Implantable biosensors

Gifford R, Kehoe JJ, Barnes SL, Komilayev BA, Alterman MA, Wilson GS. Protein interactions with subcutaneously-implanted biosensors. Biomaterials 2006, 27, 2587-2598. 

Biosensor-tissue compatibility is a significant obstacle in the development of viable, enduring implantable biosensors.1,2 The clinical literature and product development files in industry are littered with biosensor failures in many different sites and... 

Wisniewski N, Moussy F, Reichert WM. Characterization of implantable biosensor membrane biofouling. Fresenius Journal of Analytical Chemistry 2000, 366, 611-621. 

The transfer of glucose from the blood to an implanted biosensor is dictated by the proximity of the sensing surface to the host tissue, by the local tissue vascularity and perfusion, and by the response of the tissue to the implant surface.11 All of these parameters change with the length of time after implantation. The primary components of the foreign body reaction to an implant along with the potential to observe these in a tissue window chamber preparation are listed in Table 4.1. 

In addition, the ability to optimize biosensor design is of central importance and initially depends on the determination of what aspects of the foreign body reaction and biosensor surface properties are critical to the success of the implanted biosensor. To accomplish this efficiently, it would be very beneficial if active sensors could be imaged in situ. Thus, sensor performance could be quantified relative to the manipulation of local tissue and microvascular conditions in response to various implant properties. Some important implant features include surface texture, porosity, and surface material composition. Surface texture of the implant has been observed to affect the extent of collagen formation. Smooth implant surfaces, which the local... 

Quinn C, Connor R, Heller A. Biocompatible, glucose-permeable hydrogel for in situ coating of implantable biosensors. Biomaterials 1997, 18, 1665-1670. 

The major problem that has plagued these kinds of implantable biosensors is the gradual decrease in sensitivity and in some cases a complete loss of function within just hours of implantation. Biofouling, oxygen limitation, electrochemical interference and GOD inactivation have been considered as explanations of this behaviour. For instance, a tissue reaction to the sensor implantation may result in a limitation in the blood supply to the tissue surrounding the probe and thus in a lower availability of glucose and oxygen. 

Several implanted biosensors have been developed and evaluated in both animals and humans (see Chapter 4). Detection systems are based on enzymes, electrodes, or fluorescence. The most widely studied method is an electrochemical sensor that uses glucose oxidase. This sensor can be implanted intravenously or subcutaneously. Intravenous implantation in dogs for up to 3 months has demonstrated the feasibility of this approach. Alternatives to enzymes are being developed, including artificial glucose receptors. Less success has been achieved with subcutaneous implants. Implantation of a needle type of sensor into the subcutaneous tissue induces a host of inflammatory responses that alters the sensitivity of the device. Microdialysis with hoUow fibers or ultrafiltration with biologically inert material can decrease this problem. 

Implanted Biosensors for Medical Research and Health Check Applications... 

Yang, Q.L, Atanasov, P., and Wilkins, E. (1997) A novel amperometric transducer design for needle-type implantable biosensor applications. Electroanalysis, 9 (15), 1252-1255. 

Emerging synergy between nanotechnology and implantable biosensors a review. Biosensors fij Bioelearonics, 25 (7), 1553-1565. 

Implants for controlled release of drugs (nonbiodegradable) Implantable biosensor-drug delivery system Microfiuidics device for drug delivery Controlled-release microchip Implants that could benefit from local drug release Vascular stents coronary, carotid, and peripheral vascular Ocular implants Dental implants Orthopedic implants... 

The main purpose of our present studies is to investigate the details of protein-surface interactions with relevance to questions regarding biocompatibility, fouling and the possible development of (implantable) biosensors. 

Implantable biosensors have further gained value for use in the CNS by advancements in the field of wireless communication and further miniaturization. This has allowed... 

FIGURE 22.4 Schematic of glial scarring around implantable biosensor. Over time, reactive astrocytes for a physical fibrotic capsule around the implant, separating it from the tissue of intoest, reducing sensor effectiveness and further perpetuating damage at the implant site. 

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