Development of an Implantable Capacitive Pressure Sensor for Biomedical Applications

Rafael Correo, de izquierdas, y Alvaro Noboa, magnate conservador, vencieron con un discurso clientelista en el pais mas inestable de America Latina.

We propose a new packaging process for an implantable blood pressure sensor using ultrafast laser micro-welding. The sensor is a membrane type, passive device that uses the change in the capacitance caused by the membrane deformation due to applied pressure. Components of the sensor such as inductors and capacitors were fabricated on two glass (quartz) wafers and the two wafers were bonded into a single package. Conventional bonding methods such as adhesive bonding, thermal bonding, and anodic bonding require considerable effort and cost. Therefore CO2 laser cutting was used due to its fast and easy operation providing melting and bonding of the interface at the same time. However, a severe heat process leading to a large temperature gradient by rapid heating and quenching at the interface causes microcracks in brittle glass and results in low durability and production yield. In this paper, we introduce an ultrafast laser process for glass bonding because it can optimize the heat accumulation inside the glass by a short pulse width within a few picoseconds and a high pulse repetition rate. As a result, the ultrafast laser welding provides microscale bonding for glass pressure sensor packaging. The packaging process was performed with a minimized welding seam width of 100 μm with a minute. The minimized welding seam allows a drastic reduction of the sensor size, which is a significant benefit for implantable sensors. The fabricated pressure sensor was operated with resonance frequencies corresponding to applied pressures and there was no air leakage through the welded interface. In addition, in vitro cytotoxicity tests with the sensor showed that there was no elution of inner components and the ultrafast laser packaged sensor is non-toxic. The ultrafast laser welding provides a fast and robust glass chip packaging, which has advantages in hermeticity, bio-compatibility, and cost-effectiveness in the manufacturing of compact implantable sensors.

Regarding “Endoleaks after endovascular aneurysm repair lead to nonuniform intra-aneurysm sac pressure”

This paper describes the design and detailed analysis of a microelectromechanical system (MEMS) capacitive pressure sensor consisting of nested folded beam suspensions and variously shaped diaphragms that can be used as a part of an LC tank implant circuit for biomedical pressure sensing applications, designed specifically for continuous intraocular pressure (IOP) monitoring in glaucoma patients. The pressure sensor has been designed to measure pressures within the IOP sensor range of 0–8000 Pa. This paper aims to reduce the size of the sensor in comparison to previous research. Significant benefits of miniaturization include requiring less energy, being lightweight, being inexpensive, and having minimal impact on the objects being detected. The MEMS implantable pressure sensor for continuous monitoring of IOP would prevent the progression of the disease, and these tiny devices could alleviate patients’ suffering. Microbeams are likely the most widely utilized structural element in MEMS. This design adds nested folded beam suspensions to the diaphragm, which reduces the diaphragm’s residual tension and rigidity; as a result, the device’s dimension is smaller than the diaphragm without flexible beams (previous work). Due to the reduced rigidity, nested folded beam suspensions can also enhance sensitivity. Finally, the central deflection of the diaphragm will be determined under uniform external pressure. Using COMSOL/Multiphysics and SolidWorks, the design and simulation of pressure sensors have been accomplished. The outcomes reveal that the capacitive pressure sensor with nested folded beam suspensions and the rectangular diaphragm is better suited for measuring IOP, and its dimensions are also smaller than those of previous works ( 230×41×2.8(μm)3 ).

Development of an implantable artificial heart is very important to save cardiac disease patients. An undulation pump ventricular assist device (UPVAD) could be a good candidate because of the compact size. Although the implantation improves patient’s quality of life (QOL) considerably, several implications hamper the development of an implantable artificial heart. The difficulty in blood pressure measurement is the one of the implications to be solved. We have developed the im-plantable absolute pressure sensor to be integrated into a UPVAD and the algorithm to infer the blood pressure referred to gauge pressure. Noble feature of the algorithm is autonomous compensation of the offset drift with the pressure sensor in time. Thus the blood pressure could be controlled precisely with the implantable UPVAD even if the pressure sensor exhibited certain drift characteristics. Animal experiment demonstrated the effectiveness in compensating the offset drift

Soil water content measurement is crucial during compaction control of embankments. The current techniques used to measure the soil water content in the field are outlined, and their advantages and limitations are indicated. Most techniques require destructive sampling and yields late results, or involve expensive equipment and are hard to set up. Low-cost capacitive and resistive moisture sensors entered successfully in last decades in agronomy applications to automatize crops irrigation. The purpose of this study is to identify whether these sensors are reliable to be used in geotechnical engineering and, in particular, to what extent can they aid compaction control of embankments. Three resistive sensors and two capacitive sensors are tested on five types of soils prepared with a wide range of water contents. The experimental procedures are described, and the sensors output data are compared with water contents obtained from the oven-drying technique. A new device that allows calibration of the sensors on compacted soils is developed. Soils characteristics that can influence moisture measurement using capacitive and resistive sensors are also explored. Test results suggest that some of the sensors can estimate the soil water content on compacted fine grained soils, when proper calibration procedure is successfully achieved. Sensors accuracy tend to increase as the soil void ratio decreases. Such sensors may be useful for expedite measurements, especially, when later counter-prof is available, or when a wide interval for the water content is acceptable.

