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Synthetic bone grafts that promote the natural mineralization process would be excellent candidates for the repair or replacement of bone defects. In this study, a series of antioxidant-containing polyphosphazenes were evaluated for their ability to mineralize apatite during exposure to a solution of simulated body fluid (SBF). All polymers contained ferulic acid (antioxidant), cosubstituted with different amino acid esters linked to the polyphosphazene backbone. Differences in the side groups determined the hydrophobicity or hydrophilicity of the resulting polymers. All of the polymers mineralized monocalcium phosphate monohydrate, a type of biological apatite. However, the mineralization process (the amount of deposition and length of time) was dependent on the hydrophilicity or hydrophobicity of the polymers. The polymer−apatite composites were examined by electron scanning microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravametric analysis. Weight gain data were also obtained. To verify that the nucleation process was due to the presence of calcium and phosphate, two standard solutions were prepared: one solution (NaCl solution) contained only sodium chloride, and the second solution (mSBF) was similar to SBF except without known crystal growth inhibitors such as Mg 2+ and HCO 3 − . No mineralization occurred when the polymers were exposed to the NaCl solution, but mineralization took place upon exposure to mSBF. The apatite phase produced was hydroxyapatite (HAp). The mineralization process in mSBF was much more extensive, with all samples gaining more weight following exposure to SBF. A similar trend was also found (as in the case of SBF), with the amount of deposition and length of deposition time depending on the hydrophilicity/hydrophobicity of the polymer. These results suggest that the nucleation process is due to calcium and phosphate, and the absence of crystal growth inhibitors allows for the rapid nucleation of HAp. In both cases, the mineralization process was favored on hydrophilic surfaces (static water contact angle of 56−65°) versus hydrophobic surfaces (71−86°).

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Nanoparticles of complex architectures can have unique properties. Self-assembly of spherical nanocrystals is a high yielding route to such systems. In this study, we report the self-assembly of a polymer and nanocrystals into aggregates, where the location of the nanocrystals can be controlled to be either at the surface or in the core. These nanospheres, when surface decorated with nanocrystals, resemble disco balls, thus the term nanodisco balls. We studied the mechanism of this surface loading phenomenon and found it to be Ca2+ dependent. We also investigated whether excess phospholipids could prevent nanocrystal adherence. We found surface loading to occur with a variety of nanocrystal types including iron oxide nanoparticles, quantum dots, and nanophosphors, as well as sizes (10–30 nm) and shapes. Additionally, surface loading occurred over a range of polymer molecular weights (∼30–3000 kDa) and phospholipid carbon tail length. We also show that nanocrystals remain diagnostically active after loading onto the polymer nanospheres, i.e., providing contrast in the case of magnetic resonance imaging for iron oxide nanoparticles and fluorescence for quantum dots. Last, we demonstrated that a fluorescently labeled protein model drug can be delivered by surface loaded nanospheres. We present a platform for contrast media delivery, with the unusual feature that the payload can be controllably localized to the core or the surface.

Novel polyphosphazenes containing various vitamin substituents were synthesized and characterized, and their sensitivity to hydrolysis and pH behavior was investigated. Vitamins L1, E, and B6 were used because of their biocompatibility, their importance in a variety of biological functions, and their potential to increase the mechanical properties of the resulting polymers, thus making these materials promising candidates for hard tissue engineering scaffolds. Chlorine replacement reactions were carried out initially with the small molecule, hexachlorocyclotriphosphazene, as a model for high polymeric poly(dichlorophosphazene). Because of the steric hindrance generated by vitamin E as a substituent, co-substituted polymers were synthesized with either glycine ethyl ester or sodium ethoxide as the second substituent. Similarly, vitamin B6 was co-substituted with glycine ethyl ester or phenylalanine ethyl ester to favor biodegradability. To prevent cross-linking via multifunctional reagents, the hydroxyl groups in vitamin B6 were protected and subsequently deprotected under acidic conditions after side group linkage to the polymer backbone. The glass transition temperatures of the polymers ranged from −24.0 to 44.0 °C. Hydrolysis of the polymers in deionized water at 37 °C was used as an initial estimate of their hydrolytic sensitivity. Different solid polymers underwent 10−100% weight loss in 6 weeks with the generation of a broad pH range of ∼2.5−9. The weight loss during preliminary hydrolysis experiments was attributed to cleavage of the polymer backbone and/or the polymers becoming soluble in the aqueous media during hydrolytic reactions.