Scholarly Works, Mechanical Engineering

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Activation of bacterial channel MscL in mechanically stimulated droplet interface bilayers
Najem, Joseph S.; Dunlap, Myles D.; Rowe, Ian D.; Freeman, Eric C.; Grant, John Wallace; Sukharev, Sergei; Leo, Donald J. (Springer Nature, 2015-09-08)
MscL, a stretch-activated channel, saves bacteria experiencing hypo-osmotic shocks from lysis. Its high conductance and controllable activation makes it a strong candidate to serve as a transducer in stimuli-responsive biomolecular materials. Droplet interface bilayers (DIBs), flexible insulating scaffolds for such materials, can be used as a new platform for incorporation and activation of MscL. Here, we report the first reconstitution and activation of the low-threshold V23T mutant of MscL in a DIB as a response to axial compressions of the droplets. Gating occurs near maximum compression of both droplets where tension in the membrane is maximal. The observed 0.1-3 nS conductance levels correspond to the V23T-MscL sub-conductive and fully open states recorded in native bacterial membranes or liposomes. Geometrical analysis of droplets during compression indicates that both contact angle and total area of the water-oil interfaces contribute to the generation of tension in the bilayer. The measured expansion of the interfaces by 2.5% is predicted to generate a 4-6 mN/m tension in the bilayer, just sufficient for gating. This work clarifies the principles of interconversion between bulk and surface forces in the DIB, facilitates the measurements of fundamental membrane properties, and improves our understanding of MscL response to membrane tension.
Classical and adaptive control of ex vivo skeletal muscle contractions using Functional Electrical Stimulation (FES)
Cienfuegos, Paola Jaramillo; Shoemaker, Adam; Grange, Robert W.; Abaid, Nicole; Leonessa, Alexander (PLOS, 2017-03-08)
Functional Electrical Stimulation is a promising approach to treat patients by stimulating the peripheral nerves and their corresponding motor neurons using electrical current. This technique helps maintain muscle mass and promote blood flow in the absence of a functioning nervous system. The goal of this work is to control muscle contractions from FES via three different algorithms and assess the most appropriate controller providing effective stimulation of the muscle. An open-loop system and a closed-loop system with three types of model-free feedback controllers were assessed for tracking control of skeletal muscle contractions: a Proportional-Integral (PI) controller, a Model Reference Adaptive Control algorithm, and an Adaptive Augmented PI system. Furthermore, a mathematical model of a muscle-mass-spring system was implemented in simulation to test the open-loop case and closed-loop controllers. These simulations were carried out and then validated through experiments ex vivo. The experiments included muscle contractions following four distinct trajectories: a step, sine, ramp, and square wave. Overall, the closed-loop controllers followed the stimulation trajectories set for all the simulated and tested muscles. When comparing the experimental outcomes of each controller, we concluded that the Adaptive Augmented PI algorithm provided the best closed-loop performance for speed of convergence and disturbance rejection.
Cultivating Emerging & Black Swan Technologies
Mahajan, Roop L. (2012-09-15)
Cytoskeletal Disruption after Electroporation and Its Significance to Pulsed Electric Field Therapies
Graybill, Philip M.; Davalos, Rafael V. (MDPI, 2020-04-30)
Pulsed electric fields (PEFs) have become clinically important through the success of Irreversible Electroporation (IRE), Electrochemotherapy (ECT), and nanosecond PEFs (nsPEFs) for the treatment of tumors. PEFs increase the permeability of cell membranes, a phenomenon known as electroporation. In addition to well-known membrane effects, PEFs can cause profound cytoskeletal disruption. In this review, we summarize the current understanding of cytoskeletal disruption after PEFs. Compiling available studies, we describe PEF-induced cytoskeletal disruption and possible mechanisms of disruption. Additionally, we consider how cytoskeletal alterations contribute to cell–cell and cell–substrate disruption. We conclude with a discussion of cytoskeletal disruption-induced anti-vascular effects of PEFs and consider how a better understanding of cytoskeletal disruption after PEFs may lead to more effective therapies.
Enhanced vibration damping of carbon fibers-ZnO nanorods hybrid composites
Skandani, Amir A.; Masghouni, N.; Case, Scott W.; Leo, D. J.; Al-Haik, Marwan S. (AIP Publishing, 2012-08-01)
In this study, ZnO nanorods are grown on the surface of polyacrylonitrile based carbon fibers using a low temperature hydrothermal synthesis technique. Bi-layered carbon fiber-ZnO nanorod hybrid composite with epoxy matrix is prepared and tested for vibrational attenuations using dynamic mechanical analysis. Results revealed that the growth of ZnO nanorods on top of carbon fiber increases the damping performance by 50% while causing a slight decrease (similar to 7%) on the storage modulus. The enhanced damping of the hybrid composites can be related to the frictional mechanisms between the ZnO nanorod/epoxy and nanorod/nanorod interfaces combined with piezoelectric effect of ZnO. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746398]
Establishing an immunocompromised porcine model of human cancer for novel therapy development with pancreatic adenocarcinoma and irreversible electroporation
Hendricks-Wenger, Alissa; Aycock, Kenneth N.; Nagai-Singer, Margaret A.; Coutermarsh-Ott, Sheryl; Lorenzo, Melvin F.; Gannon, Jessica; Uh, Kyungjun; Farrell, Kayla; Beitel-White, Natalie; Brock, Rebecca M.; Simon, Alexander; Morrison, Holly A.; Tuohy, Joanne L.; Clark-Deener, Sherrie; Vlaisavljevich, Eli; Davalos, Rafael V.; Lee, Kiho; Allen, Irving C. (Nature Research, 2021-04-07)
New therapies to treat pancreatic cancer are direly needed. However, efficacious interventions lack a strong preclinical model that can recapitulate patients’ anatomy and physiology. Likewise, the availability of human primary malignant tissue for ex vivo studies is limited. These are significant limitations in the biomedical device field. We have developed RAG2/IL2RG deficient pigs using CRISPR/Cas9 as a large animal model with the novel application of cancer xenograft studies of human pancreatic adenocarcinoma. In this proof-of-concept study, these pigs were successfully generated using on-demand genetic modifications in embryos, circumventing the need for breeding and husbandry. Human Panc01 cells injected subcutaneously into the ears of RAG2/IL2RG deficient pigs demonstrated 100% engraftment with growth rates similar to those typically observed in mouse models. Histopathology revealed no immune cell infiltration and tumor morphology was highly consistent with the mouse models. The electrical properties and response to irreversible electroporation of the tumor tissue were found to be similar to excised human pancreatic cancer tumors. The ample tumor tissue produced enabled improved accuracy and modeling of the electrical properties of tumor tissue. Together, this suggests that this model will be useful and capable of bridging the gap of translating therapies from the bench to clinical application.
Estimation of the Tire Contact Patch Length and Normal Load Using Intelligent Tires and Its Application in Small Ground Robot to Estimate the Tire-Road Friction
Khaleghian, Seyedmeysam; Ghasemalizadeh, O.; Taheri, Saied (The Tire Society, 2016)
Tire-road friction estimation is one of the most popular problems for the tire and vehicle industry. Accurate estimation of the tire-road friction leads to better performance of the traction and antilock braking system controllers, which reduces the number of accidents. Several researchers have worked in the field of friction estimation, and many tire models have been developed to predict the tire-road friction. In this article, an intelligent tire, which has an embedded accelerometer placed on the inner liner of the tire, is used to estimate the tire contact patch length parameter and normal load. To accomplish this, first, an existing tire testing trailer equipped with a force hub to measure tire forces and moments, a high-accuracy encoder to measure the angular velocity of the wheel, and VBOX, which is a global positioning system–based device, to estimate the longitudinal speed of the trailer was used. As a practical application for the normal load algorithm, a wheeled ground robot, which is equipped with several sensors, including an accelerometer and a flexible strain sensor inside the tire (used for terrain identification purposes), was designed and built. A set of algorithms was developed and used with the test data that were collected with both the trailer and the robot, and the contact patch length and the normal load were estimated. Also, the friction potential between the tire and the road was evaluated using a small ground robot.
