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Clemson C3B, Clemson University, Clemson South Carolina 29634  College of Engineering & Science  C3B Advisory Board
Introduction to InVivo Biosensors

Background: Following injury that results is tissue hypoxia, interstitial lactate levels increase and are the main source of metabolically-produced acid responsible for tissue acidosis. Lactate levels have also been found to correlate with the severity of injury, including hemorrhage. Small molecules such as lactate and glucose exists in equilibrium between the interstitial and vascular compartments when systemic levels are elevated. Interstitial levels of lactate should thus be reflective of systemic levels when whole body tissue hypoxia occurs such as in hemorrhage. The ability to monitor in vivo lactate in the interstitium is possible but current methods are either not clinically feasible for prolonged measurement or are unreliable because they suffer from deleterious effects of endogenous interferences and fouling.
Objective: Our goal is to develop an implantable lactate-sensing biochip for temporary implantation and capable of telemetered reporting of local lactate levels as well as local glucose levels. These biochips will be temporarily injected/implanted into a skeletal muscle bed such as the deltoid muscle of rats. Lactate levels will be continuously monitored for implantation periods varying from several hours to 3 months. This will include testing of the sensor in a model of severe hemorrhagic shock with comparison of sensor-recorded levels of lactate to systemic levels of lactate and whole body oxygen debt. A suitable MEMS antenna will be developed and demonstrated in parallel. Study Design: Microlithographically fabricated biochip substrates adopting a dual "microbore" working electrode design will be constructed. We hypothesize that the biosensor membrane, fabricated from our previously demonstrated bioactive hydrogel composite polymer will confer enhanced interferent rejection properties and impart bioactive biocompatibility to these biochips.
The lactate-sensing membrane and the biochip substrate will be integrated into sustainable in vivo packaging for subcutaneous implantation in rat models including one of severe hemorrhagic shock. A BioMEMS telemeter device will be developed that will be integrated with the biosensor for telemetric reporting of lactate levels.

Relevance: The design, fabrication and deployment of implantable biosensors for the continuous in vivo monitoring of physiological analytes present many challenges. Among these are interference shielding, biocompatibility, and stability of the biorecognition layer. A sensor that can continuously monitor lactate concentrations, unchallenged by these hindrances, will be extremely useful for injured war-fighters on the battlefield. Systemic lactate levels and base-deficit levels have been demonstrated to serve as predictors of survival during severe trauma. The ability to continuously monitor lactate levels and thus cumulative oxygen debt in austere battlefield environments and its many echelons of care may improve the ability to triage casualties and to allocate valuable resources.

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Rev 11 Nov 2007