Peroxide Vapor Research Articles

Fit Testing Failure of Reprocessed "Duckbill"-Type N95 Masks.

In response to worldwide shortages of N95 masks during the severe acute respiratory syndrome-coronavirus-2 pandemic, various strategies have been used. The Centers for Disease Control and Prevention recommend several strategies, including simple isolation to reprocessing methods using vaporized hydrogen peroxide to guide reuse of masks up to five times. National Institute for Occupational Safety and Health (NIOSH) quantitative fit testing was performed after five trials of donning and doffing in one cohort of new masks and two cohorts of repeatedly sterilized "duckbill"-type N95 masks. One cohort of new masks and two cohorts of sterilized masks were repeatedly subjected to 35% vaporized hydrogen peroxide for either five or 10 cycles. Then, they were subjected to five trials of donning and doffing, with NIOSH quantitative fit testing performed after each wear cycle to assess for any degradation on fit performance caused by sterilization and/or repeated donning and doffing up to the recommended Centers for Disease Control and Prevention limit of five times. All of the fit testing was performed on a single volunteer. The means and 95% confidence intervals for each cohort and the individual results for each mask within each cohort were reported. A χ2 analysis showed significant differences in percentages of masks that pass fit testing in both recycled mask cohorts. These data show the variability of NIOSH fit testing results of both new and sterilized masks. The mask recycling program of our partner health systems thus discarded these types of masks due to the variable failure rate. Health systems should consider individual evaluation to inform their overall policies on mask reuse and recycling.

Kinetic Study of OH Radical Reactions with Cyclopentenone Derivatives.

We investigated the reactions of the hydroxyl radical (OH) with cyclopentenone derivatives and cyclopentanone in a quasi-static reaction cell at 4 Torr across a 300-500 K temperature range. The OH radicals were generated using pulsed laser photolysis of hydrogen peroxide vapors, and the ketone reactants were introduced in excess. The relative concentrations of the radicals were monitored as a function of reaction time using laser-induced fluorescence. At room temperature, the reaction rate coefficients were measured to be 1.2(±0.1) × 10-11 cm3 s-1 for reaction with 2-cyclopenten-1-one (R1); 1.7(±0.2) × 10-11 cm3 s-1 for reaction with 2-methyl-2-cyclopenten-1-one (R2); and 4.4(±0. 7) × 10-12 cm3 s-1 for reaction with 3-methyl-2-cyclopenten-1-one (R3). Over the experimental temperature range, the rate coefficients can be fitted with the modified Arrhenius expressions k1(T) = 1.2 × 10-11 (T/300)0.26 exp (6.7 kJ mol-1/R {1/T - 1/300}) cm3 s-1, k2(T) = 1.7 × 10-11 (T/300)6.4 exp (27.6 kJ mol-1/R {1/T - 1/300}) cm3 s-1, k3(T) = 4.4 × 10-12 (T/300)17.8 exp (57.8 kJ mol-1/R {1/T - 1/300}) cm3 s-1. In the cases of 2-cyclopenten-1-one and 2-methyl-2-cyclopenten-1-one, the temperature dependence of the rate coefficients is similar to that calculated or measured for noncyclic conjugated ketones. We also found that the reaction with 3-methyl-2-cyclopenten-1-one was slower, with rate coefficients similar to those measured for the reaction with the saturated cyclic ketone cyclopentanone. To discuss the experimental data, we use potential energy surfaces (PES) calculated at the CCSD(T)/cc-pVTZ//M06-2X/6-311+G** level of theory. RRKM-based Master equation calculations were also performed to infer the most likely reaction products over a wide range of temperatures and pressures. We suggest that both abstraction and addition mechanisms contribute to the overall OH removal, forming radical products stabilized by resonance. We also discuss the relevance for combustion and atmospheric chemistry.

