Preparation Of Hollow Hydroxyapatite Microspheres As A Drug Controlled Release Carrier

A drug delivery system has exhibited great potential for application in clinical medicine, and drug controlled release of the delivery system is in center location. The micromorphology, particle size, chemical composition and pore structure of the drug controlled release carrier not only influence the drug loading efficiency, but also affect the sustained release property. It is critical to selective an applicable drug carrier for following application in clinical study and practice. As the most important inorganic constituent of human teeth and bones, hydroxyapatite(HAp) has been widely used as drug controlled delivery due to their advantages such as excellent biocompatibility, biological safety and biodegradability etc.In this paper, the hollow HAp microspheres were fabricated by a hydrothermal method through an anion-exchange process by using the calcium carbonate(CaCO3) microspheres which were synthesized by precipitation method as the sacrificial template. The in vitro degradation properties of the hollow HAp microspheres were investigated, meanwhile, the drug loading capacity and controlled drug release property of the hollow HAp microspheres were investigated when we used doxorubicin hydrochloride(Dox), a anti-cancer clinical drug, as a typical drug pattern(HAp/Dox). Then, the Hoechst staining tests and DiO fluorescence obversation were used to investigate the biocompatibility and the killing capacity to human liver cancer cells(Hep-3B, Hep-G2 and Huh-7) of the HAp/Dox. The details and results of the study are as follows:1. Three kinds of CaCO3 microspheres were prepared by a precipitation reaction of calcium chloride(CaCl2) and sodium carbonate(Na2CO3)regulated by different concentration of poly(styrene sulfonic acid) sodium salt(PSS). The effects of the concentration of PSS and reactants on the micromorphology, particle size, and crystal form of CaCO3 microspheres were also studied, and the average diameter of three CaCO3 microspheres were about 1, 1.5 and 2.6 μm, respectively, which suggested the concentration of PSS had an important effect on the micromorphology, particle size, and crystal form of the as-prepared CaCO3 microspheres.2. Three kinds of hollow HAp microspheres were prepared by a hydrothermal reaction through an anion-exchange process using the as-prepared CaCO3 microspheres. The average diameter HAp microspheres, constructed with building units of hydroxyapatite nanofibers, were about 1.3, 1.8 and 2.9 μm, respectively, which correspond to the average size of CaCO3. The surface was porous urchin-like structure and the interior was hollow structure. In hydrothermal reaction process the spheric structure of CaCO3 was not only well retained, but also a hollow structure of HAp was formed. The anion exchange process gradually began from outside to inside. The midbody was the structure of shell packaging ball, and the final product was hollow HAp microspheres.3. The in vitro degradation properties of the hollow HAp microspheres were investigated. The hollow HAp microspheres showed a good biodegradability and a constant degradation rate. The lower the pH was, the faster the degradation rate was, indicating a pH-responsive property of the microspheres. After three months’ degradation, the morphology of the particle became an irregularity structure. The nanoHAp particles were scattered around the degradation products.4. The drug loading capacity and controlled drug release property of the hollow HAp microspheres were investigated by usage of Dox as a model drug. It displayed a high drug loading capacity and pH-responsive sustained-controlled drug release behavior. The drug loading efficiency was over 80% and the drug released time in different release medium was as long as 96 h. The drug release rate and cumulative release amount were increasing with the decrease of pH value.5. The biocompatibility of the hollow HAp microspheres and the killing effect to human liver cancer cells(Hep-3B, Hep-G2 and Huh-7) of the HAp/Dox delivery were investigated. The single hollow HAp microspheres without loading Dox displayed an excellent biocompatibility. As expected, the hollow HAp/Dox drug delivery showed a high ability to kill human liver cancer cells and less damage to normal human liver cells.6. The apoptosis of human liver cancer cells were examined by Hocehst staining tests. The results showed that the hollow HAp/Dox drug delivery system can induce the apoptosis of human liver cancer cells. The locating results of Dox in liver cancer cells were examined by the DiO fluorescence labeling of cytomembrane. The results showed that the Dox release from hollow HAp/Dox drug delivery system could pass through cell membranes and enter into the nucleus, and then kill human liver cancer cells.