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

Questo lavoro è stato finanziato dal National Institutes of Health (R21 AR079095) e dalla National Science Foundation (2142627).

Questo studio è stato approvato dal Pennsylvania State University Institutional Animal Care and Use Committee.
1. Preparazione dei tessuti
<ol><li>Per questo protocollo, raccogliere i tendini di Achille da topi maschi C57BL / 6 di 2-4 mesi. NOTA: potrebbero essere utilizzati anche diversi tendini o legamenti di topi o altri piccoli animali.<ol><li>Fare un'incisione sulla pelle superficiale al tendine di Achille per esporre il tendine plantare e il tessuto connettivo circ...

<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>

L'obiettivo di questo documento era fornire un metodo open source convalidato per misurare i campi di deformazione 2D nei tendini sotto carico di trazione. La base del software era basata su un algoritmo ALDIC disponibile al pubblico12. Questo algoritmo è stato incorporato in un codice MATLAB più grande con l'aggiunta della funzionalità di analisi incrementale (rispetto a cumulativa) della deformazione. Questo algoritmo adattato è stato quindi applicato alla prova di trazione dei tendini e la ...

I tendini sono tessuti meccanosensibili che si adattano e degenerano in risposta al carico meccanico 1,2,3,4. A causa del ruolo che gli stimoli meccanici svolgono nella biologia delle cellule tendinee, c'è un grande interesse nella comprensione dei ceppi che le cellule tendinee sperimentano nell'ambiente tissutale nativo durante il carico. Sono state sviluppate diverse tecniche sperimentali e analitiche per misurare i ceppi tissutali locali nei tendini. Questi includono analisi di correlazione digitale delle immagini (DIC) 2D / 3D di ceppi superficiali utilizzando modelli di macchie o linee fotosbiancate (PBL)5,6,7,8, misurazione dei cambiamenti nella distanza centroide-centroide dei singoli nuclei all'interno del tessuto 9,10 e un recente metodo DIC 3D a campo completo che considera il movimento fuori dal piano e le deformazioni 3D 11 . Tuttavia, l'accuratezza e la sensibilità di queste tecniche sono state riportate solo in pochi casi e nessuna di queste tecniche è stata resa disponibile al pubblico, il che rende difficile l'adozione e l'utilizzo diffuso di queste tecniche.
L'obiettivo di questo lavoro era quello di creare uno strumento di analisi convalidato per misurare i ceppi tissutali locali negli espianti di tendini che fosse prontamente disponibile e facile da usare. Il metodo scelto si basa su un algoritmo di correlazione digitale delle immagini agrangiane (ALDIC) disponibile pubblicamente e scritto in MATLAB sviluppato da Yang e Bhattacharya12. Questo algoritmo è stato adattato per analizzare campioni di tendini e convalidato applicandolo a immagini trasformate digitalmente e confrontando le tensioni misurate in campioni di tendini reali con i risultati ottenuti da linee fotosbiancate. Inoltre, nell'algoritmo sono state implementate funzionalità aggiuntive per confermare l'accuratezza del campo di spostamento calcolato anche in assenza di valori di deformazione noti o di una tecnica di misurazione secondaria. Pertanto, questo algoritmo è uno strumento altamente utile e adattabile per misurare con precisione i ceppi tissutali 2D locali nei tendini.

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

C'è un notevole interesse scientifico nella comprensione dei ceppi che le cellule tendinee sperimentano in situ e di come questi ceppi influenzano il rimodellamento dei tessuti. Sulla base di questo interesse, sono state sviluppate diverse tecniche analitiche per misurare i ceppi tissutali locali all'interno degli espianti di tendini durante il carico. Tuttavia, in diversi casi, l'accuratezza e la sensibilità di queste tecniche non sono state riportate e nessuno degli algoritmi è disponibile pubblicamente. Ciò ha reso difficile la misurazione più diffusa dei ceppi tissutali locali negli espianti di tendini. Pertanto, l'obiettivo di questo documento era quello di creare uno strumento di analisi convalidato per misurare ceppi tissutali locali negli espianti di tendini che fosse prontamente disponibile e facile da usare. In particolare, un algoritmo di correlazione digitale lagrangiana aumentata (ALDIC) disponibile al pubblico è stato adattato per misurare i ceppi 2D monitorando gli spostamenti dei nuclei cellulari all'interno dei tendini di Achille del topo sotto tensione uniassiale. Inoltre, l'accuratezza delle deformazioni calcolate è stata convalidata analizzando immagini trasformate digitalmente e confrontando le deformazioni con valori determinati da una tecnica indipendente (cioè linee fotosbiancate). Infine, nell'algoritmo è stata incorporata una tecnica per ricostruire l'immagine di riferimento utilizzando il campo di spostamento calcolato, che può essere utilizzato per valutare l'accuratezza dell'algoritmo in assenza di valori di deformazione noti o di una tecnica di misurazione secondaria. L'algoritmo è in grado di misurare deformazioni fino a 0,1 con una precisione di 0,00015. La tecnica per confrontare un'immagine di riferimento ricostruita con l'immagine di riferimento effettiva ha identificato con successo campioni che avevano dati errati e ha indicato che, nei campioni con dati validi, circa l'85% del campo di spostamento era accurato. Infine, i ceppi misurati nei tendini di Achille del topo erano coerenti con la letteratura precedente. Pertanto, questo algoritmo è uno strumento molto utile e adattabile per misurare con precisione i ceppi tissutali locali nei tendini.

