Adsorption of bovine serum albumin (BSA) onto positively charged core-shell latex particles with a polystyrene core and a rich poly(N-isopropylacrylamide) (NIPAM)) shell layer was investigated as a function of pH, ionic strength and temperature. Adsorption of BSA protein onto such cationic and thermosensitive particles was found negligible below the LCST of poly(NIPAM), whereas it was much higher above it. In addition, the pH and the salinity dependence of the adsorbed amount at the plateau reflected the role of electrostatic interactions. Protein adsorption behaviour was discussed by taking into account the changes in the interfacial properties of polymer particles (structure of the shell, hydrophilic-hydrophobic balance, charge density) versus temperature, suggesting that coulombic forces are mostly operating in this process. A desorption study showed that the BSA release efficiency was dependent upon the incubation time of the preliminary adsorbed step, and the effect of pH and ionic strength confirmed the contribution of electrostatic interactions. (C) 2004 Society of Chemical Industry.

The adsorption of anti-α-feto protein (anti-AFP) onto polystyrene-core-poly(N-isopropylacrylamide)-shell particles was investigated as a function of temperature, pH, and salinity. The influence of various physicochemical parameters onto the colloidal and surface properties of such stimuli-responsive particles was first studied. Then, the adsorption of anti-AFP antibody was investigated in order to point out the driving forces involved in the adsorption process. The effects of salinity, pH, and temperature demonstrated that adsorption was mainly governed by electrostatic interactions. In addition, the adsorption isotherms were analyzed on the basis of a Langmuir model leading to the determination of affinity constants. Finally, based on this adsorption study, various covalent coupling methodologies of the antibody were compared by using two different copolymers as a reactive spacer arm. The amount of chemically grafted antibody was obtained after performing the desorption step (by lowering the temperature, changing the pH, or raising ionic strength). The grafted quantity of antibody was found to be related to the adsorbed amount as a function of pH and ionic strength.

Hydrophilic and stimuli-responsive submicronic latex particles based on polyalkyl(meth)acrylamide can be prepared owing to simple radical-initiated polymerizations in heterogeneous media using a water-soluble initiator and a crosslinker (methylenebisacrylamide). The paper aims at reviewing the synthesis and properties of functionalized polystyrene-polyN-isoprpylacrylamide core-shell particles or polyN-isopropylmethacrylamide microgel particles. Particle size of analysis showed that a short nucleation period afforded the synthesis of highly monodispersed latexes. The dramatic change of the colloidal properties (particle size, electrophoretic mobility) was found to reflect the thermal sensitivity of such particles. The hydrophilic nature of the particles below the volume phase transition temperature was found to drastically reduce the physical adsorption of proteins. Some examples of biomedical applications of these stimuli-responsive particles are briefly reported.

The adsorption of HIV-1 capsid p24 protein bearing six histidine residues (named RH24) onto well-characterized thermosensitive and cationic poly(styrene)-poly(N-isopropylacrylamide) core-shell particles was investigated as a function of temperature, pH, incubation time, and salinity. The maximum amount of adsorbed RH24 was observed when the temperature was above the lower critical solution temperature (LCST) of the hydrogel, whereas a negligible adsorbed amount occurred below the LCST. Adsorption isotherms were then determined above the LCST and exhibited well-defined plateaus, which were pH and ionic strength dependent. Isotherm data were tentatively discussed using the Freundlich power law, from which the standard free enthalpy of protein adsorption was estimated. The adsorption behavior of protein was mainly governed by hydrophobic interactions above the LCST; however, differences between the two latexes gave evidence that electrostatic forces also played a significant role.

The intern al properties of submicron poly(N-isopropylmethacrylamide) la tex particles were investigated as a function of the methylene bisacrylamide (MBA) concentration used as a crosslinker. Two experimental approaches were performed. First, quasi-electric light scattering measurements provided the size variation of the particles as a function of temperature, from which the swelling capacity of the particles as a function of MBA were estimated. In addition, the broadening and lowering effects of the volume phase transition temperature were detected from the turbidity of the solutions versus the MBA concentration. Second, observations of the transverse relaxation of protons gave evidence for heterogeneous structures inside the particles; several structural parts were discriminated from one another from different proton mobilities detected through magnetic relaxation rates. Corresponding to the concentration gradients of the crosslinker, the internal particle structures were looser and looser from the core to the shell. The state of the gelation of the polymer particles was governed by the initial amount of the crosslinker introduced into the latex recipe. (C) 2000 John Wiley & Sons, Inc.

