Won the Best Paper Award
Abstract : Reduced fluid-structure interaction models have received a considerable attention in recent years being the key component of hemodynamic modeling. A variety of models applying to specific physiological components such as arterial, venous and cerebrospinal fluid (CSF) circulatory systems have been developed based on different approaches. The purpose of this paper is to apply the general approach based on Hamilton’s variational principle to create a model for a viscous Newtonian fluid – structure interaction (FSI) in a compliant bifurcated network. This approach provides the background for a correct formulation of reduced FSI models with an account for arbitrary nonlinear visco-elastic properties of compliant boundaries. The correct boundary conditions are specified at junctions, including matching points in a combined 3D/1D approach. The hyperbolic properties of derived mathematical model are analyzed and used, constructing the monotone finite volume numerical scheme, second-order accuracy in time and space. The computational algorithm is validated by comparison of numerical solutions with the exact manufactured solutions for an isolated compliant segment and a bifurcated structure. The accuracy of applied TVD (total variation diminishing) and Lax-Wendroff methods are analyzed by comparison of numerical results to the available analytical smooth and discontinuous solutions.
Microfluidics-based electronics have shown great potential in numerous applications, such as energy harvesters, bio-inspired devices, and wearable healthcare sensors. Fabrication challenges and material incompatibilities pose barriers to achieving the full potential of this emerging field. Elastomeric flexible microfluidic channels are conventionally fabricated by casting on a micro-machined mold, followed by a bonding step. Difficulty fabricating multilayers, and weak bonding to many substrates limit device capabilities and scalability. Integration of transducers within microfluidic channels is also challenging, especially for materials requiring high temperature annealing.
Novel processing techniques for the realization of scalable and flexible microfluidic electronics have been developed to suit a wide range of substrates. Biocompatible Polyethylene-glycol (PEG) is Inkjet-printed as a sacrificial layer. Elastomers, the channels’ structural material, are cast on PEG and cured. PEG can then be removed through heating above its phase-change temperature. This process allows easy modulation of the shape and dimensions of the channels on any substrate, and eliminates the need of manual realization of multilayers interconnection. Integration of ferroelectric and magnetic sensors is demonstrated with a photonic annealing process that enables film heating to over 900°C with insignificant substrate heating. Combined, these techniques enable realization of a new generation of wearable, flexible microfluidic electronics.
An essential component in the study of inner ear drug delivery is cochlear fluid
pharmacokinetics. A popular method for simulating the drug diffusion in the inner ear
(Plontke et al., Audiology and Neurotology, 12:37-48, 2007) uses a finite element
method model that relies on assumed values of the diffusion coefficients within the
scala tympani (ST), scala vestibuli (SV), scala media (SM), and spiral ligament (SL),
as well as parameters describing the permeability between them and clearance to
other regions. In this work, we investigate inverting this model to estimate diffusion
parameters given empirical concentration values derived from micro-computed
tomography (μCT) imagery of the mouse cochlea. Solving the inverse problem over
the entire set of 3-D regions can be computationally intensive, so we focus instead on
inverting the reduced 1-D problem proposed by Plontke et al. Given initial estimates
of the diffusion, permeability, and clearance parameters, we use an iterative nonlinear
least-squares technique to minimize the mean-squared error between the predicted
concentration values and those derived by averaging over regional cross-sections of
the μCT scans. Extracting the appropriate cross-sectional data from each of the four
regions in the μCT scans is a difficult task that requires accurately
identifying/segmenting the regions. So, we employed a 3-D subject-atlas image
registration technique (Z. Xu, MS Thesis, Rochester Institute of Technology, 2016).
This aligns the high-resolution atlas with pre-identified regions to the μCT scans,
enabling labels for the regions to be propagated. However, voxels are inherently
discrete, hence the registration will not be perfectly accurate, so it is likely that the
labeled regions may include data from bones near the region boundaries. For this
reason, we weight voxels based on their proximity to the center of their labeled
region, so voxels that may contain bone have less influence on the derived
concentration values. Using a set of μCT scans comprising a baseline scan and
subsequent scans of a mouse during micro-infusion delivery of a contrast agent
(ioversol) to its cochlea, we illustrate how our techniques can be used to robustly
estimate diffusion, permeability, and clearance parameters for Plontke et al.’s reduced
1-D problem. These results will accelerate pre-clinical and clinical development of
infusion paradigms, to facilitate optimal drug delivery to the cochlea, for preventing
or treating acute and chronic types of hearing loss.
Supported by the National Institute On Deafness and Other Communication Disorders
of the National Institutes of Health, under Award # R01 DC014568.
A method including a dosimetry device having at least one sensor in a housing and a dosimetry processing device with a memory. The dosimetry processing device is coupled to the at least one sensor in the housing. The dosimetry processing device is configured to execute programmed instructions stored in the memory comprising; obtaining readings from the sensor; storing the readings; conducting an analysis of the stored readings to determine an injury risk assessment; and outputting at least one of the conducted analysis of the determined injury risk assessment or the stored readings.
Biomedical engineering advances in protective and restorative inner ear biotherapies have created new opportunities to address vestibular disorders, deafness, and noise induced-, sensorineural, and age-related hearing loss. To avoid unwanted, systemic side-effects, controllable, programmable drug delivery systems are essential for therapeutic development in animal models, and for future human translation with implantable, subcutaneous or behind-the-ear systems. The mouse animal-model system offers significant advantages for studies involving specific transgenic, knock-in, and knockout variants that model different human diseases and communication disorders. However, the small size of the mouse necessitates key advances in pump miniaturization for implantation and scaling of flow rates and volumes to match cochlear anatomy. Here we present a biocompatible, fully implantable, scalable, and wirelessly controlled peristaltic micropump. The microfluidic core is based on commercially available catheter microtubing (250μm OD, 125μm ID) providing a leak-free, biocompatible flow path while avoiding complex microfluidic interconnects. Direct write micro-scale printing provides structure around the microtubing for mechanical support and actuation. Micropump features are fabricated directly on the backside of a printed circuit board assembly providing control electronics for sequenced actuation and wireless control. Peristaltic flow is achieved by compressing the microtubing via expansion and contraction of a thermal phase-change material integrated adjacent to the microtubing and within the printed micropump structure. A refillable reservoir was integrated with the micropump while maintaining a form factor optimized for subcutaneous implantation in the mouse. Pump characterization results and initial in vivo implantation tests are presented. Initially targeting the small murine cochlea, this low-cost design and fabrication methodology is inherently scalable to larger animals and for clinical applications in children and adults by appropriate scaling of the microtubing size and actuator volume.
Supported by the National Institute On Deafness and Other Communication Disorders of the National Institutes of Health, under Award # R01 DC014568.
Advanced micropumps that enable chronic delivery of therapeutic agents with controlled delivery profiles require integrated electronics and wireless communication capabilities. Traditional assembly approaches require high temperature soldering processes that preclude direct integration with micropumps designed with temperature sensitive polymer components. Here we present low temperature assembly of commercial, off-the-shelf surface mount electronic components electrically connected to the substrate interconnects through a conductive adhesive. The anisotropic conductive adhesive process uses a magnetic field to align conductive particles from 0.5 to 3 μm within the adhesive in the z-direction during curing, providing electrical bridges between the electronic components and the substrate, and insulating between pads in the x-y directions. The isotropic silver adhesive has uniform high conductivity, but must be placed precisely to prevent horizontal bridging. Micropump electronics are demonstrated including embedded microprocessor, power regulation, feedback control of thermal actuators, and Bluetooth low-energy wireless communications. The overall dimensions of the complete assembly are 8.2 mm x 8.8 mm x 1.8 mm. The controller is assembled using the smallest commercially available parts, wafer-level chip-scale packages at 0.4 mm contact pitch and 0.15 mm contact spacing. Assembly is carried out by applying the adhesive to the substrate, placing the components, and then curing at a maximum temperature of 70 °C. Integrated micropump electronics assembled using isotropic and anisotropic conductive adhesive processes are demonstrated for feasibility and performance. The approach enables use of power efficient, commercial off-the-shelf electronics and integration over low-temperature substrates. Future work will leverage this approach to integrate these electronics directly on a micropump with interconnects defined using direct-write technologies.
Supported by the National Institute On Deafness and Other Communication Disorders of the National Institutes of Health under Award Number R01DC014568.
