Effect of polyglycerol polyricinoleate concentrations on the adsorption behavior of hydroxyapatite nanoparticles at the oil-water interface of emulsion

Abstract The adsorption behavior of hydroxyapatite (HAp) nanoparticles at the oil-water interface is very important for the microstructure of organic-inorganic composite fabricated using HAp nanoparticles stabilized Pickering emulsion as template. Studies on its adsorption behavior have attracted much interest because of the importance for their applications in biomedical field. Emulsions with dichloromethane (CH2Cl2) dissolved poly(L-lactic acid) (PLLA) as the oil phase and hydroxyapatite (HAp) nanoparticles dispersed in deionized water as the aqueous phase were prepared with different polyglycerol polyricinoleate (PGPR) concentrations in order to obtain PLLA/HAp porous composite. The distribution of HAp nanoparticles at the oil-water interface with different PGPR concentrations were characterized by confocal laser scanning microscope, and the adsorption behavior of HAp nanoparticles was also discussed. Transmission electron microscope and cryo-scanning electron microscope were used to characterize the emulsion stabilized by HAp nanoparticles with PGPR concentration of 1.0 w/v%. The results indicated that HAp nanoparticles were dispersed on the surface of emulsion droplets to stabilize emulsion, and some of them were also distributed on the surface of emulsion droplets or adjacent emulsion droplets in the form of agglomerates with lower PGPR concentrations. HAp nanoparticles escaped from the oil-water interface to the oil phase with increasing PGPR concentrations, and PGPR became the main emulsion stabilizer. Pickering emulsion was changed into classical emulsion with increasing PGPR concentration because PGPR turned to be the main stabilizer instead of HAp nanoparticles. Both microspheres and porous materials were fabricated using the as-received emulsion as template. This work would be helpful to study the adsorption behavior of HAp nanoparticles as well as its effect on the emulsion properties.