Poly(2-oxazoline)-based magnetic hydrogels: Synthesis, performance and cytotoxicity

From Brush to Dendritic Structure: Tool for Tunable Interfacial Compatibility between the Iron-Based Particles and Silicone Oil in Magnetorheological Fluids

Comprehensive magnetic particle stability together with compatibility between them and liquid medium (silicone oil) is still a crucial issue in the case of magnetorheological (MR) suspensions to guarantee their overall stability and MR performance. Therefore, this study is aimed at improving the interfacial stability between the carbonyl iron (CI) particles and silicone oil. In this respect, the particles were modified with polymer brushes and dendritic structures of poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS), called CI-brushes or CI-dendrites, respectively, and their stability properties (corrosion, thermo-oxidation, and sedimentation) were compared to neat CI ones. Compatibility of the obtained particles and silicone oil was investigated using contact angle and off-state viscosity investigation. Finally, the magneto-responsive capabilities in terms of yield stress and reproducibility of the MR phenomenon were thoroughly investigated. It was found that MR suspensions based on CI-brushes had significantly improved compatibility properties than those of neat CI ones; however, the CI-dendrites-based suspension possessed the best capabilities, while the MR performance was negligibly suppressed.

Synthesis and Characterization of Agarose Hydrogels for Release of Diclofenac Sodium

Hydrogels are attractive biomaterials for the controlled release of various pharmaceuticals, due to their ability to embed biologically active moieties in a 3D polymer network. Among them, agarose-based hydrogels are an interesting, but still not fully explored, group of potential platforms for controlled drug release. In this work, agarose hydrogels with various contents of citric acid were prepared, and their mechanical and physicochemical properties were investigated using various instrumental techniques, such as rheological measurements, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Releasing tests for diclofenac sodium (DICL) were run in various environments; water, PBS, and 0.01 M NaOH; which remarkably affected the profile of the controlled release of this model drug. In addition to affecting the mechanical properties, the amount of citric acid incorporated within a hydrogel network during synthesis was also of great importance to the rate of DICL release. Therefore, due to their high biocompatibility, agarose hydrogels can be regarded as safe and potential platforms for controlled drug release in biomedical applications.

Carboxymethyl cellulose-agarose-gelatin: A thermoresponsive triad bioink composition to fabricate volumetric soft tissue constructs

Polysaccharide based hydrogels have been predominantly utilized as ink materials for 3D bioprinting due to biocompatibility and cell responsive features. However, most hydrogels require extensive crosslinking due to poor mechanical properties leading to limited printability. To improve printability without using cytotoxic crosslinkers, thermoresponsive bioinks could be developed. Agarose is a thermoresponsive polysaccharide with upper critical solution temperature (UCST) for sol-gel transition at 35-37 °C. Therefore, we hypothesized that a triad of carboxymethyl cellulose(C)-agarose(A)-gelatin(G) could be a suitable thermoresponsive ink for printing since they undergo instantaneous gelation without any addition of crosslinkers after bioprinting. The blend of agarose-carboxymethyl cellulose was mixed with 1% w/v, 3% w/v and 5% w/v gelatin to optimize the triad ratio for hydrogel formation. It was observed that a blend (C2-A0.5-G1 and C2-A1-G1) containing 2% w/v carboxymethyl cellulose, 0.5% or 1% w/v agarose and 1% w/v gelatin formed better hydrogels with higher stability for up to 21 days in DPBS at 37 °C. Further, C2-A0.5-G1 and C2-A1-G1hydrogels showed higher storage modulus 762 ± 182 Pa & 2452 ± 430 Pa, higher porosity of 96.98 ± 2% & 98.2 ± 0.8% and swellability of 1518 ± 68% & 1587 ± 25% respectively. To evaluate the in vitro potential of these bioink formulations, indirect and direct cytotoxicity were determined using NCTC clone 929 (mouse fibroblast cells) and HADF (primary human adult dermal fibroblast) cells as per the ISO 10993-5 standards. Importantly, the printability of these bioinks was confirmed using extrusion bioprinting by successfully printing different complex 3D patterns.

