Stimuli-responsive nanoparticles, nanogels and capsules for integrated multifunctional intelligent systems

Water-soluble block copolymers were prepared from the nonionic monomer N-isopropylacrylamide (NIPA) and the zwitterionic monomer 3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulfonate (SPP) by sequential free radical polymerization via the RAFT process. Such block copolymers with two hydrophilic blocks exhibit double thermoresponsive behavior in water: the poly-NIPA block shows a lower critical solution temperature, whereas the poly-SPP block exhibits an upper critical solution temperature. Appropriate design of the block lengths leads to block copolymers which stay in solution in the full temperature range between 0 and 100 degrees C. Both blocks of these polymers dissolve in water at intermediate temperatures, whereas at high temperatures, the poly-NIPA block forms colloidal hydrophobic associates that are kept in solution by the poly-SPP block, and at low temperatures, the poly-SPP block forms colloidal polar aggregates that are kept in solution by the poly-NIPA block. In this way, colloidal aggregates which switch reversibly can be prepared in water, and without any additive, their "inside" to the "outside", and vice versa. The aggregates provide microdomains and surfaces of different character, which can be controlled by a simple thermal stimulus.

Switching the inside and the outside of aggregates of water-soluble block copolymers with double thermoresponsivity

http://www.plasmachem.com/download/2004_Review_Antipov_Sukhorukov.pdf

Polyelectrolyte multilayer capsules as vehicles with tunable permeability.

“Smart” nanoparticles: Preparation, characterization and applications

Thermoresponsive polymers hold great potential in the biomedical field, since they enable the fabrication of cell sheets, in situ drug delivery and 3D-printing under physiological conditions. In this review we provide an overview of several thermoresponsive polymers and their application, with focus on poly(N-isopropylacrylamide)-surfaces for cell sheet engineering. Basic knowledge of important processes like protein adsorption on surfaces and cell adhesion is provided. For different thermoresponsive polymers, namely PNIPAm, Pluronics, elastin-like polypeptides (ELP) and poly(N-vinylcaprolactam) (PNVCL), synthesis and basic chemical and physical properties have been described and the mechanism of their thermoresponsive behavior highlighted. Fabrication methods of thermoresponsive surfaces have been discussed, focusing on PNIPAm, and describing several methods in detail. The latter part of this review is dedicated to the application of the thermoresponsive polymers and with regard to cell sheet engineering, the process of temperature-dependent cell sheet detachment is explained. We provide insight into several applications of PNIPAm surfaces in cell sheet engineering. For Pluronics, ELP and PNVCL we show their application in the field of drug delivery and tissue engineering. We conclude, that research of thermoresponsive polymers has made big progress in recent years, especially for PNIPAm since the 1990s. However, manifold research possibilities, e.g. in surface fabrication and 3D-printing and further translational applications are conceivable in near future.

/pdf/thermoresponsive-polymers-and-their-biomedical-application-1wagzuy3hq.pdf

Thermoresponsive polymers and their biomedical application in tissue engineering – a review

The phase transition of the thermoreversible polymer PNIPAM, which shows a coil-to-globule transition due to the lower critical solution temperature (LCST) behavior in aqueous solution, is investigated in the restricted geometry of an adsorption layer. Furthermore, a charged copolymer is studied to investigate the influence of charges on the phase transition. Both polymers are adsorbed to colloidal silica and studied by 1H NMR and differential scanning calorimetric (DSC) experiments. In solid state 1H NMR relaxation experiments the signals of solid spins in trains and of liquid spins in tails and loops can be identified. 1H liquid state spectra detect the phase transition of the loops and tails into immobile segments with increasing temperature. The transition is broadened as compared to the polymer in solution, especially at low surface coverage. For the copolymer, the transition is incomplete, since mobile segments remain even at high temperature. They are attributed to electrostatic repulsion from the ...

Thermoreversible polymers adsorbed to colloidal silica : a 1H NMR and DSC study of the phase transition in confined geometry

1H NMR of thermoreversible polymers in solution and at interfaces: the influence of charged groups on the phase transition

A large number of different NMR methods are of great usefulness in the investigation of molecular mobility in organic bulk systems, while studies at interfaces are rare owing to the low intrinsic sensitivity of NMR methods. This article presents two examples of the application of spin resonance in investigations of polymers at interfaces, employing polymer-coated colloids: Applying 1H liquid-state NMR to monitor segmental mobility, the phase transition of the ther-moreversible polymer poly(N-isopropylacrylamide) is investigated in the restricted geometry of an adsorption layer, and furthermore under the influence of charges in a statistical copolymer. The phase transition is substantially broader than in solution and for the charged copolymer, mobile segments remain even above the transition temperature. This is attributed to a comparatively mobile arrangement of the copolymer layer. Owing to the electrostatic repulsion from the surface, the copolymer layer is confined to a configuration with charged loops extending further from the interface. The second example concerns polyelectrolyte multilayers formed by self-assembly of polyanions and polycations onto colloidal particles. The hydration of the layer system is studied using 1H spin-relaxation rates, R2, of water, which are a measure for the immobilisation of water molecules in the multilayers. A linear increase in R 2 with the number of layers is found for [poly(sodium 4-styrenesulfate)/ poly(diallyl dimethyl ammonium chloride)]N, reflecting a constant increase in the amount of hydration water with the adsorption of each layer. For [poly(sodium 4-styrene-sulfate)/poly(allylamine hydrochlo-ride)]N, involving a weak polyelectrolyte, the data show reversible swelling behaviour with respect to the electric potential of the outer layer: A positive surface charge leads to a swelling of the multilayers, while owing to a negative surface charge deswelling occurs.

https://uni-muenster.de/imperia/md/content/physikalische_chemie/schoenhoff/pcps_02.pdf

Dynamics in polymer layers investigated by NMR techniques

Phase Transition in Confined Geometry

The thermoreversible polymer Poly-N-isopropylacrylamide (PNIPAM) shows a coil to globule transition at 32°C in solution. We address the question of whether charged groups in the polymer are affecting the phase transition, and study their influence in solution and at the interface.

1H-NMR-Investigation of the Phase Transition of Thermo-Reversible Polymers in Solution and at Interfaces

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