Cell Culture
along the underside of the specimen while simulta- neously exposing the topside to a gaseous environ- ment. The chamber accommodates sample dimen- sions of 70mm length, 20mm width and 0.1-2mm thickness. The company’s GrowthWorks Software and Controller runs on a Windows® laptop and can operate up to four mechanical stimulators. The entire system is designed to fit within a standard laboratory incubator and the chambers can be autoclaved. Founded in 1990 with the charter of becoming a world-class provider of instruments for the biomedical community, Tissue Growth Technologies has introduced bioreactors for ten- dons, ligaments, cartilage, bone, blood vessels, heart valves and other 3D tissue types (Figure 25).
Discussion Table 1 attempts to summarise the main features of the 3D cell culture offerings that vendors submit- ted for inclusion in this review. Although this list does not represent all available offerings, it is fair- ly representative of what is currently commercially obtainable to support 3D cell culture. The majority of these developments utilise some sort of biomimetic scaffold (eg hydrogel or colla- gen) (3D Biotek, BellBrook Labs, CellASIC, ECACC, Global Cell Solutions, Glycosan, Hamilton, QGel, The Automation Partnership). It is generally accepted that biomimetic scaffolds offer a better prospect to culture specific cell types and to investigate different aspects of the cell- matrix interaction in 3D. Several trends are evi- dent in this respect to biomimetic scaffolds: 1) the move to using synthetically derived materials to minimise the previously poor reproducibility between batches and the resulting lack of consis- tency between cultures (especially primary cells) (QGel); 2) the ability to design scaffold environ- ments so cells respond in a physiologically rele- vant manner, eg stem cells are thought to do bet- ter in gels rich in hyaluronic acid (ECACC, Global Cell Solutions, Glycosan); and 3) the development of biodegradable scaffolds, particularly to support applications in tissue engineering and stem cell research (3D Biotek, Glycosan). As 3D cell culture emerges in popularity, a key need for researchers in these areas is to gently and rapidly recover encapsulated cells from scaffolds for nucleic acid and protein extraction.
Apart from the biomimetic scaffolds there are what we have called in Table 1 3D structural scaf- folds. Most of these are made from the same mate- rial as 2D plate surfaces (ie polystyrene), but offer additional 3D microstructure directly on the 2D surface, or are produced separately and mounted
Drug Discovery World Summer 2010
on to a 2D surface or supplied as an insert to a 2D culture vessel to create a 3D structurally matrix (3D Biotek, Kuraray, Reinnervate, Synthecon). All provide cells with a microspace to form 3D struc- ture and demonstrate enhanced functional activity compared to cells grown under identical conditions on 2D culture plastic. Being for the most part inert polystyrene structural scaffolds are non-biodegrad- able, but are compatible with most routine (easy) 2D assays and have optically clarity allowing researchers to monitor 3D cell growth by simply using an inverted light microscope. The uniformity of the 3D matrix does however vary; where they are micro-fabricated directly on to the 2D surface they are usually highly uniform repetitive patterns. Where they are fabricated as an emulsion-templat- ed polystyrene scaffold which is subsequently mounted on to a 2D surface the architecture is slightly less regular, but is highly porous and con- sists of voids linked to one another by pores. We also report on several microfluidic devices (BellBrook Labs, CellAASIC) that have moulded microchannels contained within a microplate for- mat for ease of handling and automation. These offerings incorporate a biomimetic scaffold (gel) and are structured to enable fluidic flow or long term perfusion of cells and to facilitate high quali- ty cell imaging in a 3D environment. Currently they are optimised to quite specific 3D applications (eg invasion assay profiling) or to support specific tumour cell models.
Only three platforms that directly support the automation of 3D cell culture and/or tissue cre- ation were reported in the vendor’s snapshots. Awareness of these platforms was not particular- ly high among HTStec’s survey participants, although since all are relatively new approaches, this is not surprising. The development of micro- carriers (magnetic, spherical, pipettable sub- strates) (Global Cell Solutions) and the associated relatively small scale automation of 3D cell cul- ture on these microcarriers (Hamilton Company) represents a major advance in manipulating, cul- turing and even cryopreservation of cells, howev- er the suitability of these microcarriers to a sig- nificant proportion of cell and tumour lines used for screening is in doubt1. Nevertheless the sim- plification to the work flow of cell-based screen- ing made possible by such a format has triggered additional investigations, particularly with respect to undertaking bioassays directly on microcarriers (Biotek). An alternative approach that has yielded some success in recreating 3D embryonic, tumour and primary tissues in vitro is hanging drop scaffold-free culture. The advent of
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