Microfluidic system for generation of sinusoidal glucose waveforms for entrainment of islets of Langerhans

A microfluidic system was developed to produce sinusoidal waveforms of glucose to entrain oscillations of intracellular [Ca(2+)] in islets of Langerhans. The work described is an improvement to a previously reported device where two pneumatic pumps delivered pulses of glucose and buffer to a mixing channel. The mixing channel acted as a low pass filter to attenuate these pulses to produce the desired final concentration. Improvements to the current device included increasing the average pumping frequency from 0.83 to 3.33 Hz by modifying the on-chip valves to minimize adhesion between the PDMS and glass within the valve. The cutoff frequency of the device was increased from 0.026 to 0.061 Hz for sinusoidal fluorescein waves by shortening the length of the mixing channel to 3.3 cm. The value of the cutoff frequency was chosen between the average pumping frequency and the low frequency (approximately 0.0056 Hz) glucose waves that were needed to entrain the islets of Langerhans. In this way, the pulses from the pumps were attenuated greatly but the low-frequency glucose waves were not. With the use of this microfluidic system, a total flow rate of 1.5 +/- 0.1 microL min(-1) was generated and used to deliver sinusoidal waves of glucose concentration with a median value of 11 mM and amplitude of 1 mM to a chamber that contained an islet of Langerhans loaded with the Ca(2+)-sensitive fluorophore, indo-1. Entrainment of the islets was demonstrated by pacing the rhythm of intracellular [Ca(2+)] oscillations to oscillatory glucose levels produced by the device. The system should be applicable to a wide range of cell types to aid understanding cellular responses to dynamically changing stimuli.