Phase transition of aqueous solutions of poly(N-isopropylacrylamide) and poly(N-isopropylmethacrylamide)

Fluorescence of oligonucleotides adsorbed onto the thermoresponsive poly(isopropyl acrylamide) shell of polymer nanoparticles: Application to bioassays

The fluorescence of a rhodamine X dye covalently linked to the 5' terminus of a 25-mers thymine oligodeoxynucleotide (dT25-ROX), adsorbed on the shell of thermoresponsive core-shell polymer particles, was used to probe the polarity, mobility, and distribution of the oligodeoxynucleotides (ODNs) in the shell. The particles have a glassy core of poly(methyl methacrylate) (PMMA) with a 67-nm radius, and a thermoresponsive shell of poly(N-isopropyl acrylamide) (PNIPAM) whose thickness changes from 42 nm at 11 ºC to 5 nm at 45 ºC. The variation in polarity of the shell with temperature was obtained both from the lifetimes and from the solvatochromic shifts of the dye and shows a sharp transition at the volume phase transition temperature (TVPT) of the PNIPAM shell. Förster resonance energy transfer (FRET) between dT25-ROX and a malachite green (MG)-labeled ODN (dT25-MG) was used to obtain the distribution of the ODNs in the thermoresponsive shell. Our results show that at 23 ºC (belowTVPT) the ODNs are distributed inside the shell, sensing an environment similar to water. At this temperature, the PNIPAM shell is composed of hydrated chains with high mobility, as probed by the fluorescence anisotropy of dT25-ROX. By increasing the temperature aboveTVPT, the shell collapses and the chain mobility drastically slows down owing to the anchoring of the ODN to the dense shell of PNIPAM. Furthermore, FRET shows that the ODNs are absorbed on the 5-nm-thick collapsed shell but extend into the water. The polarity probed by the ROX averages the dyes distributed in the interior of the particle shell and in water, with 60 % of the dyes outside the particle shell (i.e., sensing pure water). Another indication that above theTVPTmost of the ODNs are oriented with the dye toward the water phase is that the mobility of the dye covalently bound to the ODNs is identical in water and in the collapsed particle shell. The hybridization efficiency between an ODN supported in the particle shell (by adsorbing the ODN belowTVPTand subsequently increasing the temperature aboveTVPT) and the complementary ODN in solution is identical to that of hybridization in water. This result opens good perspectives toward the use of the core-shell thermoresponsive nanoparticles as supports in DNA bioassays.

Stimuli-responsive coacervate induced in binary functionalized poly(N-isopropylacrylamide) aqueous system and novel method for preparing semi-ipn microgel using the coacervate

We describe a novel method for preparing a stimuli-responsive semi-interpenetrating polymer network (semi-IPN) hydrogel microsphere using a thermoresponsive-type coacervation. The coacervate droplets were formed in the two-component nonionic poly(N-isopropylacrylamide-co-2-hydroxyisopropylacrylamide) (poly(NIPAAm-co-HIPAAm)) and ionic poly(NIPAAm-co-2-carboxyisopropylacrylamide) (poly(NIPAAm-co-CIPAAm)) aqueous system by heating the solution above the lower critical solution temperature. The resulting coacervate droplets included both kinds of polymer chains. Divinyl sulfone, which cross-links the hydroxyl groups of the poly(NIPAAm-co-HIPAAm), was added to the coacervate droplets. In this way, the stimuli-responsive semi-IPN hydrogel microsphere consisting of the poly(NIPAAm-co-HIPAAm) gel matrix and the linear poly(NIPAAm-co-CIPAAm) chains could be prepared, and their sizes were relatively homogeneous. That is, by utilizing the thermoresponsive coacervate droplets induced in the binary system, we could successfully prepare the fine stimuli-responsive semi-IPN hydrogel microsphere and it was prepared in a simple and easy method without any additives.

Confocal micro-raman and infrared spectroscopic study on the phase separation of aqueous poly(2-(2-methoxyethoxy)ethyl (meth)acrylate) solutions

Thermosensitive phase separation of aqueous solutions of acrylate polymers with oligooxyethylene side groups, poly(2-(2-methoxyethoxy)ethyl acrylate) (PM2A) and poly(2-(2-methoxyethoxy)ethyl methacrylate) (PM2Ma), has been investigated by using infrared and confocal micro-Raman spectroscopy. PM2A and PM2Ma exhibited phase separation at 45 and 26 degrees C with a transition enthalpy of 21 and 36 J/g, respectively. The Raman and infrared bands for the C-H and CO stretching modes (nu(C-H) and nu(CO)) of the polymers exhibited red and blue shifts on phase separation, respectively, whereas the C-O stretching bands of the ether groups hardly shifted. The nu(C-H) and nu(CO) bands also shifted with an increase in polymer concentration. Though free carbonyl groups exist in both of the polymers even at low polymer concentrations and below the phase separation temperatures, the average number of H-bonds is lower in PM2Ma than in PM2A probably because of the steric effects of the alpha-methyl groups. Raman microscopic observation showed that polymer-rich domains appeared above the phase separation temperature and the polymer concentration reached 52%.

