TPPM Seminar - Plasma Bio-Medical Applications · Index I. Bio-Medical Applications. I Medical Sterilization. I Wound Healing (Blood Coagulation). I Tissue Regeneration. I Skin Diseases

TPPM Seminar - Plasma Bio-Medical Applications

Tomás Cruz1

1Mestrado Integrado em Engenharia F́ısica TecnológicaInstituto Superior Técnico

January 10, 2012

Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Index

I. Bio-Medical Applications.I Medical Sterilization.I Wound Healing (Blood Coagulation).I Tissue Regeneration.I Skin Diseases Treatment.

II. Plasma Sources and Technologies.I Dielectric Barrier Discharge.I Plasma Jet.

III. Interaction Plasma - Biologic Material.I Skin Cancer Treatment.I Blood Coagulation.

IV. Final Remarks.

V. Other References.


Part I - Bio-Medical Applications

Medical Sterilization


Medical Sterilization - Experiment in vitro1

I Mix of skin flora bacteria;

I Initial bacteria concentration 109 cfu/mL;

I Each sample is subjected to a specific time of direct plasmatreatment;

I Dielectric Barrier Discharge is used (no further information aboutconditions was given, but probably d ∼ mm, V ∼ 30kV, f ∼ 12kHz).

Figure: Bacteria sterilization results.

1G. Fridman et al., Plasma Process. Polym., 2007, 4, 370-375Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Medical Sterilization - Experiment in vivo

Several security issues have to be assured:

I Controlled exposure on UV;

I Control on the quantity of very reactive species that are formed in theplasma;

I Control on the electrical currents through the tissue;

I Control on the plasma temperature;

I Small electric and magnetic fields to the tissue.

In an experiment by the same research group in skin tissue2 they foundthat no visible or microscopical damage is observed in exposures up to 5minutes, while sterilization is achieved in just some seconds.

2G. Fridman et al., Plasma Chemistry and Plasma Processing, 2006 , 26, 425Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Medical Sterilization - Prokaryote vs. Eukaryote

If they are exposed to the same doses, how can the tissue cells

survive and the bacteria be completely annihilated?

Figure: Prokaryote vs. Eukaryote.

The difference in cellular organization protects eukaryotes from externaltension, the bigger size mean that poisoning rate is smaller in the sameexposure time. The regeneration capacity of eukaryotes is also verysuperior.



Wound Healing (Blood Coagulation)


Blood Coagulation - Argon Plasma Coagulator

Figure: 3Argon Plasma Coagulator.

Plasma just provides the local heat source to cauterize and dessicate theblood. Basically ”cooks” the blood. (Comments to the image).

3Matthias Zenker, GMS Krankenhhyg Interdiszip, 2008, 3(1): Doc15.Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Blood Coagulation - Experiment in vitro4

I Blood plasma samples;

I Dielectric barrier discharge (V = 35kV, f = 1kHz, d = 2mm);

I 30 seconds exposure.

Figure: Visual results (white arrow - activated platelet; black arrow -non-activated platelet).

a) is the control sample and b) is the treated sample. A conclusion to thiswork is that plasma can catalyse biological processes that occur duringblood coagulation (we will be back to this).

4S. U. Kalghatgi et al.,IEEE Transactions on Plasma Science,2007 Vol. 35, 5Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Blood Coagulation

Another experiment by Friedman et al.5 showed that a blood drop treatedduring 15 seconds with a dielectric barrier discharge (no information aboutthe parameters) coagulates in about 1 minute, while a control dropcoagulates in about 15 minutes.

There are other experiences in vivo in animals with some good results(even to beings with haemophilia). Tissue damaging have not been wellevaluated.

5G. Fridman et al., Plasma Chemistry and Plasma Processing, 2006 , 26, 425Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications


Tissue Regeneration


Tissue Regeneration

The base is to use exogenic NO generated in air plasma to promote tissueregeneration.NO major influence in pathological processes:

I Bactericidal effect;

I Promotes secretion of biologically active factors which regulate woundhealing and inflammatory processes;

I Anti-coagulant, normalization of micro circulation improves nutrientexchange;

The NO molecules are formed in the plasma and forwarded to the tissueby the gas flow (with a plasma jet, like in APC).

