Name: measuring local tissue strains in tendons via open-source digital image correlation
Uploaded: 2023-01-27T14:30:00
Description: Watch this Scientific Journal Video about Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation at JoVE.com

This work was funded by the National Institutes of Health (R21 AR079095) and the National Science Foundation (2142627).

This study was approved by the Pennsylvania State University Institutional Animal Care and Use Committee.
1. Tissue preparation
<ol>
	<li>For this protocol, harvest the Achilles tendons from 2-4 month old male C57BL/6 mice. 
	NOTE: Different tendons or ligaments from mice or other small animals could also be used.
	<ol>
		<li>Make an incision to the skin superficial to the Achilles tendon to expose the plantaris tendon and the surrounding connective tissue. Then, remove...

<ol>
	<li>Devkota, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Distributing+a+fixed+amount+of+cyclic+loading+to+tendon+explants+over+longer+periods+induces+greater+cellular+and+mechanical+responses.">Distributing a fixed amount of cyclic loading to tendon explants over longer periods induces greater cellular and mechanical responses.</a> Journal of Orthopaedic Research. 11 (4), 1609-1612 (2007).</li><li>Sun, H. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cycle-dependent+matrix+remodeling+gene+expression+response+in+fatigue-loaded+rat+patellar+tendons.">Cycle-dependent matrix remodeling gene expression response in fatigue-loaded rat patellar tendons.</a> Journal of Orthopaedic Research. 28 (10), 1380-1386 (2010).</li><li>Shepherd, J. H., Screen, H. R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fatigue+loading+of+tendon.">Fatigue loading of tendon.</a> International Journal of Experimental Pathology. 94 (4), 260-270 (2013).</li><li>Paschall, L., Pedaprolu, K., Carrozzi, S., Dhawan, A., Szczesny, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+stimulation+as+both+the+cause+and+the+cure+of+tendon+and+ligament+injuries.">Mechanical stimulation as both the cause and the cure of tendon and ligament injuries.</a> Regenerative Rehabilitation: From Basic Science to the Clinic. , 359-386 (2022).</li><li>Andarawis-Puri, N., Ricchetti, E. T., Soslowsky, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rotator+cuff+tendon+strain+correlates+with+tear+propagation.">Rotator cuff tendon strain correlates with tear propagation.</a> Journal of Biomechanics. 42 (2), 158-163 (2009).</li><li>Cheng, V. W. T., Screen, H. R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+micro-structural+strain+response+of+tendon.">The micro-structural strain response of tendon.</a> Journal of Materials Science. 42 (21), 8957-8965 (2007).</li><li>Luyckx, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Digital+image+correlation+as+a+tool+for+three-dimensional+strain+analysis+in+human+tendon+tissue.">Digital image correlation as a tool for three-dimensional strain analysis in human tendon tissue.</a> Journal of Experimental Orthopaedics. 1 (1), 7 (2014).</li><li>Duncan, N. A., Bruehlmann, S. B., Hunter, C. J., Shao, X., Kelly, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+cell-matrix+mechanics+in+tendon+fascicles+and+seeded+collagen+gels:+Implications+for+the+multiscale+design+of+biomaterials.">In situ cell-matrix mechanics in tendon fascicles and seeded collagen gels: Implications for the multiscale design of biomaterials.</a> Computer Methods in Biomechanics and Biomedical Engineering. 17 (1), 39-47 (2014).