Step-wise control of protein adsorption and bacterial attachment on a nanowire array surface: tuning surface wettability by salt concentration

The control of protein adsorption and cell attachment to materials is of great importance in many fields, including biomaterials, tissue engineering, biosensors, drug delivery and bioseparations. The wettability of a material strongly affects the binding of proteins and cells. Thus, changes in wettability and, in particular, jump-wise'' and smaller step-wise'' changes, can be exploited to control these interactions. In this work, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) was grafted onto silicon nanowire arrays (SiNWAs) by surface-initiated atom transfer radical polymerization (SI-ATRP). The wettability of the modified material was shown to be tunable by varying the environmental pH and NaCl concentration. The water contact angle (WCA) response was different for these two variables. A sharp or jump-wise'' change of WCA between similar to 10 and 110 degrees was observed at a pH of about 5.0. With decreasing ionic strength (IS), the surface wettability changed gradually in a step-wise fashion from superhydrophilic (WCA <2 degrees) to strongly hydrophobic (WCA >110 degrees). Protein adsorption and bacterial attachment on the surface varied with wettability changes caused by varying the ionic strength at pH 7.0. Thus, variations in ionic strength can be used as a means of controlling these interactions. It is concluded that fine control of protein adsorption and bacterial attachment can be achieved on PDMAEMA-modified SiNWAs by tuning surface wettability via salt concentration. This approach also has potential applications in the control of adsorption and release of drugs and cells, in biosensors and in environmental treatments using microorganisms.