Biomimetic Route to Calcium Phosphate Coated Polymeric Nanoparticles: Influence of Different Functional Groups and pH

Abstract

The controlled synthesis of organic-inorganic hybrid particles with selective morphology using polymeric nanoparticles as templates offers an effective biomimetic route to design composite materials with interesting properties for various potential applications. In this study, the formation of hybrid particles via the bio-inspired mineralization of calcium phosphate (CaP) on the surface of different surface-functionalized polymeric nanoparticles is reported. The versatile miniemulsion polymerization is used to prepare different surface functionalized nanoparticles with covalently bound carboxylic acid and phosphonic acid surface-functionalities. Functional comonomers with varying hydrophilicity like acrylic acid (AA), vinylphosphonic acid (VPA), and vinylbenzylphosphonic acid (VBPA) are employed for the copolymerization with styrene. The influence of different functional groups at different pH on the crystal phase and morphology of the calcium phosphate phase in the hybrid nanoparticles is analyzed in detail by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron as well as X-ray diffraction (ED and XRD) techniques. The calcium ion binding affinity of different surface functional groups at varying loading conditions is studied using calcium ion selective electrode to shed light on the mineralization kinetics as well as on the interfacial chemistry involved between the complexing ions and the functional groups on the particle surface. The CaP/polymer hybrid particles with well-defined crystal phases and morphologies offering varying surface topographies are interesting candidates for cell adhesion and proliferation studies for potential tissue engineering applications. They could be used as bone fillers, building blocks for the nucleation, and the growth of new bone material or implant coatings to reduce the immune response.