Mu Chiao


Relevant Thesis-Based Degree Programs


Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

An investigation of cancer effect on viscoelastic properties of prostate gland via quasi-linear viscoelastic model (2022)

Mechanical properties of biological tissues have been shown to vary in the presence of pathological disorders. This dissertation aims to investigate the effect of cancer on the viscoelastic properties of prostate gland. We use the quasi-linear viscoelastic model to characterize the elastic and viscous characteristics of thirty-five fresh prostate glands, removed within two hours of radical prostatectomy surgery. The viscoelastic properties of normal and cancerous prostates are compared to reveal the influence of cancer grade and tumor volume on the elasticity and viscosity of prostate tissue. We first present a novel method for describing the time-dependent behavior of soft materials using one-dimensional quasi-linear viscoelastic model. Our model derives the elastic (Young’s modulus) and viscous (shear relaxation modulus) properties by analyzing the stress response after a sudden uniaxial compression. The model is validated using experimental data on the phantoms that mimic the elasticity of normal and cancerous prostate tissues. The applicability of the model for material characterization is demonstrated by introducing a procedure for obtaining the mechanical properties via indentation test. Using three-dimensional equations and pre-calculated finite element analysis, the procedure introduces a fast and straightforward approach that is superior to inverse finite element methods. We evaluate our procedure by comparing the derived properties with those obtained from uniaxial compression test, where the results show high precision (standard deviation less than 10%) and good accuracy (error less than 20%). Finally, the procedure introduced for material characterization is used to characterize the viscoelastic properties of prostate gland. We test four different locations on fresh, unfixed prostate samples and compare the properties of locations where cancer spreads with those where cancer is not present. Our data-driven results demonstrate that tumor volume increases elastic and viscous properties of prostate with high statistical significance (p-value
View record

Magnetic sponges for localized and controlled drug delivery with drug combination therapy (2022)

Systemic drug administration (i.e., intravenous injection), leading to drug circulation throughout the body can be associated with adverse side effects. Alternatively, localized drug delivery systems have been developed to focus drug concentrations at target sites. This method of delivery has been widely accepted in orthopedic infection management where the poor blood supply hampers antibiotics from reaching the infected site. Antibiotic-loaded bone cement beads have been approved for clinical delivery systems for the localized treatment of bone infections (osteomyelitis). The beads, however, have some shortcomings such as incompatibility with some antibiotics, and poor drug elution, which relies on unregulated passive diffusion. This dissertation proposes an on-demand drug delivery device that can control the release pattern using a controlled magnetic field application. The drug delivery device has the same configuration as conventional bone cement beads. It provides a sustained antibiotic discharge through a PMMA shell with multiple holes, while incorporating a magnetic porous PDMS at its core to manage the release profile via external magnetic fields. The magnetic sponge’s magneto-mechanical properties are investigated under non-uniform magnetic fields. Unlike proposed models that explore the effect of uniform magnetic fields, this study presents an analytical model that demonstrates the magnetic sponge response to the magnetic field gradient. The findings of this study and the development of the drug delivery device can provide adjustable released content controlled by the strength of the applied magnetic field. The in vitro experiments confirm the antibacterial efficacy of discharged gentamicin and silver against both gram-positive and gram-negative bacteria with extended bactericidal activity up to six days after drug combination. The ex vivo assessment demonstrated a successful drug discharge upon implantation with a controllable release profile using a magnet. Furthermore, to address the increasingly prevalent problem of antibiotic-resistant bacteria, a synergy study was conducted on gentamicin and silver nitrate. The results showed a significant improvement in the antibacterial efficiency once the two agents are combined, inhibiting the growth of MRSA and E. coli by more than 3log10CFU/mL. Exploiting the drug combination therapy in conjunction with a controllable localized drug delivery device may provide a more efficient therapy for treating osteomyelitis.