</li><li>Arnoczky, S. P., Lavagnino, M., Whallon, J. H., Hoonjan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+cell+nucleus+deformation+in+tendons+under+tensile+load;+A+morphological+analysis+using+confocal+laser+microscopy.">In situ cell nucleus deformation in tendons under tensile load; A morphological analysis using confocal laser microscopy.</a> Journal of Orthopaedic Research. 20 (1), 29-35 (2002).</li><li>Screen, H. R. C., Bader, D. L., Lee, D. A., Shelton, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Local+strain+measurement+within+tendon.">Local strain measurement within tendon.</a> Strain. 40 (4), 157-163 (2004).</li><li>Fung, A. K., Paredes, J. J., Andarawis-Puri, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+image+analysis+methods+for+quantification+of+in+situ+3-D+tendon+cell+and+matrix+strain.">Novel image analysis methods for quantification of in situ 3-D tendon cell and matrix strain.</a> Journal of Biomechanics. 67, 184-189 (2018).</li><li>Yang, J., Bhattacharya, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Augmented+Lagrangian+digital+image+correlation.">Augmented Lagrangian digital image correlation.</a> Experimental Mechanics. 59 (2), 187-205 (2019).</li><li>Peterson, B. E., Szczesny, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dependence+of+tendon+multiscale+mechanics+on+sample+gauge+length+is+consistent+with+discontinuous+collagen+fibrils.">Dependence of tendon multiscale mechanics on sample gauge length is consistent with discontinuous collagen fibrils.</a> Acta Biomaterialia. 117, 302-309 (2020).</li><li>Humphrey, J. D., O'Rourke, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> An Introduction to Biomechanics. , (2015).</li><li>Reese, S. P., Weiss, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tendon+fascicles+exhibit+a+linear+correlation+between+Poisson's+ratio+and+force+during+uniaxial+stress+relaxation.">Tendon fascicles exhibit a linear correlation between Poisson's ratio and force during uniaxial stress relaxation.</a> Journal of Biomechanical Engineering. 135 (3), 34501 (2013).</li><li>Ahmadzadeh, H., Freedman, B. R., Connizzo, B. K., Soslowsky, L. J., Shenoy, V. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micromechanical+poroelastic+finite+element+and+shear-lag+models+of+tendon+predict+large+strain+dependent+Poisson's+ratios+and+fluid+expulsion+under+tensile+loading.">Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson's ratios and fluid expulsion under tensile loading.</a> Acta Biomaterialia. 22, 83-91 (2015).</li><li>Szczesny, S. E., Elliott, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interfibrillar+shear+stress+is+the+loading+mechanism+of+collagen+fibrils+in+tendon.">Interfibrillar shear stress is the loading mechanism of collagen fibrils in tendon.</a> Acta Biomaterialia. 10 (6), 2582-2590 (2014).</li><li>Han, W. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Macro-+to+microscale+strain+transfer+in+fibrous+tissues+is+heterogeneous+and+tissue-specific.">Macro- to microscale strain transfer in fibrous tissues is heterogeneous and tissue-specific.</a> Biophysical Journal. 105 (3), 807-817 (2013).</li><li>Pedaprolu, K., Szczesny, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel,+open-source,+low-cost+bioreactor+for+load-controlled+cyclic+loading+of+tendon+explants.">A novel, open-source, low-cost bioreactor for load-controlled cyclic loading of tendon explants.</a> Journal of Biomechanical Engineering. 144 (8), 084505 (2022).</li><li>Gatt, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Negative+Poisson's+ratios+in+tendons:+An+unexpected+mechanical+response.">Negative Poisson's ratios in tendons: An unexpected mechanical response.</a> Acta Biomaterialia. 24, 201-208 (2015).</li></ol>

