An Universal packaging technique for low-drift implantable pressure sensors.

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.

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

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

Nature-motivated pressure sensors have been greatly important components integrated into flexible electronics and applied in artificial intelligence. Here, we report a high sensitivity, ultrathin, and transparent pressure sensor based on wrinkled graphene prepared by a facile liquid-phase shrink method. Two pieces of wrinkled graphene are face to face assembled into a pressure sensor, in which a porous anodic aluminum oxide (AAO) membrane with the thickness of only 200 nm was used to insulate the two layers of graphene. The pressure sensor exhibits ultrahigh operating sensitivity (6.92 kPa-1), resulting from the insulation in its inactive state and conduction under compression. Formation of current pathways is attributed to the contact of graphene wrinkles through the pores of AAO membrane. In addition, the pressure sensor is also an on/off and energy saving device, due to the complete isolation between the two graphene layers when the sensor is not subjected to any pressure. We believe that our high-performance pressure sensor is an ideal candidate for integration in flexible electronics, but also paves the way for other 2D materials to be involved in the fabrication of pressure sensors.

Modeling and simulation of MEMS Intracranial pressure sensor using Graphene as the structural layer is defined. At normal health condition, the ICP pressure is in the range of 10-15 mmHg. Any variation from this range will signify the abnormalities such as neural system malfunction, nausea, vomiting, paralysis, brain tumor rupturing, and excitement.For Intracranial pressure sensing applications, to measure this slight variation of pressure a sensor having high sensitivity need to be employed and is solely depends on membrane used. properties of high young’s modulus, high thermal stability and electrical conductivity, inertness and zero band gap made it biocompatible to fabricate Intracranial piezoresistive pressure (ICP) sensor with membrane as graphene. COMSOL Multiphysics tool which is a finite element analysis (FEA) is deployed to optimize the dimensions and parameters for using graphene as a structural layer for pressure sensor diaphragm. A variability study of piezo resistors with three different meander shape are designed and simulated in COMSOL. The optimum design is further analyzed for three different type of pressure sensor specifications as conventional, with n-type dopant and graphene as a structural layer. The design with three meander resistance and graphene as a structural layer provides a strain induced of 0.14 with the pressure input of 10 mmHg.

A completely implantable intracranial pressure sensor designed for long-term measurement of intraventricular pressure in hydrocephalic patients is described. The measurement principal of the device is discussed along with the electronic and component structure and sources of instrument error. Clinical tests of this implanted pressure device involving both humans and animals showed it to be comparable to other methods of intracranial pressure measurement.

Transcranial Doppler sonography (TCD) is a noninvasive technique for measurement of cerebral blood flow velocity (CBFV) in the major arteries of the circle of Willis. Dynamic changes in the pulsatility index (PI) and the resistance index (RI), as calculated from TCD data, allow for an assessment of the forces acting on the terminal vasculature of the brain. The present study was designed to investigate a possible relationship between TCD parameters and intracranial pressure (ICP) changes in adult patients with hypertensive hydrocephalus. Blood flow velocity in the middle cerebral artery (MCA) was studied by TCD in 29 hydrocephalus patients and in 20 healthy controls. ICP was measured in the patient group before ventricular shunting and was correlated with TCD data. The mean CBFV in hydrocephalic patients prior to ventriculoperitoneal shunting was significantly lower than in the control group. Compared to normal persons, systolic and end-diastolic CBFV values in patients were significantly decreased, suggesting an increased distal cerebrovascular resistance. PI and RI values in patients with elevated ICP prior to shunting were significantly increased in comparison to those of normal persons. There was a statistically significant positive correlation of preshunting ICP and mean preshunting values of RI (r=0.50, P<0.01) in hydrocephalic patients, but no significant correlation between PI and ICP, and between CBFV and ICP. Immediately after shunting, ICP returned to normal, and PI and RI values decreased significantly, while the mean CBFV increased. In a subgroup of hydrocephalic patients with a preshunting ICP value >35 mm Hg (n=6), the changes described above were more pronounced than in the subgroup with preshunting ICP values <35 mm Hg, which suggests an exponential degree of influence of ICP on TCD parameters. In conclusion, TCD may provide a tool for assessment of ICP in adult patients with occlusive hydrocephalus, although an exact noninvasive measurement of ICP by TCD seems impossible. Changes in the RI and PI indices appear to be useful indicators of elevated ICP.

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

Congenital heart defects (CHD) remain the number one cause of death from birth defects during the first year of life. Each year, more than 32,000 babies in the U.S. are born with CHD [1] and nearly 40% of them will require a surgical intervention. In particular, during and after pediatric cardiac surgery, pressures and oxygen content in the various heart chambers provide important clinical information on the functional status of the cardiopulmonary system. These are essential for patients care. Presently, intracardiac pressures are monitored by fluid-filled catheters [2]. There are associated significant bleeding, infections, and malfunction risks and prohibits free movement of the subject. Oxygen measurements require removing significant volume of blood which not only wastes blood volume in sometimes very small patients, even blood gas analysis does not allow for continuous oxygenation monitoring in critically ill patients. There is a clinical need to develop an integrated sensor system that can simultaneously, and continuously, monitor pressure and oxygenation within the cardiovascular space wirelessly. And because of the size constraints in infants and small children, this novel sensor system needs to allow for sufficient miniaturization.

