A device, with MEMS sensors at its core, has been fabricated and tested for measuring low fluid pressure and slow flow rates. The motivation was to measure clinically relevant ranges of slow-moving fluids in living systems, such as the cerebrospinal fluid in the brain. For potential clinical utility, the device can be read transcutaneously by inductive coupling to MEMS capacitive sensors in circuits with resonance frequencies in the MHz range. Signal shifts for flow rates in the range of 0–42 mL/h and differential pressure levels between 0.1 and 2 kPa have been measured, because the sensitivity in the capacitance gap measurement is about 1 Å. The sensors have been used successfully to monitor simulated cerebrospinal fluid dynamics. The device does not utilize any internal power, since it is powered externally via the inductive coupling.
A sensor was tested subdural and in vitro, simulating a supine infant with a ventricular-peritoneal shunt and controlled occlusions. The variable MEMS capacitive device is able to detect and forecast blockages, similar to early detection procedures in cancer patients. For example, with gradual occlusion development over a year, the method forecasts a danger over one month ahead of blockage. The method also distinguishes between ventricular and peritoneal occlusions. Because the sensor provides quantitative data on the dynamics of the cerebrospinal fluid, it can help test new therapies and work toward understanding hydrocephalus as well as idiopathic normal pressure hydrocephalus. The sensor appears to be a substantial advance in treating brain injuries treated with shunts and has the potential to bring significant impact in a clinical setting.
metabolism. The luminescence lifetime measurement of oxygen-sensitive molecules is a very promising, non-invasive approach to determine pO2 in vivo. However, this measurement is frequently perturbed by the excited oxygen sensor's phototoxic effect. In this study, we compared two watersoluble oxygen sensors: Pd-meso-tetra(4-carboxyphenyl) porphyrin (PdTCPP) and dichlorotris(1, 10-phenanthroline)-ruthenium(II) hydrate ([Ru(Phen)3]2þ) for their phototoxicity and ability to measure oxygen consumption during hypericin induced photosensitization in vitro (single cells and isolated mitochondria) and in vivo (Chick's chorioallantoic membrane). Hypericin, a molecule with interesting spectral properties, does not perturb PdTCPP and [Ru(Phen)3]2þ lifetime measurements. The excitation of this molecule at 590 nm is spectrally ''far'' from the absorption bands of PdTCPP and [Ru(Phen)3]2þ, which allows induction of photodamages without contributions from these oxygen sensors. Since PdTCPP's stability in biological systems requires that it is bound with serum proteins, the impact of the serum albumins concentration in the system on the reliability of oxygen measurements was evaluated as well. In conclusions, we demonstrated optimal phototoxicity, serum albumin concentration-related lifetime variations, stability and oxygen sensitivity in vitro and in vivo for [Ru(Phen)3]2þ. We could not demonstrate a similar set of properties for PdTCPP.
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