Yichao Yang

A Two-Dimensional (2D) Distributed-Deflection Sensor for Tissue Palpation With Correction Mechanism for Its Performance Variation

This paper presents a proof-of-concept study on a two-dimensional distributed-deflection sensor for tissue palpation and the associated correction mechanism for its performance variation. The core of the sensor is one whole polydimethylsiloxane microstructure embedded with a 3 × 3 sensing-plate/transducer array. Upon pressing the sensor against a tissue, the sensing-plate array translates its elasticity distribution to the deflection distribution, which registers as resistance changes by the transducer array and is further converted into the stiffness distribution. The connection of the sensing-plate/transducer array into one piece allows the sensor interacting with a tissue in a continuous manner and, thus, unifies misalignment errors from non-ideal normal contact between the sensor and the tissue. A correction mechanism is developed to remove the effect of performance variation among the sensing-plate/transducer array on the measured stiffness distribution of a tissue. The stiffness distribution normalized to the minimum stiffness across a tissue is utilized to identify the existence and location of a tumor. The related measurement errors are both theoretically and experimentally examined.

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

A Microfluidic-based Tactile Sensor for Palpating Mice Tumor Tissues

In light of the need of tissue palpation for Robotics-assisted Minimally Invasive Surgery (RMIS), this paper presents a microfluidic-based tactile sensor for palpating mice tissues for tumor localization. The core of the sensor is a 3x3 sensing-plate/transducer array built into a single polydimethylsiloxane (PDMS) microstructure, with a transducer spacing of 3.75mmx1.5mm. Mounted on a robot, the sensor is pressed against a tissue region with a pre-defined indentation depth pattern, and consequently the stiffness distribution across the tissue region translates to the deflection distribution of the sensing-plate array and is captured by the transducer array underneath as resistance changes. Thus, the recorded data on a tissue region is the sensor deflection as a function of the indentation depth. While the continuous manner of the sensor interacting with a tissue region alleviates the error resulting from non-ideal normal contact between the sensor and the tissue region, the error related to uncertainty in contact point is removed by interpreting the palpation results in terms of the slope of the sensor deflection versus the indentation depth. Two mice tumor tissues are palpated using the sensor. After their noise being removed, the raw data on the two tissues are processed to obtain their slope distribution, the slope error and the percentage error in the slope. The slope distribution of each tissue clearly illustrates the location of a tumor. The palpation results also indicate that this sensor can be integrated into a robotic-assisted system for tumor localization.

Mechanical Characterization of Mouse Mammary Tumors via a 2-D Distributed-Deflection Sensor

This paper presents a feasibility study on mechanical characterization of mouse mammary tumors via a 2-D distributed-deflection sensor. The sensor entails a polymer microstructure embedded with a 2-D sensing-plate/transducer array. With a pre-defined indentation pattern, the sensor is pressed against a tissue and registers mechanical behavior at different tissue sites as the instant and relaxed sensor deflection. Five mouse mammary tumor tissues are palpated by the sensor to measure their relations of instant and relaxed sensor deflection versus indentation depth. A simplified theoretical model is established to obtain the instant and relaxed indentation modulus, relaxation extent, and nonlinearity from the measured relations. The instant indentation modulus distribution is utilized to determine the location, shape, and size of the tumor in a tissue. Comparison of the mechanical properties among the five tumors shows that the five tumors follow the same order of progression, in terms of indentation modulus, relaxation extent, and nonlinearity. The histological analysis of the tumors reveals that the biological structures of two relatively stiff tumors are prominently different from those of the rest tumors. Both the mechanical behavior and shape of the tumors reveal unpredictable progression variability among individuals.

Correlation between stress drop and applied strain as a biomarker for tumor detection

This is the first study to measure the viscoelastic behavior of tumor tissues using stepwise compression-relaxation testing, and investigate the measured (Δσ-ε) relation between stress drop (Δσ) and applied strain (ε) as a biomarker for tumor detection. Stepwise compression-relaxation testing was implemented via a 2D tactile sensor to measure stress drop at each applied strain of a sample. Pearson correlation analysis was conducted to quantify the measured Δσ-ε relation as slope of stress drop versus applied strain (m=Δσ/ε) and coefficient of determination (R2). The measured results on soft materials revealed no dependency of coefficient of determination on the testing parameters and dependency of slope on them. Three groups of tissues: five mouse breast tumor (BT) tissues ex vivo, two mouse pancreatic tumor (PT) tissues in vivo and six normal tissues, were measured by using different testing parameters. Coefficient of determination was found to show significant difference among the center, edge and outside sites of all the BT tissues, and no difference between the BT outside sites and the normal tissues. Coefficient of determination also revealed significant difference between before and after treatment of the PT tissues, and no difference between the PT tissues after treatment and the normal tissues. Moreover, coefficient of determination of the PT tissues before treatment was found to be significantly different from that of the BT center sites, but slope failed to capture their difference. Dummy tumors made of silicon rubbers were found to behave differently from the native tumors. By removing the need of fitting the time-dependent data with a viscoelastic model, this study offered a time-efficient solution to quantifying the viscosity for tumor detection.

A Microfluidic-Based Tactile Sensor for 3-DOF Force/Torque Detection

This paper reports on a microfluidic-based tactile sensor capable of detecting forces along two directions and torque about one direction. The 3-Degree-Of-Freedom (3-DOF) force/torque sensor encompasses a symmetric three-dimensional (3D) microstructure embedded with two sets of electrolyte-enabled distributed resistive transducers underneath. The 3D microstructure is built into a rectangular block with a loading-bump on its top and two microchannels at its bottom. Together with electrode pairs distributed along the microchannel length, electrolyte in each microchannel functions as a set of three resistive transducers. While a normal force results in a resistance increase in the two sets of transducers, a shear force causes opposite resistance changes in the two sets of transducers. Conversely, a torque leads to the opposite resistance changes in the two side transducers in each set. Soft lithography and CNC molding are combined to fabricate a prototype tactile sensor. The experimental results validate the feasibility of using this microfluidic-based tactile sensor for 3-DOF force/torque detection.Copyright

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