View record

Robust and optimal switching linear parameter-varying control (2018)

Linear parameter-varying (LPV) control is a systematic way for gain-scheduling control of a nonlinear or time-varying system that has parameter-dependent dynamics variations in its operating region. However, when the dynamics variations are large, LPV control may give the conservative performance. One way to reduce the conservatism is switching LPV (SLPV) control, in which we partition the operating region into sub-regions, design one local LPV controller for each sub-region, and switch among those local controllers according to some switching rules. On the one hand, this thesis makes three theoretical contributions to the SLPV control theory. Firstly, this thesis proposes a new approach to designing SLPV controllers with guaranteed stability and performance even when the scheduling parameters cannot be exactly measured. Secondly, this thesis presents two algorithms to optimize the switching surfaces (SSs) that can further improve the performance of an SLPV controller. One algorithm is based on sequentially optimizing the SSs and the SLPV controller for the state-feedback case. The other one is based on particle swarm optimization and can be used for both state-feedback and output-feedback cases. Finally, this thesis introduces a novel approach to designing SLPV controllers that could yield significantly improved local performance in some sub-regions without much sacrifice of the worst-case performance. This is different from the traditional approach that often leads to similar performance in all the sub-regions.On the other hand, this thesis addresses two practical problems using the theoretic approaches developed in this thesis. One is control of miniaturized optical image stabilizers with product variations. Specifically, multiple parameter-dependent robust (MPDR) controllers are designed to adapt to the product variations, while being robust against the uncertainties in measurement of the scheduling parameters that characterize the dynamics variation. Experimental results validate the advantages of the proposed MPDR controllers over a conventional robust mu-synthesis controller. The other application is control of a floating offshore wind turbine on a semi-submersible platform. SLPV controllers are designed for regulating the power and the generator speed and reducing the platform motion. The superior performance of the SLPV controllers is demonstrated in high-fidelity simulations.

View record

Magnetically actuated MEMS devices for active control of cell migration (2015)

The ability of living cells to sense and respond to mechanical cues from the surrounding environment has been the subject of much study. Over the past two decades, a variety of techniques have been used to apply mechanical stimuli and investigate cell response. Recently, with advances in the field of Microelectromechanical Systems, devices incorporating microscale actuators have been developed to apply forces and study the cell response of individual cells. Among these microdevices, micropillar arrays incorporating remotely actuated magnetic pillars have shown some success as combined actuation and sensing platforms for cell strain studies. However, issues associated with the complex fabrication techniques used, the low actuation forces generated and the high magnetic field gradients required for pillar actuation have hindered the wide-scale adoption of these devices by the general research community. Consequently, investigation into the use of these active micropatterned surfaces in eliciting or controlling specific cellular response on a multicellular level has yet to be undertaken. This thesis aims to investigate the application of remotely actuated micropillar surfaces in controlling the migration behavior of cells on a multicellular level. First, using a novel custom-made magnetically actuated cell strain assessment tool, conventional tests are performed on endothelial cells to determine the minimum strain requirements for eliciting cell response. Then, a new technique for fabrication and patterning of magnetic micropillar arrays is developed to overcome the complexities of previous fabrication methods. Using the newly developed fabrication technique, magnetic micropillar arrays of various dimensions are fabricated and their mechanical, magnetic and material properties are characterized. The fabricated magnetic micropillars generate forces of several hundred nanonewtons at moderate magnetic fields of 100mT and are favorable to previous state-of-the-art. Finally, a cell migration chip comprising various micropillar topologies is developed and the migration behavior and migration rates of sheets of cells on the micropillar surfaces in the presence and absence of micropillar actuation is studied using in-vitro experiments. We show that actuated micropillar surfaces significantly impede cell migration, reducing cell migration rates by up to 85%. The magnetically actuated micropillar surfaces could have possible in-vivo applications for preventing cell-migration induced biofouling of medical implants.

