Paper BI-TuP6
Blood Compatible Coating using Tethered Heparin to Reduce Coagulation in Microfluidic Devices

Tuesday, October 22, 2019, 6:30 pm, Room Union Station B

Hyperbilirubinemia, a condition characterized by excessive bilirubin levels, affects over half of newborn babies and can lead to serious complications including brain damage or death. Absorption of light by bilirubin leads to isomerization reactions that convert bilirubin into more readily excreted compounds (e.g. lumirubin). Here, an extracorporeal microfluidic device has been developed and optimized to isomerize bilirubin in neonates, with an efficiency that exceeds the current treatment, exchange blood transfusions. The microfluidic devices are formed from cyclic olefin copolymer and the main design challenge for this device is hemocompatibility. Our approach is to modify the blood contacting channels by tethering heparin, a powerful anti-coagulant, to the surface. This is achieved by first coating the surfaces with poly(dopamine) (PDA) and then adsorbing silver nanoparticles onto the PDA layer followed by a thiol based amine terminated self-assembled monolayer (SAM). PDA provides a route for coating virtually any surface and along with silver nanoparticles the PDA-silver interface becomes antimicrobial. The SAM formed on the PDA-silver surface can be tailored for covalent linkage of the desired molecule. For this device, heparin is chemically modified, while retaining the active site, and covalently attached to the SAM with an end-on orientation to preserve activity. Heparin’s potency, in terms of anti-coagulative power, comes from a heavily sulfated penta-saccharide sequence. This sequence selectively binds precursors that produce fibrinogen, the basis of a clot. Therefore, the heparin must be covalently bound in an end-on orientation to expose this penta-saccharide sequence as opposed to allowing it to adsorb to the surface. Fluorescent microscopy provides the relative coverage of available sites for heparin attachment. Fluorescein isothiocyanate is selective to primary amines and demonstrate the density of amines that can be covalently bonded with heparin. Additionally, surface density of these amine groups was confirmed by X-ray photoelectron spectroscopy. Finally, the activity of surface bound heparin is dependent on orientation with respect to the channel surface. Thus, sum frequency generation vibrational spectroscopy provides information on the tilt angle of heparin at an interface by probing S=O, C-H and O-H vibrational modes at the modified surface.