Influence of Magnetic Field and Temperature on Rheological Behavior of Magnetorheological Gel

In this paper, the effect of temperature on rheological properties of magnetorheological (MR) gel is investigated under rotational steady shear and oscillatory dynamic shear. A kind of fluid-like MR gel (MRG) was firstly synthesized by mixing carbonyl iron powder (CIP) with polymer matrix. Then, the relationship between yield stress, normal stress of MRG and shear rate under six temperatures and four magnetic field strengths were studied by rotational shear experiments. The results demonstrate that the dependence of shear stress on temperature displays an opposite tendency in comparison with that of normal stress on temperature. Moreover, maximum yield stress, one of the most important parameter of MR materials, decreases with the increment of temperature. Under oscillatory dynamic shear test, storage and loss moduli and normal stress of MRG all increase with temperature when a magnetic field is applied, which presents a contrary trend in the absence of a magnetic field. Related mechanisms about the alternation of microstructures of MRG were proposed to explain the above-mentioned phenomena. This paper is helpful in fabricating semi-active engineering devices using MR materials as a medium.

Poly(2-oxazoline)s as Stimuli-Responsive Materials for Biomedical Applications: Recent Developments of Polish Scientists

Poly(2-oxazoline)s are the synthetic polymers that are the products of the cationic ring-opening polymerization (CROP) of 2-oxazoline monomers. Due to their beneficial properties, from which biocompatibility, stealth behavior, high functionalization possibilities, low dispersity, stability, nonionic character, and solubility in water and organic solvents should be noted, they have found many applications and gained enormous interest from scientists. Additionally, with high versatility attainable through copolymerization or through post-polymerization modifications, this class of polymeric systems has been widely used as a polymeric platform for novel biomedical applications. The chemistry of polymers significant expanded into biomedical applications, in which polymeric networks can be successfully used in pharmaceutical development for tissue engineering, gene therapies, and also drug delivery systems. On the other hand, there is also a need to create ‘smart’ polymer biomaterials, responsive to the specified factor, that will be sensitive to various environmental stimuli. The commonly used stimuli-responsive biomedical materials are based mostly on temperature-, light-, magnetic-, electric-, and pH-responsive systems. Thus, creating selective and responsive materials that allow personalized treatment is in the interest of the scientific world. This review article focuses on recent discoveries by Polish scientists working in the field of stimuli-responsive poly(2-oxazoline)s, and their work is compared and contrasted with results reported by other world-renowned specialists.

Formulation of Magneto-Responsive Hydrogels from Dually Cross-Linked Polysaccharides: Synthesis, Tuning and Evaluation of Rheological Properties

Smart hydrogels based on natural polymers present an opportunity to fabricate responsive scaffolds that provide an immediate and reversible reaction to a given stimulus. Modulation of mechanical characteristics is especially interesting in myocyte cultivation, and can be achieved by magnetically controlled stiffening. Here, hyaluronan hydrogels with carbonyl iron particles as a magnetic filler are prepared in a low-toxicity process. Desired mechanical behaviour is achieved using a combination of two cross-linking routes—dynamic Schiff base linkages and ionic cross-linking. We found that gelation time is greatly affected by polymer chain conformation. This factor can surpass the influence of the number of reactive sites, shortening gelation from 5 h to 20 min. Ionic cross-linking efficiency increased with the number of carboxyl groups and led to the storage modulus reaching 103 Pa compared to 101 Pa–102 Pa for gels cross-linked with only Schiff bases. Furthermore, the ability of magnetic particles to induce significant stiffening of the hydrogel through the magnetorheological effect is confirmed, as a 103-times higher storage modulus is achieved in an external magnetic field of 842 kA·m−1. Finally, cytotoxicity testing confirms the ability to produce hydrogels that provide over 75% relative cell viability. Therefore, dual cross-linked hyaluronan-based magneto-responsive hydrogels present a potential material for on-demand mechanically tunable scaffolds usable in myocyte cultivation.

