Implications of wettability in biological materials science

Abstract

Understanding liquid-solid interactions through the behavior of the liquid-solid interface is of paramount interest in many applications ranging from plant surfaces to fabrics, metal casting and biomedical implants. Liquid-solid interactions may or may not include chemical reactions, and the degree of liquid spreading over the solid surface (wetting) may vary based on the chemical properties of the materials involved (surface free energy) and the topography of the solid surface (roughness). The wetting of solid surfaces by biological fluids is often necessary for a chain of biological events to unfurl so that a foreign material may be accepted in vivo and thus become bioactive. We discuss the fundamentals of wettability, and how it pertains to the biological environment. The widespread use of contact angle measurements for the determination of surface free energy is also discussed. The use of contact angle as a general test for biocompatibility has inherent pitfalls as the effects of roughness on contact angle may be significant and misleading about the true chemical nature of the surface. Techniques to characterize the surface free energy are much more reliable, but are not as easily implemented as contact angles.