Transport in Engineering and Medicine (TEM) Research Areas

Physiological flows: Clinical, In vivo, In vitro, Computational blood-artery dynamics

Two American Heart Association grants awarded to Dr. Banerjee focus on the important area of coronary stenoses (Figure 1) diagnostics, which, at present, is primarily dependent on angiographic evidence of stenosis rather than the more deterministic hemodynamic endpoints. This research is aimed towards improving the cardiovascular diagnostics using guidewires during heart attacks.

Diagnostic test showing angiographic evidence of stenosis

Through these awards, Dr. Banerjee has introduced a novel coronary diagnostic index, the so-called lesion flow coefficient, which seeks to fulfill the longstanding need for a quantitative parameter that enables simultaneous and combined assessment of pressure gradient, blood flow (Figure 2) and geometric information for any coronary stenosis.  Such an index would enable clinicians to make significant advancements in patient diagnosis and prognosis following percutaneous transluminal coronary angioplasty (PTCA) or bypass surgery by isolating the effects of epicardial stenosis from microvascular impairments.  This research has the potential to improve clinical decision making by using the lesion flow coefficient, and thus, improving on the guidelines for optimal patient care.

Heart monitor reading

Physiologic and pathophysiologic hemodynamic measurements are also obtained using in vitro test sections using guidewires. In conjunction with in vivo study, this lab is well equipped to conduct numerical analyses for validation as well as prediction of flow dynamics inside in vitro models.

Stenotic model test

Fig 3: Photograph of LAD stenotic model test section (64% or moderate area stenosis). The model is manufactured with optical grade lexan plastic. This figure shows the proximal vessel, converging section, minimal throat section, diverging section, and distal pressure recovery section. The numbered external radial pressure sensor ports along the axial direction are shown in the figure.

Pulmonary Valve Insufficiency (PI) as the name suggests is the malfunctioning of the pulmonary valve (PV). It is one of the long-term sequelae of surgical procedure to rectify Tetralogy of Fallot (TOF). TOF, also called blue-baby syndrome, is one of the most common congenital heart defects in children after infancy and is estimated to account for 10% of all congenital heart defects. TOF consists of four interrelated defects: i) Ventricular septal defect (VSD) which is the hole between right and the left ventricle, ii) Pulmonary stenosis which is the result of the stiffening of the pulmonary arteries, iii) Right ventricular hypertrophy which results in enlarged right ventricle as it takes the mail function to pump blood and (iv) Overriding Aorta, as the aorta is almost connected to right ventricle. Tetralogy of Fallot, has been successfully repaired for several decades and here are now an estimated 100,000 adult “repaired TOF” patients in the United States alone. As a result, long-term sequels of the disease and repair have become important clinical issue. Specifically, residual pulmonary valve insufficiency is one such accepted and often unavoidable sequel. Chronic pulmonary valve insufficiency (PI), when severe, abnormally alters the RV loading conditions, thereby triggering RV hypertrophy and dilatation. 

MRI of right ventricle

MRI contours of Right Ventricle

In turn, RV dilatation can evolve into irreversible RV myocardial contractile dysfunction, and has been related to sudden death in many “repaired TOF” patients. To normalize RV loading conditions, pulmonary valve replacement is often necessary and should be performed prior to the onset of irreversible RV myocardial damage. In this study we try to understand the performance of the right ventricle of the heart and the pulmonary arterial blood flow using Computational Fluid Dynamics and Fluid Structure Interactions study on patient specific data.

Hemodialysis vascular access dysfunction is one of the major causes of morbidity and hospitalization among the population undergoing hemodialysis procedure. Vascular access has three major types that include PTFE grafts, arteriovenous fistula (AVF), and catheters among which the AVF is the most preferred form due to its lower infection rate, lower risk of thrombosis, and higher patency rate. These advantages have made the AVF the first choice of the vascular access. However, failure of AVF to mature and formation of thrombosis in matured fistulas have been the major causes of morbidity and mortality in hemodialysis patients. Progression of stenosis, which occurs due to adverse remodeling in AVFs, is one of the major underlying factors under both scenarios. 

Graph showing hemodialysis vascular dysfunction

Early diagnosis of adverse modeling of the stenosis in an AVF can provide an opportunity to intervene in a timely manner for either assisting the maturation process or avoiding the thrombosis. We, at the “TEM Laboratory”, UC, conduct research on functional diagnostic parameters that can better predict the status of AVF functionality. These diagnostic parameters are developed based on fluid mechanics fundamental, which are based on the pressure drop-flow relationships in stenosed vessels. In order to achieve our goal, we have performed in vivo experiments (pig models), image processing techniques and computational fluid dynamics (CFD) over a one month period. We use CFD to obtain the flow field in the 3 dimensional models of AVF reconstructed from the CT scans or other imaging techniques. This enables us to identify the possible regions of vascular stenosis in the AVF. Subsequently, we correlate the severity of stenosis with our new diagnostic endpoints, namely as pressure drop coefficient (Cp) and resistant index (R).

