In vitro, defined

It has been pointed out (Lehninger, 1950 Vallee, 1951 Williams, 1953) that the activating effect of a metal upon an enzyme in vitro defines neither its structural association with the enzyme nor the physiological function of the metal. It is virtually impossible to assign any functional meaning to many of these observations, which may be of passing interest only. 

Cells cultured on the surfaces of hydrogels may be useful as an in vitro defined culture system to investigate the physiology and pathophysiology of both cells and tissues. The two-dimensional culture system, however, does not provide a microenvironment close to that in vivo and therefore may not represent an accurate model. The main drawbacks of the two-dimensional culture hydrogel system are the insufficient regulation of 3D architecture and the variations in biochemical cues from those of the in vivo environment, which may alter metabolism and reduce the functionalities of cells (Lutolf et al., 2009 Tibbitt and Anseth, 2009). 

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See also in sourсe #XX -- [ ]

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