Scholarly Works, Biomedical Engineering and Mechanics

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Comparison Of Flow Birefringence Data with A Numerical-Simulation Of The Hole Pressure
Baird, Donald G.; Read, M. D.; Reddy, Junuthula N. (AIP Publishing, 1988-08-01)
The penalty_Galerkin finite_element method is used to simulate the flow of a polystyrene melt over a rectangular slot placed perpendicular to the flow direction. The White_Metzner constitutive equation is used with a Carreau model viscosity function and a shear rate_dependent relaxation time defined so that the primary normal stress difference is exactly reproduced by the model in simple shear flow. Values of the stress field predicted by the simulation are compared with those obtained experimentally by means of flowbirefringence. As observed by others, the limiting elasticity value as determined by the Weissenberg number (We) for convergence of the algorithm decreased with increased refinement of the mesh. However, good agreement is still found between predicted values of stress using the coarse mesh and those measured by means of flowbirefringence. This work suggests that there may be an optimum mesh for a given flow and constitutive equation which will still give physically realistic results. The Weissenberg number for the melt used in the experimental study asymptotically approached a value of about 1.5 with increasing shear stress, suggesting that it may not be necessary to reach excessively high values of We for simulations involving some polymer melts.
Comparison Of The Rheological Properties Of Concentrated-Solutions Of A Rodlike And A Flexible Chain Polyamide
Baird, Donald G.; Ballman, R. L. (AIP Publishing, 1979)
The steady state shear rheological properties of solutions of a rodlike polyamide, poly_p_phenyleneterephthalamide (PPT), in 100% sulfuric acid have been compared with those of solutions of a flexible chain polyamide, nylon 6,6 in the same solvent. For solutions of similar concentration (c) and molecular weight (M), it was found that the primary normal stress difference (N1) and the viscosity (_), compared at the same shear rate (__), were an order of magnitude greater for solutions of PPT. It was believed that this behavior could be accounted for through the formation of an enhanced entanglement network in the PPT solutions. Plots of the zero shear viscosity(_0) versus cM_w, where M_w is the weight average molecular weight, for both systems revealed that "bends" occurred in the data corresponding to a critical entanglement molecular weight (Mc) of 1180 for PPT (this corresponds to 30 main chain atoms (z)) and to 5260 (z=330) for nylon 6,6. More significantly, _0 was found to be proportional to (cM_u)6.8 for solutions of PPT and to (cM_w)3.4 for nylon 6,6 solutions. _ versus __ curves were similar in shape for both systems and could be reduced to the same master curve with the only difference being that the relaxation times or shifting factors were considerably greater for the PPT solutions. This suggested that the process of destroying entanglements may be similar for both polymers. The overlap parameter c[_], where [_] is the intrinsic viscosity, provided a much better correlation of _0 data from the two sets of solutions than did the segment contact parameter cM_w. This suggested that the structural variable controlling the onset of entanglements may be a parameter such as the radius of gyration. Because of the inability of rodlike molecules to coil around each other, further insight into the nature of entanglements is obtained.
Immunomagnetic separation of tumor initiating cells by screening two surface markers
Sun, Chen; Hsieh, Yuan-Pang; Ma, Sai; Geng, Shuo; Cao, Zhenning; Li, Liwu; Lu, Chang (Springer Nature, 2017-01-11)
Isolating tumor initiating cells (TICs) often requires screening of multiple surface markers, sometimes with opposite preferences. This creates a challenge for using bead-based immunomagnetic separation (IMS) that typically enriches cells based on one abundant marker. Here, we propose a new strategy that allows isolation of CD44(+)/CD24(-) TICs by IMS involving both magnetic beads coated by anti-CD44 antibody and nonmagnetic beads coated by anti-CD24 antibody (referred to as two-bead IMS). Cells enriched with our approach showed significant enhancement in TIC marker expression (examined by flow cytometry) and improved tumorsphere formation efficiency. Our method will extend the application of IMS to cell subsets characterized by multiple markers.
The influence of interface bonding on thermal transport through solid-liquid interfaces
Harikrishna, H.; Ducker, William A.; Huxtable, Scott T. (AIP Publishing, 2013-06-01)
We use time-domain thermoreflectance to show that interface thermal conductance, G, is proportional to the thermodynamic work of adhesion between gold and water, W-SL, for a series of five alkane-thiol monolayers at the gold-water interface. W-SL is a measure of the bond strength across the solid-liquid interface. Differences in bond strength, and thus differences in W-SL, are achieved by varying the terminal group (omega-group) of the alkane-thiol monolayers on the gold. The interface thermal conductance values were in the range 60-190 MW m(-2) K-1, and the solid-liquid contact angles span from 25 degrees to 118 degrees. (C) 2013 AIP Publishing LLC.
