A novel amphiphilic ABA-type triblock copolymer poly(ethylene glycol)-b-poly(ethanedithiol-alt-nitrobenzyl)-b-poly(ethylene glycol) (PEG-b-PEDNB-b-PEG) is successfully prepared by sequential thiol-acrylate Michael addition polymerization in one pot. PEG-b-PEDNB-b-PEG is designed to have light-cleavable o-nitrobenzyl linkages and acid-labile β-thiopropionate linkages positioned repeatedly in the main chain of the hydrophobic block. The light and pH dual degradation of PEG-b-PEDNB-b-PEG is traced by gel permeation chromatography (GPC). Such triblock copolymer can self-assemble into micelles, which can be used to encapsulate anticancer drug doxorubicin (DOX). Because of the different degradation chemistry of o-nitrobenzyl linkages and β-thiopropionate linkages, DOX can be released from the micelles by two different manners, i.e., light-induced rapid burst release and pH-induced slow sustained release. Confocal laser scanning microscopy (CLSM) results indicated that DOX-loaded micelles exhibited faster drug release in A549 cells after UV irradiation. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) results show that the DOX-loaded micelles under UV light degradation exhibit better anticancer activity against A549 cells than that of the nonirradiated ones.

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In this letter, light-responsive protein-encapsulated polyion complex (PIC) micelles were prepared by self-assembly of cationic block copolymer poly(N,N-dimethyl-N-(2-(methacryloyloxy)ethyl)-N-((2-nitrobenzyl)oxy)-2-oxoethanaminium bromide)-block-poly(carboxybetaine methacrylate) (PDMNBMA-b-PCBMA) and negatively charged bovine serum albumin (BSA). The PIC micelles were well characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). From the zeta potential measurement, the increase of the zeta potential of PIC micelles from ∼10 to ∼20 mV was observed when the solution pH decreased from 7.4 to 6.5, which could enhance the intracellular protein delivery efficiency. Moreover, the positively charged PDMNBMA blocks can be transformed to zwitterionic carboxybetaine units under UV irradiation, which could result in the disassembly of the PIC micelles. The release of BSA can therefore be drastically accelerated in the presence of UV irradiation. Meanwhile, the circular dichroism (CD) spectroscopy confirmed that the secondary structure of BSA was unaffected during the UV irradiation process.

Functional polycaprolactone (PCL) has great potential for applications in biomedical areas. This review summarizes the recent progress in the chemical synthesis of functional PCL. The functional PCL can be synthesized by (a) homopolymerization or copolymerization of functional ε-caprolactone (ε-CL), (b) copolymerization of 2-methylene-1-3-dioxepane with functional vinyl monomers, or (c) copolymerization of ε-CL with functional carbonate monomers. This review presents the recent trends in the synthesis of functional PCL and its biomedical applications.

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