Transcript Plasma needle: the healing touch of the plasma

Biomedical applications of plasmas
E. Stoffels, Eindhoven University of Technology
The Netherlands
 Plasmas in material processing:
thermal vs. non-thermal
 Plasmas in medicine:
service: plasma decontamination
“spare parts”: plasma coating of implants
healing: plasma surgery
 New:
minimum-invasive surgery
plasma-tissue interactions on cellular level
What is plasma?
- Almost everything!
- Ionised gas:
- thermally (fire)
- electrically (gas discharge)
- radiatively (ionosphere, interstellar space)
- Artificial plasmas: generated by electric
discharges:
+
-
A+, B-, e, radicals
Plasmas in material processing
 Plasmas can perform various surface treatment:
etching - semiconductor elements
deposition - a-Si:H solar cells, hard protective
coatings, optically active layers, etc.
cutting, welding, spraying
 Refined treatment is possible with non-thermal
plasmas (no heat damage to the surface)
 Also biological materials can be treated!
Thermal
(fire)
Non-thermal
(vacuum reactor)
How to obtain non-thermal plasmas?
 Electric gas discharges: electrons/ions are heated
 In typical high-frequency plasmas only electrons
are heated
Thermal: gas heating occurs
Non-thermal: electrons hot, gas cold
 No background gas heating when:
electrons/ions in minority
not enough collisions with neutrals
Non-equilibrium cases
 low pressure:
low collision frequency of electrons with gas
electrons retain high energy, gas remains cold
(typical situation in vacuum reactors)
 short duration of the plasma pulse:
not enough time for gas heating
 small size (micro-plasma):
too much energy leaks to outside
Small size plasma
 What is the maximum length scale (L) of a “cold”
plasma?
 Electron-induced heating is balanced by thermal
conduction losses:
me
4 3
DT
 ea ne k BTe L  
4L2
ma
3
L
 We allow DT to be at most 10 degrees.
ma 3DT
L
me  ea ne k BTe
 For helium under typical conditions L  0.2 mm
(in agreement with observations).
“Plasma needle”
 RF applied to a sharp metal pin.
 breakdown obtained at ca. 200 V p-p.
 plasma operates in helium (most readily), argon,
nitrogen, hydrogen, AIR (!)
power (W)
Characteristics of the plasma needle
6
5
4
3
2
1
0
“point”
plasma
200
volume
expansion
300
voltage (V)
400
Really cool!
500
small size
450
400
350
expansion
300
250
0
2
4
6
8
10
power (W)
Temperature
measurements using
Optical Emission
Spectroscopy (N2
bands)
Temperature induced by the plasma
200
Temperature (°C)
temperature (K)
550
using thermocouples
150
Dry surface
100
Wet surface
50
0
0
1
2
3
4
5
6
7
Distance to the thermocouple
(mm)
Other geometries
 HF plasma pencil (Janca et al. Brno, Czech
Republic)
discharge created in a hollow needle/hollow
cylinder in argon
various surface treatments
Ar
 Micro-hollow cathode discharge (Schoenbach,
Norfolk, Virginia; Graves, California, Berkeley)
 Dielectric barrier discharge DBD (e.g.
Kogelschatz, ABB Corp. Research; ChangJun Liu, Tianjin, China)
UV radiation
gas conversion (e.g. methane)
Dielectric/high
resistivity material
 Resistive barrier discharge (Laroussi, Old
Dominion Univ. Virginia)
bacterial decontamination
 Atmospheric pressure plasma jet APPJ
(Selwyn, Los Alamos)
radio-frequency (13.56 MHz)
material processing
 One atmosphere uniform glow discharge
plasma OAUGDP (Reece Roth et al. Univ.
of Tennessee)
kHz frequency range
operates in air
needs cooling
used for sterilisation
Plasma sterilisation (medical tools)
 Low temperature needed
because of usage of plastic
tools.
 Plasma is non-toxic and
efficient (seconds to minutes)
 Both atmospheric (Reece
Roth, Laroussi) and reduced
pressure discharges (Moisan)
are used.
 Large-area discharges, AC,
radio-frequency and
microwave.
Air deconamination
Removal of
bacteria/bacterial spores
from ambient air (e.g.
anthrax)
Protection from
biological attacks
Example: a gas phase
corona reactor design by
Birmingham et al.
(MesoSystems
Technology Inc.,
Richland)
Water purification
Under water corona discharges (e.g. Sunka, Prague, Chech
Republic; Van Veldhuizen, Eindhoven, The Netherlands)
corona streamers propagate in contaminated liquid
not only biological threats can be removed; dangerous
chemicals are decomposed.
pulsed corona for water
cleaning
(V. Veldhuizen, Eindhoven)
Destroying enemies
prokaryotic organisms, not very complicated
most of them well-protected by cell wall
Destroying enemies
Gram positive
vs.
single plasma membrane
Spore forming (typically
gram positive)
gram negative
double membrane
more difficult to
destroy
bacillus,
clostridium
endospore
escherichia coli
Mechanisms?
log(number of survivors)
No sophisticated damage needed: necrosis
Atomic oxygen vs UV radiation.
 Typically three phases observed.
 Moisan and coworkers (Univ. of Montreal) proposed
bacterial/spore de-activation mechanisms
Direct UV
Erosion by photodesorption
and O radical etching
absorption
and DNA
destruction
 1 min
10 min
exposure time
UV
damage
to eroded
spores
1 min
Chemical effects
Various chemistries studied
argon - not very efficient
N2/O2 (air) - efficient, O radicals present
O radicals can also penetrate through the
membrane and damage the cell interior
H2O2, CO2 - particularly efficient, see Hury et al.
H2 - efficient, reducing agent.
Maybe reducing fatty acids to aldehydes and
dissolving the membrane?
Decontamination of other surfaces?
 In vivo dental cavities using plasma needle
 No temperature increase within the tooth
 Mineral matrix intact, tissue-saving method
 Under investigation: decontamination efficiency,
penetration depth, surface activation to enhance
adhesion of filling
 Pain?
 Others: root
treatment , gingiva
reattachment
Plasma coating
 Coating of artificial implants to increase biocompatibility
 Low-pressure discharges can be used
 Examples:
bone prostheses: diamond-like inert coating
on titanium substrate
spraying of hydroxyapatite
micro-patterning of surface to increase cell
adhesion
Plasma treatment in vivo
 Not always non-thermal plasmas are used,
sometimes burning is desired
 Techniques already implemented in medicine:
electro-surgery and argon plasma coagulation
 Spark erosion of atherosclerotic plaque
 New trends: minimum invasive, tissue saving
methods
 Investigation of fine surgery using plasma
needle
Electric methods in medicine
 Electrosurgery: well established technique
 High-frequency (350 kHz) cutting and
coagulation:
ERBE
monopolar & bipolar cutting devices
well-reproducible cutting
little adhesion
hemostasis obtained
by controlled coagulation
From electricity
to plasma
 Argon plasma coagulation
First beneficial plasmatissue interaction
* non contact
* self-limiting desiccation
and coagulation (plasma
stops when the area is
dry)
* no carbonization
* can be applied internally
* good post-operative
recovery
An APC device in
action
Example: treatment of
hyperplasia of the nasal
concha
After APC treatment 10 days later
Spark erosion
Developed by dr. C.J. Slager (Erasmus Univ. Rotterdam)
Plaque is vaporized by electric pulses, 250 kHz, 1200 V,
100 W. Restenosis in rabbits is limited. So far not applied
to humans.
A diseased artery
Plasma-produced crater
(cross-section):
(lipid ablation):
A few words about safety
Nerve stimulation
by electric currents
Effects of heat:
hyperthermia causes cell
death (> 43o C)
Plasma needle on tissues
(a) Low-power regime: no thermal damage,
possibility of refined action.
(b) High-power regime: denaturation of proteins,
carbonisation after long exposure.
a
b
Possibility of fine surgery must be investigated on
cellular level!
Next step: eukaryotic cells
 Much more complicated structures
 More interactions/effects possible
 For the sake of plasma surgery, understanding
plasma-induced effects on cellular level is
necessary
Plasma-cell interactions
 Cell removal:
 “coarse destruction” - necrosis (damage to the
membrane) caused e.g. by chemicals.
 “fine works” - programmed cell death (apoptosis)
Apoptosis
 Moderate damage to the cell, without affecting
the membrane integrity. The cell shrinks, DNA
in the nucleus condenses.
 Cell disappears without infection, as desired in
fine surgery.
CHO-K1 cells in culture
 CHO-K1 cells (Chinese hamster ovary) ,
fibroblasts
 Plasma treatment followed by viability assays
 Fluorescent staining and observation under
confocal fluorescence microscope
Cell Tracker Green (CTG): stains living
cells green
Propidium Iodide (PI): stains dead cells red,
allows to resolve DNA/RNA distribution in
the cell
Healthy cells:
To study long term
effects cells are cultured
after plasma treatment

