The breakdown of the sterilization industry is generally agreed to be roughly 52% ethylene oxide (EtO) gas, 36% gamma radiation, and 7% electron beam (e-beam) radiation. The remaining 5% are various modalities like steam, hydrogen peroxide, gas plasma, nitrogen dioxide (NO2), peracetic acid (PAA) and some others. In total, there are only about 25 known sterilization methods.

Gaseous sterilization

EtO, the most popular method, is growing slightly because it’s the most material-friendly. As devices get more complex (e.g. combination products, custom kits, others), they may be made of multiple materials, some of which may not be compatible with radiation. EtO can also be used in some instances where products contain computer chips, as it will not affect their performance as radiation processing might. One of its main drawbacks is its long turnaround time compared to radiation processing. But with the advent of techniques such as combining All-In-One processing with parametric release, the turnaround time rivals that of radiation sterilization.

Moist heat (steam) sterilization is arguably the best method, because it’s the least expensive, requires the lowest capital investment, is non-toxic to workers, leaves no residue, and is the fastest technique. However, due to the high temperatures required, many materials can’t tolerate steam sterilization.

Peracetic acid can be done at room temperature, which confers advantages for temperature-sensitive products. It’s a vapor formed by the reaction of acetic acid and hydrogen peroxide, with the addition of a catalyst. The compounds exist in equilibrium; once it decomposes, the byproducts are oxygen, carbon dioxide, and water. During sterilization the vapor interacts with bacteria’s cellular constituents, breaking them down and inactivating routine functionality. The vapor process is effective against all types of microorganisms.

Nitrogen dioxide is another option that’s gaining popularity. This rapid, room-temperature process can be performed without deep vacuum, so that it does not readily penetrate container closure systems and device materials. It can also be performed in-house, for increased efficiency and cost savings.

Radiation sterilization

In the radiation arena you have three options: Gamma, E-beam, and X-ray. All of these methods can be performed with relatively quick turnaround. One of the biggest factors to be addressed with this modality is material compatibility. Some materials can discolor, cross-link, become brittle, increase durometer, etc.

Gamma processing has great penetration and most products that are radiation-compatible can be effectively processed using this method. The typical turnaround time for gamma processing may be a bit longer than the other two radiation methods, because the sterilization facility typically waits on other products with similar dose ranges so they can all be processed at the same time. There is some concern in the marketplace about the diminishing supply and resultant rising cost of the cobalt used as the radioactive source for this methodology. In some instances, this may be causing companies to consider alternate radiation technologies, or perhaps gaseous sterilization.

E-beam, although a smaller overall market share than gamma, is the fastest-growing of the radiation processing methodologies on a percentage basis. It has some advantages because its source of energy is electricity and, in contrast to gamma, the radiation source can be turned off when it’s not being used. E-beam has the quickest turnaround time of all of the radiation methodologies as it can process each product in seconds. Because of the short exposure time, this technology may provide less radiation degradation to the materials being processed. In addition, dose rates can be rapidly adjusted for varying products, which also helps provide a quicker turnaround time. The limitation with this process is the density of the load, as some products may not lend themselves to E-beam processing.

Among the three radiation processes, X-ray may be the best. It has a slightly greater penetration potential than gamma and the variability in dose range across the load is generally lower. Because of the superior penetration, processing may often be performed by the pallet, which saves time and labor costs. For niche-market, temperature-sensitive products, X-ray also typically has the lowest heat production, which gives it the edge for those types of products. Despite the advantages of X-ray over the other radiation methodologies, the number one drawback at this time is economics: This method is more costly than the other two methods. As evidence of this, there is currently only one contract sterilizer doing this type of processing for medical devices, with a second due to come on-line sometime this year.

Going in-house

There is an increasing trend of companies taking sterilization in-house, both in OEM and contract manufacturing. The biggest decision point is the overall economics and how large a role sterilization plays in the final cost of the product. Other important factors that play into the decision to move this process in-house include quality, turnaround time, lower inventory, customer service, etc. It is important to note that several other factors need to be carefully assessed before making the move. Some factors to consider include safety, building space for the process, in-house expertise, and liability, just to name a few.

With this in mind, the easiest of the primary method to bring in-house is EtO (not including steam sterilization, which is and always has been primarily in-house), with the next-easiest being E-beam. Although it would be possible for a company to bring in gamma or X-ray processing, it would be uncommon for a company to do so, due to the large capital investment cost. According to some manufactures, what makes sense is to do the sterilization in-house when that’s the best choice, and use contract sterilization where it has distinct advantages.

Which method of sterilization should I use?

That ‘s the big question. Fortunately, when you boil it down to its essence, it’s actually quite easy to answer. There are only one or two questions that need to be asked and answered, and then the decision should be straightforward.

What method(s) will work to sterilize my product in a safe and effective manner? Often the answer to that question dictates the method, as one may only be able to use EtO (or another gaseous niche method) or radiation. If the product is designed with sterilization in mind and can be processed with either a gaseous or radiation method, the second question comes into play.

What methods will sterilize my product in the most cost effective manner? This is a bit more complex, as it needs to take into account things such as product and packaging materials and design, cost of the sterilization equipment and upkeep of that equipment, product transportation, sterilization indicator system, validation and re-qualification costs, routine sterilization costs, turnaround time, etc.

Once these questions are properly and thoughtfully answered, the decision as to the sterilization methodology, and whether to do this processing at a contract sterilization organization or in-house, should become self-evident.