Qualitative Comparison of Hydrogen Peroxide Decontamination Systems: Vapor vs. Aerosol

This study aimed to compare the efficiency of two methods for airborne surface decontamination: hydrogen peroxide vapor (HPV) and aerosolized hydrogen peroxide (aHP). Spores of G. stearothermophilus and B. atrophaeus were exposed to a 35% hydrogen peroxide solution under controlled laboratory conditions, including specific concentrations, exposure durations, humidity levels, and temperatures. Following each decontamination procedure, the spores were incubated for 7 days to evaluate bacterial growth and assess the efficacy of each method. The results indicate that the aHP method achieved biocidal rates of 84.76% for G. stearothermophilus and 89.52% for B. atrophaeus, while the HPV method demonstrated respective rates of 90.95% and 90.48%. These findings suggest that both the aHP and HPV methods are highly effective for microbial decontamination, with HPV showing a slight edge in overall efficacy. However, despite its comparable effectiveness, the HPV method has raised concerns regarding technical and economic factors. Observations highlighted issues such as fluctuations in humidity levels causing surface damage, a problem not encountered with the aHP method. Economically, HPV requires specific devices that can cost up to EUR 50,000, whereas aHP equipment costs do not exceed EUR 10,000. These observations emphasize the importance of critically evaluating the pros and cons of each decontamination method, taking into account factors such as biocidal efficacy, technical feasibility, and the associated costs.

Vaporized Hydrogen Peroxide Gains Support as Low-Temperature Sterilization Method.

Vaporized Hydrogen Peroxide Gains Support as Low-Temperature Sterilization Method.

Case Study: Compatibility Testing of Pre-Filled Syringe Stopper Technology with Vaporized Hydrogen Peroxide Terminal Sterilization Process.

STERIS and W.L. GORE collaborated on a case study testing the compatibility of a new prefilled syringe plunger design with VHP terminal sterilization. VHP chamber conditions require deep vacuum pulsing, which may represent challenges to prefilled syringe container integrity. The growing industry trend toward VHP sterilization is driven by the FDA search for alternative sterilization methods to EO and the recent publication of a VHP specific process standard. The purpose of the study is to test and report compatibility of the new 0.5 mL GORE IMPROJECT plunger, a silicone free syringe solution for ophthalmic application, with VHP sterilization. Various challenges have been reported when using conventional, siliconized, prefilled syringe systems for intravitreal injections such as subvisible particles, inflammation, silicone floaters, and intraocular pressure increases. The GORE plunger eliminates the need for silicone oil as a lubricant on the plunger and barrel, while meeting strict container closure and terminal sterilization requirements of ophthalmic applications. This case study presents successful results of deep vacuum VHP terminal sterilization process compatibility with the GORE plunger design and material composition. Test results include primary container integrity, stopper off-gassing/ingress, and visual inspection. Principles of VHP vacuum sterilization process, test cycle configuration, and its main parameters are presented.

Material compatibility of epoxies exposed to repeated low temperature vaporized hydrogen peroxide sterilization

ABSTRACT Through technological advancements, medical devices have evolved in their designs and have become more complex in both their design and materials of construction. Medical grade biocompatible epoxies are widely used in reusable medical devices. Choosing an epoxy that maintains its performance characteristics when subjected to repeated sterilization throughout the reusable medical device’s lifespan is a known challenge for medical device manufacturers. This study evaluated the material compatibility of seven cured 2-part and 1-part epoxies used in medical devices following exposure to 100 cycles in a low temperature vaporized hydrogen peroxide sterilizer. Six of the seven epoxies tested were found to be compatible with vaporized hydrogen peroxide sterilization based on qualitative, hardness and weight measurements conducted post exposure to 100 VHP cycles. The epoxies deemed to be compatible displayed no visual signs of physical defects, minimal reduction in hardness (≤2%) and total weight gain (≤2.9%). One of the epoxy samples did not maintain its texture and exhibited 17% loss in hardness post exposure to 100 VHP sterilization cycles and was found to be incompatible with the low temperature vaporized hydrogen peroxide process. This study verifies the need for material compatibility evaluations of epoxies prior to designing and developing a medical device while keeping in mind the application, lifecycle and intended use of medical devices.

