Nanocomposite polymer hydrogels

Structure and Rheology of Poloxamine T1107 and Its Nanocomposite Hydrogels with Cyclodextrin-Modified Barium Titanate Nanoparticles

We report the preparation of a nanocomposite hydrogel based on a poloxamine gel matrix (Tetronic T1107) and cyclodextrin (CD)-modified barium titanate (BT) nanoparticles. The micellization and sol-gel behavior of pH-responsive block copolymer T1107 were fully characterized by small-angle neutron scattering (SANS), dynamic light scattering (DLS), and Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy as a function of concentration, pH and temperature. SANS results reveal that spherical micelles in the low concentration regime present a dehydrated core and highly hydrated shell, with a small aggregation number and size, highly dependent on the degree of protonation of the central amine spacer. At high concentration, T1107 undergoes a sol-gel transition, which is inhibited at acidic pH. Nanocomposites were prepared by incorporating CD-modified BT of two different sizes (50 and 200 nm) in concentrated polymer solutions. Rheological measurements show a broadening of the gel region, as well as an improvement of the mechanical properties, as assessed by the shear elastic modulus, G' (up to 200% increase). Initial cytocompatibility studies of the nanocomposites show that the materials are nontoxic with viabilities over 70% for NIH3T3 fibroblast cell lines. Overall, the combination of Tetronics and modified BaTiO3 provides easily customizable systems with promising applications as soft piezoelectric materials.

Superabsorbent Nanohydrogels of Poly (N-Isopropyl Acrylamide-Co-Itaconic Acid) Grafted on Starch — Synthesis and Swelling Study

Biopolymer-based superabsorbent nanohydrogel consisting of N-isopropylacrylamide and itaconic acid (IA) was grafted on to starch backbone in an aqueous solution in the absence of the cross-linker agents. The copolymerization reaction occurred in the presence of ammonium persulfate (APS) as an initiator. The effect of N-isopropylacrylamide-to-IA ratio and different concentrations of initiator were investigated. The nanohydrogel composition was characterized by Fourier transform infrared spectroscopy (FTIR). The thermal stability was analyzed by Thermogravimetric analysis (TGA). Differential scanning calorimetry (DSC) studies were employed for determination of lower critical solution temperature in hydrogels. Dynamic light scattering analysis showed a narrow size distribution around 70–200[Formula: see text]nm for the synthesized nanohydrogels. The effects of pH on swelling behavior of the hydrogel were investigated. The obtained nanohydrogels, due to their pH and thermo dual sensitive properties, have the potential to be used in the drug delivery systems.

Poly(acrylic acid)-grafted poly(N-isopropyl acrylamide) networks: preparation, characterization and hydrogel behavior

Poly(acrylic acid)-grafted poly(N-isopropylacrylamide) co-polymer networks (PNIPAAm-g-PAA) were prepared via the reversible addition-fragmentation transfer (RAFT) polymerization of N-isopropyl- acrylamide (NIPAAm) with trithiocarbonate-terminated PAA as a macromolecular chain-transfer agent in the presence of N,N-methylenebisacrylamide. The PNIPAAm-g-PAA co-polymer networks were characterized by means of Fourier transform infrared spectroscopy, differential scanning calorimetry and small-angle X-ray scattering. It is found that the PNIPAAm-g-PAA co-polymer networks were microphase-separated, in which the microdomains of PNIPAAm-PAA interpolymer complexes were dispersed into the PNIPAAm matrix. The PNIPAAm-g-PAA hydrogels displayed a dual response to temperature and pH values. The thermoresponsive properties of PNIPAAm-g-PAA networks were investigated. Below the volume phase transition temperatures, the PNIPAAm-g-PAA hydrogels possessed much higher swelling ratios than control PNIPAAm hydrogel. In terms of swelling, deswelling and reswelling tests, it is judged that the PNIPAAm-g-PAA hydrogels displayed faster response to the external temperature changes than control PNIPAAm hydrogel. The improved thermoresponsive properties of hydrogels are ascribed to the formation of PAA-grafted PNIPAAm networks, in which the water-soluble PAA chains behave as the hydrophiphilic tunnels and allow water molecules to go through and, thus, to accelerate the diffusion of water molecules.