The objective of this paper was to provide an open-source, validated method to measure the 2D strain fields in tendons under tensile load. The foundation of the software was based on a publicly available ALDIC algorithm12. This algorithm was embedded into a larger MATLAB code with the added functionality of incremental (versus cumulative) strain analysis. This adapted algorithm was then applied to the tensile testing of tendons, and its accuracy was assessed by two different techniques (i.e., digi...

Tendons are mechanosensitive tissues that adapt and degenerate in response to mechanical loading1,2,3,4. Due to the role that mechanical stimuli play in tendon cell biology, there is a large interest in understanding the strains that tendon cells experience in the native tissue environment during loading. Several experimental and analytical techniques have been developed to measure local tissue strains in tendons. These include 2D/3D digital image correlation (DIC) analyses of surface strains using either speckle patterns or photobleached lines (PBLs)5,6,7,8, measurement of the changes in the centroid-to-centroid distance of individual nuclei within the tissue9,10, and a recent full-field 3D DIC method that considers out-of-plane motion and 3D deformations11. However, the accuracy and sensitivity of these techniques have been reported in only a few cases, and none of these techniques have been made publicly available, which makes the widespread adoption and utilization of these techniques difficult.
The objective of this work was to create a validated analysis tool for measuring local tissue strains in tendon explants that is readily available and easy to use. The chosen method is based on a publicly available augmented-Lagrangian digital image correlation (ALDIC) algorithm written in MATLAB that was developed by Yang and Bhattacharya12. This algorithm was adapted for analyzing tendon samples and validated by applying it to digitally transformed images and by comparing the strains measured in actual tendon samples to the results obtained from photobleached lines. Furthermore, additional functionality was implemented in the algorithm to confirm the accuracy of the calculated displacement field even in the absence of known strain values or a secondary measurement technique. Therefore, this algorithm is a highly useful and adaptable tool for accurately measuring local 2D tissue strains in tendons.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>5-DTAF (5-(4,6-Dichlorotriazinyl) Aminofluorescein), single isomer</td>
			<td>ThermoFisher</td>
			<td>D16</td>
			<td></td>
		</tr>
		<tr>
			<td>Calipers</td>
			<td>Mitutoyo</td>
			<td>500-196-30</td>
			<td></td>
		</tr>
		<tr>
			<td>Confocal Microscope</td>
			<td>Nikon</td>
			<td>A1R HD</td>
			<td></td>
		</tr>
		<tr>
			<td>Corning LSE Vortex Mixer</td>
			<td>Coning</td>
			<td>6775</td>
			<td></td>
		</tr>
		<tr>
			<td>DRAQ5 Fluorescent Probe Solution (5 mM)</td>
			<td>ThermoFisher</td>
			<td>62554</td>
			<td></td>
		</tr>
		<tr>
			<td>MATLAB</td>
			<td>MathWorks</td>
			<td>R2022b</td>
			<td></td>
		</tr>
		<tr>
			<td>Tensile Loading Device</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Tensile loading device described in Peterson et al, 2020. (ref 13)&#160;</td>
		</tr>
		<tr>
			<td>Tube Revolver Rotator</td>
			<td>ThermoFisher</td>
			<td>88881001</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring local tissue strains in tendons via open-source digital image correlation

There is considerable scientific interest in understanding the strains that tendon cells experience in situ and how these strains influence tissue remodeling. Based on this interest, several analytical techniques have been developed to measure local tissue strains within tendon explants during loading. However, in several cases, the accuracy and sensitivity of these techniques have not been reported, and none of the algorithms are publicly available. This has made it difficult for the more widespread measurement of local tissue strains in tendon explants. Therefore, the objective of this paper was to create a validated analysis tool for measuring local tissue strains in tendon explants that is readily available and easy to use. Specifically, a publicly available augmented-Lagrangian digital image correlation (ALDIC) algorithm was adapted for measuring 2D strains by tracking the displacements of cell nuclei within mouse Achilles tendons under uniaxial tension. Additionally, the accuracy of the calculated strains was validated by analyzing digitally transformed images, as well as by comparing the strains with values determined from an independent technique (i.e., photobleached lines). Finally, a technique was incorporated into the algorithm to reconstruct the reference image using the calculated displacement field, which can be used to assess the accuracy of the algorithm in the absence of known strain values or a secondary measurement technique. The algorithm is capable of measuring strains up to 0.1 with an accuracy of 0.00015. The technique for comparing a reconstructed reference image with the actual reference image successfully identified samples that had erroneous data and indicated that, in samples with good data, approximately 85% of the displacement field was accurate. Finally, the strains measured in mouse Achilles tendons were consistent with the prior literature. Therefore, this algorithm is a highly useful and adaptable tool for accurately measuring local tissue strains in tendons.