Stenosis diagram

The figures below show the distribution of pressure drop for two AVFs with favorable (FR) and adverse remodeling (AR) at 2 days (2D), 7D, and 28D post-surgery. The AVF with FR went through larger luminal dilation, had higher flow rate, lower pressure drop, and lower % area stenosis as compared to the AVF with AR. It is noteworthy that, the AVF with AR formed a severe stenosis after 28D post-surgery, while the AVF with FR remained patent. Also it can be noted that the AVF with FR had lower values of Cp and R as compared to the AVF with AR, which formed a stenosis at 28D.

Aortic stenosis is a type of valvular heart disease that results from abnormal narrowing of the aortic valve opening. In the United States, the most common cause is degenerative calcification of the aortic valve. The occurrence of calcific aortic valve disease increases with age. A narrow aortic valve opening causes an increase in resistance to the flow of blood exiting the left ventricle of the heart. With the introduction of minimally invasive procedures like Transcatheter aortic valve implantation (TAVI), treatment options are now available for patients who have aortic stenosis and are considered to have high surgical risk. Therefore, accurate assessment of the severity of aortic stenosis is critical. The ambiguities and imprecisions of the current diagnostic parameters can result in sub-optimal clinical decisions. The figure below shows a normal aortic valve that fully opens and has normal thickness and a diseased aortic valve with a narrow opening and increased thickness.

Scan showing Normal aortic valve in fully open position with normal thickness

Normal aortic valve in fully open position with normal thickness; stanford.edu

Aortic stenosis is a type of valvular heart disease that results from abnormal narrowing of the aortic valve opening. In the United States, the most common cause is degenerative calcification of the aortic valve. The occurrence of calcific aortic valve disease increases with age. A narrow aortic valve opening causes an increase in resistance to the flow of blood exiting the left ventricle of the heart. With the introduction of minimally invasive procedures like Transcatheter aortic valve implantation (TAVI), treatment options are now available for patients who have aortic stenosis and are considered to have high surgical risk. Therefore, accurate assessment of the severity of aortic stenosis is critical. The ambiguities and imprecisions of the current diagnostic parameters can result in sub-optimal clinical decisions. The figure below shows a normal aortic valve that fully opens and has normal thickness and a diseased aortic valve with a narrow opening and increased thickness.

Scan showing Aortic valve with narrow opening and increased thickness; stanford.edu

Aortic valve with narrow opening and increased thickness; stanford.edu

We, at the TEM Laboratory, have a proposed a new diagnostic parameter called aortic valve coefficient (AVC) to improve the accuracy of the non-invasive diagnosis of aortic stenosis using Doppler echocardiography. The AVC is a non-dimensional parameter and is expected to better differentiate between the different grades of severity of aortic stenosis by simultaneously accounting for the variation in pressure drop and flow. An initial retrospective clinical study was conducted to test the feasibility of using AVC to diagnose aortic stenosis. The results of this initial study demonstrated the potential of AVC to improve the diagnostic accuracy of aortic stenosis. The TEM Laboratory is currently developing a methodology to accurately calculate the flow dynamics and the associated deformations of the aortic valve and aorta using computational models. The computational models will be used for detailed evaluations of AVC before proceeding to pre-clinical and clinical studies.

We, at the TEM Laboratory, have a proposed a new diagnostic parameter called aortic valve coefficient (AVC) to improve the accuracy of the non-invasive diagnosis of aortic stenosis using Doppler echocardiography. The AVC is a non-dimensional parameter and is expected to better differentiate between the different grades of severity of aortic stenosis by simultaneously accounting for the variation in pressure drop and flow. An initial retrospective clinical study was conducted to test the feasibility of using AVC to diagnose aortic stenosis. The results of this initial study demonstrated the potential of AVC to improve the diagnostic accuracy of aortic stenosis. The TEM Laboratory is currently developing a methodology to accurately calculate the flow dynamics and the associated deformations of the aortic valve and aorta using computational models. The computational models will be used for detailed evaluations of AVC before proceeding to pre-clinical and clinical studies.

 An in vivo idealized arterial wall geometry of a dog femoral artery

An in vivo idealized arterial wall geometry of a dog femoral artery

A disease in the vasculature located outside the heart and brain is referred to as peripheral vascular disease (PVD). Typical peripheral vasculature includes pulmonary, iliac, femoral, carotid, popliteal and tibial arteries carrying blood to the kidneys, stomach, arms, legs and feet. PVD is caused by either a) atherosclerosis – a narrowing or blockage in the artery that occurs due to the deposition of fatty plaques on the inner wall, or b) arteriosclerosis – structural changes in the arterial wall causing inflammation or thickening of the artery wall. Such narrowing or thickening leads to a reduction of blood flow and a drop in pressure across the artery. Over time, if left untreated, PVD can lead to a terminal condition such as stroke or heart attack. Current diagnostic measures for PVD include Doppler ultrasound imaging, Magnetic resonance (MR) angiography, Computed tomography (CT) angiography and catheterization.

