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

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

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

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: 10 3 kPa Temperatures: o C Steam transfers sufficient heat to microorganisms to inflict demise Exposure time ~ 30 minutes Can cause permanent damage, and alter material properties significantly

Current Sterilization Means: Chemical EtO, H 2 O 2, O 3, bleach most commonly used Applications when heat is damaging to the medium Damages fiber optics, electronics, some plastics Introduces toxicity

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

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?

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

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.

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.

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

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 ~ s

Hydrogen Abstraction & Double Bond Cleavage

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

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

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

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

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

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

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

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

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

Sterilization Efficacy

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

Parameters effecting Sterilization and Plasmas

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

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

Questions?