Poly(N-isopropylacrylamide)-clay based hydrogels controlled by the initiating conditions: evolution of structure and gel formation

Nontoxic Initiator Alternatives to TEMED for Redox Hydrogel Polymerization

Polymeric hydrogels are versatile biomaterials, offering unique advantages in tunability and biocompatibility that make them well-suited to a range of applications. Cross-linking, a fundamental step in hydrogel fabrication, is often initiated using a toxic redox system, ammonium persulfate (APS), and tetramethylethylenediamine (TEMED), which hinders hydrogel utility in direct contact with cells (e.g., wound dressings). To overcome this limitation, we developed alternative redox gelation systems that serve as nontoxic replacements for TEMED. The alternate initiators were either synthetic or bioinspired amine-containing polymers, Glycofect and polyethylenimine (PEI). Used with APS, these initiator candidates produced hydrogels with short gelation time and comparable moduli to TEMED-based gels and underwent further mechanical testing and biocompatibility characterization. While achieving mechanical properties similar to those of the control, the gels based on Glycofect and PEI outperformed TEMED-based gels in two cell viability studies, with Glycofect-initiated gels displaying significantly higher cytocompatibility. Taken together, these results indicate that Glycofect may serve as a drop-in replacement for TEMED to fabricate hydrogels with improved biocompatibility.

Multifunctional chitosan-based lanthanide luminescent hydrogel with stretchability, adhesion, self-healing, color tunability and antibacterial ability

Lanthanide luminescent hydrogels have broad application prospects in various fields. However, most of lanthanide hydrogels possess relatively simple functions, which is not conducive to practical applications. Therefore, it is becoming increasingly urgent to develop multifunctional hydrogels. Herein, a multifunctional chitosan-based lanthanide luminescent hydrogel with ultra-stretchability, multi-adhesion, excellent self-healing, emission color tunability, and good antibacterial ability was prepared by a simple one-step free radical polymerization. In this work, our designed lanthanide complexes [Ln(4-VDPA)3] contain three reaction sites, which can be copolymerized with N-[tris(hydroxymethyl) methyl] acrylamide (THMA), acrylamide (AM), and diacryloyl poly(ethylene glycol) (DPEG) to form the first chemical crosslinking network, while hydroxypropyltrimethyl ammonium chloride chitosan (HACC) interacts with the hydroxyl and amino groups derived from the chemical crosslinking network through hydrogen bonds to form the second physical crosslinking network. The structure of the double network as well as the dynamic hydrogen bond and lanthanide coordination endow the hydrogel with excellent stretchability, adhesion and self-healing properties. Moreover, the introduction of lanthanide complexes and chitosan makes the hydrogel exhibit outstanding luminescence and antibacterial performances. This research not only realizes the simple synthesis of multifunctional luminescent hydrogels, but also provides a new idea for the fabrication of biomass-based hydrogels as intelligent and sustainable materials.

Poly(ethylene Glycol) Methyl Ether Methacrylate-Based Injectable Hydrogels: Swelling, Rheological, and In Vitro Biocompatibility Properties with ATDC5 Chondrogenic Lineage

Here, we present the synthesis of a series of chemical homopolymeric and copolymeric injectable hydrogels based on polyethylene glycol methyl ether methacrylate (PEGMEM) alone or with 2-dimethylamino ethyl methacrylate (DMAEM). The objective of this study was to investigate how the modification of hydrogel components influences the swelling, rheological attributes, and in vitro biocompatibility of the hydrogels. The hydrogels' networks were formed via free radical polymerization, as assured by 1H nuclear magnetic resonance spectroscopy (1H NMR). The swelling of the hydrogels directly correlated with the monomer and the catalyst amounts, in addition to the molecular weight of the monomer. Rheological analysis revealed that most of the synthesized hydrogels had viscoelastic and shear-thinning properties. The storage modulus and the viscosity increased by increasing the monomer and the crosslinker fraction but decreased by increasing the catalyst. MTT analysis showed no potential toxicity of the homopolymeric hydrogels, whereas the copolymeric hydrogels were toxic only at high DMEAM concentrations. The crosslinker polyethylene glycol dimethacrylate (PEGDMA) induced inflammation in ATDC5 cells, as detected by the significant increase in nitric oxide synthase type II activity. The results suggest a range of highly tunable homopolymeric and copolymeric hydrogels as candidates for cartilage regeneration.

Exceptionally Fast Temperature-Responsive, Mechanically Strong and Extensible Monolithic Non-Porous Hydrogels: Poly(N-isopropylacrylamide) Intercalated with Hydroxypropyl Methylcellulose

Exceptionally fast temperature-responsive, mechanically strong, tough and extensible monolithic non-porous hydrogels were synthesized. They are based on divinyl-crosslinked poly(N-isopropyl-acrylamide) (PNIPAm) intercalated by hydroxypropyl methylcellulose (HPMC). HPMC was largely extracted after polymerization, thus yielding a 'template-modified' PNIPAm network intercalated with a modest residue of HPMC. High contents of divinyl crosslinker and of HPMC caused a varying degree of micro-phase-separation in some products, but without detriment to mechanical or tensile properties. After extraction of non-fixed HPMC, the micro-phase-separated products combine superior mechanical properties with ultra-fast T-response (in 30 s). Their PNIPAm network was highly regular and extensible (intercalation effect), toughened by hydrogen bonds to HPMC, and interpenetrated by a network of nano-channels (left behind by extracted HPMC), which ensured the water transport rates needed for ultra-fast deswelling. Moreover, the T-response rate could be widely tuned by the degree of heterogeneity during synthesis. The fastest-responsive among our hydrogels could be of practical interest as soft actuators with very good mechanical properties (soft robotics), while the slower ones offer applications in drug delivery systems (as tested on the example of Theophylline), or in related biomedical engineering applications.

