**1. Introduction**

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Microfluidics [1, 2] becomes the backbone technology for bio‐medical diagnoses and thera‐ peutics due to the length scale matching between cells and fluidic devices. The micro‐electro‐ mechanical‐system (MEMS) based molecular sensors have reached the sensitivity of detecting a few nucleic acid molecules and several pg/ml of proteins [3, 4]. During the last decade, integration of microfluidic devices into a system for interacting with cellular system becomes possible and greatly advances the capability of controlling the cell fates.

While the number of microfluidic devices increasing with the desired functionalities of the microfluidic system, large number of interconnections are not just difficult to manufacture and can be a major road block. The Optoelectronic Reconfigurable Microchannel (OERM) [5] has basically alleviated the difficult design and fabrication problem. OERM is a new technology providing light‐controlled creation, annihilation and reconfiguration of microchannels within seconds. A light pattern is projected on a reconfigurable chip resulting in the formation of a corresponding microchannel network through a low power optoelectronic effect. When the light pattern is modified, the microchannel network reconfigures accordingly. Manufacturing and reconfiguration of microchannels have been demonstrated in ice, frozen cyclohexane, frozen DMSO and frozen hexadecane. As a consequence, it is expected that the technology can be used with many more materials with reasonable freezing point and latent heat of fusion. Hexadecane is immiscible with water and is widely used in microfluidic emulsions. Its use as a reconfiguration template paves the way towards aqueous droplet manipulation on the platform. Fabrication and reconfiguration happen in seconds.

The re‐configurability by defreezing and refreezing fluid certainly provide an innovative way of greatly simplifying the interconnect problem. On the other hand, most cells need to be in fluids above frozen point for proper physiological functions. For example, human cells need

© 2013 Takeuchi et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Takeuchi et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

to be in 37o C environment. Therefore, an additional microfluidic system operated at 37o C needs to be designed and integrated seamlessly with the OERM system for accomplishing the biological studies. In this article, we will introduce the design and manufacturing methods of the two‐temperature fluidic interrogative platform.

problem is accurate since no phase transition occurs. Figure 1 illustrates that the temperature and heat flux profile when melting begins are already close to steady state. In particular, heat flux is almost constant, which is detrimental to melting. An approximate calculation of the melting time can be performed based on those curves. Since the melting region is small, the problem can be linearized for a first‐order approximation. The heat used for melting the 100μm region then results from the difference between the heat flux entering the region and the heat flux leaving the region. The heat flux J entering at x = 0 is constant and has been calculated previously. The heat flux exiting the region at x = 100 *μ*m and t = 0.8s is inferred from the single

J.m‐<sup>3</sup>

*<sup>ʹ</sup>* is much longer than the characteristic transient times calculated

previously. Because meanwhile the temperature profile will evolve towards homongeneiza‐ tion of the heat flux, it entails that the real melting time will probably be longer. At this point, for better understanding and assessment of the problem, more qualitative insight is required. When melting starts, it creates an interface at the melting temperature that gradually pro‐ gresses towards its steady state location. The speed of this progression is determined by the coupling of the latent heat of fusion and the derivative of the heat flux across the interface. Because the latent heat is much higherthan the heat capacity, phase transition is a much slower process than the increase oftemperature.It also imposes a fixed temperature. As a result, phase transition thwarts the heat flux homogenization process of heat conduction across the melting interface.The characteristic transienttime for an ice region of 1mm anda waterregion of 100μm do not depend on the heat flux and are respectively *τ ice* = 0.4*s* and *τ ice* = 0.03*s*. When comparing

*<sup>ʹ</sup>* , it seems a reasonable assumption to consider that steady state is reached in a negligible time with regard to melting, both in the liquid region and the ice region. If the interface is represented by a small interval, the heat flux difference across such interval can be assessed. As a consequence, it turns out that the overall melting time can be calculated rather

. With H the water

, and l the length of the melting zone, l =

System Integration of a Novel Cell Interrogation Platform 301

phase heat conduction problem solution. Their difference equals 280W/m2

**Figure 1.** Evolution of temperature and heat flux profiles in the first 5s after heating starts.

enthalpy of fusion per unit volume, H = 3.32\*108

*<sup>J</sup>* ‐ *<sup>J</sup>* (*<sup>x</sup>* = 100*μm*, *<sup>t</sup>* = 0.8*s*) = 119*s* ≈2min

*τmelting*

<sup>ʹ</sup> = *Hl*

Unfortunately, *τmelting*

to *τmelting*

100μm, the first‐order approximation for the melting time is:
