Abstract
An improved thermal-needle approach for accurate and fast measurement of thermal conductivity of aqueous and soft biomaterials was developed using microfabricated thermal conductivity sensors. This microscopic measuring device was comprehensively characterized at temperatures from 0 °C to 40 °C. Despite the previous belief, system calibration constant was observed to be highly temperature-dependent. Dynamic thermal conductivity response during cooling (40 °C to –40 °C) was observed using the miniaturized single tip sensor for various concentrations of CPAs, i.e., glycerol, ethylene glycol and dimethyl sulfoxide. Chicken breast, chicken skin, porcine limb, and bovine liver were assayed to investigate the effect of anatomical heterogeneity on thermal conductivity using the arrayed multi-tip sensor at 20 °C. Experimental results revealed distinctive differences in localized thermal conductivity, which suggests the use of approximated or constant property values is expected to bring about results with largely inflated uncertainties when investigating bio-heat transfer mechanisms and/or performing sophisticated thermal modeling with complex biological tissues. Overall, the presented micro thermal sensor with automated data analysis algorithm is a promising approach for direct thermal conductivity measurement of aqueous solutions and soft biomaterials and is of great value to cryopreservation of tissues, hyperthermia or cryogenic, and other thermal-based clinical diagnostics and treatments.
Highlights
An improved thermal-needle approach for accurate and fast measurement of thermal conductivity of aqueous and soft biomaterials was developed using microfabricated thermal conductivity sensors
There have been a number of approaches to characterize thermal conductivity, the majority of currently available direct measuring approaches are often challenging in many situations due to practical measurement constrains, such as differences in scale, material, state and instrumentation
With an aim to establish a standardized testing protocol for directly measuring the thermal conductivity of various solutions and soft biomaterials, we describe the development of an improved transient hot-wire (THW) based micro thermal conductivity sensor with fully automated post-experiment data analysis capability
Summary
An improved thermal-needle approach for accurate and fast measurement of thermal conductivity of aqueous and soft biomaterials was developed using microfabricated thermal conductivity sensors. With an aim to establish a standardized testing protocol for directly measuring the thermal conductivity of various solutions and soft biomaterials, we describe the development of an improved transient hot-wire (THW) based micro thermal conductivity sensor with fully automated post-experiment data analysis capability. This miniaturized device utilizes a SiO2/Au/SiO2 sandwiched structure to protect the microfabricated serpentine gold coil, which functions as both a heater and a passive thermometer for measuring the temperature response of the sample. To demonstrate the potential of the presented microdevice, series of experiments were conducted using first, the single-tip sensors to investigate the temperature effect on thermal conductivity of common biologically relevant CPAs, such as 1.5 M and 40% (W/V) G, 1.5 M EG and 10% (V/V) DMSO; and second, the multi-tip arrayed sensors (four identical probes) to study localized thermal conductivity variation of biological tissues with unknown degrees of anatomical heterogeneity, namely chicken breast, chicken skin, lean porcine limb and bovine liver
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