Prior to analyzing the strain fields in actual tissue samples, the ALDIC protocol was first validated using digitally strained/transformed images of nuclei within mouse Achilles tendons. Specifically, the images were transformed to digitally produce uniform strains in the x-direction of 2%, 4%, 6%, 8%, and 10% strain with a simulated Poisson&#39;s ratio of 115,16. The accuracy of the ALDIC algorithm was then assessed by comparing the mean calculated strain values...

Watch this Scientific Journal Video about Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation at JoVE.com

Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation

This paper describes an open-source digital image correlation algorithm for measuring local 2D tissue strains within tendon explants. The accuracy of the technique has been validated using multiple techniques, and it is available for public use.

Measuring Local Tissue Strains in Tendons via Open-Source Digital Image Correlation

There is considerable scientific interest in understanding the strains that tendon cells experience in situ and how these strains influence tissue ...

This protocol enables the measurements of the local tissue strains within a tendon during loading. It is useful to understand how tendons behave mechanically and adapt to their loading environment. The main advantage of this technique is that the software used is publicly available online and provides feedback on the measurement accuracy even when the true tissue strains are unknown.Measuring local tissue strains in a tendon is valuable to understand how cells remodel tissue during tendon degeneration and repair. Demonstrating this procedure will be Stanton Godshall, an undergraduate student, and Krishna Pedaprolu, a PhD student in my laboratory. After staining the harvested Achilles tendons in DTAF, transfer the tissue from the DTAF solution to the DRAQ5 solution and incubate the tissues in a dark space for 10 minutes at room temperature.Place the tendon into the grips of the tensile loading device. Before mounting the grips in the loading device, use digital calipers to measure the distance between the calcaneus attachment and the opposite grip. Mount the grips into the loading device containing PBS to maintain tissue hydration.Align the tendon as best as possible with either the x-axis or y-axis of the microscope images so that the X strain and Y strain outputs of the algorithm correspond with the tendon axis. Preload the tendon with one gram of tension. If desired, photobleach a set of four lines spaced 80 microns apart in the center region of the tissue, and repeat the process on the left and right extremes near the grips.The change in distance between the lines in each tissue region is a secondary measurement of the local tissue strains that can be used to validate the data. Next, using the confocal microscope, acquire volumetric images of the DTAF and DRAQ5 fluorescence at one gram of preload. Perform a strain ramp to 2%strain at 0.5%per second.Note that the strain rate and incremental strain magnitude can be adjusted. After allowing the tissue to stress relax for 10 minutes, take another volumetric image of the tissue after the deformation. Repeat the process for as many strain increments as desired.To create the digitally transformed images, download the code digital_strain. m from GitHub. After downloading, open and run the code.When prompted, insert desired values for the maximum applied strain, applied strain increment, and Poisson's ratio before pressing OK.Then when prompted again, select the undeformed reference image. For each strain increment, an overlay of the reference image and the transformed image is displayed. The digitally transformed images will be saved to the directory named digitally transformed X percent strain where X is the strain increment.Open the script with the displayed name and click Run to begin image analysis. When prompted, alter the values for the augmented Lagrangian digital image correlation or ALDIC parameters as desired. After being prompted, select the yes checkbox to automatically save the mean value, standard deviation, and 2D map for the desired collection of variables.When prompted, select the desired variables like X strain, Y strain, shear strain, bad regions, et cetera, and press OK.Following the next prompt, select the folder that contains the renamed max intensity Z projections. The software automatically performs incremental ALDIC to determine the strain fields of the deformed images. When prompted, left click to create a four-point polygon to define the region of interest for measuring the strains.The folder nuclear tracking results, which can be renamed by adjusting lines 555 and 556, stores all the plots specified previously. This folder also contains a spreadsheet named results, which stores all the means and standard deviations specified before. When validated using digitally strained images, the ALDIC algorithm consistently underestimated the mean X strain and the error magnitude increased with increasing applied strain.The Y strain was also mostly underestimated. However, in all cases, the magnitude of the strain error was very small. The standard deviation of the calculated X strain and Y strain, although low in magnitude, increased with increasing applied strain.Bad region analysis revealed that the number of bad regions having invalid strain calculations in the digitally transformed images analyzed using the cumulative method increased consistently after 6%applied strain, while the incremental quantity remained at 1%In one of the four samples, which was treated as an outlier, nearly half of the image was identified as bad at the maximum strain increment. The X strains calculated by ALDIC were larger than those determined from the PBLs, the difference being within 0.005 which is similar to the standard deviation for the PBL data averaged across all the samples. Determining the magnitudes and spatial distributions of the local strains in the tendons under tensile load showed that across all samples, the X strain consistently remained below the applied strains.The mean strain in the Y direction was approximately zero for all the increments, but the standard deviation was high. The mean shear strain increased steadily throughout the strain increments. The most important point to remember is to save the images prior to applying a greater strain.The images, if not saved, are lost and cannot be recovered. While this technique is specifically validated for measuring tissue strains within tendons, it can provide insight into mechanical biology and mechanics of many other animal and human tissues.