Cells are fixed and
stained with PI to detect
apoptosis


PI
Intact nuclei stained by
General features of plasma treatment
 High precision: influenced cells are strictly
localised)
detachment
50 mm
alive
dead
Plasma treated cells
Example of apoptotic cells
After plasma treatment
Plasma treated cells: dead cells
Even dead cells
retain the integrity!
DNA damage and
condensation (other
than in apoptosis)
Cell detachment

Instantaneous effect of plasma treatment
 Cells
round up and detach from other cells and can
be removed
 Better
(faster)
than apoptosis?
Long term effects
Detached cells reattach after ca 1 hour,
their viability is demonstrated
control
15 min
1 hour
4 hours
What causes cell detachment?
 cell adhesion molecules (CAMs) - transmembrane glycoproteins
NH2
 Ca2+ dependent adhesion:
Ca
Ca
cadherins
Ca
 Detract Ca and cause
cadherin to disintegrate?
membrane
(only charging)
COOH
 Destroy the cadherin
cytoskeleton
Summary
 Plasma technology finds many medical
applications.
 Many atmospheric sources have been developed.
 Plasma de-contamination is widely studied.
 Plasma needle can be applied to organic materials
without thermal damage.
Questions
 Can plasmas perform fine surgery?
 Is cell detachment valid in tissue environment
in vivo tests