Functional poly(N-isopropylmethacrylamide) (NIPMAM) copolymer latexes were prepared at 80 degrees C using methylene-bisacrylamide (MBA) as the crosslinking agent, and potassium persulfate (KPS) as the initiator in the presence of N-(vinylbenzylimino)-diacetic acid (IDA). Adding functional monomer (IDA) was found to drastically affect particle size, but not size distribution as observed both by scanning electron microscopy and quasi elastic light scattering. However, performing the polymerization reaction at too high functional monomer concentration, led to enhanced the formation of water soluble polymers (WSP). The Lowest Critical Solubility Temperature (LCST) of cleaned latexes was measured by a turbidimetric method reflecting the thermosensitive behavior of the particles. The transition temperature was found to be around 43 degrees C, and was only slightly dependent on the concentration of functional monomer.

Monodisperse cationically charged core-shell poly[styrene[N-isopropylacrylamide] latexes, differing in their shell structure, were studied at temperatures around the lower critical solution temperature (LCST) of polyCN-isopropylacrylamide]. Near the LCST, a transition on the latex dimensions was observed by quasi-elastic light scattering measurements. The same transition could also be detected using the intensity ratio of the pyrene fluorescence vibronic bands, I-1/I-13, and the excimer to monomer fluorescence intensity ratio of 1,10-bis(1-pyrenyl)decane. The fluorescence spectra and decay curve measurements of 1,10-bis( 1-pyrenyl)decane provided a better understanding of both the hydrophilic-hydrophobic variation and the conformational changes occurring in the poly[N-isopropylacrylamide] shell of the latex particles upon temperature variation.

Thermosensitive crosslinked polymer latexes have been synthesized by precipitation polymerization of N-isopropylmethacrylamied (NIPMAM) as a main monomer, methylene bis-acrylamide (MBA) as a crosslinker, and potassium persulfate (KPS) as the initiator. Polymerizations kinetics were first investigated by studying both the influence of crosslinker (MBA) and initiator (KPS) concentrations and temperature effects on the polymerization conversion, the particle size, and water-soluble polymer (WSP) as a function of time. Particle size analysis by Scanning Electron Microscopy (SEM) showed that a short nucleation step afforded the synthesis of highly monodispersed latexes. In addition, a strong dependence of WSP formation on MBA and KPS concentration and polymerization temperature was found, as well. Comparison of particle size by SEM and quasielastic light scattering clearly evidenced the dramatic effect of temperature on particle size. Lower critical solubility temperatures (LCST) of latexes were determined and compared. Finally, based on these results, the mechanism of particle formation in this polymerization process is discussed. (C) 1999 John Wiley & Sons, Inc.

This article reports the colloidal and physicochemical characterization of crosslinked poly (N-isopropylmethacrylamide) (poly[NIPMAM]) latexes. The latex particles were first characterized by determining the lowest critical solubility temperature by measuring the optical density variation as a function of temperature. In addition, the electrophoretic mobility behaviors of all latexes were examined as a function of pH and temperature. Finally, the colloidal stability was investigated by determining the critical coagulation concentration and the critical flocculation temperature, and the corresponding results were discussed by taking into account both the effect of salinity and temperature on the solvency of poly[NIPMAM].

Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering (QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle morphology information were inferred for discussion of the polymerization mechanism of this system.

The electrokinetic properties and colloidal stability behavior of styrene/N-isopropylacrylamide and styrene/N-isopropylacrylamide-co-aminoethyl methacrylate core-shell latexes were investigated. The electrophoretic mobility was first measured as a function of pH, temperature, and ionic strength. On the basis of the results obtained for the electrokinetic measurement, a charge distribution model (volume charge distribution) was proposed to help the suggested interpretation. By use of Eversole and Bordman's equation, the shear plane positions were estimated as a function of ionic strength and good correlation was found between the calculated values and the values obtained from the quasi-elastic light scattering measurement. The colloidal stability of those core-shell latexes was examined above and below the low critical solution temperature (LCST) (similar to 32 degrees C). Below the LCST, stabilization was mainly attributed to the combination of both electrostatic and steric stability. Whereas, above the LCST, only the electrostatic stability was the driving parameter. In addition, an apparent Hamaker constant of the core-shell latex was experimentally determined above the LCST.

In a previous paper [1], the synthesis of various polystyrene– poly[NIPAM] core–shell latexes bearing cationic amidino and/or amino charges has been described. Several colloidal properties of these cationic latexes have been charac-terized such as: particle size, surface charge density, electrophoretic mobility and finally colloidal stability. Due to the poly[NIPAM]-rich layer in the shell, it was found that temperature played a significant role on all these properties, a LCST around 33 °C being exhibited. In addition, ionic strength was also found to affect the colloidal behavior of these latexes, the largest effect being observed with latexes having both amidino and amino surface charges. The critical coagulation concentra-tions (CCC) of the various latexes above and below the LCST were determined, highlighting the contribution of electrostatic and steric repulsive forces to the stability of these particles.