Thermally Responsive Hydrogel Blends: A General Drug Carrier Model for Controlled Drug Release

Affinity-based drug delivery systems for the central nervous system: exploiting molecular interactions for local, precise targeting

Objective: The effective treatment of central nervous system (CNS) disorders remains a significant challenge, primarily due to its molecular and structural complexity. Clinical translation of promising therapeutic agents is limited by the lack of optimal drug delivery systems capable of targeted, localized release of drugs to the brain and spinal cord.Approach: This review provides an overview of the potential of affinity-based drug delivery systems, which leverage molecular interactions to enhance the delivery and efficacy of therapeutic agents within the CNS.Main results: Various approaches, including hydrogels, micro- and nanoparticles, and functionalized biomaterials, are examined for their ability to provide local, sustained release of proteins, growth factors and other drugs.Significance: Furthermore, we present a detailed analysis of design considerations for developing effective affinity-based systems, incorporating insights from both existing literature and our group's research. These considerations include the biochemical modification of delivery vehicles and the optimization of physical and chemical properties to improve therapeutic outcomes.

Versatile Mechanically Tunable Hydrogels for Therapeutic Delivery Applications

Hydrogels provide a versatile platform for biomedical material fabrication that can be structurally and mechanically fine-tuned to various tissues and applications. Applications of hydrogels in biomedicine range from highly dynamic injectable hydrogels that can flow through syringe needles and maintain or recover their structure after extrusion to solid-like wound-healing patches that need to be stretchable while providing a selective physical barrier. In this study, a toolbox is designed using thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) polymeric matrices and nanocelluloses as reinforcing agent to obtain biocompatible hydrogels with altering mechanical properties, from a liquid injectable to a solid-like elastic hydrogel. The liquid hydrogels possess low viscosity and shear-thinning properties at 25 °C, which allows facile injection at room temperature, while they become viscoelastic gels at body temperature. In contrast, the covalently cross-linked solid-like hydrogels exhibit enhanced viscoelasticity. The liquid hydrogels are biocompatible and are able to delay the in vitro release and maintain the bioactivity of model drugs. The antimicrobial agent loaded solid-like hydrogels are effective against typical wound-associated pathogens. This work presents a simple method of tuning hydrogel mechanical strength to easily adapt to applications in different soft tissues and broaden the potential of renewable bio-nanoparticles in hybrid biomaterials with controlled drug release capabilities.

Strong, tough and anisotropic bioinspired hydrogels

Soft materials are widely used in tissue engineering, soft robots, wearable electronics, etc. However, it remains a challenge to fabricate soft materials, such as hydrogels, with both high strength and toughness that are comparable to biological tissues. Inspired by the anisotropic structure of biological tissues, a novel solvent-exchange-assisted wet-stretching strategy is proposed to prepare anisotropic polyvinyl alcohol (PVA) hydrogels by tuning the macromolecular chain movement and optimizing the polymer network. The reinforcing and toughening mechanisms are found to be "macromolecule crystallization and nanofibril formation". These hydrogels exhibit excellent mechanical properties, such as extremely high fracture stress (12.8 ± 0.7 MPa) and fracture strain (1719 ± 77%), excellent modulus (4.51 ± 0.76 MPa), high work of fracture (134.47 ± 9.29 MJ m-3), and fracture toughness (305.04 kJ m-2) compared with other strong hydrogels and even natural tendons. In addition, excellent conductivity, strain sensing capability, water retention, freezing resistance, swelling resistance, and biocompatibility can also be achieved. This work provides a new and effective method to fabricate multifunctional anisotropic hydrogels with high tunable strength and toughness with potential applications in the fields of regenerative medicine, flexible sensors, and soft robotics.

Naproxen release behaviour from graphene oxide/cellulose acetate composite nanofibers

The present study investigated the effect of graphene oxide in cellulose acetate-based composite nanofibers on the transdermal delivery of naproxen.

Investigation of the Release Mechanism and Mould Resistance of Citral-Loaded Bamboo Strips

In the present study, the sustained-release system loading citral was synthesised by using PNIPAm nanohydrogel as a carrier and analysed its drug-release kinetics and mechanism. Four release models, namely zero-order, first-order, Higuchi, and Peppas, were employed to fit the experimental data, and the underlying action mechanism was analysed. The optimised system was applied to treat a bamboo mould, followed by assessment of the mould-proof performance. Our experimental results revealed that the release kinetics equation of the system conformed to the first order; the higher the external temperature, the better the match was. In the release process, PNIPAm demonstrated a good protection and sustained-release effect on citral. Under the pressure of 0.5 MPa, immersion time of 120 min, and the system concentration ratio of 1, the optimal drug-loading parameters were obtained using the slow-release system with the best release parameters. Compared to the other conditions, bamboos treated with pressure impregnation demonstrated a better control effect on bamboo mould, while the control effect on Penicillium citrinum, Trichoderma viride, Aspergillus niger, and mixed mould was 100% after 28 days. Moreover, the structure and colour of bamboo remained unchanged during the entire process of mould control.