A Novel Nanosilver/Nanosilica Hydrogel for Bone Regeneration in Infected Bone Defects

Treating bone defects in the presence of infection is a formidable clinical challenge. The use of a biomaterial with the dual function of bone regeneration and infection control is a novel therapeutic approach to this problem. In this study, we fabricated an innovative, dual-function biocomposite hydrogel containing nanosilver and nanosilica (nAg/nSiO2) particles and evaluated its characteristics using FT-IR, SEM, swelling ratio, and stiffness assays. The in vitro antibacterial analysis showed that this nAg/nSiO2 hydrogel inhibited both Gram-positive and Gram-negative bacteria. In addition, this nontoxic material could promote osteogenic differentiation of rat bone marrow stromal cells (BMSCs). We then created infected bone defects in rat calvaria in order to evaluate the function of the hydrogel in vivo. The hydrogel demonstrated effective antibacterial ability while promoting bone regeneration in these defects. Our results indicate that this nAg/nSiO2 hydrogel has the potential to both control infection and to promote bone healing in contaminated defects.

Multi-stage freezing of HEUR polymer networks with magnetite nanoparticles

We observe a change in the segmental dynamics of hydrogels based on hydrophobically modified ethoxylated urethanes (HEUR) when hydrophobic magnetite nanoparticles (MNPs) are embedded in the hydrogels. The dynamics of the nanocomposite hydrogels is investigated using dielectric relaxation spectroscopy (DRS) and neutron spin echo (NSE) spectroscopy. The magnetic nanoparticles within the hydrophobic domains of the HEUR polymer network increase the size of these domains and their distance. The size increase leads to a dilution of the polymers close to the hydrophobic domain, allowing higher mobility of the smallest polymer blobs close to the "center". This is reflected in the decrease of the activation energy of the β-process detected in the DRS data. The increase in distance leads to an increase of the size of the largest hydrophilic polymer blobs. Therefore, the segmental dynamics of the largest blobs is slowed down. At short time scales, i.e. 10(-9) s < τ < 10(-3) s, the suppression of the segmental dynamics is reflected in the α-relaxation processes detected in the DRS data and in the decrease of the relaxation rate Γ of the segmental motion in the NSE data with increasing concentration of magnetic nanoparticles. The stepwise (multi-stage) freezing of the small blobs is only visible for the pure hydrogel at low temperatures. On the other hand, the glass transition temperature (Tg) decreases upon increasing the MNP loading, indicating an acceleration of the segmental dynamics at long time scales (τ∼ 100 s). Therefore, it would be possible to tune the Tg of the hydrogels by varying the MNP concentration. The contribution of the static inhomogeneities to the total scattering function Sst(q) is extracted from the NSE data, revealing a more ordered gel structure than the one giving rise to the total scattering function S(q), with a relaxed correlation length ξNSE = (43 ± 5) Å which is larger than the fluctuating correlation length from a static investigation ξSANS = (17.2 ± 0.3) Å.

Smart micro/nanoparticles in stimulus-responsive drug/gene delivery systems

New achievements in the realm of nanoscience and innovative techniques of nanomedicine have moved micro/nanoparticles (MNPs) to the point of becoming actually useful for practical applications in the near future. Various differences between the extracellular and intracellular environments of cancerous and normal cells and the particular characteristics of tumors such as physicochemical properties, neovasculature, elasticity, surface electrical charge, and pH have motivated the design and fabrication of inventive "smart" MNPs for stimulus-responsive controlled drug release. These novel MNPs can be tailored to be responsive to pH variations, redox potential, enzymatic activation, thermal gradients, magnetic fields, light, and ultrasound (US), or can even be responsive to dual or multi-combinations of different stimuli. This unparalleled capability has increased their importance as site-specific controlled drug delivery systems (DDSs) and has encouraged their rapid development in recent years. An in-depth understanding of the underlying mechanisms of these DDS approaches is expected to further contribute to this groundbreaking field of nanomedicine. Smart nanocarriers in the form of MNPs that can be triggered by internal or external stimulus are summarized and discussed in the present review, including pH-sensitive peptides and polymers, redox-responsive micelles and nanogels, thermo- or magnetic-responsive nanoparticles (NPs), mechanical- or electrical-responsive MNPs, light or ultrasound-sensitive particles, and multi-responsive MNPs including dual stimuli-sensitive nanosheets of graphene. This review highlights the recent advances of smart MNPs categorized according to their activation stimulus (physical, chemical, or biological) and looks forward to future pharmaceutical applications.