Extensive Chaos in The Lorenz-96 Model
Karimi, A.; Paul, Mark R. (AIP Publishing, 2010-12-01)
We explore the high-dimensional chaotic dynamics of the Lorenz-96 model by computing the variation of the fractal dimension with system parameters. The Lorenz-96 model is a continuous in time and discrete in space model first proposed by Lorenz to study fundamental issues regarding the forecasting of spatially extended chaotic systems such as the atmosphere. First, we explore the spatiotemporal chaos limit by increasing the system size while holding the magnitude of the external forcing constant. Second, we explore the strong driving limit by increasing the external forcing while holding the system size fixed. As the system size is increased for small values of the forcing we find dynamical states that alternate between periodic and chaotic dynamics. The windows of chaos are extensive, on average, with relative deviations from extensivity on the order of 20%. For intermediate values of the forcing we find chaotic dynamics for all system sizes past a critical value. The fractal dimension exhibits a maximum deviation from extensivity on the order of 5% for small changes in system size and the deviation from extensivity decreases nonmonotonically with increasing system size. The length scale describing the deviations from extensivity is consistent with the natural chaotic length scale in support of the suggestion that deviations from extensivity are due to the addition of chaotic degrees of freedom as the system size is increased. We find that each wavelength of the deviation from extensive chaos contains on the order of two chaotic degrees of freedom. As the forcing is increased, at constant system size, the dimension density grows monotonically and saturates at a value less than unity. We use this to quantify the decreasing size of chaotic degrees of freedom with increased forcing which we compare with spatial features of the patterns. (C) 2010 American Institute of Physics. [doi:10.1063/1.3496397]
Extracting Interactions between Flying Bat Pairs Using Model-Free Methods
Roy, Subhradeep; Howes, Kayla; Müller, Rolf; Butail, Sachit; Abaid, Nicole (MDPI, 2019-01-09)
Social animals exhibit collective behavior whereby they negotiate to reach an agreement, such as the coordination of group motion. Bats are unique among most social animals, since they use active sensory echolocation by emitting ultrasonic waves and sensing echoes to navigate. Bats’ use of active sensing may result in acoustic interference from peers, driving different behavior when they fly together rather than alone. The present study explores quantitative methods that can be used to understand whether bats flying in pairs move independently of each other or interact. The study used field data from bats in flight and is based on the assumption that interactions between two bats are evidenced in their flight patterns. To quantify pairwise interaction, we defined the strength of coupling using model-free methods from dynamical systems and information theory. We used a control condition to eliminate similarities in flight path due to environmental geometry. Our research question is whether these data-driven methods identify directed coupling between bats from their flight paths and, if so, whether the results are consistent between methods. Results demonstrate evidence of information exchange between flying bat pairs, and, in particular, we find significant evidence of rear-to-front coupling in bats’ turning behavior when they fly in the absence of obstacles.
Focused ultrasound actuation of shape memory polymers; acoustic-thermoelastic modeling and testing
Bhargava, Aarushi; Peng, Kaiyuan; Stieg, Jerry; Mirzaeifar, Reza; Shahab, Shima (The Royal Society of Chemistry, 2017-09-18)
Controlled drug delivery (CDD) technologies have received extensive attention recently. Despite recent efforts, drug releasing systems still face major challenges in practice, including low efficiency in releasing the pharmaceutical compounds at the targeted location with a controlled time rate. We present an experimentally-validated acoustic-thermoelastic mathematical framework for modeling the focused ultrasound (FU)-induced thermal actuation of shape memory polymers (SMPs). This paper also investigates the feasibility of using SMPs stimulated by FU for designing CDD systems. SMPs represent a new class of materials that have gained increased attention for designing biocompatible devices. These polymers have the ability of storing a temporary shape and returning to their permanent or original shape when subjected to external stimuli such as heat. In this work, FU is used as a trigger for noninvasively stimulating SMP-based systems. FU has a superior capability to localize the heating effect, thus initiating the shape recovery process only in selected parts of the polymer. The multiphysics model optimizes the design of a SMP-based CDD system through analysis of a filament as a constituting basestructure and quantifies its activation under FU. Experimental validations are performed using a SMP filament submerged in water coupled with the acoustic waves generated by a FU transducer. The modeling results are used to examine and optimize parameters such as medium properties, input power and frequency, location, geometry and chemical composition of the SMP to achieve favorable shape recovery of a potential drug delivery system.
Friction of Extensible Strips: an Extended Shear Lag Model with Experimental Evaluation
Mojdehi, Ahmad R.; Holmes, Douglas P.; Williams, Christopher B.; Long, Timothy E.; Dillard, David A. (2016-02-22)
Functional compartmentalization in the hemocoel of insects
Pendar, Hodjat; Aviles, Jessica; Adjerid, Khaled; Schoenewald, Caroline; Socha, John J. (Springer Nature, 2019-04-15)
The insect circulatory system contains an open hemocoel, in which the mechanism of hemolymph flow control is ambiguous. As a continuous fluidic structure, this cavity should exhibit pressure changes that propagate quickly. Narrow-waisted insects create sustained pressure differences across segments, but their constricted waist provides an evident mechanism for compartmentalization. Insects with no obvious constrictions between segments may be capable of functionally compartmentalizing the body, which could explain complex hemolymph flows. Here, we test the hypothesis of functional compartmentalization by measuring pressures in a beetle and recording abdominal movements. We found that the pressure is indeed uniform within the abdomen and thorax, congruent with the predicted behavior of an open system. However, during some abdominal movements, pressures were on average 62% higher in the abdomen than in the thorax, suggesting that functional compartmentalization creates a gradient within the hemocoel. Synchrotron tomography and dissection show that the arthrodial membrane and thoracic muscles may contribute to this dynamic pressurization. Analysis of volume change suggests that the gut may play an important role in regulating pressure by translating between body segments. Overall, this study suggests that functional compartmentalization may provide an explanation for how fluid flows are managed in an open circulatory system.
