Functional Microgels: Recent Advances in Their Biomedical Applications

MicroLOCK: Highly stable microgel biosensor using locked nucleic acids as bioreceptors for sensitive and selective detection of let-7a

Chemically modified oligonucleotides can solve biosensing issues for the development of capture probes, antisense, CRISPR/Cas, and siRNA, by enhancing their duplex-forming ability, their stability against enzymatic degradation, and their specificity for targets with high sequence similarity as microRNA families. However, the use of modified oligonucleotides such as locked nucleic acids (LNA) for biosensors is still limited by hurdles in design and from performances on the material interface. Here we developed a fluorogenic biosensor for non-coding RNAs, represented by polymeric PEG microgels conjugated with molecular beacons (MB) modified with locked nucleic acids (MicroLOCK). By 3D modeling and computational analysis, we designed molecular beacons (MB) inserting spot-on LNAs for high specificity among targets with high sequence similarity (95%). MicroLOCK can reversibly detect microRNA targets in a tiny amount of biological sample (2 μL) at 25 °C with a higher sensitivity (LOD 1.3 fM) without any reverse transcription or amplification. MicroLOCK can hybridize the target with fast kinetic (about 30 min), high duplex stability without interferences from the polymer interface, showing high signal-to-noise ratio (up to S/N = 7.3). MicroLOCK also demonstrated excellent resistance to highly nuclease-rich environments, in real samples. These findings represent a great breakthrough for using the LNA in developing low-cost biosensing approaches and can be applied not only for nucleic acids and protein detection but also for real-time imaging and quantitative assessment of gene targeting both in vitro and in vivo.

Influence of a Solid Surface on PNIPAM Microgel Films

Stimuli-responsive microgels have attracted great interest in recent years as building blocks for fabricating smart surfaces with many technological applications. In particular, PNIPAM microgels are promising candidates for creating thermo-responsive scaffolds to control cell growth and detachment via temperature stimuli. In this framework, understanding the influence of the solid substrate is critical for tailoring microgel coatings to specific applications. The surface modification of the substrate is a winning strategy used to manage microgel-substrate interactions. To control the spreading of microgel particles on a solid surface, glass substrates are coated with a PEI or an APTES layer to improve surface hydrophobicity and add positive charges on the interface. A systematic investigation of PNIPAM microgels spin-coated through a double-step deposition protocol on pristine glass and on functionalised glasses was performed by combining wettability measurements and Atomic Force Microscopy. The greater flattening of microgel particles on less hydrophilic substrates can be explained as a consequence of the reduced shielding of the water-substrate interactions that favors electrostatic interactions between microgels and the substrate. This approach allows the yielding of effective control on microgel coatings that will help to unlock new possibilities for their application in biomedical devices, sensors, or responsive surfaces.

Nanogels with Metal-Organic Cages as Functional Crosslinks

A dinuclear metal-organic cage with four acrylate side chains was prepared by self-assembly. Precipitation polymerization of the cage with N-isopropylacrylamide yielded a thermoresponsive nanogel. The host properties of the cage were retained within the gel matrix, endowing the nanogel with the capability to serve as a sorbent for chloride ions in water. Moreover, a heteroleptic cage with the drug abiraterone as co-ligand was integrated into a nanogel. The addition of chloride ions induced a structural rearrangement of the metal-ligand assembly, resulting in the gradual release of abiraterone.

Synthesis and characterization of thermosensitive 2-hydroxypropyl-trimethylammonium chitin and its antibacterial sponge for noncompressible hemostasis and tissue regeneration

Noncompressible hemorrhage is a leading cause of preventable death in battlefield/civilian trauma. The development of novel injectable and biodegradable hemostatic sponges, with rapid shape recovery and excellent antibacterial activity that can control hemorrhage in noncompressible bleeding sites and promote in situ tissue regeneration is still urgently needed. In this study, thermo/pH sensitive 2-hydroxypropyl-trimethylammonium chitins (QCHs) with low degree of quaternization substitution (DS: 0.07-0.23) and high degree of acetylation (DA: 0.91-0.94) were synthesized homogeneously for the first time. Their chemical compositions including DS and DA were characterized accurately by proton NMR for the first time. High strength QCH based sponges with good water/blood absorbency, rapid shape recovery and good antibacterial activity were prepared without using any crosslinkers but only due to their thermosensitive property, since they are soluble at low temperature but insoluble at high temperature. Compared with commercial products, the QCH sponges with cationic groups had the stronger pro-coagulant ability, better hemostatic effect in normal/heparinized liver perforation and femoral artery models in rats and porcine subclavian arteriovenous resection model. Moreover, the porous structure and biodegradability of the QCH sponges could promote in situ tissue regeneration. Overall, the QCH sponges show great clinical translational potential for noncompressible hemorrhage and tissue regeneration.

Production of letrozole-loaded alginate oxide-gelatin microgels using microfluidic systems for drug delivery applications

Microfluidic systems are capable of producing microgels with a monodisperse size distribution and a spherical shape due to their laminar flow and superior flow. A significant challenge in producing these drug-carrying microgels is simultaneous drug loading into microgels. Various factors such as the type of polymer, the type of drug, the volume ratio of the drug to the polymer, and the geometry of the microfluidic system used to generate microgels can effectively address these challenges. The overall goal of this study was to produce mono-disperse drug-carrying microgels capable of controlled drug release. To achieve this goal, this study used a stream-focused microfluidic chip containing a coating current to prevent chip clogging. Alginate oxide was synthesized with a 30 % oxidation percentage. Alginate oxide, gelatin, and compositions of them with volume ratios of 50-50, 70-30, and 30-70, by determining their appropriate weight percentage, were used for the controlled release of letrozole. The properties of the produced microgels were measured through various tests such as drug release test, loading percentage, SEM, FTIR, swelling ratio, and dimensional stability. It was found that microgels made of a combination of alginate oxide-gelatin with volume ratios of 70-30 had a good swelling ratio and structural stability. The drug loading percentages for alginate, alginate oxide, and alginate oxide-gelatin with volume ratios of 50-50 and 30-70, respectively, were 56 %, 68 %, and 66 %, 61 % and the alginate oxide-gelatin with a volume ratio of 70-30 compared to other samples had over 70 % drug loading percentages. Furthermore, samples of alginate, alginate oxide, and alginate oxide-gelatin with volume ratios of 50-50 and 30-70 had 94 %, 63 %, 56 %, and 68 % drug release in 13 days, respectively. However, alginate oxide-gelatin with a volume ratio of 70-30 had a release rate of about 50 % in 13 days, which is a more controlled release for letrozole compared to the volume ratios of 50-50 and 30-70. Examining the drug release profile, it was concluded that drug release follows the Higuchi model and therefore follows Fick's first law of diffusion. It can be concluded that the combination of alginate oxide-gelatin produces more suitable microgels than alginate and alginate oxide for the controlled-release of letrozole. A comparison of microgels of alginate oxide and gelatin with volume ratios of 50-50 and 70-30 had better results for the cytotoxicity study compared to other samples.