Low-input and multiplexed microfluidic assay reveals epigenomic variation across cerebellum and prefrontal cortex
Ma, Sai; Hsieh, Yuan-Pang; Ma, Jian; Lu, Chang (AAAS, 2018-04-18)
Extensive effort is under way to survey the epigenomic landscape of primary ex vivo tissues to establish normal reference data and to discern variation associated with disease. The low abundance of some tissue types and the isolation procedure required to generate a homogenous cell population often yield a small quantity of cells for examination. This difficulty is further compounded by the need to profile a myriad of epigenetic marks. Thus, technologies that permit both ultralow input and high throughput are desired. We demonstrate a simple microfluidic technology, SurfaceChIP-seq, for profiling genome-wide histone modifications using as few as 30 to 100 cells per assay and with up to eight assays running in parallel. We applied the technology to profile epigenomes using nuclei isolated from prefrontal cortex and cerebellum of mouse brain. Our cell type–specific data revealed that neuronal and glial fractions exhibited profound epigenomic differences across the two functionally distinct brain regions.
Modeling iontophoretic drug delivery in a microfluidic device
Moarefian, Maryam; Davalos, Rafael V.; Tafti, Danesh K.; Achenie, Luke E. K.; Jones, Caroline N. (2020-09-21)
Iontophoresis employs low-intensity electrical voltage and continuous constant current to direct a charged drug into a tissue. Iontophoretic drug delivery has recently been used as a novel method for cancer treatment in vivo. There is an urgent need to precisely model the low-intensity electric fields in cell culture systems to optimize iontophoretic drug delivery to tumors. Here, we present an iontophoresis-on-chip (IOC) platform to precisely quantify carboplatin drug delivery and its corresponding anti-cancer efficacy under various voltages and currents. In this study, we use an in vitro heparin-based hydrogel microfluidic device to model the movement of a charged drug across an extracellular matrix (ECM) and in MDA-MB231 triple-negative breast cancer (TNBC) cells. Transport of the drug through the hydrogel was modeled based on diffusion and electrophoresis of charged drug molecules in the direction of an oppositely charged electrode. The drug concentration in the tumor extracellular matrix was computed using finite element modeling of transient drug transport in the heparin-based hydrogel. The model predictions were then validated using the IOC platform by comparing the predicted concentration of a fluorescent cationic dye (Alexa Fluor 594 (R)) to the actual concentration in the microfluidic device. Alexa Fluor 594 (R) was used because it has a molecular weight close to paclitaxel, the gold standard drug for treating TNBC, and carboplatin. Our results demonstrated that a 50 mV DC electric field and a 3 mA electrical current significantly increased drug delivery and tumor cell death by 48.12% +/- 14.33 and 39.13% +/- 12.86, respectively (n = 3, p-value <0.05). The IOC platform and mathematical drug delivery model of iontophoresis are promising tools for precise delivery of chemotherapeutic drugs into solid tumors. Further improvements to the IOC platform can be made by adding a layer of epidermal cells to model the skin.
Raman chemometric urinalysis (Rametrix) as a screen for bladder cancer
Huttanus, Herbert M.; Vu, Tommy; Guruli, Georgi; Tracey, Andrew; Carswell, William; Said, Neveen; Du, Pang; Parkinson, Bing G.; Orlando, Giuseppe; Robertson, John L.; Senger, Ryan S. (2020-08-21)
Bladder cancer (BCA) is relatively common and potentially recurrent/progressive disease. It is also costly to detect, treat, and control. Definitive diagnosis is made by examination of urine sediment, imaging, direct visualization (cystoscopy), and invasive biopsy of suspect bladder lesions. There are currently no widely-used BCA-specific biomarker urine screening tests for early BCA or for following patients during/after therapy. Urine metabolomic screening for biomarkers is costly and generally unavailable for clinical use. In response, we developed Raman spectroscopy-based chemometric urinalysis (Rametrix (TM)) as a direct liquid urine screening method for detecting complex molecular signatures in urine associated with BCA and other genitourinary tract pathologies. In particular, the Rametrix(TM)screen used principal components (PCs) of urine Raman spectra to build discriminant analysis models that indicate the presence/absence of disease. The number of PCs included was varied, and all models were cross-validated by leave-one-out analysis. In Study 1 reported here, we tested the Rametrix (TM) screen using urine specimens from 56 consented patients from a urology clinic. This proof-of-concept study contained 17 urine specimens with active BCA (BCA-positive), 32 urine specimens from patients with other genitourinary tract pathologies, seven specimens from healthy patients, and the urinalysis control Surine(TM). Using a model built with 22 PCs, BCA was detected with 80.4% accuracy, 82.4% sensitivity, 79.5% specificity, 63.6% positive predictive value (PPV), and 91.2% negative predictive value (NPV). Based on the number of PCs included, we found the Rametrix(TM)screen could be fine-tuned for either high sensitivity or specificity. In other studies reported here, Rametrix(TM)was also able to differentiate between urine specimens from patients with BCA and other genitourinary pathologies and those obtained from patients with end-stage kidney disease (ESKD). While larger studies are needed to improve Rametrix(TM)models and demonstrate clinical relevance, this study demonstrates the ability of the Rametrix(TM)screen to differentiate urine of BCA-positive patients. Molecular signature variances in the urine metabolome of BCA patients included changes in: phosphatidylinositol, nucleic acids, protein (particularly collagen), aromatic amino acids, and carotenoids.