How soap bubbles freeze
Ahmadi, S. Farzad; Nath, Saurabh; Kingett, Christian M.; Yue, Pengtao; Boreyko, Jonathan B. (Springer Nature, 2019-06-18)
Droplets or puddles tend to freeze from the propagation of a single freeze front. In contrast, videographers have shown that as soap bubbles freeze, a plethora of growing ice crystals can swirl around in a beautiful effect visually reminiscent of a snow globe. However, the underlying physics of how bubbles freeze has not been studied. Here, we characterize the physics of soap bubbles freezing on an icy substrate and reveal two distinct modes of freezing. The first mode, occurring for isothermally supercooled bubbles, generates a strong Marangoni flow that entrains ice crystals to produce the aforementioned snow globe effect. The second mode occurs when using a cold stage in a warm ambient, resulting in a bottom-up freeze front that eventually halts due to poor conduction along the bubble. Blending experiments, scaling analysis, and numerical methods, the dynamics of the freeze fronts and Marangoni flows are characterized.
The influence of interface bonding on thermal transport through solid-liquid interfaces
Harikrishna, H.; Ducker, William A.; Huxtable, Scott T. (AIP Publishing, 2013-06-01)
We use time-domain thermoreflectance to show that interface thermal conductance, G, is proportional to the thermodynamic work of adhesion between gold and water, W-SL, for a series of five alkane-thiol monolayers at the gold-water interface. W-SL is a measure of the bond strength across the solid-liquid interface. Differences in bond strength, and thus differences in W-SL, are achieved by varying the terminal group (omega-group) of the alkane-thiol monolayers on the gold. The interface thermal conductance values were in the range 60-190 MW m(-2) K-1, and the solid-liquid contact angles span from 25 degrees to 118 degrees. (C) 2013 AIP Publishing LLC.
Latent heat of traffic moving from rest
Ahmadi, S. Farzad; Berrier, Austin S.; Doty, William M.; Greer, Pat G.; Habibi, Mohammad; Morgan, Hunter A.; Waterman, Josam H.C.; Abaid, Nicole; Boreyko, Jonathan B. (IOP Publishing, 2017-11-22)
Contrary to traditional thinking and driver intuition, here we show that there is no benefit to ground vehicles increasing their packing density at stoppages. By systematically controlling the packing density of vehicles queued at a traffic light on a Smart Road, drone footage revealed that the benefit of an initial increase in displacement for close-packed vehicles is completely offset by the lag time inherent to changing back into a ‘liquid phase’ when flowresumes. This lag is analogous to the thermodynamic concept of the latent heat of fusion, as the ‘temperature’ (kinetic energy) of the vehicles cannot increase until the traffic ‘melts’ into the liquid phase.These findings suggest that in situations where gridlock is not an issue, drivers should not decrease their spacing during stoppages in order to lessen the likelihood of collisions with no loss in flowefficiency. In contrast, motion capture experiments of a line of people walking from rest showed higher flow efficiency with increased packing densities, indicating that the importance of latent heat becomes trivial for slower moving systems.
Modeling iontophoretic drug delivery in a microfluidic device
Moarefian, Maryam; Davalos, Rafael V.; Tafti, Danesh K.; Achenie, Luke E. K.; Jones, Caroline N. (2020-09-21)
Iontophoresis employs low-intensity electrical voltage and continuous constant current to direct a charged drug into a tissue. Iontophoretic drug delivery has recently been used as a novel method for cancer treatment in vivo. There is an urgent need to precisely model the low-intensity electric fields in cell culture systems to optimize iontophoretic drug delivery to tumors. Here, we present an iontophoresis-on-chip (IOC) platform to precisely quantify carboplatin drug delivery and its corresponding anti-cancer efficacy under various voltages and currents. In this study, we use an in vitro heparin-based hydrogel microfluidic device to model the movement of a charged drug across an extracellular matrix (ECM) and in MDA-MB231 triple-negative breast cancer (TNBC) cells. Transport of the drug through the hydrogel was modeled based on diffusion and electrophoresis of charged drug molecules in the direction of an oppositely charged electrode. The drug concentration in the tumor extracellular matrix was computed using finite element modeling of transient drug transport in the heparin-based hydrogel. The model predictions were then validated using the IOC platform by comparing the predicted concentration of a fluorescent cationic dye (Alexa Fluor 594 (R)) to the actual concentration in the microfluidic device. Alexa Fluor 594 (R) was used because it has a molecular weight close to paclitaxel, the gold standard drug for treating TNBC, and carboplatin. Our results demonstrated that a 50 mV DC electric field and a 3 mA electrical current significantly increased drug delivery and tumor cell death by 48.12% +/- 14.33 and 39.13% +/- 12.86, respectively (n = 3, p-value <0.05). The IOC platform and mathematical drug delivery model of iontophoresis are promising tools for precise delivery of chemotherapeutic drugs into solid tumors. Further improvements to the IOC platform can be made by adding a layer of epidermal cells to model the skin.