Prima di analizzare i campi di deformazione in campioni di tessuto reali, il protocollo ALDIC è stato convalidato utilizzando immagini tese / trasformate digitalmente di nuclei all'interno dei tendini di Achille del topo. In particolare, le immagini sono state trasformate per produrre digitalmente ceppi uniformi nella direzione x del 2%, 4%, 6%, 8% e 10% di deformazione con un rapporto di Poisson simulato di 115,16. L'accuratezza dell'algoritmo ALDIC è stata qu...

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

Questo documento descrive un algoritmo di correlazione delle immagini digitali open source per misurare ceppi tissutali 2D locali all'interno di espianti di tendini. L'accuratezza della tecnica è stata convalidata utilizzando più tecniche ed è disponibile per uso pubblico.

Misurazione di ceppi tissutali locali nei tendini tramite correlazione di immagini digitali open source

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

Questo protocollo consente la misurazione delle tensioni tissutali locali all'interno di un tendine durante il carico. È utile capire come i tendini si comportano meccanicamente e si adattano al loro ambiente di carico. Il vantaggio principale di questa tecnica è che il software utilizzato è pubblicamente disponibile online e fornisce un feedback sull'accuratezza della misurazione anche quando i veri ceppi tissutali sono sconosciuti.Misurare le tensioni tissutali locali in un tendine è prezioso per capire come le cellule rimodellano il tessuto durante la degenerazione e la riparazione del tendine. A dimostrare questa procedura saranno Stanton Godshall, uno studente universitario, e Krishna Pedaprolu, uno studente di dottorato nel mio laboratorio. Dopo aver colorato i tendini di Achille raccolti in DTAF, trasferire il tessuto dalla soluzione DTAF alla soluzione DRAQ5 e incubare i tessuti in uno spazio buio per 10 minuti a temperatura ambiente.Posizionare il tendine nelle impugnature del dispositivo di carico della trazione. Prima di montare le impugnature nel dispositivo di caricamento, utilizzare calibri digitali per misurare la distanza tra l'attacco del calcagno e l'impugnatura opposta. Montare le impugnature nel dispositivo di caricamento contenente PBS per mantenere l'idratazione dei tessuti.Allineare il tendine nel miglior modo possibile con l'asse x o y delle immagini del microscopio in modo che le uscite della deformazione X e della deformazione Y dell'algoritmo corrispondano all'asse del tendine. Precaricare il tendine con un grammo di tensione. Se lo si desidera, fotocandeggina una serie di quattro linee distanziate di 80 micron nella regione centrale del tessuto e ripetere il processo sugli estremi sinistro e destro vicino alle impugnature.La variazione della distanza tra le linee in ciascuna regione tissutale è una misura secondaria dei ceppi tissutali locali che può essere utilizzata per convalidare i dati. Successivamente, utilizzando il microscopio confocale, acquisire immagini volumetriche della fluorescenza DTAF e DRAQ5 a un grammo di precarico. Eseguire una rampa di deformazione al 2% di deformazione allo 0,5% al secondo.Si noti che la velocità di deformazione e l'entità della deformazione incrementale possono essere regolate. Dopo aver permesso al tessuto di rilassarsi per 10 minuti, prendere un'altra immagine volumetrica del tessuto dopo la deformazione. Ripetere il processo per tutti gli incrementi di deformazione desiderati.Per creare le immagini trasformate digitalmente, scarica il codice digital_strain. m da GitHub. Dopo il download, apri ed esegui il codice.Quando richiesto, inserire i valori desiderati per la deformazione massima applicata, l'incremento della deformazione applicata e il rapporto di Poisson prima di premere OK. Quindi, quando richiesto, selezionate l'immagine di riferimento non deformata. Per ogni incremento di deformazione, viene visualizzata una sovrapposizione dell'immagine di riferimento e dell'immagine trasformata. Le immagini trasformate digitalmente verranno salvate nella directory denominata deformazione X percentuale trasformata digitalmente dove X è l'incremento di deformazione.Aprire lo script con il nome visualizzato e fare clic su Esegui per iniziare l'analisi dell'immagine. Quando richiesto, modificare i valori per la correlazione dell'immagine digitale lagrangiana aumentata o i parametri ALDIC come desiderato. Dopo essere stato richiesto, selezionare la casella di controllo Sì per salvare automaticamente il valore medio, la deviazione standard e la mappa 2D