15 nm and a width of 60 nm. Using chemical vapor deposition we have prepared substrates with different nanopyramid densities to study the impact on contact angles, protein adsorption and cell behavior. The advancing contact angle of a water droplet of millimeter size significantly raises with nanopyramid density. The dynamic contact angle measurements reveal that the substrate surface is highly hydrophilic. On such a surface the adsorption of hydrophilic proteins, i.e. albumin and globulin, is drastically increased by the presence of nanopyramids. More important, however, the globulin is inactive after adsorption on nanopyramid edges. This observation is supported by the cytokine release of IL-1β and TNF-α of monocyte-like cell line U937. Consequently, the presence of nanopyramidal structures gives rise to less inflammatory reactions.