Lumen surface of the branched pulmonary arteries obtained from geometry reconstruction

Lumen surface of the branched pulmonary arteries obtained from geometry reconstruction


In addition to the above-mentioned clinical diagnostic procedures, computational modeling and simulation has gained increasing importance among the engineering community for medical research. Past and current research in the TEM Lab in this area focuses on improving computational models for assessing the functional and anatomical characteristics of diseased vasculature. For example, an inverse algorithm was developed to compute and predict the stresses in the artery wall under an intact (in vivo) condition in the human body (pre-stressed condition) using physiologic pulsatile pressure and flow in conjunction with a hyperelastic material model. The algorithm was initially developed and validated using a straight arterial segment of a canine femoral artery (idealized geometry), as shown in Figure 1. The pre-stressed arterial wall geometry, predicted by the algorithm was within 0.55% of the actual geometry obtained in vivo. Subsequently, the physiologic arterial wall pre-stress was used in assessing the pulsatile pressure-flow response of the artery. Coupled equations of wall deformation and flow conservation were solved using a computational finite element software. In addition to the idealized geometry, the inverse algorithm was implemented and tested on a patient-specific 3-dimensional geometry of the branched pulmonary arteries, shown in Figure 2, which was reconstructed from CT images of a human subject.

Additional research in this area is conducted by the TEM Lab to advance and develop novel techniques for diagnosis and treatment of peripheral vascular diseases.

Developing Pulsatile Flow in a Deployed Coronary Stent

Mesh Plot of Coronary Artery with Deployed Palmaz Stent

Figure 1. Mesh Plot of Coronary Artery with Deployed Palmaz Stent

Interventional techniques like balloon angioplasty with and without stent placement are used to treat arterial stenosis. American Heart Association statistics show serious complications in 1-2% of cases following Percutaneous Transluminal Coronary Angioplasty (PTCA). In contrast, after 6 months following procedure, 30-40% of patients develop restenosis. Stent implantation improves the arterial blood flow by redistributing the plaque. A major consequence of stent implantation is restenosis which occurs due to neointimal formation around the deployed stent. Recent evidence suggests that there are several factors such as geometry and size of vessel, and stent design that alters hemodynamic parameters, including local wall shear stress distributions, which influence the progression of restenosis. The present three-dimensional analysis of pulsatile flow in a deployed coronary stent (Figure 1) evaluates the effect of entrance (developing) flow (deve and compares with that of a developed flow. The study quantifies hemodynamic parameters and illustrates the changes in local wall shear stress distributions and their impact on restenosis.

Lower magnitude of wall shear stress exists between adjacent struts while negative shear stress is observed at the immediate downstream of strut intersection, showing recirculation. For developing flow, the wall shear stress near the entrance is nearly twice that of developed flow. The results indicate that the immediate downstream of each strut intersection may be prone to restenosis.

Drag Forces on Stent-Grafts

Abdominal aortic aneurysm (AAA) is the abnormal enlargement of the abdominal aorta. If left untreated, an AAA continues to expand until it ruptures. The rupture of an AAA can lead to severe internal bleeding. In the past open repair was the only available treatment which results in traumatic and stressful experience. In the recent years an alternative procedure has been developed where the stent-graft is introduced, via iliac vessels into the AAA site. If placed correctly, blood will flow through the stent-graft and relieve the stress on the AAA walls, which eventually heals in the due course of time.

In this Lab, computational fluid (blood)-structure (arterial wall) interaction technique for compliant arteries and grafts is used to investigate the pulsatile displacement forces on a stent-graft within an artery. This allows the determination of displacement forces translate into motion of the stent-graft. The velocity from the particle image velocimeter and pressure data can be used as the input boundary conditions for the blood flow-arterial wall computation. The forces from the computation are then compared with the experimental forces as recorded in-vitro model. Several different variations of stent-graft geometries are being studied. This research has being conducted in collaboration with Cleveland clinic foundation and Case Western Reserve University.

Graph showing the velocity profile for Sinusoidal wave form

Velocity profile for Sinusoidal wave form

Peristaltic pumping a form of fluid transport, is a physiological flow dynamics in the human body that propels the fluids from one place to another. Peristaltic action is an inherent neuromuscular property of any tubular smooth muscle structure. The fluid is driven by a periodic progressive wave of contraction and expansion along the length of the distensible tube of uniform or varying cross-section. 