Low flow rate micropumps play an increasingly important role in drug therapy research. Infusions to small biological structures and lab-on-a-chip applications require ultra-low flow rates and will benefit from the ability to expend no power in the blocked-flow state. Here we present a planar micropump based on gallium phase-change actuation that leverages expansion during solidification to occlude the flow channel in the off-power state. The presented four chamber peristaltic micropump was fabricated with a combination of Micro Electro Mechanical System (MEMS) techniques and additive manufacturing direct write technologies. The device is 7 mm × 13 mm × 1 mm (<100 mm3) with the flow channel and exterior coated with biocompatible Parylene-C, critical for implantable applications. Controllable pump rates from 18 to 104 nL/min were demonstrated, with 11.1 ± 0.35 nL pumped per actuation at an efficiency of 11 mJ/nL. The normally-closed state of the gallium actuator prevents flow and diffusion between the pump and the biological system or lab-on-a-chip, without consuming power. This is especially important for implanted applications with periodic drug delivery regimens.
Pulse wave velocity (PWV) is an important index of arterial hemodynamics, which lays the foundation for continuous, noninvasive blood pressure automated monitoring. The goal of this paper is to examine the accuracy of PWV prediction based on a traditional homogeneous structural model for thin-walled arterial segments. In reality arteries are described as composite heterogeneous hyperelastic structures, where the thickness dimension cannot be considered small compared to the cross section size. In this paper we present a hemodynamic fluid – structure interaction model accounting for the variation of geometry and material properties in a radial direction. The model is suitable to account for the highly nonlinear orthotropic material undergoing finite deformation for each layer. Numerical analysis of single and two layer arterial segments shows that a single thick layer model provides sufficient accuracy to predict PWV. The dependence of PWV on pressure for three vessels of different thicknesses is compared against a traditional thin wall model of a membrane shell interacting with an incompressible fluid. The presented thick wall model provides greater accuracy in the prediction of PWV, and will be important for blood pressure estimation based on PWV measurements.
Lead Zirconate Titanate (PZT) is a commonly used piezoelectric material due to its high piezoelectric response. We demonstrate a new method of printing and sintering micro-scale PZT films with low substrate temperature increase. Self-prepared PZT ink was Aerosol-Jet printed on stainless steel substrates. After drying for 2 h in vacuum at 200°C, the printed PZT films were divided into two groups. The first group was traditionally sintered, using a thermal process at 1000°C for 1 h in an Argon environment. The second group was photonically sintered using repetitive sub-msec pulses of high intensity broad spectrum light in an atmospheric environment. The highest measured substrate temperature during photonic sintering was 170.7°C, enabling processing on low melting point substrates. Ferroelectric measurements were performed with a low-frequency sinusoidal signal. The remanent polarization (Pr) and coercive field (Ec) for thermally sintered PZT film were 17.1 μC/cm2 and 6.3 kV/cm, respectively. The photonically sintered film had 32.4 μC/cm2 Pr and 6.7 kV/cm Ec. After poling the samples with 20 kV/cm electric field for 2 h at 150°C, the piezoelectric voltage constant (g33) was measured for the two film groups yielding −16.9 × 10−3 (V·m)·N−1 (thermally sintered) and −17.9 × 10−3 (V·m)·N−1(photonically sintered). Both factors indicate the PZT films were successfully sintered using both methods, with the photonically sintered material exhibiting superior electrical properties. To further validate photonic sintering of PZT on low melting point substrates, the process and measurements were repeated using a polyethylene terephthalate (PET) substrate. The measured Pr and Ec were 23.1 μC/cm2 and 5.1 kV/cm, respectively. The g33 was −17.3 × 10−3 (V·m)·N−1. Photonic sintering of thick film PZT directly on low melting point substrates eliminates the need for complex layer transfer processes often associated with flexible PZT transducers.
Hypertension is a significant worldwide health issue. Continuous blood pressure monitoring is important for early detection of hypertension, and for improving treatment efficacy and compliance. Pulse wave velocity (PWV) has the potential to allow for a continuous blood pressure monitoring device; however published studies demonstrate significant variability in this correlation. In a recently presented physics-based mathematical model of PWV, flow velocity is additive to the classic pressure wave as estimated by arterial material properties, suggesting flow velocity correction may be important for cuff-less non-invasive blood pressure measures. The present study examined the impact of systolic flow correction of a measured PWV on blood pressure prediction accuracy using data from two published in vivo studies. Both studies examined the relationship between PWV and blood pressure under pharmacological manipulation, one in mongrel dogs and the other in healthy adult males. Systolic flow correction of the measured PWV improves the R2 correlation to blood pressure from 0.51 to 0.75 for the mongrel dog study, and 0.05 to 0.70 for the human subjects study. The results support the hypothesis that systolic flow correction is an essential element of non-invasive, cuff-less blood pressure estimation based on PWV measures.
Controllable drug delivery systems will become increasingly important as protective and restorative biotherapies for noise induced-, sensorineural-, and age-related hearing loss; deafness, and vestibular disorders are developed. Miniaturized pumps create opportunities for therapy development in animal models, and will be essential for fully implanted or behind the ear systems for human translation. In particular, since mice have become such a successful biomedical, genetic and bioengineering lab animal of choice, development of micropumps that can be implanted subcutaneously in mice is quite important. This will allow in vivo testing of novel drug treatments in transgenic, knock-in, knockout and various strains of mice that model different human diseases. Here we present progress on a scalable micropump platform based on direct, phase change actuation of either microtubing or micro-fabricated diaphragms for peristalsis. The first approach integrates commercially available 250 μm outer diameter/125 µm inner diameter polyurethane catheter tubing that serves as the micropump flow channel, reservoir interconnect, and cannula connection to the drug delivery site. Direct-write, 3D print technologies are used for definition of micropump features, heaters, and accurate delivery of paraffin wax for phase change actuation. In the latter case, the fluid pumping chambers are formed by a spin-coated PDMS (polydimethyl siloxane) layer peeled off from a 3D printed mold. Then the chambers are bonded with directly-written heaters/paraffin wax actuators embedded in the PDMS diaphragm to integrate a micropump. Results with a proof-of principal device are presented showing an ability to deliver volumes at less than 10 nL per actuation event. This can be scaled readily to higher flow rates by increasing the tubing/paraffin reservoir size and frequency of peristalsis. To test for biocompatibility, procedures consistent with the ISO 10993 standard for implantable medical devices were used. An epithelial cell line was cultured under standard conditions. The micropump components were sterilized with ethylene oxide and then inserted into the center of the cell culture wells. Biocompatibility data analyses are ongoing, but assays of cell cytotoxicity so far reveal no toxicity. Future work will integrate the micropump with a drug reservoir and control electronics for wireless communication and in vivo testing in the mouse model system.
Supported by the National Institute On Deafness and Other Communication Disorders of the National Institutes of Health under Award Number R01DC014568.
Pulse wave velocity (PWV) quantification commonly serves as a highly robust prognostic parameter being used in a preventative cardiovascular therapy. Being dependent on arterial elastance, it can serve as a marker of cardiovascular risk. Since it is influenced by a blood pressure (BP), the pertaining theory can lay the foundation in developing a technique for noninvasive blood pressure measurement. Previous studies have reported application of PWV, measured noninvasively, for both the estimation of arterial compliance and blood pressure, based on simplified physical or statistical models. A new theoretical model for pulse wave propagation in a compliant arterial segment is presented within the framework of pseudo-elastic deformation of biological tissue undergoing finite deformation. An essential ingredient is the dependence of results on nonlinear aspects of the model: convective fluid phenomena, hyperelastic constitutive relation, large deformation and a longitudinal pre-stress load. An exact analytical solution for PWV is presented as a function of pressure, flow and pseudo-elastic orthotropic parameters. Results from our model are compared with published in-vivo PWV measurements under diverse physiological conditions. Contributions of each of the nonlinearities are analyzed. It was found that the totally nonlinear model achieves the best match with the experimental data. To retrieve individual vascular information of a patient, the inverse problem of hemodynamics is presented, calculating local orthotropic hyperelastic properties of the arterial wall. The proposed technique can be used for non-invasive assessment of arterial elastance, and blood pressure using direct measurement of PWV, with account of hyperelastic orthotropic properties.
