Christine (2017). Use of hydrogel scaffolds to develop an in vitro 3D culture model of human intestinal epithelium. Acta biomaterialia. Copyright and re-use policy

The effects of thermo-mechanical auxetic foam conversion parameters on the Young's modulus and Poisson's ratio of open-cell polyurethane foam are related to changes in chemical bonding and cell structure. Applied volumetric compression, conversion temperature, and duration are reported on foam Young's modulus, Poisson's ratio, and structural stability. Fourier transform infrared spectral analysis on samples converted at and above 160 C strongly indicates a hydrogen bond interaction increase in urea groups (C¼O---H-N) and an increase in hydrogen bonding population. Spectral changes inferred soft segment degradation following extensive heat exposure (200 C, 180 min), specifically a shift and intensity change in CH 2 and C-O-C polyol bands and a broad baseline increase between 3600 and 2400 cm À1 . These changes are linked to (i) resistance to dimensional recovery over time and during re-heating; (ii) Poisson's ratio becoming negative, then zero in tension or marginally positive in compression; (iii) Young's Modulus reducing then increasing; (iv) mass loss, evidenced by thermogravimetric analysis increasing from 150 C. The minimum mean values of Poisson's ratio of %À0.2 (to 10% compression/tension) are comparable to other studies. All samples that retain their imposed compression over time are isotropic, with near constant Young's moduli and Poisson's ratio (to 10% compression/tension).

Cell cultures ofNicotiana tabacum were grown on M & S medium containing 0-2.0 ppm of two auxins. Cellular nicotine was estimated for given auxin concentrations and highest levels determined. Feeding suspensions with amino acids either alone, or in combination with nicotinic acid and nicotinamide produced decresed nicotine levels. The presence of anatabine, anabasine, myosmine, anatalline and nicotelline in the cultures was established and it was noted that precursor feeding which decreased nicotine concentration caused elevated levels of the other alkaloids, notably anatabine.

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