Trace Pt-loading transition metal hydroxides as efficient catalyst for vaporized hydrogen peroxide decomposition

Vaporized hydrogen peroxide (VHP) holds great promise for the decontamination of space environment. Nevertheless, following the decontamination process, highly concentrated VHP within confined spaces is harmful to the human body. Hence, trace Pt-loading (0.57 wt%) transition metal hydroxides nanosheets anchored on Ni foam (Pt@NiAlCrFe-LDHs/NF) were prepared for VHP decomposition. Importantly, a strong electronic interaction between NiAlCrFe layer double hydroxides (NiAlCrFe-LDHs) and Pt was evidenced by XPS. Meanwhile, unique nanosheet-like morphology and rich mesoporous structure endow the catalyst with excellent performance. The catalytic activity of Pt@NiAlCrFe-LDHs/NF is approximately twice that of NiAlCrFe-LDHs/NF and seven times that of Pt/NF. The improved catalytic efficiency of Pt@NiAlCrFe-LDHs/NF results from the reduction in energy barrier for VHP decomposition reaction caused by the introduction of trace Pt. After ten recycling experiments, this catalyst still shows good durability with no significant deterioration in VHP decomposition efficiency. Finally, the growth mechanism of Pt@NiAlCrFe-LDHs/NF was also proposed and discussed.

Sprayable Diacetylene-Containing Amphiphile Coatings for Visual Detection of Gas-Phase Hydrogen Peroxide

Colorimetric chemical sensing of target gases, such as hydrogen peroxide vapors, is an evolving area of research that implements responsive materials that undergo molecule-specific interaction, resulting in a visible color change. Due to the intuitive nature of an observable color change, such sensing systems are particularly desirable as they can be widely deployed at low cost and without the need for complex analytical instrumentation. In this work, we describe our development of a new spray-on sensing material that can provide a colorimetric response to the presence of a gas-phase target, specifically hydrogen peroxide vapor. By providing a cumulative response over time, we identified that part per million concentrations of hydrogen peroxide vapor can be detected. Specifically, we make use of iron chloride-containing formulations to enable the catalysis of hydrogen peroxide to hydroxyl radicals that serve to initiate polymerization of the diacetylene-containing amphiphile, resulting in a white to blue color transition. Due to the irreversible nature of the color change mechanism, the cumulative exposure to hydrogen peroxide over time is demonstrated, enabling longitudinal assessment of target exposure with the same coatings. The versatility of this approach in generating a colorimetric response to hydrogen peroxide vapor may find practical applications for environmental monitoring, diagnostics, or even industrial safety.

FDA Facilitates Expand Adoption of Vaporized Hydrogen Peroxide for Medical Device Sterilization

FDA Facilitates Expand Adoption of Vaporized Hydrogen Peroxide for Medical Device Sterilization

Environmentally Friendly Bleaching Process of the Cellulose Fibres Materials Using Ozone and Hydrogen Peroxide in the Gas Phase.

The paper presents the new eco-friendly method of bleaching process of the cellulose fibre materials. Cellulose materials were bleached using hydrogen peroxide (both in aqueous solution, vapours, ozone and by the combined action of gaseous hydrogen peroxide and ozone. The method using hydrogen peroxide in aqueous solution presents the standard procedure and was used as the comparison technique. The bleaching processes using gaseous oxidants were carried out in a prototype device for dry, low-temperature treatment of fibrous materials with the use of oxidising agents in the gas phase. The influence of the innovative gas-phase bleaching method on the cotton samples' properties was analysed by Scanning Electron Microscopy (SEM), evaluation of the colour and whiteness, assessment of the polymerisation degree (DP), analysis of the mechanical properties and sorption capacity as well as microbiological assessment against colonies of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The comparison of the obtained results led to the conclusion that the bleaching processes using gas-phase agents-vaporised hydrogen peroxide, ozone or their combination-are non-invasive. The applied bleaching processes resulted in a slightly lower whiteness parameters than standard bath bleaching. After the bleaching processes with ozone and vaporised hydrogen peroxide separately, the decrease in the DP and tensile strength was similar to that observed after the bleaching with aqueous H2O2. When both processes were used together, a higher reduction in DP and tensile strength was noticed. Both oxidising agents showed a strong biocidal effect against bacteria. Gas-phase bleaching procedures, due to the lower temperature (35 °C vs. 98 °C) and minimal water consumption, have economic and environmental advantages, which allows their use in semi-industrial applications. It has been shown that the treatment of cotton fabrics using ozone and hydrogen peroxide in the gas phase allows to simultaneously obtain the bleaching and disinfection effect.

