Preparation and Characterization of Stimuli-Responsive Magnetic Nanoparticles

In this work, the main attention was focused on the synthesis of stimuli-responsive magnetic nanoparticles (SR-MNPs) and the influence of glutathione concentration on its cleavage efficiency. Magnetic nanoparticles (MNPs) were first modified with activated pyridyldithio. Then, MNPs modified with activated pyridyldithio (MNPs-PDT) were conjugated with 2, 4-diamino-6-mercaptopyrimidine (DMP) to form SR-MNPs via stimuli-responsive disulfide linkage. Fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize MNPs-PDT. The disulfide linkage can be cleaved by reduced glutathione (GHS). The concentration of glutathione plays an important role in controlling the cleaved efficiency. The optimum concentration of GHS to release DMP is in the millimolar range. These results had provided an important insight into the design of new MNPs for biomedicine applications, such as drug delivery and bio-separation

Well-defined cholesterol polymers with pH-controlled membrane switching activity

Cholesterol has been used as an effective component of therapeutic delivery systems because of its ability to cross cellular membranes. Considering this, well-defined copolymers of methacrylic acid and cholesteryl methacrylate, poly(methacrylic acid-co-cholesteryl methacrylate) P(MAA-co-CMA), were generated as potential delivery system components for pH-controlled intracellular delivery of therapeutics. Statistical copolymers with varying cholesterol contents (2, 4, and 8 mol %) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Dynamic light scattering (DLS) analysis showed that the hydrodynamic diameters of the copolymers in aqueous solutions ranged from 5 ± 0.3 to 7 ± 0.4 nm for the copolymers having 2 and 4 mol % CMA and 8 ± 1.1 to 13 ± 1.9 nm for the copolymer having 8 mol % CMA with increasing pH (pH 4.5-7.4). Atomic force microscopy (AFM) analysis revealed that the copolymer having 8 mol % CMA formed supramolecular assemblies while the copolymers having 2 and 4 mol % CMA existed as unimers in aqueous solution. The pH-responsive behavior of the copolymers was investigated via UV-visible spectroscopy revealing phase transitions at pH 3.9 for 2 mol % CMA, pH 4.7 for 4 mol % CMA, and pH 5.4 for 8 mol % CMA. Lipid bilayers and liposomes as models for cellular membranes were generated to probe their interactions with the synthesized copolymers. The interactions were determined in a pH-dependent manner (at pH 5.0 and 7.4) using surface plasmon resonance (SPR) spectroscopy and liposome leakage assay. Both the SPR analyses and liposome leakage assays indicated that the copolymer containing 2 mol % CMA displayed the greatest polymer-lipid interactions at pH 5.0, presenting the highest binding ability to the lipid bilayer surfaces, and also demonstrating the highest membrane destabilization activity. CellTiter-Blue assay showed that the copolymers did not affect the cell viability up to 30 μM over a period of 72 h. © 2012 American Chemical Society

PEGylated functional nanoparticles from a reactive homopolymer scaffold modified by thiol addition chemistry

Well-defined reactive polymer scaffolds are useful building blocks for a variety of biomedicine and nanotechnology applications. In this study, we have converted a RAFT-synthesized thiol-functional homopolymer scaffold (poly(pyridyl disulfide ethyl methacrylate), PPDSM) to poly(ethylene glycol) conjugated (PEGylated) nanoparticles via a straightforward approach. Poly(ethylene glycol) (PEG) was grafted to the reduced PPDSM via radical-mediated thiol - ene or Michael additions. The yield of PEG grafting via radical-mediated thiol - ene reaction and Michael addition was 68 ± 2 and 73 ± 1 mol %, respectively, of the total functional groups on the scaffold, as determined by 1H NMR spectroscopy. The grafting yield via Michael addition reactions was non-linearly proportional to the reducing agent concentration used (thus the number of free thiols created on the polymer chain). It was observed by UV - vis spectroscopy that PEG grafting via Michael addition to the PPDSM takes place simultaneously with inter- and intrachain thiol - disulfide exchange reactions. Dynamic light scattering (DLS) measurements of PEG-acrylate (M n = 2000 g/mol) grafted PPDSM (74 mol % grafting yield) in water showed the presence of particles with an average hydrodynamic diameter of 99 ± 8 nm and polydispersity index (PDI) of 0.22 ± 0.02. Atomic force microscopy (AFM) analysis of the same sample revealed the presence of spherical shape particles. 1H NMR analysis of the same PEG grafted PPDSM nanoparticles in different solvents revealed that the PPDSM backbone in water was surrounded by PEG chains. Overall, the results indicate that simply grafting PEG to PPDSM homopolymer scaffold can be a straightforward route to the generation of nanoparticles with a biocompatible, stealth shell, and the present synthetic approach can be exploited further for the generation of PEGylated functional nanoparticles for potential drug delivery applications. © 2010 American Chemical Society