Local Water Content in Polymer Gels Measured with Super-Resolved Fluorescence Lifetime Imaging

Water molecules play an important role in the structure, function, and dynamics of (bio-) materials. A direct access to the number of water molecules in nanoscopic volumes can thus give new molecular insights into materials and allow for fine-tuning their properties in sophisticated applications. The determination of the local water content has become possible by the finding that H2 O quenches the fluorescence of red-emitting dyes. Since deuterated water, D2 O, does not induce significant fluorescence quenching, fluorescence lifetime measurements performed in different H2 O/D2 O-ratios yield the local water concentration. We combined this effect with the recently developed fluorescence lifetime single molecule localization microscopy imaging (FL-SMLM) in order to nanoscopically determine the local water content in microgels, i.e. soft hydrogel particles consisting of a cross-linked polymer swollen in water. The change in water content of thermo-responsive microgels when changing from their swollen state at room temperature to a collapsed state at elevated temperature could be analyzed. A clear decrease in water content was found that was, to our surprise, rather uniform throughout the entire microgel volume. Only a slightly higher water content around the dye was found in the periphery with respect to the center of the swollen microgels.

Emerging granular hydrogel bioinks to improve biological function in bioprinted constructs

Advancements in 3D bioprinting have been hindered by the trade-off between printability and biological functionality. Existing bioinks struggle to meet both requirements simultaneously. However, new types of bioinks composed of densely packed microgels promise to address this challenge. These bioinks possess intrinsic porosity, allowing for cell growth, oxygen and nutrient transport, and better immunomodulatory properties, leading to superior biological functions. In this review, we highlight key trends in the development of these granular bioinks. Using examples, we demonstrate how granular bioinks overcome the trade-off between printability and cell function. Granular bioinks show promise in 3D bioprinting, yet understanding their unique structure-property-function relationships is crucial to fully leverage the transformative capabilities of these new types of bioinks in bioprinting.

Liquid Metal Nanocores Initiated Construction of Smart DNA-Polymer Microgels with Programmable and Regulable Functions and Near-Infrared Light-Driven Locomotion

Due to their sequence-directed functions and excellent biocompatibility, smart DNA microgels have attracted considerable research interest, and the combination of DNA microgels with functional nanostructures can further expand their applications in biosensing and biomedicine. Gallium-based liquid metals (LMs) exhibiting both fluidic and metallic properties hold great promise for the development of smart soft materials; in particular, LM particles upon sonication can mediate radical-initiated polymerization reactions, thus allowing the combination of LMs and polymeric matrix to construct "soft-soft" materials. Herein, by forming active surfaces under sonication, LM nanoparticles (LM NPs) initiated localized radical polymerization reactions allow the combination of functional DNA units and different polymeric backbones to yield multifunctional core/shell microgels. The localized polymerization reaction allows fine control of the microgel compositions, and smart DNA microgels with tunable catalytic activities can be constructed. Moreover, due to the excellent photothermal effect of LM NPs, the resulting temperature gradient between microgels and surrounding solution upon NIR light irradiation can drive the oriented locomotion of the microgels, and remote control of the activity of these smart microgels can be achieved. These microgels may hold promise for various applications, such as the development of in vivo and in vitro biosensing and drug delivery systems.

Optimized DOX Drug Deliveries via Chitosan-Mediated Nanoparticles and Stimuli Responses in Cancer Chemotherapy: A Review

Chitosan nanoparticles (NPs) serve as useful multidrug delivery carriers in cancer chemotherapy. Chitosan has considerable potential in drug delivery systems (DDSs) for targeting tumor cells. Doxorubicin (DOX) has limited application due to its resistance and lack of specificity. Chitosan NPs have been used for DOX delivery because of their biocompatibility, biodegradability, drug encapsulation efficiency, and target specificity. In this review, various types of chitosan derivatives are discussed in DDSs to enhance the effectiveness of cancer treatments. Modified chitosan-DOX NP drug deliveries with other compounds also increase the penetration and efficiency of DOX against tumor cells. We also highlight the endogenous stimuli (pH, redox, enzyme) and exogenous stimuli (light, magnetic, ultrasound), and their positive effect on DOX drug delivery via chitosan NPs. Our study sheds light on the importance of chitosan NPs for DOX drug delivery in cancer treatment and may inspire the development of more effective approaches for cancer chemotherapy.

Continuous generation of cross-linked polymer nanoparticles employing an ultrasonic microreactor

In this article, a new system employing an ultrasonic microreactor coupled with a tubular reactor is presented for the continuous generation of polymer nanoparticles. The continuous generation of cross-linked polymer nanoparticles utilizing the monomer butyl methacrylate and the cross-linker ethylene glycol dimethacrylate is demonstrated. Firstly, the miniemulsion polymerization of a monomer-in-water miniemulsion is studied in a batch system. Secondly, a coiled tubular reactor is employed for the continuous polymerization of the miniemulsion generated by an ultrasonic microreactor. Finally, the influence of monomer volume fraction and surfactant concentration on the synthesized polymer nanoparticles is studied. Polymer particles in a size range of 50-250 nm are synthesized and a high polymerization conversion is achieved utilizing the system demonstrated in this article.

Porous Microgels for Delivery of Curcumin: Microfluidics-Based Fabrication and Cytotoxicity Evaluation

Polymeric microgels, fabricated via microfluidic techniques, have garnered significant interest as versatile drug delivery carriers. Despite the advances, the loading and release of hydrophobic drugs such as curcumin from polymeric microgels is not trivial. Herein, we report that effective drug loading can be achieved by the design of porous particles and the use of supramolecular cyclodextrin-based curcumin complexes. The fabrication of porous microgels through the judicious choice of chemical precursors under flow conditions was established. The evaluation of the curcumin loading dependence on the porosity of the microgels was performed. Microgels with higher porosity exhibited better curcumin loading compared to those with lower porosity. Curcumin-loaded microgels released the drug, which, upon internalization by U87 MG human glioma cancer cells, induced cytotoxicity. The findings reported here provide valuable insights for the development of tailored drug delivery systems using a microfluidics-based platform and outline a strategy for the effective delivery of hydrophobic therapeutic agents such as curcumin through supramolecular complexation.

