Hydrodynamics in Porous Media with Applications to Tissue Engineering - Porous Media: Applications in Biological Systems and Biotechnology - page 88

The spatial variability of this potential generates electrophoretic movement
of the mobile charges, inducing a conduction Ohmic current, which opposes
the streaming current and consequently slows down the counterions of the
diffuse double layer. Owing to the viscous drag interaction, the ions pull the
solvent, resulting in a concomitant electroosmotic seepage flow opposing the
pressure-gradient driven flow. This electrokinetic coupling has been commonly
referred to as the electro-viscous effect as its overall influence upon the flow
is usually treated through an increase in the viscosity of the liquid (Hunter
1981).
Many efforts have been made to better understand the role of coupled
electro-hydraulic phenomena on the stimulation of cell activity. For instance,
Lemaire et al . (2006, 2008) carried out a multiscale approach to quantify the
viscous shear stresses, τ , generated by interstitial flow by taking into account
the electrokinetic phenomena occurring at the scale of the cell membrane.
Dealing with cortical tissue, these studies proposed a coupled Darcy law to
describe the bone interstitial fluid flow that develops not only because of
the pressure gradient effect but also in response to streaming potential and
chemical gradients. Indeed, this description includes chemical-osmotic driven
effects (gradient of the Nernst potential) that are also manifested particularly
when the salinity or the pH varies spatially (Gu et al . 1998). This example
indicates the potentiality of stimulating cell culture using electrokinetic effects
(Funk et al . 2009).
3.4 Bioreactors and Implants
Tissue engineering not only promises for the future development of a new
generation of artificial organs, but also provides a basis for quantitative in
vitro studies of tissue genesis by culturing cells on three-dimensional sub-
strates in the presence of specific biochemical and physical factors. Bioreac-
tors and substrates are designed to maintain ad hoc levels of physiological
parameters in the cell environment, including enhancement of mass trans-
port rates and exposure to specific mechanical stimuli. Thus, functional tis-
sue engineering not only requires cellular components capable of differenti-
ating in appropriate lineages, but also necessitates the use of specific struc-
tural templates whose material nature and structural design foster the tis-
sue growth. Moreover, it requires the development of bioreactors provid-
ing necessary biochemical and physical regulatory signals predisposing cell
population growth, guiding differentiation, and inducing extracellular matrix
production.