The Cell–Surface Interaction - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 3

events, including protein adsorption, cell adhesion and signal mechanotransduc-
tion, are substrate-dependent. This can make understanding the cell-material
interaction more challenging as the system under study is dynamic from both
the cell and the material side. Furthermore, extrapolation of information collated
in vitro to results observed in in vivo studies is not as straightforward as the state-
ment that 'micro-rough surfaces enhance osseointegration' may lead one to believe.
The aim of this chapter, therefore, is to introduce the reader to the basic concepts of
the cell-material interaction and to provide an insight into the factors involved in
determining the cell and tissue response to specific surface features, with specific
emphasis on surface microtopography and the osteoblast/bone response.
2 Surface Conditioning upon Implantation of a Device
The nanoseconds subsequent to a device being implanted determine the fate of the
implant. This instantaneous reaction is a result of tissue biomolecules interfacing
with surface properties such as hydrophobicity, charge, chemistry and topography.
All of these properties help determine which proteins adsorb to the surface and the
types of intermolecular forces that ensue.
2.1 Initial Interactions upon Implantation
The primary biological reaction to an implanted device is the formation of a water
layer via hydroxyl groups of converged dissociated water molecules, within which
naturally occurring ions such as calcium (Ca 2+ ) and sodium (Na + ) become
incorporated [ 1 , 2 ]. The formation of a surface water layer with hydrated ions is
specific and dynamic depending on different surface chemical properties. There-
fore, surfaces with varying topography and chemical composition will ultimately
produce layers of different biological compositions.
Upon contact with blood, the implant becomes covered in a protein-enriched
film, which adheres to the surface via weak temporary bonds or stronger perma-
nent covalent bonds [ 1 ]. Blood has more than 2,000 proteins. The proteins that
come from the blood provide a provisional matrix for the cells to adhere to. Cells
never interact directly with the actual implant surface. The surface itself initially
determines which proteins absorb to it and also determines the orientation of their
attachment. Blood proteins on the surface adsorb and desorb according to elec-
trostatic and hydrophobic interactions with the surface, and their concentration,
size and stability to ensure the formation of thermodynamically stable properties.
Albumin (66 kDa) is the most concentrated protein in blood; therefore, it generally
dominates the initial surface interactions. Fibrinogen (340 kDa), in lower con-
centration within blood, is much slower to arrive at the implant surface owing to its
larger size. Upon arrival at the surface, however, it usually dominates the surface