Piezoelectric nanocomposite bioink and ultrasound stimulation modulate early skeletal myogenesis

Despite the significant progress in bioprinting for skeletal muscle tissue engineering, new stimuli-responsive bioinks to boost the myogenesis process are highly desirable. In this work, we developed a printable alginate/Pluronic-based bioink including piezoelectric barium titanate nanoparticles (nominal diameter: ∼60 nm) for the 3D bioprinting of muscle cell-laden hydrogels. The aim was to investigate the effects of the combination of piezoelectric nanoparticles with ultrasound stimulation on early myogenic differentiation of the printed structures. After the characterization of nanoparticles and bioinks, viability tests were carried out to investigate three nanoparticle concentrations (100, 250, and 500 μg mL^-1) within the printed structures. An excellent cytocompatibility was confirmed for nanoparticle concentrations up to 250 μg mL^-1. TEM imaging demonstrated the internalization of BTNPs in intracellular vesicles. The combination of piezoelectric nanoparticles and ultrasound stimulation upregulated the expression of MYOD1, MYOG, and MYH2 and enhanced cell aggregation, which is a crucial step for myoblast fusion, and the presence of MYOG in the nuclei. These results suggest that the direct piezoelectric effect induced by ultrasound on the internalized piezoelectric nanoparticles boosts myogenesis in its early phases.

A Comparison Study on the Magneto-Responsive Properties and Swelling Behaviors of a Polyacrylamide-Based Hydrogel Incorporating with Magnetic Particles

This work investigates the mechanical properties, microstructures, and water-swelling behavior of a novel hydrogel filled with magnetic particles. The nanoparticles of magnetite (Fe₃O₄) and the micro-particles of carbonyl iron (CI) were selected and filled into a polyacrylamide (PAAM) hydrogel matrix to create two types of magnetic hydrogels. The isotropy and anisotropy of magnetic hydrogels are also presented in this study. The isotropic samples were cured without applying a magnetic field (MF), and the anisotropic samples were cured by applying an MF in the direction perpendicular to the thickness of the samples. The effects of the size, content, and inner structures of magnetic particles on the magneto-responsive and swelling properties of magnetic hydrogels were investigated. It was found that the magnetorheological (MR) effect of anisotropic samples was apparently higher than that of isotropic samples, and the hydrogels with CI exhibited a noticeable MR effect than those with Fe₃O₄. The storage modulus can be enhanced by increasing the filler content and size, forming an anisotropic structure, and applying an external MF. In addition, the magnetic hydrogels also have a swelling ability that can be tuned by varying the content and size of the particle fillers.

Preparation of Magnetic Hydrogel Microparticles with Cationic Surfaces and Their Cell-Assembling Performance

Cationic magnetic hydrogel microparticles with high retention on cell surfaces were prepared using a two-step procedure. Using these magnetic hydrogel microparticles, cells were clustered with each other, and cell aggregates were prepared effectively. Cross-linked poly(vinyl alcohol) (PVA) hydrogel microparticles containing iron oxide nanoparticles were prepared. The diameter of the microparticles was in the range of 200-500 nm. Water-soluble cationic polymers containing both trimethyl ammonium (TMA) groups and phenylboronic acid (PBA) groups were synthesized for the surface modification of the microparticles. To regulate the composition, electrically neutral phosphorylcholine groups were introduced into the polymer. Covalent bonds were formed between the hydroxy groups of PVA microparticles and PBA groups in the polymer. The surface zeta potential of the microparticles reflected the composition of the TMA groups. The particles responded to an external magnetic field and clustered rapidly. Microparticles were adsorbed on the floating cell surface and induced cell aggregation quickly when a magnetic field was applied. Under the most effective conditions, the diameter of the cell aggregates increased to approximately 1 mm after 30 min. Denser cell aggregates were formed by the synergistic effects of the magnetic field and the properties of the microparticles. The formed cell aggregates continued to grow for more than 4 days under an applied magnetic field, indicating that the ability of the cells in the aggregate to proliferate was well maintained.

