Compressive properties of yeast cell-loaded Ca-alginate hydrogel layers: Comparison with alginate–CaCO3 microparticle composite gel structures

The mechanical strength of alginate gel layers containing varying amounts of yeast cells was assessed by static uniaxial compression tests and compared to that of gel structures filled with equivalent quantities of inert mineral microparticles. Suitable gelation conditions were first determined by compression experiments on neat gel structures: alginate concentration, 2% w/v; Ca2+ ion concentration of the cross-linking solution, 100 mM; gelation time, 2 h. The presence of yeast cells in alginate disks led to the weakening of the gel structures, this effect increasing with the immobilized-cell content. By contrast, calcium chloride microparticles showing granulometric characteristics similar to those of yeast cells induced gel strengthening. The storage for 3 weeks at 4 °C in phosphate-free buffer induced noticeable weakening of alginate structures, whether filled with yeasts or not. These results are discussed in light of literature data on composite materials, in particular matrix–filler interactions.