Ribbon-like and rod-like hydroxyapatite crystals deposited on titanium surface with electrochemical method

Homogeneous coatings were attained by electrochemical method in electrolytes containing Ca2+ and PO43− ions with Ca/P ratio being 1.67. SEM observation showed that the hydroxyapatite (HAp,Ca10(PO4)6(OH)2) crystals prepared with higher concentration electrolyte (4 × 10− 2 M Ca2+) are ribbon-like with thickness of nanometer size, a morphology seldom reported previously. In an electrolyte of lower concentration (6 × 10− 4 M Ca2+), the HAp crystals formed are rod-like with a hexagonal cross section and diameter of about 70–80 nm. XRD patterns and IR spectra confirmed that the coatings consist of HAp crystals. TEM micrographs and SAD indicated that the longitude direction for both ribbon-like and rod-like crystal is [002], and the flat surface of the ribbon is (110). HRTEM showed that the ribbon-like crystal is a mixture of HAp and octacalcium phosphate (OCP, Ca8H2(PO4)6.5H2O).