The Rametrix (TM) PRO Toolbox v1.0 for MATLAB (R)
Senger, Ryan S.; Robertson, John L. (2020-01-06)
Background. Existing tools for chemometric analysis of vibrational spectroscopy data have enabled characterization of materials and biologicals by their broad molecular composition. The Rametrix (TM) LITE Toolbox v1.0 for MATLAB (R) is one such tool available publicly. It applies discriminant analysis of principal components (DAPC) to spectral data to classify spectra into user-defined groups. However, additional functionality is needed to better evaluate the predictive capabilities of these models when "unknown" samples are introduced. Here, the Rametrix (TM) PRO Toolbox v1.0 is introduced to provide this capability. Methods. The Rametrix (TM) PRO Toolbox v1.0 was constructed for MATLAB (R) and works with the Rametrix (TM) LITE Toolbox v1.0. It performs leave-one-out analysis of chemometric DAPC models and reports predictive capabilities in terms of accuracy, sensitivity (true-positives), and specificity (true-negatives). Rametrix (TM) PRO is available publicly through GitHub under license agreement at: https://github.com/SengerLab/RametrixPROToolbox. Rametrix (TM) PRO was used to validate Rametrix (TM) LITE models used to detect chronic kidney disease (CKD) in spectra of urine obtained by Raman spectroscopy. The dataset included Raman spectra of urine from 20 healthy individuals and 31 patients undergoing peritoneal dialysis treatment for CKD. Results. The number of spectral principal components (PCs) used in building the DAPC model impacted the model accuracy, sensitivity, and specificity in leave-one-out analyses. For the dataset in this study, using 35 PCs in the DAPC model resulted in 100% accuracy, sensitivity, and specificity in classifying an unknown Raman spectrum of urine as belonging to a CKD patient or a healthy volunteer. Models built with fewer or greater number of PCs showed inferior performance, which demonstrated the value of Rametrix (TM) PRO in evaluating chemometric models constructed with Rametrix (TM) LITE.
Ratio of dynamic moduli and estimation of relaxation times
Huang, J. H.; Baird, Donald G. (AIP Publishing, 2002-07-01)
In this paper, the theoretical interrelation between the ratio of dynamic moduli and the number and distribution of relaxation times required to fit the generalized Maxwell model to the data was investigated. Theorems were derived for making interval estimation of the relaxation times of the generalized Maxwell model from the ratio of linear combinations of the dynamic moduli at different frequencies. According to these theorems, given dynamic moduli (G' and G") at two frequencies a and b or three frequencies a, b, and (ab)(1/2), one must select at least one relaxation time in the relevant interval (tau(A), tau(B)) for the model to fit the data precisely. As a result, from a set of dynamic data G' and G", one can determine a series of (tau(A), tau(B)) from which the minimum number (N-min) and distribution (interval estimation of tau(i)) of relaxation times of the model can be estimated. The approach was applied to polystyrene data reported in the literature. The results were discussed and compared with those of relevant work, especially the nonlinear regression model-fitting procedure. (C) 2002 The Society of Rheology.
Rheological Properties Of Copolyester Liquid-Crystalline Melts .1. Capillary Rheometry
Jerman, R. E.; Baird, Donald G. (AIP Publishing, 1981)
Rheological properties of two copolyesters which exhibit liquid crystalline behavior in the melt state were determined using an Instron capillary rheometer. The two polymer melts with nematic liquid crystalline order consisted of copolymers of polyethylene terephthalate (PET) and 60 and 80 mole % of p_hydroxybenzoic acid (PHB). Data was also obtained on PET which was used as a control. Measurements included the temperature and shear rate dependence of viscosity, entrance pressure losses (_Pent), and die swell (Dj/D). The viscosity of the liquid crystalline melts are as much as two orders of magnitude less than those of PET at temperatures at which they are ordinarily processed. The extrudate actually contracts at the lower end of processing temperatures but does increase to values greater than one with increasing temperature for the liquid crystalline polymers. Although the die swell data indicate that there is negligible elastic recovery at the capillary exit, values of the ratio of _Pent to wall shear stress (_w) are considerably higher for liquid crystalline melts than for PET. Some explanation of these data is presented but more rheological measurements are needed before our understanding of these unique systems is complete.