This technology is already used in in the most serious patients in a lot ofmedicine fields like Pulmonology, Traumathology and Orthopedics,Dentistry, etc.



Skin Diseases Treatment


Skin Diseases Treatment - Apoptosis vs. Necrosis

Apoptosis is the programmed cell death, the biochemical process ofcontrolled self destruction of a cell.Necrosis is the cellular death provoked by an exterior factor (the cellbasically burst).

When the cell detects some problems, the apoptosis is provoked. In cancercells, the process of detection is somehow deactivated, that allow them tosurvive and multiply.

Today treatments are chemical treatments that provoke a local apoptosisof all cells (low selectivity is not very good). This application try toprovoke the apoptosis in cancer cells applying low doses of cold plasma


Skin Diseases Treatment - Experiment in vitro6

I Samples of Melanoma cancer cells;

I Treatment using Dielectric Barrier Discharge (VDC = 10− 30kV,d = 3mm).

Figure: Results of the treatment of melanoma skin cancer.

Plasma treatment provoke both necrosis and apoptosis, in small doses theapoptosis is the predominant effect.

6G. Fridman et al., Plasma Chemistry and Plasma Processing, 2007, 27,163-176


Part II - Plasma Sources and Technologies

Dielectric Barrier Discharge


Dielectric Barrier Discharge - Schematic7

Figure: Schematic of the DBD used by Fridman et al. in some of the experimentspreviously shown.

General features:

I Atmospheric pressure;

I 2 electrodes;

I Dielectric Barrier;

I Discharge proceeds by charged channels (microdischarges).

7G. Fridman et al., Plasma Chem. and Plasma Proc., 2006, 26, 425-442Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Dielectric Barrier Discharge - Gas Breakdown Mechanism

(part 1)

Consider a gap d , and an electric field E = Vd. Electrons are emitted in

the cathode and accelerated by E .The increase in the electron flux can be write in the form:

dΓe(z) = α(z)Γedz ⇔ Γe = Γe0e∫ z0α(z ′)dz ′

Where we can define λi (z) =1

α(z) as a mean free path of ionization.

The ion flux coming back to the cathode will be:

Γi (0)− Γi (z) = Γe(0)(

e∫ z0α(z ′)dz ′ − 1

)



(part 2)

Condition to breakdown: Γe(0) = γseΓi(0) and Γi (d) = 0. Where γse isthe secondary emission coefficient.So, one can write:

Γi (0) = γseΓi(0)(

e∫ z0α(z ′)dz ′ − 1

)

⇔1 + γseγse

= e∫ z0α(z ′)dz ′

If we make α independent from z (Townsend coefficient):

αd = ln

(

1 + γseγse

)

α is in reality a complicated function of pressure and electric field, but weexpect it to be of the form:

α =Cte

λee−

εiEλe

Where λe is the mean free path and εi is the ionization energy.Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications


(part 3)

Knowing that λe ∝ 1/p, p is the pressure.

α

p= Ae−

BpE

Where A and B are constants to be determined experimentally.

Apde−Bpd

V = ln

(

1 + γseγse

)

⇔

⇔ −Bpd

V= ln

(

ln

(

1 + γseγse

))

− ln (Apd)⇔

⇔ V =Bpd

ln (Apd)− ln(

ln(

1+γseγse

))



(end)

Vbk =Bpd

ln (Apd)− ln(

ln(

1+γseγse

))

This is the equation of the characteristic curves used to construct/studythis devices (Paschen curves) :

Figure: A set of Paschen curves for various gases8.

8S. Wright, PhD thesis, 2009Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Dielectric Barrier Discharge - Avalanche

The gas breakdown gives rise to an avalanche.