View record

Microfabricated electromagnetic actuators for confocal measurements and imaging (2013)

Various optical microscopy techniques have been developed for micrometer level imaging of biological tissue samples. Among those techniques, confocal imaging provides superior image contrast and high resolution with a modest system cost. Confocal microscopy allows vertical optical sectioning (imaging a section perpendicular to the surface of tissue) or horizontal optical sectioning (imaging a section parallel to the surface of tissue) and provides high-resolution tissue morphology that is analogous to conventional histopathology images. This has brought up a tremendous potential for guiding surgical biopsies and in vivo non-invasive diagnosis of diseases such as cancer. The challenge in moving microscopic imaging modalities into clinical applications is miniaturization into a form of hand-held devices or catheters for endoscopic applications.In this thesis, micro-fabrication techniques such as Microelectromechanical Systems (MEMS) fabrication process and laser micromachining have been employed to develop magnetic actuators. The actuators are then used to move lenses and optical fibers in order to scan a laser beam across a sample. Lens and fiber actuators are integrated in catheter and hand-held devices for confocal thickness measurement and optical sectioning imaging of biological samples.Thickness measurement is performed by scanning the focal point of a microlens across the thickness of thin films or layered biological tissues and collecting the intensity signal of the single scattering light reflected back from the samples as a function of lens position. A catheter was developed and thickness measurements of polymer layers and biological tissues were demonstrated. The device has optical resolution of 32 µm with expanded uncertainty of measurement of 11.86 µm. Lens and fiber optic actuators have been coupled to form two-dimensional imaging devices. Direct and real-time vertical and horizontal cross-sectional imaging of biological samples has been demonstrated. Vertical imaging is performed by transverse (X-axis) and axial (Z-axis) scanning of a focused laser beam using an optical fiber and a microlens actuator respectively. Horizontal imaging is done by a 2-axis fiber optic scanner. All the developed actuators are driven by electromagnetic forces and require low driving voltages. Confocal imaging of biological samples, with lateral resolution of 1.55 µm, has been demonstrated.

View record

A battery-less MEMS device for on-demand and controlled drug delivery (2011)

Drug therapy efficacy depends on therapeutic concentrations of drugs at disease sites. An ideal controlled and localized drug delivery system would deliver drugs to a target tissue and would locally maintain the required drug concentration. Furthermore, for many diseases, the delivery of therapeutic concentrations on an “on-demand” basis would be of tremendous benefit.In this thesis, a MEMS (Microelectromechanical Systems) based drug delivery device has been developed that provides on-demand release of defined drug quantities. The device consists of a drug-loaded microreservoir that is sealed with an elastic PDMS (polydimethylsiloxane) magnetic membrane with a laser-drilled aperture. The drug release is triggered in the presence of an external magnetic field by deforming the magnetic membrane and therefore discharging the drug solution. The use of magnetic actuation for on-demand and controlled dose sequencing eliminates the need for an on-board power source. A new magnetic membrane material has been developed for the proposed drug delivery device. The polymeric magnetic composites were developed by incorporating coated iron oxide nanoparticles within a PDMS matrix. The new composites show improvement in reducing particle agglomeration compared to existing polymeric magnetic materials. Free-standing PDMS magnetic membranes with a thickness of 35 µm have been fabricated and have shown to deflect in applied magnetic fields. The MEMS drug delivery device has been used to deliver an antiproliferative, taxane-based drug, docetaxel (DTX). On-demand and controlled release of DTX with a dosage suitable for treatment of diabetic retinopathy has been achieved for 35 days. Biological activity of the released DTX was investigated two months after the drug was packaged in the device. These studies confirmed that the antiproliferative effect of DTX can be maintained for 2 months, and the drug does not degrade within the device. This device is a proof-of-concept development for on-demand and controlled delivery of taxane-based agents for treatment of proliferative retinopathy, which requires accurate delivery of nanomolar drug concentrations.

