Sterilization of medical devices plays an important role in the product development although it is not heavily invovled or nealy not involved in academic research in universities. It need to be considered in the earlier stage of prototype development, which can avoid the complex or even failure in the later stage.
Sterilization is defined as a “validated process used to render product free from viable microorganisms.” Terminal sterilization is defined as the “process whereby product is sterilized within its sterile barrier system.” The terminal sterilization process is considered a manufacturing process step itself and usually takes place at, or near, the end of the manufacturing process.
The presence of microorganisms is expressed as a probability. While the probability can be reduced to a very low number, it can never with certainty be reduced to zero. This is why we use the term Sterility Assurance Level (SAL) to express a sterile claim. SAL is the probability of a viable microorganism being present on a product after sterilization. Normally expressed as 10-n. 10-3 or a 10-6 value being used most frequently for sterilization. Common SAL for medical devices is 10-6.
Sterilization is defined as a “validated process used to render product free from viable microorganisms.” Terminal sterilization is defined as the “process whereby product is sterilized within its sterile barrier system.” The terminal sterilization process is considered a manufacturing process step itself and usually takes place at, or near, the end of the manufacturing process.
The presence of microorganisms is expressed as a probability. While the probability can be reduced to a very low number, it can never with certainty be reduced to zero. This is why we use the term Sterility Assurance Level (SAL) to express a sterile claim. SAL is the probability of a viable microorganism being present on a product after sterilization. Normally expressed as 10-n. 10-3 or a 10-6 value being used most frequently for sterilization. Common SAL for medical devices is 10-6.
Sterilization is accomplished principally by radiation, chemical sterilants, steam under pressure, dry heat, and filtration or combinations thereof. General application and method of sterilization can be learned in Wiki. A more detailed Guideline for Disinfection and Sterilization in Healthcare Facilities can be found in Centers for Disease Control and Prevention (CDC)
It is important to distinguish sterilization from disinfection, which does not ensure the same security level and does not necessarily inactivate all forms of microorgan- isms – bacterial spores, for instance.
A sterile medical device is one that is free of viable microorganisms. For a sterile medical device this can be achieved through:
It is important to distinguish sterilization from disinfection, which does not ensure the same security level and does not necessarily inactivate all forms of microorgan- isms – bacterial spores, for instance.
A sterile medical device is one that is free of viable microorganisms. For a sterile medical device this can be achieved through:
- A terminal sterilization process
- Sterilization of components, followed by sterile filtration and aseptic filling into a sterilized container
- A combination of chemical/physical sterilization and aseptic processing
The choice of the sterilization method for medical devices depends on a number of factors including the type of material used in medical devices, the type of packaging materials (product packaging and final packaging), the number and type of microorganisms involved, and the classification of the item.
Herein, I summary the commonly used terminal sterilization methods (traditioanl methods recognized by FDA except dry heat and moist heat) in the medical device industry. International standards of medical device sterilization can be found in another blog page and there is the guidance document from FDA. Validation, materials and packaging compatibility of medical device sterilization will be summaried in future blogs.
Ethylene Oxide (EO)
EO sterilization accounts for approximately 50% of the industrial terminal sterilization market. The microbicidal activity of ETO is considered to be the result of alkylation of protein, DNA, and RNA. Alkylation, or the replacement of a hydrogen atom with an alkyl group, within cells prevents normal cellular metabolism and replication.
The main advantage is that it can sterilize heat- or moisture-sensitive medical equipment without deleterious effects on the material used in the medical devices, has excellent penetration and relatively simple to operate.
The main disadvantages associated with EO are the lengthy cycle time, the cost, its potential hazards to patients and staff, leaving toxic residues, which require aeration time.
The main advantage is that it can sterilize heat- or moisture-sensitive medical equipment without deleterious effects on the material used in the medical devices, has excellent penetration and relatively simple to operate.
The main disadvantages associated with EO are the lengthy cycle time, the cost, its potential hazards to patients and staff, leaving toxic residues, which require aeration time.
Radiation
Radiation sterilization accounts for most of the remaining 50% of the industrial terminal sterilization market. It results in minimal or no rise in temperature, leaves no residue, and requires no quarantine time post processing.
Radiation is considered a “clean” process – no chemicals are involved, only pure energyGamma ray
Gamma rays from a cobalt-60 isotope source or machinegenerated ac- celerated electrons are used. Gamma irradiation is the most popular form of radiation sterilization (approximately 80% of the radiation sterilization market). A key characteristic of Gamma radiation is the high penetration capability. This enables moderately dense or sealed products to be processed with relative ease and facilitates treatment of palletised product. Exposure is achieved when the packages are transported around an exposed cobalt-60 source for a defined period of time. The most commonly validated dose used to sterilise medical devices is 25 kGy.Electron-Beam Radiation
E-beam radiation is a form of ionizing energy that is generally characterized by its low penetration and high dosage rates. The beam, a concentrated, highly charged stream of electrons, is generated by the acceleration and conversion of electricity. The electrons are generated by equipment referred to as accelerators which are capable of producing beams that are either pulsed or continuous.
E-beam radiation is similar to gamma processing in that, upon contact with the exposed product, electrons alter various chemical and molecular bonds, including the reproductive cells of microorganisms by destroying their DNA chains. The low penetration properties of the electron beam means that the width and density of products that can be irradiated are limited.X-ray
X-ray has only recently been used for commercial sterilization such as in LBA Sterilization. X-ray and E-Beam are very similar in how they work. An electron beam produced using an electric-powered machine source called an accelerator disrupts living cells through damage to DNA and other cellular structures. X-rays are produced using an electron beam directed onto an X-ray converter target. Because the radiation is in the form of photons, the depth of penetration issues with electrons is avoided; however, the conversion rate to X-rays is inefficient and therefore costly due to high electricity consumption.
Non-traditional methods recognized by FDA are:
- hydrogen peroxide (H2O2) gas plasma
- ozone (O3)
Novel non-traditional methods are:
- chlorine dioxid
- ethylene oxide-in-a-bag
- high intensity light or pulse light
- microwave radiation
- sound waves
- ultraviolet light
- vaporized chemical sterilant systems (e.g., hydrogen peroxide or peracetic acid).
Several methods cleared by FDA and others are still under development and not cleared by FDA. However, there is no guarantee that these new sterilization technologies will receive FDA clearance for use in healthcare facilities. None of these methods has been widely accepted to be used by medical device.
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