Dynamic contrast enhanced (DCE) Micro-computed tomography (µCT) imagery of the rodent inner ear has been successfully used to noninvasively characterize drug delivery inside the cochlea (Haghpanahi et al., Annals of Biomedical Engineering, 41(10):2130- 2142, 2013). Using a series of manually segmented and labeled histological sections of a mouse inner ear as an atlas, Haghpanahi et al. registered selected 2-D atlas images to slices of the µCT image, allowing the atlas labels to be propagated to identify and segment the intracochlear structures in the subject mouse. With this technique, drug concentration profiles can be quantified in each segmented structure. In this work, we present two improvements in the atlas-based registration step; i) full automation, which improves analysis by removing the need for an expert user to select specific slices from the µCT image for registration, and ii) full three-dimensional registration, which improves segmentation accuracy by incorporating all atlas images instead of a user-selected subset. To enable full automation, we carry out the following steps: (i) threshold the µCT image to identify bone regions (+700 to +3000 HU), (ii) identify the sagittal plane by maximizing the Jaccard index (a measure of symmetry) between the left and right bone regions, and (iii) localize the region containing the inner ear by searching for geometric features matching those of the atlas that are preserved when reflected through the sagittal plane. Once the inner ear region has been automatically localized, we perform 3-D atlas-based registration by first identifying the 3-D affine transformation that optimally aligns the atlas with the inner ear, and then refining the registration result by performing 3-D deformable registration. Using the 3-D deformation aligning atlas to subject, we propagate the manually identified region labels from the atlas to yield estimates of the locations of the scala media, scala tympani, and scala vestibule. Finally, we refine the predicted boundaries of the different scalae via a level-set energy minimization approach. Using multiple µCT subject images, we illustrate that our fully automated approach that uses the full three dimensions of data from the atlas and subject images enables more accurately segmented scalae regions than are attainable using the previous approach of estimating a collection of 2-D transformations between atlas and subject slices and interpolating the results.
Supported by the National Institute On Deafness and Other Communication Disorders of the National Institutes of Health under Award Number R01DC014568.
Here we show that the electric field inside an ultrathin membrane is weaker than conventional theory would predict, and that the reduced field is predictive of measured electroosmotic flow rates. Our theoretical analysis shows that the electric field inside a charged nanopore is affected by end effects and dependent on the Dukhin number Du when the pore length-to-diameter aspect ratio λ is less than 80 for Du ≪ 1 or 300 for Du ≫ 1. The electric field follows an unconventional scaling law; it no longer scales uniformly with the thickness of membrane, but with the local value of λ for each nanopore.
While pressure and flow waveforms, calculated from computationally inexpensive one dimensional analysis, reflect the real picture of the process related to the inviscid flow, local three-dimensional viscous flow analysis brings an additional insight, highlighting the area of elevated level of circulations and wall shear stress. The latter according the experimental evidence is leading to the atherosclerotic lesions and triggers unfavorable biological events in the development of the intimal hyperplasia. To validate the implementation of the code in an arterial network, analysis has been applied to the simple “fork” type bifurcation. Three-dimensional Navier – Stokes simulation has been used to optimize the graft artery junction geometry from the view point of wall shear stress level minimization. We managed to reduce recirculation zone in the bifurcated area by minimization the maximum values of a wall shear stress gradient across all vessels varying the bypass vessel orientation angle within the frame of implied geometric constraints. It was shown that the typically used for the bypass T-junction topology is not the best. The best orientations of a bypass configuration was found for a set of specified flow rates across each bifurcated vessel.
Pulse wave velocity (PWV) is an important index of arterial hemodynamics, which lays the foundation for continuous, noninvasive blood pressure automated monitoring. The goal of this paper is to re-examine the accuracy of PWV prediction based on a traditional homogeneous structural model for thin-walled arterial segments. In reality arteries are described as composite heterogeneous hyperelastic structures, where the thickness dimension cannot be considered small compared to the cross section size. In this paper we present a hemodynamic fluid – structure interaction model accounting for the 3D material description of multilayer arterial segments based on its histological information. The model is suitable to account for the highly nonlinear orthotropic material undergoing finite deformation for each layer. An essential ingredient is the notable dependence of results on nonlinear aspects of the model: convective fluid phenomena, hyperelastic constitutive relation for each layer, and finite deformation. The dependence of PWV on pressure for three vessels of different thicknesses is compared against a simplified thin wall model of a membrane shell interacting with an incompressible fluid. Results show an asymptotic accuracy of an order of h/r0 is predicted. This work help lays the foundation for continuous, noninvasive blood pressure automated monitoring based on PWV.
Pressure wave velocity (PWV) is commonly used as a clinical marker of vascular elasticity. Recent studies have increased clinical interest in also analyzing the impact of heart rate (HR), blood pressure, and left ventricular ejection time (LVET) on PWV. In this article we focus on the development of a theoretical one-dimensional model and validation via direct measurement of the impact of ejection time and peak pressure on PWV using an in vitro hemodynamic simulator. A simple nonlinear traveling wave model was developed for a compliant thin-walled elastic tube filled with an incompressible fluid. This model accounts for the convective fluid phenomena, elastic vessel deformation, radial motion, and inertia of the wall. An exact analytical solution for PWV is presented which incorporates peak pressure, ejection time, ejection volume, and modulus of elasticity. To assess arterial compliance, the solution is introduced in an alternative form, explicitly determining compliance of the wall as a function of the other variables. The model predicts PWV in good agreement with the measured values with a maximum difference of 3.0%. The results indicate an inverse quadratic relationship (R^2=.99) between ejection time and PWV, with ejection time dominating the PWV shifts (12%) over those observed with changes in peak pressure (2%). Our modeling and validation results both explain and support the emerging evidence that, both in clinical practice and clinical research, cardiac systolic function related variables should be regularly taken into account when interpreting arterial function indices, namely PWV.
This paper reports an Aerosol-Jet printed micro scale Lead Zirconate Titanate (PZT) energy harvester directly sintered on a low melting point substrate in less than 1 msec using photonic sintering technology. To improve the output signal, d33 piezoelectric mode was employed by patterning silver electrodes as an interdigitated structure on top of a PZT film. The size of the device is 15.5 mm ×13.5 mm ×0.2 mm. Up to 2.4 V was measured at 145 MPa tensile bending stress level in the device after poling at 180 °C for 2 hours with an electric field of 30 kV/cm. Using an oscillating stress (~2.5 Hz) of approximately 145 MPa, the power as a function of load was determined by connecting the device with various series resistive loads. A maximal power of 0.1 μW was generated when driving into a 10 MΩ load. A PZT energy harvester, for the first time, is demonstrated which has been directly printed and sintered on a low melting temperature flexible substrate without a film transfer processes. This not only dramatically simplifies the fabrication process, but expands the possible substrate materials for PZT energy harvesters.
A method, non-transitory computer readable medium, and apparatus that includes obtaining, by a dosimetry computing device, sensor readings from at least one sensor. An event is identified, by the dosimetry computing device, based on at least one of one or more of the obtained sensor readings or one or more determinations based on the obtained sensor readings meeting one or more selection. At least one of the one or more de terminations or the sensor readings which meet one or more of the selection criteria when the event is identified is stored by the dosimetry computing device.
A method, non-transitory computer readable medium, and apparatus that includes obtaining, by a dosimetry computing device, sensor readings from at least one sensor. An event is identified, by the dosimetry computing device, based on at least one of one or more of the obtained sensor readings or one or more determinations based on the obtained sensor readings meeting one or more selection. At least one of the one or more determinations or the sensor readings which meet one or more of the selection criteria when the event is identified is stored by the dosimetry computing device.
A dosimetry apparatus includes at least one sensor in a housing, a cover configured to permit compression waves to pass through, the cover is seated over the at least one sensor, and a dosimetry processing device with a memory. The dosimetry pro CA cessing device is coupled to the at least one sensor in the housing. The dosimetry processing device is configured to execute programmed instructions stored in the memory comprising: obtaining readings from the at least one sensor; storing the readings with a time and date stamp when obtained; conducting an analysis based on the obtained readings; and outputting at least one of the stored readings or the conducted analysis.
