plasma sterilization
DESCRIPTION
geeTRANSCRIPT
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Plasma SterilizationApplications of plasmas for sterilization in medical, food processing, ventilating, and air conditioning industries
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OutlineWhat is sterilization?Current sterilization meansSolution: Plasma SterilizationHow it worksDisadvantagesMethods of Plasma Sterilization
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What is Sterilization?Sterilization is any process or procedure designed to entirely eliminate microorganisms from a material or medium
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Current Sterilization Means: HeatTypes: dry and moist heatMedium is exposed to moist heat (steam) generated by an autoclave, or dry heat in a heaterPressures: 103 kPaTemperatures: 120-140 oCSteam transfers sufficient heat to microorganisms to inflict demiseExposure time ~ 30 minutesCan cause permanent damage,and alter material propertiessignificantly
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Current Sterilization Means: ChemicalEtO, H2O2, O3, bleach most commonly usedApplications when heat is damaging to the mediumDamages fiber optics, electronics, some plasticsIntroduces toxicity
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Current Sterilization Means: IrradiationTypes: Gamma radiation, Bremsstrahlung, X RaysMedium is subjected to radiation radiochemical and radionucleic reactions cellular deathDisadvantages:EmbrittlementChain ScissionCross LinkingCostly
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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?
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Plasma Sterilization in SummaryA plasma is a quasi-neutral collection of electrons, positive ions, and neutrals capable of collective behaviorPositive ions = free radicalsPlasma sterilization operates synergistically via three mechanisms:Free radicals interactionsUV/VUV radiative effectsVolatilizationDead microorganisms = sterilization
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Plasma Sterilization Mechanics: IR VolatilizationIR 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.
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Plasma Sterilization Mechanics: Ionizing Radiation (IR)IR (UV/VUV radiation) can damage DNA/RNA, chemical cellular bonds, and induces free radicals to perpetuate the processDamaged DNA/RNA microbial death by 4 mechanisms:Apoptosis nucleases become hardwired to shrink and cause cell to commit suicide. Caused by DNA/RNA damageAutophagy Formation of double membrane vacuoles in cytoplasm separation of mitochondria and ribosomes protein production stopped cell deathNecrosis Murder by cell swellingMitotic Catastrophe radiation causes mis-segregation of chromosomes, leading to Apoptosis.
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Plasma Sterilization Mechanics: IR (Cellular View)IR impacts the cell, three outcomes can result.
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Plasma Sterilization Mechanics: IR (Chemical View)Free radicals O* and OH* play crucial role in microorganism destruction by way of chemical reactionsO*, OH* highly reactive ~ 10-9 s
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Hydrogen Abstraction & Double Bond Cleavage
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Plasma Sterilization Mechanics: IR (Nucleic Acid View), UV RadiationUV/VUV radiation causesformation of thymine dimers in DNA, inhibiting bacterial replication.Base damageStrand breaks
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Plasma Sterilization Mechanics: IR (Nucleic Acid View), Charged ParticlesCharged species in the plasma can damage DNA if formed in the vicinity of chromatin.RSH act as radical scavengers
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Quantifying Sterilization Efficacy
i.e. Time required for the microbial population to be reduced to one decimal
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Disadvantages of Plasma SterilizationWeak penetrating power of the plasma species. Complications arise in:Presence of organic residuePackaging materialComplex geometriesBulk sterilization of many devicesSolutions: Introduce preferentially targetting UV/VUV radiation of proper wavelength
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Methods of Plasma SterilizationDielectric Discharge Barrier (DBD)Inductively Coupled Plasmas (ICP)Atmospheric Pressure Plasma Jet (AAPJ)Microwave (MW) Plasmas
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Dielectric Discharge Barrier (DBD)High AC voltage (1.2 kV), atmospheric pressure, 200-300 WDielectric layers allow for plasma discharge to reach material surface
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Inductively Coupled Plasmas (ICP)Plasma generated via coils oppositely faced, 13.56 MHz RF sourceMagnetic flux perpendicular to substrate E field envelopes volume of chamberRoughing pump needed
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Atmospheric Pressure Plasma Jet (AAPJ)RF coupled capacitive discharge neutral, cold effluent with high concentrations of reactive species and UV/VUV radiation.Atmospheric pressureOxygen formed by interactions at the exit
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Microwave (MW) PlasmasGas enters through an inletInteracts with incoming microwaves from a waveguidekW magnetron power supply
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Sterilization Efficacy
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Sterilization EfficacyMW plasma most effective ( ~ s)All methods < 10 min treatment time (much less than conventional methods!)
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Parameters effecting Sterilization and Plasmas
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Parameters contdPressure: volatilization rate, EEDF, residence time of active speciesPower: increased power increased electron density. Thermolabile concerns.Frequency: determines EEDFQuantity: loading effectMicrobiological layer: inhibits free radical reaction, requires volatilizationGeometry: complex geometries impede reaction ratesPackaging: plasmas have low penetrability efficacy low
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ConclusionsPlasmas accomplish sterilization on order of minutes, or even secondsMedium preservationNo toxicity introducedEconomical
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Questions?