The synthesis of proline methyl ester substituted polyphosphazene and the biomineralization experiment in SBF, where calcium phosphates form on its surface after 24 hours of incubation, is presented on page 1318. The CaPs are also found in nanofibers prepared with this same polymer. Proline methyl ester is chosen based on the presence of this amino acid in collagen, the main component of the organic part in bone structure. In the image, Virginia P. Silva Nykänen, Mervi A. Puska, Antti Nykänen, and Janne Ruokolainen show the SEM micrograph of calcium phosphate particles entrapped in a cavity on the surface of the polymer. This feature could be seen throughout the samples after the biomineralization experiments.