Synthesis and Characterization of Gelatin-Based Magnetic Hydrogels

Plasmonic-Hydrogel Hybrid Biomaterials Via In Situ Seeded Growth

The combination of hydrogels and functional plasmonic metal nanoparticles affords the development of unique hybrid systems, such as actuators, biosensors, and drug delivery systems, among others. Being typically prepared in colloidal suspension, incorporating shape-controlled plasmonic nanoparticles on polymer substrates typically requires lengthy processes involving synthesis, washing, and self-assembly. We report an alternative, robust in situ seed-mediated growth method whereby either isotropic or anisotropic gold and silver nanoparticles can be prepared directly on gelatin-based hydrogels, taking advantage of the polymer's native chemical functionalities. In-depth characterization of gold precursor-polymer interactions enabled the rational growth of branched gold nanoparticles on biocompatible hydrogels with different physicochemical properties. In situ seeded growth circumvents traditional limitations imposed by the need for colloidal stability, thereby enabling gold nanoparticle synthesis under surfactant-free conditions and in high ionic strength solutions, thus enhancing their suitability for applications involving live cells. This method can be expanded to create libraries of hybrid plasmonic materials with potential impact in the fabrication of functional 3D cell culture substrates, as well as biological and chemical sensors.

A portable hydrogel kit based on Au@GM88A/I combined with mobile phone for polychromatic semi-quantitative and quantitative sensing analysis

The development of an affordable, portable, and instrument-free colorimetric biosensor holds significant importance for routine monitoring and clinical diagnosis. To overcome the limitations that traditional monochromatic colorimetric kits struggle to distinguish subtle color changes with the naked eye, we designed and constructed a portable hydrogel kit for polychromatic semi-quantitative and quantitative sensing analysis. When the actual samples and I- were introduced into a gelatin hydrogel encapsulated with MIL-88A(Fe), Au NRs and oxidase (Au@GM88A/I), a noticeable color change occurred. Additionally, a mathematic model between Hue and multicolor signal was set up for the first time by mobile phone photo technology, successfully applied to the glucose detection in serum. The visual detection had a wide concentration range of 0.02-0.80 mM with a limit of detection down to 0.02 mM. Above all, hydrogel kit prepared with gelatin as a carrier addressed the issues of uneven color and slow response rate commonly seen in gels like sodium alginate and agarose. This improvement would be beneficial for enhancing the accuracy of color captured by mobile phone assisted hydrogel kits, making it a valuable tool for biomarker analysis.

A Superparamagnetic Composite Hydrogel Scaffold as In Vivo Dynamic Monitorable Theranostic Platform for Osteoarthritis Regeneration

Osteoarthritis (OA) is a prevalent disease, characterized by subchondral fractures in its initial stages, which has no precise and specific treatment now. Here, a novel multifunctional scaffold is synthesized by photopolymerizing glycidyl methacrylate-modified hyaluronic acid (GMHA) as the matrix in the presence of hollow porous magnetic microspheres based on hydroxyapatite. In vivo subchondral bone repairing results demonstrate that the scaffold's meticulous design has most suitable properties for subchondral bone repair. The porous structure of inorganic particles within the scaffold facilitates efficient transport of loaded exogenous vascular endothelial growth factor (VEGF). The Fe3O4 nanoparticles assembled in microspheres promote the osteogenic differentiation of bone marrow mesenchymal stem cells and accelerate the new bone generation. These features enable the scaffold to exhibit favorable subchondral bone repair properties and attain high cartilage repair scores. The therapy results prove that the subchondral bone support considerably influences the upper cartilage repair process. Furthermore, magnetic resonance imaging monitoring demonstrates that Fe3O4 nanoparticles, which are gradually replaced by new bone during osteochondral defect repair, allow a noninvasive and radiation-free assessment to track the newborn bone during the OA repair process. The composite hydrogel scaffold (CHS) provides a versatile platform for biomedical applications in OA treatment.

Magnetic hydrogel applications in articular cartilage tissue engineering

Articular cartilage defects afflict millions of individuals worldwide, presenting a significant challenge due to the tissue's limited self-repair capability and anisotropic nature. Hydrogel-based biomaterials have emerged as promising candidates for scaffold production in artificial cartilage construction, owing to their water-rich composition, biocompatibility, and tunable properties. Nevertheless, conventional hydrogels typically lack the anisotropic structure inherent to natural cartilage, impeding their clinical and preclinical applications. Recent advancements in tissue engineering (TE) have introduced magnetically responsive hydrogels, a type of intelligent hydrogel that can be remotely controlled using an external magnetic field. These innovative materials offer a means to create the desired anisotropic architecture required for successful cartilage TE. In this review, we first explore conventional techniques employed for cartilage repair and subsequently delve into recent breakthroughs in the application and utilization of magnetic hydrogels across various aspects of articular cartilage TE.

