Investigation of Ca-alginate hydrogel rheological behaviour in conjunction with immobilized yeast cell growth dynamics

Abstract

The rheological model is developed to elucidate the mechanism of Ca-alginate microbead deformation in the course of cell growth within. It is a complex process influenced by relaxation of the expanded polymer network inside a bead, and forces generated by cell growth inside the bead and interactions between solvent, network parts and cells as well. The resulting effects are measured experimentally by estimating isotropic volumetric deformations of beads with yeast cells as function of time and cell concentration per bead. The mathematical model of the process is developed based on a modified general Zener model with fractional derivatives. It is particularly suitable for incorporating effects of different nature also during different stages of such complex process development. The results of theoretical analyses using the model developed and comparison with experimental values obtained, indicate a high impact of partial decomposition, i.e. plastic response of polymer network inside a bead due to cell growth, on bead deformation. For comparison, corresponding deformation measurements and modelling were performed on the same network system exposed to swelling in the solvent, but without the cells. In this case elastic forces are dominant, indicating different mechanism of relaxation without the influence of cells, in agreement with previous conclusions.

Key Words: :

• Microbead
• yeast
• alginates
• cell growth
• gel deformation mechanism

Acknowledgement

This research was supported by grants from the Ministry of Science and Environmental Protection, Republic of Serbia.

Notes

Notes

 α, the order of fractional differentiation (-); λ, strain (-): φ, volume fraction of cells per microbead (-); η, constitutive parameter Pa s^α; ρ, concentration of cells per microbead (cells/ml); c, mass of water per microbead (g/ml); m, mass of water passed into gel matrix (g); p, component of stress tensor (Pa); V_c, volume of single cell (m³); V_b, volume of microbead (m³); V_eff, effective volume of hydrogel subsystem (m³); V₀, volume of dried gel (m³).