3D printing in pediatric neurosurgery: experimental study of a novel approach using biodegradable materials.

3D printing technologies have become an integral part of modern life, and the most routinely used materials in reconstructive surgery in children are biodegradable materials. The combination of these two technologies opens up new possibilities for the application of innovative methods in neurosurgery and a patient-centered approach in medical care. The aim of the study was to determine whether a physician without specialized programming and printing skills could independently create materials in a clinical setting for the treatment of patients. We conducted a preclinical study on 15 male Balb-C mice. Cylindrical materials made of polylactic acid (PLA) plastic were 3D printed. Sterilization of the obtained material was performed using a cold plasma sterilizer with hydrogen peroxide vapor and its plasma. The sterile material was implanted subcutaneously into the mice for 30days, followed by histological examination. Using open-source software for modeling and printing, plates and screws made of PLA plastic were manufactured. The produced components were tested in the biomedical laboratory of the institute. The histological material showed that no inflammatory changes were observed at the implantation site during the entire observation period. The cellular composition is mainly represented by macrophages and fibroblasts. There was a gradual resolution of the material and its replacement by native tissues. Research conducted to assess the effectiveness of material sterilization in a cold plasma sterilizer demonstrated its high bactericidal efficiency. The method we developed for obtaining biodegradable plates and fixation elements on a 3D printer is easy to use and has demonstrated safety in a preclinical study on an animal model.

Low temperature vaporized hydrogen peroxide sterilization of 3D printed devices

BackgroundLow temperature vaporized hydrogen peroxide sterilization (VH2O2) is used in hospitals today to sterilize reusable medical devices. VH2O2 sterilized 3D printed materials were evaluated for sterilization, biocompatibility and material compatibility.Materials & methodsTest articles were printed at Formlabs with BioMed Clear™ and BioMed Amber™, and at Stratasys with MED610™, MED615™ and MED620™. Sterilization, biocompatibility and material compatibility studies with 3D printed materials were conducted after VH2O2 sterilization in V-PRO™ Sterilizers. The overkill method was used to evaluate sterilization in a ½ cycle. Biocompatibility testing evaluated the processed materials as limited contact (< 24-hours) surface or externally communicating devices. Material compatibility after VH2O2 sterilization (material strength and dimensionality) was evaluated via ASTM methods and dimensional analysis.Results3D printed devices, within a specific design window, were sterile after VH2O2 ½ cycles. After multiple cycle exposure, the materials were not cytotoxic, not sensitizing, not an irritant, not a systemic toxin, not pyrogenic and were hemo-compatible. Material compatibility via ASTM testing and dimensionality evaluations did not indicate any significant changes to the 3D printed materials after VH2O2 sterilization.ConclusionLow temperature vaporized hydrogen peroxide sterilization is demonstrated as a suitable method to sterilize 3D printed devices. The results are a subset of the data used in a regulatory submission with the US FDA to support claims for sterilization of 3D printed devices with specified materials, printers, and device design 1.

Use of Hydrogen Peroxide Vapour for Microbiological Disinfection in Hospital Environments: A Review.

