Hydrothermal synthesis of hydroxyapatite nanorods and nanowires using riboflavin-5 '-phosphate monosodium salt as a new phosphorus source and their application in protein adsorption

Hydroxyapatite (HA), as the main inorganic constituent in vertebrate hard tissues, is an important biomaterial for the application in drug delivery and protein adsorption. Herein, we report a simple and green hydrothermal synthesis of HA nanorods and nanowires by using the biocompatible biomolecule riboflavin-5'-phosphate monosodium salt (RP) as a new phosphorus source. In this method, the RP molecules hydrolyze to form inorganic phosphate ions under hydrothermal conditions, and these phosphate ions react with calcium ions to form HA nanorods or nanowires after nucleation and crystal growth. The effects of experimental conditions including hydrothermal temperature, heating time and pH value of the initial solution on the hydrolysis process of RP molecules are investigated. A possible formation mechanism of HA nanorods and nanowires is proposed. The as-prepared HA nanorods and nanowires are explored for the potential application in protein adsorption. The hemoglobin (Hb) loading capacities of HA nanowires and HA nanorods increase with increasing initial Hb concentration. The Hb loading capacities of HA nanowires and HA nanorods are determined to be as high as 289 mg g(-1) and 298 mg g(-1), respectively, at an initial Hb concentration of 2000 mg mL(-1). The pH-dependent Hb release property of Hb-loaded HA nanowires and HA nanorods has been found. The experimental results indicate that the products are promising for applications in protein adsorption.