Inadequate control of blood glucose contributes to the complications of diabetes (renal, retinal, neural). A glucose sensor implanted subcutaneously could provide continuous glucose data, help prevent these complications, and give early warning for hypoglycemia, but the useful life of current devices is limited by foreign body encapsulation. The goal of this work is to develop coatings that will reduce the foreign body reaction to implanted glucose sensors, thereby extending their useful life. Specifically, studies of protein coatings that will reduce monocyte/macrophage adhesion are proposed. The role of fibrinogen and its macrophage-binding region will also be explored. The effect of these coatings will be addressed during chronic studies of glucose sensors implanted subcutaneously in rats. 1. Passivating protein coatings will be created and characterized as follows: a. The degree to which four proteins in buffered solutions will adsorb to polyurethane-coated surfaces will be measured using Iodine-125 radiolabeled proteins. The proteins will include von Willebrand factor, high molecular weight kininogen, albumin, and hemoglobin. Protein concentration will be varied to determine the isotherms for each protein, in order to establish concentrations needed to attain saturation or monolayer adsorption. b. For each protein, the resistance to displacement by blood plasma will be measured. Methods to reduce displacement will be evaluated, including variations in adsorption time and postadsorptive residence time. c. Adsorption conditions found to give coatings that are substantially resistant to displacement will be evaluated in regard to their ability to inhibit macrophage adhesion and foreign body giant cell formation in vitro. d. Glucose sensors preadsorbed with protein under conditions resulting in the least displacement by plasma and the greatest inhibition of monocyte adhesion and foreign body giant cell [FBGC] formation will be sent to Legacy where they will be evaluated to assess useful in vivo lifetime. 2. Passivating antibody coatings will be created and characterized as follows: a. The surface polyurethane will be preadsorbed with flbrinogen and treated with a monoclonal antibody that binds to fibrinogen's macrophage binding region. b. The ability of glutaraldehyde to further stabilize the fibrinogen/antibody-treated surfaces will be assessed. c. The resistance to displacement of the antibody by exposure to plasma will be evaluated. d. The efficacy of antibody blockade to reduce monocyte adhesion and FBGC formation will be evaluated. e. Glucose sensors preadsorbed with fibrinogen and antibody, with or without glutaraldehyde, will be prepared for chronic in vivo evaluation of sensor function. 3. The role of fibrinogen adsorption in the foreign body reaction will be studied as follows: a. A series of gas plasma-deposited polyethylene oxide-like coatings on the sensor will be created under conditions that cause variations in their fibrinogen adsorption. b. The variation of in vitro phagocyte uptake on these surfaces and will be measured. c. Sensor surfaces with high and with low amounts of fibrinogen, including some passivated with antibodies and glutaraldehyde, will be prepared for evaluation in the Legacy animal laboratory. 4. Glucose sensor function will be evaluated after protein adsorption in vitro to assess any coating-induced change. 5. Sensors will be serially evaluated in vivo during normoglycemia and hyperglycemia in order to assess the effect of passivating proteins and antibody-blocked fibrinogen coatings on lag time, sensitivity, stability, and useful sensor life. 6. Because future users with diabetes will wish to minimize capillary blood calibrations, there will be an assessment in coated sensors as to whether calibrations performed only once per week will lead to sufficient sensor accuracy. 7. After explantation, percent of remaining radiolabeled protein will be measured and correlated with in vivo function in order to better understand the effects of displacement of passivating proteins or antibody-blocked fibrinogen. 8. A histologic evaluation will be performed to assess the effect of passivating proteins and antibody blocked fibrinogen on the nature of the foreign body capsule.
| Nie, Ying; Bergendahl, Veit; Hei, Derek J et al. (2009) Scalable culture and cryopreservation of human embryonic stem cells on microcarriers. Biotechnol Prog 25:20-31 |
| Geelhood, Steven J; Horbett, Thomas A; Ward, W Kenneth et al. (2007) Passivating protein coatings for implantable glucose sensors: evaluation of protein retention. J Biomed Mater Res B Appl Biomater 81:251-60 |
