Diffusion of Nicotinamide Adenine Dinuncleotide in Calcium Alginate Hydrogel Beads Doped with Carbon and Silica Nanotubes

Alginate gel beads doped with nanotubes or nanoparticles were prepared using four kinds of dopants: 
carbon nanotubes (CNTs), silica nanotubes, graphite, or silica nanoparticles (SiO2). The effective diffusion
coefficients (De) of reduced nicotinamide adenine dinuncleotide (NADH) in hybrid gels were calculated
using an unsteady-state model developed by Nguyen and Luong. The maximum De values of NADH in
the four kinds of hybrid gels obey the following sequence:  De (CNTs-alginate) > De (silica nanotubes-alginate) > De (SiO2-alginate) > De (graphite-alginate). The effect of the dopant concentration on De was
examined at five dopant concentration levels (0.3, 0.5, 0.9, and 1.25) g/L. For the CNTs-alginate and
silica nanotubes-alginate gels, the maximum De values of NADH were obtained at 0.3 g/L and 0.9 g/L
dopant concentrations, respectively. For the silica-alginate and graphite-alginate gels, the maximum De
values of NADH were obtained at 0.5 g/L dopant concentration. The maximum De value of NADH in the
CNTs-alginate gel is 50 % larger than the value for the pure alginate gel (De0). Owing to their more
favorable diffusion characteristics, the doped alginate gels could be used as novel and effective immobilizing
carriers for encapsulating biomolecules such as enzymes and cells.