3D printed architected conducting polymer hydrogels

Conducting polymer hydrogels combine electrical conductivity and tunable water content, rendering them strong candidates for a range of applications including biosensors, cell culture platforms, and energy storage devices. However, these hydrogels are mechanically brittle and prone to damage, prohibiting their use in emerging applications involving dynamic movement and large mechanical deformation. Here, we demonstrate that applying the concept of architecture to conducting polymer hydrogels can circumvent these impediments. A stereolithography 3D printing method is developed to successfully fabricate such hydrogels in complex lattice structures. The resulting hydrogels exhibit elastic compressibility, high fracture strain, enhanced cycling stability, and damage-tolerant properties despite their chemical composition being identical to their brittle, solid counterparts. Furthermore, concentrating the deformation to the 3D geometry, rather than polymer microstructure, effectively decouples the mechanical and electrical properties of the hydrogel lattices from their intrinsic properties associated with their chemical composition. The confluence of these new physical properties for conducting polymer hydrogels opens broad opportunities for a myriad of dynamic applications.

Biofriendly molecular and protein release substrate with integrated piezoelectric motivation and anti-oxidative stress capabilities

Self-powered piezoelectrically active molecular or protein delivery devices have provoked great interest in recent years. However, electric fields used to promote delivery or healing may also induce the redox of water or oxygen to generate reactive oxygen species (ROS) and bring unintended oxidative pressure to the organism and harm biological functions. In addition, protein molecules are easily inactivated in the polymer reservoir matrix due to the pull of strong electrostatic effects. In this study, a multifunctional molecular delivery substrate was fabricated by integrating a piezoelectric-dielectric polymeric substrate, nanoscopic polyelectrolyte films and in-film deposited biomimetic porous CaP coating. The piezoelectric substrate promoted molecular release, and the mineralized coating effectively stored molecules or proteins and simultaneously eliminated ROS, reducing the oxidative stress response generated by oxidative pressure. The present work opens a new way for the development of multifunctional and biofriendly drug delivery devices.

Stimuli-Responsive Biomolecule-Based Hydrogels and Their Applications

This Review presents polysaccharides, oligosaccharides, nucleic acids, peptides, and proteins as functional stimuli-responsive polymer scaffolds that yield hydrogels with controlled stiffness. Different physical or chemical triggers can be used to structurally reconfigure the crosslinking units and control the stiffness of the hydrogels. The integration of stimuli-responsive supramolecular complexes and stimuli-responsive biomolecular units as crosslinkers leads to hybrid hydrogels undergoing reversible triggered transitions across different stiffness states. Different applications of stimuli-responsive biomolecule-based hydrogels are discussed. The assembly of stimuli-responsive biomolecule-based hydrogel films on surfaces and their applications are discussed. The coating of drug-loaded nanoparticles with stimuli-responsive hydrogels for controlled drug release is also presented.

Theranostic Nanoplatform with Hydrogen Sulfide Activatable NIR Responsiveness for Imaging-Guided On-Demand Drug Release

NIR light responsive nanoplatforms hold great promise for on-demand drug release in precision cancer medicine. However, currently available systems utilize "always-on" photothermal transducers that lack target specificity, and thus inaccurately differentiate tumors from normal tissues. Developed here is a theranostic nanoplatform featuring H₂ S-mediated in situ production of NIR photothermal agents for imaging-guided and photocontrolled drug release. The system targets H₂ S-rich cancers. This nanoplatform shows H₂ S-activatable NIR-II emission and NIR light controllable release of the drug Camptothecin-11. Upon administering the system to HCT116 tumor-bearing mice, the tumor is greatly suppressed with minimal side effects, arising from the synergy of the cancer-specific and NIR light activated therapy. This theranostic nanoplatform thus sheds light on precision medicine with guidance through NIR-II imaging.

