Harnessing Cell–Biomaterial Interactions for Osteochondral Tissue Regeneration - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 88

7.4.1 Surface Properties

Wetability

Surface hydrophilicity/hydrophobicity of the biomaterials can be one of the
important parameters to regulate a series of cellular functions, including attach-
ment, migration, cytoskeletal organization, and differentiation [ 181 ]. Although it is
known that hydrophobic surface characteristics favor protein adsorption from the
aqueous surrounding solution, a hydrophilic surface is also necessary to initiate
cell attachment [ 117 ]. Therefore, controlling the optimum level of hydrophilicity/
hydrophobicity of the material surface could induce positive cell responses.
Technical methods to increase the hydrophilicity of hydrophobic synthetic poly-
meric biomaterials include grafting hydrophilic polymer through copolymerization
[ 182 ], plasma treatment to increase the number of oxygen-containing groups such
as -OH and -C=O [ 183 , 184 ], and photooxidation to introduce peroxide groups
onto the material surface with the aid of UV treatment [ 117 ]. For instance,
increasing hydrophilicity in copolymeric hydrogels by increasing the hydrophilic
PEG content relative to the hydrophobic PCL content resulted in higher prolif-
eration of primary rabbit chondrocytes [ 182 ]. In addition, more hydrophilic gels
(e.g., 14 wt% PEG and 6 wt% PCL) could be optimum to induce chondrogenic
differentiation, as determined by stimulated gene expression levels of type II
collagen, aggrecan, SOX9, and COMP. Plasma-treated electrospun PCL nanofibers
also showed higher chondrocyte adhesion and proliferation than untreated

hydrophobic PCL surfaces [ 184 ].

Roughness and Topography

Modulation of the hydrophilicity of the material surface can usually be related to
changes in topography and roughness [ 181 , 184 - 186 ]. Cell adhesion of both
human MSCs and porcine chondrocytes mediated by integrin b was influenced
by different topologies and surface roughness of PLGA-, PLA-, and PCL-coated
plates [ 187 ]. In addition to initial cell adhesion, topographical changes of the
material surface also affected chondrocyte aggregation (i.e., mesenchymal con-
densation) [ 188 ] and the osteoblastic signaling pathway [ 186 ]. Another study
using a composite bone scaffold also demonstrated the related changes in
increasing hydrophilicity and roughness by incorporation of hydroxyapatite
nanoparticles into a hydrophobic poly(propylene fumarate) scaffold [ 185 ]. In this
study, a mineral particle content of 20 wt% resulted in higher hydrophilicity and
roughness, and the changes in the physicochemical properties of the composite
material influenced osteogenic signal expression of rat bone marrow stromal
cells.