Bacteria Viability in Sol−Gel Materials Revisited:  Cryo-SEM as a Suitable Tool To Study the Structural Integrity of Encapsulated Bacteria

Abstract

Biocompatibility is an important issue that still needs research if one desires to fully preserve the metabolic activity of cells encapsulated in any type of material. Spectroscopic techniques (e.g., NMR and fluorescence) have been used to study the viability decrease upon aging time of bacteria encapsulated in silica gel materials. Unfortunately, none of these spectroscopic techniques are able to provide insights about the detrimental causes affecting the viability of encapsulated cells. The current work uses cryo-scanning electron microscopy (cryo-SEM) for the in situ study of hydrated biocomposites, given its ability for mapping the water distribution within the host matrix. Cryo-SEM is accompanied by fluorescence experiments which allow correlating the metabolic activity of the cells with their structural integrity. The combination of these techniques provides useful information for the design of new biocomposites where encapsulated bacteria preserve their structural integrity and, thus, are viable for periods of time in a range similar to those found for bacteria suspended in buffered solutions.

An Introduction to Bio‐nanohybrid Materials

“…In order to overcome this drawback, the authors explored other possibilities such as the incorporation of glycerol in the silica matrix to increase bacteria viability ( Figure 1.4C), leading to almost 50 % of viable bacteria after one month of ageing [63], or the addition of quorum sensing molecules involved in intercellular communication, which increase the cells viability to 100 % after one month [64]. Similar results have been achieved recently by Ferrer et al [65], who showed that gluconolactone-bearing organopolysiloxane matrices are more efficient than pure silica in extending E. coli the cells viability due to their increased biocompatibility (Figure 1.4D).…”

Hybrid and biohybrid silicate based materials: molecular vs. block-assembling bottom–up processes

“…Organopolysiloxane precursors bearing biocompatible groups such as gluconolactone seem also helpful for this purpose, producing a biocompatible matrix. 330 The aim of all these approaches is to produce robust biohybrid materials in which the viability of cells is guaranteed, showing a long-term stability. These properties are of major importance for the diverse areas of application.…”

Advances in Biomimetic and Nanostructured Biohybrid Materials

“…[77] The increased biocompatibility of gluconolactone-bearing organopolysiloxane matrices is more efficient than pure silica in extending the cell viability of Escherichia coli. [78] Alcohol added or released during the hydrolysis process of alkoxysilanes, the usually employed acid or base catalysts in sol-gel routes, as well as the excess sodium concentration and the high value of ionic strength as a result of the use of sodium silicate, can be harmful for most of biologicals. To overcome these drawbacks, alcohol-and catalyst-free routes that make use of a water-soluble ethylene glycol-containing precursor such as tetrakis(2-hydroxyethyl)orthosilicate (THEOS) [17c] or even the commonly employed alkoxysilanes (tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS), etc.)…”