When a biomaterial is placed in the human body different molecular interactions take place at the material surface. The types of interactions are affected by the surface properties of the material such as surface chemistry, wettability and surface roughness. The surface phenomena can be roughly divided into four stages, water-surface interactions, protein adsorption, cell attachment and cell spreading, and proliferation.
The initial response when a material is placed in the biological surroundings is the water molecule adsorption to its surface. This happens within the first few nanoseconds. It is commonly known that water behaves differently with different materials. It can either spread on the surface or form a droplet on it with a measurable angle (i.e. contact angle). Based on this the surface is classified either hydrophilic or hydrophobic.
The behavior of water on biomaterial surface has long been under investigation as that is the basis of the role of a biomaterial surface in biological response. To what extend water – surface interactions affect the protein adsorption and later cell – biomaterial interactions are still under investigation.
In the second stage, the protein adsorption occurs. Proteins are observed on a biomaterial surface under a second after implantation in a living system. In seconds to minutes, a monolayer of protein adsorbs to the most surfaces. 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 a greater affinity towards the surface [1]. The affinity of the proteins is a major principle determining the outcome of the competitive adsorption process. For example, the three major plasma proteins are albumin, IgG, and fibrinogen whereas the amount of hemoglobin in plasma is much less. Still adsorbed amounts of hemoglobin are similar to predominant proteins due to higher surface affinity [2].
The third stage of biological response includes the cell attachment to the surface. This stage is influenced by the adsorbed protein layer as well as surface topography. As the protein adsorption occurs well before cells arrive at the surface, the cells primarily see the adsorbed protein layer rather than the biomaterial surface itself.
Cell spreading and differentiation are known to be influenced especially by both microscale roughness and wettability. It is usually reported that biomaterial surfaces with moderate hydrophilicity improved cell growth and higher biocompatibility. However, cell adhesion can decrease as the material becomes very hydrophilic. This points out the existence of a range of optimal surface energies [3].
As the nano- and microscale roughness also plays a role here, it is important to be able to determine when the cell spreading is modulated by surface free energy, topography or both [4].
If you are interested in reading more about why wettability is important in biomedical applications, please download the overview through the link below.
Susanna is an Application Scientist at Biolin Scientific. In her PhD thesis, she developed fabrication methods for a new type of inorganic-organic polymers. Microfabricated polymer chips were utilized as tool for biomolecule separation in analytical chemistry.
