Comparative physicochemical properties and cytotoxicity of polyphosphoester ionomers with bisphosphonates

Abstract

This work reports the effect of polyphosphoester ionomers on mineralization and cell viability in comparison with the fundamental actions of bisphosphonates. Poly(2-benzoxy-2-oxo-1,3,2-dioxaphospholane-co-2-ethoxy-2-oxo-1,3,2-dioxaphospholane) was synthesized by ring-opening polymerization using an organocatalyst. The benzyl group of polyphosphoesters was completely deprotected as a result of preparing polyphosphoester ionomers. The sodium salt of the ionomer was also prepared by neutralization with an aqueous NaOH solution. The amount of polyphosphoester ionomers adsorbed on hydroxyapatite (HAp) microparticles increased with an increase in the number of ionized units in the polyphosphoesters. The affinity of the ionomers for the HAp microparticles was enhanced by the formation of sodium salt. The adsorption mass of the ionomers having 0.09 ionized unit fraction was approximately equal to that of pamidronate when in contact with HAp microparticles from their 24 μM solution. Compared to pamidronate, polyphosphoester ionomers could significantly reduce HAp formation. Furthermore, similar to that of pamidronate, the resorption of HAp was also reduced with the addition of polyphosphoester ionomers. The cytotoxicity of polyphosphoester ionomers was significantly lower than that of pamidronate and the cell compatibility of the polyphosphoester ionomer was further improved by sodium salt formation. Selective adsorption of polyphosphoester ionomers on the mineral deposits generated from MC3T3-E1 cells was also observed.

Keywords:

• polyphosphoester ionomer
• bisphosphonate
• osteoblast
• hydroxyapatite
• biocompatibility

Acknowledgments

This work was supported by a Kansai University Grant-in-Aid for Progress of Research in a Graduate Course, 2010 and by a Grant-in-Aid for Young Scientists (A) from the Ministry of Education, Culture, Sports, Science and Technology of Japan (#21680043, #24500532).