Improving silica matrices for encapsulation of Escherichiacoli using osmoprotectors

Abstract

The development of sol-gel based processes for the encapsulation of living cells is a challenging task where the host material must be optimized both in terms of intrinsic properties and impact on cell viability. Here, the mechanical stability of silica hosts obtained via a mixed aqueous route based on sodium silicate-silica nanoparticle mixtures could be improved by increasing the relative content of molecular precursors over colloidal silica. The specific surface area, pore volume and diffusion properties of the host were also modified. Moreover, this resulted in an increase in the ionic strength, inducing high osmolarity that is detrimental to encapsulated Escherichia coli bacteria. Glycine betaine, a well-known E. coli osmoprotector, could be successfully used as an additive to the sol-gel formulation to limit this osmotic stress. Compared to the previously studied glycerol additive, glycine betaine was found more efficient to preserve the bacterial viability. Moreover, this efficiency was obtained with much lower amounts of glycine betaine, whose addition has therefore no detrimental impact on the silica host structure. These data provide new information about the different cellular stresses resulting from the sol-gel encapsulation process and demonstrate the importance of combining chemical and biological approaches to design more robust functional ''living'' materials.

Engineering of a silica encapsulation platform for hydrocarbon degradation using Pseudomonas sp. NCIB 9816‐4

“…a). These data agreed well with previous reports (Perullini et al, ) showing that inclusion of SNPs in the alkoxide gels negatively impacts the gel mechanical properties.…”

“…The ω = 0.11 gel microstructure was distinctly different with alkoxide aggregates gluing clusters of loosely packed SNPs together. The conclusions of the microstructural analysis was consistent with what was reported previously in similar gels (Mutlu et al, ; Perullini et al, ) and supported the mechanical testing results.…”

The physics and chemistry of silica-in-silicates nanocomposite hydrogels and their phycocompatibility

“…In order to improve the optical properties and mechanical stability of these hosts, extension of the precursor concentration range was proposed but it required the addition of cell-protective agents. 23 However, if the encapsulation of more robust organisms, such as algal cells, is targeted, it should be possible to extend the conditions of preparation, and therefore the range of properties, of these nanocomposites while preserving their cytocompatibility. The here-presented screening of the concentration and pH conditions evidences that among the two precursors, silicates play the most prominent role in the kinetics of gel formation, even though it is introduced at concentrations ca.…”

“…Noticeably, previous reports on silicate:Ludox hydrogels showed that, at a fixed total silica concentration (2.1 M), the Young's modulus slightly decreases as the relative amount of Ludox increases, which was correlated with the increase in the porous volume. 23 The mechanical properties of tetraethoxysilane:Ludox (HS-40) silica hydrogels were also reported, 58 showing that the mechanical stability of the gel increased with increasing alkoxide content at constant particle concentration. Using larger particles, for a given total silica concentration, the elastic modulus of the gel decreased with increasing particle size.…”

“…22 However, for the majority of micro-organisms, a high sodium ion concentration can cause an osmotic shock and dehydration or at least a very significant stress during encapsulation. 23 This issue has been successfully addressed by treating sodium silicate solutions with a cation-exchange resin resulting in a sodium-free precursor source, 24 but the fast gelation kinetics of these solutions do not allow forming gels with a high silica concentration. Alternatively, colloidal gels obtained from silica particles (Ludox s ) have been described 20 but the absence of covalent interactions between these particles can lead to cellular hosts with low stability.…”