Gd/hafnium oxide@gold@chitosan core-shell nanoparticles as a platform for multimodal theranostics in oncology research

In the current study, we synthesized thiolated chitosan-stabilized gold-coated, gadolinium-doped hafnium oxide nanoparticles (CAuGH NPs) with the capability of acting as a multifunctional system to deliver anticancer drug doxorubicin (DOX), to enhance radiosensitization by ROS generation, and to provide magnetic resonance (MR) imaging contrast for biomedical applications.

Photoinduced Mechanical Cloaking of Diarylethene-Crosslinked Microgels

The serial connection of multiple stimuli-responses in polymer architectures enables the logically conjunctive gating of functional material processes on demand. Here, a photoswitchable diarylethene (DAE) acts as a crosslinker in poly(N-vinylcaprolactam) microgels and allows the light-induced shift of the volume phase-transition temperature (VPTT). While swollen microgels below the VPTT are susceptible to force and undergo breakage-aggregation processes, collapsed microgels above the VPTT stay intact in mechanical fields induced by ultrasonication. Within a VPTT shift regime, photoswitching of the DAE transfers microgels from the swollen to the collapsed state and thereby gates their response to force as demonstrated by the light-gated activation of an embedded fluorogenic mechanophore. This photoinduced mechanical cloaking system operates on the polymer topology level and is thereby principally universally applicable.

Compartmentalized Polyampholyte Microgels by Depletion Flocculation and Coacervation of Nanogels in Emulsion Droplets

In pH-responsive drug carriers, the distribution of charges has been proven to affect delivery efficiency but is difficult to control and verify. Herein, we fabricate polyampholyte nanogel-in-microgel colloids (NiM-C) and show that the arrangement of the nanogels (NG) can easily be manipulated by adapting synthesis conditions. Positively and negatively charged pH-responsive NG are synthesized by precipitation polymerization and labelled with different fluorescent dyes. The obtained NG are integrated into microgel (MG) networks by subsequent inverse emulsion polymerization in droplet-based microfluidics. By confocal laser scanning microscopy (CLSM), we verify that depending on NG concentration, pH value and ionic strength, NiM-C with different NG arrangements are obtained, including Janus-like phase-separation of NG, statistical distribution of NG, and core-shell arrangements. Our approach is a major step towards uptake and release of oppositely charged (drug) molecules.

Adsorption of Preformed Microgel-Enzyme Complexes as a Novel Strategy toward Engineering Microgel-Based Enzymatic Biosensors

A novel approach to surface modification, which consists of the adsorption of microgel-enzyme complexes preformed in solution, is highlighted. Accordingly, the microgel-enzyme complexes were formed due to the electrostatic interaction of the oppositely charged interacting components, that is, a cationic poly(N-isopropylacrylamide)-based microgel and glucose oxidase taken as a model enzyme. The spontaneous adsorption of the prepared microgel-enzyme complexes, examined by means of quartz crystal microbalance with dissipation monitoring and atomic force microscopy, was observed, resulting in the formation of well-adhered microgel-enzyme coatings. Further, the preformed microgel-enzyme complexes were adsorbed onto the modified graphite-based screen-printed electrodes, and their enzymatic responses were determined by means of amperometry, demonstrating a remarkable analytical performance toward the quantification of β-D-glucose in terms of high sensitivity (0.0162 A × M-1 × cm-2), a low limit of detection (1 μM), and an expanded linear range (1-2000 μM). The fabricated microgel-enzyme biosensor constructs were found to be very stable against manifold-repeated measurements. Finally, the pH- or salt-induced release of glucose oxidase from the adsorbed preformed microgel-enzyme complexes was demonstrated. The findings obtained for the microgel-enzyme coatings prepared via adsorption of the preformed microgel-enzyme complexes were compared to those found for the microgel-enzyme coatings fabricated via a previously exploited two-stage sequential adsorption, which includes the adsorption of the microgel first, followed by the electrostatic binding of glucose oxidase by the adsorbed microgel.

Free-flowing, self-crosslinking, carboxymethyl starch and carboxymethyl cellulose microgels, as smart hydrogel dressings for wound repair

Hydrogels are widely recognized and favoured as moist wound dressings due to their beneficial properties. However, their limited capacity to absorb fluids restricts their use in highly exuding wounds. Microgels are small sized hydrogels that have recently gained considerable attention in drug delivery applications due to their superior swelling behaviour and ease of application. In this study, we introduce dehydrated microgel particles (μGeld) that rapidly swell and interconnect, forming an integrated hydrogel when exposed to fluid. These free-flowing microgel particles, derived from the interaction of carboxymethylated forms of starch and cellulose, have been designed to significantly absorb fluid and release silver nanoparticles in order to effectively control infection. Studies using simulated wound models validated the microgels ability to efficiently regulate the wound exudate and create a moist environment. While the biocompatibility and hemocompatibility studies confirmed the safety of the μGel particles, its haemostatic property was established using relevant models. Furthermore, the promising results from a full-thickness wounds in rats have highlighted the enhanced healing potential of the microgel particles. These findings suggest that the dehydrated microgels can evolve as a new class of smart wound dressings.

Biodegradable redox sensitive chitosan based microgels for potential agriculture application

In this work, we report redox sensitive, 2,3-dihydroxybenzoic acid (DH) functionalized chitosan/stearic acid microgels (DH-ChSt MGs) for controlled delivery of insecticide and capturing of heavy metal ions. DH-ChSt MGs (≈146 nm) are prepared by disulfide crosslinking of SH functionalized chitosan and stearic acid rendering them biodegradable. DH-ChSt MGs exhibit high loading (≈8 %) and encapsulation (≈85 %) efficiency for imidacloprid insecticide, and offer its prolonged release (≈75 % after 133 h) under reducing conditions. Functionalization with DH provides enhanced foliar adhesion on pea leaves. DH-ChSt MGs also bind Fe³⁺ very efficiently due to the strong chelation of Fe³⁺ by DH, offering the opportunity of supplying Fe³⁺ nutrient for plant care. MTT assay results using different cells confirm that DH-ChSt MGs are nontoxic up to the experimental concentration of 120 μg/mL. Additionally, reduced DH-ChSt MGs having free thiol groups are also capable of binding heavy metal ions, thus presenting the reported formulation as a promising platform for agriculture application.

