Polyphosphazenes with amino acid citronellol ester side groups for biomedical applications

Abstract

In order for a material to be considered a potential candidate as a scaffolding substrate, it should be biodegradable to non-toxic products, and possess similar physical characteristics to those of the living tissue being replaced. Previous work centered on the direct linkage of citronellol, an anti-inflammatory molecule, to a polyphosphazene backbone. Moreover, the hydrolysis rate in that study was tuned by incorporating alanine ethyl ester co-substituent units thereby decreasing the amount of citronellol in the final polymer. By contrast, in this work citronellol was used as an ester unit linked to the carboxylic acid moiety of the amino acids glycine, alanine, valine, and phenylalanine that were in turn linked to the polymer backbone through the amino functionality. This method allowed the hydrolysis rate to be controlled via the steric hindrance generated by the amino acid ester while still providing two crosslinkable sites per repeat unit from the citronellol units. A hydrolysis study of the uncrosslinked polymers at physiological temperature showed between a 19.8% and 28.8% mass loss and between a 80.4% and 98.9% molecular weight decline after 12weeks. The double bond in the citronellol structure also allowed polymer crosslinking by UV radiation to further control the polymer properties.