Plastics

Plastics are a group of materials which are used extensively in biochemistry and molecular biology. Plastics can be defined as non-metallic polymeric materials which can be molded or extruded into a shape. A plastic can be a single polymeric component such as polypropylene, a blend of several polymers or a block copolymer consisting of joined segments of two or more individual polymers such as a block copolymer of polybutadiene and poly(ethylene oxide). The physical properties of a plastic are a combination of the polymeric composition and additives such as plasticizers. Plasticizers are high molecular weight liquids or solids melting a low temperature which are blended with thermoplastic resins such as polyvinyl chloride to change physical properties. Plasticizers including phthalate derivatives such as di(2-ethyl)hexylphthalate, derivatives of organic acids such as di-2-ethylhexyladipate, and polyglycols (polyethylene glycol). Other materials included in the manufacture of plastics include antioxidants, lubricants, stabilizers, and colorants. All of these components can influence the property of the final plastic product. It must be emphasized that the biomedical market for plastics is quite small in volume compared to the overall market. Thus, unless a vendor makes their own raw material, most suppliers to biochemistry and molecular biology purchase bulk product from a large chemical company. As a result there can be batch-to-batch and vendor-to-vendor variation in product. Another issue which confounds the use of plastics is the addition of stabilizers. Stabilizers are chemicals such as hydroxybenzophenones and hydroxyphenylbensotriazoles which are added to prevent damage from ultraviolet irradiation. These compounds do absorb ultraviolet light in the 200-400 nm range and do present problems in biochemical analyses. The careful investigator will assure the source of the plastics used in products such as microplates and incubation flasks (Clinchy, B., Youssefi, M.R., and Håkansson, L., Differences in adsorption of serum proteins and production of IL-1ra by human monocytes incubated in different tissue culture microtiter plates, J.Immunol.Methods 282, 53–61, 2003).