Chia-Hung Dylan Tsai

A New Dimensionless Index for Evaluating Cell Stiffness-Based Deformability in Microchannel

This paper proposes a new index for evaluating the stiffness-based deformability of a cell using a microchannel. In conventional approaches, the transit time of a cell through a microchannel is often utilized for the evaluation of cell deformability. However, such time includes both the information of cell stiffness and viscosity. In this paper, we eliminate the effect from cell viscosity, and focus on the cell stiffness only. We find that the velocity of a cell varies when it enters a channel, and eventually reaches to equilibrium where the velocity becomes constant. The constant velocity is defined as the equilibrium velocity of the cell, and it is utilized to define the observability of stiffness-based deformability. The necessary and sufficient numbers of sensing points for evaluating stiffness-based deformability are discussed. Through the dimensional analysis on the microchannel system, three dimensionless parameters determining stiffness-based deformability are derived, and a new index is introduced based on these parameters. The experimental study is conducted on the red blood cells from a healthy subject and a diabetes patient. With the proposed index, we showed that the experimental data can be nicely arranged.

Applying viscoelastic contact modeling to grasping task: An experimental case study

In this paper, we employ Fungpsilas viscoelastic model discussed by Tiezzi and Kao to study the experimental data presented by Sakamoto et al. for grasping viscoelastic objects using a parallel-jaw gripper. The viscoelastic contact modeling presented in this paper is characterized by two separate responses: elastic response and temporal response. Two main and intriguing results were found in the modeling and analysis of experimental data. The first is the consistency on the normalized coefficients for the curve fitting of the temporal response during the relaxation period of the grasping. Such consistency suggests that the proposed model is applicable to the grasping task at hand. The other result is the generic pattern of the elastic response deduced from the experimental data. The pattern of elastic response represents different physical significance of grasping which involves viscoelastic contact interface.

On-chip actuation transmitter for enhancing the dynamic response of cell manipulation using a macro-scale pump

An on-chip actuation transmitter for achieving fast and accurate cell manipulation is proposed. Instead of manipulating cell position by a directly connected macro-scale pump, polydimethylsiloxane deformation is used as a medium to transmit the actuation generated from the pump to control the cell position. This actuation transmitter has three main advantages. First, the dynamic response of cell manipulation is faster than the conventional method with direct flow control based on both the theoretical modeling and experimental results. The cell can be manipulated in a simple harmonic motion up to 130 Hz by the proposed actuation transmitter as opposed to 90 Hz by direct flow control. Second, there is no need to fill the syringe pump with the sample solution because the actuation transmitter physically separates the fluids between the pump and the cell flow, and consequently, only a very small quantity of the sample is required (<1 μl). In addition, such fluid separation makes it easy to keep the experiment platform sterilized because there is no direct fluid exchange between the sample and fluid inside the pump. Third, the fabrication process is simple because of the single-layer design, making it convenient to implement the actuation transmitter in different microfluidic applications. The proposed actuation transmitter is implemented in a lab-on-a-chip system for red blood cell (RBC) evaluation, where the extensibility of red blood cells is evaluated by manipulating the cells through a constriction channel at a constant velocity. The application shows a successful example of implementing the proposed transmitter.

Dynamic Nonprehensile Manipulation for Rotating a Thin Deformable Object: An Analogy to Bipedal Gaits

A rigid plate end-effector at the tip of a high-speed manipulator can remotely manipulate an object without grasping it. This paper discusses a dynamic nonprehensile manipulation strategy to rotate thin deformable objects on a rigid plate with two degrees of freedom (DOFs). The deformation of the object due to dynamic effects is exploited to produce fast and stable rotation. By varying the frequency of the rotational component of the plates motion, we show that the dynamic behavior of the object mimics either a sliding, walking, or running gait of a biped. We introduce a model to simulate this type of system in which the object is constructed of multiple nodes that are connected by viscoelastic joint units with three DOFs. The joints viscoelastic parameters are estimated experimentally in order to model real food. Afterward, simulation analysis is used to investigate how the objects rotational behavior and its angular velocity change with respect to the plates motion frequency. We show how the objects behavior during rotation is analogous to bipedal sliding, walking, and running gaits and then obtain optimal plate motions leading to the maximal angular velocity of the object. We also reveal that an appropriate angular acceleration of the plate is essential for a dynamically stable and fast objects rotation. We further show that the friction coefficient that maximizes the objects angular velocity depends on its gait.

The latency model for viscoelastic contact interface in robotics: Theory and experiments

Viscoelasticity is the phenomenon of time-dependent strain and/or stress in elastic solids. Various contact interfaces with anthropomorphic end-effectors and polymeric solids found in robots and manipulators are intrinsically viscoelastic. It is therefore important to model such behavior and to study the effects of such time-dependent strain and stress on the stability and sustainability of grasping and manipulation. Various models have been proposed over the years to describe such behavior of time-dependent strain and stress. Furthermore, viscoelastic solids also display typically nonlinear elastic response. Built upon a variety of literature, a new and practical latency model is proposed in this paper for the application of contact interface involving viscoelasticity in robotics. Latency model can describe various features of viscoelastic materials, such as stress relaxation, creep, and material clock. The theoretical modeling was supported by experiments in which we found two types of relaxation, depending on the loading and unloading of grasping or contact. One type is well documented in existing literature; but the other type has not been, to our best knowledge, presented before. The proposed theory can unify both types of time-dependent relaxation responses.

