Preparation of Biocompatible Liquid Marbles Stabilized by Food-Grade Stearate Microparticle for Aerobic Bacteria Cultivation.

Liquid marble (LM), a non-stick drop coated with micro- or nano-scale particles, has great potential in a wide range of applications. LMs have an advantageous feature in which gas or vapor can freely transport through their particle shell; therefore, it makes them an ideal candidate to be utilized as microbioreactor containing aerobic microorganisms. In this study, safer and more biocompatible LMs were successfully prepared using a food-grade calcium stearate microparticle as a stabilizer. As the volume of core liquid increased, the height of LM increased and reached a constant value, as a similar trend has been reported in conventional LMs. The drying rate curve of the LMs confirmed that the LMs have a similar pattern with the drying of typical wet powders. The drying rate depended on the salt species in the core solution and the environmental humidity. For instance, in the case of MgCl, by changing humidity from 40 to 80% RH, the lifetime of LMs (time in which the LM dried completely) was increased to about 900 min. This is nearly three times longer than those have no salt and at 40% RH. Model aerobic bacteria Bacillus subtilis has actively proliferated inside the LM during 24-h incubation. Comparing with the test tube cultivations under O-rich stationary or O rich-shaken conditions, the cultivation in the LM system showed a higher proliferation than the test tube systems. As a conclusion, we demonstrated that the calcium stearate LM system would be an ideal candidate for safer and easily available microbioreactor containing aerobic bacteria.