Microstructured hydroxyapatite membranes for ion conducting and orthopedic applications

Thesis (Ph. D.)--University of Rochester. Dept. of Chemical Engineering, 2014.Hydroxyapatite (Ca5(PO4)3OH) is a highly studied material because of its similar composition to bone and its ionic conducting capabilities. This thesis investigates a novel electrochemical-hydrothermal synthesis method for depositing a hydroxyapatite membrane on metal substrates. The deposited membrane is highly crystalline, oriented along the crystallographic c-axis, which is perpendicular to the substrate, and is a uniform array of single crystals. The novel synthesis method was modified by adding the dopants yttrium, ytterbium, and fluoride during the hydrothermal synthesis. The thermal stability of the films was characterized using scanning electron microscopy and X-ray diffraction. It was shown that fluoride helped reduce dehydroxylation of the membrane at elevated temperatures. The stored charge of yttrium-fluoride co-doped membranes was measured using the thermally stimulated depolarization current test. The samples were shown to have extremely high stored charge values even without electrical polarization. Ytterbium doped membranes were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Conductivity tests were also performed using electrochemical impedance spectroscopy, as well as fuel cell performance tests. Finally, a new method of electrochemically depositing silver nanoparticles onto hydroxyapatite films was developed and characterized in order to make an antimicrobial coating. Preliminary experiments with Staphylococcus aureus demonstrated the silver coated sample’s ability to retard bacteria growth