Jatin N. Kumar

Redox-responsive hyperbranched poly(amido amine)s with tertiary amino cores for gene delivery.

Redox-responsive hyperbranched poly(amido amine)s (PAAs) with tertiary amino cores and amine, poly(ethylene glycol) (PEG) and hydroxyl terminal groups were prepared for DNA delivery respectively. The DNA condensation capability of PAAs was investigated using gel electrophoresis, and the results showed that PAA terminated with 1-(2-aminoethyl)piperazine (AEPZ) (BAA) is the most efficient in binding plasmid DNA (pDNA). The diameter and zeta-potential of polyplexes from PAAs were characterized using dynamic light scattering (DLS), and the morphology of the polyplexes was obtained using atomic force microscopy (AFM). All the PAAs were able to condense pDNA into nanoparticles with diameters between 50 and 200 nm with a positive surface charge when the weight ratio of polymer/DNA was higher than 20. Glutathione (GSH)-induced DNA release from polyplexes and the buffering capability of PAAs were investigated as well. Cytotoxicity of PAAs and in vitro gene transfection of polyplexes were evaluated in HEK293, COS-7, MCF-7 and Hep G2 cell lines, respectively. The results reflect that PAAs show remarkably low or even no cytotoxicity, and that PAA with amino terminal groups mediates the most efficient gene transfection with the transfection efficiency comparable to that of 25 kDa polyethylenimine. Further the effects of the presence of buthionine sulfoximine (BSO) on the transfection efficiency and cytotoxicity of BAA polyplexes were investigated.

Cationic Micelles Based on Polyhedral Oligomeric Silsesquioxanes for Enhanced Gene Transfection

The synthesis and gene transfection efficiency of a series of amphiphilic copolymers, poly(2-(dimethylamino)ethyl methacrylate)-poly (methacrylate isobutyl polyhedral oligomeric silsesquioxane) (PDMAEMA-POSS) copolymers are reported. The hydrophobic POSS interior allows a cell-sensitizing drug such as paclitaxel to be incorporated, whereas the cationic and hydrophilic PDMAEMA corona allows the complexation of anionic DNA to form a nano-sized polyplex. These drug-encapsulated copolymers display excellent gene transfection efficiency compared with polyethylenimine or PDMAEMA homopolymers.

pH- and Redox-Responsive Poly(ethylene glycol) and Cholesterol-Conjugated Poly(amido amine)s Based Micelles for Controlled Drug Delivery

An optimized condition is identified to prepare linear poly(amido amine)s via Michael Addition polymerization of trifunctional amine, 4-(aminomethyl)piperidine (AMPD), with an equimolar diacrylamide, N,N-cystaminebis(acrylamide) (BAC). Poly(ethylene glycol) (PEG) and cholesterol (CE) are conjugated to linear poly(BAC-AMPD) through the reactions with the secondary amino groups in the backbone, respectively, to form poly(BAC-AMPD)-g-PEG-g-CE. The chemical structures of poly(BAC-AMPD) and poly(BAC-AMPD)-g-PEG-g-CE are characterized using NMR and gel permeation chromatography (GPC). Transmission electron microscopy (TEM), dynamic light scattering (DLS) and (1)H NMR results show that micelles with PEG shells and hydrophobic cores composed of poly(BAC-AMPD) and CE are formed via self-assembly of poly(BAC-AMPD)-g-PEG-g-CE in aqueous solution, and the micelles of poly(BAC-AMPD)-g-PEG-g-CE can be degraded by the presence of L-dithiothreitol and show a limited cytotoxicity in vitro. The anti-cancer drug, doxorubicin (DOX), can be loaded into the micelles. The DOX loaded micelles of poly(BAC-AMPD)-g-PEG-g-CE show pH- and redox-responsive drug release and redox-induced formation of aggregates, and it is shown that the DOX loaded micelles can deliver DOX into cells and show a higher efficacy in killing cancer cells than free drug.

