Synthesis and Fluorescent Property of Biodegradable Polyphosphazene Targeting Long-Term <i>in Vivo</i> Tracking

The importance of developing photoluminescent biodegradable scaffolding materials for tissue engineering is obvious, but it meets challenges with conventional biodegradable polymers such as aliphatic polyesters. In this study, photoluminescent biodegradable polyphosphazenes (PTA) were suggested as alternatives to target for long-term in vivo tracking applications. The PTA polymers were synthesized via nucleophilic cosubstitution of linear poly­(dichloro­phosphazene) with a fluorescent compound (TPCA) and alanine ethyl ester. The TPCA, with high fluorescent intensity and high quantum yield (∼0.5), was synthesized from citric acid and 2-amino­ethanethiol. The resulted PTA polymers demonstrated adjustable degradation rates and fluorescent intensities in relating to their chemical compositions. In comparison with TPCA, the photostability of PTA polymers has been significantly improved, which made the long-term <i>in vivo</i> tracking feasible. PTA polymers were proven biocompatible and noncytotoxic for biomedical applications via both <i>in vitro</i> cell culture and <i>in vivo</i> implantation evaluations. During the 24-week subcutaneous implantation in mouse, the location and the degradation of PTA polymer were clearly visualized with the aid of fluorescent excitation and emission. In summary, PTA polymers were envisioned as good choices for tissue regeneration as scaffolding materials with <i>in situ</i> bioimaging potentials