Nanoparticle-Hydrogel: A Hybrid Biomaterial System for Localized Drug Delivery

Nanoparticles have offered a unique set of properties for drug delivery including high drug loading capacity, combinatorial delivery, controlled and sustained drug release, prolonged stability and lifetime, and targeted delivery. To further enhance therapeutic index, especially for localized application, nanoparticles have been increasingly combined with hydrogels to form a hybrid biomaterial system for controlled drug delivery. Herein, we review recent progresses in engineering such nanoparticle-hydrogel hybrid system (namely 'NP-gel') with a particular focus on its application for localized drug delivery. Specifically, we highlight four research areas where NP-gel has shown great promises, including (1) passively controlled drug release, (2) stimuli-responsive drug delivery, (3) site-specific drug delivery, and (4) detoxification. Overall, integrating therapeutic nanoparticles with hydrogel technologies creates a unique and robust hybrid biomaterial system that enables effective localized drug delivery.

Controlling Hydrogel Mechanics via Bio-Inspired Polymer-Nanoparticle Bond Dynamics

Interactions between polymer molecules and inorganic nanoparticles can play a dominant role in nanocomposite material mechanics, yet control of such interfacial interaction dynamics remains a significant challenge particularly in water. This study presents insights on how to engineer hydrogel material mechanics via nanoparticle interface-controlled cross-link dynamics. Inspired by the adhesive chemistry in mussel threads, we have incorporated iron oxide nanoparticles (Fe3O4 NPs) into a catechol-modified polymer network to obtain hydrogels cross-linked via reversible metal-coordination bonds at Fe3O4 NP surfaces. Unique material mechanics result from the supra-molecular cross-link structure dynamics in the gels; in contrast to the previously reported fluid-like dynamics of transient catechol-Fe(3+) cross-links, the catechol-Fe3O4 NP structures provide solid-like yet reversible hydrogel mechanics. The structurally controlled hierarchical mechanics presented here suggest how to develop hydrogels with remote-controlled self-healing dynamics.

Controlled Cell Growth and Cell Migration in Periodic Mesoporous Organosilica/Alginate Nanocomposite Hydrogels

Nanocomposite (NC) hydrogels with different periodic mesoporous organosilica (PMO) concentrations and a NC hydrogel bilayer with various PMO concentrations inside the layers of the hydrogel matrix are prepared. The effect of the PMO concentration on cell growth and migration of cells is reported. The cells migrate in the bilayer NC hydrogel towards higher PMO concentrations and from cell culture plates to NC hydrogel scaffolds.

Photocrosslinkable and elastomeric hydrogels for bone regeneration

Nanocomposite biomaterials are extensively investigated for cell and tissue engineering applications due their unique physical, chemical and biological characteristics. Here, we investigated the mechanical, rheological, and degradation properties of photocrosslinkable and elastomeric nanocomposite hydrogels from nanohydroxyapatite (nHAp) and gelatin methacryloyl (GelMA). The addition of nHAp resulted in a significant increase in mechanical stiffness and physiological stability. Cells readily adhere and proliferate on the nanocomposite surfaces. Cyclic stretching of cells on the elastomeric nanocomposites revealed that nHAp elicited a stronger alignment response in the direction of strain. In vitro studies highlight enhanced bioactivity of nanocomposites as determined by alkaline phosphate (ALP) activity. Overall, the elastomeric and photocrosslinkable nanocomposite hydrogels can be used for minimally invasive therapy for bone regeneration.

A semi-interpenetrating network polyampholyte hydrogel simultaneously demonstrating remarkable toughness and antibacterial properties

A hydrogel with toughness and antibacterial properties was prepared via interpenetrating CMCH with AM and MA while employing carboxylic–Fe³⁺.

Quantitative X-ray microscopic analysis of individual thermoresponsive microgel particles in aqueous solution

The temperature dependent phase transition of individual thermoresponsive microgel particles in aqueous solution has been studied by high resolution soft X-ray transmission microscopy (STXM).

