Polymer Microgels: Synthesis and Application

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Chemistry".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 20679

Special Issue Editor

Istituto dei Sistemi Complessi del Consiglio Nazionale delle Ricerche (ISC-CNR), Sede Sapienza, 00185 Roma, Italy
Interests: soft matter; colloids; polymers; structure; dynamics; glasses; gels; experiments; scattering techniques; rheology; calorimetry

Special Issue Information

Dear Colleagues,

Polymer microgels have attracted great attention in fundamental studies as good model systems for understanding the intriguing behaviors of soft colloids thanks to their elastic and deformable particles that provide a very rich phenomenology. These cross-linked particles with nanometric to micrometric dimensions are characterized by many fascinating properties such as swelling, softness, and responsivity that depend on their macromolecular architecture and can be triggered during the synthesis process. Moreover, they are highly attractive systems for several technological applications due to their high sensitivity to external stimuli. Smart microgels have indeed many applications in the pharmaceutics industries, in artificial organs, tissue engineering, agriculture, construction, and cosmetics.

This Special Issue focuses on experiments, simulation, synthesis methods, and applications of homopolymeric, interpenetrating polymer network (IPN), copolymerized, and core-shell microgels. The topics may include local structure, phase diagrams, interparticle interactions, and synthesis methods besides the manifold applications.

Both original contributions and reviews are welcome.

Dr. Roberta Angelini
Guest Editor

Manuscript Submission Information

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Keywords

  • Microgels
  • Polymers
  • Crosslinking
  • Colloids
  • Stimuli-responsive
  • Synthesis
  • Swelling
  • PNIPAM
  • Core-shell
  • Interpenetrated networks
  • Rheology
  • Scattering
  • Drug delivery
  • Tissue engineering
  • Sensors

Published Papers (6 papers)

