Development of Fluorophore-tagged Biodegradable Star Polymers

Abstract

This work showcases the design of a novel TPE (tetraphenyl ethene)-based initiator library with initiating sites varying from two to eight. The synthesized hydroxy-functionalized TPE derivatives could be utilized for the ROP (ring-opening polymerization) of a tailor-made carboxy-substituted caprolactone using tin-based catalyst Sn(Oct)2 in melt conditions. The polymers thus synthesized are biodegradable due to the aliphatic ester backbone and fluorescent due to the AIE (aggregation induced emission) activity of TPE. NMR, SEC, and thermal characterizations of the polymers were carried out. Deprotection of the Boc group resulted in amphiphilic polymers, which were self-assembled and monitored for their photophysical properties. The studies reveal that the fluorescence intensity of the resulting star polymers is dependent on the substitution of the TPE core- the higher the substitution at the core, the higher the fluorescence intensity due to AIE. The polymers are amenable to bioimaging due to the presence of TPE. This was confirmed by cellular uptake studies which showed localization of polymer in the cytoplasm. The polymers were also found to be non-toxic to cells. Anticancer drug encapsulation studies revealed that they can load DOX with a DLC of ~2%. These drug-loaded polymers were found to be as effective as free DOX in cytotoxicity. The synthesized TPE-PCL system thus shows promising theranostic applications, along with providing an opportunity to study TPE photophysics.