Rheological Properties Of Liquid-Crystalline Solutions Of Poly-P-Phenyleneterephthalamide in Sulfuric-Acid
Baird, Donald G. (AIP Publishing, 1980)
The steady state shear and linear viscoelasticproperties of both isotropic and liquid crystalline solutions of the rigid chain polymer poly_p_phenyleneterephthalamide in sulfuric acid have been determined. Both the primary normal stress coefficient and the linear viscoelasticproperties show the same characteristic concentration behavior as does the viscosity. The unique rheological properties of the anisotropic phase can be attributed to the formation of a suspension of highly ordered regions in a matrix of isotropic fluid. The rheological properties were compared against the Bird_Carreau model and Hand's anisotropic fluid theory. Remarkably good agreement was found between the Bird_Carreau model and data especially at high shear rates. This suggested that at high shear rates very little difference may exist between anisotropic and isotropic phases. Hand's model was more applicable to solutions which were only slightly anisotropic.
Role Of Solvent Nature on Rheological Properties Of Nylon 6,6 Solutions
Baird, Donald G. (AIP Publishing, 1981)
The rheological properties of concentrated solutions of nylon 6,6 of various molecular weights in various solvents have been determined in steady shear flow. Four solvents including 90% formic acid,m_cresol, 97% H2SO4, and 100% H2SO4 were selected based on their effect on the ionic nature of nylon 6,6 in dilute solutions. The magnitude of the rheological properties of concentrated solutions depended on the solvent when compared at the same shear rate (__) and segment contact parameter (cM_w, where c is the concentration and M_w is the weight average molecular weight). However, as observed by others, the critical value of cM_w for the onset of entanglements was independent of the solvent. The contact parameter was effective in reducing values of _0 versus cM_w to a single curve for three of the solvents but values of _0 for formic acidsolutions were consistently two orders of magnitude lower than for the other solutions. Values of the equilibrium compliance, J0e, were highest for the formic acidsolutions. However values of the reduced compliance (JeR) for all four solutions were around 0.4 which is in reasonable agreement with the Rouse theory. The onset of non_Newtonian viscosity depended on the solvent but the shape of the flow curves was similar for all polymer/solvent systems. It is concluded that the solventviscosity may contribute more to the rheological properties of concentrated solutions than the solvent's influence on the ionic nature of polymer chains.
Spectral characteristics of urine specimens from healthy human volunteers analyzed using Raman chemometric urinalysis (Rametrix)
Senger, Ryan S.; Kavuru, Varun; Sullivan, Meaghan; Gouldin, Austin; Lundgren, Stephanie; Merrifield, Kristen; Steen, Caitlin; Baker, Emily; Vu, Tommy; Agnor, Ben; Martinez, Gabrielle; Coogan, Hannah; Carswell, William; Karageorge, Lampros; Dev, Devasmita; Du, Pang; Sklar, Allan; Orlando, Giuseppe; Pirkle, James, Jr.; Robertson, John L. (PLOS, 2019-09-27)
Raman chemometric urinalysis (Rametrix™) was used to analyze 235 urine specimens from healthy individuals. The purpose of this study was to establish the “range of normal” for Raman spectra of urine specimens from healthy individuals. Ultimately, spectra falling outside of this range will be correlated with kidney and urinary tract disease. Rametrix™ analysis includes direct comparisons of Raman spectra but also principal component analysis (PCA), discriminant analysis of principal components (DAPC) models, multivariate statistics, and it is available through GitHub as the Rametrix™ LITE Toolbox for MATLAB®. Results showed consistently overlapping Raman spectra of urine specimens with significantly larger variances in Raman shifts, found by PCA, corresponding to urea, creatinine, and glucose concentrations. A 2-way ANOVA test found that age of the urine specimen donor was statistically significant (p < 0.001) and donor sex (female or male identification) was less so (p = 0.0526). With DAPC models and blind leave-one-out build/test routines using the Rametrix™ PRO Toolbox (also available through GitHub), an accuracy of 71% (sensitivity = 72%; specificity = 70%) was obtained when predicting whether a urine specimen from a healthy unknown individual was from a female or male donor. Finally, from female and male donors (n = 4) who contributed first morning void urine specimens each day for 30 days, the co-occurrence of menstruation was found statistically insignificant to Rametrix™ results (p = 0.695). In addition, Rametrix™ PRO was able to link urine specimens with the individual donor with an average of 78% accuracy. Taken together, this study established the range of Raman spectra that could be expected when obtaining urine specimens from healthy individuals and analyzed by Rametrix™ and provides the methodology for linking results with donor characteristics.

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