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Research

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17 pages, 2964 KiB  
Article
Thermal Behaviour of Microgels Composed of Interpenetrating Polymer Networks of Poly(N-isopropylacrylamide) and Poly(acrylic acid): A Calorimetric Study
by Silvia Franco, Elena Buratti, Valentina Nigro, Monica Bertoldo, Barbara Ruzicka and Roberta Angelini
Polymers 2022, 14(1), 115; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14010115 - 29 Dec 2021
Cited by 3 | Viewed by 2131
Abstract
Stimuli-responsive microgels have recently attracted great attention in fundamental research as their soft particles can be deformed and compressed at high packing fractions resulting in singular phase behaviours. Moreover, they are also well suited for a wide variety of applications such as drug [...] Read more.
Stimuli-responsive microgels have recently attracted great attention in fundamental research as their soft particles can be deformed and compressed at high packing fractions resulting in singular phase behaviours. Moreover, they are also well suited for a wide variety of applications such as drug delivery, tissue engineering, organ-on-chip devices, microlenses fabrication and cultural heritage. Here, thermoresponsive and pH-sensitive cross-linked microgels, composed of interpenetrating polymer networks of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAAc), are synthesized by a precipitation polymerization method in water and investigated through differential scanning calorimetry in a temperature range across the volume phase transition temperature of PNIPAM microgels. The phase behaviour is studied as a function of heating/cooling rate, concentration, pH and PAAc content. At low concentrations and PAAc contents, the network interpenetration does not affect the transition temperature typical of PNIPAM microgel in agreement with previous studies; on the contrary, we show that it induces a marked decrease at higher concentrations. DSC analysis also reveals an increase of the overall calorimetric enthalpy with increasing concentration and a decrease with increasing PAAc content. These findings are discussed and explained as related to emerging aggregation processes that can be finely controlled by properly changing concentration, PAAc content an pH. A deep analysis of the thermodynamic parameters allows to draw a temperature–concentration state diagram in the investigated concentration range. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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26 pages, 2138 KiB  
Article
The Double-Faced Electrostatic Behavior of PNIPAm Microgels
by Simona Sennato, Edouard Chauveau, Stefano Casciardi, Federico Bordi and Domenico Truzzolillo
Polymers 2021, 13(7), 1153; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13071153 - 04 Apr 2021
Cited by 17 | Viewed by 3220
Abstract
PNIPAm microgels synthesized via free radical polymerization (FRP) are often considered as neutral colloids in aqueous media, although it is well known, since the pioneering works of Pelton and coworkers, that the vanishing electrophoretic mobility characterizing swollen microgels largely increases above the lower [...] Read more.
PNIPAm microgels synthesized via free radical polymerization (FRP) are often considered as neutral colloids in aqueous media, although it is well known, since the pioneering works of Pelton and coworkers, that the vanishing electrophoretic mobility characterizing swollen microgels largely increases above the lower critical solution temperature (LCST) of PNIPAm, at which microgels partially collapse. The presence of an electric charge has been attributed to the ionic initiators that are employed when FRP is performed in water and that stay anchored to microgel particles. Combining dynamic light scattering (DLS), electrophoresis, transmission electron microscopy (TEM) and atomic force microscopy (AFM) experiments, we show that collapsed ionic PNIPAm microgels undergo large mobility reversal and reentrant condensation when they are co-suspended with oppositely charged polyelectrolytes (PE) or nanoparticles (NP), while their stability remains unaffected by PE or NP addition at lower temperatures, where microgels are swollen and their charge density is low. Our results highlight a somehow double-faced electrostatic behavior of PNIPAm microgels due to their tunable charge density: they behave as quasi-neutral colloids at temperature below LCST, while they strongly interact with oppositely charged species when they are in their collapsed state. The very similar phenomenology encountered when microgels are surrounded by polylysine chains and silica nanoparticles points to the general character of this twofold behavior of PNIPAm-based colloids in water. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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15 pages, 8937 KiB  
Article
Microstructured Macromaterials Based on IPN Microgels
by Irina Rashitovna Nasimova, Vladimir Yurievich Rudyak, Anton Pavlovich Doroganov, Elena Petrovna Kharitonova and Elena Yurievna Kozhunova
Polymers 2021, 13(7), 1078; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13071078 - 29 Mar 2021
Cited by 8 | Viewed by 2669
Abstract
This study investigates the formation of microstructured macromaterials from thermo- and pH-sensitive microgels based on interpenetrating networks of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA). Macromaterials are produced as a result of the deposition of microgel particles and subsequent crosslinking of polyacrylic acid subnetworks [...] Read more.
This study investigates the formation of microstructured macromaterials from thermo- and pH-sensitive microgels based on interpenetrating networks of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA). Macromaterials are produced as a result of the deposition of microgel particles and subsequent crosslinking of polyacrylic acid subnetworks to each other due to the formation of the anhydride bonds during annealing. Since both PNIPAM and PAA are environment-sensitive polymers, one can expect that their conformational state during material development will affect its resulting properties. Thus, the influence of conditions of preparation for annealing (pH of the solution, the temperature of preliminary drying) on the swelling behavior, pH- and thermosensitivity, and macromaterial inner structure was investigated. In parallel, the study of the effect of the relative conformations of the IPN microgel subnetworks on the formation of macromaterials was carried out by the computer simulations method. It was shown that the properties of the prepared macromaterials strongly depend both on the temperature and pH of the PNIPAM-PAA IPN microgel dispersions. This opens up new opportunities to obtain materials with pre-chosen characteristics and environmental sensitivity. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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17 pages, 4666 KiB  
Article
Importance of pH in Synthesis of pH-Responsive Cationic Nano- and Microgels
by Marco Annegarn, Maxim Dirksen and Thomas Hellweg
Polymers 2021, 13(5), 827; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13050827 - 08 Mar 2021
Cited by 18 | Viewed by 3669
Abstract
While cationic microgels are potentially useful for the transfection or transformation of cells, their synthesis has certain drawbacks regarding size, polydispersity, yield, and incorporation of the cationic comonomers. In this work, a range of poly(N-isopropylacrylamide) (PNIPAM) microgels with different amounts of [...] Read more.
While cationic microgels are potentially useful for the transfection or transformation of cells, their synthesis has certain drawbacks regarding size, polydispersity, yield, and incorporation of the cationic comonomers. In this work, a range of poly(N-isopropylacrylamide) (PNIPAM) microgels with different amounts of the primary amine N-(3-aminopropyl)methacrylamide hydrochloride (APMH) as the cationic comonomer were synthesized. Moreover, the pH-value during reaction was varied for the synthesis of microgels with 10 mol% APMH-feed. The microgels were analyzed by means of their size, thermoresponsive swelling behavior, synthesis yield, polydispersity and APMH-incorporation. The copolymerization of APMH leads to a strong decrease in size and yield of the microgels, while less than one third of the nominal APMH monomer feed is incorporated into the microgels. With an increase of the reaction pH up to 9.5, the negative effects of APMH copolymerization were significantly reduced. Above this pH, synthesis was not feasible due to aggregation. The results show that the reaction pH has a strong influence on the synthesis of pH-responsive cationic microgels and therefore it can be used to tailor the microgel properties. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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Review