Ropivacaine-Loaded Poloxamer Binary Hydrogels for Prolonged Regional Anesthesia: Structural Aspects, Biocompatibility, and Pharmacological Evaluation

This study reports the development of thermosensitive hydrogels for delivering ropivacaine (RVC), a wide clinically used local anesthetic. For this purpose, poloxamer- (PL-) based hydrogels were synthesized for evaluating the influence of polymer concentration, hydrophilic-lipophilic balances, and binary system formation on biopharmaceutical properties and pharmacological performance. Transition temperatures were shifted, and rheological analysis revealed a viscoelastic behavior with enhanced elastic/viscous modulus relationship (G'/G " = 1.8 to 22 times), according to hydrogel composition and RVC incorporation. The RVC release from PL407 and PL407/338 systems followed the Higuchi model (R 2 = 0.923-0.989), indicating the drug diffusion from hydrogels to the medium. RVC-PL hydrogels were potentially biocompatible evoking low cytotoxic effects (in fibroblasts and Schwann cells) and mild/moderate inflammation signs on sciatic nerve nearby histological evaluation. In vivo pharmacological assays demonstrated that PL407 and PL407/338 evoked differential analgesic effects, by prolonging the sensory blockade duration up to ~340 and 250 min., respectively. All those results highlighted PL407 and PL407/338 as promising new strategies for sustaining analgesic effects during the postoperative period.

Effect of Dexamethasone on Thermoresponsive Behavior of Poly(2-Oxazoline) Diblock Copolymers

Thermoresponsive polymers play an important role in designing drug delivery systems for biomedical applications. In this contribution, the effect of encapsulated hydrophobic drug dexamethasone on thermoresponsive behavior of diblock copolymers was studied. A small series of diblock copoly(2-oxazoline)s was prepared by combining thermoresponsive 2-n-propyl-2-oxazoline (nPrOx) and hydrophilic 2-methyl-2-oxazoline (MeOx) in two ratios and two polymer chain lengths. The addition of dexamethasone affected the thermoresponsive behavior of one of the copolymers, nPrOx₂₀-MeOx₁₈₀, in the aqueous medium by shifting the cloud point temperature to lower values. In addition, the formation of microparticles containing dexamethasone was observed during the heating of the samples. The morphology and number of microparticles were affected by the structure and concentration of copolymer, the drug concentration, and the temperature. The crystalline nature of formed microparticles was confirmed by polarized light microscopy, confocal Raman microscopy, and wide-angle X-ray scattering. The results demonstrate the importance of studying drug/polymer interactions for the future development of thermoresponsive drug carriers.

Adjustable dual temperature-sensitive hydrogel based on a self-assembly cross-linking strategy with highly stretchable and healable properties

Developing smart temperature-sensitive hydrogels with a wide response range and highly stretchable and healable properties for simulation of the temperature perception function of human skin remains a great challenge. Here, a novel PNIPAm/PNAGA double-network hydrogel was developed by a self-assembly cross-linking strategy to achieve this goal. Benefiting from the double-network structure and a large number of multiple hydrogen bond interactions between the PNIPAm and PNAGA, the PNIPAm/PNAGA hydrogel realizes wide and adjustable dual temperature response behaviors of 0-32.5 °C (LCST) and 32.5-65 °C (UCST) and exhibits extraordinary mechanical properties with a maximum tensile strength of 51.48 kPa, elongation at break over 1400%, compressive stress over 1 MPa, and Young's modulus approximately 5.51 kPa, and excellent healable properties of nearly 100% temperature-sensitive repair rate. To the best of our knowledge, this is the highest mechanical strength of the reported PNIPNm-based dual temperature-sensitive hydrogels and simultaneously achieved the healable performance of dual temperature-sensitive hydrogels for the first time. The PNIPAm/PNAGA hydrogel displayed superior capability for simulation of the human skin to monitor various ambient temperatures, such as human skin temperature, hot and cold water, a refrigerator, room temperature and oven temperature, indicating promising applications in the fields of electronic skin, wearable device, bionics, etc.

