High Edge Consulting

There are a number of different sterilisation technologies available, each with positives and negatives. Listed below are the more common technologies.

Often carried out in conjunction with filtration, this process is normally associated with liquid products, for example contact lens solutions. The premise is that the bulk product and the receptacles are already sterile and that the filling process does not introduce any microorganisms into the product. This technology requires rigorous controls and may be appropriate to high volume production or for those fluids that cannot undergo other sterilisation technologies.

This can be used very effectively to remove microorganisms from fluids. A typical sterilising grade filter is rated at 0.2µm and physically removes organisms from the product. The technology is not well suited to viscous liquids and the filters require regular monitoring, replacement and integrity testing to demonstrate the filter matrix has not broken down and contaminated the products.

This sterilisation process is self explanatory, products are heated to high temperatures, typically 180°C for a defined period, typically 2 hours, but both temperature and time do vary according to individual circumstances. This process is relatively low tech and easy to carry out in house. Because of the temperatures involved it is not suitable for temperature labile devices.

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High energy electrons are used to sterilise products by Electron Beam Irradiation. Electron beams are produced from an electron accelerator, not unlike a CRT used in traditional televisions. The electron beam produces a beam of high energy electrons through which products are passed, usually quite quickly because of the intensity of the beam. The process is quick to run and produces same day sterilisation. Irradiation measurement is taken in kiloGrays (kGy) and is measured by the colour change of dosimeters.

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Gas plasma works by applying a charge to gaseous hydrogen peroxide thereby creating the plasma. The plasma contains destructive free radicals that disrupt cell walls resulting in cell death. By-products of plasma sterilization are primarily water and oxygen meaning there is no need for product aeration or emission controls. This is a low temperature and relatively quick process of sterilisation which lends itself to compatibility with products and components that are unsuited to other technologies. It is however not compatible with paper, cellulose, linen, liquids, oils, powders or biological tissues.

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Ethylene Oxide Gas (EtO) sterilisation works by alkylation of nucleic acids and proteins disrupting an organism’s ability to function and reproduce. The sterilisation process is dependent on several variables, being: temperature, relative humidity, gas concentration and exposure time. These factors can all be varied resulting in a tailored cycle that best suits your products. Widely used in medical device sterilisation, Ethylene Oxide Gas (EtO) is an extremely effective sterilant. It has high penetration properties and is able to sterilise a wide range of materials and configurations.

In recent years Parametric release has transformed the in process time traditionally associated with EtO sterilisation. By monitoring actual process parameters in each sterilisation load, sterility can be assured without the need for Biological Indicators (BIs), removing the 7 day BI incubation time previously required before products could be released

High energy photons are used in Gamma Irradiation to sterilise products. Gamma irradiation is typically produced from Cobalt 60 source that emits radiation in all directions all of the time. Whenever the sterilisation process is not required, the source is normally lowered into a pool of water to safely and harmlessly absorb all of the radiation. When the source is required, it is raised again and products may be passed around the source, typically on a conveyor system. Irradiation measurement is also by dosimeters.

Steam sterilisation, often referred to as moist heat, is normally carried out in an autoclave. Steam normally exists at approximately 100°C and under positive pressure the temperature of steam can be increased to achieve sterilisation in relatively short times. Two commonly used moist heat sterilisation cycles are 121°C for 15 minutes and 134°C for 3 minutes. The temperature and time duration are calculated around D and Z values for specified microorganisms.

The efficacy of a moist heat sterilisation process is typically measured using test vials of Bacillus stearothermophilus, a microorganism renowned for its heat resistance properties. Steam sterilisation is not suitable for products and packaging sensitive to heat and moisture.

This sterilisation process uses a form of radiation using X-ray generators that are more powerful that that used for x-ray imaging in hospitals. Similarly to electron beam sterilisation, X-rays are produced from an accelerator but the x-ray bean is more focussed and penetration into solids is greater than that of electron beams. Of course, there are no residues left on the products and, at typical dose settings in-process temperature increases do not adversely affect the products.

