How surface roughness and wettability affects biocompatibility

VARIOUS TYPES OF artificial materials are being utilized as implants in all fields of medicine. The surface properties of the implant determine its interactions with the surrounding host tissue. Physicochemical properties of the surface, like wettability and surface roughness, are of prime importance for the optimization of adhesion, spreading and proliferation of cells.

Different types of metal substrates like stainless steel, titanium and titanium alloys have been utilized as implant materials, especially for dental and bone implants. Polymers are often used either together with metals in hard tissue replacements or in applications where mechanical durability is not needed. The initial response when a material is placed in the biological surroundings, is water molecule adsorption to its surface. This happens within the first few nanoseconds. In the second stage, protein adsorption occurs. It is generally accepted that the small proteins will be the first to adsorb due to their rapid transport to the surface. Over time these proteins are replaced by bigger ones that have greater affinity towards the surface.

Wettability of the substrate is known to influence protein adsorption. It is usually reported that biomaterial surfaces with moderate hydrophilicity improve cell growth and have higher biocompatibility. However, cell adhesion can deacrease as the material becomes very hydrophilic. This points out the existence of a range of optimal surface energies. The third stage of biological response includes cell attachment to the surface. This stage is influenced by the adsorbed protein layer as well as the surface roughness. Cell spreading and differentiation is known to be influenced especially by both micro scale roughness and wettability. It is thus important to be able to determine when the cell spreading is modulated by surface free energy, surface roughness or both.