Regular monitoring of blood flow and pressure in vascular reconstructions or grafts would provide early warning of graft failure and improve salvage procedures. Based on biocompatible materials, we have developed a new type of thin, flexible pulsation sensor (FPS) which is wrapped around a graft to monitor blood pressure and flow. The FPS uses carbon black (CB) nanoparticles dispersed in polydimethylsiloxane (PDMS) as a piezoresistive sensor layer, which was encapsulated within structural PDMS layers and connected to stainless steel interconnect leads. Because the FPS is more flexible than natural arteries, veins, and synthetic vascular grafts, it can be wrapped around target conduits at the time of surgery and remain implanted for long-term monitoring. In this study, we analyze strain transduction from a blood vessel and characterize the electrical and mechanical response of CB-PDMS from 0-50% strain. An optimum concentration of 14% CB-PDMS was used to fabricate 300-μm thick FPS devices with elastic modulus under 500 kPa, strain range of
Because mid-infrared (mid-IR) spectroscopy is not a promising method to noninvasively measure glucose in vivo, a method for minimally invasive high-precision glucose determination in vivo by mid-IR laser spectroscopy combined with a tunable laser source and small fiber-optic attenuated total reflection (ATR) sensor is introduced. The potential of this method was evaluated in vitro. This research presents a mid-infrared tunable laser with a broad emission spectrum band of 9.19 to 9.77[Formula: see text](1024~1088 cm(-1)) and proposes a method to control and stabilize the laser emission wavelength and power. Moreover, several fiber-optic ATR sensors were fabricated and investigated to determine glucose in combination with the tunable laser source, and the effective sensing optical length of these sensors was determined for the first time. In addition, the sensitivity of this system was four times that of a Fourier transform infrared (FT-IR) spectrometer. The noise-equivalent concentration (NEC) of this laser measurement system was as low as 3.8 mg/dL, which is among the most precise glucose measurements using mid-infrared spectroscopy. Furthermore, a partial least-squares regression and Clarke error grid were used to quantify the predictability and evaluate the prediction accuracy of glucose concentration in the range of 5 to 500 mg/dL (physiologically relevant range: 30~400 mg/dL). The experimental results were clinically acceptable. The high sensitivity, tunable laser source, low NEC and small fiber-optic ATR sensor demonstrate an encouraging step in the work towards precisely monitoring glucose levels in vivo.
Real-time monitoring of arteriovenous graft blood flow would provide early warning of graft failure to permit interventions such as angioplasty or graft replacement to avoid catastrophic failure. We have developed a new type of flexible pulsation sensor (FPS) consisting of a 3D printed elastic cuff wrapped around a graft and thus not in contact with blood. The FPS uses multi-walled carbon nanotubes (MWCNTs) dispersed in polydimethylsiloxane (PDMS) as a piezoresistive sensor layer, which is embedded within structural thixotropic PDMS. These materials were specifically developed to enable sensor additive manufacturing via 3D Bio-plotting, and the resulting strain sensor is more compliant and has a wider maximum strain range than graft materials. Here, we analyze the strain transduction mechanics on a vascular graft and describe the memristive properties of MWCNT-PDMS composites, which may be mitigated using AC biasing. In vitro testing of the FPS on a vascular graft phantom showed a robust, linear sensor output to pulsatile flows (170–650 mL/min) and pressures (62–175 mmHg). The FPS showed an RMS error when measuring pressure and flow of 7.7 mmHg and 29.3 mL/min, with a mean measurement error of 6.5% (pressure) and 8.0% (flow).
Traditionally, implantable electronic devices have used metal-based hermetic encapsulation to protect the internal components from damage by the aggressive in vivo environment. Concurrently, hermetic encapsulation protects the surrounding tissue from harmful substances that might be leached from the packaged components (Bazaka & Jacob, 2012). In some cases, however, there is risk of electrochemical corrosion on the metallic surfaces because of the presence of various ions, amino acids, proteins and dissolved oxygen (Eliaz, 2019). Hermeticity is defined as the ability of sealed packages to resist foreign gases and liquids from penetrating the seal or encapsulating material (Madduri, Sammakia, Infantolino, & Chaparala, 2008). Hermetic packages are conventionally made from glass, metal or ceramic materials whereby the gas and moisture permeability through the material is negligible (Madduri et al., 2008; Schuettler, Schatz, Ordonez, & Stieglitz, 2011). Hermetic materials have been successfully used to package devices for chronic applications, some of the most notable being cochlear implants and cardiac pacemakers (Kirsten, Wetterling, Uhlemann, Wolter, & Zigler, 2013). Titanium is the most commonly used metal for hermetic encapsulation because of its biocompatibility, low permeability for ions and moisture, mechanical durability and the ability to create viable hermetic seals by laser welding (Amanat, James, & McKenzie, 2010). Ceramics have also been used for implants for wireless devices to address issues related to attenuation of electromagnetic transmission by metallic packaging (El Khatib, Pothier, Crunteanu, & Blondy, 2007; Schubring & Fujita, 2007; Shen & Maharbiz, 2019). Driven by the increased functionality and scalability offered by innovations in application-specific integrated circuits (ASICs) and the desire to create highly miniaturized devices on flexible polymer substrates, significant efforts have been made in creating miniaturized implants by integrating the majority of components on a single chip. As the
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