Disinfection of nosocomial pathogens in hospitals is crucial to combat healthcare-acquired infections, which can be acquired by patients, visitors and healthcare workers. However, the presence of a wide range of pathogens and biofilms, combined with the indiscriminate use of antibiotics, presents infection control teams in healthcare facilities with ongoing challenges in the selection of biocides and application methods. This necessitates the development of biocides and innovative disinfection methods that overcome the shortcomings of conventional methods. This comprehensive review finds the use of hydrogen peroxide vapour to be a superior alternative to conventional methods. Motivated by observations in previous studies, herein, we provide a comprehensive overview on the utilisation of hydrogen peroxide vapour as a superior high-level disinfection alternative in hospital settings. This review finds hydrogen peroxide vapour to be very close to an ideal disinfectant due to its proven efficacy against a wide range of microorganisms, safety to use, lack of toxicity concerns and good material compatibility. The superiority of hydrogen peroxide vapour was recently demonstrated in the case of decontamination of N95/FFP2 masks for reuse to address the critical shortage caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the COVID-19 pandemic. Despite the significant number of studies demonstrating antimicrobial activity, there remains a need to critically understand the mechanism of action by performing studies that simultaneously measure damage to all bacterial cell components and assess the correlation of this damage with a reduction in viable cell count. This can lead to improvement in antimicrobial efficacy and foster the development of superior approaches.

Nanoporous materials as carriers of hydrogen peroxide vapour: A new bio-decontamination technology

High-level bio-decontamination, which involves reducing microorganisms by 99.9999%, is essential in preventing Hospital Acquired Infections and controlling pandemics. This study demonstrates that nanoporous materials, which can retain molecules within their pores, and subsequently release them, can be used in high level bio-decontamination. H2O2 vapour is a golden-standard in high level bio-decontamination. This work demonstrates that various nanoporous materials, particularly mesoporous silicas, can be utilized to store and release H2O2 in the vapour phase. H2O2 concentrations of over 2500 ppm were achieved by desorbing it from the carrier material at low temperatures of 60–80 °C. Generation of H2O2-vapour by desorption from nanoporous materials is technically much simpler than vaporization of aqueous H2O2 solutions, which use flash vaporization processes occurring at 130–150 °C. This has important technical implications, highlighting the potential of nanoporous materials as carriers for H2O2 for high-level bio-decontamination.

Implementation of contact precautions for multidrug-resistant organisms in the post-COVID-19 pandemic era: An updated national Emerging Infections Network (EIN) survey.

To understand how healthcare facilities employ contact precautions for patients with multidrug-resistant organisms (MDROs) in the post-coronavirus disease 2019 (COVID-19) era and explore changes since 2014. Cross-sectional survey. Emerging Infections Network (EIN) physicians involved in infection prevention or hospital epidemiology. In September 2022, we sent via email an 8-question survey on contact precautions and adjunctive measures to reduce MDRO transmission in inpatient facilities. We also asked about changes since the COVID-19 pandemic. We used descriptive statistics to summarize data and compared results to a similar survey administered in 2014. Of 708 EIN members, 283 (40%) responded to the survey and 201 reported working in infection prevention. A majority of facilities (66% and 69%) routinely use contact precautions for methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) respectively, compared to 93% and 92% in 2014. Nearly all (>90%) use contact precautions for Candida auris, carbapenem-resistant Enterobacterales (CRE), and carbapenem-resistant Acinetobacter baumannii. More variability was reported for carbapenem-resistant Pseudomonas aeruginosa and extended-spectrum β-lactamase-producing gram-negative organisms. Compared to 2014, fewer hospitals perform active surveillance for MRSA and VRE. Overall, 90% of facilities used chlorhexidine gluconate bathing in all or select inpatients, and 53% used ultraviolet light or hydrogen peroxide vapor disinfection at discharge. Many respondents (44%) reported changes to contact precautions since COVID-19 that remain in place. Heterogeneity exists in the use of transmission-based precautions and adjunctive infection prevention measures aimed at reducing MDRO transmission. This variation reflects a need for updated and specific guidance, as well as further research on the use of contact precautions in healthcare facilities.