Ultra-Tough Self-Healing Hydrogel via Hierarchical Energy Associative Dissipation

Owing to high water content and homogeneous texture, conventional hydrogels hardly reach satisfactory mechanical performance. Tensile-resistant groups and structural heterogeneity are employed to fabricate tough hydrogels. However, those techniques significantly increase the complexity and cost of material synthesis, and have only limited applicability. Here, it is shown that ultra-tough hydrogels can be obtained via a unique hierarchical architecture composed of chemically coupled self-assembly units. The associative energy dissipation among them may be rationally engineered to yield libraries of tough gels with self-healing capability. Tunable tensile strength, fracture strain, and toughness of up to 19.6 MPa, 20 000%, and 135.7 MJ cm⁻3 are achieved, all of which exceed the best known records. The results demonstrate a universal strategy to prepare desired ultra-tough hydrogels in predictable and controllable manners.

3D printed and stimulus responsive drug delivery systems based on synthetic polyelectrolyte hydrogels manufactured via digital light processing

Hydrogels are three-dimensional hydrophilic polymeric networks absorbing up to and even more than 90 wt% of water. These superabsorbent polymers retain their shape during the swelling process while enlarging their volume and mass. In addition to their swelling behavior, hydrogels can possess other interesting properties, such as biocompatibility, good rheological behavior, or even antimicrobial activity. This versatility qualifies hydrogels for many medical applications, especially drug delivery systems. As recently shown, polyelectrolyte-based hydrogels offer beneficial properties for long-term and stimulus-responsive applications. However, the fabrication of complex structures and shapes can be difficult to achieve with common polymerization methods. This obstacle can be overcome by the use of additive manufacturing. 3D printing technology is gaining more and more attention as a method of producing materials for biomedical applications and medical devices. Photopolymerizing 3D printing methods offer superior resolution and high control of the photopolymerization process, allowing the fabrication of complex and customizable designs while being less wasteful. In this work, novel synthetic hydrogels, consisting of [2-(acryloyloxy) ethyl]trimethylammonium chloride (AETMA) as an electrolyte monomer and poly(ethylene glycol)-diacrylate (PEGDA) as a crosslinker, 3D printed via Digital Light Processing (DLP) using a layer height of 100 μm, are reported. The hydrogels obtained showed a high swelling degree q∞m,t ∼ 12 (24 h in PBS; pH 7; 37 °C) and adjustable mechanical properties with high stretchability (ε_max ∼ 300%). Additionally, we embedded the model drug acetylsalicylic acid (ASA) and investigated its stimulus-responsive drug release behaviour in different release media. The stimulus responsiveness of the hydrogels is mirrored in their release behavior and could be exploited in triggered as well as sequential release studies, demonstrating a clear ion exchange behavior. The received 3D-printed drug depots could also be printed in complex hollow geometry, exemplarily demonstrated via an individualized frontal neo-ostium implant prototype. Consequently, a drug-releasing, flexible, and swellable material was obtained, combining the best of both worlds: the properties of hydrogels and the ability to print complex shapes.

Self-Healing and Super-Elastomeric PolyMEA-co-SMA Nanocomposites Crosslinked by Clay Platelets

Novel solvent-free ultra-extensible, tough, and self-healing nanocomposite elastomers were synthesized. The self-assembled materials were based on the copolymer matrix poly(methoxyethyl acrylate-co-sodium methacrylate) physically crosslinked by clay nano-platelets (‘poly[MEA-co-SMA]/clay’). Depending on the content of SMA, the super-elastomers were predominantly hydrophobic, water-swelling, or fully water-soluble, and hence repeatedly processible. The SMA co-monomer introduces a tremendous increase in tensile strength, an increase in toughness, while ultra-extensibility is preserved. By tuning the contents of nano-clay and SMA co-monomer, a very wide range of product properties was achieved, including extreme ultra-extensibility, or high stiffness combined with more moderate super-extensibility, or very different values of tensile strength. There was very attractive, great improvement in autonomous self-healing ability induced by SMA, combined with tremendously enhanced self-recovery of internal mechanical damage: even complete self-recovery could be achieved. The ionic SMA repeat units were found to assemble to multiplets, which are phase-separated in the hydrophobic polyMEA matrix. The dynamics of SMA-units-hopping between these aggregates was of key importance for the mechanical, visco-elastic, tensile, and self-healing properties. The studied super-elastomers are attractive as advanced self-healing materials in engineering, soft robotics, and in medical or implant applications.

Reactive Additive Capillary Stamping with Double Network Hydrogel-Derived Aerogel Stamps under Solvothermal Conditions

Integration of solvothermal reaction products into complex thin-layer architectures is frequently achieved by combinations of layer transfer and subtractive lithography, whereas direct additive substrate patterning with solvothermal reaction products has remained challenging. We report reactive additive capillary stamping under solvothermal conditions as a parallel contact-lithographic access to patterns of solvothermal reaction products in thin-layer configurations. To this end, corresponding precursor inks are infiltrated into mechanically robust mesoporous aerogel stamps derived from double-network hydrogels. The stamp is then brought into contact with a substrate to be patterned under solvothermal reaction conditions inside an autoclave. The precursor ink forms liquid bridges between the topographic surface pattern of the stamp and the substrate. Evaporation-driven enrichment of the precursors in these liquid bridges, along with their liquid-bridge-guided conversion into the solvothermal reaction products, yields large-area submicron patterns of the solvothermal reaction products replicating the stamp topography. For example, we prepared thin hybrid films, which contained ordered monolayers of superparamagnetic submicron nickel ferrite dots prepared by solvothermal capillary stamping surrounded by nickel electrodeposited in a second orthogonal substrate functionalization step. The submicron nickel ferrite dots acted as a magnetic hardener, halving the remanence of the ferromagnetic nickel layer. In this way, thin-layer electromechanical systems, transformers, and positioning systems may be customized.