Hot Brownian Motion of Thermoresponsive Microgels in Optical Tweezers Shows Discontinuous Volume Phase Transition and Bistability

Microgels are soft microparticles that often exhibit thermoresponsiveness and feature a transformation at a critical temperature, referred to as the volume phase transition temperature. Whether this transformation occurs as a smooth or as a discontinuous one is still a matter of debate. This question can be addressed by studying individual microgels trapped in optical tweezers. For this aim, composite particles are obtained by decorating  Poly-N-isopropylacrylamide (pNIPAM) microgels with iron oxide nanocubes. These composites become self-heating when illuminated by the infrared trapping laser, performing hot Brownian motion within the trap. Above a certain laser power, a single decorated microgel features a volume phase transition that is discontinuous, while the usual continuous sigmoidal-like dependence is recovered after averaging over different microgels. The collective sigmoidal behavior enables the application of a power-to-temperature calibration and provides the effective drag coefficient of the self-heating microgels, thus establishing these composite particles as potential micro-thermometers and micro-heaters. Moreover, the self-heating microgels also exhibit an unexpected and intriguing bistability behavior above the critical temperature, probably due to partial collapses of the microgel. These results set the stage for further studies and the development of applications based on the hot Brownian motion of soft particles.

Hydrogels for Mucosal Drug Delivery

Mucosal tissues are often a desirable site of drug action to treat disease and engage the immune system. However, systemically administered drugs suffer from limited bioavailability in mucosal tissues where technologies to enable direct, local delivery to these sites would prove useful. In this Spotlight on Applications article, we discuss hydrogels as an attractive means for local delivery of therapeutics to address a range of conditions affecting the eye, nose, oral cavity, gastrointestinal, urinary bladder, and vaginal tracts. Considering the barriers to effective mucosal delivery, we provide an overview of the key parameters in the use of hydrogels for these applications. Finally, we highlight recent work demonstrating their use for inflammatory and infectious diseases affecting these tissues.

Buckling and Interfacial Deformation of Fluorescent Poly(N-isopropylacrylamide) Microgel Capsules

Hollow microgels are fascinating model systems at the crossover between polymer vesicles, emulsions, and colloids as they deform, interpenetrate, and eventually shrink at higher volume fraction or when subjected to an external stress. Here, we introduce a system consisting of microgels with a micrometer-sized cavity enabling a straightforward characterization in situ using fluorescence microscopy techniques. Similarly to elastic capsules, these systems are found to reversibly buckle above a critical osmotic pressure, conversely to smaller hollow microgels, which were previously reported to deswell at high volume fraction. Simulations performed on monomer-resolved in silico hollow microgels confirm the buckling transition and show that the presented microgels can be described with a thin shell model theory. When brought to an interface, these microgels, that we define as microgel capsules, strongly deform and we thus propose to utilize them to locally probe interfacial properties within a theoretical framework adapted from the Johnson-Kendall-Roberts (JKR) theory. Besides their capability to sense their environment and to address fundamental questions on the elasticity and permeability of microgel systems, microgel capsules can be further envisioned as model systems mimicking anisotropic responsive biological systems such as red blood and epithelial cells thanks to the possibility offered by microgels to be synthesized with custom-designed properties.

A Facile yet Versatile Strategy to Construct Liquid Hybrid Energy-Saving Windows for Strong Solar Modulation

Smart windows with light management and indoor solar heating modulation capacities are of paramount importance for building energy conservation. Thermochromic poly(N-isopropylacrylamide) (PNIPAm) hydrogel smart windows exhibit advantages of the relatively suitable transition temperature of 32 °C, high cost-effective and automatic passive sunlight regulation, but sustain slow response rate and unsatisfactory solar modulation efficiency. Herein, a strategy of one-step copolymerization of NIPAm and different olefine acids (OA) using reverse atom transfer radical polymerization method is developed to fabricate various chain/microparticle hybrids (CMH) for liquid energy-saving windows. Synergetic mechanisms of thermal-induced dissolution and aggregation of linear polymer chains integrated with water capture and release of microgel particles contribute to tunable light-scattering behaviors and adaptive solar modulation. Without any post-treatment, the as-prepared poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAm-co-AA))-based CMH suspension is injected into sandwich glass to construct energy-saving windows, which exhibits appreciated near-room-temperature transition (26.7 °C), rapid response (5 s), extraordinary luminous transmittance (91.5%), and solar modulation efficiency (85.8%), resulting in a substantial decline of indoor temperature of 24.5 °C in simulation experiment. Combining the versatile strategy with flexible adjustment on transition temperature, multifarious P(NIPAm-co-OA)-based CMH windows with eminent light management capacity are obtained. This work will powerfully promote the development and renovation of energy-efficient windows.

Dextran/eudragit S-100 based redox sensitive nanoparticles for colorectal cancer therapy

Herein, we present disulfide crosslinked dextran/eudragit S-100 nanoparticles (DEEU NPs) (≈55 nm) for colorectal cancer treatment. These redox environment sensitive DEEU NPs are synthesized by simple oxidation of thiolated polymers in air. This approach allows avoiding the use of any additional chemical crosslinker. These DEEU NPs have high encapsulation efficiency for the doxorubicin (DOX) model drug (≈95%). The prepared DEEU NPs are redox sensitive owing to disulfide units and exhibit ≈80% DOX release in the reducing environment of GSH. Additionally, DOX-DEEU NPs display enhanced cytotoxicity for HCT116 cancer cells as compared to free DOX. Annexin V staining results also support the higher anticancer efficiency of DOX-DEEU NPs via induction of apoptosis. In vivo biodistribution results demonstrate that DEEU NPs can remain in the colon region for up to 24 hours. These results indicate that DEEU NPs can act as a promising platform for colorectal cancer treatment.

Biodegradable dual stimuli responsive alginate based microgels for controlled agrochemicals release and soil remediation

To meet the growing food demand of increasing world population while reducing the harmful environmental effects of agrochemicals, development of smart nanoformulation is of prime importance. Herein, dual stimuli responsive alginate based microgels (OAlgDP MGs) (≈160 nm) are developed for controlled release of agrochemicals and soil remediation. These microgels are prepared using octyl amine functionalized alginate which is crosslinked by 3, 3'-dithiopropionohydrazide crosslinker providing both hydrazone and disulfide bonds in microgels network. OAlgDP MGs are further loaded with hydrophobic diuron herbicide displaying ≈85 % encapsulation efficiency. Sustained release of diuron is obtained in 2 mM GSH (≈100 % after 380 h) and at pH 5 (≈72 % after 240 h). Furthermore, OAlgDP MGs are nontoxic up to 150 μg/mL against HEK293T cells while their reduced form is capable of capturing the heavy metal ions (Cu²⁺ and Hg²⁺) showing the potential of the developed system for moving toward sustainable agriculture.

