Ex vivo optical characterization of in vivo grown tissues on dummy sensor implants using double integrating spheres measurement

Abstract

A glucose implantable sensor based on near infrared (NIR) spectroscopic measurements is expected to produce reliable glucose levels in human body for the long term to justify the surgical implantation procedure. Once implanted in body, the sensor will be influenced by surrounding biological environment. In context of glucose sensor, examples of such influences may include the growth of wound healing tissue encapsulating the sensor, and/or gradual growth of a thin tissue layer in the optical path of sensor over time. The former issue can be tackled by using bio-compatible polymeric materials which do not produce aggressive reaction in the body. Furthermore, the surface of such materials can be activated using antibodies which help to attract blood vessels and promote vascularization. However, no such remedy is available at hand to handle the growth of tissue layer in optical path of the sensor which might result in large variation in optical output. In a perfect world situation, this issue can be handled by increasing the input light signals, but for an implantable sensor, there are restrictions from power budget point of view ruling out the option of increasing light input. Most importantly, the output light signals depend on optical properties (especially scattering) of tissue layer grown in the optical path. In view of above, ex vivo optical characterization of wound healing tissues will be carried out. For the purpose, the in vivo grown tissues are obtained from dummy implants placed surgically in selected animals (goats). The estimated optical properties are interpreted in view of their significance in building a transmission based implantable glucose sensor.