Fluorescent carbon dot (C-dot) nanoclusters

Fluorescent carbon dot (C-dot) nanoclusters composed of C-dot-loaded hollow silica spheres are obtained via the dehydration of mannose, which is adsorbed onto hollow silica spheres or poly(ethylene glycol)-graft-hollow silica spheres (PEG-g-hollow silica). The structure of C-dot nanoclusters are confirmed using 1H NMR, FTIR, TEM and TGA. C-dot nanoclusters show a redshifted fluorescence emission with an increased excitation wavelength. Passivation with PEG diamines improve the quantum yields to ∼2%. Confocal laser scanning microscopy (CLSM) results reflect the fact that C-dot nanoclusters can provide good cytoplasm imaging of live Hep G2 cells and live MCF-7 cells, and the imaging obtained is brighter and more even than those from free C-dots. With their combination of good photostability and low cytotoxicity, C-dot nanoclusters are promising for the production of higher quality bioimaging.

The Effect of Different Clay Dispersion Methods on the Properties of Polyurethane/Clay Nanocomposites

Polyurethane/clay (PU/clay) nanocomposites were synthesised using polymerisation and dispersion blending methods. The intercalation and exfoliation properties of the PU/clay nanocomposites were investigated by X-ray diffraction and transmission electron microscope. Clay intercalation of polymerised PU/nanocomposites was achieved and the interlayer spacing of clay was greatly enlarged from 17 A to ~30 A. Expansion in d-spacing was also observed for PU/clay nanocomposites prepared using dispersion methods. PU/clay nanocomposites prepared from dispersion of clay particles in the prepolymer matrix, followed by chain extension reaction, showed much high molecular weight and significant improvement in mechanical properties as compared with PU/clay nanocomposites produced using polymerisation or a simple high speed blending method in which clay was blended into the PU matrix. For PU/clay nanocomposites prepared using the blending method, high speed dispersion of 2 % clay in PU resulted in approximately a two-fold increase in the Young’s modulus. Further increase in the clay loading from 2 to 6 % made the corresponding nanocomposite polymer films more rigid and stiffer. This study shows that PU/clay nanocomposite properties are highly dependent on the preparation methods and provides useful guidelines for the future design and preparation of PU/clay nanocomposites.

Surfactant-Free Emulsion-Based Preparation of Redox-Responsive Nanogels

A surfactant-free emulsion-based approach is developed for preparation of nanogels. A water-in-oil emulsion is generated feasibly from a mixture of water and a solution of disulfide-containing hyperbranched PEGylated poly(amido amine)s, poly(BAC2-AMPD1)-PEG, in chloroform. The water droplets in the emulsion are stabilized and filled with poly(BAC2-AMPD1)-PEG, and the crosslinked poly(amido amine)s nanogels are formed via the intermolecular disulfide exchange reaction. FITC-dextran is loaded within the nanogels by dissolving the compound in water before emulsification. Transmission electron microscopy and dynamic light scattering are applied to characterize the emulsion and the nanogels. The effects of the homogenization rate and the ratio of water/polymer are investigated. Redox-induced degradation and FITC-dextran release profile of the nanogels are monitored, and the results show efficient loading and redox-responsive release of FITC-dextran. This is a promising approach for the preparation of nanogels for drug delivery, especially for neutral charged carbohydrate-based drugs.

Calcium triggered self-assembly of alginate-graft-POEGMA via RAFT for the encapsulation of lipophillic actives

Alginate based comb copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT). Alginate was used both in its supplied (213 kDa) and depolymerized (73 kDa) forms and prepared into a macroRAFT agent by solubility modification with tetrabutyl ammonium ions and functionalization with a RAFT agent on its hydroxyl moieties. Poly(oligo ethylene glycol methacrylate) (POEGMA) was then polymerized from the macroRAFT agents in organic solvent demonstrating pseudo first-order kinetics. The copolymers dissolved well in a range of organic solvents and demonstrated self-assembly into nanoparticles upon the introduction of calcium chloride in both aqueous and methanolic solutions with particle sizes ranging between 100 and 500 nm. Remarkable encapsulation efficiencies of 4-n-butylresorcinol, a lipophillic active pharmaceutical ingredient, were demonstrated in methanol, and a sustained release profile was observed over 6 hours in aqueous acidic media. These new materials complement a growing library of biodegradable and sustainable polymers that show notable potential for the use in encapsulation and drug delivery.