Recent advances in cellulose microgels: Preparations and functionalized applications

Microgels are soft, deformable, permeable, and stimuli-responsive microscopic polymeric particles that are now emerging as prospective multifunctional soft materials for delivery systems, interface stabilization, cell cultures and tissue engineering. Cellulose microgels are emerging biopolymeric microgels with unique characteristics such as abound hydroxyl structure, admirable designability, multiscale pore network and excellent biocompatibility. This review summarizes the fabrication strategies for microgel, then highlights the fabrication routes for cellulose microgels, and finally elaborates cellulose microgels' bright application prospects with unique characteristics in the fields of controlled release, interface stabilization, coating, purification, nutrition/drug delivery, and bio-fabrication. The challenges to be addressed for further applications and considerable scope for development in future of cellulose microgels are also discussed.

Redox responsive poly(allylamine)/eudragit S-100 nanoparticles for dual drug delivery in colorectal cancer

Herein, we report redox responsive, colon cancer targeting poly(allylamine) (PA)/eudragit S-100 (EU) nanoparticles (PAEU NPs) (≈59 nm). These disulfide crosslinked PAEU NPs are developed via air oxidation of thiolated PA and thiolated EU, eliminating the need of any external crosslinking agent for dual drug delivery. PAEU NPs can effectively encapsulate both hydrophilic doxorubicin (DOX) and hydrophobic curcumin (Cur) drug with ≈85 % and ≈97 % encapsulation efficiency respectively. Here, the combination of drugs having different anticancer mechanism offers the possibility of developing nanosystem with enhanced anticancer efficacy. The developed PAEU NPs show good colloidal stability and low drug release under physiological conditions, while high DOX (≈98 %) and Cur (≈93 %) release is observed in reducing environment (10 mM GSH). Further, DOX and Cur loaded PAEU NPs exhibit higher cancer cell killing efficiency as compared to individual free drugs. In vivo biodistribution studies with Balb/C mice display the retention of PAEU NPs in the colon region up to 24 h presenting the developed approach as an efficient way for colorectal cancer therapy.

Advanced application of collagen-based biomaterials in tissue repair and restoration

In tissue engineering, bioactive materials play an important role, providing structural support, cell regulation and establishing a suitable microenvironment to promote tissue regeneration. As the main component of extracellular matrix, collagen is an important natural bioactive material and it has been widely used in scientific research and clinical applications. Collagen is available from a wide range of animal origin, it can be produced by synthesis or through recombinant protein production systems. The use of pure collagen has inherent disadvantages in terms of physico-chemical properties. For this reason, a processed collagen in different ways can better match the specific requirements as biomaterial for tissue repair. Here, collagen may be used in bone/cartilage regeneration, skin regeneration, cardiovascular repair and other fields, by following different processing methods, including cross-linked collagen, complex, structured collagen, mineralized collagen, carrier and other forms, promoting the development of tissue engineering. This review summarizes a wide range of applications of collagen-based biomaterials and their recent progress in several tissue regeneration fields. Furthermore, the application prospect of bioactive materials based on collagen was outlooked, aiming at inspiring more new progress and advancements in tissue engineering research.

Graphical Abstract

Biodegradable disulfide crosslinked chitosan/stearic acid nanoparticles for dual drug delivery for colorectal cancer

Herein, redox responsive chitosan/stearic acid nanoparticles (CSSA NPs) (≈200 nm) are developed for dual drug delivery. These degradable nanoparticles are prepared based on disulfide (SS) crosslinking chemistry avoiding the use of any external crosslinking agent. CSSA NPs are further loaded with both DOX (hydrophilic) and curcumin (hydrophobic) drugs with ≈86 % and ≈82 % encapsulation efficiency respectively. This approach of combining anticancer therapeutics having different mode of anticancer action allows to develop systems for cancer therapy with enhanced efficacy. In vitro drug release experiments clearly exhibit the low leakage of drug under physiological conditions while ≈98 % DOX and ≈96 % curcumin is released after 136 h under GSH reducing conditions. The cytotoxicity experiments against HCT116 cells demonstrate higher cytotoxicity of dual drug loaded CSSA NPs. In vivo biodistribution experiments with c57bl/6j mice confirms the retention of CSSA NPs in the colon area up to 24 h exhibiting their potential for colorectal cancer therapy.

Targeted Therapy of Ischemic Stroke via Crossing the Blood-Brain Barrier Using Edaravone-Loaded Multiresponsive Microgels

Ischemic stroke, as a prevalent neurological disorder, often results in rapid increases in the production of reactive oxygen species (ROS) and inflammatory factors in the focal ischemic area. Though edaravone is an approved treatment, its effect is limited due to its weak ability to cross the blood-brain barrier (BBB) and short half-life. Other effective pharmacological treatment options are clearly lacking. In this study, PNIVDBrF-3-Eda (also named MG-3-Eda) was prepared using a thermo- and pH dual-responsive PNIVDBrF microgel. These were designed with a positively charged network, as synthesized by simultaneous quaternization cross-linking and surfactant-free emulsion copolymerization, to be loaded with the negatively charged edaravone. We then investigated whether such a targeted delivery of edaravone could provide enhanced neuroprotection. Cytotoxicity assays confirmed that the microgel (<1 mg/mL) exhibited promising cytocompatibility with no remarkable effect on cell viability, cell cycle regulation, or apoptosis levels. In vitro and in vivo experiments demonstrated that the microgels could successfully penetrate the blood-brain barrier where efficient BBB crossing was observed after disruption of the BBB due to ischemic injury. This enabled MG-3-Eda to target the cerebral ischemic area and achieve local release of edaravone. Treatment with MG-3-Eda significantly reduced the cerebral infarct area in transient middle cerebral artery occlusion (tMCAO) mice and significantly improved behavioral scores. MG-3-Eda treatment also prevented the reduction in NF200 expression, a neuronal marker protein, and attenuated microglia activation (as detected by Iba1) in the local ischemic area via local antioxidant and anti-inflammatory effects. A superior neuroprotective effect was noted for MG-3-Eda compared to that for free edaravone. Our results indicate that MG-3-Eda administration represents a clear potential treatment for cerebral ischemia via its targeted delivery of edaravone to ischemic areas where it provides significant local antioxidant and anti-inflammatory effects.