Figure: Avalanche formation9.

Accounting the electron drift and diffusion, the electron density:

ne =1

(4πDet)32

e−

(x−µeEt)2+r2

4De t+αµeEt

Convolution of the movement in x and r with statistical diffusion +Charge amplification factor.

9A. Fridman et al., J. Phys. D: Appl. Phys., 2005, 38, 1-24Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Dielectric Barrier Discharge - Avalanche to Streamer

Figure: Avalanche to Streamer10.

I Electric field of the avalanche ∼ E , EA =eeαd

4πε0r2≈ E (Meek criteria);

I Avalanche reaches the anode and electrons are lost to the anodewhile ions remain in the discharge;

I Streamer initiates in the anode and goes to the cathode, propagationis limited by ions neutralization.

10A. Chirokov et al., Pure and Appl. Chem., 2007, 77, 487-495Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Dielectric Barrier Discharge - Dielectric Barrier

Why the dielectric barrier?

I Dielectric barrier accumulate charges, no big currents to thesubstrate, heating is small;

I Charge scattering, the charge is scattered in the dielectric, so therewill be an uniform distribution of the microdischarges (uniformplasma);

I Charge accumulation prevents new avalanches in the same spot (untilpolarization is reversed);

I If polarization is reversed charge accumulation makes it easieravalanches and streamers in the same spot.

The what is observed is a bright filament connecting the substrate and theactive electrode.


Dielectric Barrier Discharge - Uniformity of

Microdischarges11 12

Figure: V ∼ 35kV, d ∼ 1mm.

Figure: V ∼ 10kV, d ∼ 1mm.

Microdischarge properties depend only in the gas, pressure and electrodeconfiguration, an increase in power implies an increase in the number ofmicrodischarges.

11G. Fridman et al., Plasma Chem. and Plasma Proc., 2006 , 26, 42512U. Kogelschatz et al., Journal de Physique III, 1997 , 26, 425


Dielectric Barrier Discharge - Global Features (Part 1)

If we apply a sinusoidal V :

Figure: Voltage vs Charge.

I Cg is charged;

I Vbk is achieved, then CDis charged;

I Reverse process occurswhen voltagepolarization is reversed;

P = 4fC 2D

CD + CgUmin (Umax − Umin)

Dissipated power, important parameter for safety.


Dielectric Barrier Discharge - Global Features (Part 2)

Other important criteria for safety, coupled power.

Figure: Equivalent circuit.

I Approximate thedischarge to a RC circuit(Rd , Cd );

I Skin tissue approximateto a RC circuit (RH ,CH);

I Current |I | = VD|Zd |+|ZH | ;

I Voltage |V | = |ZH |VD|Zd |+|ZH | ;

As RH ∼ 1MΩ and CH ∼ 50pF, |I | will always be small. To have |V |small, |Zd | � |ZH |. Normal values Cd ∼ 50pF and Rd ∼ 5− 10MΩ, sothe criteria is satisfied (electrically is safe to touch).


Part II - Plasma Sources and Technologies

Plasma Jet


Plasma Jet - Schematic

Figure: Sketch of a plasma jet13.

General features:

I Plasma generation zone;

I Gas flow;

I Nozzle;

I Usually 2 gas inputs.13T. Shimizu, 7th Int. Conf. on Flow Dyn., 2010


Plasma Jet - Global Features

The discharge is usually capacitive or inductive, and occurs away from thetreatment zone.The gas flow transports the residuals from the discharge to the exterior,and the nozzle accelerate them.Advantages:

I Tool-like;

I Small and versatile;

I Allow 3D movement;

I Indirect application;

The fact that the treatment zone is away from the discharge avoids themost energetic UV, the reactive specimens of very short life time and thecurrent flow. Depending on the application this is an advantage. Thistechnology is already on market, like kinpenr.