Spherical Glycopolymer Architectures using RAFT: From Stars with a ?-Cyclodextrin Core to Thermoresponsive Core–Shell Particles

Glycopolymers with a seven-arm star architectures based on a β-cyclodextrin core (β-CD-RAFT) were successfully prepared using reversible addition–fragmentation chain transfer (RAFT) polymerization. A bimodal molecular weight distribution was observed in the early stages of the polymerization. At monomer conversions of N-acryloyl glucose (AGA) above 10% the polymerization proceeded according to a living behaviour and molecular weights of more than 200000 g mol–1 were obtained. However, the resulting star polymers did not undergo well-controlled chain extension with N-isopropyl acrylamide (NIPAAm) and the formation of block structures in each arm was prevented. Alternatively, the arm-first technique was employed. Block copolymers based on AGA and PNIPAAm were self-assembled into micelles at a solution temperature above the lower critical solution temperature. Subsequent core-crosslinking with hexan-1,6-diol diacrylate resulted in unimolecular micelles with thermoresponsive properties. Dynamic light scattering studies, surface tensiometry, and transmission electron microscopy confirmed the formation of core–shell particles.

Microwave, photo- and thermally responsive PNIPAm-gold nanoparticle microgels

Microwave-, photo- and thermo-responsive polymer microgels that range in size from 500 to 800 microm and are swollen with water were prepared by a novel microarray technique. We used a liquid-liquid dispersion technique in a system of three immiscible liquids to prepare hybrid PNIPAm- co-AM core-shell capsules loaded with AuNPs. The spontaneous encapsulation is a result of the formation of double oil-in-water-in-oil (o/w/o) emulsion. It is facilitated by adjusting the balance of the interfacial tensions between the aqueous phase (in which a water-soluble drug may be dissolved), the monomer phase and the continuous phase. The water-in-oil (w/o) droplets containing 26 wt% NIPAm and Am monomers, 0.1 wt% Tween-80 surfactant, FITC fluorescent dye and colloidal gold nanoparticles spontaneously developed a core-shell morphology that was fixed by in situ photopolymerization. The results demonstrate new reversibly swelling and deswelling AuNP/PNIPAm hybrid core-shell microcapsules and microgels that can be actuated by visible light and/or microwave radiation (<or=1,250 nm) and/or temperature. This is the first study to demonstrate that incorporating AuNPs speeds up the response kinetics of PNIPAm, and hence enhances the sensitivity to external stimuli of PNIPAm. These microgels can have potential applications for microfluidic switches or microactuators, photosensors, and various nanomedicine applications in controlled delivery and release.

Selective synthesis of double temperature-sensitive polymer-peptide conjugates

A novel synthetic route has been developed to couple selectively a modified octa-peptide, that is able to gel at low temperature, to the prototypical thermoresponsive polymer poly(N-isopropylacrylamide) to give a bioconjugate that exhibits double thermoresponsiveness.

Contact angles of oils on solid substrates in aqueous media: correlation with AFM data on protein adhesion

This study presents a method to measure the contact angles of oils on a substrate in water. Diiodomethane and perfluorodecalin were used as model oils. Self-assembled monolayers (SAMs) were prepared by adjusting the mole ratio of CH 3- and OH-terminated alkanethiols. The contact angles of the two oils in water increased with increasing hydrophilicity of the SAMs, and the results are contrasted with the contact angles of oils on these surfaces in air. In addition, perfluorodecalin showed higher contact angles than diiodomethane on the same surface. On the poly(N-isopropylacrylamide) (PNiPAAM) monolayer surface, the contact angles of the two oils in water decreased sharply at the transition temperature of PNiPAAM (approximately 30 degrees C), but the surface retained fairly high hydrophilicity even after the transition. The above results are correlated with atomic force microscopy (AFM) measurements of the adhesion force between protein-immobilized AFM tips (human fibrinogen and bovine serum albumin) and these monolayers.

Surface plasmon optical study of the interfacial phase transition of elastinlike polypeptide grafted on gold

The conformational changes in elastinlike polypeptides (ELPs) grafted to a solid/solution interface via different architectures were studied using surface plasmon resonance spectroscopy and surface plasmon field-enhanced fluorescence spectroscopy (SPFS). SPFS provides a simple and convenient optical method to study the influence of the grafting method and the graft density on the conformational changes in ELPs at the solid-solution interface as a function of environmental variables. A typical response of the ELP, consistent with its stimuli responsiveness, was a gradual collapse upon increasing the ionic strength; this effect was inversely correlated with the surface graft density of the ELP.