Facile synthesis of biogenic silica nanomaterial loaded transparent tragacanth gum hydrogels with improved physicochemical properties and inherent anti-bacterial activity

In this report, biogenic, crystalline (∼60.5 ± 2%) bowknot structured silica nanoparticles (BSNPs) of length ∼ 274 ± 7 nm and width ∼ 36 ± 2 nm were isolated from invasive species viz. Lantana camara. These were then chemically modified using nitrogen containing moieties viz. APTES and CTAB. These modified BSNPs were then used as electrostatic cross-linking agents for the formation of tragacanth gum (TG) hydrogels. The cytocompatible CTAB@BSNP-TG hydrogels documented ∼10-12 fold enhancement in anti-bacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa when compared with TG hydrogels. Disruption of the bacterial membrane by ROS generation and protein leakage were responsible for anti-bacterial activity. A cell migration assay suggested that CTAB@BSNP-TG augmented the cell proliferation of NIH-3T3 cells compared to other TG hydrogels. The present study will pave the path for the development of organic-inorganic hybrid nanocomposite-based hydrogels for anti-bacterial and cell migration applications.

Biodegradable porous micro/nanoparticles with thermoresponsive gatekeepers for effective loading and precise delivery of active compounds at the body temperature

Stimuli-responsive controlled delivery systems are of interest for preventing premature leakages and ensuring precise releases of active compounds at target sites. In this study, porous biodegradable micro/nanoparticles embedded with thermoresponsive gatekeepers are designed and developed based on Eudragit RS100 (PNIPAM@RS100) and poly(N-isopropylacrylamide) via a double emulsion solvent evaporation technique. The effect of initiator types on the polymerization of NIPAM monomer/methylene-bis-acrylamide (MBA) crosslinker was investigated at 60 °C for thermal initiators and ambient temperature for redox initiators. The crosslinked PNIPAM plays a key role as thermal-triggered gatekeepers with high loading efficiency and precise release of a model active compound, Nile Blue A (NB). Below the volume phase transition temperature (T_VPT), the gatekeepers possess a swollen conformation to block the pores and store NB within the cavities. Above its T_VPT, the chains rearrange, allowing gate opening and a rapid and constant release rate of the compound until completion. A precise “on–off” switchable release efficiency of PNIPAM@RS100 was demonstrated by changing the temperatures to 4 and 40 °C. The materials are a promising candidate for controlled drug delivery systems with a precise and easy triggering mechanism at the body temperature for effective treatments.

Comparison of globular albumin methacryloyl and random-coil gelatin methacryloyl: Preparation, hydrogel properties, cell behaviors, and mineralization

Bovine serum albumin methacryloyl (BSAMA) is a newly emerging photocurable globular protein-based material whereas gelatin methacryloyl (GelMA) is one of the most popular photocurable fibrous protein-based materials. So far, the influence of their different structural conformations as building blocks on hydrogel properties and mineral deposition has not been investigated. Here, we compared their differences in structures, gelation kinetics, hydrogel properties, mineralization, and cell behaviors. BSAMA maintained a stable globular structure while GelMA exhibited temperature-sensitive conformations (4 - 37 °C). BSAMA displayed slower gelation kinetics and much more retarded enzymatic degradation compared to GelMA. Photocurable BSAMA (6.41 - 390.95 kPa) and GelMA hydrogels (36.09 - 199.70 kPa) exhibited tunable mechanical properties depending on their concentrations (10 - 20%). Interestingly, BSAMA hydrogels mineralized needle-like apatite (Ca/P: 1.409) with higher crystallinity compared to GelMA hydrogels (Ca/P: 1.344). BSAMA and GelMA supported satisfactory cell (MC3T3-L1) viability of 99.43 ± 0.57% and 97.14 ± 0.69%, respectively. However, BSAMA gels were less favorable to cell proliferation and migration than GelMA gels. In serum-free environments, cells on GelMA displayed a higher amount of attachment, a more elongated shape, and a longer protrusion compared to those on BSAMA (p < 0.01) during the early adhesion.

Insight into the aqueous Laponite® nanodispersions for self-assembled poly(itaconic acid) nanocomposite hydrogels: The effect of multivalent phosphate dispersants

HYPOTHESIS

We hypothesize, that physical network between Laponite® nanoparticles and high molecular weight polyelectrolyte formed by mixing of Laponite® nanodispersion (containing multivalent phosphate dispersant) and polyelectrolyte solution is strongly influenced by the type and content of dispersant, which forms electric double layer (EDL) closely to the Laponite® edges. Thus, optimum dispersant concentration is necessary to overcome clay-clay interactions (excellent clay delamination), but should not be exceeded, what would result in the EDL compression and weakening of attractions forming clay-polyelectrolyte network. Thus, deeper investigation of Laponite® nanodispersions is highly demanded since it would enable to better design the self-assembled clay-polyelectrolyte hydrogels.