Development of Smart Composites Based on Doped-TiO2 Nanoparticles with Visible Light Anticancer Properties

In this study, the synthesis of smart, polymerically embedded titanium dioxide (TiO2) nanoparticles aimed to exhibit photo-induced anticancer properties under visible light irradiation is investigated. The TiO2 nanoparticles were prepared by utilizing the sol gel method with different dopants, including nitrogen (N-doped), iron (Fe-doped), and nitrogen and iron (Fe,N-doped). The dopants were embedded in an interpenetrating (IP) network microgel synthesized by stimuli responsive poly (N-Isopropylacrylamide-co-polyacrylicacid)-pNipam-co-PAA forming composite particles. All the types of produced particles were characterized by X-ray powder diffraction, micro-Raman, Fourier-transform infrared, X-ray photoelectron, ultra-violet-visible spectroscopy, Field Emission Scanning Electron, Transmission Electron microscopy, and Dynamic Light Scattering techniques. The experimental findings indicate that the doped TiO2 nanoparticles were successfully embedded in the microgel. The N-doped TiO2 nano-powders and composite particles exhibit the best photocatalytic degradation of the pollutant methylene blue under visible light irradiation. Similarly, the highly malignant MDA-MB-231 breast cancer epithelial cells were susceptible to the inhibition of cell proliferation at visible light, especially in the presence of N-doped powders and composites, compared to the non-metastatic MCF-7 cells, which were not affected.

Visible-light-triggered supramolecular valves based on β-cyclodextrin-modified mesoporous silica nanoparticles for controlled drug release

Visible-light triggered drug delivery system based on tetra-ortho-methoxy-substituted azobenzene (mAzo) and β-cyclodextrin (β-CD) modified mesoporous silica nanoparticles (MSNs-CD).

A multifunctional biomimetic hybrid nanocarrier for the controlled delivery of chemotherapy drugs by near-infrared light

We have constructed a biocompatible magnetic nanoparticle-based nanocomposite material by integrating the features of Fe₃O₄ nanoparticles, mesoporous silica and lipid bilayer for the treatment of tumor.

A Microstructured Graphene/Poly(N-isopropylacrylamide) Membrane for Intelligent Solar Water Evaporation

Intelligent solar water evaporation (iSWE) was achieved with a thermally responsive and microstructured graphene/poly(N-isopropylacrylamide) (mG/PNIPAm) membrane. As the solar intensity varies, the water evaporation is tuned through reversible transformations of microstructures reminiscent of the stomatal opening and closing of leaves. Consequently, this mG/PNIPAm membrane displays a high water evaporation rate change (ΔWER) of 1.66 kg m^-2  h^-1 under weak sunlight (intensity<1 sun) and a low ΔWER of 0.24 kg m^-2  h^-1 under intense sunlight (1 sun<intensity<2 sun). Because of the double-layer structure with predictable shape and dynamics, the leaf-like membrane can further autonomously modulate the water evaporation by self-curling under intense solar irradiation in accordance with simulation results. This mG/PNIPAm membrane provides a smart material platform with self-adaptability in response to changing environments.

Muscle-Inspired Highly Anisotropic, Strong, Ion-Conductive Hydrogels

Biological tissues generally exhibit excellent anisotropic mechanical properties owing to their well-developed microstructures. Inspired by the aligned structure in muscles, a highly anisotropic, strong, and conductive wood hydrogel is developed by fully utilizing the high-tensile strength of natural wood, and the flexibility and high-water content of hydrogels. The wood hydrogel exhibits a high-tensile strength of 36 MPa along the longitudinal direction due to the strong bonding and cross-linking between the aligned cellulose nanofibers (CNFs) in wood and the polyacrylamide (PAM) polymer. The wood hydrogel is 5 times and 500 times stronger than the bacterial cellulose hydrogels (7.2 MPa) and the unmodified PAM hydrogel (0.072 MPa), respectively, representing one of the strongest hydrogels ever reported. Due to the negatively charged aligned CNF, the wood hydrogel is also an excellent nanofluidic conduit with an ionic conductivity of up to 5 × 10^-4 S cm^-1 at low concentrations for highly selective ion transport, akin to biological muscle tissue. The work offers a promising strategy to fabricate a wide variety of strong, anisotropic, flexible, and ionically conductive wood-based hydrogels for potential biomaterials and nanofluidic applications.

