Jiayue Shen

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.

A Two-Dimensional Microfluidic-Based Tactile Sensor for Tissue Palpation Under the Influence of Misalignment

This paper reports on a proof-of-concept study of applying a two-dimensional (2D) microfluidic-based tactile sensor for tissue palpation under the influence of misalignment. Two unavoidable misalignment issues, uncertainty in contact point and non-ideal normal contact, severely distort the genuine elasticity distribution of a tissue region, yielding false identification of abnormality. The core of the 2D tactile sensor is one whole microstructure embedded with an electrolyte-enabled 2D resistive transducer array underneath. This unique configuration allows the tactile sensor to interact with a tissue region in a continuous manner that mimics manual palpation: the whole microstructure (fingertip) presses a tissue region and the corresponding deflection distribution is captured concurrently by the embedded transducer array (distributed sensors under the skin). This continuous manner tackles the misalignment issues encountered by an individual sensor or a sensor array, in that any misalignment encountered by the 2D sensor is manifested as an increasing trend of the distributed deflection-depth relations along the tilt direction. Tissue phantoms with embedded nodules and extrusions are prepared and are measured using the 2D tactile sensor, validating the capability of the tactile sensor to identify abnormalities in soft tissue under the influence of misalignment.Copyright

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.

Performance Investigation of a Wearable Distributed-Deflection Sensor in Arterial Pulse Waveform Measurement

This paper presents a performance investigation of a wearable distributed-deflection sensor in arterial pulse waveform measurement. Built on a flexible substrate, the sensor entails a polymer microstructure embedded with an electrolyte-enabled resistive transducer array. By pressing the sensor against an artery with hold-down pressure exerted by two fingers, the pulse signal from the artery deflects the microstructure and registers as a resistance change by the transducer at the artery site. The radial and carotid pulse signals of five subjects are recorded via the sensor. Related signal-processing algorithms are written in Matlab to remove motion artifacts from a recorded pulse signal, extract its key tonometric parameters, and calculate the Pulse Wave Velocity (PWV) and radial and carotid Augmentation Index (AI). Whereas the tonometric parameters of the measured radial and carotid pulse waveforms on each subject are consistent with the related findings in the literature, the difference in tonometric parameters among the subjects also reveals physiological significance. The measured PWV and radial and carotid AI of the subjects show good agreement with how they should vary with age, gender and hypertension. Finally, the effect of the hold-down pressure on a measured pulse signal and the repeatability of the sensor are examined.

Preliminary Study of a Polymer-Based Microfluidic Device for Detecting Distributed Shear Loads

This paper reports on a polymer-based microfluidic device for detecting distributed shear loads. This device is comprised of a symmetric 3D polydimethylsiloxane (PDMS) microstructure, two electrolyte-filled microchannels embedded underneath the microstructure, and a set of electrode pairs distributed along the length of each microchannel. In conjunction with its electrode pairs, one body of electrolyte in each microchannel functions as distributed resistive transducers along the microchannel length. The 3D microstructure is built into a rectangular block with a narrow shear-loading bump on its top. The edges of the bump are aligned right at the width centers of the two microchannels. Thus, distributed shear loads acting on the bump translate to normal loads of opposite directions on the tops of the two microchannels, and consequently opposite geometrical changes in the microchannels, which register as resistance changes by the distributed resistive transducers. Together with a CNC mold, a two-mask photolithographic fabrication process is employed to fabricate a prototype device. The fabricated device is tested using a custom experimental setup. The experimental results validate the design concept of the device and further show that the device exhibits a linear response to shear loads with good repeatability.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