Multicomponent metal nanoparticles supported on nickel foam for efficient catalytic decomposition of vaporized hydrogen peroxide

Residual high-concentration vaporized hydrogen peroxide (VHP) after disinfection poses a significant threat to human health and the disinfection space. The considerable concerns make it necessary to develop efficient catalysts for VHP decomposition. In this work, three-dimensional (3D) porous Ni foam (NF)-based multicomponent nanocomposites were fabricated via a facile in-situ hydrothermal method. The effect of the composition and content of elements on the catalytic decomposition of VHP was studied. The AlCrFePt0.64/NF catalyst exhibits the best catalytic performance among all catalysts and requires only 59 min to reduce the VHP concentration from 250 ppm to 1 ppm. Furthermore, the AlCrFePt0.64/NF shows superior stability and no obvious change in VHP decomposition performance after ten recycling tests. The decomposition of VHP follows a pseudo-first-order kinetics rate law. The catalytic decomposition mechanism of VHP proceeds through O-O splitting and consecutive H-transfer reactions. The enhanced catalytic activity of the AlCrFePt0.64/NF is ascribed to the synergetic effect of noble-metal Pt and transition metals, which leads to the presence of initially larger amounts of surface O* and HO* species, and lower activation energy of the O-O bond splitting.

Effect of Vaporized Hydrogen Peroxide and Nitrogen Dioxide Sterilization on Nitinol.

Background: Nitinol is used as the structural framework in numerous types of medical devices (e.g., guidewires, transcatheters, stents). The desire to understand the material compatibility of nitinol with vaporized hydrogen peroxide (VH2O2) and nitrogen dioxide (NO2) sterilization is increasing in healthcare technology. As a result of increased regulatory pressure and capacity limitations related to ethylene oxide (EO) sterilization, the industry is seeking alternative, sustainable sterilization options. Objective: This study sought to characterize the corrosion resistance of nitinol metal alloy wire when exposed to varying levels of VH2O2 and NO2 sterilization. Methods: Scanning electron microscopy (SEM) imaging and energy-dispersive X-ray spectroscopy (EDS) scans were performed to understand the effects of VH2O2 and NO2 sterilization treatments on the surface morphology and chemical composition of nitinol. Results: From the SEM-EDS results, no notable difference was observed when comparing VH2O2 and NO2 test samples with nonsterile control samples. In addition, cyclic potentiodynamic polarization measurements were performed per ASTM F2129-19a to determine corrosion susceptibility. No considerable changes were detected in the electrochemical potential after VH2O2 and NO2 sterilization treatments, when compared with the nonsterile control samples. Conclusion: SEM-EDS and corrosion test results indicated no considerable changes in the surface properties or electrochemical potential of the sterilized samples compared with the nonsterilized control samples. Therefore, nitinol metal showed promising results for compatibility with VH2O2 and NO2 sterilization.

An Investigation of the Visual Impact of the Combined Exposure to Residual Cleaning Agents and Vaporized Hydrogen Peroxide on Materials used in Barrier Systems

Vaporized Hydrogen Peroxide (vapor-phase hydrogen peroxide, vH₂O₂) treatment is the main approach for sporicidal surface bio-decontamination in restricted access barrier systems and isolators. Prior to vH₂O₂ exposure, surfaces are cleaned to prepare the barrier system for the decontamination cycle, removing surface residues that could impede the cycles effectiveness. The presence of residual cleaning agents alongside vH₂O₂ exposure could potentially impact the integrity and longevity of materials, necessitating a comprehensive understanding of these interactions. To gain more knowledge about the influence of cleaning agents and vH₂O₂, various materials were exposed to a combination of cleaning agents and vH₂O₂ in order to visually assess the interaction. Introduction: Vaporized Hydrogen Peroxide has emerged as a valuable tool for bio-decontamination due to its ability to efficiently eliminate a wide range of microorganisms, including bacteria, viruses, and spores [1]. The penetration of vH₂O₂ is limited, so surfaces are cleaned to remove contaminants that may interfere with vH₂O₂ penetration and effectiveness prior to vH₂O₂ exposure. While studies have investigated the compatibility of materials with vH₂O₂ or cleaning agents alone [2,3], the interactions between residual cleaning agents and vH₂O₂ have received limited attention until now. Residual cleaning agents might persist even after thorough rinsing, potentially influencing the interaction of the vapour phase gas with materials. Reactive components within cleaning agents could react with vH₂O₂, probably leading to material deterioration, discoloration, or altered mechanical properties. Additionally, accumulated residues within surface microstructures might hinder vH₂O₂ diffusion, thus impacting its efficacy. Investigating these combined effects is pivotal to prevent unintended material outcomes during decontamination processes.

