CELLS OF THE NERVOUS SYSTEM AND ELECTRICAL STIMULATION - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 613

fore, electrical stimulation has shown potential in achieving axonal growth across
the glial scar, which is one of the greatest challenges in spinal cord repair.
More recent use of electrical stimulation to repair spinal cord injury (SCI)
has also been researched in guinea pigs and dogs. The research of Borgens et al.
in guinea pigs, fi rst demonstrated that axons could grow into the glial scar and in
some cases around the glial scar (Borgens, Blight, and Murphy 1986; Borgens,
Blight, Murphy et al. 1986). However, axons were not shown to grow through the
glial scar. Despite this, functional recovery occurred in guinea pigs with SCI
treated with a 200

V/mm voltage gradient was demonstrated (Borgens et al.
1987). Behavioral recovery was studied using the cutaneous trunci muscle refl ex,
a useful refl ex when studying SCI recovery (Blight et al. 1990). This led to trials in
dogs (Borgens et al. 1999) using implantable electrical stimulators. The trials in
dogs used an oscillating electrical fi eld switching polarity every 15 minutes as
opposed to the previous studies in guinea pigs where the fi eld did not oscillate.
The use of an oscillating EF on dogs with SCI showed improvement in every cat-
egory of functional evaluation at six weeks and six months, with no reverse trend.
The stimulators used in dogs were designed for future use in human clinical trials
in humans. Recently, human phase 1 clinical trials of SCI with oscillating electric
fi eld stimulation were shown to be safe and neurologically benefi cial to patients.
No severe adverse effects were observed after one year of treatment in ten
patients and there was an improvement in somatosensory tests (Shapiro et al.
2005). These trials are evidence that electrical stimulation may achieve signifi cant
therapeutic use. However, these trials have failed to show benefi ts if implemented
after the initial recovery period post SCI. Yet, other studies that use functional
electrical stimulation in combination with locomotive training to treat chronic
SCI have shown to help rehabilitate walking (Barbeau et al. 2002). In either case,
electrical stimulation was shown to have a promising future in the regeneration of
the spinal cord, and possibly in the entire nervous system.

μ

18.5.6 Extracellular Electrical Stimulation In Vitro
When undertaking extracellular stimulation, one encounters the complexity of
merging into one, three fi elds of study: electrical engineering, electrochemistry,
and cellular biology. There are many possible choices to make when designing a
system to stimulate cells. The electrical stimulation apparatuses and the charac-
teristics of the stimuli that may be applied gives researchers a myriad of condi-
tions or stimuli to choose from. This can be frustrating when determining the
appropriate variable combination that will produce a desired result. The proba-
bility of discerning those values can require many repetitions and thorough statis-
tical analysis. Since experiments are done on live cells/tissue, one must consider
possible electrochemical reactions that occur when placing electrodes in cell
culture media/tissue. Electrode and stimulation device material must be chosen
wisely as not to affect the health of the cells or render the electrodes useless. Most
cells are sensitive to minute changes in the media and thus any change in the
media will usually negatively affect the cells. Finally, the assays used to determine