Correlation between corneal and contact lens deformation with changes in intraocular pressure for wearable monitoring systems.

OBJECTIVE: The aim of this work is to evaluate the extent to which the eye's curvature deformation, due to changes in the intraocular pressure (IOP), can be directly tracked by an overlying contact lens. METHOD: In this experimental study, using 12 cadaveric eyes, the IOP was increased from 10 to 36 mmHg, while video imaging was used to capture the three experimental variations. The deformation of the bare eye was used as a control, while the deformation of an overlying silicone grided contact lens and an overlying microfluidic IOP-sensing contact lens were examined and compared. RESULTS: The relation between the slope of the radius of corneal curvature versus the IOP for both the bare eye and the marker contact lens yielded a linear relationship with a R2 value of 0.83. The microfluidic contact lens resulted in an average performance of 0.40 mm indicator movement/mmHg (SD 0.006). Comparing the slope of the marker contact lens deformation, to the performance of the microfluidic contact lens resulted in a R2 value of 0.78. The strain map of the overlaying grided contact lens showed most deformation occurring along the outer edge of the lens with increased deformation as increase IOP occurs; as well as with some negative, compressive movement near the central points. CONCLUSION: The deformation from the curvature of the eye is significant enough from 10 to 36 mmHg that a silicone contact lens can capture and mimic those changes. The results show promise for optimization in contact lens-based IOP monitoring.

A V-Shaped Microcantilever Sensor Based on a Gap Method for Real-Time Detection of E. coli Bacteria.

This paper presents a dynamic-mode microcantilever sensor based on a gap method. The sensor has a V-shaped microcantilever and a fixed structure at a distance of 2 µm from its free end. The microcantilever is excited by applying an ac electric potential (3 Vp) to its piezoelectric pads and vibrates at its fundamental resonant frequency. An independent ac electric potential (200 kHz, 15 Vpp) is applied to the fixed structure. This creates a non-uniform electric field with its maxima at the gap and exerts a dielectrophoresis (DEP) force. The DEP force attracts and adsorbs the E. coli bacteria to the cantilever edge at the gap. The binding of the bacteria to the cantilever creates a shift in the resonant frequency of the microcantilever sensor, which is detected by a laser vibrometer. The real-time detection of E. coli bacteria samples, diluted in distilled water, was performed for concentrations of 105-103 cells/mL and the real-time frequency shifts were -2264.3 to -755 Hz in 4 min, respectively. The tests were expanded to study the effect of the electric potential amplitude (10, 12, 15 Vpp) and higher frequency shifts were observed for higher amplitudes.

Design, analysis, and experimental investigation of micro-displacement amplification compliant mechanism for micro-transducers.

This paper presents experimental force and buckling analysis of a compliant micro-displacement amplification mechanism fabricated using the commercially available PolyMUMPs process. The proposed mechanism proficiently amplifies displacement, at two output ends, with an optimal amplification factor of 7.2. Buckling analysis revealed that an amplification factor ranging from 2.8 to 11 may be achieved for an input displacement varying from 0.1 to 7.5 µm. Based on the analysis, the optimal value of the amplification factor is found to be 7.2 with an input displacement of 3.5 µm at the operational force of 60 µN having a buckling load factor (BLF) >1. Critical load magnitude is 187 µN having BLF = 1. Buckling occurred when loading exceeded the critical load value, having BLF <1, and the mechanism failed to produce a significant amplification factor. Static analysis showed that stresses produced are within the safe region, and the structural integrity of the mechanism is not compromised having a factor of safety of 1.4. Modal analysis predicted that the natural frequency of the desired mode is 35.47 kHz. Dynamic simulations, under 15 g dynamic load with a frequency range of 30-40 kHz, confirm the possibility of integrating the proposed mechanism with MEMS devices. Parametric optimization comprehends that length and angle are the two major geometric parameters that govern the working range, force, and amplification factor. For input displacements below 1 µm, the amplification factor is even higher, which is highly beneficial for amplifying small displacements. Static, modal, and dynamic analyses of the designed mechanism have been carried out using finite element method based commercial software IntelliSuite®. The experimental results showed that this mechanism can provide the same amplified displacement at two output points and is self-sufficient to be incorporated as an intermediate compliant mechanism for enhancing the output in the case of both static and dynamic micro-devices.

Effect of variations of corneal physiology on novel non-invasive intraocular pressure monitoring soft contact lens.

Glaucoma is the leading cause of irreversible blindness around the world. With its slow asymptomatic progression, there is an emphasis on early detection and frequent monitoring. A novel microfluidic contact lens has been established as a potential way to track the fluctuations of the intraocular pressure (IOP) which is a key indicator for diagnosing and monitoring glaucoma progression. The purpose of this article is to determine the effect of physiological variations of the eye on the performance of the microfluidic contact lens. Ultrasound biomicroscopy (UBM) was used to measure the central corneal thickness (CCT) and radius of corneal curvature (RCC) for a series of 16 fresh enucleated porcine eyes. The effect of these corneal anatomic features on device performance was then assessed by systematically adjusting intraocular pressure from 10 to 34 mmHg and monitoring the device indicator response. The performance of the microfluidic contact lens was determined by finding the amount the indicator fluid shifted in position as a result of 1 mmHg IOP increase. The relationship between IOP and indicator fluid was found to be linear for all eyes. The slope of the indicator fluid movement as a result of the IOP was evaluated against the CCT and RCC of each porcine eye. This yielded low correlation coefficients, 0.057 for CCT and 0.024 for RCC, meaning that these physiological differences showed no systematic impact on the measurements made with the contact lens.

