Spontaneous Formation of Vesicles by Self-Assembly of Cationic Block Copolymer in the Presence of Anionic Surfactants and Their Application in Formation of Polymer Embedded Gold Nanoparticles

Polymer grafted magnetic nanoparticles for delivery of anticancer drug at lower pH and elevated temperature

Efficient and controlled delivery of therapeutics to tumor cells is one of the important issues in cancer therapy. In the present work, a series of pH- and temperature-responsive polymer grafted iron oxide nanoparticles were prepared by simple coupling of aminated iron oxide nanoparticle with poly(N-isopropylacrylamide-ran-poly(ethylene glycol) methyl ether acrylate)-block-poly(acrylic acid) (P(NIPA-r-PEGMEA)-b-PAA). For this, three water soluble block polymers were prepared via reversible addition fragmentation transfer (RAFT) polymerization technique. At first, three different block copolymers were prepared by polymerizing mixture of NIPA and PEGMEA (with varying mole ratio) in presence of poly(tert-butyl acrylate) (PtBA) macro chain transfer agent. Subsequently, P(NIPA-r-PEGMEA)-b-PAA copolymers were synthesized by hydrolyzing tert-butyl acrylate groups of the P(NIPA-r-PEGMEA)-b-PtBA copolymers. The resulting polymers were then grafted to iron oxide nanoparticles, and these functionalized nanoparticles were thoroughly characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), zeta potential measurements, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). Doxorubicin (DOX), an anti-cancer drug, was loaded into the polymer coated nanoparticles and its release behavior was subsequently studied at different pH and temperatures. The drug release pattern revealed a sustained release of DOX preferentially at the desired lysosomal pH of cancer cells (pH 5.0) and slightly above the physiological temperature depending upon the composition of the copolymers. The potential anticancer activity of the polymer grafted DOX loaded nanoparticles were established by MTT assay and apoptosis study of cervical cancer ME 180cells in presence of the nanoparticles. Thus, these particles can be utilized for controlled delivery of anticancer drugs at the desired lysosomal pH and/or by slightly heating the cells using magnetic hyperthermia.

pH-induced vesicle-to-micelle transition in amphiphilic diblock copolymer: investigation by energy transfer between in situ formed polymer embedded gold nanoparticles and fluorescent dye

The ability to regulate the formation of nanostructures through self-assembly of amphiphilic block copolymers is of immense significance in the field of biology and medicine. In this work, a new block copolymer synthesized by using reversible addition-fragmentation chain transfer (RAFT) polymerization technique from poly(ethylene glycol) monomethyl ether acrylate (PEGMA) and Boc-l-tryptophan acryloyloxyethyl ester (Boc-l-trp-HEA) was found to spontaneously form pH-responsive water-soluble nanostructures after removal of the Boc group. While polymer vesicles or polymerosomes were formed at physiological pH, the micelles were formed at acidic pH (< 5.2), and this facilitated a pH-induced reversible vesicle-to-micelle transition. Formation of these nanostructures was confirmed by different characterization techniques, viz. transmission electron microscopy, dynamic light scattering, and steady-state fluorescence measurements. Further, these vesicles were successfully utilized to reduce HAuCl4 and stabilize the resulting gold nanoparticles (AuNPs). These AuNPs, confined within the hydrophobic shell of the vesicles, could participate in energy transfer process with fluorescent dye molecules encapsulated in the core of the vesicles, thus forming a nanometal surface energy transfer (NSET) pair. Subsequently, following the efficiency of energy transfer between this pair, it was possible to monitor the process of transition from vesicles to micelles. Thus, in this work, we have successfully demonstrated that NSET can be used to follow the transition between nanostructures formed by amphiphilic block copolymers.

Functional group-dependent self-assembled nanostructures from thermo-responsive triblock copolymers

The ability to control the formation of nanostructures through self-assembly of amphiphilic block copolymers is of great interest in the field of biology and catalysis. In this work we have studied the self-assembling behavior of a new class of thermo-responsive triblock copolymers containing poly(ethylene glycol), and demonstrated the manner in which the aggregation pattern changed on simple functional group transformation on the copolymers. Two different triblock copolymers, poly(ethylene glycol)-b-poly(N-ispropylacrylamide)-b-poly(t-butyl acrylate) (P1) and poly(ethylene glycol)-b-poly(N-isopropylacrylamide)-b-poly(glycidyl methacrylate) (P2) were synthesized using reversible addition-fragmentation chain transfer (RAFT) technique. It was observed that P1 and P2 displayed different temperature dependent solution properties in water, with P1 forming micelles above the LCST of the PNIPA while P2 showing macroscopic phase separation under similar conditions. Thereafter, the tert-butyl group of P1 was converted to the corresponding acid (P1a) and the epoxy groups of P2 was converted to diols (P2a), thus transforming the hydrophobic blocks to hydrophilic ones. Quite interestingly, such transformations led to significant changes in their self-assembling behavior, as both P1a and P2a were seen to form vesicles beyond the LCST of PNIPA. Changes in the hydrophilic fraction in the block copolymers by subtle changes in the functionality and temperature led to the formation of varied nanostructured assemblies, as evident from dynamic light scattering (DLS), transmisison electron microscopy (TEM), and steady-state fluorescence analysis. Such formation of thermo-responsive vesicles induced by simple structural changes in the copolymers is quite interesting and highly significant in drug delivery applications.