Thermosensitive biomimetic polyisocyanopeptide hydrogels may facilitate wound repair

Changing wound dressings inflicts pain and may disrupt wound repair. Novel synthetic thermosensitive hydrogels based on polyisocyanopeptide (PIC) offer a solution. These gels are liquid below 16 °C and form gels beyond room temperature. The architecture and mechanical properties of PIC gels closely resemble collagen and fibrin, and include the characteristic stiffening response at high strains. Considering the reversible thermo-responsive behavior, we postulate that PIC gels are easy to apply and remove, and facilitate healing without eliciting foreign body responses or excessive inflammation. Biocompatibility may be higher in RGD-peptide-functionalized PIC gels due to enhanced cell binding capabilities. Full-thickness dorsal skin wounds in mice were compared to wounds treated with PIC gel and PIC-RGD gel for 3 and 7 days. No foreign body reactions and similar wound closure rates were found in all groups. The level of macrophages, myofibroblasts, epithelial migration, collagen expression, and blood vessels did not significantly differ from controls. Surprisingly, granulocyte populations in the wound decreased significantly in the PIC gel-treated groups, likely because foreign bacteria could not penetrate the gel. RGD-peptides did not further improve any effect observed for PIC. The absence of adverse effects, ease of application, and the possibilities for bio-functionalization make the biomimetic PIC hydrogels suitable for development into wound dressings.

Highly efficient solar vapour generation via hierarchically nanostructured gels

Solar vapour generation is an efficient way of harvesting solar energy for the purification of polluted or saline water. However, water evaporation suffers from either inefficient utilization of solar energy or relies on complex and expensive light-concentration accessories. Here, we demonstrate a hierarchically nanostructured gel (HNG) based on polyvinyl alcohol (PVA) and polypyrrole (PPy) that serves as an independent solar vapour generator. The converted energy can be utilized in situ to power the vaporization of water contained in the molecular meshes of the PVA network, where water evaporation is facilitated by the skeleton of the hydrogel. A floating HNG sample evaporated water with a record high rate of 3.2 kg m^-2 h^-1 via 94% solar energy from 1 sun irradiation, and 18-23 litres of water per square metre of HNG was delivered daily when purifying brine water. These values were achievable due to the reduced latent heat of water evaporation in the molecular mesh under natural sunlight.

Stretchable All-Gel-State Fiber-Shaped Supercapacitors Enabled by Macromolecularly Interconnected 3D Graphene/Nanostructured Conductive Polymer Hydrogels

Nanostructured conductive polymer hydrogels (CPHs) have been extensively applied in energy storage owing to their advantageous features, such as excellent electrochemical activity and relatively high electrical conductivity, yet the fabrication of self-standing and flexible electrode-based CPHs is still hampered by their limited mechanical properties. Herein, macromolecularly interconnected 3D graphene/nanostructured CPH is synthesized via self-assembly of CPHs and graphene oxide macrostructures. The 3D hybrid hydrogel shows uniform interconnectivity and enhanced mechanical properties due to the strong macromolecular interaction between the CPHs and graphene, thus greatly reducing aggregation in the fiber-shaping process. A proof-of-concept all-gel-state fibrous supercapacitor based on the 3D polyaniline/graphene hydrogel is fabricated to demonstrate the outstanding flexibility and mouldability, as well as superior electrochemical properties enabled by this 3D hybrid hydrogel design. The proposed device can achieve a large strain (up to ≈40%), and deliver a remarkable volumetric energy density of 8.80 mWh cm^-3 (at power density of 30.77 mW cm^-3 ), outperforming many fiber-shaped supercapacitors reported previously. The all-hydrogel design opens up opportunities in the fabrication of next-generation wearable and portable electronics.

A Chiral Ligand Assembly That Confers One-Electron O2 Reduction Activity for a Cu2+ -Selective Metallohydrogel

The design of functional metallohydrogels is attractive but challenging. A rational approach is introduced for designing functional metallohydrogels using chiral ligands, a phenylalanine derivative with a pyridyl group (l/d-PF). Intriguingly, the as-prepared metallohydrogel exhibits excellent O₂ binding and activating properties. Insights into the O₂ binding pathway reveals the presence of a novel [(l+d)-PF-Cu³⁺ -O₂^- ] species, which can efficiently reduce ferric cytochrome c with the reactive O₂^- by receiving an electron from reductant ascorbic acid. This study provides helpful instructions for developing new artificial systems with specific functions through the effective combination of chiral ligands with metal ions.

Ruthenium-Crosslinked Hydrogels with Rapid, Visible-Light Degradation

Incorporation of photoresponsive molecules within soft materials can provide spatiotemporal control over bulk properties and address challenges in targeted delivery and mechanical variability. However, the kinetics of in situ photochemical reactions are often slow and typically employ ultraviolet wavelengths. Here, we present a novel photoactive crosslinker Ru(bipyridine)2 (3-pyridinaldehyde)2 (RuAldehyde), which was reacted with hydrazide-functionalized hyaluronic acid to form hydrogels capable of encapsulating protein cargo. Visible light irradiation (400-500 nm) initiated rapid ligand exchange on the ruthenium center, which degraded the hydrogel within seconds to minutes, depending on gel thickness. An exemplar enzyme cargo, TEM1 β-lactamase, was loaded into and photoreleased from the Ru-hydrogel. To expand their applications, Ru-hydrogels were also processed into microgels using a microfluidic platform.