A dosimetry device includes at least one sensor in a housing and a dosimetry processing device with a memory. The dosimetry processing device is coupled to the at least one sensor in the housing. The dosimetry processing device is configured to ex ecute programmed instructions stored in the memory comprising: obtaining readings from the sensor; storing the readings; conducting an analysis of the stored readings to determine an injury risk assessment; and outputting at least one of the conducted analysis of the de termined injury risk assessment or the stored readings.
The ornamental design of a device for detecting an impact event, as shown and described.
Traumatic brain Injury (TBI) has emerged as the signature injury of modern war, impacting over 300,000 Servicemembers since 2000. While 82% of these injuries are classified mild, there is significant concern with the potential for long-lasting neurocognitive and neuro degenerative effects. Diagnosis of mild TBI is difficult, with symptoms that are wide-ranging, non-specific, and often delayed in onset. The Blast Gauge® System was created to provide an objective measure of blast overpressure and acceleration exposure, providing triage data to assist in identifying soldiers at risk of TBI and detailed waveforms to enable correlation of singular and repetitive exposure to acute and chronic injury. From concept to deployment in 11 months and company formation to first product shipment in 4 months, this MEMS-based soldier-borne blast dosimeter has rapidly provided a new capability to track exposure in training and operations for the US DoD, law enforcement, and international militaries. Widespread deployment of the technology has yielded new insight into previously unrecognized dangers of heavy weapons training and captured valuable information about lED exposures in theater.
Hard of hearing individuals frequently cite intelligibility problems in multi-talker environments. Microphone arrays performing time delay beamforming address conditions of poor signal-to-noise ratio by spatially filtering incoming sound. Existing beampattern metrics including peak side lobe level, integrated side lobe level, beamwidth, and planar directivity index fail to quantitatively capture all elements essential for improving speech intelligibility in multi- talker situations. The focal index (FI) was developed here to address these deficiencies. Simulations were performed to exemplify the robust nature of the FI and to demonstrate the utility of this metric for driving array parameter selection. Beampatterns were generated and the metrics were calculated and evaluated against the strict unidirectional requirements for the array. Array performance was assessed by human subjects in a speech recognition task with competing speech from multiple locations. Simulations of array output were presented under conditions differing in array sparsity. The resulting human subject data was used to demonstrate the linear relationship (R2 > 0.975) between speech-intelligibility-weighted FI (SII-FI) and the signal-to- noise ratio thresholds for 20% and 80% correct responses. Data indicate that the FI and SII-FI are robust singular metrics for determining the effectiveness of the array.
Blast related traumatic brain injury (bTBI) is characterized by neurological impairment including loss of consciousness, disorientation , memory loss, impaired cognition, and headache. Of significant concern is mild bTBI where symptoms are wide ranging, non-specific, and difficult to distinguish from psychological co-morbidities. The Blast Gauge System was created to provide an objective measure of blast overpressure exposure to assist in identifying soldiers at risk of bTBI, and to enable correlation of singular and repetitive exposure to acute and chronic injury for future refinement of thresholds. While capturing full blast overpressure and acceleration waveform data for post-event analysis, this system uses two thresholds to aid in triage. These thresholds were developed based on recent human and large animal studies correlating blast overpressure exposures to neurological effects and changes in physiological, histochemical, immunohistochemical, and protein biomarkers. These thresholds are consistent with those identified for blast-related upper respiratory and gastrointenstinal tract trauma.
Currently the Neurocognitive Assessment of Blast Exposure Sequela in Training (NC-BEST) and Investigating the Neurologic Effects of Training Associated Blast (I-TAB) studies have incorporated the Blast Gauge into their protocols to allow for a correlation between objective measures of blast exposure during combat training and physiological and behavioral measurements. These studies will allow for an increased understanding of blast exposure dose response curves in relation to multiple blast variables, repetitive blast exposures, and individual genetic and physiological characteristics associated with development of chronic neurocognitive sequela. The results will guide refinement of our current blast exposure thresholds, and may help determine whether certain structural changes in weapon systems, training areas, or CONOPS can mitigate or minimize these overpressure exposures. This is critical, as training associated blasts currently account for 67% of all recorded blast exposures in military personnel. Anecdotally, concussive-symptoms are commonly reported by instructors and trainees participating in Breacher and heavy weapons training programs. Tate et al. recently reported that 11 of the 21 participants in a 2-week breacher course had positive biomarkers indicative of bTBI with associated neurobehavioral symptoms and decreased cognitive functioning.
Development of ECG delineation algorithms has been an area of intense research in the field of computational cardiology for the past few decades. However, devising evaluation techniques for scoring and/or merging the results of such algorithms, both in the presence or absence of gold standards, still remains as a challenge. This is mainly due to existence of missed or erroneous determination of fiducial points in the results of different annotation algorithms. The discrepancy between different annotators increases when the reference signal includes arrhythmias or significant noise and its morphology deviates from a clean ECG signal. In this work, we propose a new approach to evaluate and compare the results of different annotators under such conditions. Specifically, we use sequence alignment techniques similar to those used in bioinformatics for the alignment of gene sequences. Our approach is based on dynamic programming where adequate mismatch penalties, depending on the type of the fiducial point and the underlying signal, are defined to optimally align the annotation sequences. We also discuss how to extend the algorithm for more than two sequences by using suitable data structures to align multiple annotation sequences with each other. Once the sequences are aligned, different heuristics are devised to evaluate the performance against a gold standard annotation, or to merge the results of multiple annotations when no gold standard exists.
A family of classical Boussinesq system of nonlinear wave theory is presented in a form of conservative equations supplemented by Riemann solver, which is a fundamental block in the Godunov frame formulation of flow problems. The governing system simulates different physical phenomena, such as propagation of a small amplitude waves on a surface of water, or pulse wave propagation in compliant thin walled arterial systems. While the first model is for verification purpose only, pulse wave propagation through the junction of thin walled elastic branches is of primary interest. The inertial effects associated with transversal motion of the wall are introduced, affirming the dispersive nature of pulsating waves. The problem of accounting for branching and possible discontinuity of wall properties is addressed. Preliminary analysis is presented which leads to the correct jump conditions across bifurcated area. As a result, the model accurately describes the formation of transmission and reflection waves at bifurcation, including effects of discontinuities. The Riemann solver supplies the inter cell flux and junction fluxes, based on conservation of volume, momentum and energy, with account of losses associated with the flow turn angle at bifurcation. An implicit monotonic total variation diminishing (TVD) scheme, second order accurate in time and space has been applied for the analysis of solitary wave solution in bifurcated arteries. Numerical results are in a good agreement with the known analytical and numerical solutions reported elsewhere. Based on direct computational analysis the inverse solution was obtained, calculating the local elastic properties of the arterial wall, using typical diagnostic measurements. Mathematical modelling presented in this work leads to a physiological understanding and interpretation of diagnostic measurements of the wave forms of a blood pressure, flow rate and an artery wall deflection.
A series of laboratory and field tests were conducted using the BG with industry standard pencil probes (PP) as controls. Three different models of the BG were used: H1 (High Sensitivity), S1 (Standard Sensitivity, DARPA), and S2 (High-G). Laboratory tests were conducted with two shock tubes. The WRAIR/NMRC shock tube used 4 different membrane thicknesses (OP range 4 – 15 psi, n=9–12 trials per level while the DSTO shock tube used 2 thicker membrane levels (OP range 30 – 70 psi, n = 3 trials per level). Three distinct field tests were conducted with high explosive charges or during weapons systems training: 1. Two iterations of an explosive door breach were conducted (OP range: 2–11 psi) using the same charge weight (CW); 2. Within a blast chamber, high explosives were detonated with BG and PP sensor locations varied during 5 separate detonations at the same CW (OP range: 4–72 psi); 3. Field artillery (M119, 105 mm Howitzer) firing with 3 different propellant charge levels (OP range: 0.9–3.5 psi). Within the optimal sampling range (H1:0.25–30 psi, S1:2.5–100 psi, S2:2.5–100 psi), BG readings were 1–19% lower than PP readings and hypothesis tests showed no statistically significant difference (SSD) between BG and PP in 9 of 11 conditions (p > 0.05). Above the optimal sampling range, BG was 1 –30% lower than PP and hypothesis tests showed no SSD in 3 of 5 conditions (p > 0.05). These differences are likely due to the slower sampling rate of the BG and piezoresistive properties of the sensing element. This data supports the repeatability and reliability of the BG for the measurement of both reflected and incident overpressures in the field environment. Additional examples of the utility, interpretation challenges and limitations associated with OP measurement (eg. detonation in confined spaces) will be discussed.
