Nanogels and Microgels: From Model Colloids to Applications, Recent Developments, and Future Trends

Abstract

Nanogels and microgels are soft, deformable, and penetrable objects with an internal gel-like structure that is swollen by the dispersing solvent. Their softness and the potential to respond to external stimuli like temperature, pressure, pH, ionic strength, and different analytes make them interesting as soft model systems in fundamental research as well as for a broad range of applications, in particular in the field of biological applications. Recent tremendous developments in their synthesis open access to systems with complex architectures and compositions allowing for tailoring microgels with specific properties. At the same time state-of-the-art theoretical and simulation approaches offer deeper understanding of the behavior and structure of nano- and microgels under external influences and confinement at interfaces or at high volume fractions. Developments in the experimental analysis of nano- and microgels have become particularly important for structural investigations covering a broad range of length scales relevant to the internal structure, the overall size and shape, and interparticle interactions in concentrated samples. Here we provide an overview of the state-of-the-art, recent developments as well as emerging trends in the field of nano- and microgels. The following aspects build the focus of our discussion: tailoring (multi)­functionality through synthesis; the role in biological and biomedical applications; the structure and properties as a model system, e.g., for densely packed arrangements in bulk and at interfaces; as well as the theory and computer simulation.

Recent advances in stimuli-responsive core-shell microgel particles: synthesis, characterisation, and applications

“…A lot of these publications deal with smart microgels. Microgels are fascinating materials because they are able to respond to changes of external parameters like temperature, pH, ionic strength, or external fields by changing their state of swelling [2][3][4]. This makes them interesting for applications in sensors [5], optics, and colloidal crystals [6][7][8].…”

Resolving the internal morphology of core–shell microgels with super-resolution fluorescence microscopy

“…Smart micro-and nanogels respond to an external stimulus, such as temperature or pH, with a change in size and therefore network morphology. [1][2][3][4] For the most widely studied system based on N-isopropylacrylamide (NIPAM) crosslinked with N,N 0methylenebisacrylamide the polymer changes from a swollen network at temperatures below the so-called volume phase transition temperature (VPTT) to a collapsed particle above the VPTT ($33 C for NIPAM based microgels in water). This property grants such microgels the label "smart" and is the reason for the steadily growing interest in these systems.…”

“…This property grants such microgels the label "smart" and is the reason for the steadily growing interest in these systems. 4 Microgels can be used for drug delivery, 5,6 in sensors 7,8 or as surface coatings, e.g. for vertebrate cell culture applications.…”

Thermo-responsive plasmonic systems: old materials with new applications

“…This has been studied since the late 1990s, and is still actively investigated ( Fig. 1) for different applications, 25 such as sensing, 26 catalysis, 27,28 drug delivery, 29 tissue engineering, 30 articial muscles, 31 etc.…”