Biomedical Engineering

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Publications by the Vanderbilt University Department of Biomedical Engineering.

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    Adsorption of methylene blue on papaya bark fiber: Equilibrium, isotherm and kinetic perspectives
    (Results In Engineering, 2022-12-21) Nipa, Sumaya Tarannum; Shefa, Nawrin Rahman; Parvin, Shahanaz; Khatun, Most Afroza; Alam, Md Jahangir; Chowdhury, Sujan; Khan, M. Azizur R.; Shawon, Sk Md Ali Zaker; Biswas, Biplob K.; Rahman, Md Wasikur
    Rapid population growth and industrial expansion lead us to be habitat of a polluted planet. One of the major pollutants that badly affect the ecosystem being organic dyes released from various chemical industries where cleaner production concept is straightway adopted. Papaya (Carica papaya) bark fiber (PBF) is a natural product used for Methylene Blue (MB) dye removal as a cost-effective adsorbent from aqueous solution by batch method. Several parameters as the effect of pH, initial dye concentration, contact time, and adsorbent dosage were studied and optimized for maximum dye recovery. Reaction kinetics of the process and Langmuir and Freundlich adsorption isotherms were investigated. Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) were used to confirm the surface properties of the PBF adsorbent. The maximum MB uptake capacity of PBF adsorbent was found to be 66.67 mg/g. Based on the results, the papaya bark fiber might be employed as a cost-effective bio-sorbent for the exclusion of dyestuffs from industrial effluent for cleaner production.
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    Cold exposure induces dynamic, heterogeneous alterations in human brown adipose tissue lipid content
    (Scientific Reports, 2019-09-19) Coolbaugh, Crystal L.; Damon, Bruce M.; Bush, Emily C.; Welch, E. Brian; Towse, Theodore F.
    Brown adipose tissue undergoes a dynamic, heterogeneous response to cold exposure that can include the simultaneous synthesis, uptake, and oxidation of fatty acids. The purpose of this work was to quantify these changes in brown adipose tissue lipid content (fat-signal fraction (FSF)) using fat-water magnetic resonance imaging during individualized cooling to 3 degrees C above a participant's shiver threshold. Eight healthy men completed familiarization, perception-based cooling, and MRI-cooling visits. FSF maps of the supraclavicular region were acquired in thermoneutrality and during cooling (59.5 +/- 6.5 min). Brown adipose tissue regions of interest were defined, and voxels were grouped into FSF decades (0-10%, 10-20%. 90-100%) according to their initial value. Brown adipose tissue contained a heterogeneous morphology of lipid content. Voxels with initial FSF values of 60-100% (P < 0.05) exhibited a significant decrease in FSF while a simultaneous increase in FSF occurred in voxels with initial FSF values of 0-30% (P < 0.05). These data suggest that in healthy young men, cold exposure elicits a dynamic and heterogeneous response in brown adipose tissue, with areas initially rich with lipid undergoing net lipid loss and areas of low initial lipid undergoing a net lipid accumulation.
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    Discrimination of Liver Malignancies with 1064 nm Dispersive Raman Spectroscopy
    (2015) Pence, Isaac J.; Patil, Chetan A.; Lieber, Chad A.; Mahadevan-Jansen, Anita
    Raman spectroscopy has been widely demonstrated for tissue characterization and disease discrimination, however current implementations with either 785 or 830 nm near-infrared (NIR) excitation have been ineffectual in tissues with intense autofluorescence such as the liver. Here we report the use of a dispersive 1064 nm Raman system using a low-noise Indium-Gallium-Arsenide (InGaAs) array to discriminate highly autofluorescent bulk tissue ex vivo specimens from healthy liver, adenocarcinoma, and hepatocellular carcinoma (N = 5 per group). The resulting spectra have been combined with a multivariate discrimination algorithm, sparse multinomial logistic regression (SMLR), to predict class membership of healthy and diseased tissues, and spectral bands selected for robust classification have been extracted. A quantitative metric called feature importance is defined based on classification outputs and is used to guide the association of spectral features with biological indicators of healthy and diseased liver tissue. Spectral bands with high feature importance for healthy and liver tumor specimens include retinol, heme, biliverdin, or quinones (1595 cm−1); lactic acid (838 cm−1); collagen (873 cm−1); and nucleic acids (1485 cm−1). Classification performance in both binary (normal versus tumor, 100% sensitivity and 89% specificity) and three-group cases (classification accuracy: normal 89%, adenocarcinoma 74%, hepatocellular carcinoma 64%) indicates the potential for accurately separating healthy and cancerous tissues and suggests implications for utilizing Raman techniques during surgical guidance in liver resection.