Hybrid cross-linked hydrogels based on fibrous protein/block copolymers and layered silicate nanoparticles: tunable thermosensitivity, biodegradability and mechanical durability

Schematic representation of LAPONITE® reinforced pluronic/chitosan/keratin nanocomposite hydrogel crosslinked with Genipin.

A tough nanocomposite hydrogel for antifouling application with quaternized hyperbranched PEI nanoparticles crosslinking

We reported a series of tough nanocomposite hydrogels with good antifouling properties based on quaternized hybranched polyethylenimine (HPEI) nanoparticles.

Polyacrylamide strengthened mixed-charge hydrogels and their applications in resistance to protein adsorption and algae attachment

Mixed-charge polymer hydrogels were successfully prepared by copolymerization of different ratios of [2-(meth-acryloyloxy)ethyl]trimethylammonium (TMA) and 3-sulfopropyl methacrylate (SA).

Hydrogels 2.0: improved properties with nanomaterial composites for biomedical applications

The incorporation of nanomaterials in hydrogels (hydrated networks of crosslinked polymers) has emerged as a useful method for generating biomaterials with tailored functionality. With the available engineering approaches it is becoming much easier to fabricate nanocomposite hydrogels that display improved performance across an array of electrical, mechanical, and biological properties. In this review, we discuss the fundamental aspects of these materials as well as recent developments that have enabled their application. Specifically, we highlight synthesis and fabrication, and the choice of nanomaterials for multifunctionality as ways to overcome current material property limitations. In addition, we review the use of nanocomposite hydrogels within the framework of biomedical and pharmaceutical disciplines.

Local structure of temperature and pH-sensitive colloidal microgels

The temperature dependence of the local intra-particle structure of colloidal microgel particles, composed of interpenetrated polymer networks, has been investigated by small-angle neutron scattering at different pH and concentrations, in the range (299÷315) K, where a volume phase transition from a swollen to a shrunken state takes place. Data are well described by a theoretical model that takes into account the presence of both interpenetrated polymer networks and cross-linkers. Two different behaviors are found across the volume phase transition. At neutral pH and T ≈ 307 K, a sharp change of the local structure from a water rich open inhomogeneous interpenetrated polymer network to a homogeneous porous solid-like structure after expelling water is observed. Differently, at acidic pH, the local structure changes almost continuously. These findings demonstrate that a fine control of the pH of the system allows to tune the sharpness of the volume-phase transition.

Composites of Polymer Hydrogels and Nanoparticulate Systems for Biomedical and Pharmaceutical Applications

Due to their unique structures and properties, three-dimensional hydrogels and nanostructured particles have been widely studied and shown a very high potential for medical, therapeutic and diagnostic applications. However, hydrogels and nanoparticulate systems have respective disadvantages that limit their widespread applications. Recently, the incorporation of nanostructured fillers into hydrogels has been developed as an innovative means for the creation of novel materials with diverse functionality in order to meet new challenges. In this review, the fundamentals of hydrogels and nanoparticles (NPs) were briefly discussed, and then we comprehensively summarized recent advances in the design, synthesis, functionalization and application of nanocomposite hydrogels with enhanced mechanical, biological and physicochemical properties. Moreover, the current challenges and future opportunities for the use of these promising materials in the biomedical sector, especially the nanocomposite hydrogels produced from hydrogels and polymeric NPs, are discussed.

Production in Pichia pastoris of protein-based polymers with small heterodimer-forming blocks

Some combinations of leucine zipper peptides are capable of forming α-helical heterodimeric coiled coils with very high affinity. These can be used as physical cross-linkers in the design of protein-based polymers that form supramolecular structures, for example hydrogels, upon mixing solutions containing the complementary blocks. Such two-component physical networks are of interest for many applications in biomedicine, pharmaceutics, and diagnostics. This article describes the efficient secretory production of A and B type leucine zipper peptides fused to protein-based polymers in Pichia pastoris. By adjusting the fermentation conditions, we were able to significantly reduce undesirable proteolytic degradation. The formation of A-B heterodimers in mixtures of the purified products was confirmed by size exclusion chromatography. Our results demonstrate that protein-based polymers incorporating functional heterodimer-forming blocks can be produced with P. pastoris in sufficient quantities for use in future supramolecular self-assembly studies and in various applications.

