A two-dimensional microarray of ten thousand (100100) chondrocyte-spheroids was successfully constructed with a 100-µm spacing on a micropatterned gold electrodes that were coated with poly(ethylene glycol) (PEG) hydrogels. The PEGylated surface as a cytophobic region was regulated by controlling the gel structure through photolithography. In this way, a PEG hydrogel was modulated enough to inhibit outgrowth of chondrocytes from cell adhering region in the horizontal direction. These structural control of PEG hydrogel was critical for inducing formation of three-dimensional chondrocyte condensations (spheroids) within 24 hours. We report noninvasive monitoring of the cellular functional change at the cell membrane using a chondrocyte-based field effect transistor (FET), which is based on detection of extracellular potential change induced as a result of the interaction between extracellular matrix (ECM) protein secreted from spheroid and substrate at the cell membrane. The interface potential change at the cell membrane/gate insulator interface can be monitored during the uptake of substrate without any labeling materials. Our findings on the time course of the interface potential would provide important information to understand the uptake kinetics for cellular differentiation.

This paper describes high power density and low distortion characteristics of a novel InGaP channel field-modulating plate FET (InGaP FP-FET) under high voltage operation of over 50 V. The developed InGaP FP-FET exhibited an extremely high breakdown voltage of 100 V with an impact ionization coefficient about 103 times smaller than that of GaAs. These superior breakdown characteristics indicate that the InGaP FP-FET is one of the most desirable device structures for high-voltage high-power operation. The InGaP FP-FET delivered an output power density of 1.6 W/mm at 1.95 GHz operated at a drain bias voltage of 55 V. As power operation moves from class A to class AB, both 3rd-order intermodulation distortion (IM3) and power-added efficiency (PAE) at higher output-power region were improved, resulting from a suppressed gate leakage current near the power saturation point. These results promise that the developed InGaP FP-FET is suited for applications in which both high efficiency and low distortion are required.