Shaped Magnetogel Microparticles for Multispectral Magnetic Resonance Contrast and Sensing

Multispectral magnetic resonance imaging (MRI) contrast agents are microfabricated three-dimensional magnetic structures that encode nearby water protons with discrete frequencies. The agents have a unique radiofrequency (RF) resonance that can be tuned by engineering the geometric parameters of these microstructures. Multispectral contrast agents can be used as sensors by incorporating a stimulus-driven shape-changing response into their structure. These geometrically encoded magnetic sensors (GEMS) enable MRI-based sensing via environmentally induced changes to their geometry and their corresponding RF resonance. Previously, GEMS have been made using thin-film lithography techniques in a cleanroom environment. While these approaches offer precise control of the microstructure, they can be a limitation for researchers who do not have cleanroom access or microfabrication expertise. Here, an alternative approach for GEMS fabrication based on soft lithography is introduced. The fabrication scheme uses cheap, accessible materials and simple chemistry to produce shaped magnetic hydrogel microparticles with multispectral MRI contrast properties. The microparticles can be used as sensors by fabricating them out of shape-reconfigurable, "smart" hydrogels. The change in shape causes a corresponding shift in the resonance of the GEMS, producing an MRI-addressable readout of the microenvironment. Proof-of-principle experiments showing a multispectral response to pH change with cylindrical shell-shaped magnetogel GEMS are presented.

Advancements in gelatin-based hydrogel systems for biomedical applications: A state-of-the-art review

A gelatin-based hydrogel system is a stimulus-responsive, biocompatible, and biodegradable polymeric system with solid-like rheology that entangles moisture in its porous network that gradually protrudes to assemble a hierarchical crosslinked arrangement. The hydrolysis of collagen directs gelatin construction, which retains arginyl glycyl aspartic acid and matrix metalloproteinase-sensitive degeneration sites, further confining access to chemicals entangled within the gel (e.g., cell encapsulation), modulating the release of encapsulated payloads and providing mechanical signals to the adjoining cells. The utilization of various types of functional tunable biopolymers as scaffold materials in hydrogels has become highly attractive due to their higher porosity and mechanical ability; thus, higher loading of proteins, peptides, therapeutic molecules, etc., can be further modulated. Furthermore, a stimulus-mediated gelatin-based hydrogel with an impaired concentration of gellan demonstrated great shear thinning and self-recovering characteristics in biomedical and tissue engineering applications. Therefore, this contemporary review presents a concise version of the gelatin-based hydrogel as a conceivable biomaterial for various biomedical applications. In addition, the article has recapped the multiple sources of gelatin and their structural characteristics concerning stimulating hydrogel development and delivery approaches of therapeutic molecules (e.g., proteins, peptides, genes, drugs, etc.), existing challenges, and overcoming designs, particularly from drug delivery perspectives.

Fabrication and characterization of fish gelatin-based magnetic nanocomposite for biomedical applications

Bionanocomposite is considered an advanced way to bridge the gap between the structural and functional material and achieve the desired properties in the nanocomposite. This present study highlighted the synthesis of fish gelatin-based magnetic nanocomposite (GMNC) using three different concentrations of gelatin (6% w/v, G12% w/v, and 18% w/v) individually, through the in situ coprecipitation method. The effect of gelatin concentration on the structural, functional, magnetic properties, and biocompatibility of the GMNC was studied successfully. This variation reduces the crystallite size from 20.8 to 12.2 nm. GMNC obtained at minimum gelatin concentration (6% w/v) produced well-dispersed sphere-shaped magnetite nanoparticles with an average particle size of 33 nm without aggregation. All three reported superparamagnetic behavior at 293 K. It also noted the highly biocompatible and biodegradable nature of GMNC with a high magnetic response at a low magnetic field. This study reported the perspective of this functionalization method for biomedical applications, as GMNC is a potential carrier material that is easily attached to drug molecules through the free functional residues of gelatin molecules. The present study also performed the in vitro drug release behavior of 5'Fluorouracil-loaded GMNC (GF) at physiological conditions (pH 7.4 and 37 °C). It indicates the prepared GF exhibits a sustained drug-release profile for up to 48 h. Hence, these results strongly supported that the functionalized GMNC would be a potential carrier material for advanced drug delivery applications.

