Improving bacteria viability in metal oxide hosts via an alginate-based hybrid approach

A two-step process relying on cell encapsulation in alginate beads followed by inorganic gelation from colloidal metal oxides was successfully applied to the immobilization of Escherichia coli bacteria in the presence of boehmite and zirconium oxyhydroxide particles. In the case of the Al-based gel, the alginate bead obtained at low biopolymer content provides an efficient barrier against the encapsulation stress. In contrast, an increase in the alginate concentration together with the phosphate-induced mineralization of the biopolymer bead is found necessary to maintain the viability of entrapped bacteria in Zr-based gels. Diffusion studies using model molecular and colloidal species put in evidence that positively charged Zr-oligomers and ZrO2 nanoparticles may be involved in the cytotoxicity of the precursor solution. This optimization of the encapsulation process allows the first observation of E. coli growth within such metal oxide-alginate hybrid gels. Results presented in this work give a clear evidence that sol-gel based cell encapsulation can now be envisioned within a wide variety of metal oxide hosts through the optimization of the pre-encapsulation environment.