Mechanism of Microgel Formation via Cross-Linking of Polymers in Their Dilute Solutions: Mathematical Explanation with Computer Simulations

Biocompatible Preparation of Beta-Lactoglobulin/Chondroitin Sulfate Carrier Nanoparticles and Modification of Their Colloidal and Hydropathic Properties by Tween 80

The electrostatic complexation of the protein beta-lactoglobulin (β-LG) with the anionic polysaccharide chondroitin sulfate (CS) and the subsequent stabilization by thermal treatment were studied to achieve the well-defined nanoparticles (NPs). The formation of the well-defined NPs was obtained at pH 4 with a hydrodynamic radius from 60 to 80 nm. NP aggregation was observed at pH 1.5 because of the loss of the anionic charge of chondroitin sulfate on the surface of the NPs. After thermal treatment, the NPs exhibited stability against a pH increase to pH 7 while a stronger aggregation at pH 1.5 was observed. Core-shell structures were found at pH 7 after thermal treatment, indicating a possible mechanism of partial disintegration. The addition of Tween 80 (T80) before thermal treatment led to the formation of T80 self-assemblies inside the NPs. This caused an increase in the hydrophobicity of the inner and outer surfaces of the NPs as it was observed by fluorescence spectroscopy. The ζ-potential of the complexes and NPs was about -20 mV while the presence of T80 did not affect it. FTIR spectra verified changes of the secondary structure of β-LG in its complexes with CS and T80. The thermally treated NPs exhibited high surface and overall hydrophobicity and stability in high salinity and biocompatible solutions. The thermally treated NPs showed colloidal and physicochemical stability for 1 month, which were enhanced by the addition of T80. Due to the nature of the precursors and their colloidal properties, the NPs are highly promising for applications as biocompatible drug delivery nanocarriers while T80 acts as an agent to modify their properties.

Thermally stabilized chondroitin sulfate-hemoglobin nanoparticles and their interaction with bioactive compounds

The preparation of nanoparticles (NPs) based on hemoglobin (Hb) with a fully biocompatible methodology is presented. The spontaneous formation of electrostatic complexes of Hb with chondroitin sulfate (CS) at pH 4 in the polysaccharide/protein mass ratio regime where charge neutrality is met leads to spherical nanostructures with monomodal hydrodynamic radii distribution in the range of 50-100 nm. The integrity of the electrostatic complexes is disturbed at pH 7 as the net electric charge of Hb is very low. Treating the NPs at mildly elevated temperature stabilizes them against the pH increase taking advantage of Hb's ability of unfolding and self-associating upon thermal treatment. The NPs surface charge is pH-tunable and changes from positive to strongly negative upon pH increase to 7 proving the presence of negative surface patches of Hb and CS segments in their exterior. The α-helix content of Hb does not change significantly by thermal treatment. The NPs are found to bind the bioactive compounds curcumin and β-carotene and are stable in solutions with high salt content. This investigation introduces a straightforward method to formulate Hb in NPs with possibilities in the nanodelivery of nutrients and drugs.

Association and Internal Morphology of Self-Assembled HPPhOx/BSA Hybrid Nanoparticles in Aqueous Solutions

We investigate the formation of hybrid polyelectrolyte/protein nanoparticles by associations between aggregates of partially hydrolyzed poly(2-phenyl-2-oxazoline) (HPPhOx) and bovine serum albumin (BSA) in aqueous solutions. Light scattering experiments show that at conditions of low salt, BSA creates interaggregate bridges and increases the size of the HPPhOx nanoparticles. At high salt contents, breaking of aggregates leads to well-defined nanoparticles. The interior of the formed nanoparticles is probed by small-angle neutron scattering. At low salt, diffuse arrangements are observed, whereas at high salt concentration, scattering is dominated by well-defined hydrophobic domains enhanced by the incorporation of BSA. This system shows that the combination of hydrophobic and electrostatic interactions in random-amphiphilic-polyelectrolyte/protein complexes can be used to determine the properties of self-assembled hybrid multifunctional nanoparticles.