Graph showing instantaneous wall location at time t=0.9 for different wave forms

Instantaneous wall location at time t=0.9 for different wave forms

It is responsible for the transport of biological fluids in several physiological processes such as passage of urine from the kidneys to the bladder, the movement of chime in the gastro-intestinal tract, transport of food bolus through the esophagus, transport of blood in small devices, embryo transport in non-pregnant uterus, and movement of spermatozoa in human reproductive tract. Flawed or improper peristaltic motion in the ejaculatory duct may lead to retrograde ejaculation (ejaculation in which seminal fluid is discharged in the wrong direction, traveling up towards the bladder instead of outside the body through the urethra) a cause for infertility in men. 

Temporal variations of pressure gradient along the tube length for different wave forms with power law indices, n=1, 0.8 & 0.6 and amplitude ratios

Temporal variations of pressure gradient along the tube length for different wave forms with power law indices, n=1, 0.8 & 0.6 and amplitude ratios

Retrograde ejaculation is caused by diabetes, bladder neck surgery, alpha-antagonists, transurethral prostatectomy (TURP), colon or rectal surgery, multiple sclerosis, or spinal cord injury. The objectives of this research are to compare the flow characteristics of different non - Newtonian fluid models namely power law, Bingham, and Herschel-Buckley models and investigate the effects of different wall motions (sinusoidal, multi-sinusoidal, triangular, trapezoidal and square wave forms) on the fluid flow . We also aim to study the reflux phenomenon. Figure 1 shows the instantaneous wall location for different waveforms. Straight lines depict the position of the wall before the start of peristalsis. Figure 2 shows the positive and negative velocity profiles obtained for a sinusoidal wave form.

Thermal Therapy

Velocity profile diagram

High Intensity Focused Ultrasound (HIFU) shows considerable promise as a minimally invasive medical procedure, in applications such as tumor ablation, vessel cauterization, and 'bloodless' resection. In order to maximize the efficacy of HIFU procedures, and to minimize the damage to healthy tissue, it is important to predict tissue response through quantification of temperature rise during absorption of high-intensity ultrasound energy. In this regard, mathematical analyses of energy transfer during HIFU procedures are very valuable.

Characterization of HIFU transducers
Firstly velocity profiles are obtained using digitial particle image velocimetry (DPIV) and the intensity profile is obtained for the particular transducer using the optimization algorigthms. The velocity profile is shown below.

No-flow model

Figure shows the schematic of (a) No-flow model no large blood vessel near the ablation region (b) Parallel flow model blood vessel oriented parallel to the ultrasound beam axis and (c) Perpendicular flow model blood vessel oriented perpendicular to the ultrasound beam axis.

Effect of large blood vessels on the efficacy of HIFU ablation procedures
A three-dimensional computational model was developed for studying the efficacy of high intensity focused ultrasound (HIFU) procedures targeted near large blood vessels.  The model was first validated in a tissue phantom, to verify the absence of bubble formation and nonlinear effects.  Temperature rise and lesion-volume calculations were then performed for different beam locations and orientations relative to a large vessel.

Graph of the temperature rise (oC) as a function of radial distance (cm) at t = 10 and 20 sec (ultrasound is turned off after 10 sec) for no flow, parallel flow, and perpendicular flow models.

Figure shows the temperature rise (oC) as a function of radial distance (cm) at t = 10 and 20 sec (ultrasound is turned off after 10 sec) for no flow, parallel flow, and perpendicular flow models.

Figure shows the 3D geometry obtained from MRI images using image reconstruction. Figure shows the reconstructed geometry in an isometric view. Figure shows the speed and temperature contour plots for different arterial velocities. Increasing the blood flow rate from no flow to hyperemic flow (velocity = 41.4 cm/s) not only reduced the maximum temperature rise but also shifted the location of the maximum temperature rise. While the presence of blood perfusion is responsible for the reduction in maximum temperature rise, the large blood vessel is responsible for the shift in the location of the maximum temperature from the center. Thus, both blood perfusion in microvessels and proximity of blood vessels influence the temperature rise.

3D image of reconstructed artery

3D image of reconstructed artery

Radio-frequency (RF) ablation is a minimally invasive procedure that has the potential for widespread use in hepatic cancer therapy. This RF energy generates heat, which destroys the tumor. Temperatures in the range of 50-600oC can start the process of denaturization in minutes. 

Reconstructed flow geometry

Reconstructed flow geometry

Treatment sessions are generally 10-30 min in duration and produce spherical necrotic regions that are 3-5.5 cm in diameter. Accurate mathematical models are valuable for predicting the temperature rise obtained during RF ablation, thereby enhancing the likelihood of tumor denaturization with minimal damage to surrounding tissue.

Graph showing speed and temperature

Speed and temperature contours within the tumor zone, in the x-z plane at time t=32 min and at inlet velocity = 13.8cm/s

Previous numerical research have used the Pennes bio-heat equation to model the heat transfer in the tissue domain.