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    Effects of Prolonged Head-Down Bed Rest on Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals
    (Frontiers in Pyhsiology, 2019-08-23) Barbic, Franca; Heusser, Karsten; Minonzio, Maura; Shiffer, Dana; Cairo, Beatrice; Tank, Jens; Jordan, Jens; Diedrich, Andre; Gauger, Peter; Zamuner, Roberto Antonio; Porta, Alberto; Furlan, Raffaello
    Orthostatic intolerance commonly occurs after prolonged bed rest, thus increasing the risk of syncope and falls. Baroreflex-mediated adjustments of heart rate and sympathetic vasomotor activity (muscle sympathetic nerve activity - MSNA) are crucial for orthostatic tolerance. We hypothesized that prolonged bed rest deconditioning alters overall baroreceptor functioning, thereby reducing orthostatic tolerance in healthy volunteers. As part of the European Space Agency Medium-term Bed Rest protocol, 10 volunteers were studied before and after 21 days of -6 degrees head down bed rest (HDBR). In both conditions, subjects underwent ECG, beat-by-beat blood pressure, respiratory activity, and MSNA recordings while supine (REST) and during a 15-min 80 degrees head-up tilt (TILT) followed by a 3-min -10 mmHg stepwise increase of lower body negative pressure to pre-syncope. Cardiac baroreflex sensitivity (cBRS) was obtained in the time (sequence method) and frequency domain (spectrum and cross-spectrum analyses of RR interval and systolic arterial pressure - SAP, variability). Baroreceptor modulation of sympathetic discharge activity to the vessels (sBRS) was estimated by the slope of the regression line between the percentage of MSNA burst occurrence and diastolic arterial pressure. Orthostatic tolerance significantly decreased after HDBR (12 +/- 0.6 min) compared to before (21 +/- 0.6 min). While supine, heart rate, SAP, and cBRS were unchanged before and after HDBR, sBRS gain was slightly depressed after than before HDBR (sBRS: -6.0 +/- 1.1 versus -2.9 +/- 1.5 burst% x mmHg(-1), respectively). During TILT, HR was higher after than before HDBR (116 +/- 4 b/min versus 100 +/- 4 b/min, respectively), SAP was unmodified in both conditions, and cBRS indexes were lower after HDBR (alpha index: 3.4 +/- 0.7 ms/mmHg; BRSSEQ 4.0 +/- 1.0) than before (alpha index: 6.4 +/- 1.0 ms/mmHg; BRSSEQ 6.8 +/- 1.2). sBRS gain was significantly more depressed after HDBR than before (sBRS: -2.3 +/- 0.7 versus -4.4 +/- 0.4 burst% x mmHg(-1), respectively). Our findings suggest that baroreflex-mediated adjustments in heart rate and MSNA are impaired after prolonged bed rest. The mechanism likely contributes to the decrease in orthostatic tolerance.
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    Engineered fluidic systems to understand lymphatic cancer metastasis
    (Biomicrofluidics, 2020-01) Greenlee, Joshua D.; King, Michael R.