Novel planar sensor using stretchable vapor phased polymerized PEDOT/PDMS film

Now a days MEMS based for biomedical applications with high performance parameters like sensitivity and linearity are required for low pressure range.The low-pressure range (1–5 kPa) is a significant range that comprises intra-body pressures like intracranial pressure (ICP) and intraocular pressure (IOP).A lot of work on piezoresistive pressure sensor with different shapes diaphragms like squared, circular and rectangular has been carried out.In MEMS Piezoresistive Pressure sensors the most important pressure-sensitive component is the squared diaphragm. The performance of the Micro-sensor is directly determined, under uniform applied pressure with its deformation. In pressure sensor design, the accurate relationship between pressure and deformation plays a very consequence role. In this paper, squared diaphragm of silicon material is modeled and simulate using the analytical equations for a thin plate, along with the theory of small-deflection to providing quick insight regarding important parameter like stress and Deformation for the operating pressure range of 0 kPa–5 kPa. The mechanical behavior of micro-machined silicon diaphragm in terms of stress and deflection generation has been simulated.The piezoresistivity principle is used to assess the sensor's sensitivity. The mechanical change in the thin diaphragm in the form of deflection and stress is calculated and presented. In this Modeling both the analytical and simulated(FEA) results for the performance parameters such as stress, Deflection and the output voltage is computed and compared, it is found that the error between analytical and simulation results is no more than 5.6–6.5%.

The article describes and analyzes the existing problems when using linear measuring devices for measuring temperature. When measuring temperature with resistive temperature sensors, a modified null method is proposed to use, which ensures the invariance of the meter to changes in the measuring path gain. The null balance in the measuring path is maintained automatically by synchronous pulse-amplitude and pulse-width modulations and using of a tracking circuit for adjustment of the width signal. Once the null balance is achieved, the width modulation control pulse duration will be linearly related to the resistance of the temperature sensor. Modification of the null method simplifies the design of a thermometer with a resistive sensing element. In this proposed mechanism, two precision resistors which are passive units replace the active precision units to increase the accuracy and improve the linearity of its conversion characteristics. The work reports the errors of temperature measurements by the modified null method and describes the calibration of a manufactured digital thermometer with a miniature platinum resistance temperature sensor. The proposed modification of the null measurement method can be used to construct devices comprising a sensor with a sensing element, namely electrical resistance that is altered under the influence of a non-electrical parameter.

Cardiovascular diseases, including hypertension and atherosclerosis, account for over 30% of deaths worldwide. To diagnose and monitor these diseases, hemodynamic parameters, such as pressures, flow rates, and flow resistances, are measured. Current measurement techniques include expensive imaging processes and repetitive invasive catheterizations. These methods provide a narrow view of hemodynamics that may fail to capture significant abnormalities and may be inaccurate due to patient discomfort. Continuous monitoring would offer distinct advantages for clinical and research applications. However, implantable hemodynamic sensors are lacking due to stringent mechanical and electrical requirements. Wireless communication through tissue is required for noninvasive monitoring, but narrow blood vessels (<5 mm-diameter) with tortuous geometries prevent the use of conventional rigid electronic components. Additionally, implantable vascular sensors should be compatible with conventional catheter deployment procedures, which require mechanical stability under crimping, sheath introduction, and expansion. The only commercially available implantable sensor is a bulky, rigid package restricted for blood pressure monitoring in larger vessels. Existing research works are severely limited by short wireless communication distances and fragile designs.Here, we introduce a low-profile, wireless biosensor system comprised of an inductive medical stent and capacitive pressure sensor. The smart stent is designed and fabricated to maximize inductance to achieve functional readout distances, while maintaining its medical purpose. Analytical and experimental study optimizes the stent design for wireless communication via inductive coupling. The low-profile capacitive sensor is fabricated via aerosol jet printing, an additive manufacturing process. The sensor employs a microstructured PDMS layer as the dielectric of a highly flexible parallel-plate structure to achieve high pressure sensitivity (6 fF/mmHg). Experimental study optimizes the printed PDMS structures to maximize sensitivity. The capacitive sensor is integrated with the inductive stent to form an LC circuit with a resonant frequency dependent on pressure. The device is experimentally proven to be readily expandable by balloon catheter to allow for compatibility with existing catheter and stent placement procedures. The low-profile biosensor system is also shown to minimize disruption to normal hemodynamics compared to available commercial devices. Quantitative analysis of transient sensor signals identifies resonant frequency to allow for wireless monitoring of hemodynamics. Sensor functionality is displayed in mock blood vessels with pulsatile flow, which will enable continuous, wireless monitoring of hemodynamics throughout the vascular system. Figure 1