Graph showing temperature and speed

Speed and temperature contours within the tumor zone, in the x-z plane at time t=32 min and at inlet velocity = 27.6 cm/s

In the Pennes approach, heat transfer due to blood flow is modeled using a non-directional lumped heat sink and it does not accurately model the convective effect of blood flow near a large vessel. 

Graph showing temperature rise within a tumor

Temperature rise within the tumor as a function of axial distance, for different ablation times z=0 denotes tumor center

This work aims to provide an alternate to the Pennes equation by treating the perfusion in the tissue with a statistical approach i.e. as a porous medium. The vascular geometry is represented realistically by reconstructing the arterial geometry from MRI images of a porcine liver.

Laser-Ocular Media Interaction during photocoagulation

Eye model

Axi-symmetric eye model

Choroidal neovascularization (CNV) in exudative age-related macular degeneration (AMD) is the leading cause of blindness. Until recently, laser photocoagulation was the only well-established and widely accepted treatment for AMD. However, it has a high rate of CNV persistence and recurrence and results in iatrogenic, collateral damage to the overlying retina. Numerical studies of photocoagulation is being studied to compare the effect of latest technique pulsed lasers with conventional laser treatment in minimizing the damage to the inner and outer bands of neural retina. The research aims at finding optimum laser parameters for selective treatment of retinal pigment epithelium (RPE) sparing neural retina. Due to symmetry of the problem two dimensional axi-symmetric eye model was developed as shown in the figure. 

Graph showing Power distribution for CW and pulsed laser

Power distribution for CW and pulsed laser

The Figures show the energy and temperature distribution for continuous wave and pulsed (10% duty factor) laser respectively. The temperature rise for 10% duty factor at the RPE is higher than that of continuous wave laser. 

Graph showing Temperature distribution along center line

Temperature distribution along center line

This shows that only RPE can be destroyed by use of pulsed laser without a significant rise in temperature in the neural retina.

Diagram showing the Two Layer Method

A) TLM experimental setup (B) Velocity vector at 5 min of tissue surrogate preservation (C) 2D Axi-symmetric model used for numerical computation

Hypothermic preservation is one of the main-stream organ preservation methods. The Two-Layer Method (TLM) of organ preservation is found to be the most effective of all available hypothermic cold storage methods. The objective of this work is to test the hypothesis that the putative functional efficiency of the TLM is due to the favorable heat transfer effect between pancreas tissues and the two solutions viz. the University of Wisconsin (UW) solution and Perfluorocarbon (PFC) solution. In this research, both experimental and numerical approaches are undertaken to study the heat transfer phenomena involved.

Diagram showing axis of symmetry

The numerical analysis of the problem involves natural convection within two phases of the immiscible fluids namely the UW and PFC solutions and hence a multiphase model is employed. The experimental study deals with measuring the cooling rates of a pancreatic tissue preserved in the following fluids: 1) UW solution only 2) PFC solution only 3) TLM comprising of UW and PFC solutions.

A 2D axi-symmetric model of the TLM with a pancreas tissue surrogate and container modeled as co-axial cylinders is as shown in the figure. A multi-phase heat transfer model is employed to solve for natural convection. The velocity vectors near interface section at the 5th minute of preservation obtained by numerical computation are as shown in the figure.

Whole body thermal modeling is a computational analysis technique to determine the temperature changes occurring within the human body under different environmental and physiologic conditions. Differences in the environment can include scenarios of extreme heat stress such as a fire fighting condition inside a building, or being immersed in cold water. Changes in the physiologic conditions can be caused by variable physical loads on the human body, including exercise scenarios, firefighting activities, skydiving (gravity effects), or deep sea diving (water pressure at increased depths of water). Being able to predict the temperature changes enables one to design or modify the appropriate clothing gear, determine the safe duration for each activity, and provide insights on the need and frequency for food or water replenishments.

The human body can be divided into multiple sub-domains such as the head, the muscle, and the internal organs. Each of these sub domains is assigned with their respective metabolism rate that generates body heat and blood perfusion. The blood perfusion assists in distributing the heat within the body. The interactions of these subdomains, their physiological parameters, and the immediate surroundings results in a complex interplay of heat transfer from the human body to the environment or vice versa.

 Tissue temperature distribution in the human body diagram

Tissue temperature distribution in the human body A) after 150 minutes of water immersion in 0 °C and B) after 150 minutes of exercise at the maximum walking speed of 1.8 m/s

The figure below shows the transient temperature profile of the human body model during cold water immersion at fixed water temperature of 0 °C (A) and during exercise condition (B) at the end of 150 minutes. The core body temperature (Tc), which is the primary outcome of the computational study, is defined as the average temperature of the internal organs. The TEM lab expertizes in research to de-termine the temperature changes in firefighters during firefighting operation.