EXPERIMENTS

To study clay interparticle interactions in the presence of various multivalent phosphates, complementary methods providing wide nanodispersion characterization have been applied: zeta potential measurement and SAXS technique (electrostatic interactions), oscillatory rheology (nanodispersion physical state) and NMR experiments (ion immobilization degree).

FINDINGS

It was found that multivalent phosphates induce and tune strength of clay-polyelectrolyte interactions forming hydrogel network in terms of varying EDL on the Laponite® edges. Moreover, phosphate dispersing efficiency depends on the molecular size, chemical structure, and valence of the anion; its potential as efficient dispersant for hydrogel preparation can be evaluated by estimation of anion charge density.

Novel Tough and Transparent Ultra-Extensible Nanocomposite Elastomers Based on Poly(2-methoxyethylacrylate) and Their Switching between Plasto-Elasticity and Viscoelasticity

Novel stiff, tough, highly transparent and ultra-extensible self-assembled nanocomposite elastomers based on poly(2-methoxyethylacrylate) (polyMEA) were synthesized. The materials are physically crosslinked by small in-situ-formed silica nanospheres, sized 3-5 nm, which proved to be a very efficient macro-crosslinker in the self-assembled network architecture. Very high values of yield stress (2.3 MPa), tensile strength (3.0 MPa), and modulus (typically 10 MPa), were achieved in combination with ultra-extensibility: the stiffest sample was breaking at 1610% of elongation. Related nanocomposites doubly filled with nano-silica and clay nano-platelets were also prepared, which displayed interesting synergy effects of the fillers at some compositions. All the nanocomposites exhibit 'plasto-elastic' tensile behaviour in the 'as prepared' state: they display considerable energy absorption (and also 'necking' like plastics), but at the same time a large but not complete (50%) retraction of deformation. However, after the first large tensile deformation, the materials irreversibly switch to 'real elastomeric' tensile behaviour (with some creep). The initial 'plasto-elastic' stretching thus causes an internal rearrangement. The studied materials, which additionally are valuable due to their high transparency, could be of application interest as advanced structural materials in soft robotics, in implant technology, or in regenerative medicine. The presented study focuses on structure-property relationships, and on their effects on physical properties, especially on the complex tensile, elastic and viscoelastic behaviour of the polyMEA nanocomposites.

Exploring the role of Muscovite in poly(alkyl methacrylate)-based ternary nanocomposite cryogels with selective functional groups: formation via cryogelling with the aid of inorganic clay

Easy fabrication of inorganic clay muscovite (MUS) embedded poly(2-acrylamido-2-methyl-1-propane sulfonic acid-co-diethylaminoethyl methacrylate-co-hydroxyethyl methacrylate) (PADH) nanocomposite cryogels with dual temperature/pH dependent catalytic potential was reported. Nanocomposite cryogels were fabricated by a method involving cryogelation and free radical crosslinking of aqueous systems containing MUS ranging from 0% to 1.50% (w/v). The changes in the properties of polybasic PADH networks were investigated to explain how the network parameters and gel properties were affected by the addition of clay, with the formation of a single terpolymer-MUS structure. The potential of the addition of different amounts of MUS to strengthen the prepared terpolymer matrix was investigated by uniaxial compression tests. By lowering the polymerization temperature or increasing the MUS content, the PADH/MUS nanocomposite cryogels became more elastic and compressible with stronger entanglement of terpolymer chains between the clay layers. With the addition of 1.50% (w/v) MUS, the swelling capacity was reduced by 50%, resulting in a two-fold increase in compression elasticity. The nanocomposite gels showed a strong pH-dependence, and when the pH of the swelling medium decreased from 9.8 to 2.1, there was a significant increase in the degree of swelling with increasing protonation of tertiary amine groups. Under an acidic environment, the swelling capacity of the nanocomposite gel containing 1.10% (w/v) MUS increased by 49.5%. In temperature dependent swelling between 15 and 75 °C, all ternary PADH/MUS-Ngels showed a tendency to swell at low and high swelling temperatures, by the predominance of DEAEM units at low temperatures and HEMA monomers at high temperatures, respectively. As the temperature was increased to 55 °C, the swelling decreased and reached a minimum, and then the nanocomposite gels tended to swell again. The obtained results provide an insight into the effect of MUS addition on the properties of poly(alkyl methacrylate)-based ternary nanocomposite gels and demonstrate a simple and efficient way to produce multiple response systems with enhanced elasticity.

Concentration Polarization Enabled Reactive Coating of Nanofiltration Membranes with Zwitterionic Hydrogel

In this study, the bottleneck challenge of membrane fouling is addressed via establishing a scalable concentration polarization (CP) enabled and surface-selective hydrogel coating using zwitterionic cross-linkable macromolecules as building blocks. First, a novel methacrylate-based copolymer with sulfobetain and methacrylate side groups was prepared in a simple three-step synthesis. Polymer gelation initiated by a redox initiator system (ammonium persulfate and tetramethylethylenediamine) for radical cross-linking was studied in bulk in order to identify minimum ("critical") concentrations to obtain a hydrogel. In situ reactive coating of a polyamide nanofiltration membrane was achieved via filtration of a mixture of the reactive compounds, utilizing CP to meet critical gelation conditions solely within the boundary layer. Because the feasibility was studied and demonstrated in dead-end filtration mode, the variable extent of CP was estimated in the frame of the film model, with an iterative calculation using experimental data as input. This allowed to discuss the influence of parameters such as solution composition or filtration rate on the actual polymer concentration and resulting hydrogel formation at the membrane surface. The zwitterionic hydrogel-coated membranes exhibited lower surface charge and higher flux during protein filtration, both compared to pristine membranes. Salt rejection was found to remain unchanged. Results further reveal that the hydrogel coating thickness and consequently the reduction in membrane permeance due to the coating can be tuned by variation of filtration time and polymer feed concentration, illustrating the novel modification method's promising potential for scale-up to real applications.

