Hollow mesoporous hydroxyapatite nanostructures; smart nanocarriers with high drug loading and controlled releasing features

We report the development of effective drug loaded nanocarriers to combat multidrug resistant infection especially in case of osteomyelitis. The hollow mesoporous hydroxyapatite nanoparticles (hmHANPs) and solid/non-hollow hydroxyapatite nanoparticles (sHANPs) were synthesized by core-shell and co-precipitation techniques respectively. High encapsulation of the drug (ciprofloxacin) was observed in hmHANPs as compared to sHANPs, which may be due to the hollow porous structure of hmHANPs. These nanoparticles were characterized by scanning electron microscope (FESEM), N-2 adsorption/desorption, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Thermogravimetric analysis (TGA). Approximately 80% of the encapsulated drug was released at pH 4.5 within 5 days in case of hmHANPs while at pH 7.4, a sustained drug release profile was obtained and only 48.73% of the drug was released after 9 days. The results of kinetic drug release revealed that drug loaded hmHANPs showed fickian diffusion and anomalous drug diffusion mechanism at pH 4.5 and 7.4 respectively. Owing to their porous structure and high drug loading capacity, hmHANPs showed enhanced antibacterial activity against Staphylococcus aureus and Escherichia coli (drug resistant strains of osteomyelitis) in comparison to that with sHANPs. In addition, hmHANPs showed a pH sensitive drug release profile, high surface area (105.33 m(2)/g) with increased pore volume (0.533 cm(3)/g) and superior antimicrobial activity against osteomyelitis as compared to sHANPs.