Abstract
Microorganisms are typically grown in a culture dish or a tube, an isolated environment does not allow mass transfer and therefore significantly limits their growth. The accumulation of metabolites in the culture can also exert feedback regulation and reduce the final yields of the desired product. Current commercially available bioreactors can overcome these problems by providing efficient mass transfer mechanisms, although generally the instrumentation of the systems is sophisticate and the required medium volume is large. This study aims to develop a microscale bacterial culture system with a capability of continuous nutrient supply and waste removal. The photoresponsive hydrgel poly-ethylene glycol diacrylate (PEG-DA) was employed in fabricating the bioreactor because it is biocompatible, meshed and permselective, and can be made into microstructure conveniently through photopatterning techniques. This study first investigates the swelling ratio of PEG-DA of different percentages. The results showed that the swelling ratios of 100% and 20% PEG-DA were 10% and 210%, respectively. The diffusion rates of compounds of different sizes in the PEG-DA were also determined. The results revealed that PEG-DA at 50% concentration allows free diffusion of molecules smaller than 1000 Da. Subsequently, two growth chambers in H-, U-, and round shape were designed, fabricated, and tested for acetoin (3-hydroxy-2-butanone) production by Klebsiella pneumoniae. Among them, the U-shape micro-chamber array is the most suitable for bacterial cultures. The U-shape micro-bioreactor contains an array of 21 U-shape PEG-DA micro-chambers, each with a dimension of 300 μm × 2 mm × 500 μm (w × l × h). The optimal flow rate to achieve the highest yield of acetoin was determined to be 2 μl/min. The growth chamber can hold the bacteria inside and allows the acetoin diffuse out and 90% viability can be maintained for at least 24 h, indicating its suitability for long term bacteria growth. To sum up, this novel micro-scale chip-based bioreactor system will be useful in applications such as metabolite collection, drug toxicity and high-yield strain screening.