Microbioreactors with microfluidic control

摘要

The majority of screening and process development in biotechnology is performed in microtiter plates (MTP). But fermentations performed in this environment are often not comparable to industrial processes because of the lack of active pH control or substrate feeding. Other setups dealing with controlled microcultures mostly consist of complex and expensive systems, limiting their application for higher throughputs [1-3]. Recent developments in optical sensor technologies provide the possibility of online-monitoring even in the microscale format of a microtiter plate. The BioLector technology, first described by Samorski et al. [4] and available from the company m2p-labs (www.m2plabs. com), is a fiber-optical measurement system for monitoring all relevant culture parameters. Therefore, it is the ideal base for our integration of microfluidic process control into microtiter plates. The individual dispensing of small volumes into each well of a microtiter plate can be carried out by microfluidic devices with integrated valves and pumps. Softlithography is a suitable fabrication technique for the realization of active microfluidic components and has little requirements in laboratory equipment. Polydimethylsiloxane (PDMS), as a material often used in softlithography, fulfils the requirements of good chemical and mechanical durability and optical transparency [5]. Pneumatically actuated microvalves made of PDMS enable small dispensing volumes, short actuation times and high reliability under alternating loads [6-9]. Miniaturized bioreactors have to be convenient and user friendly in order to find acceptance. Therefore, they should be as easy to handle as the widely-used MTPs. In fermentation experiments, MTPs are usually attached to shaker plates by simple clamping devices. The best way of operating our MTP-based system would be the synchronous connection of the pneumatic actuation lines for the microfluidic device and the fixation on the shaker plate in one clamping step. In order not to interfere with the optical measurements, the actuator connections have to be grouped space-saving in compact arrays. This requires the design of special gaskets. They have to be able to withstand the pneumatic pressure and to compensate production tolerances resulting in height variations of the microfluidic devices. In this paper a user-friendly microbioreactor with optical online monitoring and microfluidic control of fermentation processes is presented. This microbioreactor was equipped with specially designed connections between the microfluidic device and the actuator hardware. The performance of the system is finally demonstrated in a fermentation experiment using Escherichia coli.