Tuning the solution organization of cationic polymers through interactions with bovine serum albumin

The interactions of bovine serum albumin (BSA) with aggregates of cationic polymers, i.e. quaternized poly(chloromethyl styrene) chains (QIm-PCMS), in aqueous solutions are investigated using small angle neutron scattering on length scales relevant to the size of BSA. The arrangement of the macromolecular chains within their aggregates is consistent with a blob description of overlapping chains that contain hydrophobic domains. The local conformations depend on the salt content as in typical linear polyelectrolytes. Although the hydrophobic content of the cationic polymers does not cause measurable local morphology differences, the interactions with BSA are enhanced in the case of the not fully quaternized polymer. The secondary structure of BSA is critically compromised by the interaction with the quaternized polymers as the signature of the alpha helix conformation is lost. The complexation with BSA and the resulting enhancement of interchain associations on higher length scales are verified using dynamic light scattering experiments. This study demonstrates the ability to tune the polyelectrolyte/protein interactions and polyelectrolyte chain-chain associations by modifying the hydrophobic content of the polyelectrolytes.

Radiation Engineering of Multifunctional Nanogels

Nanogels combine the favourable properties of hydrogels with those of colloids. They can be soft and conformable, stimuli-responsive and highly permeable, and can expose a large surface with functional groups for conjugation to small and large molecules, and even macromolecules. They are among the very few systems that can be generated and used as aqueous dispersions. Nanogels are emerging materials for targeted drug delivery and bio-imaging, but they have also shown potential for water purification and in catalysis. The possibility of manufacturing nanogels with a simple process and at relatively low cost is a key criterion for their continued development and successful application. This paper highlights the most important structural features of nanogels related to their distinctive properties, and briefly presents the most common manufacturing strategies. It then focuses on synthetic approaches that are based on the irradiation of dilute aqueous polymer solutions using high-energy photons or electron beams. The reactions constituting the basis for nanogel formation and the approaches for controlling particle size and functionality are discussed in the context of a qualitative analysis of the kinetics of the various reactions.

Geometrical Characteristics of Polyelectrolyte Nanogel Particles and Their Polyelectrolyte Complexes Studied by Dynamic and Static Light Scattering

The geometric characteristics of nanogel particles in aqueous solutions were studied by determining their ratios of radius of gyration (mean-square radius; Rg) to hydrodynamic radius (Rh), Rg/Rh, derived from static light scattering and dynamic light scattering experiments, respectively. The various nanogel samples studied included ones composed of lightly cross-linked N-isopropylacrylamide (NIPA) polymer, NIPA-based anionic or cationic copolymers, and amphoteric terpolymers. Polyelectrolyte complexes between anionic or cationic nanogels and oppositely charged polyions or nanogels having opposite charges were also studied. Most NIPA and NIPA-based polyelectrolyte nanogels in a swollen state had Rg/Rh values >0.775, which is the theoretically predicted value for a solid sphere. In a collapsed state, one may expect nanogel particles to be spherical in shape; however, this was not the case for a variety of nanogel samples, either with or without charges. These data were consistent with the idea that the surfaces of these nanogel particles were decorated with attached dangling chains. The Rg/Rh data from polyelectrolyte-nanogel complexes, however, indicated different structures from this. It was found that most of the polyelectrolyte-nanogel complex particles had Rg/Rh approximately 0.775. This suggested that the complexed nanogel particles were spherical in shape and that there were no dangling surface chains.

Effect of Shear on Intramolecular and Intermolecular Association during Cross-Linking of Hydroxyethylcellulose in Dilute Aqueous Solutions

Intramolecular and intermolecular associations of dilute aqueous alkali solutions of hydroxyethylcellulose (HEC) in the presence of a chemical cross-linker agent (divinyl sulfone, DVS) are studied with the aid of dynamic light scattering (DLS) and rheological methods. At quiescent state, DLS detected only interchain aggregation of HEC during the cross-linker reaction, and the magnitude and start of this effect depend on the cross-linker concentration. The growth of clusters has been investigated at various stages in the course of the cross-linking process by quenching the reaction mixture to a lower pH. After quenching, no further association of the species occurred. When the dilute reaction mixtures are subjected to shear, intrapolymer cross-linking with contraction of the molecules is observed, and at moderate shear rates this effect is followed by interpolymer cross-linking and the formation of aggregates at longer times. The rate of the growth of the multichain aggregates decreases with increasing shear rate, and at sufficiently high shear rates no cross-linking effect is observed. Depending on the shear rate, the aggregates continue to grow until they reach a certain size where an incipient breakup of interaggregate chains can be observed. The delicate interplay between intramolecular and intermolecular association effects is governed by factors such as the magnitude of the shear rate, polymer concentration, and cross-linker density.