Wenting Gu

Detection of distributed static and dynamic loads with electrolyte-enabled distributed transducers in a polymer-based microfluidic device

This paper reports on the use of electrolyte-enabled distributed transducers in a polymer-based microfluidic device for the detection of distributed static and dynamic loads. The core of the device is a polymer rectangular microstructure integrated with electrolyte-enabled distributed transducers. Distributed loads acting on the polymer microstructure are converted to different deflections along the microstructure length, which are further translated to electrical resistance changes by electrolyte-enabled distributed transducers. Owing to the great simplicity of the device configuration, a standard polymer-based fabrication process is employed to fabricate this device. With custom-built electronic circuits and custom LabVIEW programs, fabricated devices filled with two different electrolytes, 0.1 M NaCl electrolyte and 1-ethyl-3-methylimidazolium dicyanamide electrolyte, are characterized, demonstrating the capability of detecting distributed static and dynamic loads with a single device. As a result, the polymer-based microfluidic device presented in this paper is promising for offering the capability of detecting distributed static and dynamic loads in biomedical/surgical, manufacturing and robotics applications.

Performance study of a PDMS-based microfluidic device for the detection of continuous distributed static and dynamic loads

This paper presents a comprehensive study on the performance of a polydimethylsiloxane-based microfluidic device for the detection of continuous distributed static and dynamic loads. The core of this device is a single-compliant polymer microstructure integrated with a set of electrolyte-enabled distributed transducers, which are equally spaced along the microstructure length. The microstructure converts continuous distributed loads to continuous deflection, which is translated to discrete resistance changes by the distributed transducers. One potential application of this device is to measure spatially varying elasticity/viscoelasticity of a heterogeneous soft material, through quasi-static, stress relaxation and dynamic mechanical analysis tests. Thus, by controlling the displacement of a rigid probe, three types of loads (i.e., static, step and sinusoidal) are exerted on the device, and the performance of the device is experimentally characterized and analytically examined. As a result, this work establishes not only an experimental method for characterizing the performance of the device under various loading conditions, which can be directly adopted to measure the spatially varying elasticity/viscoelasticity of a heterogeneous soft material, but also the correlation of the device performance to its design parameters.

Concurrent spatial mapping of the elasticity of heterogeneous soft materials via a polymer-based microfluidic device

In this paper, built upon a polymer-based microfluidic device, a novel experimental technique called concurrent spatial mapping (CSM) is presented for measuring the spatially-varying elasticity of heterogeneous soft materials. Comprised of a single compliant polymer microstructure and a set of electrolyte-enabled distributed resistive transducers, this device is capable of detecting continuous distributed loads. In this experimental technique, a rigid probe is employed to press a material specimen against the device with precisely controlled displacements, and consequently the spatially-varying elasticity of the specimen translates to continuous distributed loads acting on the device, where continuous distributed loads give rise to continuous deflection of the polymer microstructure and register as discrete resistance changes at the locations of the distributed transducers. Performance characterization is first conducted on the device as a control experiment. Then, CSM is implemented on several heterogeneous and homogeneous polydimethylsiloxane specimens, as well as a rabbit tissue specimen. The associated data analysis is performed on the measured data for extracting the spatially-varying load-deflection relations of these specimens. In conjunction with its dimensions, the extracted spatially-varying load-deflection relations of a specimen result in its spatially-varying elasticity by the related theoretical formula. For the first time, this paper demonstrates the feasibility of using a single polymer-based microfluidic device to concurrently map out the spatially-varying elasticity of heterogeneous soft materials. As a result, CSM will pave the way for efficiently examining biological tissues and cell-seeded engineering scaffolds, while without excluding the interaction among neighboring compositions in such materials.

Synchronized Heterogeneous Indentation Behavior of Viscoelastic Materials Upon Macroscopic Compression via a Distributed-Deflection Sensor

Built upon a distributed-deflection sensor, an experimental technique is presented in this paper that allows for measuring the synchronized heterogeneous indentation behavior of viscoelastic materials upon macroscopic compression. The core of the distributed-deflection sensor is a whole polymer microstructure embedded with a resistive transducer array underneath. A cylinder probe is utilized to exert macroscopic compression on a material sample placed on the distributed-deflection sensor, and the synchronized heterogeneous indentation behavior of the sample is then translated to distributed deflections of the microstructure and is recorded as distributed resistances by the transducer array. In a measurement, the input signal is the indentation depth of the probe, the output signals are the macroscopic compression load and the distributed resistance changes of the sensor. From the measured distributed load-deflection relations of a sample along its length at multiple indentation depths with the same 5s hold time and 5s recovery time, the instant and the 5s relaxed indentation modulus of a sample are extracted, revealing non-negligible effect of the neighboring regions on the indentation behavior at a location in a sample.

