Coro Echeverria

Effect of Gold Nanoparticles on the Thermosensitivity, Morphology, and Optical Properties of Poly(acrylamide–acrylic acid) Microgels

Novel positive thermosensitive microgels of poly(acrylamide-acrylic acid) with embedded gold nanoparticles have been synthesized and characterized by means of dynamic light scattering, UV-vis spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These systems show temperature (upper critical solution temperature-like volume phase transition) and optical responsiveness making them externally triggered systems.

Novel strategy for the determination of UCST-like microgels network structure: effect on swelling behavior and rheology

UCST-type interpenetrated and random copolymer microgels of polyacrylamide and poly(acrylic acid) were obtained via inverse emulsion polymerization method. The morphology of the microgels was determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Dynamic light scattering was used to study both the swelling behavior as a function of temperature and pH and the particle size distribution of the system. Concerning the structural characterization, a combination of the equilibrium swelling theory (Peppas–Merrill equation) and AFM technique was used to determine the mesh size of microgels. An oscillatory rheometer was used to study the viscoelastic properties. The moduli, G′ and G′′, of the microgel dispersions suggested a solid-like behaviour and structure formation. Scaling theory was applied to describe the structure formation (clustering) and the fractal dimension. The influence of composition and type of microgel, random or interpenetrated, was discussed in the above mentioned properties and behaviors.

Towards the development of multifunctional hybrid fibrillary gels: production and optimization by colloidal electrospinning

The incorporation of thermosensitive microgels that can act as active sites into polymeric fibers through colloidal electrospinning originates multifunctional, highly porous, and biocompatible membranes suitable for biomedical applications. The use of polyvinylpyrrolidone (PVP), a biocompatible, water-soluble polymer as a fiber template, not only allows the use of a simple set-up to produce composite membranes, but also avoids the use of organic solvents to prepare such systems. Further crosslinking with ultraviolet (UV) radiation avoids membrane dissolution in physiological conditions. Highly porous, UV crosslinked composite membranes with monodisperse mean fiber diameters around 530 nm were successfully produced. These composite membranes showed a Young Modulus of 22 MPa, and an ultimate tensile strength of 3 MPa, accessed in the mechanical tests. Furthermore, the same composite membranes were able to swell about 30 times their weight after 1 hour in aqueous medium. In this work composite multifunctional membranes were designed and extensively studied. PVP, a biocompatible water-soluble polymer, was used as a fiber template to incorporate thermoresponsive poly-(N-isopropylacrylamide) (PNIPAAm)-based microgels into the composite membrane using colloidal electrospinning. The design of multifunctional membranes can be further tailored to several biomedical applications such as temperature-controlled drug delivery systems.

Confinement of thermoresponsive microgels into fibres via colloidal electrospinning: experimental and statistical analysis

The strategy of confining stimuli-responsive microgels in electrospun fibres would allow the fabrication of polymeric networks that combine the microgels swelling ability and properties with the interest features of the electrospun fibres. Colloidal electrospinning is an emerging method in which fibres containing microgels can be produced by a single-nozzle and designed through the solution carrier materials. The incorporation of poly(N-isopropylacrylamide) (PNIPAAM) and PNIPAAM–chitosan (PNIPAAM–CS) in poly(ethyleneoxyde) (PEO) fibres via colloidal electrospinning producing composite fibres was the main purpose of the present work, which was confirmed by means of Scanning Electron Microscopy (SEM). Dynamic light scattering was used to analyse the microgels hydrodynamic diameter ranging up to 900 nm depending on the composition and temperature of the surrounding medium. By performing a statistical analysis the relationship of the processing variables over the fibre size was evaluated following the response surface methodology (RSM). From the set of parameters aimed to minimize the fibre diameter, composite fibres with an average diameter of 63 nm were produced. Only the as-prepared microgels with higher monodispersity provided “bead-on-a-string” morphologies.

Functional Stimuli-Responsive Gels: Hydrogels and Microgels

One strategy that has gained much attention in the last decades is the understanding and further mimicking of structures and behaviours found in nature, as inspiration to develop materials with additional functionalities. This review presents recent advances in stimuli-responsive gels with emphasis on functional hydrogels and microgels. The first part of the review highlights the high impact of stimuli-responsive hydrogels in materials science. From macro to micro scale, the review also collects the most recent studies on the preparation of hybrid polymeric microgels composed of a nanoparticle (able to respond to external stimuli), encapsulated or grown into a stimuli-responsive matrix (microgel). This combination gave rise to interesting multi-responsive functional microgels and paved a new path for the preparation of multi-stimuli “smart” systems. Finally, special attention is focused on a new generation of functional stimuli-responsive polymer hydrogels able to self-shape (shape-memory) and/or self-repair. This last functionality could be considered as the closing loop for smart polymeric gels.