Noninvasive fetal ECG (fECG) monitoring has potential applications in diagnosing congenital heart diseases in a timely manner and assisting clinicians to make more appropriate decisions during labor. However, despite advances in signal processing and machine learning techniques, the analysis of fECG signals has still remained in its preliminary stages. In this work, we describe an algorithm to automatically locate QRS complexes in noninvasive fECG signals obtained from a set of four electrodes placed on the mother’s abdomen. The algorithm is based on an iterative decomposition of the maternal and fetal subspaces and filtering of the maternal ECG (mECG) components from the fECG recordings. Once the maternal components are removed, a novel merging technique is applied to merge the signals and detect the fetal QRS (fQRS) complexes. The algorithm was trained and tested on the fECG datasets provided by the PhysioNet/CinC challenge 2013. The final results indicate that the algorithm is able to detect fetal peaks for a variety of signals with different morphologies and strength levels encountered in clinical practice.
A novel and easily implemented delineation algo- rithm is presented, which allows the foot of the photoplethsymo- gram to be located with sufficient accuracy for heart rate vari- ability applications. This algorithm combines classical delineation techniques with the robustness of the wavelet transform. It can be implemented with a set of FIR filters and simple non-adaptive thresholding, making it suitable for real-time ambulatory appli- cations. Results show that the accuracy of the algorithm matches that of a standard electrocardiogram delineation algorithm, the current standard for heart rate variability applications. The algorithm presented herein is also compared against four state- of-the-art delineation algorithms. Using a database that contains exercise data from thirteen patients across six activity levels and 7012 beats, a temporal accuracy of 3.8±2.6 ms (mean±std) was achieved with a sensitivity of 99.29% and a positive predictive value of 99.23%.
Tactical officers and military personnel who train in explosive entry techniques regularly put themselves at risk of blast exposure. The overpressure conditions in complex military and law enforcement environments, such as interior doors, hallways, and stairwells, cannot be accurately predicted by standard blast models which were developed from outdoor, free-field blasts. In both training and operations, small, low- cost blast overpressure sensors would provide the benefit of tracking exposure levels of at-risk individuals. The sensors would allow, for the first time, direct determination of safe stand-off distances and positioning for personnel during explosive breaching. Overpressure, impulse, and acceleration data has been captured for a series of interior and exterior blasts, demonstrating the utility of the Blast Gauge system as a training and research tool to quantify blast overpressure in complex environments.
Delivery of therapeutic compounds to the inner ear via absorption through the round window membrane (RWM) has advantages over direct intracochlear infusions; specifically, minimizing impact upon functional hearing measures. However, previous reports show that significant basal- to-apical concentration gradients occur, with the potential to impact treatment efficacy. Here we present a new approach to inner ear drug delivery with induced advection aiding distribution of compounds throughout the inner ear in the murine cochlea. Polyimide microtubing was placed near the RWM niche through a bullaostomy into the middle ear cavity allowing directed delivery of compounds to the RWM. We hypothesized that a posterior semicircular canalostomy would induce apical flow from the patent cochlear aqueduct to the canalostomy due to influx of cerebral spinal fluid. To test this hypothesis, young adult CBA/CaJ mice were divided into two groups: bullaostomy approach only (BA) and bullaostomy + canalostomy (B+C). Cochlear function was evaluated by distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) thresholds during and after middle ear infusion of salicylate in artificial perilymph (AP), applied near the RWM. The mice recovered for 1 week, and were re-tested. The results demonstrate there was no significant impact on auditory function utilizing the RWM surgical procedure with or without the canalostomy, and DPOAE thresholds were elevated reversibly during the salicylate infusion. Comparing the threshold shifts for both methods, the B+C approach had more of a physiological effect than the BA approach, including at lower frequencies representing more apical cochlear locations. Unlike mouse cochleostomies, there was no deleterious auditory functional impact after 1 week recovery from surgery. The B+C approach had more drug efficacy at lower frequencies, underscoring potential benefits for more precise control of delivery of inner ear therapeutic compounds.
Local delivery of drugs to the inner ear has the potential to treat inner ear disorders including permanent hearing loss or deafness. Current mathematical models describing the pharmacokinetics of drug delivery to the inner ear have been based on large rodent studies with invasive measurements of concentration at few locations within the cochlea. Hence, estimates of clearance and diffusion parameters are based on fitting measured data with limited spatial resolution to a model. To overcome these limitations, we developed a noninvasive imaging technique to monitor and characterize drug delivery inside the mouse cochlea using micro-computed tomography (μCT). To increase the measurement accuracy, we performed a subject-atlas image registration to exploit the information readily available in the atlas image of the mouse cochlea and pass segmentation or labeling information from the atlas to our μCT scans. The approach presented here has the potential to quantify concentrations at any point along fluid-filled scalae of the inner ear. This may permit determination of spatially dependent diffusion and clearance parameters for enhanced models.
Electroosmotic pumps (EOPs) are a class of pumps in which fluid is driven through a capillary or porous media within an electric field. Current research on EOPs concerns the development of new materials in which high electroosmotic flow rates can be achieved for low voltages. Such pumps could be used for portable microfluidic devices. Porous nanocrystalline silicon (pnc-Si) is a material that is formed into a 15-nm-thick nanomembrane. pnc-Si membranes are shown here to have high electroosmotic flow rates at low applied voltages due to the high electric fields achieved over the ultrathin membrane. A prototype EOP was designed using pnc-Si membranes and shown to pressurize fluid through capillary tubing at voltages as low as 250 mV.
An algorithm to automatically locate QRS complexes in noninvasive fetal ECG signals is described and was entered in the PhysioNet/CinC 2013 “Noninvasive Fetal ECG” challenge. The algorithm is based on an iterative subspace decomposition and filtering of the maternal ECG components from the recordings of a set of electrodes placed on the mother’s abdomen. Once the maternal components are removed, a novel merging technique is applied to merge the recordings and generate a signal with a higher SNR to perform fetal peak detection. The algorithm produces an annotation file for each data set containing the location of the fetal QRS complexes in that set. The final results indicate that the algorithm is able to detect fetal peaks under different scenarios and for variety of devices and signals encountered in clinical practice.
Compressed sensing has the possibility to signif- icantly decrease the power consumption of wireless medical devices. The photoplethysmogram (PPG) is a device which can greatly benefit from compressed sensing due to the large amount of power needed to capture data. The aim of this paper is to determine if the least absolute shrinkage and selection operator (LASSO) optimization algorithm is the best approach for reconstructing a compressively sampled PPG across varying physiological states. The results show that LASSO reconstruction approaches but does not surpass, the reliability of constrained optimization.
Delivery of potentially therapeutic compounds to the inner ear via the round window membrane (RWM) has advantages over alternative methods. Specifically, the RWM approach minimizes bleeding, with little impact upon functional hearing measures. However, some previous reports show that significant basal-to-apical concentration gradients occur (Plontke et al. Laryngoscope 2007;117:1191-1198). The new surgical approach presented here utilizes polyimide infusion tubing placed onto the niche near the RWM, through a bulla-ostomy. Inclusion of a posterior semicircular canalostomy provides additional opportunities to reduce drug concentration gradients. Methods: Young adult CBA/CaJ mice were divided into two groups: bulla-ostomy approach only (B) and bulla-ostomy + canalostomy (B+C). Cochlear function was evaluated by distortion product otoacoustic emissions (DPOAEs) thresholds and auditory brainstem responses (ABRs) (8-51 kHz). Mice were infused with 50mM salicylate in artificial perilymph at a flow rate of 50nl/min for a total volume of 1000nl (20 min); DPOAEs were measured before and after surgery, and at intervals during the infusion. The mice recovered for 1 week, and re-tested. Results: there was no significant impact on auditory function utilizing the RWM surgical procedure, and DPOAE thresholds were elevated reversibly during the salicylate infusion. Comparing the threshold shifts for both methods, the B+C approach had more of a physiological effect than the B approach, especially at lower frequencies – more apical cochlear locations. Unlike mouse cochleostomies, there was no deleterious auditory functional impact after 1 week recovery from surgery. Regarding the B+C approach, it had more drug efficacy at lower frequencies indicating reduced concentration gradients, underscoring potential benefits for more precise control of delivery of inner ear therapeutic compounds.