View record

MEMS Pressure, Temperature and Conductivity Sensors for High Temperature and Harsh Environments (2011)

Kraft pulp digesters have been used to convert wood chips into pulp for manufacturing a wide variety of paper products. Inside a kraft digester, chemical reactions remove lignin from their wood matrix in a caustic environment (pH~13.5, 170°C, 2MPa). Data on actual internal operating conditions in a kraft digester is needed to optimize kraft digester operation and obtain maximum production quality. Currently, this information is limited to selected static locations on the periphery of the digester. The objective of this thesis is to develop miniature temperature, pressure, and liquid conductivity sensors for use in autonomous flow-following SmartChips to measure kraft process variables within the digester during their passage through the process. Combined capacitive pressure and temperature sensors were fabricated by bonding silicon and Pyrex chips using a new polymeric gap-controlling layer and a high temperature adhesive. A simple chip bonding technique involving insertion of the adhesive into the gap between two chips was developed. A silicon dioxide layer and a thin layer of Parylene were deposited to passivate the pressure sensor diaphragm against the caustic environment in kraft digesters. The sensors were characterized at both high temperatures and pressures and no signs of corrosion could be identified on the sensors.Integrated piezoresistive pressure and temperature sensors consisting of a square silicon diaphragm and high resistance piezoresistors were developed. A new Parylene and silicone conformal coating process were developed to passivate the pressure sensors against the caustic environment. The sensors were characterized up to 2MPa and 180°C in an environmental chamber. The sensors’ resistances were measured before and after testing in a kraft pulping cycle and showed no change in their values. SEM pictures and topographical surface analyses were also performed before and after pulp liquor exposure and showed no observable changes.Combined liquid conductivity and temperature sensor packages consisting of a platinum resistance temperature detector (RTD) and a four-electrode conductivity sensor formed by stainless steel electrodes and installed on a polyetheretherketone (PEEK) enclosure were developed. The sensors were characterized up to 180°C at NaOH concentrations of 10-100g/l in the presence of wood chips and survived with no signs of corrosion.

View record

MEMS-based anti-biofouling - mechanism, devices and application (2009)

A novel anti-biofouling mechanism based on the combined effects of electric field and shear stress was reported. The mechanism was observed in millimeter-scale piezoelectric plates coated with different metal materials and microfabricated Micro-Electro-Mechanical Systems (MEMS) devices. Experimental observation on the quantities of protein desorption and theoretical calculations on surface interactions (van der Waals, electrostatic, hydrophobic, shear stress) have been carried out. This anti-fouling mechanism can also be activated by a vibrating micromachined Si/SiO₂ membrane. The combined effect of polyethylene glycol (PEG) grafting and application of vibration on attenuation of protein adsorption was also investigated. Vibrating PEG-grafted surfaces significantly attenuate protein adsorption, especially at low PEG grafting densities. Polymer steric interaction dominates over vibration interaction with protein on surfaces with high PEG grafting densities.Monothiol-functionalized hyperbranched polyglycidols (HPG-SH) were synthesized and self-assembled on the gold surface. The characteristics of the polymer were studied and compared with linear PEG using various surface analysis techniques. This hyperbranched polyglycidol is more resistant to protein adsorption than is linear PEG of similar molecular weight. In addition, higher molecular weight HPG shows less protein adsorption than does lower molecular weight HPG.The hyperbranched polyglycidols (without a thiol group) were further modified to generate functionality for microchannel-based liquid chromatography applications. The microchannel surface was first amino modified by allylamine plasma, and amino groups then reacted with N-hydroxy succinimide-functionalized HPGs to form strong amide bonds. The grafted HPGs are resistant to nonspecific protein adsorption. The succinimidyl ester groups degrade in water to form carboxyl groups on HPGs. By giving extra carboxyl groups to each HPG, the HPG can selectively capture positive avidin from a mixture of avidin and bovine serum albumin (BSA). To increase the capture efficiency, the microchannel was integrated with micropillar arrays as the liquid chromatography column.