In this paper, Poly-crystalline silicon carbide (poly-sic) Micro-electromechanical systems (MEMS) capacitive pressure sensor operating in harsh environment in touch mode is proposed, The principle of the paper is to design, obtain analytical solution and compare the results with the simulation for a circular diaphragm deflection before and after touch point. The sensor demonstrated a high temperature sensing capability up to 400°C, the device achieves a linear characteristic response and consists of a circular clamped-edges poly-sic diaphragm suspended over sealed cavity on a silicon carbide substrate. The sensor is operating in touch mode capacitive pressure sensor, The advantages of a touch mode are the robust structure that make the sensor to withstand harsh environment, near linear output, and large over-range protection, operating in wide range of pressure, higher sensitivity than the near linear operation in normal mode, The material is considered to be used for harsh environment is SiC (Silicon Carbide), Because of SiC owing excellent electrical stability, mechanical robustness, and chemical inertness properties and the application of pressure sensors in harsh environments are, such as automotive industries, aerospace, oil/logging equipments, nuclear station, and power station. We are simulating MEMS capacitive pressure sensor to optimize the design, improve the performance and reduce the time of fabricating process of the device. The proposed touch mode MEMS capacitive pressure sensor demonstrated diaphragm ranging from 150 μm to 360 μm in diameter, with the gap depth from 0.5 μm to 7.5 μm and the sensor exhibit a linear response with pressure from 0.05 Mpa to 10 Mpa.

Monitoring bodily pressures provide valuable diagnostic and prognostic information. In particular, long-term measurement through implantable sensors is highly desirable in situations where percutaneous access can be complicated or dangerous (e.g., intracranial pressure in hydrocephalic patients). In spite of decades of progress in the fabrication of miniature solid-state pressure sensors, sensor drift has so far severely limited their application in implantable systems. In this paper, we report on a universal packaging technique for reducing the sensor drift. The described method isolates the pressure sensor from a major source of drift, i.e., contact with the aqueous surrounding environment, by encasing the sensor in a silicone-filled medical-grade polyurethane balloon. In-vitro soak tests for 100days using commercial micromachined piezoresistive pressure sensors demonstrate a stable operation with the output remaining within 1.8 cmH2O (1.3mmHg) of a reference pressure transducer. Under similar test conditions, a non-isolated sensor fluctuates between 10 and 20 cmH2O (7.4-14.7mmHg) of the reference, without ever settling to a stable operation regime. Implantation in Ossabow pigs demonstrate the robustness of the package and its in-vivo efficacy in reducing the baseline drift.

This study develops an implantable bladder pressure sensor sealed in a novel biocompatible silicone-oil modified PDMS. The silicon-oil modified PDMS exhibits higher elasticity and smaller Young's modulus such that this material is a good candidate to seal a pressure sensing device and forms a pressure sensor capsule. To enhance the sensitivity of the pressure sensor capsule, this study tunes the silicon-oil ratio to adjust the mechanical characteristics of the PDMS elastomer to form the pressure sensor capsule. Results show that the developed pressure sensor capsule exhibits a good linear response in the range of 0–90 hPa. In addition, an in-vitro flow meter is also integrated with the pressure sensor capsule to measure the urine flow rate and the pee urinary kinetics. The comprehensive urination parameters are experimentally measured and calculated by the integrated uroflowmetry and the bladder implantable pressure sensor capsule.

This paper presents a miniature wireless energy transfer system design for implantable pressure sensor used for health monitoring applications. The implantable pressure sensor can be wirelessly powered through strongly coupled magnetic resonance based wireless energy transfer system. The wireless power transfer system has been built up by using a power transmitting circuit which will be placed outside the body and a receiving unit connected to the implantable pressure sensor to be kept inside the body. Experimentally, it has been found that the wireless power transfer from the transmitting coil to the implantable receiving coil depends on the operating frequency, separation distance between the coils and configuration of the coils. It has been found that maximum wireless power transfer occurs from the transmitting unit to the implantable receiving unit at the operating resonant frequency of the system. At the resonant frequency of 562 kHz and optimum load of 40 Ω, a maximum power of 0.186 W and energy transfer efficiency of 26% have been achieved wirelessly with a separation distance of 3 cm between the transmitter and receiver resonators. Electromagnetic simulation has also been carried out using the different forms of transmitting and receiving coils in order to obtain a strong magnetic coupled wireless energy transfer system, which plays an important role in the energy transfer efficiency.

Micro electro-mechanical systems (MEMS) based capacitive pressure sensors are typically fabricated using silicon micromachining techniques. In this paper, novel liquid crystal polymer (LCP) based capacitive pressure sensors, fabricated using printed circuit processing techniques, are reported. LCP exhibits good dimensional stability, material flexibility, high chemical resistance, and extremely low moisture absorption, which makes it suitable for MEMS applications. The pressure sensor comprises of a cylindrical cavity formed by a sandwich of LCP substrate, LCP spacer layer with circular holes and LCP top layer. The bottom electrode and the top electrode of the capacitive pressure sensor are defined on the top surface of the LCP substrate and the bottom surface of the top LCP layer, respectively. A typical pressure sensor with a diaphragm diameter of 3.2 mm provides a total capacitance change of 0.7627 pF for an applied pressure in the range of 0-170 kPa.