The inner ear represents one of the most technologically challenging targets for local drug delivery, but its clinical significance is rapidly increasing. The prevalence of sensorineural hearing loss and other auditory dis- eases, along with balance disorders and tinnitus, has spurred broad efforts to develop therapeutic compounds and regenerative approaches to treat these conditions, necessitating advances in systems capable of targeted and sustained drug delivery. The delicate nature of hearing structures combined with the relative inaccessibility of the cochlea by means of conventional delivery routes together necessitate significant advancements in both the precision and miniaturization of delivery systems, and the nature of the molecular and cellular targets for these therapies suggests that multiple compounds may need to be delivered in a time- sequenced fashion over an extended duration. Here we address the various approaches being developed for inner ear drug delivery, including micropump-based devices, reciprocating systems, and cochlear prosthesis-mediated delivery, concluding with an analysis of emerging challenges and opportunities for the first generation of technologies suitable for human clinical use. These developments represent exciting advances that have the potential to repair and regenerate hearing structures in millions of patients for whom no currently available medical treatments exist, a situation that requires them to function with electronic hearing augmentation devices or to live with severely impaired auditory function. These advances also have the potential for broader clinical applications that share similar requirements and challenges with the inner ear, such as drug delivery to the central nervous system.
Introduction: Arterial compliance is a marker for cardiac burden in atherosclerotic disease, with the pressure Pulse Wave Velocity (PWV) correlated to compliance. Current clinical practice employs pulsed wave Doppler to measure Flow Wave Velocity (FWV) as a surrogate of PWV. We hypothesized that PWV and FWV are not directly related and are affected by left ventricular ejection time (LVET). Furthermore, we proposed that aortic PWV is independent of mean arterial pressure (MAP) in the setting of isolated systolic hypertension.
Methods: Using a physiologically accurate electromechanical cardiovascular simulator, two solid state manometer-tipped pressure transducers and two transit time flow sensors were located at the aortic root and at the aortic bifurcation. PWV and FWV were directly measured while individually varying contractility and thus LVET. The experiments were repeated at various systemic vascular resistances (SVR) and vascular compliances. Automated signal processing and data extraction techniques were used to calculate the key parameters.
Results: As LVET increased, FWV decreased but PWV increased while MAP remained constant for a fixed SVR and compliance. (Figure 1) This trend held consistent at different SVR’s and compliances. The relationship of PWV and FWV with LVET appeared to be exponential and linear respectively. For a constant MAP, the associated PWV varied by up to 50m/s and FWV by up to 10m/s for a change in LVET of 225ms.
Conclusions: In conclusion, our data shows that PWV and FWV appear to be inversely related. Our data also suggest that PWV and FWV are independent of MAP in the setting of isolated systolic hypertension. These findings suggest that FWV measured by pulsed wave Doppler may not be a simple surrogate for true PWV. Future work is needed to elucidate the hemodynamic principals governing the relationship between PWV and FWV.
Small mammals, particularly mice, are very useful animal models for biomedical research. But extremely small anatomical dimensions make design of implantable microsystems quite challenging. A method for coupling external fluidic systems to microfluidic channels via in-plane interconnects is presented. Capillary tubing is inserted into channels etched in the surface of a silicon wafer with a seal created by Parylene-C deposition. A model has been developed based on Parylene-C deposition characterizations which allows prediction of deposition into tapered channels for design optimization. Low volume interconnects using biocompatible, chemical resistant materials have been demonstrated and shown to withstand pressure as high as 827 kPa (120 psi) with average pull test strength of 2.9 N. Each interconnect consumes less than 0.018 mm3 (18 nl) of volume. The low added volume makes this an ideal interconnect technology for medical applications where implant volume is critical.
A MEMS fabrication technique is presented that extends the capabilities of micromachining by combining traditional approaches with direct write dispensing technology. A test device was designed and fabricated to demonstrate the capability of the technique to integrate additional features with three-dimensional direct-write dispensing tools (Optomec, Albuquerque, NM, USA) and (nScrypt, Inc. Orlando, FL, USA). Micro-diaphragms, fabricated using traditional MEMS techniques, are actuated pneumatically via multilayer structures written directly upon the MEMS device.
Computer modeling of biological systems has proven to be an invaluable tool in numerous applications. In developing therapies for the cochlea involving direct application of biotherapeutic compounds, multiple parameters of the infusion/delivery system must first be established; concentration of the therapeutic agent, volume and flow rate of the infusion, and which delivery system leads to the optimal concentration profile are all parameters that can be investigated with a biologically accurate fluid dynamic model of the inner ear. Existing models for intracochlear drug delivery utilize clearance and interscala transport parameters based on limited in vivo measurements using implanted ion-selective electrodes [1,2]. Measurement of transport parameters within the fluid spaces along the length of the cochlea would enhance the accuracy of these models.
These preliminary studies show the ability to image delivery of contrast agent to the cochlea and determine concentrations in each region of interest. This will lead to the eventual calculation of interscala transport and clearance parameters. The use of real-time in vivo experimentation to gather these parameters will aid in the construction of a fluid dynamic model of the inner ear with higher accuracy than is currently available.
Advanced deafness therapies that restore normal auditory function will require carefully timed and dosed, site-directed delivery of multiple therapeutic compounds over a period of time. Syringe and osmotic pumps have proven effective for baseline investigations in animal models, but lack the flexibility required for more sophisticated therapy development. An implantable micropump with controllable flow rate and dosing profile is being developed using MEMs technologies. The pump initially targets murine intracochlear drug delivery for deafness therapy research. Key integration technologies have been created to minimize both size and power for this implanted device. A method for coupling fine capillary tubing to microfluidic channels via in-plane interconnects is presented. Capillary tubing inserted into micro-channels etched in the surface of a silicon wafer is sealed in place via room temperature polymer deposition providing a low volume, biocompatible interconnect. These microfluidic connections withstand pressures as high as 827 kPa (120 psi) with average pull test strength of 2.9 N. The interconnects consume less than 20 nl of volume and exit in- plane with the pump, facilitating implantation. Resistive micro-bridges integrated into the middle of the fluid channel provide an optimal means of flow rate measurement via hot-wire anemometry. Multiphysics modeling is used to determine the sensor geometry that provides the most favorable trade-off between sensitivity and power consumption. Analog circuit solutions are explored for in-situ fluid temperature compensation without digital computation. A process for creation of deformable membranes over pump chambers with simultaneous coating of the microfluidic channels has been developed allowing integration of a biocompatible fluid flow path. These integration technologies represent critical steps towards micropump development suitable for implantation in mice.
Direct delivery of compounds to the mammalian inner ear is most commonly achieved by absorption or direct injection through the round window membrane (RWM), or infusion through a basal turn coch- leostomy. These methods provide direct access to cochlear structures, but with a strong basal-to-apical concentration gradient consistent with a diffusion-driven distribution. This gradient limits the efficacy of therapeutic approaches for apical structures, and puts constraints on practical therapeutic dose ranges. A surgical approach involving both a basal turn cochleostomy and a posterior semicircular canal canal- ostomy provides opportunities for facilitated perfusion of cochlear structures to reduce concentration gradients. Infusion of fixed volumes of artificial perilymph (AP) and sodium salicylate were used to evaluate two surgical approaches in the mouse: cochleostomy-only (CO), or cochleostomy-plus-canal- ostomy (CþC). Cochlear function was evaluated via closed-system distortion product otoacoustic emis- sions (DPOAE) threshold level measurements from 8 to 49 kHz. AP infusion confirmed no surgical impact to auditory function, while shifts in DPOAE thresholds were measured during infusion of salicylate and AP (washout). Frequency dependent shifts were compared for the CO and CþC approaches. Computer simulations modeling diffusion, volume flow, interscala transport, and clearance mechanisms provided estimates of drug concentration as a function of cochlear position. Simulated concentration profiles were compared to frequency-dependent shifts in measured auditory responses using a cochlear tonotopic map. The impact of flow rate on frequency dependent DPOAE threshold shifts was also evaluated for both surgical approaches. Both the CþC approach and a flow rate increase were found to provide enhanced response for lower frequencies, with evidence suggesting the CþC approach reduces concentration gradients within the cochlea.