Introduction | Product Design | Matererial Compatibility |
Technology Choice | Validation Review

Sterilisation is the process applied to render products sterile. The state of sterility is an absolute; a product is either sterile or non-sterile. A text book definition of sterility is ‘the absence of viable microorganisms’, however in terms of medical devices, sterility is, in fact, a probability; its so called Sterility Assurance Level or SAL. The requisite SAL for a medical device is 10-6, that is to say a 1 in a 1 million chance of an individual item not being sterile.
The reasons behind this approach involve the inactivation dynamics of sterilisation that work on the principals of logarithmic reductions in microorganism population. Once you reduce a population below 100 (i.e. 1 organism) you enter a realm of probability. A population of 10-3 is equivalent to a 1 in 1000 chance of a surviving microorganism. The origins of the 10-6 SAL are difficult to find, but the general consensus is that it is not based on any great science, moreover that a figure of 10-6, being a 1 in 1 million probability feels like a reassuringly remote chance.
For products intended to be sterile, you will need to consider which sterilisation process will be the most suitable. It is broadly accepted that no single sterilisation technology is capable of sterilising all medical devices.

With a substantial knowledge of sterilisation, especially but not limited to medical devices, our consultants offer independent impartial advice. We can help you identify the most appropriate method of sterilisation for you product. We will consider the most appropriate sterilisation technology for your product based on the materials from which your product is made and the speed of sterilisation processing turn around you require. There are, of course, other factors we consider such as processing costs, product design features and ability to validate the sterilisation process, all of which will have an impact on the final choice of technology for your product. As we are independent we will serve your best interest and provide you with an unbiased choice of sterilisation technology.

If you are currently in the process of designing your medical device product, you should consider your sterilisation options now. By considering the options early on in the design stages the consequences of routine sterilisation can have a much lesser impact on processing costs and product turn around. All too frequently, sterilisation of the product is only considered once the design has been established.
With our in depth knowledge of medical devices and the sterilisation processes, we are able to offer you consultancy at design stage to ensure your medical device can be sterilised effectively, easily and cost effectively. Using one of our consultants on sterilisation at the design stage, it may in the long term prove prudent and pay for itself many times over.

Linked to Product Design and another important factor to consider are the materials that will be used for the product and its packaging. Certain materials are not suitable for particular sterilisation processes, for example some plastics can become discoloured or brittle under radiation technologies (Gamma, Electron Beam and X-ray); steam sterilisation tends to destroy paper maché bowls and heat sensitive items; gas sterilisation (EtO, Gas Plasma and Steam) require packaging to be breathable so foil pouches are unsuitable.
Our consultants can advice you on material compatibility with desired sterilisation technologies and the implications of one technology over another.

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There are a number of different sterilisation technologies available to medical device manufacturers. Some technologies can be carried out either in-house others are more suited to contract sterilisation companies. The technology of choice is largely dependent on the compatibility of the sterilisation technology with the medical device and/or the design of the device. Other considerations include site location, processing costs, duration of the process and toxic residuals. Some of the more common technologies include, Aseptic Fill, Filtration, Dry Heat, Steam, Gas Plasma, Ethylene Oxide Gas, X-ray Radiation, Electron Beam Irradiation and Gamma Irradiation.

If you need independent guidance in selecting the most appropriate technology for your medical device, we have expertise in sterilisation within High Edge Consulting

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All sterilisation technologies require comprehensive validation because sterility of an individual item cannot be verified without rending the product non-sterile. A range of international standards exist that give the requirements for the sterilisation technologies.
ISO 13408 for Aseptic Fill and Filtration
ISO 17665 for Moist Heat
ISO 14937 for general sterilization, applied to the following in the absence of specific standards: Gas Plasma; Dry Heat;
ISO 11135 for Ethylene Oxide
ISO 11137 for Radiation (Gamma, Electron Bream and X-Ray)

Our specialist consultants can lead you through the validation process and give expert guidance on the regulatory requirements and interpretation of results.

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