Alginate-chitosan-alginate (ACA) microcapsules have been widely studied as devices for the immuno-isolation and transplantation of living cells.However, long-term survival of the micro-encapsulated cell grafts and thus their potential clinical applications are hampered by the pericapsular fibrotic overgrowth induced by adsorbed protein.In this study, the adsorption behavior of plasma fibrinogen (Fgn) onto ACA microcapsules was studied by using the batch technique.The results showed that the equilibrium time for the adsorption was 24 h.The adsorption of Fgn onto ACA microcapsules fitted very well with Freundlich isotherm, which was indicative of multilayer adsorption.The kinetic experimental data correlated well with the second-order kinetic model,indicating that chemical sorption was the rate-limiting step.The effects of pH and ionic strength on the adsorption were also studied to interpret the mechanism of adsorption.It was found that the amount of adsorbed Fgn decreased with increasing pH in the range of 4.9—7.4.At pH 7.4, the amount of adsorbed Fgn increased with increasing NaCl concentration, and then decreased with further increase in NaCl concentration.At pH 6.0, the amount of adsorbed Fgn decreased with increasing NaCl concentration, indicating that electrostatic interaction was one of the main interactions between Fgn and ACA microcapsules and the positively charged chitosans which was not sufficiently neutralized on the surface of microcapsules induced the adsorption.
In this paper,calcium alginate gel beads were prepared through a homemade microcapsule preparation system with multi-nozzles under forced high-voltage electrostatic field.The effect of operation parameters on the large-scale preparation of gel beads was analyzed.The results showed that the air pressure of feed was the decisive factor affecting the size and yield of gel beads,and the size distribution was dependent on several factors including the distribution of electric field,pulse potential,air pressure of feed,pulse frequency,pulse width and threshold potential.The gel beads with good sphericity,smooth surface and low dispersivity(CV<20%)can be prepared by adjusting and optimizing above parameters.It is more important that the yield of gel beads by the microcapsule preparation system is 20—40 folds higher than the traditional electrostatic droplet generator,which makes it possible to realize the large-scale preparation of gel beads.
