Novel temperature- and pH-responsive microgels based on poly(vinylcaprolactam-co-acetoacetoxy methacrylate) (VCL/AAEM) functionalized with vinylimidazole (VIm) has been prepared in aqueous medium using simple batch dispersion polymerization procedure. Obtained microgel particles are characterized by narrow particle size distribution and their hydrodynamic radius can be varied from 200 to 500 nm (pH = 6, T = 20 °C). The T- and pH-sensitivity of obtained particles can be easily tuned by the variation of the Vim content in the copolymer structure. Increase of VIm content in the microgel structure led to increased swelling of the microgels in acidic medium and strong shift of the volume phase transition temperature to higher temperatures. It has been found that sedimentation behavior of obtained microgels is strongly pH-dependent, and this effect can be used for controlled particle separation.

We demonstrate a simple route for the preparation of novel hybrid particles with multiple sensitivities. Aqueous polymeric microgels are modified by magnetite nanoparticles in the preparation of temperature- and pH-sensitive hybrids with a high magnetic response. Up to 15 wt % of magnetite nanoparticles are loaded into microgels. The influence of the amount of magnetite in the microgel structure on the morphology and colloidal properties is discussed. The presence of the magnetite nanoparticles in the microgel decreases its degree of swelling and shifts the volume phase-transition temperature to higher values. Nanostructured composite films with controlled morphologies can be prepared by water evaporation and deposition of the hybrid microgels on a solid substrate.

This work concerns interfacial adsorption and attachment of swollen microgel with low- to medium-level cross-linking density. Compared to colloids that form a second, dispersed phase, the suspended swollen microgel particles are ultrahigh molecular weight molecules, which are dissolved like a linear polymer, so that solvent and solute constitute only one phase. In contrast to recent literature in which microgels are treated as particles with a distinct surface, we consider solvent-solute interaction as well as interfacial adsorption based on the chain segments that can form trains of adsorbed segments and loops protruding from the surface into the solvent. We point out experimental results that support this discrimination between particles and microgels. The time needed for swollen microgels to adsorb at the air/water interface can be 3 orders of magnitude shorter than that for dispersed particles and decreases with decreasing cross-linking density. Detailed analysis of the microgels deformation, in the dry state, at a solid surface enabled discrimination particle like microgel in which case spreading was controlled predominantly by the elasticity and molecule like adsorption characterized by a significant overstreching, ultimately leading to chain scission of microgel strands. Dissipative particle dynamics simulations confirms the experimental findings on the interfacial activity and spreading of microgel at liquid/air interface.

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b S Supporting Information ' INTRODUCTIONMaterials of micro/nanosize dimensions often show unique characteristics which are not expected from the bulk. For this reason, studies on such micro/nanomaterials are attracting a lot of attention and are widely extending into diverse fields of science and technology. In this way, when focusing into the polymer area, microgels are currently becoming the focus of considerable scientific studies.Microgel particles are cross-linked polymeric particles with dimensions in the colloidal range. A promising feature deriving from their microsize is their rather fast capability to swell compared to the macroscopic gels. This is one of the reasons why these materials have generated an increasing interest in the past decades, particularly stimulus-responsive microgels. These microgels are able to alter their volume and properties in response to external stimuli, such as pH, temperature, pressure, and ionic strength. This fact proved them to be attractive candidates for many potential applications including drug delivery, biosensing, or separation techniques. 1,2 Special interest is focused on the hydrogels based on polymers, which have a lower critical solution temperature (LCST) near the temperature of the human body. The temperature-responsive nature of these polymers leads to a variety of biological applications. Hydrogels made from these polymers have been considered as drug delivery devices, materials for tissue engineering, and materials for preventing surgical adhesion. Poly(Nisopropylacrilamide) (PNIPAAm) is the most widely studied hydrogel and has a LCST of 34°C (ref 3 and references therein). Our systems are based on poly(N-vinylcaprolactam) (PVCL), which also has the LCST in the physiological range of around 32°C. It is biocompatible and materials based on this polymer can be potentially used in biomedical applications.The attempts to determine the structure of aqueous microgel particles have been reported in the literature. Wu and Pelton 4 reported that during the formation of poly(NIPAM) particles by precipitation polymerization the cross-linking agent (bis-(acrylamide)) was consumed faster compared to NIPAM and therefore preferentially incorporated into microgels. Because of the fact that poly(NIPAM) or poly(VCL) microgel particles are prepared at above the LCST of the linear polymer, it is believed that the core regions of the final particles contain a relatively higher amount of the monomers consumed in the early ABSTRACT: The Flory temperature-induced volume transition theory for homopolymer microgels was generalized for the case of bimodal heterogeneous morphology. The most probable morphological parameters were selected from the microscopic and thermodynamic constraints imposed by 1 H transverse relaxation NMR and Flory equation of state in the approximation of a homogeneous morphology. Proton transverse magnetization relaxation NMR proved directly the existence of a bimodal heterogeneous morphology of the PVCL microgel particle. The volume polymer fractions in the...

We report synthesis of amphoteric microgels by copolymerization of N-vinylcaprolactam (VCL), itaconic acid dimethyl ester (IADME), and vinylimidazole (VIm) in the precipitation−polymerization process. After hydrolysis of ester groups of IADME, component microgels contain acidic and basic groups in their structure. Proton high-resolution transverse magnetization relaxation under magic angle sample spinning (MAS) was used to measure the dynamic heterogeneity corroborated with the chemical structure of a multicomponent amphoteric microgel. NMR results indicate that itaconic acid groups (originated from hydrolyzed IADME component) are localized mostly in the microgel core. The core−shell morphology of poly(N-vinylcaprolactam)-based microgels was suggested with carboxylic acid groups in the core and imidazole groups in the shell. The variation of the IADME and VIm content in microgel structure allows varying microgel charge and swelling degree in basic and acidic pH, respectively. Obtained amphoteric microgels exhibit narrow size distribution and superior colloidal stability.

In the present paper, we report the preparation of hybrid temperature-sensitive microgels which include magnetite nanoparticles in their structure. Polymeric microgels have been prepared by surfactant-free emulsion copolymerization of acetoacetoxyethyl methacrylate (AAEM) and N-vinylcaprolactam (VCL) in water with a water-soluble azo-initiator. The obtained microgels possess a low critical solution temperature (LCST) in water solutions, with a rapid decrease of the particle size being observed at elevated temperatures. Magnetite was deposited directly into microgels, leading to the formation of composite particles which combine both temperature-sensitive and magnetic properties. The influence of magnetite load on microgel size, morphology, swelling-deswelling behavior, and stability is discussed.

Efficient and safe drug delivery across the blood-brain barrier (BBB) remains to be one of the major challenges of biomedical and (nano-) pharmaceutical research. Here, we show that poly(butyl cyanoacrylate)-based microbubbles (MB), carrying ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles within their shell, can be used to mediate and monitor BBB permeation. Upon exposure to transcranial ultrasound pulses, USPIO-MB are destroyed, resulting in acoustic forces inducing vessel permeability. At the same time, USPIO are released from the MB shell, they extravasate across the permeabilized BBB and they accumulate in extravascular brain tissue, thereby providing non-invasive R*-based magnetic resonance imaging information on the extent of BBB opening. Quantitative changes in R* relaxometry were in good agreement with 2D and 3D microscopy results on the extravascular deposition of the macromolecular model drug FITC-dextran into the brain. Such theranostic materials and methods are considered to be useful for mediating and monitoring drug delivery across the BBB, and for enabling safe and efficient treatment of CNS disorders.