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Engineering

Echo Particle Image Velocimetry

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.2 For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.3,4,5,6 In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine7 with a PC running commercial particle image velocimetry (PIV) software8 is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported.
For the EPIV measurements, a phased array probe connected to the medical ultrasound machine is used to generate a two-dimensional ultrasound image by pulsing the piezoelectric probe elements at different times. Each probe element transmits an ultrasound pulse into the fluid, and tracer particles in the fluid (either naturally occurring or seeded) reflect ultrasound echoes back to the probe where they are recorded. The amplitude of the reflected ultrasound waves and their time delay relative to transmission are used to create what is known as B-mode (brightness mode) two-dimensional ultrasound images. Specifically, the time delay is used to determine the position of the scatterer in the fluid and the amplitude is used to assign intensity to the scatterer. The time required to obtain a single B-mode image, t, is determined by the time it take to pulse all the elements of the phased array probe. For acquiring multiple B-mode images, the frame rate of the system in frames per second (fps) = 1/&delta;t. (See 9 for a review of ultrasound imaging.)
For a typical EPIV experiment, the frame rate is between 20-60 fps, depending on flow conditions, and 100-1000 B-mode images of the spatial distribution of the tracer particles in the flow are acquired. Once acquired, the B-mode ultrasound images are transmitted via an ethernet connection to the PC running the PIV commercial software. Using the PIV software, tracer particle displacement fields, D(x,y)[pixels], (where x and y denote horizontal and vertical spatial position in the ultrasound image, respectively) are acquired by applying cross correlation algorithms to successive ultrasound B-mode images.10 The velocity fields, u(x,y)[m/s], are determined from the displacements fields, knowing the time step between image pairs, &Delta;T[s], and the image magnification, M[meter/pixel], i.e., u(x,y) = MD(x,y)/&Delta;T. The time step between images &Delta;T = 1/fps + D(x,y)/B, where B[pixels/s] is the time it takes for the ultrasound probe to sweep across the image width. In the present study, M = 77[&mu;m/pixel], fps = 49.5[1/s], and B = 25,047[pixels/s]. Once acquired, the velocity fields can be analyzed to compute flow quantities of interest.

An echo particle image velocimetry (EPIV) system capable of acquiring two-dimensional fields of velocity in optically opaque fluids or through optically opaque geometries is described, and validation measurements in pipe flow are reported.

The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 ...

Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input bias voltage. However, the tradeoff for the improved switching performance is a relatively long settling time to reach each gap height in response to various applied voltages. Transient applied bias waveforms are employed to facilitate reduced switching times for electrostatic fringing-field MEMS actuators with high mechanical quality factors. Removing the underlying substrate of the fringing-field actuator creates the low mechanical damping environment necessary to effectively test the concept. The removal of the underlying substrate also a has substantial improvement on the reliability performance of the device in regards to failure due to stiction. Although DC-dynamic biasing is useful in improving settling time, the required slew rates for typical MEMS devices may place aggressive requirements on the charge pumps for fully-integrated on-chip designs. Additionally, there may be challenges integrating the substrate removal step into the back-end-of-line commercial CMOS processing steps. Experimental validation of fabricated actuators demonstrates an improvement of 50x in switching time when compared to conventional step biasing results. Compared to theoretical calculations, the experimental results are in good agreement.

