Sterilization Methods for Microplates
Typical molding temperatures for polypropylene microplates are 450°F or greater and most post-molding and packaging operations occur under ISO quality standards in certified clean rooms. Nevertheless, if you are doing everything known to man to support biological growth or replication in your experiments, you would want to start out with sterile materials.
Sterile labeling indicates that the final packaged products have been surveyed and validated to be below 10-6 chance of contamination. Lot to lot monitoring and certification of sterility is expensive and adds considerable costs to the delivered product.
Sterility may be achieved by several treatment methods. There are recommendations for each treatment type to achieve the 10-6 specification. In order to reduce the final product price, many accept treatment application certification to infer the status of sterile without additional testing and documentation. Individual product packaging includes a treatment sensitive tag that visibly confirms treatment completion. The following are the most common treatments to achieve sterilization of polypropylene microplates:
- Gamma irradiation – typical 15-40kGy (ANSI/AAMI/ISO 11137-1994)
- E-beam irradiation – typical 15-40kGy (ANSI/AAMI/ISO 11137-1994)
- High pressure steam (autoclave) – 121°C (250°F), 20min, 15psi (1.03 bar); longer time frames permit lower temperatures and pressures (ISO 17665-1:2006)
- Ethylene oxide gas – (ISO 11135-1:2007)
Indicators on the packaging confirm that the products have completed the specified treatments.
1. Gamma Irradiation
Gamma irradiation has been the standard approach for sterilizing microplates. However, polypropylene is, relative to most other polymers, sensitive to gamma rays. Polypropylene can become brittle and discolored over time after treatment; thus, the products are commonly labeled with an expiration date. While additives have been developed to increase tolerance to these effects, the presence of additional chemical species within the polymer is a risk that must be evaluated.
2. E-beam Irradiation
E-beam technology is similar to gamma irradiation in most respects and is gaining in popularity due to reduced effects noted with gamma exposure and to a reduced processing time that translates into reduced costs and lower prices. Access to electron accelerators is currently limited, but is likely to become more available as demand increases.
3. High-Pressure Steam
Steam, generated in an autoclave, requires unsealed products during processing, thus they are more suited for end-user implementation rather than by the manufacturer/packager. In addition, the heating process can cause minor changes in dimensions that may render the product problematic for use in automation equipment.
4. Ethylene Oxide Gas
Ethylene oxide may be applied to products sealed in gas permeable packaging. It is most commonly employed for products that cannot withstand other sterilizing techniques. However, the toxic and flammable/explosive characteristics of the gas often limit a cost-effective application. In addition, the approach is prone to persistent residuals that could influence experimental results.
Typically, manufacturers of microplates and other plastic labware send their products to an off-site facility for irradiation treatments. Individual product packaging and scheduled shipping to and from the irradiation facility add to the total product price and influence delivery timelines. Blanket ordering of such products optimizes the balance between product availability and the additional warehousing costs which are passed on to the customer.
Seahorse Microplates offers individually sealed and indicator labeled gamma irradiated treatment of any product in the catalog with a minimum order. See the New Products page for the introduction of five irradiated standard products for immediate delivery in case lots. For an overview of all of the Seahorse Microplates capabilities, download the Optimized Microplate Solutions brochure.