Structural and mechanical anisotropy in rheotactically aligned bacterial cellulose

Abstract

In this work, we demonstrate the preparation of oriented bacterial cellulose from Komagataeibacter sucrofermentans by rheotactic growth in a simple and adaptable setup. The resulting materials were assessed by their yields, geometric densities, and by X-ray diffraction, scanning electron and optical microscopy, and mechanical testing. They exhibited large differences in toughness, resulting from differences in fracture strain or highly anisotropic strengths. Their growth characteristics, structural and mechanical anisotropies and crystalline phase characteristics are discussed and compared to statically grown references and to instances from the literature. Here, we consider the length scales of structural anisotropy in native bacterial cellulose pellicles, and the origin of mechanical anisotropy. Further, we identify a tentative limit on achievable structural alignment in bacterial cellulose, as well as a correlation between crystallinity and disorder in the crystalline phase of bacterial cellulose.

Threedimensionally patterned, hierarchically and anisotropically structured bacterial cellulose

“…In earlier works, we observed preferred orientation of fibers on the nanometer scale in compact BC films [9] and the formation of superstructural patterns on the centimeter scale in BC strands [10] when grown under flowing nutrient medium, which we termed rheotactic growth. In both cases, shear flow-inducing obstacles were used as anchoring points for the forming BC.…”

“…Sample growth 2.1.1. Microbial strains and chemicals We used the same microbial strain, consumables and pre-culturing method as described in an earlier work [9]. These were, for all experiments, the non-motile [15] Komagataeibacter sucrofermentans (DSM-15973, German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany) and agar, yeast extract, disodium hydrogen phosphate, citric acid, ethanol absolut (VWR, Darmstadt, Germany), D-(+)-Sucrose, chloramphenicol, peptone from meat (Carl Roth, Karlsruhe, Germany) and sodium hydroxide (Acros Organics, Geel, Belgium).…”

“…From these, we prepared the medium of Hestrin and Schramm [16], composed of deionized water with 0.5 cg/g peptone, 0.5 cg/g yeast extract, 0.27 cg/g disodium hydrogen phosphate and 0.12 cg/g citric acid, adjusted to an initial of pH 6.5 with 1 M NaOH. 2 cg/g autoclaved sucrose was used as the carbon source, as opposed to the sterile-filtered sucrose used earlier [9].…”

“…In both cases, shear flow-inducing obstacles were used as anchoring points for the forming BC. In the compact BC films, we observed considerable changes to the directional mechanical properties, arguably most importantly to the work of fracture, which increased by almost a full order of magnitude from isotropic to anisotropic BC films of similar densities [9].…”

“…There are numerous reports in the literature on the preparation and properties of aligned BC films, as compiled in an earlier work [9]. However, those studies known to us and concerned with preparing 3D patterned BC structures have not aimed at achieving -and therefore not reported on the presence of-an overall structural alignment [3,4,14].…”