The robust device design of fringing-field electrostatic MEMS actuators results in inherently low squeeze-film damping conditions and long settling times when performing switching operations using conventional step biasing. Real-time switching time improvement with DC-dynamic waveforms reduces the settling time of fringing-field MEMS actuators when transitioning between up-to-down and down-to-up states.

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input ...

Taking Advantage of Reduced Droplet-surface Interaction to Optimize Transport of Bioanalytes in Digital Microfluidics

Digital microfluidics (DMF), a technique for manipulation of droplets, is a promising alternative for the development of &#8220;lab-on-a-chip&#8221; platforms. Often, droplet motion relies on the wetting of a surface, directly associated with the application of an electric field; surface interactions, however, make motion dependent on droplet contents, limiting the breadth of applications of the technique.
Some alternatives have been presented to minimize this dependence. However, they rely on the addition of extra chemical species to the droplet or its surroundings, which could potentially interact with droplet moieties. Addressing this challenge, our group recently developed Field-DW devices to allow the transport of cells and proteins in DMF, without extra additives.
Here, the protocol for device fabrication and operation is provided, including the electronic interface for motion control. We also continue the studies with the devices, showing that multicellular, relatively large, model organisms can also be transported, arguably unaffected by the electric fields required for device operation.

The protocol for fabrication and operation of field dewetting devices (Field-DW) is described, as well as the preliminary studies of the effects of electric fields on droplet contents.

Digital microfluidics (DMF), a technique for manipulation of droplets, is a promising alternative for the development of &#8220;lab-on-a-chip&#8221; ...

Scanning SQUID Study of Vortex Manipulation by Local Contact

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual vortices is necessary in order to study how vortices interact with each other, with the lattice, and with other magnetic objects. Here, we present a protocol for vortex manipulation in thin superconducting films by local contact, without applying current or magnetic field. Vortices are imaged using a scanning superconducting quantum interference device (SQUID), and vertical stress is applied to the sample by pushing the tip of a silicon chip into the sample, using a piezoelectric element. Vortices are moved by tapping the sample or sweeping it with the silicon tip. Our method allows for effective manipulation of individual vortices, without damaging the film or affecting its topography. We demonstrate how vortices were relocated to distances of up to 0.8 mm. The vortices remained stable at their new location up to five days. With this method, we can control vortices and move them to form complex configurations. This technique for vortex manipulation could also be implemented in applications such as vortex based logic devices.

We present a protocol for manipulation of individual vortices in thin superconducting films, using local mechanical contact. The method does not include applying current, magnetic field or additional fabrication steps.

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer coefficient as a function of the liquid flow rate in a transparent pipe. With certain amendments, the approach is extended to gas-liquid flows, with a particular emphasis on the effect of a single elongated (Taylor) air bubble on heat transfer enhancement. A non-invasive thermography technique is applied to measure the instantaneous temperature of a thin metal foil heated electrically. The foil is glued to cover a narrow slot cut in the pipe. The thermal inertia of the foil is small enough to detect the variation in the instantaneous foil temperature. The test section can be moved along the pipe and is long enough to cover a considerable part of the growing thermal boundary layer.
At the beginning of each experimental run, a steady state with a constant water flow rate and heat flux to the foil is attained and serves as the reference. The Taylor bubble is then injected into the pipe. The heat transfer coefficient variations due to the passage of a Taylor bubble propagating in a vertical pipe is measured as function of the distance of the measuring point from the bottom of the moving Taylor bubble. Thus, the results represent the local heat transfer coefficients. Multiple independent runs preformed under identical conditions allow accumulating sufficient data to calculate reliable ensemble-averaged results on the transient convective heat transfer. In order to perform this in a frame of reference moving with the bubble, the location of the bubble along the pipe has to be known at all times. Detailed description of measurements of the length and of the translational velocity of the Taylor bubbles by optical probes is presented.