Phase Transition Behavior and Catalytic Activity of Poly(N-acryloylglycinamide-co-methacrylic acid) Microgels

Poly(N-acryloyl glycinamide) is a well-known thermoresponsive polymer possessing an upper critical solution temperature (UCST) in water. By copolymerizing N-acryloyl glycinamide (NAGA) with methacrylic acid (MAA) in the presence of a crosslinker, poly(N-acryloyl glycinamide-co-methacrylic acid) [P(NAGA-MAA)] copolymer microgels with an MAA molar fraction of 10-70 mol % were obtained. The polymerization kinetics suggests that the copolymer microgels have a random structure. The size of the microgels was between 60 and 120 nm in the non-aggregated swollen state in aqueous medium and depending on the solvent conditions, they show reversible swelling and shrinking upon temperature change. Their phase transition behavior was studied by a combination of methods to understand the process of the UCST-type behavior and interactions between NAGA and MAA. P(NAGA-MAA) microgels were loaded with silver nanoparticles (AgNPs) by the reduction of AgNO₃ under UV light. Compared with the chemical reduction of AgNO₃, the photoreduction results in smaller AgNPs and the amount and size of the AgNPs are dependent on the comonomer ratio. The catalytic activity of the AgNP-loaded microgels in 4-nitrophenol reduction was tested.

Thermoresponsive hydrogels physically crosslinked with magnetically modified LAPONITE® nanoparticles

Recently, considering the potential applications of hydrogel nanocomposites in biomedical engineering, there has been a growing interest in the synthesis of hydrogels with improved mechanical properties. Among magnetic materials, iron oxides are of particular interest due to their magnetic properties and biocompatibility. At the same time, LAPONITE®, a synthetic clay, can be used to improve the mechanical properties of polymer-based nanocomposites. In this study we report the effects of hydrogel composition and structure on its thermoresponsive properties and hydrogel sorption and release of a model anticancer drug - 5-fluorouracil. Using one-step coprecipitation method we synthesized magnetic LAPONITE® (LAM) nanoparticles with magnetite-to-LAPONITE® weight ratios from 2 : 1 to 1 : 8. With increase in magnetite concentration the ferrofluidic properties of LAM nanoparticles are getting improved, while fluorouracil absorptivity - decreases. Exfoliation of the clay is observed when the magnetite content exceeds the LAPONITE® content. Physical crosslinking of poly(N-isopropylacrylamide) with LAM nanoparticles yields magnetic thermosensitive hydrogel nanocomposites with controllable temperature-induced drug release. All hydrogel nanocomposites have a distinct volume phase transition from a swollen state to a collapsed state upon heating within the physiologically acceptable temperature range of 33-36 °C.

Chitosan reinforced hydrogels with swelling-shrinking behaviors in response to glucose concentration

Different hydrogels of poly(acrylamide-co-3-acrylamido phenylboronic acid-co-chitosan grafted maleic acid) (P(AM-co-AAPBA-co-CSMA)s) were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as a crosslinker to serve for glucose sensing and insulin delivery. The structure and morphology of the hydrogels, named as CSPBA were studied by FTIR and SEM, while the mechanical properties were tested using dynamic mechanical analysis (DMA) and universal testing machine. The prepared hydrogels shrinked at low glucose concentration due to the 2:1 boronate-glucose binding, and swelled at high glucose concentration because of 1:1 boronate-glucose complexation. Both binding mechanisms are useful for glucose sensing and insulin delivery. The integration of CSMA into hydrogels network not only enhanced the response to glucose at physiological pH, but also improved the mechanical properties and increased the encapsulation efficiency of the prepared hydrogels. These CSPBA may find potential as implantable hydrogels in applications were continuous glucose monitoring and controlled release is beneficial.

Synthesis and Evaluation of a Thermoresponsive Degradable Chitosan-Grafted PNIPAAm Hydrogel as a "Smart" Gene Delivery System

Thermoresponsive hydrogels demonstrate tremendous potential as sustained drug delivery systems. However, progress has been limited as formulation of a stable biodegradable thermosensitive hydrogel remains a significant challenge. In this study, free radical polymerization was exploited to formulate a biodegradable thermosensitive hydrogel characterized by sustained drug release. Highly deacetylated chitosan and N-isopropylacrylamide with distinctive physical properties were employed to achieve a stable, hydrogel network at body temperature. The percentage of chitosan was altered within the copolymer formulations and the subsequent physical properties were characterized using ¹H-NMR, FTIR, and TGA. Viscoelastic, swelling, and degradation properties were also interrogated. The thermoresponsive hydrogels were loaded with RALA/pEGFP-N1 nanoparticles and release was examined. There was sustained release of nanoparticles over three weeks and, more importantly, the nucleic acid cargo remained functional and this was confirmed by successful transfection of the NCTC-929 fibroblast cell line. This tailored thermoresponsive hydrogel offers an option for sustained delivery of macromolecules over a prolonged considerable period.

