Coatings for Biomedical Applications

Abstract

DefinitionCapillary force and surface wettability are related phenomena happening at the interfaces of solid, liquid, and air phases, and are highly dependent upon the interaction between liquids and solid surfaces. Scientific Fundamental Surface WettabilityWhen a liquid is in contact with a solid surface in air, in general, a droplet of the liquid will be formed. The shape of the droplet depends upon the interaction between the liquid and the solid surface. If the interaction is strong, i.e., the liquid "likes" the surface, the liquid drop will be "flat." On the contrary, if the interaction is weak, i.e., the liquid "hates" the surface, it will "bead up." Scientifically, such a property is described quantitatively by the concept of contact angle, which demonstrates the angle (y) at which the air-liquid and solid-liquid interfaces meet (see Fig. 1). Such a situation is the result of the force balance at the location where air, liquid, and solid phase meet, the socalled "three phase contact line." The interfacial tension of air-liquid, air-solid, and liquid-solid interface is denoted by g al , g as , and g ls , respectively. The force balance is described by the well-known Young's equation (Blake 1993; Butt et al. 2003; Isrealachvili 2003):This is a clear description of the interaction between the solid and liquid, as a smaller value of contact angle exhibits a larger difference between g as and g ls and, therefore, a much lower interfacial tension between the solid and liquid.The contact angle measurement is also an informative way to show the surface wettability of a liquid on a solid surface. If the interaction between the liquid and the solid surface is strong, a much lower interfacial energy results, and, as a result, the surface will be covered more by the liquid so that more area with higher air-solid interfacial energy is replaced by much lower interfacial energy of the liquid and solid. The result is that the liquid droplet is more spread out and has a lower value of contact angle. On the other hand, an unfavorable interaction between the liquid and solid surface generates a higher interfacial energy and, therefore, the system will maximize the area of the solid-air interface and minimize that of the interface between the liquid and solid surface. Consequently, the liquid forms a droplet with a small footprint on the surface and has a higher value of contact angle.

Low pressure plasma modifications for the generation of hydrophobic coatings for biomaterials applications

“…Furthermore, existing information has suggested the DLC coatings to be susceptible to oxidation upon exposure to air aging, high‐temperature ht or acidic etching. While the DLC interfacial strength also decreased when exposed to prolonged bio‐fluid incubation, some early success in using multiple Ta layers (i.e., Ta(CoCrMo) 0.5–2.0 /alphaTa/Ta carbide) as the interlayer to promote adhesion and to reduce bio‐corrosion = induced delamination has been reported . However, the chemical bonding and microstructure of these DLC coatings have, sadly, not been reported in most open literature to provide insights into their failure mechanisms to enable improvement in the next generation of DLC products.…”