View record

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

A model-based fusion technique for ocular motion sensing (2019)

Electrooculography (EOG) uses an electrical signal that records the cornea-retinaldifferential potential of the eyeball, which is linearly proportional to the eye movement.In EOG, the electrodes placed in the outer canthus and lateral frontalis recordthe horizontal and vertical eye movements. A main challenge in these signals isthat the eye movement information is compressed in the 0-35Hz range of the fullspectrum of the recording (0-250/1000/2000Hz) depending on the dynamic rangeof the device. Moreover, these signals, like any other bio-signals, are contaminatedheavily by artifacts and noises such as electroencephalography (EEG), eye-lid motions,illumination drift, skin drift, impedance drop of electrode, eye blinks, headmovements, and DC drift. Researchers have attempted to addressing these issuesusing traditional techniques, including finite impulse response (FIR) filters, morphologicalfilters, time series motifs and wavelet-based approaches. However, mostof these approaches have not been able to improve the performance significantlywithout compromising other features of the system such as the computational cost,real-time performance and time lag. This thesis presents a model-based fusiontechnique for ocular motion sensing to improve the signal quality. The developedapproach is tested with five different model-based approaches (Brownian, constantvelocity, constant acceleration, Westheimer, and linear reciprocal). Among these,the approach based on the linear reciprocal human eye model show a significantoverall improvement in the signal(500-700% improvement in SNR w.r.t. FIR and40-50% decrement in computational cost). Therefore, it is concluded that the approachbased on the linear reciprocal model provides the best fit in the implementationof high quality eye tracking systems.

View record

Development of a pneumatic PDMS MEMS actuator using a closed loop controller for endoscopic applications (2019)

Gastrointestinal (GI) cancer is one of the most significant public health issues globally. Early diagnosis results in increasing the probability of surviving GI cancers. However, it is difficult to develop diagnostic tools for early GI cancer detection. One of the challenges is to design an endoscope with adequate optical quality. This thesis demonstrated a pneumatic miniaturized PDMS (Polydimethylsiloxane) MEMS (Microelectromechanical Systems) actuator with high stability to improve optics. Theoretical, experimental, and simulation methods were used to characterize the actuator. An electronic platform with a PID (Proportional–Integral–Derivative) controller was designed to control the actuator. A feedback control mechanism was designed to eliminate disturbances, and provide a stable position for the actuator. A trial-and-error method, the Matlab® PID Tuner, and Genetic Algorithm were used to find and verify the PID parameters.To demonstrate the functionality of the actuator, a confocal system was used to obtain images of paper fiber and onion epidermis. The actuator shows an axial resolution of 1.12 μm and the optical resolution of 21.5 μm. The actuator designed in this study has several advantages, such as ease of miniaturization and stability that make it attractive for further development.

View record

Assessment of using a Tesla expander to harvest waste heat from a photovoltaic panel for residential applications (2018)

Solar energy is an abundant source of energy for generating electricity. The main challenge is that the solar photovoltaic (PV) panels are typically used in regions where solar radiation is high; consequently, the temperature of the panels will increase, and the efficiency of the panel will decrease. Water cooling systems are typical methods of cooling, and the resulting hot water can be used for space heating or other purposes. In regions that have high solar radiation; however, the demand for hot water is not high.In this research, we investigated combinations of PV panel, an expander with a Rankin cycle, and a new working fluid to generate extra electrical power for residential applications. To achieve the goal, different working fluids were analyzed, and R-245-fa was found to be the ideal fluid for this purpose. To design the cooling system, a new algorithm was developed to find the optimal number, spacing, and diameter of the cooling tubes. The accuracy of the new model was determined by a CFD simulation, and for possible future industrial uses, a user-friendly application was developed using COMSOL® Multiphysics.A Tesla expander was built and tested, and the torque was measured experimentally. The results were compared to typical methods of modeling the turbine to determine the accuracy of each model. Finally, for real data for a day in Egypt, the system was analyzed, and the cooling cycle was shown to yield an average improvement of 12% in terms of generated power.