Phase decomposition of a cell passing through a μ-channel: A method for improving the evaluation of cell stiffness

Two-phase motion of a cell inside a μ-channel is observed by the high-speed vision system. Two phases are defined as the phase of deformation and the phase of constant shape according to their characteristics. Red blood cells were used for experimental validation, and a mechanical model consisting of a spring and a damper in parallel is utilized for interpreting the behavior of the RBCs. An analysis method for acquiring the transition point between two phases is proposed, and is utilized in the analysis of the experimental results presented in this paper. Two different initial velocities of red blood cells approaching the μ-channel were used in the experiment. The experimental results show that the red blood cells with the higher initial velocity require longer distance to reach the steady state comparing to the ones with the lower initial velocity.

Mechanical diagnosis of human erythrocytes by ultra-high speed manipulation unraveled critical time window for global cytoskeletal remodeling

Large deformability of erythrocytes in microvasculature is a prerequisite to realize smooth circulation. We develop a novel tool for the three-step “Catch-Load-Launch” manipulation of a human erythrocyte based on an ultra-high speed position control by a microfluidic “robotic pump”. Quantification of the erythrocyte shape recovery as a function of loading time uncovered the critical time window for the transition between fast and slow recoveries. The comparison with erythrocytes under depletion of adenosine triphosphate revealed that the cytoskeletal remodeling over a whole cell occurs in 3 orders of magnitude longer timescale than the local dissociation-reassociation of a single spectrin node. Finally, we modeled septic conditions by incubating erythrocytes with endotoxin, and found that the exposure to endotoxin results in a significant delay in the characteristic transition time for cytoskeletal remodeling. The high speed manipulation of erythrocytes with a robotic pump technique allows for high throughput mechanical diagnosis of blood-related diseases.

An On-Chip RBC Deformability Checker Significantly Improves Velocity-Deformation Correlation

An on-chip deformability checker is proposed to improve the velocity–deformation correlation for red blood cell (RBC) evaluation. RBC deformability has been found related to human diseases, and can be evaluated based on RBC velocity through a microfluidic constriction as in conventional approaches. The correlation between transit velocity and amount of deformation provides statistical information of RBC deformability. However, such correlations are usually only moderate, or even weak, in practical evaluations due to limited range of RBC deformation. To solve this issue, we implemented three constrictions of different width in the proposed checker, so that three different deformation regions can be applied to RBCs. By considering cell responses from the three regions as a whole, we practically extend the range of cell deformation in the evaluation, and could resolve the issue about the limited range of RBC deformation. RBCs from five volunteer subjects were tested using the proposed checker. The results show that the correlation between cell deformation and transit velocity is significantly improved by the proposed deformability checker. The absolute values of the correlation coefficients are increased from an average of 0.54 to 0.92. The effects of cell size, shape and orientation to the evaluation are discussed according to the experimental results. The proposed checker is expected to be useful for RBC evaluation in medical practices.

Gravity-Based Precise Cell Manipulation System Enhanced by In-Phase Mechanism

This paper proposes a gravity-based system capable of generating high-resolution pressure for precise cell manipulation or evaluation in a microfluidic channel. While the pressure resolution of conventional pumps for microfluidic applications is usually about hundreds of pascals as the resolution of their feedback sensors, precise cell manipulation at the pascal level cannot be done. The proposed system successfully achieves a resolution of 100 millipascals using water head pressure with an in-phase noise cancelation mechanism. The in-phase mechanism aims to suppress the noises from ambient vibrations to the system. The proposed pressure system is tested with a microfluidic platform for pressure validation. The experimental results show that the in-phase mechanism effectively reduces the pressure turbulence, and the pressure-driven cell movement matches the theoretical simulations. Preliminary experiments on deformability evaluation with red blood cells under incremental pressures of one pascal are successfully performed. Different deformation patterns are observed from cell to cell under precise pressure control.

On-chip pressure sensing by visualizing PDMS deformation using microbeads

A novel pressure sensing technique based on visualizing Polydimethylsiloxane (PDMS) deformation using microbeads is proposed here for measuring local pressure inside a microfluidic device. By the proposed method, the pressure can be directly “seen” without attaching any wire foils, such as a strain gauge, nor complex fabrication process, such as multilayer design or surface grating. Experimental results are shown and analyzed based on brightness value from captured images of microbeads pattern. The developed sensor is firstly calibrated by a commercial pressure sensor with feedback controlled syringe pump connected externally. According to the experimental results, the proposed sensing method is stable and repeatable in the steady state under dynamic pressure change, and the variation for the same given pressure from time to time is less than 1%. The correlation, R, between the pressure obtained from the proposed method and the reference pressure connected outside is up to 0.9953.