| The development of polymer membranes suitable for encapsulation of a fluorescence-based optical glucose affinity sensor with the potential for transdermal sensing is presented. Glucose detection is by reversible competitive displacement of a donor-labeled ligand from an acceptor-labeled receptor protein with binding sites for certain carbohydrates, and ratiometric detection of intensity changes from energy transfer between labels. Mathematical models were developed and compared with experimental results for similar sensors. Lack of agreement was attributed to slow reaction kinetics. Simulations of the in vivo environment indicated that fibrotic capsule formation at the sensor surface would be problematic.; Commercial hollow fiber membranes were screened for biocompatibility and protein retention, but a candidate for the retaining membrane of a transdermal glucose affinity sensor could not be selected from among those studied. Membranes were rejected either for inappropriate host response and fibrotic capsule formation, or for an inability to retain a model protein for more than 24 hours. As an alternative, membranes of crosslinked poly(2-hydroxyethyl methacrylate) (pHEMA) were prepared. Permeabilities of the membranes to creatinine and IgG-Fab fragment were used to evaluate membrane performance. Flat sheet and tubular membranes prepared with 4% crosslinker and 40 v/v% water were visually transparent and demonstrated higher permselectivities than 1000 MWCO dialysis membranes. Membranes retained their clarity and integrity over a 6 week subcutaneous implantation, with minimal, but avascular, fibrotic capsule formation (∼30 μm).; To improve vascularization near the pHEMA membranes, delivery of the angiogenic endothelial cell growth factor (ECGF) was investigated. ECGF coatings on subcutaneously implanted membranes evoked extensive vascularization in the surrounding tissue, but not in the fibrotic capsule. Membranes with ECGF in the core for sustained release resulted in moderate increases in vascular structures in the fibrotic capsule.; Sensor performance was tested using Concanavalin A as the receptor and dextran as the ligand, and two energy transfer pairs. Sensor assemblies were prepared that consisted of a poly(ethylene glycol) hydrogel layer with covalently attached ConA and physically entrapped dextran, sandwiched between two flat sheet pHEMA membranes. The sensors responded to glucose reversibly, but magnitudes were small from loss of probe fluorescence during photopolymerization. |