View record

Improved in vitro methods for differentiating induced pluripotent stem cells to cardiomyocytes (2018)

Human adult cardiomyocytes are hard to obtain and difficult to culture. This has led to patient-specific induced pluripotent stem (iPS) cell-derived cardiomyocytes (iCMs) becoming an attractive alternative, serving as a platform for cardiovascular disease modeling, drug toxicity screening, regenerative therapies, and the understanding of human physiology. Unfortunately, current protocols of generating iCMs remain unpredictable, yielding cellular subtypes (ventricular, atrial, nodal cells, cardiac fibroblasts and others) that vary in proportion and levels of maturity, depending primarily on the methodology employed. This led to the scope of my research, which was to understand the minimal biological and physical parameters governing cardiac differentiation from iPS cells, so as to improve current cardiac differentiation systems. My experiments into the effects of substrate stiffness on differentiation revealed that cardiac maturity could be accelerated for iPS cells differentiated on hard substrates (~1.72MPa) compared to cells differentiated on soft (~5kPa) or intermediate (~130kPa) substrates. Experiments investigating the effects of topography also showed that freshly differentiated iCMs could be directed to form uniaxial contracting cardiac tissues by seeding them into millimeter-sized linear grooved channels. Finally, proof-of-principle experiments into inductive co-cultures revealed that previously differentiated iCMs co-cultivated with iPS cells constituted a sufficient stimulatory system to induce cardiac differentiation – as determined by the exhibition of spontaneous self-contractions, expression of cardiac specific markers, and structural organization of sarcomeres. This process was achieved without the exogenous addition of pathway inhibitors and morphogens, suggesting that ‘older’ iCMs serves as an adequate stimulatory source capable of recapitulating the necessary culture environment for cardiac differentiation.

View record

Design, fabrication and characterization of a double-network alginate-pHEMA hydrogel coating for PDMS-based biomedical implants (2017)

Traditional silicone biomedical implants, such as urinary catheters, often suffer from high surface friction, high stiffness, and a lack of hydrophilicity, which can cause discomfort or discomfort. To tackle these challenges, we developed a double-network alginate-pHEMA hydrogel “cushion” coating for polydimethylsiloxane (PDMS) biomedical implants. The double-network hydrogel presented here consists of two distinct networks made of alginate and pHEMA, respectively. The alginate network is covalently bonded to PDMS substrates as scaffolding, and the denser pHEMA network fills the free space within the alginate network. In this proof of concept study, the double-network hydrogel achieved a compressive fracture stress of 502.04±14.41 kPa, which is 5.8-fold stronger than the alginate hydrogel, while its elasticity is still comparable to soft tissues. The proposed double-network hydrogel has a negligible amount of swelling in biological fluids and exhibits no cytotoxicity, which are desirable qualities for biomedical and coating applications. Both chemical modification using APTES and micropillar anchors have been used to improve the coating stability. We found that the adhesion strength of the hydrogel coating on micropillar PDMS substrates is 55% stronger than on bare PDMS substrates when both substrates are grafted with APTES. In comparison to native PDMS and K-Y Jelly-lubricated PDMS, the double-network alginate-pHEMA hydrogel-coated PDMS demonstrated significantly less friction and superior hydrophilicity.

