Eradication of Wound Biofilms by Electrical Stimulation - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 428

concluded that pH changes caused by HVPC are not the predominant reason for the
observed bacterial inhibition. What also negates pH change as the proposed mech-
anism is that when HVPC was applied to human tissue for 30 min it was not shown
to cause electrochemical changes at either electrode (Newton and Karselis 1983 ).
The reason for this is that HVPC produces a minimal average current in the tissue,
and thus there are negligible chemical reactions in tissue near the electrode (unlike
LIDC) (Campolo 1999 ). More in-depth studies are required to determine the exact
biofilm inhibitory mechanism of action of HVPC, and with minimal in vivo studies,
the in vitro results should be taken with caution. Other drawbacks of the current
literature examining HVPC and biofilm inhibition are that none of the studies
examined the effect of HVPC on mature biofilms and biofilm-specific experiments
were not conducted (e.g., crystal violet assays, antimicrobial tolerance, electron
microscopy). The HVPC studies used biofilms that were grown on solid, rather than
in liquid, media, or directly on the electrodes. One final gap in the current literature
is that no study to date has examined the potential of HVPC therapy to enhance
antibiotic efficacy against bacterial biofilms. This effect has clearly been
established with DC (the bioelectric effect), and hopefully future studies will
shed more light on this.
13 Alternating Current Background
AC refers to the uninterrupted bidirectional flow of charged particles which oscil-
late from a positive charge to a negative charge (Fig. 1C ), based on the frequency of
the AC. Much like the “War of the Currents” in the early 1900s, DC was the first
established form of electricity used in ESTHR, but in this war AC eventually
supplanted the use of DC as the standard form of electricity used in the USA. At
present, however, there still have not been any clinical trials examining the effec-
tiveness of AC in promoting wound healing. Some authors have incorrectly
reported that the electricity supplied by transcutaneous electrical nerve stimulation
(TENS) devices is AC (Kloth 2005 ). Yet, TENS devices produce pulsed
monophasic pulsed current (DC) or biphasic pulsed current (AC), not continuous
AC. The studies examining this form of pulsed AC are limited and report minimal
(Maadi et al. 2010 ) to no effect (Merriman et al. 2004 ) on bacterial killing. This lack
of antibiofilm activity does not seem to only be associated with low-intensity,
low-frequency (LILF) pulsed AC, since low-intensity pulsed DC is also reported
to be similarly ineffective (Merriman et al. 2004 ). In addition, there are few in vitro
studies suggesting that LILF constant AC can inhibit biofilm formation (Gabi
et al. 2011 ; Kang et al. 2011 ) so this form of AC could show promise in the future.