With growing interest in leveraging in vitro models to reduce costs, increase throughput, and minimize ethical concerns throughout the early stages of drug discovery and development, microplates utilized in in vitro assays have become increasingly specialized. But, with the wide variety of microplate types on the market today, plate choice can be a daunting decision when setting up any new assay. Many considerations need to be taken into account such as culture approach (if any), throughput requirements, and analytical needs. Below we summarize a few of these considerations.
If an in vitro assay requires extended cell culture (rather than a simple “plate and read” approach), microplate surface treatment becomes a crucial factor. For example, standard culture of adherent cells typically requires treatment of the plate surface to enhance cell adhesion and thus facilitate cell survival. Most commonly, oxygen plasma treatment (as in “tissue-culture (TC) treated” polystyrene) is utilized to render a surface more hydrophilic, though other commonly implemented surface treatments include collagen or poly-L-lysine for more specialized applications. Alternatively, if the cell type of interest is typically cultured in a suspension format or if spheroids are to be formed, tissue culture plastics may be left untreated or even coated with a polymer that deters cell adhesion. For example, at Visikol, we often utilize Corning’s Ultra-Low Attachment Treated Spheroid Microplates, which feature a noncytotoxic, biologically inert, thin, bonded hydrogel coating that acts to prevent cell attachment to the plate and thus facilitate cell aggregation into a spheroidal configuration.
Additionally, well shape can play an important role in cell culture approaches. For spheroid aggregation or suspension cell culture, U-bottom plates are often choice, whereas adherent cell growth is best facilitated in flat bottom plates. U- or V- bottom plates can also be valuable when an application requires many media exchanges wherein centrifuging a sample facilitates removal of supernatant without disruption of the cell population.
Regardless of surface treatment or well shape, when live cells are to be plated, one should always consider culture plastics that have been sterilized via gamma-irradiation or other validated protocol.
In most in vitro screening applications, plate formats featuring at least 96 wells are typically required (in order ensure adequate wells for replicates, control groups, treatment conditions, and buffer wells to manage media evaporation), but smaller and larger formats are indeed available. However, while larger 384 well plates are manageable with minimal automation, 1,536 or more numerous well plates require pipetting robots or other aids to ensure accuracy of small-volume liquid handling.
Depending on the analysis approach, a number of other microplate features must be considered. For example, black- or white-walled plates can be used to absorb excitation signal or maximize signal reflectance in fluorescence- and luminescence-based assays, respectively. Many plates can be purchased with either colored walls or colored walls and bottoms, so it’s important to choose the correct format for your analytical system configuration (i.e. for top-read plate readers, colored bottoms may be preferable, whereas bottom-read plate readers and imagers require transparent bottoms).
In addition to plate color, well shape can have a profound influence on the quality of your results. For example, many imaging systems, particularly those with LED excitation sources are not well suited for imaging in U-bottom plates (though laser-based systems are much more amenable to U-bottom imaging). Where this limitation exists, if a U-bottom plate is required for culture purposes, samples can always be transferred to thin, flat-bottom plates to facilitate the highest-quality images, though this process dramatically reduces throughput.