Specific Binding of Ligand-Functionalized Thermoresponsive Microgels: Effect of Architecture, Ligand Density, and Hydrophobicity

The biomolecular interaction of ligand-presenting switchable microgels is studied with respect to the polymer type, composition, and structure of the microgels. Monodisperse microgels are prepared through precipitation polymerization of N-isopropylacrylamide (PNIPAM microgels) or oligo(ethylene glycol methacrylamide)s (POEGMA microgels) in the presence of crosslinkers or in their absence (self-crosslinked). Functionalization with mannose or biotin as model ligands and affinity measurements upon heating/cooling are conducted to obtain mechanistic insights into how the microgel phase transition affects the specific interactions. In particular, we are interested in adjusting the crosslinking, swelling degree, and ligand density of mannose-functionalized microgels to reversibly catch and release mannose binding Escherichia coli by setting the temperature below or above the microgels' volume phase transition temperature (VPTT). The increased mannose density for collapsed microgels above the VPTT results in stronger E. coli binding. Detachment of E. coli by reswelling the microgels below the VPTT is achieved only for self-crosslinked microgels showing a stronger decrease in ligand density compared to microgels with dedicated crosslinkers. Owing to a reduced mannose density in the shell of POEGMA microgels, their E. coli binding was lower compared to PNIPAM microgels, as supported by ultraresolution microscopy. Importantly, an inverse temperature-controlled binding of microgels decorated with hydrophilic mannose and hydrophobic biotin ligands is observed. This indicates that hydrophobic ligands are inaccessible in the collapsed hydrophobic network above the VPTT, whereas hydrophilic mannose units are then enriched at the microgel-water interface and thus are more accessible.

Microfluidics Fabrication of Micrometer-Sized Hydrogels with Precisely Controlled Geometries for Biomedical Applications

Micrometer-sized hydrogels are cross-linked three-dimensional network matrices with high-water contents and dimensions ranging from several to hundreds of micrometers. Due to their excellent biocompatibility and capability to mimic physiological microenvironments in vivo, micrometer-sized hydrogels have attracted much attention in the biomedical engineering field. Their biological properties and applications are primarily influenced by their chemical compositions and geometries. However, inhomogeneous morphologies and uncontrollable geometries limit traditional micrometer-sized hydrogels obtained by bulk mixing. In contrast, microfluidic technology holds great potential for the fabrication of micrometer-sized hydrogels since their geometries, sizes, structures, compositions, and physicochemical properties can be precisely manipulated on demand based on the excellent control over fluids. Therefore, micrometer-sized hydrogels fabricated by microfluidic technology have been applied in the biomedical field, including drug encapsulation, cell encapsulation, and tissue engineering. This review introduces micrometer-sized hydrogels with various geometries synthesized by different microfluidic devices, highlighting their advantages in various biomedical applications over those from traditional approaches. Overall, emerging microfluidic technologies enrich the geometries and morphologies of hydrogels and accelerate translation for industrial production and clinical applications.

In situ 3D bioprinting with bioconcrete bioink

In-situ bioprinting is attractive for directly depositing the therapy bioink at the defective organs to repair them, especially for occupations such as soldiers, athletes, and drivers who can be injured in emergency. However, traditional bioink displays obvious limitations in its complex operation environments. Here, we design a bioconcrete bioink with electrosprayed cell-laden microgels as the aggregate and gelatin methacryloyl (GelMA) precursor solution as the cement. Promising printability is guaranteed with a wide temperature range benefiting from robust rheological properties of photocrosslinked microgel aggregate and fluidity of GelMA cement. Composite components simultaneously self-adapt to biocompatibility and different tissue mechanical microenvironment. Strong binding on tissue-hydrogel interface is achieved by hydrogen bonds and friction when the cement is photocrosslinked. This bioink owns good portability and can be easily prepared in urgent accidents. Meanwhile, microgels can be cultured to mini tissues and then mixed as bioink aggregates, indicating our bioconcrete can be functionalized faster than normal bioinks. The cranial defects repair results verify the superiority of this bioink and its potential in clinical settings required in in-situ treatment.

Bioinks used in current in-situ bioprinting have limitations when applied to complex operational environments. Here, the authors report on the creation of a microgel reinforced GelMA bioink which can be simply prepared and used in different biomedical settings. The application is demonstrated in a cranial defect model.

Polysaccharide-Based Theranostic Systems for Combined Imaging and Cancer Therapy: Recent Advances and Challenges

Designing novel systems for efficient cancer treatment and improving the quality of life for patients is a prime requirement in the healthcare sector. In this regard, theranostics have recently emerged as a unique platform, which combines the benefits of both diagnosis and therapeutics delivery. Theranostics have the desired contrast agent and the drugs combined in a single carrier, thus providing the opportunity for real-time imaging to monitor the therapy results. This helps in reducing the hazards related to treatment overdose or underdose and gives the possibility of personalized therapy. Polysaccharides, as natural biomolecules, have been widely explored to develop theranostics, as they act as a matrix for simultaneously loading both contrast agents and drugs for their utility in drug delivery and imaging. Additionally, their remarkable physicochemical attributes (biodegradability, satisfactory safety profile, abundance, and diversity in functionality and charge) can be tuned via postmodification, which offers numerous possibilities to develop theranostics with desired characteristics. Hence, we provide an overview of recent advances in polysaccharide matrix-based theranostics for drug delivery combined with magnetic resonance imaging, computed tomography, positron emission tomography, single photon emission computed tomography, and ultrasound imaging. Herein, we also summarize the toxicity assessment of polysaccharides, associated contrast agents, and nanotoxicity along with the challenges and future research directions.

Methacrylic acid based microgels and hybrid microgels

Methacrylic acid based microgels have got much consideration in the last two decades because of their potential uses in different fields owing to their responsive behaviour towards external stimuli. Synthesis, properties and uses of methacrylic acid based microgels and their hybrids have been critically reviewed in this article. With minute change in external stimuli such as pH and ionic strength of medium, these microgels show quick swelling/deswelling reversibly. The methacrylic acid based microgels have been widely reported for applications in the area of nanotechnology, drug delivery, sensing and catalysis due to their responsive behaviour. A critical review of current research development in this field along with upcoming perception is presented here. This discussion is concluded with proposed probable future studies for additional growth in this field of research.

Adsorption of soft NIPAM nanogels at hydrophobic and hydrophilic interfaces: Conformation of the interfacial layers determined by neutron reflectivity

The application of stimuli-responsive microgels and nanogels in drug delivery, catalysis, sensing, and coatings is restricted currently by the limited understanding of the factors influencing their adsorption dynamics and structural changes at interfaces. We have used neutron reflectivity to resolve, on the Ångström scale, the structure of 5% crosslinked N-isopropylacrylamide nanogels at both hydrophobic and hydrophilic interfaces in situ, as a function of temperature and bulk nanogel concentration. Our results show that the higher flexibility given by the low crosslinker content allows for a more ordered structure and packing. The adsorption of the thermoresponsive nanogels is primarily driven by temperature, more specifically its proximity to its volume phase transition temperature, while concentration plays a secondary role. Hydrophobic interactions drive the conformation of the first layer at the interface, which plays a key role in influencing the overall nanogel structure. The mobility of the first layer at the air-water interface as opposed to the interfacial confinement at the solid (SiC8)-liquid interface, results in a different conformation, a more compact and less deformed packing structure, which ultimately drives the structure of the subsequent layers. The evidence for the different structural conformations determined by the degree of hydrophobicity of the interface provides new knowledge, which is essential for the development of further applications. The key role of hydrophobic interactions in driving adsorption and interfacial behavior was also confirmed by fluid AFM experiments which visualized adherence of the nanogels to SiC8 modified surfaces.

