Chemistry Reference
In-Depth Information
D
2
hasbeeninvestigatedwithDBDs
at atmospheric pressure discharges, too [116]. The first (slow) phase is explained as
a period of damaging alterations on outer cell structures due to the action of active
species. The rapid second phase begins when the reactive species can enter the interior
of MO trough its damaged outer structure, causing cell death.
Direct treatment of a water reservoir with the plasma jet described earlier has led
to significant acidification [128]. Water is always present in biological systems and
duetoreactivespecies(e.g.,OH,NO)secondaryproducts(e.g.,HNO
3
)canbeformed.
Similar effects have been found by treatment of water with a surface barrier discharge
[111]. The enhancement of inactivation efficiency by moistening the atmosphere has
already been mentioned in the literature [102] and has been observed for gliding arc
discharges at atmospheric pressure, too [129]. Thus, secondary chemical processes
should always be considered in realization and interpretation of experimental studies
as well as in the development of new industrial applications [128].
MO can form biofilms, complex aggregation of cells marked by the excretion
of a protective, and adhesive matrix (e.g., dental plaque). Cells in biofilms are more
resistant to chemicals than free-floating planktonic cells. Biofilms could represent
serious health hazards and cause damage, such as corrosion, to the surfaces of the
materials they attach to. Attempts to evaluate the effects of nonthermal plasmas on
biofilms illustrated the inherent difficulty to destroy them [130,131]. In conclusion,
any organic material that covers or alliances the MO will increase the dose to achieve
sterilization since slow erosion processes will be involved. Therefore, not only the
initial number of MO has to be considered when comparing different conditions and
plasmas. Furthermore, the sample load and density of MO per cm
2
as well as the
properties and cleanliness of the suspension have to be taken into account.
ICwithtwoinactivationphasesbutwith
D
1
>
8.2.2.4 Examples of Plasma Processes for Sterilization
8.2.2.4.1 Commercial Plasma-Assisted Sterilizers
Two sterilization systems using medium pressure plasmas were already commercial-
ized in the 1980s: the Sterrad
system (advanced sterilization products, a Johnson &
Johnson comp., Irvine, California) and the Plazlyte
TM
sterilization system (AbTox,
Inc., Mundelein, Illinois). In both processes, the plasma appears to have no biocidal
action, since the dominant role is played by a purely chemical phase of diffusion
of biocidal vapors (H
2
O
2
in Sterrad; peracetic acid in Plazlyte) [102,104,132]. The
plasma (RF or microwave sustained, respectively) is generated in the periphery of the
sterile-packedproductsandmainlyservesasadetoxifyingagentbyremovingnoxious
residues and limiting the oxidation effects of the gases. These processes are typical
plasma-assisted gas sterilization processes. Sterrad is widely used, e.g., in reprocess-
ing of medical instruments [133]. Plazlyte was stopped in 1998 because of serious
eye injuries following eye surgery using instruments sterilized with Plazlyte [134].
8.2.2.4.2 Plasma-Based Processes
The first commercialized plasma-based process at atmospheric pressure is the Tip-
Charger
TM
system (CerionX, Inc., Pennsauken, New Jersey). Based on a DBD, the
system cleans and sterilizes liquid transfer devices such as pipette tips, cannulae, and
pin tools. TipCharger cleaning stations can substitute traditional solvent-based wash