View record

Design, fabrication, and characterization of a magnetic porous pdms as an on-demand drug delivery device (2016)

We introduce a novel, on-demand drug delivery device based on a biocompatible magnetic sponge. The sponge is made of a porous polydimethylsiloxane (PDMS) mixed with carbonyl iron (CI) particles. The sponge is deformed under a magnetic field and consequently leads to releasing its contents. As a proof of concept study, three different CI/PDMS wt% ratios of 50%, 100%, and 150% were selected where, the 100% showed the most deformation under various magnetic fields. Although this sponge can solely be used as a potential drug delivery agent, a separate reservoir has been fabricated to protect the sponge and control the release rate. The final device has a diameter of 6 mm with a thickness of 2 mm. Controlled release of methylene blue (MB) and docetaxel (DTX) have been investigated to demonstrate the consistency and flexibility in adjusting the release rate from the device to suit different treatment requirements. Ex vivo tissue implantation has also been accomplished. This device is able to be implanted and deliver therapeutic agents at prescribed dosages.

View record

A 3D Printing and Moulding Method of the Fabrication of a Miniature Voice Coil Motor Actuator (2015)

The goal of this project is to apply 3D printing and moulding (3DPM) methods for the fabrication of a miniature magnetic actuator for optical image stabilization (OIS) applications. Polydimethylsiloxane (PDMS) and strontium ferrite (SrFe) nano powder were used as the main structural material. Young’s modulus and the magnetization of the material with SrFe-doping ratios ranging from 20% to 60% by weight were characterized. The actuator, consisting of four coils, an actuating plate, and a base supporter was assembled and tested with a Laser Doppler Velocimetry (LDV) system. A tilting angle of 0.6º was achieved with the application of 500 mA (50 turns/9 mm long coils). A Taguchi’s orthogonal experimental design was used in the finite element analysis (FEA) simulation to examine the effect of dimension variations on the eigenfrequencies. Frequency response of the actuator was characterized and the experimental results matched with the simulation results between 1 and 450 Hz showing less than 5% errors. A series of replica experiments were also performed and analyzed.

View record

A minimally-invasive MEMS drug delivery device for the treatment of prostate cancer (2015)

We have developed a cylindrical shape magnetically-actuated MEMS drug delivery device for localized prostate cancer treatment. The device is small enough for implantation through a needle with minimally invasive procedures with potentially fewer side effects compared with full prostate removal. This method of implantation will be similar to brachytherapy, a standard procedure to implant radioactive seeds inside the prostate through a needle. The drug delivery device consists of a drug reservoir, a PDMS membrane, a magnetic block and housing. Docetaxel (DTX), an anti-proliferative drug, is deposited in the reservoir in solid form. The reservoir is then filled with fluids to form a saturated drug solution. When an external magnetic field is applied, it attracts the magnetic block towards the positive field gradient and causes the membrane to deflect. As a result, DTX is discharged from the reservoir, through a laser-drilled aperture on the membrane and into the housing. The housing has a 10 mm long opening which allows the released drug to diffuse to the surrounding tissues while it would prevent the tissues from touching the thin membrane.We have achieved a 1.8 fold increase of the actuating distance and a 3.6 fold increase in the magnetic force compared to the state-of-the-art magnetically-actuated drug delivery devices under the same actuation parameters. We have also demonstrated device implantation with a needle into swine bladder tissue and successful drug release of the device in the tissue.

View record

A vertical and horizontal 3-axis hand-held confocal scanner for skin imaging applications (2015)

The goal of this project is to develop a hand-held size, confocal optical scanner for clinical skin imaging. Both vertical and horizontal image scanning have been successfully achieved. Vertical scanning is performed by a voice coil actuator in the Z axial direction and a resonant galvanometer scanner in the X lateral direction. Horizontal scanning is conducted with the same resonant galvanometer scanner and a regular galvo mirror in X and Y lateral directions. The vertical imaging plane is perpendicular to the sample surface, while the horizontal imaging plane is parallel to the sample surface. The developed device is capable of providing image resolutions of 0.9-1.1μm and 5-8μm in the lateral and axial directions, respectively. The operational scanning speed is adjustable from 8 to 20 frames per second. Imaging results in both vertical and horizontal directions are presented with biological samples, including onion and mouse skin. By using this hand-held scanner, physicians may be able to reduce the number of unnecessary and repetitive biopsies, which will lower the cost to the health care system.

