Artificial teeth : dental biofilm analysis on a chip

Abstract

In this thesis, an "artificial teeth" microfluidic device is developed that provides unprecedented control over the conditions required to simulate the growth of complex dental biofilm. Dental plaque formation is not only a precursor to tooth decay, but also induces more serious systemic health problems such as cardiovascular disease, pre-term labor, and diabetes. Therefore, understanding the conditions promoting colonization and subsequent biofilm development involving complex bacteria coaggregation is particularly important. The requirement of the continuous culture and analysis systems for large quantities of growth media and reagents has pushed the move toward microfluidics - the miniaturization and chip-based control of fluidic operations. Microfluidic oxygenation is necessary to regulate the cellular gas condition of culture medium, especially for mixed population biofilms consisting of both anaerobic and aerobic cell populations. A double-layer gas perfusion network structure fabricated above the cell culture regions is developed for culture oxygenation. Throughout the modeling and analysis of the oxygen transfer in microfluidic oxygenators, design strategies for such devices are proposed for different configurations. Various designs of oxygen-nitrogen mixer networks providing parallel oxygenation with differential or tunable oxygen concentrations are described and verified experimentally to test the corresponding applicability in microbiological culture. The microfluidic "artificial teeth" platform, integrated with the microfluidic oxygenators, functions as an effective and inexpensive analysis tool to dynamically adjust critical growth parameters such as bacteria population, growth medium composition, medium flow rate and dissolved oxygen levels. The first single-chamber "artificial tooth" chip is developed for long-term dental biofilm culture with better medium handling, such as mixing, humidification and automated growth medium replenishment. This device is also compatible with different analysis techniques using optical microscopy in order to determine the biofilm thickness, the ratio between viable and dead cells, and the visualization of spatial distribution of different dental bacteria in the biofilm. Furthermore, the single-chamber design is extended to a device containing up to 128 chambers. This "artificial teeth" chip is developed to achieve high-throughput parallel biofilm culture and analysis with a matrix of different growth conditions that can contribute to the quantitative studies of the physiology of dental biofilms. The artificial teeth device is applied to investigate the response of two key dental bacteria, Streptococci sp. and Fusobacterium nucleatum, in the biofilm under different microenvironments, including their growth under different gas conditions and their adherence properties with different sucrose concentrations. This work demonstrates a successful application of microfluidics to long-term biofilm culture applications.