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11 pages, 1378 KiB  
Review
How Microgels Can Improve the Impact of Organ-on-Chip and Microfluidic Devices for 3D Culture: Compartmentalization, Single Cell Encapsulation and Control on Cell Fate
by Simona Argentiere, Pietro Aleardo Siciliano and Laura Blasi
Polymers 2021, 13(19), 3216; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13193216 - 23 Sep 2021
Cited by 10 | Viewed by 3473
Abstract
The Organ-on-chip (OOC) devices represent the new frontier in biomedical research to produce micro-organoids and tissues for drug testing and regenerative medicine. The development of such miniaturized models requires the 3D culture of multiple cell types in a highly controlled microenvironment, opening new [...] Read more.
The Organ-on-chip (OOC) devices represent the new frontier in biomedical research to produce micro-organoids and tissues for drug testing and regenerative medicine. The development of such miniaturized models requires the 3D culture of multiple cell types in a highly controlled microenvironment, opening new challenges in reproducing the extracellular matrix (ECM) experienced by cells in vivo. In this regard, cell-laden microgels (CLMs) represent a promising tool for 3D cell culturing and on-chip generation of micro-organs. The engineering of hydrogel matrix with properly balanced biochemical and biophysical cues enables the formation of tunable 3D cellular microenvironments and long-term in vitro cultures. This focused review provides an overview of the most recent applications of CLMs in microfluidic devices for organoids formation, highlighting microgels’ roles in OOC development as well as insights into future research. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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25 pages, 4686 KiB  
Review
Chemical-Physical Behaviour of Microgels Made of Interpenetrating Polymer Networks of PNIPAM and Poly(acrylic Acid)
by Valentina Nigro, Roberta Angelini, Monica Bertoldo, Elena Buratti, Silvia Franco and Barbara Ruzicka
Polymers 2021, 13(9), 1353; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13091353 - 21 Apr 2021
Cited by 16 | Viewed by 3779
Abstract
Microgels composed of stimuli responsive polymers have attracted worthwhile interest as model colloids for theorethical and experimental studies and for nanotechnological applications. A deep knowledge of their behaviour is fundamental for the design of new materials. Here we report the current understanding of [...] Read more.
Microgels composed of stimuli responsive polymers have attracted worthwhile interest as model colloids for theorethical and experimental studies and for nanotechnological applications. A deep knowledge of their behaviour is fundamental for the design of new materials. Here we report the current understanding of a dual responsive microgel composed of poly(N-isopropylacrylamide) (PNIPAM), a temperature sensitive polymer, and poly(acrylic acid) (PAAc), a pH sensitive polymer, at different temperatures, PAAc contents, concentrations, solvents and pH. The combination of multiple techniques as Dynamic Light Scattering (DLS), Raman spectroscopy, Small Angle Neutron Scattering (SANS), rheology and electrophoretic measurements allow to investigate the hydrodynamic radius behaviour across the typical Volume Phase Transition (VPT), the involved molecular mechanism and the internal particle structure together with the viscoelastic properties and the role of ionic charge in the aggregation phenomena. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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