Interaction ofCartilage andCeramic Matrix - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 299

2 Relevant Substrate Properties for Tissue Engineering
Many requirements for biomaterials have been defined for the attachment of cells,
proliferation, differentiation or tissue development depending on the host tissue. At
an elementary level, the biomaterial has to be non-toxic, biocompatible, biode-
gradable if needed and must not elicit an inflammatory response from the body [ 9 ].
Besides these basic demands, the structural properties of scaffolds have recently
become relevant during development of the material. The role of biomaterials has
changed from bio-inert cell carriers to bio-functional materials whose properties
are used to interfere in cell behaviour, e.g. by mimicking the natural microenvi-
ronment [ 12 ]. Physical parameters such as the overall architecture, grain size,
surface structure, porosity, pore size and mechanical properties, as well as the
chemical composition, surface chemistry and charge of biomaterials, are known to
influence the process and quality of in vitro generated tissue and its adhesion to the
material [ 11 , 13 - 15 ].
Physical characteristics of biomaterials have attracted attention for more than
three decades, with clinical studies showing a more effective integration of
implants into bone for rough than for smooth surfaces [ 16 , 17 ]. As a consequence,
several studies have investigated surface properties of biomaterials, not only of in
vivo implants but also in the field of tissue engineering for a number of host tissues
[ 18 ]. In cell culture experiments, it was found that several cell types react to
modified substrate surface topographies, e.g. with an increase in adhesion,
acceleration of cell movement, orientation, morphological changes of the cells,
cytoskeletal changes, changes in contact inhibition, activation of phagocytosis or
changes in gene expression [ 19 - 22 ]. Furthermore, porosity and pore size are rel-
evant on the macroscopic scale to reduce mass transfer limitations of nutrients and
waste products or to allow tissue ingrowth [ 15 , 23 ].
However, it is difficult and often not possible to separate chemical and physical
influences of biomaterials on cells. Hence, there is still an ongoing discussion of
the importance of chemical and physical aspects [ 24 , 25 ]. One study differentiating
between physical and chemical effects showed that surface chemistry plays a role
during short-term attachment of cells, while the topography can be correlated to
the long-term adhesion [ 25 ]. Parameters which are influenced by substrate
chemistry and physical characteristics such as wetting properties, surface energy
and surface groups play a role in cell behavior [ 11 , 13 , 26 - 29 ]. It was further
observed that differentiation of certain cell types was supported by substrate
surface characteristics, even in the absence of differentiating factors added to the
culture medium [ 25 , 30 ]. These results confirm that the choice of an adequate
scaffold during tissue engineering is an essential prerequisite for success [ 23 , 31 ].
One reason for the reaction of cells to modified surfaces is the selective adsorption
and arrangement of proteins which may induce cell attachment, proliferation or
differentiation of cells [ 11 ]. Adsorption of molecules from culture liquid of body
fluids, including proteins for cell attachment, growth factors, lipids, sugars and
ions, is well studied. The adsorption of these molecules was shown to be specific