Noncoalescence in the Oblique Collision of Fluid Jets
Wadhwa, Navish; Vlachos, Pavlos P.; Jung, Sunghwan (American Physical Society, 2013-03-20)
When two jets of fluid collide, they can "bounce'' off each other, due to a thin film of air which keeps them separated. We describe the phenomenon of stable noncoalescence between two jets of the same fluid, colliding obliquely with each other. Using a simple experimental setup, we carry out a parametric study of the bouncing jets by varying the jet diameter, velocity, angle of inclination, and fluid viscosity, which suggests that the contact time of bouncing jets scales as the square root of the normal Weber number We. A dimensionless parameter K = (We root Re/sin alpha)(1/2), where Re is the normal Reynolds number and alpha the angle of inclination of the jets, quantitatively captures the transition of colliding jets from bouncing to coalescence. This parameter draws parallels between jet coalescence and droplet splashing and indicates that the transition is governed by a surface instability. Stable and continuous noncoalescence between fluid jets makes it a good platform for experimental studies of the interaction between fluid interfaces and the properties of the interfacial air films.
On the energy harvesting potential of piezoaeroelastic systems
Erturk, Alper; Vieira, W. G. R.; De Marqui, C.; Inman, Daniel J. (AIP Publishing, 2010-05-01)
This paper investigates the concept of piezoaeroelasticity for energy harvesting. The focus is placed on mathematical modeling and experimental validations of the problem of generating electricity at the flutter boundary of a piezoaeroelastic airfoil. An electrical power output of 10.7 mW is delivered to a 100 k load at the linear flutter speed of 9.30 m/s (which is 5.1% larger than the short-circuit flutter speed). The effect of piezoelectric power generation on the linear flutter speed is also discussed and a useful consequence of having nonlinearities in the system is addressed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3427405]
Passive water ascent in a tall, scalable synthetic tree
Shi, Weiwei; Dalrymple, Richard M.; McKenny, Collin J.; Morrow, David S.; Rashed, Ziad T.; Surinach, Daniel A.; Boreyko, Jonathan B. (Nature Research, 2020)
The transpiration cycle in trees is powered by a negative water potential generated within the leaves, which pumps water up a dense array of xylem conduits. Synthetic trees can mimic this transpiration cycle, but have been confined to pumping water across a single microcapillary or microfluidic channels. Here, we fabricated tall synthetic trees where water ascends up an array of large diameter conduits, to enable transpiration at the same macroscopic scale as natural trees. An array of 19 tubes of millimetric diameter were embedded inside of a nanoporous ceramic disk on one end, while their free end was submerged in a water reservoir. After saturating the synthetic tree by boiling it underwater, water can flow continuously up the tubes even when the ceramic disk was elevated over 3 m above the reservoir. A theory is developed to reveal two distinct modes of transpiration: an evaporation-limited regime and a flow-limited regime.
A piezomagnetoelastic structure for broadband vibration energy harvesting
Erturk, Alper; Hoffmann, J.; Inman, Daniel J. (AIP Publishing, 2009-06-01)
This letter introduces a piezomagnetoelastic device for substantial enhancement of piezoelectric power generation in vibration energy harvesting. Electromechanical equations describing the nonlinear system are given along with theoretical simulations. Experimental performance of the piezomagnetoelastic generator exhibits qualitative agreement with the theory, yielding large-amplitude periodic oscillations for excitations over a frequency range. Comparisons are presented against the conventional case without magnetic buckling and superiority of the piezomagnetoelastic structure as a broadband electric generator is proven. The piezomagnetoelastic generator results in a 200% increase in the open-circuit voltage amplitude (hence promising an 800% increase in the power amplitude).

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