Hydrogel-clay Nanocomposites as Carriers for Controlled Release

The present review aims to summarize the research efforts undertaken in the last few years in the development and testing of hydrogel-clay nanocomposites proposed as carriers for controlled release of diverse drugs. Their advantages, disadvantages and different compositions of polymers/biopolymers with diverse types of clays, as well as their interactions are discussed. Illustrative examples of studies regarding hydrogel-clay nanocomposites are detailed in order to underline the progressive researches on hydrogel-clay-drug pharmaceutical formulations able to respond to a series of demands for the most diverse applications. Brief descriptions of the different techniques used for the characterization of the obtained complex hybrid materials such as: swelling, TGA, DSC, FTIR, XRD, mechanical, SEM, TEM and biology tests, are also included. Enlightened by the presented data, we can suppose that hydrogel-clay nanocomposites will still be a challenging subject of global assiduous researches. We can dare to dream to an efficient drug delivery platform for the treatment of multiple affection concomitantly, these being undoubtedly like "a tree of life" bearing different kinds of fruits and leaves proper for human healing.

Comparison of Dynamic Light Scattering and Rheometrical Methods to Determine the Gel Point of a Radically Polymerized Hydrogel under Mechanical Shear

The phase transition of nanocomposite hydrogels made of N-isopropylacrylamide (NIPAm) and clay (Laponite^® XLS) was investigated under mechanical shear influencing the gelation. The hydrogels were synthesized by free radical polymerization. For the processing of cross-linked gels, the phase transition (liquid–solid) and its dependence on mechanical stress are of paramount importance. On the one hand, the determination of the gel point (tg) is possible with rheometry and, on the other hand, with dynamic light scattering (DLS). With rotational rheometry, by identifying the abrupt increase of viscosity, the gel point is evaluated. The DSL is an alternative method to rheometry, to investigate hydrogels under the action of the shear flow, to make results comparable to the rheometric investigations, with and without shear. Experimental parameters were chosen based on preparatory work to obtain comparable results regarding the determination of the gel point of a radically polymerized NIPAm hydrogel.

Swelling characteristics and biocompatibility of ionic liquid based hydrogels for biomedical applications

Polymers are commonly used in medical device manufacturing, e.g. for drug delivery systems, bone substitutes and stent coatings. Especially hydrogels exhibit very promising properties in this field. Hence, the development of new hydrogel systems for customized application is of great interest, especially regarding the swelling behavior and mechanical properties as well as the biocompatibility. The aim of this work was the preparation and investigation of various polyelectrolyte and poly-ionic liquid based hydrogels accessible by radical polymerization. The obtained polymers were covalently crosslinked with N,N'-methylenebisacrylamide (MBAA) or different lengths of poly(ethyleneglycol)diacrylate (PEGDA). The effect of different crosslinker-to-monomer ratios has been examined. In addition to the compression curves and the maximum degree of swelling, the biocompatibility with L929 mouse fibroblasts of these materials was determined in direct cell seeding experiments and the outcome for the different hydrogels was compared.

Highly Tough, Biocompatible, and Magneto-Responsive Fe3O4/Laponite/PDMAAm Nanocomposite Hydrogels

Magneto-responsive hydrogels (MRHs) have attracted considerable attention in various applications owing to their smart response to an externally applied magnetic field. However, their practical uses in biomedical fields are limited by their weak mechanical properties and possible toxicity to the human body. In this study, tough, biocompatible, and magneto-responsive nanocomposite hydrogels (MR_NCHs) were developed by the in-situ free-radical polymerization of N, N-dimethylacrylamide (DMAAm) and laponite and Fe3O4 nanoparticles. The effects of the concentrations of DMAAm, water, and laponite and Fe3O4 nanoparticles in the pre-gel solutions or mixtures on the viscoelastic and mechanical properties of the corresponding hydrogels were examined by performing rheological and tensile tests, through which the mixture composition producing the best MR_NCH system was optimized. The effects were also explained by the possible network structures of the MR_NCHs. Moreover, the morphology, chemical structure, and thermal and mechanical properties of the MR_NCHs were analyzed, while comparing with those of the poly(DMAAm) (PDMAAm) hydrogels and laponite/PDMAAm NCHs. The obtained optimal MR_NCH exhibited noticeable magnetorheological (MR) behavior, excellent mechanical properties, and good biocompatibility. This study demonstrates how to optimize the best Fe3O4/laponite/PDMAAm MR_NCH system and its potential as a soft actuator for the pharmaceutical and biomedical applications.

The structure-property relationship in LAPONITE® materials: from Wigner glasses to strong self-healing hydrogels formed by non-covalent interactions

Rheology, small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) analysis, zeta potential measurement, scanning electron microscopy (SEM), and micro-FTIR and absorbance spectroscopy were used to enlighten the controversial literature about LAPONITE® materials. Our data suggest that pristine LAPONITE® in water does not form hydrogels induced by the so-called "house of cards" assembly, but rather forms Wigner glasses governed by repulsive forces. Ionic interactions between anisotropic LAPONITE® nanodiscs, sodium polyacrylate and inorganic salts afforded hydrogels that were transparent, self-standing, moldable, strong, and biocompatible with shear-thinning and self-healing behavior. An extensive study on the role of salts in the gelification process dictates a trend that relates the valence of cations with the viscoelastic properties of the bulk material (G' values follow the trend, monovalent < divalent < trivalent). These hydrogels present G' values up to 5.1 × 104 Pa, which are considered high values for non-covalent hydrogels. Hydrogels crosslinked with sodium phosphate salts are biocompatible, and might be valid candidates for injectable drug delivery systems due to their shear-thinning behavior with rapid self-healing after injection.

