Stearate Liquid Marbles for Bacterial Cellulose Production: Influence of the Liquid Marble Interface on Bacterial Cellulose Properties

Abstract

We report aerobic bacteria culture performed in liquid marbles (LMs) for bacterial cellulose (BC) production. LMs are droplets stabilized by coating an aqueous solution with hydrophobic particles, which allow vapor and gas transfer through the liquid core−hydrophobic particle interface. We used safe foodgrade stearate microparticles for LM formation. An LM containing an aerobic acetic acid bacterium, Komagataeibacter xylinus (K. xylinus), which produces BC, was successfully prepared by dropping a culture medium solution inoculated with the bacteria onto a calcium stearate powder layer and rolling it to full coverage by calcium stearate microparticles. After the LMs containing the cells were statically cultured, the core solution became a hydrogel due to the production of BC by the cells. The obtained hydrogel (LM−BC gel) had a higher water holding capacity than that prepared by using a conventional test tube or Erlenmeyer flask. Scanning electron microscopy (SEM) observations showed that the BC fibers on the surface of the LM−BC gel were thicker than those prepared in conventional systems and formed a network structure with large holes, which was different from the conventional BC structure. We found that the BC prepared in LMs had the characteristic structure only on the outer surface of the gel. Considering that the bacterium movement is driven by the inverse force of the secretion of cellulose fibers, we found that the cells in the vicinity of the LM interface moved differently compared to that in conventional culture systems. The amount of BC produced per LM was linearly proportional to the core volume of the LM. In addition, changing the core volume significantly affected the surface area to volume ratio (A/V), whereas it did not affect the amount of BC produced per culture medium volume. Thus, the stearate LM system allows the production of BC by aerobic acetic acid bacteria, and the LM interface plays a critical role in the produced BC properties.

pH-Responsive Liquid Marbles Stabilized with Chitosan-Stearic Acid-Conjugated Particles

“…LMs that can be disrupted by external stimuli have attracted considerable interest because of their wide range of applications, such as in miniature reactors, − carriers for substances, − pressure-sensitive adhesives, and microsensors. − Herein, the “pH-responsive” character of LMs stabilized with CS-SA particles was investigated. The LMs remained intact after transfer from the particle bed to the glass substrate.…”

“…Due to the particulate shell, the LMs move freely on the air–liquid and air–solid interfaces in an amphibious manner without leakage of the inner liquid. Various kinds of solid particles, including organic, inorganic, and hybrid particles, which repel liquid droplets, have been utilized as LM stabilizers. − Due to the facile designability of synthetic particles, functional LMs have been developed, and their movements, shapes, structures, and stabilities can be controlled on demand with external stimuli such as pH, temperature, light, electric field, and organic solvents. ,, The stimulus responses have made LMs attractive for use in a wide range of applications, such as miniature reactors, − microcentrifuges, microfluidics, carriers for substances, − pressure-sensitive adhesives, and microsensors. − Considering sustainable material chemistry based on sustainable development goals, solid particles derived from nature will be important LM stabilizers. However, studies on LMs stabilized by solid particles derived from nature have been limited at this stage and are still challenging research topics. ,− …”

Biofabrication with microbial cellulose: from bioadaptive designs to living materials

“…Notably, BNC grown in liquid marbles exhibited a distinct morphology compared to planar BNC films: the BNC shells of liquid marbles were thicker, possessed larger pores, and exhibited higher water-holding capacity. [134][135][136] The presence of nanoparticles at the liquid marble surface hindered bacterial mobility during cultivation and disrupted the oxygen gradient near the droplet surface. 137 This phenomenon resulted in less uniform cell movement during biofabrication, potentially BNC capsules can serve as biocompatible and biobased coatings to encapsulate given cargos such as chitosan, gold nanoparticles (Fig.…”

“…141,142 Thus, future research should consider bio-based nanoparticles, This journal is © The Royal Society of Chemistry 2024 such as hydrophobized cellulose powder, 143,144 lycopodium grains, 145 or calcium stearate. 134 Lastly, there is still a lack of understanding of bacteria-nanoparticle interactions at the interfaces. Current approaches suggest a complete removal of the encapsulating particles; 16,134 however, future applications should target the incorporation of multifunctional nanoparticles within the BNC shell during biofabrication, which is anticipated to add values to the final biocomposites.…”

Photo- and Thermoresponsive Liquid Marbles Based on Fatty Acid as Phase Change Material Coated by Polypyrrole: From Design to Applications

“…A wide variety of synthetic and natural solid particles, whose surfaces are sufficiently hydrophobic, have been applied as an LM stabilizer. − In the last decade, we witnessed development of LMs stimulus-responsive to temperature, pH, light, ultrasonic waves, and magnetic and electric fields, which can change their shape, stability, and movement . The stimulus-responsive characters have made the LMs attractive in a wide range of applications such as miniature reactors, − microsensors, − microcentrifuges, microfluidics, carriers for substances, − and pressure-sensitive adhesives . Development of dual stimuli-responsive LMs is a growing important research topic because there are some applications that require an independent response from a separate stimulus. ,, Disruption of the LMs triggered by external stimulus has gained significant interest among the types of stimulus-responsive modes due to capability of on-demand release of inner content. , By now, disruptions of the LMs have been induced by application of external stimuli, which can change the hydrophilicity–hydrophobicity balance of the particulate stabilizer from hydrophobic to hydrophilic ,, or can change the phase of the stabilizer from solid to liquid .…”