How to Control Surface Cleanliness?

Microplate well density A single 3.25" x 4.5" microplate may contain more than 1500 wells. Individual wells can have diameters of 3 mm and depths of 10 mm. These wells are frequently coated in batch vacuum processes. The miniscule cell size and submicron coating thickness makes testing the uniformity of these coatings extremely challenging. Few appropriate techniques exist for quantitatively ensuring quality and consistency of important device surface properties. The century-old technique of contact angle measurement, however, can be adapted to provide an excellent quantitative interrogation of these properties. Water contact angles Contact angle measurements provide vital insight into the chemical state of a material surface. When a drop of liquid is deposited on a surface, the surface will repel or attract the droplet, causing it to bead up or flatten out, respectively. The attraction between the surface and the water is quantified by measuring the angle formed between the substrate surface and the drop edge. A surface that will be coated or bonded will be chemically clean and have a high surface energy. This is characterised by a water droplet that spreads to form a low contact angle across the surface. This indicates that there are many active chemical groups on the surface pulling the water droplet to the surface . The way that these chemical groups attract the water droplet indicates how a coating or adhesive will spread. If the water droplet does not spread, neither will the coating. A high contact angle indicates the presence of a surface contaminant or the need for additional surface preparation before bonding or coating. When a coating has been homogenously applied, contact angles will be uniform across the surface. Various types of coatings are used in the medical industry. As described above, when capillary action is required for diagnostic devices and a hydrophilic coating is in place, contact angles should be low (high surface energy). Alternatively, hydrophobic coatings, like those used for catheter applications, require high contact angles (low surface energy). In either case, contact angles provide a direct method for quantifying the surface wetting properties both before and after applying a coating or adhesive.