Preparation and Characterization of Thermoresponsive Poly(N-vinylisobutyramide) Microgels

Microgels are soft, adaptive materials exhibiting various properties not only like hydrogels and microparticles but also like macromolecules, colloids, and surfactants. To widen the range of their biomedical and environmental applications, the exploration of an alternative for poly(N-alkylacrylamide)s without potential safety risks is of great importance. In this article, thermoresponsive poly(N-vinylisobutyramide) (PNVIBA) microgels of uniform size were synthesized with NVIBA as a monomer and N,N'-5-oxanonamethyene-bis-N-vinylacetamide as a cross-linker in the presence of sodium dodecyl sulfate by aqueous free radical precipitation polymerization. The introduction of cationic groups into PNVIBA microgels was also accomplished using N-vinylformamide (NVF) as a comonomer and the subsequent conversion of NVF into vinylamine by hydrolysis.

Copolymerization Kinetics of Dopamine Methacrylamide during PNIPAM Microgel Synthesis for Increased Adhesive Properties

Combining stimuli-responsive properties of gels with adhesive properties of mussels is highly interesting for a large field of applications as, e.g., in life science. Therefore, the present paper focuses on the copolymerization of poly(N-isopropylacrylamide) (PNIPAM) microgels with dopamine methacrylamide (DMA). A detailed understanding of reaction kinetics is crucial to figure out an optimized synthesis strategy for tailoring microgels with adhesive properties. The present study addresses the influence of relevant synthesis parameters as the injection time of DMA during the microgel synthesis and the overall reaction time of the microgel. Reaction kinetics were studied by mass spectrometry of time samples taken during the microgel synthesis. This allowed us to determine the monomer consumption of NIPAM, the cross-linker N,N'-methylenebisacrylamide (BIS), and DMA. A second-order reaction kinetics was found for DMA incorporation. The amount of DMA incorporated in the resulting microgel was successfully determined by a combination of UV-vis and NMR spectroscopy to level off limitations of both methods. The dependence of the hydrodynamic radius on temperature was determined by DLS measurements for the microgels. While an early injection of DMA stops the PNIPAM polymerization due to scavenging, it greatly enhances the reaction speed of DMA. The faster reaction of DMA and the incomplete NIPAM and BIS conversion also compensate for shorter reaction times with respect to the incorporated amount of DMA. On the contrary, a later injection of DMA leads to a full NIPAM monomer and BIS cross-linker consumption. An overall reaction time of 60 min ensures the DMA incorporation. Longer reaction times lead to clumping. First adhesion tests show an increased adhesion of P(NIPAM-co-DMA) microgels compared to pure PNIPAM microgels, when mechanical stress is applied.

Thermosensitive Microgels Containing AIEgens: Enhanced Luminescence and Distinctive Photochromism for Dynamic Anticounterfeiting

The proposal of the aggregation-induced emission (AIE) effect shines a light on the practical application of luminescent materials. The AIE-active luminescence microgels (TPEC MGs) with photo-induced color-changing behavior were developed by integrating positively charged AIE luminogens (AIEgens) into the anionic network of microgels, where AIEgens of TPEC were obtained from the quaternization reaction between tetra-(4-pyridylphenyl)ethylene (TPE-4Py) and 7-(6-bromohexyloxy)-coumarin. The aqueous suspensions of TPEC MGs exhibit a significant AIE effect following the enhancement of quantum yield. In addition, further increase in fluorescence intensity and blueshift occur at elevated temperatures due to the collapse of microgels. The distinctive photochromic behavior of TPEC MGs was observed, which presents as the transition from orange-yellow to blue-green color under UV irradiation, which is different from TPEC in good organic solvents. The phenomenon of color changing can be ascribed to the competition between photodimerization of the coumarin part and photocyclization of TPE-4Py in TPEC. The photochromic TPEC MG aqueous suspensions can be conducted as aqueous microgel inks for information display, encryption, and dynamic anticounterfeiting.

One-step surface modification strategy with composition-tunable microgels: From bactericidal surface to cell-friendly surface

As modifiers for biomaterial surfaces, soft colloidal particles not only have good film-forming properties, but can also contribute to the function of the biomaterial via their chemical and biological properties. This general approach has proven effective for surface modification, but little is known about methods to control the properties of the colloidal particles to regulate film formation and biological function. In this work, we prepared poly (N-isopropylacrylamide) microgels (ZQP) containing both a zwitterionic component (Z) to provide anti-fouling functionality, and a quaternary ammonium salt (Q) to give bactericidal functionality. Fine-tuning of the Z and Q contents allowed the preparation of microgels over a range of particle size, size distribution, charge, and film-forming capability. The films showed anti-adhesion and contact-killing properties versus Escherichia coli (E. Coli), depending on the chemical composition. They also showed excellent cytocompatibility relative to L929 cells. A variety of microgel-coated substrates (silicon wafer, PDMS, PU, PVC) showed long-term anti-bacterial activity and resistance to chemical and mechanical treatments. It is concluded that this approach allows the preparation of effective bactericidal, cytocompatible surfaces. The properties can be fine-tuned by regulation of the microgel composition, and the method is applicable universally, i.e., independent of substrate.

Microgels react to force: mechanical properties, syntheses, and force-activated functions

Microgels are colloidal polymer networks with high molar mass and properties between rigid particles, flexible macromolecules, and micellar aggregates. Their unique stimuli-responsiveness in conjunction with their colloidal phase behavior render them useful for many applications ranging from engineering to biomedicine. In many scenarios either the microgel's mechanical properties or its interactions with mechanical force play an important role. Here, we firstly explain microgel mechanical properties and how these are measured by atomic force microscopy (AFM), then we equip the reader with the synthetic background to understand how specific architectures and chemical functionalities enable these mechanical properties, and eventually we elucidate how the interaction of force with microgels can lead to the activation of latent functionality. Since the interaction of microgels with force is a multiscale and multidisciplinary subject, we introduce and interconnect the different research areas that contribute to the understanding of this emerging field in this Tutorial Review.