Nanoparticle-Integrated Hydrogels as Multifunctional Composite Materials for Biomedical Applications

This review focuses on the most recent developments in the field of nanocomposite hydrogels intended for biomedical applications. Nanocomposite hydrogels are hydrated polymeric networks with a physically or covalently crosslinked three-dimensional (3D) structure swollen with water, in the presence of nanoparticles or nanostructures. A wide array of nanomaterials (polymeric, carbon-based, metallic, ceramic) can be incorporated within the hydrogel network to obtain reinforced nanocomposite hydrogels. Nanocomposites represent a new class of materials with properties absent in the individual components. In particular, the incorporation of nanomaterials within a polymeric hydrogel network is an attractive approach to tailor the mechanical properties of the hydrogels and/or to provide the nanocomposite with responsiveness to external stimuli.

Enzyme Induced Stiffening of Nanoparticle-Hydrogel Composites with Structural Color

The passive monitoring of biological environments by soft materials has a variety of nanobiotechnology applications; however, invoking distinct transitions in geometric, mechanical or optical properties remains a prevalent design challenge. We demonstrate here that close-packed nanoparticle-hydrogel composites can progress through a substantial shift in such properties by the use of a chemical-to-physical cross-link transition mediated by the catalytic activity of different proteases. Catalytic cleavage of the original hydrogel network structure initiates the self-assembled formation of a secondary, physically cross-linked network, causing a 1200% increase in storage modulus. Furthermore, this unique mechanism can be fabricated as a 3D photonic crystal with broad (∼240 nm), visible responses to the targeted enzymes. Moreover, the material provided threshold responses, requiring a certain extent of proteolytic activity before the transition occurred. This allowed for the fabrication of Boolean logic gates (OR and AND), which responded to a specific assortment of proteases. Ultimately, this mechanism enables the design of stimuli-responsive hydrogels, which can proceed through a secondary network formation, after an energetic barrier has been breached. Protease responsive hydrogel nanocomposites, described here, could offer avenues in degradation-stiffening and collapsing materials for a variety of biomaterial applications.

Anion-Responsive Metallopolymer Hydrogels for Healthcare Applications

Metallopolymers combine a processable, versatile organic polymeric skeleton with functional metals, providing multiple functions and methodologies in materials science. Taking advantage of cationic cobaltocenium as the key building block, organogels could be simply switched to hydrogels via a highly efficient ion exchange. With the unique ionic complexion ability, cobaltocenium moieties provide a robust soft substrate for recycling antibiotics from water. The essential polyelectrolyte nature offers the metallopolymer hydrogels to kill multidrug resistant bacteria. The multifunctional characteristics of these hydrogels highlight the potential for metallopolymers in the field of healthcare and environmental treatment.

Enhancing the energy density of asymmetric stretchable supercapacitor based on wrinkled CNT@MnO2 cathode and CNT@polypyrrole anode

With the advantages of high stickiness and stretchability of the hydrogel electrolyte as well as the resilient properties of film electrodes, the facile "prestrain-stick-release" strategy can be utilized for the assembly of a stretchable supercapacitor. Two major issues of concern are the relatively low mechanical strength of the hydrogel electrolyte and the low energy density of the assembled device. Herein, vinyl group grafted silica (CH2═CH-SiO2) nanoparticles were used as a nanoparticle cross-linker for polyacrylamide (PAAM), enhancing the tensile strength of 844 kPa at the strain of 3400% for the KCl-CH2═CH-SiO2/PAAM hydrogel electrolyte. Besides, carbon nanotube supported polypyrrole (CNT@PPy) and manganese dioxide (CNT@MnO2) film electrodes are prepared to assemble the stretchable asymmetric CNT@MnO2//KCl-CH2═CH-SiO2/PAAM//CNT@PPy supercapacitor, significantly enhancing the potential window to 0-2.0 V and achieving a high energy density of 40 Wh kg(-1) at the power density of 519 kW kg(-1) with the strain of 100%, which is the best known for the reported stretchable supercapacitors.

