b2815 Tissue Engineering and Nanotheranostics “9.61x6.69”18 Tissue Engineering and Nanotheranosticsapplied strains through axonal elongation. Other researchers have
found that neurite outgrowth is increased by cyclic equibiaxial
stretching.^70
Human neuroblastoma (SH-SY5Y) cells were cultured on BioFlex
culture plates and mechanically stimulated to 10% at 0.25 Hz.^70 This
culture was performed either with or without the addition of retinoic
acid (RA), a well-known mediator of neurite outgrowth.^70 It was
found that by simply applying this biaxial strain, neurite length and
numbers per cell was significantly increased.^70 Stretch also tended to
increase the expression of neurofilament light chain (NFL), which is
an important part of the neural cytoskeleton, but this change was not
statistically significant.^70 This cyclic stretching is more relevant to skel-
etal muscle tissue than the axonal stretch growth, however, both stud-
ies demonstrate that carefully applied forces are able to improve
outcomes for neuron cultures.
4.2.4. Electrical stimulation
It is well established that muscles that are not used will atrophy, and
muscles that becomes denervated for any number of reasons will often
undergo the same. Building on this knowledge, tissue engineers have
attempted to use electrical stimulation as a biomimicking signal to
enhance the efficacy of muscle constructs. A study done with C2C12
cells found that application of a sine-wave stimulus led to more pro-
nounced striation, larger myofibers, and more MYH expression.^57
The electrical current was oscillating at 1 Hz and had a current of 22
mA. Another study found that periodic stimulation by application of
a square voltage waveform has the potential to increase the total pro-
tein content and force generated by a construct.^71 It also found that
there is a potential for overstimulation in terms of field strength.^71
Best results were obtained when cells were cultured at a field strength
of 0.3 V/mm.^71 This work also found a good response at the 1 Hz
frequency, in agreement with the first paper. Electrical stimulation,
therefore, should have a role in promoting better muscle tissue devel-
opment. However, it must be done in a manner that prevents
overstimulation.
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