Microfluidic approaches to bacterial biofilm formation

Abstract

Bacterial biofilms-aggregations of bacterial cells and extracellular polymeric substrates (EPS)-are an important subject of research in the fields of biology and medical science. Under aquatic conditions, bacterial cells form biofilms as a mechanism for improving survival and dispersion. In this review, we discuss bacterial biofilm development as a structurally and dynamically complex biological system and propose microfluidic approaches for the study of bacterial biofilms. Biofilms develop through a series of steps as bacteria interact with their environment. Gene expression and environmental conditions, including surface properties, hydrodynamic conditions, quorum sensing signals, and the characteristics of the medium, can have positive or negative influences on bacterial biofilm formation. The influences of each factor and the combined effects of multiple factors may be addressed using microfluidic approaches, which provide a promising means for controlling the hydrodynamic conditions, establishing stable chemical gradients, performing measurement in a high-throughput manner, providing real-time monitoring, and providing in vivo-like in vitro culture devices. An increased understanding of biofilms derived from microfluidic approaches may be relevant to improving our understanding of the contributions of determinants to bacterial biofilm development.

Figure 1

Pseudomonas aeruginosa biofilm development sequence; step 1 initial adhesion of a bacterial cell to a surface; step 2 induce irreversible adhesion by EPS generation; step 3 early structural development; step 4 maturation of the biofilm; step 5 dispersion of cells from the biofilm matrix.

Figure 2

Advantages of microfluidics approach to bacterial biofilm studies. Microfluidics and micro-fabricated platforms have various characteristics as shown in the box that are suitable for biofilm studies. These characteristics allow developing micro-platforms for evaluating the interaction with hydrodynamic environment and bacterial chemotaxis, high throughput biofilm array, real-time monitoring, and in vivo like biological environments.

Figure 3

Microfluidic devices used in the bacterial biofilm studies. (a) Schematic diagram of a microfluidic device used for bacterial biofilm formation. The effects of shear stress were quantified by analyzing the biofilm area in the microfluidic channel [66]; (b) Multi-layer microfluidic device for generating an oxygen gradient. Blue dye was injected into the channel and yellow dye was injected into the chamber. Simulation results modeled the oxygen saturation gradient in the growth chamber [13]; (c) Microfluidic flow cell for high throughput bacterial biofilm studies. The device included a glass coverslip and two PDMS layers. A bacterial biofilm developed in the microfluidic channel upon exposure to the signaling molecules [75]; (d) Model for the co-culture of epithelial cells and bacterial biofilms. A 3D rendering image showed the pneumatically-actuated trapping regions for producing biofilm islands among the epithelial cells. The colored dyes show the different regions of the co-culture device [78].