Drug delivery and mass transport

Severe vision loss from vitreoretinal (VR) diseases such as age-related macular degeneration (AMD), retinitis pigmentosa (RP), intraocular lymphoma (IOL), uveitis and proliferative retinopathy (PVR ) accounts for most cases of irreversible ocular diseases world-wide. Existing therapeutic procedures for treatment of VR diseases are limited as: 1) systemic drug therapy administered through mouth or injected into the bloodstream, and topical administration such as eye drops, fail to penetrate the physiological barriers; 2) intravitreal injections can lead to uneven drug distribution causing increased toxicity for non-target ocular tissues; and 3) in comparison to lipophilic (not water soluble) drugs, sustained release devices for hydrophilic (water soluble) drugs for treating VR diseases are difficult to fabricate, as these hydrophilic drugs do not bind well with existing FDA approved lipophilic materials.

At present, research is being conducted in developing a novel polymer-based biodegradable intravitreal micro-implant platform (Figure. 1) which administers therapeutic release of hydrophilic drug such as Methotrexate (MTX) over a period of more than 1 month. This study involves formulation and fabrication of the micro-implant drug delivery platform along with the in-vitro material characterization and pharmacokinetics analysis. The micro-implant has been further evaluated in vivo, in a limited number of rabbit eyes where it showed therapeutic release of the drug for > 1 month without any evidence of toxicity.

Ocular drug delivery, xray of eye

Figure 1. Intravitreal micro-implant

In the recent past our group has also conducted several numerical studies which included a) development of a 3D finite element eye model to compare the pharmacokinetics of drug distribution between an intravitreal injection and a sustained release device, b) evaluating the influence of drug transport parameters such as retinal permeability, drug diffusivity and hydrodynamic conditions within the VR domain of the eye, and c) determining the optimal range of sustained drug release for therapeutic efficacy to treat VR diseases.

Our group has also carried out ex vivo studies related to ocular drug delivery where, the therapeutic efficacy 2-Methoxyestradiol (2ME2), a potential antitumor agent with minimal toxicity, was assessed in relation to MTX, for treating lymphoma using Farage and Pfeiffer cell lines.

The above research has been conducted in collaboration with Department of Ophthalmology resulting in 7 journal publications and 1 patent.

Oxygen is supplied to the avascular region of arterial wall by diffusion from the luminal blood and from the vasa vasorum. The abnormalities in this supply of oxygen are linked with the conditions of hypoxia or hyperoxia, which accelerates the human atherosclerosis by initiating a chain reaction of self sustaining metabolic abnormalities. The changes in the supply of the oxygen to the avascular arterial wall have always been a subject of research over the period of past few decades. This research aims at finding the oxygen concentration distribution in normal artery as well as its pathophysiologic counterpart. This includes i) various degrees of area occlusion representing a wide range of stenoses for ii) flow rates varying from basal to hyperemic conditions, and iii) effect of the viscosity changes due to hematocrit (Hct) variations. The coupled flow and oxygen transport equations in luminal blood flow and oxygen consuming arterial wall are solved and validated with previous studies. 

Graph describing contours of oxygen concentration distal to stenosis.

Contours of oxygen concentration distal to stenosis.

The figure shows the contour plot of the oxygen concentration distal to a moderate occlusion in a stenotic artery at basal flow condition. In the region immediately distal to stenosis closed concentric iso-contours of oxygen concentration similar to the flow streamlines are observed. This is due to the flow separation downstream of the stenosis. The oxygen transport across the concentration contours occurs only by diffusion.

Graphs depicting radial pO2 variation in the recirculation region for the basal flow

Radial pO2 variation in the recirculation region for the basal flow (A) and the hyperemic flow (B).

Figure 2 shows the effect of hematocrit (Hct) variations on the radial pO2 profile for the basal flow (50 ml/min) and the hyperemic flow (180 ml/min). Hct variations from 25% to 65% cause the pO2 in the medial region to drop by ~ 20% for the basal flow (arrow in Fig. 2A), while to increase by ~ 13% for the hyperemic flow (arrow in Fig. 2B).  Thus, current results with the moderate stenosed artery indicate that reducing Hct might be favorable in terms of increasing O2 flux and pO2, min in the medial region of the wall for the basal flow, while higher Hct is advantageous for the hyperemic flow beyond the diverging section.

Rotating Wall Vessel

NASA developed Rotating Wall Vessel (Synthecon, TX)

DNA Microarray study: This study uses the rotating wall vessel bioreactor (RWV) designed at NASA to simulate microgravity. Gene expression in PC12 cells in response to microgravity was analyzed by DNA microarray technology. 

Cluster diagram

Parts of Cluster diagram (PC12 cells): Red indicates up-regulation, while Green down, and Black no change.

