Three-dimensional (3D) printing is advantageous over conventional technologies for the fabrication of sophisticated structures such as 3D micro-channels for future applications in tissue engineering and drug screening. We aimed to apply this technology to cell-based assays using polydimethylsiloxane (PDMS), the most commonly used material for fabrication of micro-channels used for cell culture experiments. Useful properties of PDMS include biocompatibility, gas permeability and transparency. We developed a simple and robust protocol to generate PDMS-based devices using a soft lithography mold produced by 3D printing. 3D chemical gradients were then generated to stimulate cells confined to a micro-channel. We demonstrate that concentration gradients of growth factors, important regulators of cell/tissue functions in vivo, influence the survival and growth of human embryonic stem cells. Thus, this approach for generation of 3D concentration gradients could have strong implications for tissue engineering and drug screening.
The Taft steric, E,, and the Hancock corrected steric, Ea°, constants of a set of various alkyl-and heteroatomsubstituted groups were analyzed as to whether they are separable into components. The analyses were carried (1) R.
When the relative hydrogen-bonding effect of drugs on phases involved in the binding at the site of biological action differs from that in the 1-octanol-H2O partitioning phases used as the reference to estimate the hydrophobicity, a parameter (or parameters) which represents the "extra" hydrogen-bonding effect on the biological activity is required in the Hansch-type correlations. As a first approximation, the effect is analyzed in terms of the ratio of hydrogen-bonding association constants and the ratio of molarities of hydrogen-bonding species constituting the biological and organic phases. Sometimes, the association constants in both phases are so similar that they are not important in determining the extra hydrogen-bonding effect. The net result is that the effect is expressible by an indicator variable term the slope of which corresponds to the molarity ratio. The variable only applies to substituents having appreciable association capability in correlating a certain biological action exhibited by a series of congeners.
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