    The majority of all cancers metastasize initially through the lymphatic system. Despite this, the mechanisms of lymphogenous metastasis remain poorly understood and understudied compared to hematogenous metastasis. Over the past few decades, microfluidic devices have been used to model pathophysiological processes and drug interactions in numerous contexts. These devices carry many advantages over traditional 2D in vitro systems, allowing for better replication of in vivo microenvironments. This review highlights prominent fluidic devices used to model the stages of cancer metastasis via the lymphatic system, specifically within lymphangiogenesis, vessel permeability, tumor cell chemotaxis, transendothelial migration, lymphatic circulation, and micrometastases within the lymph nodes. In addition, we present perspectives for the future roles that microfluidics might play within these settings and beyond.
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    Engineered models to parse apart the metastatic cascade
    (NPJ Precision Oncology, 2019-08-21) Hapach, Lauren A.; Mosier, Jenna A.; Wang, Wenjun; Reinhart-King, Cynthia A.
    While considerable progress has been made in studying genetic and cellular aspects of metastasis with in vitro cell culture and in vivo animal models, the driving mechanisms of each step of metastasis are still relatively unclear due to their complexity. Moreover, little progress has been made in understanding how cellular fitness in one step of the metastatic cascade correlates with ability to survive other subsequent steps. Engineered models incorporate tools such as tailored biomaterials and microfabrication to mimic human disease progression, which when coupled with advanced quantification methods permit comparisons to human patient samples and in vivo studies. Here, we review novel tools and techniques that have been recently developed to dissect key features of the metastatic cascade using primary patient samples and highly representative microenvironments for the purposes of advancing personalized medicine and precision oncology. Although improvements are needed to increase tractability and accessibility while faithfully simulating the in vivo microenvironment, these models are powerful experimental platforms for understanding cancer biology, furthering drug screening, and facilitating development of therapeutics.
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    Thermal block of action potentials is primarily due to voltage-dependent potassium currents: a modeling study
    (Journal of Neural Engineering, 2019-06) Ganguly, Mohit; Jenkins, Michael W.; Jansen, E. Duco; Chiel, Hillel J.
    Objective. Thermal block of action potential conduction using infrared lasers is a new modality for manipulating neural activity. It could be used for analysis of the nervous system and for therapeutic applications. We sought to understand the mechanisms of thermal block. Approach. To analyze the mechanisms of thermal block, we studied both the original Hodgkin/Huxley model, and a version modified to more accurately match experimental data on thermal responses in the squid giant axon. Main results. Both the original and modified models suggested that thermal block, especially at higher temperatures, is primarily due to a depolarization-activated hyperpolarization as increased temperature leads to faster activation of voltage-gated potassium ion channels. The minimum length needed to block an axon scaled with the square root of the axon's diameter. Significance. The results suggest that voltage-dependent potassium ion channels play a major role in thermal block, and that relatively short lengths of axon could be thermally manipulated to selectively block fine, unmyelinated axons, such as C fibers, that carry pain and other sensory information.
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    Thermal block of action potentials is primarily due to voltage-dependent potassium currents: a modeling study
    (Journal of Neural Engineering, 2019-06) Ganguly, Mohit; Jenkins, Michael W.; Jansen, E. Duco; Chiel, Hillel J.
    Objective. Thermal block of action potential conduction using infrared lasers is a new modality for manipulating neural activity. It could be used for analysis of the nervous system and for therapeutic applications. We sought to understand the mechanisms of thermal block. Approach. To analyze the mechanisms of thermal block, we studied both the original Hodgkin/Huxley model, and a version modified to more accurately match experimental data on thermal responses in the squid giant axon. Main results. Both the original and modified models suggested that thermal block, especially at higher temperatures, is primarily due to a depolarization-activated hyperpolarization as increased temperature leads to faster activation of voltage-gated potassium ion channels. The minimum length needed to block an axon scaled with the square root of the axon's diameter. Significance. The results suggest that voltage-dependent potassium ion channels play a major role in thermal block, and that relatively short lengths of axon could be thermally manipulated to selectively block fine, unmyelinated axons, such as C fibers, that carry pain and other sensory information.