Enzymatic Indicators in Vaporized Hydrogen Peroxide Decontamination Cycles: Application-related Research focusing on Fractional Kill Time (FKT) and Reverse Fractional Kill Time (RFKT) Studies

The accepted standard from a regulatory perspective for vaporized hydrogen peroxide (vH2O2) cycle validation is the use of biological indicators (BIs). Novel enzymatic indicators (EIs) are gaining more importance in this field, relying on specific enzymatic reactions for their functionality. The aim of this work is to determine how enzymatic indicators can contribute to the cycle development process. Emphasis was placed on the initial informative study, the fractional kill time study, which is a basis for future studies. The results indicate that enzymatic indicators have the potential to facilitate further development of the cycle. This requires an analysis of the determined data, measured in relative light units (RLU), and aligning it with the BI growth, resulting in Full Kill/ No Kill limits. The use of enzymatic indicators for decontamination cycle development opens new perspectives and holds considerable potential for practical use in the development and validation of decontamination processes.

Bacterial and fungal bioburden reduction on material surfaces using various sterilization techniques suitable for spacecraft decontamination.

Planetary protection is a guiding principle aiming to prevent microbial contamination of the solar system by spacecraft (forward contamination) and extraterrestrial contamination of the Earth (backward contamination). Bioburden reduction on spacecraft, including cruise and landing systems, is required to prevent microbial contamination from Earth during space exploration missions. Several sterilization methods are available; however, selecting appropriate methods is essential to eliminate a broad spectrum of microorganisms without damaging spacecraft components during manufacturing and assembly. Here, we compared the effects of different bioburden reduction techniques, including dry heat, UV light, isopropyl alcohol (IPA), hydrogen peroxide (H2O2), vaporized hydrogen peroxide (VHP), and oxygen and argon plasma on microorganisms with different resistance capacities. These microorganisms included Bacillus atrophaeus spores and Aspergillus niger spores, Deinococcus radiodurans, and Brevundimonas diminuta, all important microorganisms for considering planetary protection. Bacillus atrophaeus spores showed the highest resistance to dry heat but could be reliably sterilized (i.e., under detection limit) through extended time or increased temperature. Aspergillus niger spores and D. radiodurans were highly resistant to UV light. Seventy percent of IPA and 7.5% of H2O2 treatments effectively sterilized D. radiodurans and B. diminuta but showed no immediate bactericidal effect against B. atrophaeus spores. IPA immediately sterilized A. niger spores, but H2O2 did not. During VHP treatment under reduced pressure, viable B. atrophaeus spores and A. niger spores were quickly reduced by approximately two log orders. Oxygen plasma sterilized D. radiodurans but did not eliminate B. atrophaeus spores. In contrast, argon plasma sterilized B. atrophaeus but not D. radiodurans. Therefore, dry heat could be used for heat-resistant component bioburden reduction, and VHP or plasma for non-heat-resistant components in bulk bioburden reduction. Furthermore, IPA, H2O2, or UV could be used for additional surface bioburden reduction during assembly and testing. The systemic comparison of sterilization efficiencies under identical experimental conditions in this study provides basic criteria for determining which sterilization techniques should be selected during bioburden reduction for forward planetary protection.