Monolithic intercalated PNIPAm/starch hydrogels with very fast and extensive one-way volume and swelling responses to temperature and pH: prospective actuators and drug release systems

Remarkable monolithic (non-porous) hydrogels based on poly(NIPAm-co-sodium methacrylate) intercalated by starch were prepared, and were found to display very fast and extensive one-way solvent (water) release, induced by both pH and temperature. With centimeter-sized 3D specimens, the achieved response times were as short as 4 min (for 70% water release), in combination with very large volume responses (shrinking ratios up to 15). The response time can be tuned from minutes, over tens of minutes, up to hours. The pH-induced deswelling is always slower than the temperature-induced one, but at the highest starch content, ca. 5.5 min are needed for 70% completion of the pH-triggered process. Simultaneous temperature- and pH-stimuli expectedly also lead to very fast water release. The unique intercalated structure and the temperature-dependent hydrogen bridging between the intercalated phases, as well as between these phases and water, were found to play the key role in the ability of the gels to rapidly release water and shrink, which was deeper elucidated in this work. The hydrogels are of interest as soft actuators, but also for chemical release systems or for drug release applications. The latter was successfully tested with theophylline as the drug.

X10 expansion microscopy enables 25-nm resolution on conventional microscopes

Expansion microscopy is a recently introduced imaging technique that achieves super‐resolution through physically expanding the specimen by ~4×, after embedding into a swellable gel. The resolution attained is, correspondingly, approximately fourfold better than the diffraction limit, or ~70 nm. This is a major improvement over conventional microscopy, but still lags behind modern STED or STORM setups, whose resolution can reach 20–30 nm. We addressed this issue here by introducing an improved gel recipe that enables an expansion factor of ~10× in each dimension, which corresponds to an expansion of the sample volume by more than 1,000‐fold. Our protocol, which we termed X10 microscopy, achieves a resolution of 25–30 nm on conventional epifluorescence microscopes. X10 provides multi‐color images similar or even superior to those produced with more challenging methods, such as STED, STORM, and iterative expansion microscopy (iExM). X10 is therefore the cheapest and easiest option for high‐quality super‐resolution imaging currently available. X10 should be usable in any laboratory, irrespective of the machinery owned or of the technical knowledge.

Collagenase nanocapsules: An approach to fibrosis treatment

Fibrosis is a common lesion in different pathologic diseases and defined by the excessive accumulation of collagen. Different approaches have been used to treat different conditions characterized by fibrosis. The FDA and EMA approved the use of collagenase to treat palmar fibromatosis (Dupuytren's contracture). The EMA approved additionally its use in severe Peyronie's disease, but it has been used off label in other conditions [1,2]. The approved treatment includes up to three (in palmar fibromatosis) or up to eight (in penile fibromatosis) injections followed by finger extension or penile modeling procedures, typically causing severe pain. Frequent single injections are adequate to treat palmar fibromatosis [3]. The need to repeatedly inject doses of this enzyme can be due to the labile nature of collagenase, which exhibits a complete activity loss after a short period of time. This study presents a novel strategy to manage this enzyme based on the synthesis of polymeric nanocapsules that contain collagenase encapsulated within their matrix. These nanocapsules have been engineered for achieving a gradual release of the encapsulated enzyme for a longer time, which can be up to ten days. The efficacy of these nanocapsules has been tested in a murine model of local dermal fibrosis, and the results demonstrate a reduction in fibrosis greater than that with the injection of free enzyme; this type of treatment showed a significant improvement compared to conventional therapy of free collagenase.

STATEMENT OF SIGNIFICANCE

The use of proteins as therapeutic molecules has recently attracted great interest. Collagenase injection is the current treatment for fibrotic diseases. Unfortunately, proteins have a low stability and presume several repetition cycles to obtain an effective treatment. This article describes a novel treatment for these types of diseases using collagenase nanocapsules designed to exhibit a sustainable release of the encapsulated enzyme, which maintains the enzymatic activity for a long period of time. The therapeutic effect of nanocapsules was tested in a murine mouse model of local dermal fibrosis, and the results showed an important improved effect compared to the effect of the administration of free enzyme. These results indicate a high potential for this novel system to improve the current treatment for fibrotic diseases.

Nanotechnological Strategies for Protein Delivery

The use of therapeutic proteins plays a fundamental role in the treatment of numerous diseases. The low physico-chemical stability of proteins in physiological conditions put their function at risk in the human body until they reach their target. Moreover, several proteins are unable to cross the cell membrane. All these facts strongly hinder their therapeutic effect. Nanomedicine has emerged as a powerful tool which can provide solutions to solve these limitations and improve the efficacy of treatments based on protein administration. This review discusses the advantages and limitations of different types of strategies employed for protein delivery, such as PEGylation, transport within liposomes or inorganic nanoparticles or their in situ encapsulation.

Poly(ethylene oxide monomethyl ether)- block-poly(propylene succinate) Nanoparticles: Synthesis and Characterization, Enzymatic and Cellular Degradation, Micellar Solubilization of Paclitaxel, and in Vitro and in Vivo Evaluation

