Biomedical Engineering Reference
In-Depth Information
termination at the synaptic junction or receptor. As noted above the hydrolysis
of ATP yields the energy required for operation of the pump, but the rate of
metabolism increases significantly during the propagation of the action
potential. Obviously, in nerve tissue of varying types the overall behavior will
reflect the compounding of a vast number of action potentials and signals, the
most complex of this being the human brain.
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2.5 Cell Adhesion, Growth, Guidance and Proliferation
on Substrates
2.5.1 General Considerations
The cell-substrate interaction has been the subject of intense research for many
years, with the most activity being directed at the biomaterials sector. The main
focus of this research has been on producing a 'scaffold', whether of synthetic
or natural material, that allows the structural support and maintenance of
healthy cells when in contact with such a material. Research with the aim of
'repair' in mind is often associated with the marketing term 'regenerative
medicine', although the developments can hardly be described as regenerative
in the strictest sense of the word! In the biomaterials world, the biodegrad-
ability of the substrate is, additionally, an important factor. The reason for this
lies in the potential inadvisability of the presence of foreign entities in the body.
As outlined at the end of this chapter, there are medical consequences as a
result of the deleterious effects of surfaces on blood components, including
various cells.
There are two strategies to achieve cellular adhesion and growth—substrate
chemical modification and sub-micrometer patterning of the surface
topography. Wells, pillars and grooves of different dimensions are fabricated
using standard microfabrication techniques, including photolithography, wet
etching, reactive ion etching and laser fabrication. Chemical modification
means changing the surface composition and properties by chemically binding
different proteins and molecules that promote cell adhesion. An unexpected
finding is that cellular response to engineered surfaces is specific to the cell type.
This result clearly implies that there is no general method that fits all cells types,
including neurons.
Neuronal cells are functionally and morphologically unique among cells for
various reasons. They are polarized, possessing receptive dendrites on one end
and axons with synaptic terminals on the other. Impressively, the brain is not a
static structure but it is capable of neuroplasticity, an essential process for
cognition and learning. It is possible to induce physiological changes that lead
to anatomical changes, including pruning of preexisting connections and
growth of new connections. These amazing properties of the brain are explored
in the research on neuronal prosthesis for neuronal recovery. Neurite guidance,
especially axonal guidance, is one of the key processes during embryogenesis
and is explored in neural tissue engineering. Neural cells find their counterparts
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