Correlation of the adhesive properties of cells to N-isopropylacrylamide/N-tert-butylacrylamide copolymer surfaces with changes in surface structure using contact angle measurements, molecular simulations, and Raman spectroscopy

A series of copolymers of N-isopropylacrylamide (NIPAM) and the more hydrophobic comonomer N-tert-butylacrylamide (NTBAM), with increasing NTBAM content (i.e., increasing hydrophobicity) were prepared. The adhesion of human epithelial cells on polymer films prepared from copolymers of NIPAM: NTBAM was observed to increase with increasing polymer hydrophobicity. However, in the absence of serum, cell adhesion to the different surfaces was statistically indistinguishable. Thus, it appears that the copolymer films differentially support cell adhesion due to selective adsorption of proteins from the physiological environment (the serum). Using contact angle measurements, molecular simulations, and Raman spectroscopy to characterize the different surfaces, we show evidence that the different behavior of cells on the films of increasing hydrophobicity is actually due to the different chemical properties of the surfaces with increasing content of NTBAM in the copolymers. As the NTBAM content is increased, the number of NH residues at the surface decreases, due to the additional steric hindrance of the bulkier NTBAM group, which results in decreased hydrogen bonding and thus decreased adsorption of proteins such as albumin. However, in some cases, the adsorption is driven by hydrophobic interactions, and proteins such as fibronectin were found to adsorb more to the films with a higher content of NTBAM. There appears, thus, to be a direct correlation between surface composition, i.e., the functional groups exposed at the surface, and protein binding and subsequent cell adhesion

Comparative production and nutritional value\ud of "sea grapes" — the tropical green seaweeds Caulerpa\ud lentillifera and C. racemosa

"Sea grapes" is a collective term for the edible varieties of the green seaweed genus Caulerpa. Here we conduct comparative analyses of the biomass productivities and biochemical properties of C. lentillifera and C. racemosa from tropical Australia. Commercial-scale production was evaluated using 1 m2 culture units with high stocking densities (>5 kg m−2). Productivity of C. lentillifera in a 6-week period yielded, on average, 2 kg week−1, whereas C. racemosa yielded <0.5 kg week−1. Morphometric comparisons of the harvestable biomass revealed that C. lentillifera had a higher proportion of fronds (edible portions) to horizontal runners (stolons) and a higher density of fronds per unit area. C. racemosa fronds, however, were significantly longer. The nutritional value of C. racemosa was higher than C. lentillifera for both polyunsaturated fatty acids (10.6 vs. 5.3 mg g−1 DW) and pigments (9.4 vs. 4.2 mg g−1 DW). The content of eicosapentaenoic acid (EPA) and β-carotene decreased with increasing frond size in both species. Trace element contents also varied substantially between the species, including higher levels of zinc, magnesium and strontium in C. lentillifera, and higher levels of selenium in C. racemosa. Some less desirable elements were higher in C. lentillifera, including arsenic (1 vs. 0.1 ppm) and cadmium, whereas others were higher in C. racemosa, including lead, copper and vanadium. Overall C. lentillifera has a high biomass production potential in monoculture and distinct nutritional properties that warrant a focus on its commercialisation as a new aquaculture product in tropical Australia and in Southeast Asia more broadly