Cell-mediated deposition of porous silica on bacterial biofilms

Living hybrid materials that respond dynamically to their surrounding environment have important applications in bioreactors. Silica based sol-gels represent appealing matrix materials as they form a mesoporous biocompatible glass lattice that allows for nutrient diffusion while firmly encapsulating living cells. Despite progress in sol-gel cellular encapsulation technologies, current techniques typically form bulk materials and are unable to generate regular silica membranes over complex geometries for large-scale applications. We have developed a novel biomimetic encapsulation technique whereby endogenous extracellular matrix molecules facilitate formation of a cell surface specific biomineral layer. In this study, monoculture Pseudomonas aeruginosa and Nitrosomonas europaea biofilms are exposed to silica precursors under different acid conditions. Scanning electron microscopy (SEM) imaging and electron dispersive X-ray (EDX) elemental analysis revealed the presence of a thin silica layer covering the biofilm surface. Cell survival was confirmed 30 min, 30 days, and 90 days after encapsulation using confocal imaging with a membrane integrity assay and physiological flux measurements of oxygen, glucose, and NH 4⁺. No statistical difference in viability, oxygen flux, or substrate flux was observed after encapsulation in silica glass. Shear induced biofilm detachment was assessed using a particle counter. Encapsulation significantly reduced detachment rate of the biofilms for over 30 days. The results of this study indicate that the thin regular silica membrane permits the diffusion of nutrients and cellular products, supporting continued cellular viability after biomineralization. This technique offers a means of controllably encapsulating biofilms over large surfaces and complex geometries. The generic deposition mechanism employed to form the silica matrix can be translated to a wide range of biological material and represents a platform encapsulation technology.