View record

Cardiomyocyte Differentiation with Cyclic Mechanical Strain (2015)

The creation of cardiomyocytes from pluripotent stem cells has the potential to revolutionize the treatment of heart disease, the discovery and testing of drugs, and our understanding of human physiology. Thus far, differentiation protocols have mainly focused on recapitulating the biochemical signalling events of cardiac organogenesis, and the resulting cardiomyocytes exhibit a fetal-like phenotype. We postulated that cyclic mechanical strain can mimic the mechanical environment of the developing heart, and, when applied in conjunction to biochemical differentiation protocols, can increase the efficiency of differentiation and the maturity of the resulting cells. Using an induced pluripotent stem cell line derived from human fibroblasts, we derived spontaneously contracting cardiomyocytes via treatment with activin A and bone morphogenetic protein 4 (BMP4). We observed that differentiation of induced pluripotent stem cells to cardiomyocytes is sensitive to cyclic strain, with the application of 5% continuous cyclic strain at 1Hz having the effect of inhibiting spontaneous contractions and disrupting sarcomere formation.

View record

A microsphere based microfluidic check valve (2011)

Biomedical applications of Micro-Electro-Mechanical System (MEMS) technology have sprung growth in the field of microfluidic systems and have been attracting much attention from scientific researchers and industry. Implantable drug delivery devices can deliver localized dosage which can reduce the side effects of medication. Such devices can maintain therapeutic concentrations of the drug over extended periods by providing small doses minimizing the risk of systemic toxicity.Recently, ocular drug delivery devices with micropumps using check valves have been demonstrated. The use of external magnetic actuation in a MEMS-based drug delivery device has been verified in reciprocating diaphragm micropumps. However, the magnetic diaphragm generates low pressures resulting in low flow rates (Re
View record

Surface Elasticity Models for Static and Dynamic Response of Nanoscale Beams (2010)

Nanoscale beam-like structures have attracted much attention due to their superior mechanical properties for applications in nanomechanical and nanoelectromechanical systems (NEMS). Nanoscale structures are characterized by a high surface to volume ratio. The elastic response of surface layers of atoms is different from that of the bulk atoms due to reduced connectivity. Thus, surface energy has a significant effect on the response of nanoscale structures, and is associated with their size-dependent behavior. The classical continuum mechanics fails to capture the surface energy effects and hence is not directly applicable at nanoscale. To overcome this limitation, modified continuum models incorporating surface energy effects need to be developed in order to evaluate the size-dependent mechanical response of nanoscale structures.This thesis presents a modified continuum model and finite element formulation to study the static and dynamic response of nanoscale beams. The objective is to provide NEMS designers with an efficient set of tools that can predict static deflections, natural frequencies of vibrations, and uniaxial buckling loads of nanoscale beams with different geometries, applied forces, and boundary conditions. A general beam model based on Gurtin-Murdoch continuum surface elasticity theory is developed for the analysis of thin and thick beams of arbitrary cross-section. Closed-form analytical solutions for static bending of thin and thick beams under different loadings and boundary conditions are obtained. Their free vibration characteristics are also investigated. Analytical expressions for critical buckling loads of thin beam are presented. An intrinsic length scale depending on both surface and bulk elastic properties is defined to characterize surface energy effects in beam bending problems. The finite element simulation results of static bending, free vibration and axial buckling of nanoscale beams are compared with the analytical solutions for validation. Selected numerical results are presented for aluminum and silicon beams to demonstrate their salient response features. A technique is proposed to estimate surface elastic properties from measured natural frequencies of GaAs cantilever specimen. The surface elasticity continuum mechanics and finite element models developed in this work provide designers efficient tools to predict mechanical response of beam structures in nano devices.

View record

Current Students & Alumni

This is a small sample of students and/or alumni that have been supervised by this researcher. It is not meant as a comprehensive list.

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.


Follow these steps to apply to UBC Graduate School!