Magnetorheological Effect of Magnetoactive Elastomer with a Permalloy Filler

Within the frames of this study, the synthesis of a permalloy to be used as a filler for magnetoactive and magnetorheological elastomers (MAEs and MREs) was carried out. By means of the mechanochemical method, an alloy with the composition 75 wt.% of Fe and 25 wt.% of Ni was obtained. The powder of the product was utilized in the synthesis of MAEs. Study of the magnetorheological (MR) properties of the elastomer showed that in a ~400 mT magnetic field the shear modulus of the MAE increased by a factor of ~200, exhibiting an absolute value of ~8 MPa. Furthermore, we obtained experimentally a relative high loss factor for the studied composite; this relates to the size and morphology of the synthesized powder. The composite with such properties is a very perspective material for magnetocontrollable damping devices. Under the action of an external magnetic field, chain-like structures are formed inside the elastomeric matrix, which is the main determining factor for obtaining a high MR effect. The effect of chain-like structures formation is most pronounced in the region of small strains, since structures are partially destroyed at large strains. A proposed theoretical model based on chain formation sufficiently well describes the experimentally observed MR effect. The peculiarity of the model is that chains of aggregates of particles, instead of individual particles, are considered.

Rheological, Microstructural and Thermal Properties of Magnetic Poly(Ethylene Oxide)/Iron Oxide Nanocomposite Hydrogels Synthesized Using a One-Step Gamma-Irradiation Method

Magnetic polymer gels are a new promising class of nanocomposite gels. In this work, magnetic PEO/iron oxide nanocomposite hydrogels were synthesized using the one-step γ-irradiation method starting from poly(ethylene oxide) (PEO) and iron(III) precursor alkaline aqueous suspensions followed by simultaneous crosslinking of PEO chains and reduction of Fe(III) precursor. γ-irradiation dose and concentrations of Fe³⁺, 2-propanol and PEO in the initial suspensions were varied and optimized. With 2-propanol and at high doses magnetic gels with embedded magnetite nanoparticles were obtained, as confirmed by XRD, SEM and Mössbauer spectrometry. The quantitative determination of γ-irradiation generated Fe²⁺ was performed using the 1,10-phenanthroline method. The maximal Fe²⁺ molar fraction of 0.55 was achieved at 300 kGy, pH = 12 and initial 5% of Fe³⁺. The DSC and rheological measurements confirmed the formation of a well-structured network. The thermal and rheological properties of gels depended on the dose, PEO concentration and initial Fe³⁺ content (amount of nanoparticles synthesized inside gels). More amorphous and stronger gels were formed at higher dose and higher nanoparticle content. The properties of synthesized gels were determined by the presence of magnetic iron oxide nanoparticles, which acted as reinforcing agents and additional crosslinkers of PEO chains thus facilitating the one-step gel formation.

Revealing importance of particles' surface functionalization on the properties of magnetic alginate hydrogels

Iron/silica core-shell microparticles (IMPs) were functionalized by different functional groups including amine, glycidoxy, phenyl, and thiocyanate. Many of the IMPs modifications are reported for the first time. The resulting surface chemistry turned out to affect the properties of magnetic alginate hydrogels fabricated from sodium alginate and dispersed IMPs. Differences in magnetorheological properties of the obtained magnetic hydrogels can be at least partially attributed to the interactions between alginate and surface functionalities of IMPs. Density Functional Theory (DFT) calculations were carried out to get detailed insight into those interactions in order to link them with the observed macroscopic properties of the obtained hydrogels. For example, amine groups on the IMPs surface resulted in well-formed hydrogels while the presence of thiocyanate or phenyl groups - in poorly formed ones. This observation can be used for tuning the properties of various carbohydrate-based hydrogels.