Polyester-based nanostructures are widely studied as drug-delivery systems due to their biocompatibility and biodegradability. They are already used in the clinic. In this work, we describe a new and simple biodegradable and biocompatible system as the Food and Drug Administration approved polyesters (poly-ε-caprolactone, polylactic acid, and poly(lactic- co-glycolic acid)) for the delivery of the anticancer drug paclitaxel (PTX) as a model drug. A hydrophobic polyester, poly(propylene succinate) (PPS), was prepared from a nontoxic alcohol (propylene glycol) and monomer from the Krebs's cycle (succinic acid) in two steps via esterification and melt polycondensation. Furthermore, their amphiphilic block copolyester, poly(ethylene oxide monomethyl ether)- block-poly(propylene succinate) (mPEO- b-PPS), was prepared by three steps via esterification followed by melt polycondensation and the addition of mPEO to the PPS macromolecules. Analysis of the in vitro cellular behavior of the prepared nanoparticle carriers (NPs) (enzymatic degradation, uptake, localization, and fluorescence resonance energy-transfer pair degradation studies) was performed by fluorescence studies. PTX was loaded to the NPs of variable sizes (30, 70, and 150 nm), and their in vitro release was evaluated in different cell models and compared with commercial PTX formulations. The mPEO- b-PPS copolymer analysis displays glass transition temperature < body temperature < melting temperature, lower toxicity (including the toxicity of their degradation products), drug solubilization efficacy, stability against spontaneous hydrolysis during transport in bloodstream, and simultaneous enzymatic degradability after uptake into the cells. The detailed cytotoxicity in vitro and in vivo tumor efficacy studies have shown the superior efficacy of the NPs compared with PTX and PTX commercial formulations.

Insight into the cryopolymerization to form a poly(N-isopropylacrylamide)/clay macroporous gel: structure and phase evolution

The cryopolymerization and formation of a macroporous poly(N-isopropylacrylamide) (PNIPA)/clay cryogel were investigated. The mechanism of the cryopolymerization and cryogel formation was elucidated. Two processes, cryostructuration and cryopolymerization, proceed simultaneously and their relative rates determine the structure evolution and the cryogel morphology - porosity. The cryostructuration in the PNIPA/clay system during freezing, controlled by the freezing temperature and the rate of cooling, includes both water and NIPA crystallization, formation of a highly concentrated non-frozen liquid phase (NFLP) and clay aggregation. The rate of cryopolymerization and gelation is governed by the following effects: by a low polymerization temperature and after freezing, by the high cryoconcentration and a steric confinement, manifested by a reduced reagent mobility. Moreover, it depends on the cooling rate and the evolution of cryostructuration. The progress of cryostructuration and cryopolymerization during freezing was described and experimentally proved step by step. Both the phase development during freezing and the progress of cryopolymerization including gelation were monitored in situ by NMR, DSC, chemorheology and SAXS. The morphology and porosity of the cryogels were characterized by SEM and TEM.

Design, preparation and characterization of pH-responsive prodrug micelles with hydrolyzable anhydride linkages for controlled drug delivery

We report a new prodrug micelle-based approach in which a model hydrophobic non-steroidal anti-inflammatory drug (NSAID), ibuprofen (Ibu), is tethered to amphiphilic methoxy polyethylene glycol-polypropylene fumarate (mPEG-PPF) diblock copolymer via hydrolytic anhydride linkages for potential controlled release applications of NSAIDs. Synthesized mPEG-PPF-Ibu polymer drug conjugates (PDCs) demonstrated high drug conjugation efficiency (∼90%) and self-assembled to form micellar nanostructures in aqueous medium with critical micelle concentrations ranging between 16 and 30μg/mL. The entrapment efficiency of Ibu in prepared PDC micelles was as high as 18% (w/w). Crosslinking of prodrug micelles with N,N'-dimethylaminoethyl methacrylate conferred pH-responsive characteristics. pH-responsive PDC micelles averaged 100nm in size at pH 7.4 and exhibited concomitant changes in size upon incubation in physiologically relevant mildly acidic conditions. Ibu release was observed to increase with increasing acidic conditions and could be controlled by varying the amount of crosslinker used. Furthermore, the prepared mPEG-PPF-based micelles demonstrated excellent cytocompatibility and cellular internalization in vitro. More importantly, PDC micelles exerted anti-inflammatory effects by significantly decreasing monosodium urate crystal-induced prostaglandin E2 levels in rabbit synoviocyte cultures in vitro. Cumulatively, our results indicate that this new prodrug micelle approach is promising for NSAID-based therapies in the treatment of arthritis and cancer.

The Influence of Anionic Initiator on the Selected Properties of Poly-N-Isopropyl Acrylamide Evaluated for Controlled Drug Delivery

The aim of the study was to monitor the influence of increasing initiator concentrations on the properties of poly-N-isopropylacrylamide (polyNIPA) nanoparticles obtained via surfactant free precipitation polymerization (SFPP). In all studied systems P-001 to P-1, the same amount of monomer was used, and increasing amounts of potassium persulphate (KPS). The course of each reaction was monitored by measuring the conductivity of the whole system. The resulting composition of products was confirmed by attenuated total reflectance within Fourier transformed infrared spectroscopy (ATR-FTIR) measurements. The hydrodynamic diameters with polydispersity index (PDI) and zeta potential (ZP) were measured in aqueous dispersions of the synthesized polymers in dynamic light scattering (DLS) device (λ = 678 nm), and were found to be for P-1: 20.33 nm (PDI = 0.49) and −7 mV, for P-05: 22.24 nm (PDI = 0.39) and −5 mV, for P-01: 50.14 nm (PDI = 0.49) and −3 mV, for P-005: 62.75 nm (PDI = 0.54) and −3 mV and for P-001: 509.4 nm (PDI = 0.61) and −12 mV at 18 °C, respectively. Initiator concentration affects the size and ZP of particles. The hydrodynamic diameter decreases with initiator concentration increase, whereas the time of the reaction decreases when the initiator concentration increases. This fact is reflected in the observed values of conductivity in the course of the performed reaction. Evaluated volume phase transition temperature in the range of 32 °C enables further research of the nanoparticles as thermosensitive drug carriers.