The microarray analysis of PC12 cells cultured for four days under simulated microgravity under standardized oxygen environment conditions revealed more than 100 genes whose expression levels were changed at least two fold compared with those from cells in the unit gravity control. This study observed that genes involved in the oxidoreductase activity category were most significantly differentially expressed under microgravity conditions. A typical up and down regulation of genes is shown.

Scheme showing the similarity of rat tail model to human finger tissue

Scheme showing the similarity of rat tail model to human finger tissue

Hand arm vibration syndrome (HAVS) is a debilitating disorder which causes vasospasticity and vibration white finger (VWF) in the finger tissue of industrial workers who use hand held powered tools like chippers and grinders, repeatedly. Even though, HAVS is a mélange of musculoskeletal, vascular and sensorineural disorders, the vascular disorder has remained a subject of avid research in recent years and the knowledge of its early pathophysiology is still underappreciated. The ‘frequency weighting’ proposed by current ISO 2001 guidelines on vibration exposures, which places lower risk for vibration frequencies >100 Hz, has been criticized by researchers who have documented that high frequencies > 100 Hz, can potentially cause damage to vascular tissue. This has been validated using a rat tail model of vibration injury which exhibits a biodynamic response at these frequencies similar to that observed in a human finger tissue.

Vacuole formation (shown by red arrows) in the artery vibrated at 125 Hz for 5 day (125:5d) and 250 Hz for 10 days (250Hz: 10d). No vacuoles form in control artery (X400).

Vacuole formation (shown by red arrows) in the artery vibrated at 125 Hz for 5 day (125:5d) and 250 Hz for 10 days (250Hz: 10d). No vacuoles form in control artery (X400).

In this research, our aim is to assess the frequency dependence of vascular damage and the effects of duration of vibration exposure in progression of early vascular injury. Typically, we use histopathological methods to quantify the response of two primary cells in artery (EC- Endothelial Cell; SMC- Smooth Muscle Cell) under high frequency vibration. The response parameters we measure are formation of vacuoles in these cells, which are a potent index of cellular injury and loss of cellular morphology and integrity.

Formation of Nitrotyrosine (red arrows) in EC in vibrated artery (X1000)

Formation of Nitrotyrosine (red arrows) in EC in vibrated artery (X1000)

Additionally, we use a potential biomarker of oxidative injury, namely Nitrotyrosine, which has been reported in several vascular pathologies such as renal, pulmonary and cardiovascular, before. Vibrated arteries exhibit intense brown staining for NT.

  • Oxygen-dependent gene expression in microgravity
    • The bio-transport research under simulated microgravity conditions, such as those that would apply during a long-duration spaceflight, has the potential to improve understanding of the oxygen transport process, which becomes more complex as the arterial wall structure, e.g. endothelial cells and its biochemical compositions are altered. Earlier reports have documented physiological changes such as reduction in red blood cell (RBC) count, reduced pulsatile blood ejection rate from the heart, changes in blood volume and distribution within the components of the cardiovascular systems, and bone loss as the duration of spaceflight increases. These changes are adaptive processes, which were formerly attributed to reduced levels of metabolic activities and less demand for oxygen by the astronauts during long-duration spaceflights. Evaluation of the effect of simulated microgravity on altered demand for oxygen and metabolic activities has been limited. Even for terrestrial gravity (~1 g) condition, few data are available for oxygen transport in cells in conjunction with microcirculation. Cellular mechanics and oxygen-sensitive gene expression under simulated microgravity have been investigated and correlated to the patho-physiological changes that occur at the cellular and molecular (DNA, RNA, and Protein) level.
  • Protein Study
    • Based on the microarray study, the present study is in the process of analyzing the activation of typical oxygen-dependent proteins, and to further identify the regulatory pathways and effector molecules using EMSA, Western blotting and ELISA. The results are now being analyzed and prepared to be submitted to a related journal.
  • Computational Analysis of O2 Transport in RWV
    • The present study is to determine the appropriate suspension conditions for the microcarrier beads/cell distribution and evaluate oxygen transport and to validate the physio-chemical changes in the RWV bioreactor. The results are submitted to a related journal and now under review. This research is partially funded by NASA-Glenn: Microgravity Division.

 

Micro- and nano- fluidic heat transfer

Traditionally, fluid pumping techniques have been mainly based on using mechanical pumps that have different types and operation principles. Due to increased development in MEMs and Lap-on-chip (LOC) devices, there is a need to develop small-scale, reliable, and low-cost pump. One of the most promising pumping techniques is to use the electro-hydrodynamic (EHD) fluid pumping principle. This pumping technique is based on the fact that when an aqueous solution is brought into contact with a surface such as a channel wall, the surface will acquire a negative charge. The positively-charged ions in the solution will be attracted to the surface leading to a higher concentration of positive ions in its vicinity. The concentration of positive ions in the fluid bulk will be lower. When an electric field is applied between two points in the fluid, a bulk motion of the fluid occurs. This is known as electro-osmotic flow (EOF).