A thermo-/pH-responsive hydrogel (PNIPAM-PDMA-PAA) with diverse nanostructures and gel behaviors as a general drug carrier for drug release

The aim of this research was to develop thermo- and pH-responsive hydrogels based on H-bonds for the sustained release of the small-molecule model drug Methylene Blue (MB).

Surface-immobilized and self-shaped DNA hydrogels and their application in biosensing

Surface-immobilized pure DNA hydrogels were formed using a surficial primer-induced strategy and adopted as scaffold materials for biosensing applications.

Hydrogels are of great interest in the field of biosensing for their good biocompatibility, plasticity, and capability of providing 3D scaffolds. Nevertheless, the application of hydrogels has not been linked with broad surface biosensing systems yet. To overcome the limitations, here for the first time, surface-immobilized pure DNA hydrogels were synthesized using a surficial primer-induced strategy and adopted for biosensing applications. The DNA hydrogel 3D scaffold is successfully constructed on a transparent ITO electrode, which facilitates both colourimetric and electrochemical measurements. Results show that the hydrogel is able to wrap enzymes solidly and exhibits favourable stability under different conditions. Owing to the free diffusion of the micromolecular targets throughout the hydrogel, while isolating the enzymes from the macromolecular interferences outside the hydrogel, the direct colourimetric and electrochemical detection of hydrogen peroxide and bilirubin in serum is achieved. The detection limit of hydrogen peroxide in serum is 22 nM by colourimetric analysis and 13 nM by electrochemical measurement. The detection limit of bilirubin is 32 nM, a favourable limit that could be used in jaundice diagnosis. In addition, the enzyme@hydrogel can be easily regenerated and the catalytic activity is retained for a few cycles, thus allowing the recycling of the hydrogel-based biosensing system. The successful integration of DNA hydrogels with surface biosensing systems will greatly expand the applications of hydrogels for diagnostic and environmental monitoring purposes.

Reduced Graphene Oxide-Containing Smart Hydrogels with Excellent Electro-Response and Mechanical Properties for Soft Actuators

A novel reduced graphene oxide/poly(2-acrylamido-2-methylpropanesulfonic acid-co-acrylamide) (rGO/poly(AMPS-co-AAm)) nanocomposite hydrogel that possesses excellent electro-response and mechanical properties has been successfully developed. The rGO nanosheets that homogeneously dispersed in the hydrogels could provide prominent conductive platforms for promoting the ion transport inside the hydrogels to generate significant osmotic pressure between the outside and inside of such nanocomposite hydrogels. Thus, the electro-responsive rate and degree of the hydrogel for both deswelling and bending performances become rapid and remarkable. Moreover, the enhanced mechanical properties including both the tensile strength and compressive strength of rGO/poly(AMPS-co-AAm) hydrogels are improved by the hydrogen-bond interactions between the rGO nanosheets and polymer chains, which could dissipate the strain energy in the polymeric networks of the hydrogels. The proposed rGO/poly(AMPS-co-AAm) nanocomposite hydrogels with improved mechanical properties exhibit rapid, significant, and reversible electro-response, which show great potential for developing remotely controlled electro-responsive hydrogel systems, such as smart actuators and soft manipulators.

CO2-responsive self-healable hydrogels based on hydrophobically-modified polymers bridged by wormlike micelles

A versatile and simple strategy is proposed to design CO₂-responsive self-healable hydrogels based on hydrophobically-modified polymers bridged by worm like micelles.

Reversible bidirectional bending of hydrogel-based bilayer actuators

Semi-IPN hydrogel-based bilayers were fabricated and exhibited unique bidirectional bending behavior in response to solution temperature and pH, which is vastly different from what is observed for bilayers composed of only conventional hydrogels.

Microwave-responsive polymeric core–shell microcarriers for high-efficiency controlled drug release

A general drug carrier with a unique conjugated polymer/PNIPAM core–shell structure is synthesized for high-efficiency controlled drug release under microwave irradiation.

Nioplexes encapsulated in supramolecular hybrid biohydrogels as versatile delivery platforms for nucleic acids

Supramolecular hydrogels based on N-protected phenylalanine (Fmoc–Phe–OH) were used to encapsulate non-ionic surfactant vesicles (niosomes).