Abraham, Alexander Anil (2015-05). Development of an Encapsulation Strategy for an Implantable Optical Glucose Sensing Technology Compatible with a Self-Cleaning Membrane. Doctoral Dissertation.
The concerning rate of diabetes mellitus prevalence and its associated chronic complications accentuates the urgency for continuous glucose monitoring. Optical techniques, especially fluorescence-affinity assays, offer a strategy that transcends current transcutaneous sensors by enabling subcutaneous implantation and interrogation. Biosensors can initiate an immune response that ultimately leads to a dense fibrous capsule surrounding the sensor. This biological interference, termed "biofouling," severely limits implantable sensor lifetimes by slowing analyte diffusion and decreasing optical signal propagation. In an effort to control biofouling, a thermoresponsive, "self-cleaning," hydrogel membrane based on poly(N-isopropylacrylamide) (PNIPAAm) has been proposed. Further, a continuous glucose monitoring system based on a competitive binding assay using Concanavalin A (ConA) as a component in a F?rster resonance energy transfer (FRET) approach is being developed for encapsulation within the thermoresponsive hydrogel. In this research, a double network nanocomposite PNIPAAm (DNNC) hydrogel's glucose diffusion, thermosensitivity, cytocompatibility, in vitro cellular release, and in vivo compatibility and efficacy were thoroughly investigated. Further, an encapsulation strategy was developed for retaining the glucose assay within the hydrogel and yet allowing glucose diffusion. The methods and systems for obtaining the in vitro and in vivo results of the hydrogel are presented along with the glucose encapsulation strategies. In general, the research showed that the hydrogel could adequately diffuse glucose at temperatures associated with subcutaneous implantation, maintain a stable thermal cycling profile, promote cellular release without toxic effects in vitro, and decrease the extent of biofouling in vivo. Furthermore, the hydrogel revealed its feasibility to be embedded with layer-by-layer (LbL) microsphere assemblies, which exhibited the ability to encapsulate the components of a competitive binding glucose assay. Overall, the results of this research demonstrate that the hydrogel combined with the encapsulated glucose assay is a promising approach for an implantable continuous glucose monitoring biosensor.