Structural changes of Ca-alginate beads caused by immobilized yeast cell growth

Structural changes of Ca-alginate bead due to yeast cell loading and the impact on their mechanical properties were studied based on experimental data of cell number density per beads, cell rearrangement within the bead surface and core regions, bead average volume and density, bead storage and loss moduli. Structural changes could be explained by (1) mechanical and electrostatic cell-matrix interactions and (2) chemical interactions of the matrix with the components of the nutrition medium which include: wash out of Ca2+ ions by presence of non-gelling ions and by chelating compounds such as phosphate. According to obtained results, it was estimated that: (1) cell-matrix electrostatic interactions within the hydrogel matrix at t=0 induced the bead weakening, (2) wash out of Ca2+ ions by presence of non-gelling ions and by chelating compounds such as phosphate led to the bead weakening (regime 1, t is an element of (left perpendicular0, 2 daysright perpendicular), (3) the bead stiffness remained constant (regime 2, t is an element of (left perpendicular2, 4 daysright perpendicular)) and (4) the bead reinforcement was caused by cell clusters rapid increase and their inter connections within the bead surface region (regime 3, t is an element of (left perpendicular4, 5 daysright perpendicular)). Regulation of the matrix resistance stress and the rate of its change could lead to decrease of the micro-environmental restriction effects and the whole process optimization. (C) 2015 Elsevier B.V. All rights reserved.