A Polymer-Based Microfluidic Resistive Sensor for Detecting Distributed Loads

This paper reports on a polymer-based microfluidic resistive sensor for detecting distributed loads. The sensor is comprised of a polymer rectangular microstructure with an embedded electrolyte-filled microchannel and an array of electrodes aligned along the microchannel length. Electrolyte solution in the microchannel serves as impedance transduction. Distributed loads acting on the polymer microstructure give rise to different deflection along the microstructure length, which is recorded as the resistance change in electrolyte solution. This sensor can detect distributed loads by monitoring the resistance change at each pair of electrodes. A sensor with an in-plane dimension of ∼20mm×10mm and five pairs of electrodes is fabricated using a CNC machine. 1M KCl solution is used as the electrolyte. Using a custom built electronic circuit on breadboard and a custom LabVIEW program, the static and dynamic performance of the sensor is characterized, demonstrating the feasibility of employing this sensor to detect distributed loads.Copyright

Concurrent Spatial Mapping of the Elasticity of Heterogeneous Soft Materials via a Polymer-Based Microfluidic Device: A Preliminary Study

This paper presents a preliminary study on achieving concurrent spatial mapping of the spatially-varying elasticity of heterogeneous soft materials via a polymer-based microfluidic device. Comprised of a single compliant polymer rectangular microstructure and a set of electrolyte-enabled distributed resistive transducers, this device is capable of detecting continuous distributed loads. Through pressing a specimen against the device by a rigid probe with precisely-controlled displacements, the spatially-varying elasticity of a specimen is captured by continuous distributed loads acting on the device and is further registered as discrete resistance changes at the locations of the transducers in the device. Concurrent spatial mapping is conducted on homogeneous and heterogeneous specimens, and the related data analysis is performed on the measured results to extract their elasticity. The obtained results demonstrate the feasibility of concurrent spatial mapping of the spatially-varying elasticity of heterogeneous soft materials via this polymer-based microfluidic device.Copyright

Synchronized Heterogeneous Viscous Behavior of Soft Materials Upon Macroscopic Loading

This paper presents a preliminary study on characterizing the synchronized heterogeneous viscous behavior of soft materials upon macroscopic sinusoidal loading. Built upon a polymer-based microfluidic device capable of detecting distributed normal loads at a spatial resolution of 1.5mm, a rigid cylinder probe is employed to exert a macroscopic sinusoidal load on a sample placed on the device. Consequently, the synchronized heterogeneous viscous behavior of a sample translates to sinusoidal distributed loads, which are captured by the device. In a measurement, the input and output signals of a sample are the macroscopic sinusoidal load and the DC voltage outputs of the device, respectively, with the latter being representative of the sinusoidal deflections of a sample along its length. A preliminary data analysis is conducted on the recorded input and output signals to obtain their phase shifts at different frequencies, which are representative of the heterogeneous viscosity of a sample along its length. Several agar and polydimethylsiloxane (PDMS) samples and two animal cartilage tissue samples are prepared and measured. Variations among the measured phase shifts in a sample manifest its structural heterogeneity and demonstrate the feasibility of using the device to characterize the synchronized heterogeneous viscous behavior of soft materials upon macroscopic loading.Copyright

Synchronized Heterogeneous Indentation and Stress Relaxation Behavior of Articular Cartilage Upon Macroscopic Compression: A Preliminary Study

By using a newly-developed experimental technique that is enabled by a polymer-based microfluidic device for detecting distributed normal loads, a preliminary study is presented on the synchronized heterogeneous indentation and stress relaxation behavior of articular cartilage upon macroscopic compression. In a measurement, a rigid cylinder probe is employed to exert macroscopic indentation or step input to a cartilage sample on the device. Consequently, the synchronized heterogeneous viscoelastic behavior of the sample translates to distributed normal loads acting on the device and is captured by the device. While the macroscopic load acting on a sample is recorded by a load cell, the deflections of a sample along its length are captured by the device. Thus, the measured results essentially are the load-deflection relations of a sample along its length. Full-thickness lapine and bovine articular cartilage samples are prepared and measured. A thorough data analysis is implemented on the recorded data for extracting their instant and relaxed indentation modulus, as well as Young’s relaxation modulus.Copyright

Performance Characterization of a PDMS-Based Microfluidic Device for Detecting Continuous Distributed Loads

In this paper, the performance of a PDMS-based microfluidic device is thoroughly characterized for detecting continuous static and dynamic loads. This device comprises of a single PDMS rectangular microstructure and a set of electrolyte-enabled distributed transducers. It is fabricated by a standard fabrication process well developed for PDMS-based microfluidic devices. One potential application of this device is to measure spatially-varying mechanical properties of heterogeneous soft materials, through quasi-static, stress relaxation and dynamic mechanical analysis (DMA) tests. Thus, the response of this device to three types of inputs: static, step and sinusoidal, is examined with a custom experimental setup. For the first time, the capability of using a polymer-based microfluidic device to detect sinusoidal inputs is reported. The characterized results demonstrate the potential of using this device to measure soft materials.Copyright

Stress Relaxation Measurement of Agar Using a Polymer-Based Microfluidic Device

In light of the significance of the viscoelastic property of agar to cell-based tissue engineering, this paper presents the stress relaxation measurement of agar using a polymer-based microfluidic device. Comprised of a single polymer rectangular microstructure and a set of electrolyte-enabled distributed transducers, this device is capable of detecting continuous distributed static and dynamic loads. In the measurement, an agar specimen is placed on the device and a rigid probe is utilized to press the specimen against the device with a step displacement input. Consequently, the stress relaxation behavior of the specimen translates to time-dependent continuous distributed loads acting on the device and is further registered as discrete resistance changes by the device. Two agar specimens of 1% and 3% in concentration, respectively, are measured using this device; and the data analysis is conducted on the measured results to extract Young’s relaxation modulus, which is further expressed by a Prony-series representation of the Maxwell model with two exponential terms. The results demonstrate the feasibility of using this device to measure the stress relaxation behavior of soft materials.Copyright