Sterilization by dry heat

Darmady, E. M.; Hughes, K.E.; Jones, J. D.; Prince, David A.; Tuke, Winifred

doi:10.1136/jcp.14.1.38

Cited by 37 publications

(23 citation statements)

References 4 publications

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“…Other methods of decontamination that are being suggested include heating in a dry oven at 70˚ C for 30 minutes 3 , and hydrogen peroxide vapor treatment 13 . The thermal treatment is well below the 160˚C for 2 hours recommended for medical sterilization by dry heat 14 . Low heat methods have not been tested on coronavirus outside of solution, nor for effectiveness against COVID-19 specifically 3 .…”

Section: Comparison With Other Methods and Facilitiesmentioning

confidence: 93%

Ethanol-Drying Regeneration of N95 Respirators

Nazeeri

Hilburn

et al. 2020

Preprint

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A critical shortage of respirators, masks and other personal protective equipment (PPE) exists due to the COVID-19 pandemic. Of particular need are N95 respirators, which use meltblown microfibers of charged polypropylene. An intensive search is underway to find reliable methods to lengthen the useful life of these normally disposable units. Recent experiments on respirators cleaned with ethanol solutions found drastic post-treatment drops infiltration efficiency (>40%). This has been attributed to a mechanism whereby ethanol disrupts the charges in the microfibers, reducing their ability to trap particles. The CDC/NIOSH has issued guidance directing clinicians and researchers to pursue other methods of decontamination. In our experiments, we replicated the drop in efficiency after 70% ethanol treatment, but we found that the efficiency rose again after more effective drying, which we achieved with a vacuum chamber. After drying at pressures of < ~6 mbar (0.6 kPa), the measured filtering efficiency rose to within 2% of the pre-washing value, and we found that this was sustained for 5 cleaning-drying cycles in three models of N95 masks. We stress that our tests are not meant to certify that the respirators are safe for use, which would require further, standardized, testing under NIOSH protocols. The tests presented here are used to understand basic mechanisms by which treatments can decrease or increase filtration efficiency. The main mechanism underlying the loss and recovery of filter efficiency seems to be the deposition and removal of water molecules adsorbed on the fiber surfaces, a hypothesis which is supported by several observations: (A) the filtering efficiency increases non-linearly with the weight loss during drying. (B) filtration efficiency shows an abrupt recovery as the vacuum pressure drops from 13 to 6 mbar, the range physically attributable to the removal of adsorbed water. (C) Optical microscopy of the microfiber layer reveals surface wetting of the fibers, which is most resistant to drying in dense regions of the fiber network. These observations indicate that losses in filter efficiency may be caused by the wicking of water into the dense fiber networks, reducing the available surface area for filtration. Such a degradation mechanism has two implications: (A) Ethanol and other aqueous decontamination methods may be more viable than previously assumed. Investigations of such methods should specify drying methods in their protocols. We employ vacuum chambers in this study, but other methods of removing adsorbed water could be equivalent. (B) This mechanism presents the possibility that mask filtration performance may be subject to degradation by other sources of moisture, and that the mask would continue to be compromised even if it appears dry. Further research is needed to determine the conditions under which such risks apply, and whether drying should be a routine practice for respirators undergoing extended use. This study introduces a number of methods which could be developed and validated for use in resource-limited settings. As the pandemic continues to spread in rural areas and developing nations, these would allow for local efforts to decontaminate, restore, and test medical masks.

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Section: Comparison With Other Methods and Facilitiesmentioning

confidence: 93%

Ethanol-Drying Regeneration of N95 Respirators

Nazeeri

Hilburn

et al. 2020

Preprint

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“…To prevent fermentation and to inactivate endogenous enzymes, the flours were dry heat sterilised at 190°C for 6 min prior to enzyme treatment (Darmady, Hughes, Jones, Prince, & Tuke, 1961). After enzyme treatment, flours were lyophilised prior to in vitro bioaccessibility tests.…”

Section: Enzymatic Treatmentsmentioning

confidence: 99%

Enzymatic degradation of phytate, polyphenols and dietary fibers in Ethiopian injera flours: Effect on iron bioaccessibility

Baye

Guyot²,

Icard‐Vernière³

et al. 2015

Food Chemistry

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“…Dry heat sterilization, which is the most basic sterilization procedure, heats the material at 170°C for over 1 hr, which will coagulate proteins and thus destroy any microorganisms present. 17 Because of this high temperature, most polymers would soften or melt, and may also begin to degrade, leading to compromised thermomechanical properties and potentially altering the drug release profile of the non-sterilized material. 6 Autoclave sterilization, which is the process of exposing the polymer to pressurized steam at 121°C, causes microorganisms to break down in the heated steam environment.…”

Section: Introductionmentioning

confidence: 99%

Thermomechanical properties, antibiotic release, and bioactivity of a sterilized cyclodextrin drug delivery system

et al. 2014

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Various local drug delivery devices and coatings are being developed as slow, sustained release mechanism for drugs, yet the polymers are typically not evaluated after commercial sterilization techniques. We examine the effect that commercial sterilization techniques have on the physical, mechanical, and drug delivery properties of polyurethane polymers. Specifically we tested cyclodextrin-hexamethyl diisocyanate crosslinked polymers before and after autoclave, ethylene oxide, and gamma radiation sterilization processes. We found that there is no significant change in the properties of polymers sterilized by ethylene oxide and gamma radiation compared to non-sterilized polymers. Polymers sterilized by autoclave showed increased tensile strength (p<0.0001) compared to non-sterilized polymers . In the release of drugs, which were loaded after the autoclave sterilization process, we observed a prolonged release (p<0.05) and a prolonged therapeutic effect (p<0.05) but less drug loading (p<0.0001) compared to non-sterilized polymers. The change in the release profile and tensile strength in polymers sterilized by autoclave was interpreted as being caused by additional crosslinking from residual, unreacted, or partially-reacted crosslinker contained within the polymer. Autoclaving therefore represents additional thermo-processing to modify rate and dose from polyurethanes and other materials.

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Sterilization by dry heat

Cited by 37 publications

References 4 publications

Ethanol-Drying Regeneration of N95 Respirators

Ethanol-Drying Regeneration of N95 Respirators

Enzymatic degradation of phytate, polyphenols and dietary fibers in Ethiopian injera flours: Effect on iron bioaccessibility

Thermomechanical properties, antibiotic release, and bioactivity of a sterilized cyclodextrin drug delivery system

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