Non-invasive Intraocular pressure monitoring with contact lens.

BACKGROUND: Glaucoma is the second leading cause of blindness in the world and the first leading cause of irreversible vision loss. Currently, the primary methodology of testing for the intraocular pressure (IOP) is during clinical office hours, which only provide a limited amount of information on the trends and fluctuations of the IOP. Therefore, a continuous monitoring system is required to properly determine the peaks of pressure and to negate any false results obtained by sparse, clinic hour testing. The objective of this study is to determine the ability of a newly designed contact lens with an embedded microchannel, to accurately measure the fluctuations in the IOP. METHODS: Experimentation was completed on fresh enucleated porcine eyes. The contact lens was placed on the porcine eye and utilising a camera the fluid movement, within the microchannel in the contact lens, was recorded. A micro-pressure catheter, threaded into the centre of the vitreous chamber, recorded the true IOP and was compared with the displacement of the indicator fluid within the microchannel. RESULTS: The contact lenses showed a consistent linear responsiveness to changes in IOP and robust to the effects of anatomical differences among eyes. The indicator fluid had an average fluid movement of 28 um/mm Hg between all the trials. Additionally, the devices showed the ability to measure both increases and decreases in IOP during cyclical fluctuations. CONCLUSION: The described inexpensive and non-invasive sensor is able to reliably monitor the IOP changes based on porcine eye model.

Assessment of hepatoprotective potential of Radix Fici Hirtae on alcohol-induced liver injury in Kunming mice.

OBJECTIVE: The objective of the present study was to investigate the hepatoprotective role of Radix Fici Hirtae on acute alcohol-induced liver injury in mice. METHODS: The component of Radix Fici Hirtae was extracted using petroleum ether, chloroform, ethyl acetate and n-butanol and divided into three dose groups of high, medium and low according to the clinical man's normal dose of the 50 g crude drug/d (0.83 g/kg body weight). Saline in concentration of 10 mg/mL, 5 mg/mL and 2.5 mg/mL and a dose of mouse lavage (0.2 mL/10 g mouse body weight) were added to the solution. Histopathlogical analysis of liver was performed. Finally, liver protection was validated by examining the effect of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (AKP), and lactate dehydrogenase (LDH) on the hepatic function of mice in alcohol-induced liver injury model. RESULTS: Except for group with saturated n-butyl alcohol, for the rest of the groups, pathological changes of hepatic lipid and inflammatory cells infiltration were alleviated and liver sinus was normal. As compared to model group, the concentrations of AST, ALT, AKP and LDH in chloroform groups and ethyl acetate groups were significantly decreased. CONCLUSIONS: Extracts of Radix Fici Hirtae are effective for the prevention of alcohol-induced hepatic damage in mice. The results revealed that extracts of Radix Fici Hirtae could be used as hepatoprotective agent.

Note: Exciting higher-order flexural modes of freestanding microstructures with square wave driving signals.

We examine using the harmonics of low fundamental frequency (f(1)) square waveforms to electrostatically excite higher-order flexural modes of a micromechanical structure in higher (>f(1)) frequency regimes. Square wave signals swept between a fundamental frequency range of approximately 0-333 kHz demonstrated an effective high magnitude spectral excitation of approximately 0-1 MHz. This enabled optical heterodyne detection of structural resonant frequencies above 333 kHz. Low frequency square wave signals were also used to selectively excite modes at higher frequencies.

Thermal Actuation Based 3-DoF Non-Resonant Microgyroscope Using MetalMUMPs.

High force, large displacement and low voltage consumption are a primary concern for microgyroscopes. The chevron-shaped thermal actuators are unique in terms of high force generation combined with the large displacements at a low operating voltage in comparison with traditional electrostatic actuators. A Nickel based 3-DoF micromachined gyroscope comprising 2-DoF drive mode and 1-DoF sense mode oscillator utilizing the chevron-shaped thermal actuators is presented here. Analytical derivations and finite element simulations are carried out to predict the performance of the proposed device using the thermo-physical properties of electroplated nickel. The device sensitivity is improved by utilizing the dynamical amplification of the oscillation in 2-DoF drive mode using an active-passive mass configuration. A comprehensive theoretical description, dynamics and mechanical design considerations of the proposed gyroscopes model are discussed in detail. Parametric optimization of gyroscope, its prototype modeling and fabrication using MetalMUMPs has also been investigated. Dynamic transient simulation results predicted that the sense mass of the proposed device achieved a drive displacement of 4.1µm when a sinusoidal voltage of 0.5V is applied at 1.77 kHz exhibiting a mechanical sensitivity of 1.7µm /°/s in vacuum. The wide bandwidth frequency response of the 2-DoF drive mode oscillator consists of two resonant peaks and a flat region of 2.11 kHz between the peaks defining the operational frequency region. The sense mode resonant frequency can lie anywhere within this region and therefore the amplitude of the response is insensitive to structural parameter variations, enhancing device robustness against such variations. The proposed device has a size of 2.2 × 2.6 mm(2), almost one third in comparison with existing M-DoF vibratory gyroscope with an estimated power consumption of 0.26 Watts. These predicted results illustrate that the chevron-shaped thermal actuator has a large voltage-stroke ratio shifting the paradigm in MEMS gyroscope design from the traditional interdigitated comb drive electrostatic actuator. These actuators have low damping compared to electrostatic comb drive actuators which may result in high quality factor microgyroscopes operating at atmospheric pressure.