An implantable
enzyme-based
monitoring system suitable for long term
in vivo use to measure the concentration of prescribed substances such as glucose is provided. In one embodiment, the implantable
enzyme-based
monitoring system includes at least one sensor
assembly, an outer membrane surrounding the sensor
assembly and having a window therein, and a polymeric window cover affixed to the outer membrane and covering the window. Preferably, the outer membrane of the
monitoring system is
silicone and the window cover is a
polymer of 2-
hydroxyethyl methacrylate (HEMA), N,N,-dimethylaminoethyl
methacrylate (DMAEMA) and
methacrylic acid (MA). Also provided herein is an implantable
enzyme-based monitoring
system having at least one sensor
assembly, an outer membrane surrounding the sensor assembly and a
coating affixed to the exterior surface of the outer membrane, wherein the
coating resists blood coagulation and
protein binding to the exterior surface of the outer membrane. Preferably, the
coating is
polyethylene glycol (PEG) and
heparin in an 80:20
molar ratio. Finally, provided herein is a method of coating the exterior surface of the outer membrane of an implantable enzyme-based monitoring
system comprising the steps of forming hydroxyl groups on the
silicone surface by
plasma etching; reacting the
silicone surface with
amino functionalized silane, thereby forming amino groups on the silicone surface; simultaneously, covalently binding
polyethylene glycol (PEG) and
heparin to the amino groups; and ionically binding
heparin to the monitoring
system surface.