per la raccolta desiderata di variabili.Quando richiesto, selezionare le variabili desiderate come ceppo X, ceppo Y, ceppo di taglio, regioni danneggiate, eccetera e premere OK. Dopo il prompt successivo, selezionare la cartella che contiene le proiezioni Z di intensità massima rinominate. Il software esegue automaticamente ALDIC incrementali per determinare i campi di deformazione delle immagini deformate. Quando richiesto, fare clic con il pulsante sinistro del mouse per creare un poligono a quattro punti per definire la regione di interesse per la misurazione delle deformazioni.La cartella risultati del tracciamento nucleare, che può essere rinominata regolando le righe 555 e 556, memorizza tutti i grafici specificati in precedenza. Questa cartella contiene anche un foglio di calcolo denominato risultati, che memorizza tutte le medie e le deviazioni standard specificate in precedenza. Quando convalidato utilizzando immagini tese digitalmente, l'algoritmo ALDIC ha costantemente sottostimato la deformazione X media e l'entità dell'errore è aumentata con l'aumentare della tensione applicata.Anche il ceppo Y è stato per lo più sottovalutato. Tuttavia, in tutti i casi, l'entità dell'errore di deformazione era molto piccola. La deviazione standard del ceppo X calcolato e del ceppo Y, sebbene di bassa entità, aumentava con l'aumentare della deformazione applicata.L'analisi delle regioni danneggiate ha rivelato che il numero di regioni danneggiate con calcoli di deformazione non validi nelle immagini trasformate digitalmente analizzate utilizzando il metodo cumulativo è aumentato costantemente dopo il 6% di deformazione applicata, mentre la quantità incrementale è rimasta all'1% In uno dei quattro campioni, che è stato trattato come anomalo, quasi la metà dell'immagine è stata identificata come cattiva al massimo incremento di deformazione. I ceppi X calcolati da ALDIC erano più grandi di quelli determinati dai PBL, la differenza era compresa tra 0,005, che è simile alla deviazione standard per i dati PBL mediati in tutti i campioni. La determinazione delle grandezze e delle distribuzioni spaziali delle deformazioni locali nei tendini sotto carico di trazione ha mostrato che in tutti i campioni, il ceppo X è rimasto costantemente al di sotto delle deformazioni applicate.La deformazione media nella direzione Y era approssimativamente zero per tutti gli incrementi, ma la deviazione standard era elevata. La deformazione media di taglio è aumentata costantemente durante gli incrementi di deformazione. Il punto più importante da ricordare è salvare le immagini prima di applicare uno sforzo maggiore.Le immagini, se non salvate, vengono perse e non possono essere recuperate. Mentre questa tecnica è specificamente convalidata per misurare i ceppi tissutali all'interno dei tendini, può fornire informazioni sulla biologia meccanica e sulla meccanica di molti altri tessuti animali e umani.

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

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 ...

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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.

Real-Time DC-dinamica Metodo di polarizzazione per il tempo di commutazione miglioramento Severamente sottosmorzato frangente campo elettrostatico MEMS Attuatori

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.

Approfittando di ridotta interazione Droplet-superficie per ottimizzare il trasporto di Bioanalytes in microfluidica digitale

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.

La scansione SQUID Studio di Vortex manipolazione da locale Contatto

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.

La ricombinazione Dynamics nel fotovoltaici a film sottile Materiali tramite risolta nel tempo Microonde Conducibilità

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.

Misure di scambio di calore convettivo istantanea locale in un tubo - flusso singolo e due fasi

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.

Misurare la polarizzazione ferroelettrica magneticamente-sintonizzati in cristalli liquidi

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.

Misurazione della forza dinamica ha agito sulla gamba di Strider acqua saltando verso l'alto dal sensore Film PVDF

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.

Misure estensimetriche a pieno campo per affaticamento Microstructurally piccola crepa propagazione utilizzando il metodo di correlazione di immagini digitali

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.