Plasma Sterilization

1. Plasma Sterilization Applications of plasmas for sterilization in medical, food processing, ventilating, and air conditioning industries

2. Outline • What is sterilization? • Current sterilization means • Solution: Plasma Sterilization • How it works • Disadvantages • Methods of Plasma Sterilization

3. What is Sterilization? • Sterilization is any process or procedure designed to entirely eliminate microorganisms from a material or medium

4. Current Sterilization Means: Heat • Types: dry and moist heat • Medium is exposed to moist heat (steam) generated by an autoclave, or dry heat in a heater • Pressures: 103 kPa • Temperatures: 120-140 oC • Steam transfers sufficient heat to microorganisms to inflict demise • Exposure time ~ 30 minutes • Can cause permanent damage, and alter material properties significantly

5. Current Sterilization Means: Chemical • EtO, H2O2, O3, bleach most commonly used • Applications when heat is damaging to the medium • Damages fiber optics, electronics, some plastics • Introduces toxicity

6. Current Sterilization Means: Irradiation • Types: Gamma radiation, Bremsstrahlung, X Rays • Medium is subjected to radiation  radiochemical and radionucleic reactions  cellular death • Disadvantages: • Embrittlement • Chain Scission • Cross Linking • Costly

7. Current Sterilization Means: Plasmas? • Yes. • Plasmas are currently employed in many industries to accomplish both highly effective, and delicate sterilization. • Not future technology! Plasmas are used today! • But, how do they work?

8. Plasma Sterilization in Summary • A plasma is a quasi-neutral collection of electrons, positive ions, and neutrals capable of collective behavior • Positive ions = free radicals • Plasma sterilization operates synergistically via three mechanisms: • Free radicals interactions • UV/VUV radiative effects • Volatilization • Dead microorganisms = sterilization

9. Plasma Sterilization Mechanics: IR Volatilization • IR is able to vaporize microbiological matter, causing physical destruction of spores. • Charged particles react with cellular chemical bonds of microbiological layer to form gaseous compounds  volatile compounds.

10. Plasma Sterilization Mechanics: Ionizing Radiation (IR) • IR (UV/VUV radiation) can damage DNA/RNA, chemical cellular bonds, and induces free radicals to perpetuate the process • Damaged DNA/RNA  microbial death by 4 mechanisms: • Apoptosis – nucleases become hardwired to shrink and cause cell to commit suicide. Caused by DNA/RNA damage • Autophagy – Formation of double membrane vacuoles in cytoplasm  separation of mitochondria and ribosomes  protein production stopped  cell death • Necrosis – Murder by cell swelling • Mitotic Catastrophe – radiation causes mis-segregation of chromosomes, leading to Apoptosis.

11. Plasma Sterilization Mechanics: IR (Cellular View) • IR impacts the cell, three outcomes can result.

12. Plasma Sterilization Mechanics: IR (Chemical View) • Free radicals O* and OH* play crucial role in microorganism destruction by way of chemical reactions • O*, OH* highly reactive ~ 10-9 s

13. Hydrogen Abstraction & Double Bond Cleavage

14. Plasma Sterilization Mechanics: IR (Nucleic Acid View), UV Radiation • UV/VUV radiation causes • formation of thymine dimers in DNA, inhibiting bacterial replication. • Base damage • Strand breaks

15. Plasma Sterilization Mechanics: IR (Nucleic Acid View), Charged Particles • Charged species in the plasma can damage DNA if formed in the vicinity of chromatin. • RSH act as radical scavengers

16. Quantifying Sterilization Efficacy i.e. Time required for the microbial population to be reduced to one decimal

17. Disadvantages of Plasma Sterilization • Weak penetrating power of the plasma species. Complications arise in: • Presence of organic residue • Packaging material • Complex geometries • Bulk sterilization of many devices • Solutions: Introduce preferentially targetting UV/VUV radiation of proper wavelength

18. Methods of Plasma Sterilization • Dielectric Discharge Barrier (DBD) • Inductively Coupled Plasmas (ICP) • Atmospheric Pressure Plasma Jet (AAPJ) • Microwave (MW) Plasmas

19. Dielectric Discharge Barrier (DBD) • High AC voltage (1.2 kV), atmospheric pressure, 200-300 W • Dielectric layers allow for plasma discharge to reach material surface

20. Inductively Coupled Plasmas (ICP) • Plasma generated via coils oppositely faced, 13.56 MHz RF source • Magnetic flux perpendicular to substrate  E field envelopes volume of chamber • Roughing pump needed

21. Atmospheric Pressure Plasma Jet (AAPJ) • RF coupled capacitive discharge  neutral, cold effluent with high concentrations of reactive species and UV/VUV radiation. • Atmospheric pressure • Oxygen formed by interactions at the exit

22. Microwave (MW) Plasmas • Gas enters through an inlet • Interacts with incoming microwaves from a waveguide • kW magnetron power supply

23. Sterilization Efficacy

24. Sterilization Efficacy • MW plasma most effective ( ~ s) • All methods < 10 min treatment time (much less than conventional methods!)

25. Parameters effecting Sterilization and Plasmas

26. Parameters cont’d • Pressure: volatilization rate, EEDF, residence time of active species • Power: increased power  increased electron density. Thermolabile concerns. • Frequency: determines EEDF • Quantity: loading effect • Microbiological layer: inhibits free radical reaction, requires volatilization • Geometry: complex geometries impede reaction rates • Packaging: plasmas have low penetrability  efficacy low

27. Conclusions • Plasmas accomplish sterilization on order of minutes, or even seconds • Medium preservation • No toxicity introduced • Economical

28. Questions?