Due to the very small size of the mouse inner ear, 600 nL volume, developing effective, controlled infusion systems is quite challenging. Key technologies have been created to minimize both size and power for an implantable pump for murine intracochlear infusions. A method for coupling fine capillary tubing to microfluidic channels is presented which provides low volume, biocompatible interconnects withstanding pressures as high as 827 kPa (120 psi) and consuming less than 20 nL of volume exiting in-plane with the pump. Surface micromachined resistive bridges integrated into the flow channel for anemometry based flow rate measurement have been optimized for low power operation in the ultra-low flow rate regime. A process for creation of deformable diaphragms over pump chambers with simultaneous coating of the microfluidic channels has been developed allowing integration of a biocompatible fluid flow path. These advances represent enabling capabilities for a drug delivery system suitable for space constrained applications such as subcutaneous implantation in mice.
Compound delivery to the cochlea generally results in strong basal-to-apical concentration gradients, limiting the efficacy of therapeutic approaches for apical structures, and constraining therapeutic dose ranges. These gradients depend on the location of cochlear entry, the resulting fluid flow path, and diffusion / clearance mechanisms, offering few options for control and reduction. In the present study, infusion flow rate was examined as a parameter for reducing concentration gradients within the cochlea for basal turn scala tympani cochleostomy infusions with and without a posterior semicircular canal canalostomy. Fixed volumes of artificial perilymph (AP) and sodium salicylate (10 mM) were infused. Cochlear function was measured via closed-system DPOAE threshold measurements from 8-44 kHz, with threshold shifts compared for both surgical approaches using two flow rates; 16 and 32 nl/min. Neither flow rate had an acute impact on auditory function as demonstrated by stable thresholds during the initial AP infusion and subsequent threshold recovery during the washout phase. The cochleostomy-only approach exhibited statistically significant enhancements in DPOAE threshold shifts with the higher flow rate at 12 and 16 kHz, suggesting higher concentrations of salicylate at these more apical locations. Flow rate did not impact DPOAE thresholds for the cochleostomy-plus-canalostomy approach. Simulations were used to investigate the impact of higher flow rates on salicylate concentration along the length of the cochlear spiral, with clearance rates examined as a potential influencing factor.
Infusion flow rate may be an important variable in optimization of intracochlear drug delivery paradigms. Elucidating the details of threshold shifts will provide information critical for development of more advanced models of cochlear infusate flow patterns and optimization of inner ear infusion protocols.
Direct delivery of compounds to the inner ear in animals is most commonly achieved by absorption or direct injection through the round window membrane, or infusion through a basal turn cochleostomy. These methods provide direct access to cochlear structures, but with a strong basal-to-apical concentration gradient consistent with a diffusion-driven distribution. This gradient limits the efficacy of therapeutic approaches for apical structures, and puts constraints on practical therapeutic dose ranges. A surgical approach involving both a basal turn cochleostomy and a posterior semicircular canal canalostomy provides opportunities for facilitated perfusion of cochlear structures to reduce concentration gradients. A cannula inserted into scala tympani at the cochleostomy site allows controlled delivery of solutions into perilymph, with the canalostomy in the PSCC serving as a fluidic exit port. The theoretical flow pattern is from base to apex in scala tympani, through the helicotrema, from apex to base in scala vestibuli, and then through the semicircular canals. This contrasts with infusion at the basal turn of scala tympani with no exit hole (cochleostomy only) where presumably excess fluid is pushed through the cochlear aqueduct.
Infusion (1μl/hr) of fixed volumes of artificial perilymph (AP) and sodium salicylate were used to evaluate the two surgical approaches in the mouse. Cochlear function was evaluated via closed-system DPOAE threshold level measurements. AP infusion confirmed no surgical impact to auditory function, while shifts in DPOAE thresholds were measured during infusion of sodium salicylate (10 mM) and AP (washout). Different fluids were separated by 10 nl air bubbles within the infusion tubing to avoid within-tube diffusion. Frequency dependent shifts were compared for the cochleostomy-only and the cochleostomy-plus-canalostomy approaches.
Intracochlear drug delivery in the mouse is challenging due to the extremely small size and volume of the inner ear. Physiological measures can access the impact of delivered compounds on peripheral auditory function, but infusate distribution characteristics must be inferred. Computer simulations offer opportunities to calculate cochlear concentration gradients for different delivery approaches and are an excellent complement to in vivo studies. Fluid modeling software is available to simulate a variety of delivery protocols representing infusions, perfusions, and extracochlear round window drug applications. Diffusion, volume flow, interscala transport, and clearance mechanisms are modeled allowing determination of drug concentration with position in the cochlea. When coupled with a cochlear tonotopic map, simulated concentration profiles can be correlated with shifts in measured auditory responses as a function of sound frequency. Two different drug delivery approaches are considered in the present investigation involving mice: scala tympani infusion through a basal turn cochleostomy, and this approach coupled with a fluidic exit hole in the posterior semicircular canal. Distortion product otoacoustic emission thresholds were measured from 8-44 kHz before and during delivery of artificial perilymph and sodium salicylate. Shifts in threshold were compared to simulated concentration gradients to highlight the relationship between drug concentration and frequency-dependent changes in auditory function. Model parameters were adjusted to match the profile of these characteristics and to provide insight into mechanisms impacting drug distribution in the cochlea. Strengths and limitations of currently available cochlear infusion models are discussed and critiqued for improvements.
Purpose of review
Treatment of auditory and vestibular dysfunction has become increasingly dependent on inner ear drug delivery. Recent advances in molecular therapy and nanotechnology have pushed development of alternate delivery methodologies involving both transtympanic and direct intracochlear infusions. This review examines recent developments in the field relevant to both clinical and animal research environments.
Transtympanic delivery of gentamicin and corticosteroids for the treatment of Meniere’s disease and sudden sensorineural hearing loss continues to be clinically relevant, with understanding of pharmacokinetics becoming more closely studied. Stabilizing matrices placed on the round window membrane for sustained passive delivery of compounds offer more controlled dosing profiles than transtympanic injections. Nanoparticles are capable of traversing the round window membrane and cochlear membranous partitions, and may become useful gene delivery platforms. Cochlear and vestibular hair cell regeneration has been demonstrated by vector delivery to the inner ear, offering promise for future advanced therapies.
Optimal methods of inner ear drug delivery will depend on toxicity, therapeutic dose range, and characteristics of the agent to be delivered. Advanced therapy development will likely require direct intracochlear delivery with detailed understanding of associated pharmacokinetics.
The honors program in the Kate Gleason College of Engineering at Rochester Institute of Technology began in 2002. The program admits approximately thirty first year students each year and focuses upon product innovation in a global economy. The goal of the program is to provide talented engineering students with a full appreciation of the product development cycle, from concept to realization; in particular, how products are conceived, how decisions are made at the corporate level to pursue certain products and not others, and how product concepts are refined, engineered, and then manufactured for the marketplace. The first strategy being used is a two academic year course sequence covering topics ranging from teamwork and leadership to globalization. The second strategy involves taking students on two comprehensive “field trips” – one domestic and the other international, where students explore how companies, large and small, address product development. Prior to each trip students present background material on each company and after the company visit students engage in a discussion of the company’s strengths, weaknesses, opportunities and threats. This paper will describe the successful integration of this specialized series of courses with the domestic and international company visits to achieve student appreciation of product development in a global marketplace. Program and course assessment results will be presented.
The design, fabrication, and testing of micro- cannulae with integrated insertion stops is presented. The micro-cannulae were engineered through the use of a silicon micro-mold fabricated via bulk-silicon micro-machining techniques. The use of microelectronic fabrication techniques allows precise control of three critical parameters, insertion depth, interface contact area, and tubing out of round. Worst case variations were found to be 5μm for insertion depth, 502μm2 for interface contact area, and 7% for tip out of round. Histological evaluation revealed the cannula to be located correctly within the basal portion of scala tympani.
