Contamination-free non-contact wettability assessment system

Surface wettability is one of most important indexes for understanding the interfacial characteristics between a solid surface and a liquid, especially such physico-chemical properties as hydrophilicity and water repellency. Recently, non-contact wettability assessment by monitoring the behavior of liquid covering a sample surface by jet-flow application to the liquid has been proposed. This method is applicable to the in-liquid assessment of high wettability materials for which it is difficult to measure the contact angle, such as cultured cells in a liquid culture medium. However, when the flow is dirty, the contamination of the cell culture system by particles (e.g. microorganisms, virus, and aerosols) may occur. To solve this problem, we developed a contamination-free non-contact wettability assessment system that is composed of a clean-air source having a particle filter and an automated system for image processing instrumentation and motorized alignment device for sample positioning. We confirmed that the filtered air-jet contained no particles, although over ten thousand particles had been included in the air source. Furthermore, we detected no microorganisms on agar culture plates, which had been exposed to the air-jet before being incubated. With the image instrumentation, we automatically measured the liquid-squeezed size, which was the main index of surface wettability. The motorized alignment device allowed us to control the sample position without human direct operation. This developed system is compatible with wettability assessment in a high-level clean environment such as quality control of culture cells for regenerative medicine and in vitro assay of drug efficacy and safety.