Silicon alkoxide cross-linked silica nanoparticle gels for encapsulation of bacterial biocatalysts

Abstract

A method is developed for encapsulation of bacterial biocatalysts in silica gels formed by silica nanoparticles (SNP) and a silicon alkoxide crosslinker. Formulation of the gel was optimized by changing the SNP size, SNP to crosslinker ratio and crosslinker functionality. Hydrolysis and condensation reactions of silicon alkoxide were controlled by water to alkoxide ratio (r) and pH of the solution. FTIR analysis verified that a reactive and temporally stable silicon alkoxide crosslinker was obtained. As a case study, recombinant Escherichia coli (E. coli) cells expressing the atrazine dechlorinating enzyme AtzA were encapsulated. Synthesized catalytic biomaterials (silica gel encapsulated bacterial biocatalysts) were evaluated based on their gelation time, biocatalytic activity and mechanical strength. Diffusivity assays and SEM were used for characterization of the gel structure. We found that SNP to crosslinker ratio affected all the features of the gel, whereas crosslinker functionality primarily affected the gelation time and SNP size affected the mechanical strength and diffusivity. Based on systematic evaluation, we selected three gel formulations and subjected them to long-term activity measurements in a continuous-flow bioreactor for removing trace levels of atrazine. The effluent atrazine concentration was sustained below 30% of the influent concentration, <3 ppb, for 2 months.

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

“…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.…”

Bacterial Cyanuric Acid Hydrolase for Water Treatment

“…This increase was attenuated when using cells encapsulated into silica gels (Fig. 2B), due to the diffusion limitation imposed by the silica gel matrix (13,18). This limitation also causes an order-of-magnitude difference between the activity rates of suspended and encapsulated cells (compare Fig.…”

“…Cells were encapsulated as hemispherical silica beads (1.0 to 1.5 mm in diameter) in molds as previously described (18). A 6.6-g quantity of the beads was placed in the bioreactors.…”

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

“…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.…”

“…However, it was observed that small variations in the protocol could have a large impact on the hydrogel structure and therefore on its chemical and mechanical stability, as well as on its optical properties. 30 While successful results have been recently obtained by substituting silicates with silicon alkoxides, 31 most research in this area turned towards the design of (nano)biocomposite hosts, in which biological molecules such as phospholipids 32,33 or polysaccharides 34,35 were used not only to provide a more cytocompatible environment to the cells but also as the template to control the internal structure and morphology of the hosts. Nanocomposites associating silica nanoparticles with organic polymers with promising mechanical properties were also described but their use for cell encapsulation was not reported so far.…”