Inner ear disease therapy research involving cochlear infusions in mice is challenging due to anatomical size, and the lack of commercially available cannulae with integrated insertion stops. Historically researchers have created custom cannula by insertion of micro-tubing into larger tubing to create a stepped profile, or by manually applying a small volume of silicone Silastic® a fixed distance from the tip of the micro-tubing. These approaches rely on the effective change in tubing diameter to provide an insertion stop to limit cannula intrusion into the intracochlear space. The profile also facilitates bonding the cannula to the bony tympanic bulla for long term infusion studies. While successful in some applications, the methods of construction make consistency and reliability difficult to achieve, particularly for mice. In the present investigation, a method has been developed to facilitate controlled interfaces for intracochlear infusions. Using microfabrication technologies, precision molds have been created that allow control of the size and shape of a Silastic® insertion stop molded around capillary tubing. The insertion depth is controlled by mold design. The approach allows consistent manufacture of micro-cannulae of varying tubing size specifically designed for intracochlear infusions in mice or other small rodents. Details of the mold fabrication process, molding techniques, and data on dimensional consistency of produced micro-cannulae are presented. Preliminary results of intracochlear infusions in the mouse using micro-cannulae designed specially for the surgical approach and anatomical limitations are analyzed and discussed. This approach has the potential to enhance infusion consistency, and mitigate complications associated with variable insertion depths and leakage at the cochleostomy site.
A method for determining an unknown starting quantity of a target nucleic acid sequence in a test sample comprises amplifying the unknown starting quantity of the target nucleic acid sequence in the test sample and known starting quantities of a calibration nucleic acid sequence in respective calibration samples; and determining a respective threshold value for each of the nucleic acid sequences using a derivative of a growth curve derived for the sequence. The starting quantity of the target nucleic acid sequence in the test sample is determined using the threshold value determined for the target sequence and a calibration curve derived from the threshold values determined for the known starting quantities of the calibration nucleic acid sequences.
An apparatus for determining a threshold value (e.g., a threshold cycle number or a time value) in a nucleic acid amplification reaction comprises a detection mechanism for measuring, at a plurality of different times during the amplification reaction, at least one signal whose intensity is related to the quantity of a nucleic acid sequence being amplified in the reaction. A controller in communication with the detection mechanism is programmed to store signal values defining a growth curve for the nucleic acid sequence, determine a derivative of the growth curve, and calculate a cycle number or time value associated with a characteristic of the derivative.
A method for determining a threshold cycle number or time value in a nucleic acid amplification reaction comprising the steps of amplifying a nucleic acid sequence in a reaction mixture; at a plurality of different times during the amplification reaction, measuring at least one signal whose intensity is related to the quantity of the nucleic acid sequence in the reaction mixture; and storing signal values defining a growth curve for the nucleic acid sequence. A derivative of the growth curve is determined and the threshold cycle number or time value is calculated as a cycle number or time value corresponding to a characteristic (e.g., maximum, minimum, or zero-crossing) of the derivative.
An apparatus for determining a threshold value (e.g., a threshold cycle number or a time value) in a nucleic acid amplification reaction comprises a detection mechanism for measuring, at a plurality of different times during the amplification reaction, at least one signal whose intensity is related to the quantity of a nucleic acid sequence being amplified in the reaction. The apparatus also includes a controller in communication with the detection mechanism. The controller is programmed to perform the steps of deriving a growth curve from the measurements of the signal; calculating a derivative of the growth curve; identifying a characteristic of the derivative; and determining a threshold value associated with the characteristic of the derivative. Embodiments of an apparatus for determining a starting quantity of a nucleic acid sequence in a test sample are also provided.
Biologically active compounds are classified according to their effect on ion channels, changes in membrane potential and ionic currents, and the frequency content of action potentials that the compound(s) evoke in excitable cells. The spectral density changes of such evoked membrane potential or action potential are a characteristic for each channel type that is modulated by the test compound. A pattern of spectral changes in membrane potential is determined by contacting a responsive cell with a compound, and monitoring the membrane potential or ionic currents over time. These changes correlate with the effect of that compound, or class of compounds, on the ion channels of the responding cell. This pattern of spectral changes provides a unique signature for the compound, and provides a useful method for characterization of channel modulating agents.
Combining several one-dimensional miniaturized separation techniques in series has the potential to be an exceptionally comprehensive analysis approach. Sample species can be separated and identified based on a battery of characteristics not available from any single technique. µIEF is attractive as a first dimension of such a multi-dimensional system due to the equilibrium nature of the final separation, rapid separation capabilities (1min), concentrating qualities (100×), and high resolution (ΔpI = 0.005). As a step towards integration of µIEF with a second dimension (e.g., miniaturized capillary electrophoresis), this work investigates the robustness of µIEF as an initial dimension and explores means to reliably extract a purified, concentrated sample zone from a complete µIEF assay.
A miniature scanning fluorescent detector has been developed for plastic microchannel isoelectric focusing (mIEF) analysis. The detector, comprised of a lamp and photomultiplier tube (PMT) on a moving stage, measured the real-time distribution of fluorescently labeled peptides subjected to gel-free mIEF. During the run, the effective length of the 6-cm channel was scanned every 9 s. Analysis was completed within 5 min while still obtaining high resolution and sensitivity. In addition, the scanning detector was used to characterize peptide migration properties within the channel by providing simultaneous temporal and spatial measurements.
This work focuses on capillary isoelectric focusing (cIEF) as a high-resolution sample separation technique applicable for miniaturization and use in portable hand-held analysis systems. Miniaturization of cIEF reduces the amount of time necessary to complete a separation and allows for full-field array detection instead of traditional single-point detection. A miniature cIEF system was employed for rapid cIEF separations of fluorescently-labeled peptides. For enhanced portability, superbright blue LED’s were used as excitation sources and a CCD camera was used for detection. This system offers minimized sample dispersion, a 1nM detection limit, and a separation time of less than I minute.
Sample handling in miniaturized bioanalytical instruments typically depends on pressure or electrokinetic effects. This is particularly true of post-separation detection processes where a sample is moved past a single point detector. In contrast to such methods, the present study investigates a separation system that takes advantage of a steady-state, stationary separation technique known on the macroscale as capillary isoelectric focusing (cIEF). Due to the stationary nature of the final separation, sample analysis is conducted entirely without mobilization. This work explores the merits and limitations associated with miniaturizing this technique. Analyses were conducted on fluorescent peptide and protein samples in miniaturized separation columns (capillaries and glass micromachined channels between 8 and 14 mm long). In the interest of developing overall system portability, blue light emitting diodes (LED’s) were used for sample excitation. Detection was accomplished using a charge-coupled device (CCD). This approach yielded complete multi-sample separations in less than 1 minute.
The invention relates to an apparatus and method for monitoring cells and to a method for monitoring changes in cells upon addition of an analyte to the cell’s environment, comprising a device which includes an array of microelectrodes disposed in a cell culture chamber, upon which array a portion of cells adhere to the surfaces of the microelectrodes. The diameter of the cells are larger than the diameters of the microelectrodes. A voltage signal is applied across each of the microelectrodes and a reference electrode. Detection and monitoring of the signals resulting from the application of the voltage signal provides information regarding the electrical characteristics of the individual cells, including impedance (combined cell membrane capacitance and conductance), action potential parameters, cell membrane capacitance, cell membrane conductance, and cell/substrate seal resistance. Such an invention is useful in detecting or screening a variety of biological and chemical agents.
Application of a full-field detection approach to a biological sample separation scheme known as capillary isoelectric focusing (cIEF) has yielded detailed spatial and temporal information about the transport processes associated with this technique, as well as the efficiency of this separation scheme. The full-field cIEF detection technique utilizes an illumination source such as blue light emitting diodes or a mercury arc lamp, microscope objectives, and a charged coupled device (CCD) camera to image fluorescently labeled proteins and peptides. Interest in this approach arises from the ability to collect, in real time, information from the entire length of the separation channel. This full-field detection eliminates the need for flow mobilization and aids in the empirical analysis of the separation process. In an effort to optimize a miniaturized cIEF system, the full-field detection approach was used as a diagnostic to gauge the effect of varying the channel wall surface charge distribution.
A prototype cartridge system is described that rapidly disrupts Bacillus spores by sonication, adds PCR reagent to the disrupted spores, and dispenses the mixture into a PCR tube. The total time to automatically process the spores in the cartridge and then detect the spore DNA by real-time PCR was 20 min.