EOF has a unique feature that can suitable for LOC applications. EOF has a plug flow profile that can reduce sample dispersion. Also, for heat transfer in micro-channels, plug profile increases the amount of heat transfer due to the increase in the heat transfer coefficient.

I. Sample transport and micro-reactions control:  Research investigated controlled sample transport to micro-reactors where pinching and switching techniques were implemented. The research was conducted experimentally and was verified using numerical calculations. Nano-liter discrete samples were transported to a micro-reactor using EOF. The samples were allowed to react for a specific amount of time while their concentrations were monitored in the reactor. Sample pinching process is shown in Fig. 2. The lab is in the process of developing diagnostic devices for immunoassays that help detect biomolecules, cells, and pathogens in throughput screening. One such method of immunoassay is magnetophoretic separation that uses magnetic microbeads conjugated with antibodies against specific cell surface epitopes (antigens) and are used to tag cells of interest.

Numerical and experimental results of sample pinching process at different times

Numerical and experimental results of sample pinching process at different times

II. Heat transfer in micro-channels using EOF:  Heat transfer in micro-channels using EOF, as a flow pumping technique, is currently being studied. Experimental studies are being conducted as well as numerical calculations for verification. Silicon-based micro-channels were fabricated and a micro-scale heat exchanger device was assembled using various components. 

Diagram of SEM photograph of micro-channels used in the fabrication of micro-scale heat exchangers

SEM photograph of micro-channels used in the fabrication of micro-scale heat exchangers

Micro-channels used in one of our micro-scale heat exchanger are shown in the figure. Flow and heat transfer data were gathered and analyzed to assess the performance of the device.
Additionally, studies are being performed on hybrid micro-channels heat exchangers using combinations of different materials. Also, the use of different cooling liquids is being evaluated for optimal heat transfer characteristics.

Analysis of liquid samples for pathogens and toxins is a crucial step to determining the quality of liquid, e.g. water, and how to most efficiently treat a particular water supply. Currently, analysis of liquid supplies for particular toxins is both expensive and time consuming. The analytical methods require the transport of samples to fully stocked labs where lengthy assays have to be performed to determine the concentration of a pathogen in the sample. However, through the use of functionalized magnetic microbeads, an electro-osmotic driven system, and an external magnetic field, it is possible to quickly analyze liquid samples for pathogen content.

We in the TEM Lab at the University of Cincinnati are working on developing an easy to use, portable, and efficient lab-on-chip device that can be used in the field to analyze liquid samples. We have developed a novel approach that a magnet and an electro-osmotic flow field to enhance the capture of microbeads in the channel. We ran experimental tests (Figure 1) to analyze the capture efficiency of the magnetic microbeads that confirmed our predictions regarding the effectiveness of flow switching. Through the use of microfluidic channels, we are able to efficiently capture targeted microbeads, and therefore the pathogens of interest, using an inexpensive, portable, and self-contained system. 

Fluorescent image of microbeads captured against the upper wall of the experimental channel.

Figure 1. Fluorescent image of microbeads captured against the upper wall of the experimental channel.

Tissue and cell mechanics

  • Vibration induced tissue damage

Macro-fluidics and heat transfer

The principle investigator for the heat transfer research in bio-crystal is Professor Michael J. Kazmierczak (Ph: (513) 556-0259; e-mail: mike.kazmierczak@uc.edu).  The BioFHM lab is assisting in this effort and is a resource to this study. For further information, please contact Professor Kazmierczak.  

In this ongoing research a laser or an x-ray beam is used to heat a bio-crystal that is immersed in uniform external flow. Temperature distributions as well as local and average convective heat transfer coefficients are being calculated in order to evaluate the efficacy of cooling the bio-crystal.  This research extend previous studies by: applying unique heat sources imposed by irradiating the bio-crystal with an intense x-ray energy beam; performing the conjugate heat transfer analysis in fluid and solid domain; and calculating the internal and surface temperature distribution. Absorption of the irradiation results in non-uniform heat generation, having an exponential spatial distribution of heat source. The limiting cases of heat source distribution are localized surface “laser” heating and a near uniform heat generation throughout the bio-crystal.  Results that are being investigated are: the maximum internal temperature, the local and average Nusselt numbers (Nu). The diameter of the source beam striking the bio-crystal is varied (small and large) without altering the incident power.  This results in a significant change in the magnitude of the maximum temperature and an increased variation in the internal local temperature distribution within the bio-crystal. A bio-crystal having a high thermal conductivity maintains itself at a near uniform temperature resulting in a nearly constant average Nu over the range of heat source variation. However as the thermal conductivity decreases, the temperature distribution becomes more distinctive resulting in larger variations in local and surface integrated heat transfer rate, Nu and maximum temperatures.