Temperature-responsive self-assembled monolayers of oligo(ethylene glycol): Control of biomolecular recognition

Self-assembled monolayers (SAMs) of oligo(ethylene glycol) (OEG)-tethered molecules on gold are important for various biorelevant applications ranging from biomaterials to bioanalytical devices, where surface resistance to nonspecific protein adsorption is needed. Incorporation of a stimuli-responsive character to the OEG SAMs enables the creation of nonfouling surfaces with switchable functionality. Here we present an OEG-derived structure that is highly responsive to temperature changes in the vicinity of the physiological temperature, 37 °C. The temperature-responsive solution behavior of this new compound was demonstrated by UV - vis and nuclear magnetic resonance spectroscopy. Its chemisorption onto gold(111), and the retention of responsive behavior after chemisorption have been demonstrated by surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), and atomic force and scanning tunneling microscopy. The OEG-clerived SAMs have been shown to reversibly switch the wettability of the surface, as determined by contact angle measurements. More importantly, SPR and AFM studies showed that the OEG SAMs can be utilized to control the affinity binding of streptavidin to the biotintethered surface in a temperature-dependent manner while still offering the nonspecific protein-resistance to the surface. © 2008 American Chemical Society

Synthesis of versatile thiol-reactive polymer scaffolds via RAFT polymerization

Well-defined polymer scaffolds convertible to (multi)functional polymer structures via selective and efficient modifications potentially provide an easy, versatile, and useful approach for a wide variety of applications. Considering this, a homopolymer scaffold, poly(pyridyldisulfide ethylmethacrylate) (poly(PDSM)), having pendant groups selectively reactive with thiols, was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. Soluble polymers with controlled molecular weights and narrow PDIs were generated efficiently. The versatility of the scaffold to generate random co- and ter-polymers combining multiple functionalities with controlled-composition was shown by separate and simultaneous conjugation of different mercapto-compounds, including a tripeptide in one-step. Conversion of water-insoluble scaffold to peptide-containing water-soluble copolymers was observed to yield nanometer-size particles with narrow polydispersity. The overall results suggest that the well-defined PDSM homopolymer scaffold generated via RAFT polymerization can be a versatile building block for generation of new structures having potential for drug delivery applications via a straightforward synthetic approach

Acid-cleavable polymeric core-shell particles for delivery of hydrophobic drugs

Here we describe the combined use of acid-labile microgel approach and RAFT-mediated seeded dispersion polymerization technique to prepare an acid-cleavable core-shell like polymeric colloidal system for the delivery of hydrophobic drugs at slightly acidic sites. A new bisacrylate acetal crosslinker was copolymerized with n-butyl acrylate (BA) in the presence of a RAFT agent using a dispersion polymerization technique, which yielded crosslinked spherical particles with the size ranging between 150 and 500 nm. The particles were cleaved in a pH-dependent manner similar to the acid-labile hydrolysis behaviour of the crosslinker. In order to mask the hydrophobic surface of the particles, polyethylene glycol acrylate (PEG-A) was grafted onto poly(BA) seed particles via the RAFT agent groups on the particle surface. The acidic-site selective delivery potential of the poly(BA)-g-poly(PEG-A) particles was assessed in-vitro using a lipophilic fluorescent dye as a model hydrophobic drug. Ca. 73% and 34% of the total dye loaded in the particles was found to be released at pH 5.0 and 7.4 in 24 h, respectively. The growth of human neuroblastoma cells was not affected by the incubation with the core-shell particles and their cleavage by-products up to 3 mg/ml concentration. The physicochemical and the functional features support the potential value of the acid-cleavable poly(BA) core-poly(PEG-A) shell particles as carriers for the delivery of hydrophobic drugs at acidic sites. © 2006 Elsevier B.V. All rights reserved