Porous Materials for Hydrolytic Dehydrogenation of Ammonia Borane

Hydrogen storage is still one of the most significant issues hindering the development of a “hydrogen energy economy”. Ammonia borane is notable for its high hydrogen densities. For the material, one of the main challenges is to release efficiently the maximum amount of the stored hydrogen. Hydrolysis reaction is a promising process by which hydrogen can be easily generated from this compound. High purity hydrogen from this compound can be evolved in the presence of solid acid or metal based catalyst. The reaction performance depends on the morphology and/or structure of these materials. In this review, we survey the research on nanostructured materials, especially porous materials for hydrogen generation from hydrolysis of ammonia borane.

Novel pH sensitive ferrogels as new approach in cancer treatment: Effect of the magnetic field on swelling and drug delivery

Ferrogels (or magnetic hydrogels) are cross-linked polymer networks containing magnetic nanoparticles: they are mechanically soft and highly elastic and at the same time they exhibit a strong magnetic response. Our work focuses on an combinatorial strategy to improve the efficacy of 5-Fluorouracil (5-FU) assisted chemotherapy, by developing novel multifunctional pH-sensitive ferrogels. We designed gels based on N,N'-dimethylacrylamide monomers polymerized in presence of methacrylic acid or 2-aminoethyl methacrylate hydrochloride, containing ferro-nanoparticles. The influence of polymeric matrix composition and exposition to magnetic field (MF) on swelling behavior and drugs release were investigated at pH 7.4 and 5. In particular, the magnetic field was obtained by using permanent magnetic bar (0.25 T) or electromagnet (0.5 and 1.2 T), with the aim to analyze quantitatively the magnetic effects. A strong influence of the magnetic field on ferrogels properties have been observed. Swelling analysis indicated a dependence on both pH and network composition, reaching a maximum at pH 7.4, for formulations containing methacrylic acid, while the application of MF appeared to decrease the swelling percentages. Release profiles of 5-FU showed effective modulation in release by application of MF: drug release is always higher in the presence of a magnetic field and generally increases with its intensity. The combining effect of pH sensitive properties and application of MF improved the performance of the systems. Results showed that our ferrogels may be technologically applicable as devices for delivery of 5-FU in a controllable manner.

Soft Nanocomposites--From Interface Control to Interphase Formation

We report measurements of structure, mechanical properties, glass transition temperature, and contact angle of a novel nanocomposite material consisting of swellable silsesquioxane nanoparticles with grafted poly(ethyl methacrylate) (PEMA) brushes and PEMA matrices with varying molecular weight. We measured the interparticle distance at the surface of the composites using scanning probe microscopy (SPM) and in the bulk of ∼0.5 μm thick films by grazing incidence small angle X-ray scattering (GISAXS). For a given molecular weight of the brush unstable dispersions at high molecular weight of the matrix indicate an intrinsic incompatibility between polymer-grafted-nanoparticles and homopolymer matrices. This incompatibility is affirmed by a high contact angle between the polymer-grafted-nanoparticles and the high molecular weight matrix as measured by SPM. For unstable dispersions, we measured a decreased glass transition temperature along with a decreased plateau modulus by dynamic mechanical thermal analysis (DMTA) which indicates the formation of a liquid-like layer at the brush-matrix interface. This proves the ability to decouple the structural and mechanical properties from the potential to be swollen with small molecules. It opens a new area of use of these soft nanocomposites as slow release materials with tailored mechanical properties.

Electro-response characteristic of starch hydrogel crosslinked with Glutaraldehyde

The facile synthesis of the starch hydrogel with anisotropic microstructure and dynamic behaviors was developed in the presence (A-gel) and absence of DC electric field (B-gel). The microstructures of hydrogels were characterized by environmental scanning electron microscope. Their electro-responsive property of hydrogels was investigated with their storage modulus (G'). The result demonstrates that the G' of A-gel is greater than that of B-gel, and the modulus of A-gel increases along with the external field, which signifies positive electroresponse. In addition, the G' of A-gel and B-gel ((G'(A) and G'(B)) also continuously increases with increasing starch concentration, whereas both the maximum of modulus increment (ΔG' = G'(A)−G'(B) ) and that of modulus increment sensitivity (ΔG'/G'(B)) occur with the starch weight fraction at around 36.5%. To enhance the electro-responsive effects of the hydrogels, dielectric particles were dispersed in the hydrogel. It is found that BaTiO3/chitosan core-shell composite particles significantly enhance the electroresponse of the hydrogel. The mechanism of the electro-response mode is proposed.