Part III - Interaction Plasma - Biologic Material

Skin Cancer Treatment


Skin Cancer Treatment

In low doses, the plasma treatment provoke preferentially apoptosis in themalignant cell instead of necrosis.Obviously, the active factor in the plasma that will make this possible issome active specimen created in the plasma that catalyse the apoptosisprocess. (Physical interactions would provoke necrosis).

Figure: Emission spectrum of aplasma with 200 SCCM Ar and5 SCCM O2 taken at 4mm(plasma jet).

Problems:

I A lot of specimens aregenerated in a plasma,who is the one (or ones)?

I The plasma affects thecell directly or indirectlyby the growth media?

I Is it harmless to thehealthy cells?


Skin Cancer Treatment - Experiment in vitro pH14

I Dielectric Barrier Discharge (VDC ' 10− 30kV, d ∼ 3mm,P = 0.8± 0.2W/cm2).

Figure: Study of the effect of the plasma in the pH and the effect on pH onmalignant cells.

Conclusion, the plasma treatment acidify the media, but the difference inpH is not the cause of death of the malignant cells. This power densitiesfor short treatment times are below the threshold of damaging healthytissue.

14G. Fridman et al., Plasma Chem. Plasma Proc., 2007, 27, 163-176Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Skin Cancer Treatment - Experiment in vitro O• and OH•15

I Plasma Jet, Argon + Oxygen plasma.

In this work there have been studied the effects of different concentrationsof oxygen in the plasma to the death of malignant cells (big concentrationof oxygen would kill the plasma - attachment, small concentration havebetter efficiency than no concentration). By comparing spectra they alsofound that O• and OH• are the critical agents that can arrive at thebottom of solution and provoke the cell death.

15X. Zhang et al., App. Phys. Letters, 2008, 93Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Part III - Interaction Plasma - Biologic Material

Blood Coagulation


Blood Coagulation

Same type of problems previously seen.In order to specify the mechanisms responsible for the blood coagulation alot of tests are made to pH, electric fields, temperature, proteinconcentration, ions concentration.The process of blood coagulation is a complex and has been studiedextensively.

Figure: Simplified coagulation cascade.


Blood Coagulation - Ca2+ and pH16

It was proposed that plasma increases the Ca2+ concentration through aredox reaction and than catalyse the coagulation:

Ca2+R2− + H+ ←→ H+R2− + Ca2+

Figure: Calcium concentration indifferent types of blood treated withDBD(V ∼ 35kV, P ∼ 1.5W/cm2).

Figure: pH in different solutions,same Dielectric Barrier Discharge.

Since the treatment time of 15 seconds is enough, none of this effects canbe the source of coagulation by plasma.

16S. U. Kalghatgi et al.,IEEE Trans. on Plasma Science,2007 Vol. 35, 5Tomás Cruz TPPM Seminar - Plasma Bio-Medical Applications

Part IV - Final Remarks


Final Remarks

I This is a field very recent and in expansion, some great andmotivating results have been obtained;

I The technologies used are well known, optimization experiments arestill in progress;

I It is very important to understand the mechanism of interactionplasma vs. biologic material, and it is very hard to understand them.Plasma is a very complex media and biological processes are verycomplexes too. A lot of work to do until this technologies take theplace of the ones that are used nowadays.


Part V - Other References


Other References

I G. Fridman et al., Plasma Process. Polym., 2008, 5, 503-533.

I kinpenr - New chances in surface technology.

I U. Kogelschatz, IEEE Trans. on Plasma Science, 2003, 30, 1400-1408.

I S. Coulombe et al., Pure Appl. Chem., 2006, 78, 1147-1156.

I M. G. Kong et al., New Journal of Physics, 2009, 11.

I G. Fridman et al., 32nd IEEE International Conference on Plasma Science, 2005.

I J. Heinlin et al., Journal of the German Society of Dermathology, 2010, 8.


Documents

TPPM Seminar - Plasma Bio-Medical Applications · Index I. Bio-Medical Applications. I Medical Sterilization. I Wound Healing (Blood Coagulation). I Tissue Regeneration. I Skin Diseases