Sterilization Method A Cold-Process NO2 Gas Approach for Sensitive Medical Devices

This patent describes a sterilization process that uses nitrogen dioxide (NO2) gas as the antimicrobial agent, designed to deliver hospital-grade sterility on heat-sensitive and chemistry-sensitive medical devices that cannot tolerate steam autoclaving or ethylene oxide.

The Problem

Hospital sterile-supply departments and contract sterilizers have, for decades, depended on two workhorse processes. Steam autoclaving at around 121 to 135 degrees Celsius is fast and reliable but rules out anything plastic, polymeric, electronic, or impregnated with a heat-sensitive drug or biologic. Ethylene oxide gas (ETO) is gentler thermally but introduces a different set of constraints: long aeration times to flush residual ETO, regulatory pressure on ETO emissions, occupational-health concerns, and slow cycle turnover. Gamma irradiation works for many disposables but degrades certain polymers and biologics. As the universe of medical devices broadens to include drug-eluting stents, electronic implants, sensors, and combination products, the available sterilization toolkit has not kept pace.

What This Invention Does

The invention applies nitrogen dioxide gas inside a controlled chamber as the sterilizing agent. The cycle controls the NO2 partial pressure, humidity, exposure time, and temperature so that microbial spores and vegetative organisms are inactivated, while the device load itself remains at near-ambient temperature. After the kill phase, the chamber is purged and the device load is aerated to remove residual gas. Because NO2 is reactive but breaks down to easily-handled byproducts, residue management is far less burdensome than with ETO.

The disclosed method covers several variations: cycle parameters tuned for different bioburden levels, humidification strategies, multi-pulse exposure profiles, and validation regimes that match the SAL (Sterility Assurance Level) requirements expected for terminally-sterilized medical devices. The patent positions NO2 sterilization as a drop-in alternative to ETO in many applications.

Key Features

• Low-temperature operation. The cycle runs near ambient temperature, making it compatible with electronics, sensors, drug coatings, polymers and biologics that cannot survive steam.
• Short cycle and aeration times. Compared with ETO’s typical multi-day aeration, NO2 residuals dissipate much faster, freeing devices for release sooner.
• Defined NO2 dosing parameters. Specific ranges for partial pressure, humidity, and dwell time are described, providing the building blocks for validating cycles that meet medical-device SAL requirements.
• Compatible with combination products. Suitable for devices that include heat-sensitive components such as drug coatings, sensors, optical elements or biologic surfaces.
• Reduced occupational and environmental footprint. NO2 is reactive in much smaller quantities than ETO and breaks down without leaving long-lived residues, reducing emissions abatement requirements.

Who Is Behind It?

The applicant is Noxilizer, Inc., a Maryland-based medical device sterilization specialist that has developed nitrogen-dioxide sterilization equipment and contract sterilization services. Noxilizer has been one of the principal commercial players advocating NO2 as an ETO alternative. The named inventor is David Opie. The Australian application is a divisional of AU 2023269290, which entered the national phase from PCT/US2023/022064 (published as WO 2023/220384), with US provisional priority from US 63/341,912 filed in May 2022. The Australian patent agent is Spruson and Ferguson in Sydney.

Why It Matters

Pressure on ETO has been intensifying. The US Environmental Protection Agency has tightened ETO emission limits, several state regulators have moved to constrain or shut down ETO sterilization plants, and device manufacturers are looking for credible alternatives that do not force redesign of the device itself. A sterilization process that is low-temperature, short-cycle, and operates without ETO’s residue-management overhead has direct commercial relevance for hundreds of FDA-cleared devices currently sterilized by ETO. The Australian filing extends Noxilizer’s protection to a market with active medical-device manufacturing and a similar regulatory drift away from ETO.

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AU 2026201804 was published in the Australian Official Journal of Patents on 2 April 2026 and is open for public inspection. Patent applications represent inventions that are sought to be protected and do not necessarily reflect commercially available products.