This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Measurement of Dynamic Force Acted on Water Strider Leg Jumping Upward by the PVDF Film Sensor

This study aimed to make an explanation for the phenomenon in nature that water strider usually jumps or glides on the water surface easily but quickly, with its peak locomotion speed reaching 150 cm/s. First of all, we observed the microstructure and hierarchy of water strider legs using the scanning electron microscope. On the basis of the observed morphology of the legs, a theoretical model of the detachment from water surface was established, which explained water striders' capability to slide on water surface effortlessly in terms of energy reduction. Secondly, a dynamic force measurement system was devised using the PVDF film sensor with excellent sensitivity, which could detect the whole interaction process. Subsequently, a single leg in contact with water was pulled upward at different speeds, and the adhesion force was measured at the same time. The results of the departing experiment suggested a deep understanding of the fast jumping of water striders.

The protocol here is dedicated to investigating the free and quick maneuvering of water strider on water surface. The protocol includes observing the microstructure of legs and measuring the adhesion force when departing from water surface at different speeds.

This study aimed to make an explanation for the phenomenon in nature that water strider usually jumps or glides on the water surface easily but quickly, ...

Full-field Strain Measurements for Microstructurally Small Fatigue Crack Propagation Using Digital Image Correlation Method

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the growth of microstructurally small fatigue cracks. The proposed strain field analysis methodology is based on the use of a unique pattering technique with a characteristic speckle size of approximately 10 &#181;m. The developed methodology is applied to study the small fatigue crack behavior in body centered cubic (bcc) Fe-Cr ferritic stainless steel with a relatively large grain size allowing a high spatial measurement accuracy at the sub-grain level. This methodology allows the measurement of small fatigue crack growth retardation events and associated intermittent shear strain localization zones ahead of the crack tip. In addition, this can be correlated with the grain orientation and size. Thus, the developed methodology can provide a deeper fundamental understanding of the small fatigue crack growth behavior, required for the development of robust theoretical models for the small fatigue crack&#160;propagation in polycrystalline materials.

Microstructurally small fatigue crack growth behavior is investigated using a novel methodological approach combining crack growth rate measurement and strain-field analysis to reveal the cumulative deformation field at sub-grain level.

A novel measurement approach is used to reveal the cumulative deformation field at a sub-grain level and to study the influence of microstructure on the ...

Intermediate Strain Rate Material Characterization with Digital Image Correlation

The mechanical response of a material under dynamic load is typically different than its behavior under static conditions; therefore, the common quasistatic equipment and procedures used for material characterization are not applicable for materials under dynamic loads. The dynamic response of a material depends on its deformation rate and is broadly categorized into high (i.e., greater than 200/s), intermediate (i.e., 10&#8722;200/s) and low strain rate regimes (i.e., below 10/s). Each of these regimes calls for specific facilities and testing protocols to ensure the reliability of the acquired data. Due to the limited access to high-speed servo-hydraulic facilities and validated testing protocols, there is a noticeable gap in the results at the intermediate strain rate. The current manuscript presents a validated protocol for the characterization of different materials at these intermediate strain rates. Strain gauge instrumentation and digital image correlation protocols are also included as complimentary modules to extract the utmost level of detailed data from every single test. Examples of raw data, obtained from a variety of materials and test setups (e.g., tensile and shear) is presented and the analysis procedure used to process the output data is described. Finally, the challenges of dynamic characterization using the current protocol, along with the limitations of the facility and methods of overcoming potential problems are discussed.

Here we present a methodology for the dynamic characterization of tensile specimens at intermediate strain rates using a high-speed servo-hydraulic load frame. Procedures for strain gauge instrumentation and analysis, as well as for digital image correlation strain measurements on the specimens, are also defined.