Long-term monitoring of intracranial pressure (ICP) is limited by the lack of an implantable sensor with low drift. The goal of this study was to demonstrate that a new capacitive transducer system will produce accurate and stable ICP records over extended periods. Intracranial pressure sensors were implanted into the frontal white matter of four dogs. In addition, a fluid-filled catheter was placed in the cisterna magna (CM) to measure cerebrospinal fluid (CSF) pressure. The animals were tested using standard physiological maneuvers such as jugular vein compression, head elevation, and CSF withdrawal from and saline injection into the CM to verify that the ICP sensor precisely matched CSF pressure changes. The mean ICP pressure and CM pressure were compared for months to demonstrate that the transducer system produced minimal drift over time. The change in the ICP sensor record closely duplicated that of the CSF waveform in the CM in response to well-known physiological stimuli. More important, mean ICP pressure remained within 3 mm Hg of CM pressure for months, with a mean difference of less than 0.3 mm Hg. Histological examination of the dog brains revealed only minimal tissue reaction to the presence of the sensor. The authors demonstrate a new implantable solid-state sensor that reliably measures ICP for months, with minimal drift. The clinical application of this sensor and its telemetry is for long-term monitoring of patients with head injury, mass lesions, and hydrocephalus.

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

In this study, a subminiature implantable capacitive pressure sensor is proposed for biomedical applications. The proposed pressure sensor comprises an array of elastic silicon nitride (SiN) diaphragms formed by the application of a polysilicon (p-Si) sacrificial layer. In addition, using the p-Si layer, a resistive temperature sensor is also integrated into one device without additional fabrication steps or extra cost, thus enabling the device to measure pressure and temperature simultaneously. The sensor with a size of 0.5 × 1.2 mm was fabricated using microelectromechanical systems (MEMS) technology and was packaged in needle-shaped metal housing that is both insertable and biocompatible. The packaged pressure sensor immersed in a physiological saline solution exhibited excellent performance without leakage. The sensor achieved a sensitivity of approximately 1.73 pF/bar and a hysteresis of about 1.7%, respectively. Furthermore, it was confirmed that the pressure sensor operated normally for 48 h without experiencing insulation breakdown or degradation of the capacitance. The integrated resistive temperature sensor also worked properly. The response of the temperature sensor varied linearly with temperature variation. It had an acceptable temperature coefficient of resistance (TCR) of approximately 0.25%/°C.

Textile-based pressure sensor arrays: A novel scalable manufacturing technique

Miniaturized pressure sensors attached to catheters have numerous applications in the biomedical and life science fields including the monitoring of arterial, ventricular, intracranial and intraocular pressures. Recent advances in MEMS (microelectromechanical systems) technology and its associated fabrication processes, such as DRIE (deep reactive ion etching), have allowed for further miniaturization of these devices, expanding the application landscape to include small animal models and new human applications. One such human application is the wireless measurement of radial arterial blood pressure (BP). The goal of this research program is to produce a truly portable wireless radial arterial monitoring system using a custom-designed ultra-miniature pressure sensor appropriately sized to fit within the tip of a 1-French catheter (333 micron), so that convenient in-vivo measurements of BP are possible. The proposed system consists of two assemblies. The sensor, catheter, and wristband containing the battery and telemetry circuit form one assembly and the portable wireless PDA-sized transceiver module forms the other. This paper reports on the custom miniature MEMS pressure sensor developed for this application.

Electronic skin (E-skin) has gained significant attention due to its potential applications in the Internet of Things (IoT), artificial intelligence (AI), and flexible multi-sensing systems. Mimicking human skin, e-skin sensing devices can be employed in various scenarios. Among the most important sensing elements for tactile e-skin sensors are pressure and temperature sensors, which have increasingly garnered research interest over the past few decades. However, the design and fabrication of advanced pressure and temperature sensors can be challenging owing to complications such as signal interference, complex mechanism integration, and structural design issues. This review provides an overview of flexible pressure and temperature sensors used in e-skin, covering four main perspectives: material selection, mechanism integration, structural design, and manufacturing methods. The materials of different elements in the entire sensing system are comprehensively discussed, along with single and compound mechanisms of pressure and temperature sensing. Pressure and temperature sensors are divided into two types based on their electric output signals, which are exemplified in detail. The manufacturing methods used to fabricate these sensors, including printing methods, are outlined. Lastly, a summary of the future challenges faced by flexible pressure and temperature sensors used in e-skin is presented.