System and method for continuous analyte monitoring

#The present invention relates to analyte monitoring systems, and more particularly to a continuous analyte monitoring system wherein fluid is extracted from an organism and monitored outside of the organism to obtain a measurement of a characteristic of the fluid, such as analyte measurement.

#Monitoring systems that sample and measure characteristics of fluids from an organism, such as a human, are well known. Many of these systems involve implanting sensors and related devices into the organism (such as under the skin) in order to obtain samples and make measurements of those samples. Even for short term implants, it has been shown that within the first several hours after implantation a rapid deposition of fibroblasts, macrophage plaques, fibrogen growth and other natural physiological encapsulation processes surround the implant and thereby impair, restrict, and modify, in a dynamic fashion, the free flow of the analytes of interest into the active sensor region of the implanted device. The typical method for compensating for these encapsulation effects involves calibrating the sensor against a conventional in vitro analysis method several times over the first few days. Further, once implanted, the sensors must be frequently calibrated, resulting in trauma to the implanted site and additional finger sticks to obtain the blood for calibration. The need to conduct multiple calibrations largely eliminates much of the advantages for many of the implanted continuous monitoring systems.

#An additional restriction on the performance of the implantable sensors is that the internal environment is typically low in oxygen. This can limit the performance of many classes of reactive bio-sensors that invoke an analyte specific reaction which requires oxygen. One solution employed in some of the implants being developed is to use a restrictive diffusion membrane which limits the proportional amount of the analyte of interest which is allowed to reach the assay element, thereby extending the useable life of the implanted sensor in the oxygen lean internal environment. This compromise solution can have detrimental effects on response time, linearity of response to serum level changes in the analyte, and basic assay signal-to-noise ratio (SNR)

#FIG. 1 is a block diagram generally showing the continuous analyte monitoring system according to the present invention.

#FIG. 2 is a schematic diagram of a tissue interface device for use in the system and method of the present invention.

#FIGS. 3 and 4 are side views of suitable tissue interface devices through which micropores in the tissue are formed and fluid is collected and analyzed.

#Definitions

#As used herein, the term “biological membrane” means the structure separating one area of an organism from another area of the organism, such as a capillary wall, or the outer layer of an organism which separates the organism from its external environment, such as skin, buccal mucosa or other mucous membrane. The term “epithelial tissue,” when used herein is mean to mean skin, mucosa and linings of the body cavities of an organism.

#As used herein, the term “stratum corneum” means the outermost layer of the skin, consisting of from about 15 to about 20 layers of cells. The stratum corneum provides a barrier to the loss of water from inside the body to the external environment and from attack from the external environment to the interior of the body. The term “epidermis” means the metabolically active region of the skin. It is found just below the stratum corneum and is approximately 10 times as thick as the stratum corneum. The epidermis does not contain blood transport structures, i.e., capillaries. The term “dermis” means the region of skin approximately 10 times as thick as the epidermis and found just below the epidermis. The dermis contains large amounts of collagen, which provides structural integrity to the skin. The dermis contains a layer of small blood capillaries that provide oxygen and nutrients to the rest of the layers of skin.