Microgels and Nanogels for the Delivery of Poorly Water-Soluble Drugs

While microgels and nanogels are most commonly used for the delivery of hydrophilic therapeutics, the water-swollen structure, size, deformability, colloidal stability, functionality, and physicochemical tunability of microgels can also offer benefits for addressing many of the barriers of conventional vehicles for the delivery of hydrophobic therapeutics. In this review, we describe approaches for designing microgels with the potential to load and subsequently deliver hydrophobic drugs by creating compartmentalized microgels (e.g., core-shell structures), introducing hydrophobic domains in microgels, leveraging host-guest interactions, and/or applying "smart" environmentally responsive materials with switchable hydrophobicity. In particular, the challenge of promoting hydrophobic drug loading without compromising the inherent advantages of microgels as delivery vehicles and ensuring practically relevant release kinetics from such structures is highlighted, with an eye toward the practical translation of such vehicles to the clinic.

Rheology Applied to Microgels: Brief (Revision of the) State of the Art

The ability of polymer microgels to rapidly respond to external stimuli is of great interest in sensors, lubricants, and biomedical applications, among others. In most of their uses, microgels are subjected to shear, deformation, and compression forces or a combination of them, leading to variations in their rheological properties. This review article mainly refers to the rheology of microgels, from the hard sphere versus soft particles' model. It clearly describes the scaling theories and fractal structure formation, in particular, the Shih et al. and Wu and Morbidelli models as a tool to determine the interactions among microgel particles and, thus, the viscoelastic properties. Additionally, the most recent advances on the characterization of microgels' single-particle interactions are also described. The review starts with the definition of microgels, and a brief introduction addresses the preparation and applications of microgels and hybrid microgels.

In-Line Characterization of the Temperature-Responsive Behavior of Surface-Bound Microgel Coatings by QCM-D: A Novel Strategy for Protein Repellence Evaluation

In this work, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to develop a new method to evaluate the protein repellency of microgel coatings. Compared to traditional protocols for surface analysis, QCM has the advantage of a real-time quantitative approach with high sensitivity, allowing us to describe variations of the adsorbed mass with unprecedented accuracy. To enable the detectability of the film throughout the whole operational temperature interval, a poly(N-isopropylacrylamide-co-glycidyl methacrylate) p(NIPAm-co-GMA) microgel monolayer with defined thickness and rigidity was designed. Covalent adhesion of the film to the silica surface was achieved by epoxy-thiol click chemistry and tested for repeated temperature cycles, showing substantial reproducibility. Further functionalization of microgel surfaces by grafting polyzwitterionic chains remarkably improved the protein repellence leaving the strong surface adhesion unaltered. Before and after exposure to fluorescein-tagged bovine serum albumin (FITC-BSA), the coatings showed identical responsive behavior, proving the absence of protein deposition. In nonrepellent coatings, QCM monitoring instead displayed a characteristic shift in the volume phase transition (VPT), pointing out the effect of adsorbed proteins on the swelling behavior of pNIPAm. The combination of QCM-D and UV-visible (UV-vis) was used to evaluate the effect of increasing surface coverage, enabling to distinguish between the protein deposition occurring over the coated and the uncoated portion of the sensor.

Microgel assembly: Fabrication, characteristics and application in tissue engineering and regenerative medicine

Microgel assembly, a macroscopic aggregate formed by bottom-up assembly of microgels, is now emerging as prospective biomaterials for applications in tissue engineering and regenerative medicine (TERM). This mini-review first summarizes the fabrication strategies available for microgel assembly, including chemical reaction, physical reaction, cell-cell interaction and external driving force, then highlights its unique characteristics, such as microporosity, injectability and heterogeneity, and finally itemizes its applications in the fields of cell culture, tissue regeneration and biofabrication, especially 3D printing. The problems to be addressed for further applications of microgel assembly are also discussed.

Translating Therapeutic Microgels into Clinical Applications

Microgels are crosslinked, water-swollen networks with a 10 nm to 100 µm diameter and can be modified chemically or biologically to render them biocompatible for advanced clinical applications. Depending on their intended use, microgels require different mechanical and structural properties, which can be engineered on demand by altering the biochemical composition, crosslink density of the polymer network, and the fabrication method. Here, the fundamental aspects of microgel research and development, as well as their specific applications for theranostics and therapy in the clinic, are discussed. A detailed overview of microgel fabrication techniques with regards to their intended clinical application is presented, while focusing on how microgels can be employed as local drug delivery materials, scavengers, and contrast agents. Moreover, microgels can act as scaffolds for tissue engineering and regeneration application. Finally, an overview of microgels is given, which already made it into pre-clinical and clinical trials, while future challenges and chances are discussed. This review presents an instructive guideline for chemists, material scientists, and researchers in the biomedical field to introduce them to the fundamental physicochemical properties of microgels and guide them from fabrication methods via characterization techniques and functionalization of microgels toward specific applications in the clinic.

Mechanoresponsive diselenide-crosslinked microgels with programmed ultrasound-triggered degradation and radical scavenging ability for protein protection

In the context of controlled delivery and release, proteins constitute a delicate class of cargo requiring advanced delivery platforms and protection. We here show that mechanoresponsive diselenide-crosslinked microgels undergo controlled ultrasound-triggered degradation in aqueous solution for the release of proteins. Simultaneously, the proteins are protected from chemical and conformational damage by the microgels, which disintegrate to water-soluble polymer chains upon sonication. The degradation process is controlled by the amount of diselenide crosslinks, the temperature, and the sonication amplitude. We demonstrate that the ultrasound-mediated cleavage of diselenide bonds in these microgels facilitates the release and activates latent functionality preventing the oxidation and denaturation of the encapsulated proteins (cytochrome C and myoglobin) opening new application possibilities in the targeted delivery of biomacromolecules.

Mechanoresponsive diselenide-crosslinked microgels undergo controlled ultrasound-triggered degradation and can be used for protein delivery due to their dual protection properties acting as radical scavengers and conformation stabilizers.

Detachment of bovine corneal endothelial cell sheets by cooling-induced surface hydration of poly[(R)-3-hydroxybutyrate]-based thermoresponsive copolymer coating

A smart surface was prepared by non-covalently coating of a thermoresponsive copolymer via a simple drop-casting method. The smart surface was conducive to cell culture, from which intact cell sheets could be effectively detached by cooling.

Core–shell Microgels Having Zwitterionic Hydrogel Core and Temperature-responsive Shell Prepared via Inverse Miniemulsion RAFT Polymerization

Stimuli-responsive core–shell microgels are of significant interest because of their fascinating applications due to the different swelling/shrinkage properties of their core and shell networks. Because such stimuli-responsive core–shell microgels are...