Numerical simulation, fabrication, and characterization of a heating system for integration into an Organ-on-a-Chip
Gabriel M. Ferreira, F. Azevedo, Paulo Sousa, Vânia Pinto, Susana O. Catarino, Patrícia C. Sousa, Graça Minas
Abstract
In an organ-on-a-chip (OoC) device, temperature control is essential for a well-controlled and human representative microenvironment. This work presents the design, numerical simulation, fabrication and characterization of three aluminium microheater geometries for temperature control into an OoC device. Two of them are circular-based, with different curvature filleting angles and different line widths, and the third is a Hilbert-based geometry. Numerical simulations in COMSOL Multiphysics were performed to evaluate the heat distribution and power consumption of each resistive microheater, by Joule effect, according to target temperature range needed: 35 ºC (physiological) to 45 ºC (hyperthermia). Those simulated microheaters were fabricated on top of a glass substrate, using standard microfabrication technologies and bonded to a polydimethylsiloxane chamber that will contain the cultured organ model. An infrared thermal camera was used for the experimental heating tests and a proportional–integral–derivative (PID) controller, implemented on a printed circuit board, was used for monitoring and controlling the chamber temperature around its target range. Despite the observed differences between the numerical and experimental power consumption, needed for reaching the target temperatures, the obtained heating distribution and the temperature variations showed a good match for all geometries. Both the numerical and experimental results of the Hilbert-based geometry showed an ellipsoidal heat distribution in the circular culture chamber, which allowed to conclude an impair in the chamber temperature uniformity. Regarding the PID controller of the heating system, it was tested for long periods of time (>12 h) without loss of performance or overheating and the results showed a variation of 0.05 ºC/s during the cooling and 0.02 ºC/s during the heating phases, with a resolution of 1 ºC for temperatures up to 42 ºC, and ~0.5 ºC for temperatures below 38 ºC. Thus, the developed numerical approach enabled to qualitatively predict the performance of different microheater geometries, allowing to optimize the heating system performance, required for integration into an OoC.