Soft Viscoelastic Magnetic Hydrogels from the In Situ Mineralization of Iron Oxide in Metal-Coordinate Polymer Networks

The design of soft magnetic hydrogels with high concentrations of magnetic particles is complicated by weak retention of the iron oxide particles in the hydrogel scaffold. Here, we propose a design strategy that circumvents this problem through the in situ mineralization of iron oxide nanoparticles within polymer hydrogels functionalized with strongly iron-coordinating nitrocatechol groups. The mineralization process facilitates the synthesis of a high concentration of large iron oxide nanoparticles (up to 57 wt % dry mass per single cycle) in a simple one-step process under ambient conditions. The resulting hydrogels are soft (kPa range) and viscoelastic and exhibit strong magnetic actuation. This strategy offers a pathway for the energy-efficient design of soft, mechanically robust, and magneto-responsive hydrogels for biomedical applications.

Magnetically anisotropic hydrogels for tissue engineering

Many soft tissues of the human body possess hierarchically anisotropic structures, exhibiting orientation-specific mechanical properties and biological functionality. Hydrogels have been proposed as promising scaffold materials for tissue engineering applications due to their water-rich composition, excellent biocompatibility, and tunable physico-chemical properties. However, conventional hydrogels with homogeneous structures often exhibit isotropic properties that differ from those of biological tissues, limiting their further application. Recently, magnetically anisotropic hydrogels containing long-range ordered magneto-structures have attracted widespread interest owing to their highly controllable assembly strategy, rapid magnetic responsiveness and remote spatiotemporal regulation. In this review, we summarize the latest progress of magnetically anisotropic hydrogels for tissue engineering. The fabrication strategy of magnetically anisotropic hydrogels from magnetic nanofillers with different dimensions is systemically introduced. Then, the effects of magnetically anisotropic cues on the physicochemical properties of hydrogels and the cellular biological behavior are discussed. And the applications of magnetically anisotropic hydrogels in the engineering of different tissues are emphasized. Finally, the current challenges and the future perspectives for magnetically anisotropic hydrogels are presented.

A CMC-g-poly(AA-co-AMPS)/Fe3O4 hydrogel nanocomposite as a novel biopolymer-based catalyst in the synthesis of 1,4-dihydropyridines

A CMC-g-poly(AA-co-AMPS)/Fe₃O₄ hydrogel nanocomposite was successfully designed and prepared via graft copolymerization of AA and AMPS on CMC followed by the cross-linking addition of FeCl₃/FeCl₂. The synthesized hydrogel nanocomposite was characterized by Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, elemental mapping, thermogravimetric analysis/differential thermal analysis (TGA/DTA), and vibrating sample magnetometry (VSM). The CMC-g-poly(AA-co-AMPS)/Fe₃O₄ hydrogel nanocomposite was employed as a biocompatible catalyst for the green synthesis of 1,4-dihydropyridine (1,4-DHP) derivatives under thermal and ultrasound-assisted reaction conditions. High efficiency, low catalyst loadings, short reaction time, frequent catalyst recovery, environmental compatibility and mild conditions were found in both methods.

Optimization strategies of mesenchymal stem cell-based therapy for acute kidney injury

Considering the high prevalence and the lack of targeted pharmacological management of acute kidney injury (AKI), the search for new therapeutic approaches for it is in urgent demand. Mesenchymal stem cells (MSCs) have been increasingly recognized as a promising candidate for the treatment of AKI. However, clinical translation of MSCs-based therapies is hindered due to the poor retention and survival rates as well as the impaired paracrine ability of MSCs post-delivery. To address these issues, a series of strategies including local administration, three-dimensional culture, and preconditioning have been applied. Owing to the emergence and development of these novel biotechnologies, the effectiveness of MSCs in experimental AKI models is greatly improved. Here, we summarize the different approaches suggested to optimize the efficacy of MSCs therapy, aiming at promoting the therapeutic effects of MSCs on AKI patients.

Matrix-Directed Mineralization for Bulk Structural Materials

Mineral-based bulk structural materials (MBSMs) are known for their long history and extensive range of usage. The inherent brittleness of minerals poses a major problem to the performance of MBSMs. To overcome this problem, design principles have been extracted from natural biominerals, in which the extraordinary mechanical performance is achieved via the hierarchical organization of minerals and organics. Nevertheless, precise and efficient fabrication of MBSMs with bioinspired hierarchical structures under mild conditions has long been a big challenge. This Perspective provides a panoramic view of an emerging fabrication strategy, matrix-directed mineralization, which imitates the in vivo growth of some biominerals. The advantages of the strategy are revealed by comparatively analyzing the conventional fabrication techniques of artificial hierarchically structured MBSMs and the biomineral growth processes. By introducing recent advances, we demonstrate that this strategy can be used to fabricate artificial MBSMs with hierarchical structures. Particular attention is paid to the mass transport and the precursors that are involved in the mineralization process. We hope this Perspective can provide some inspiring viewpoints on the importance of biomimetic mineralization in material fabrication and thereby spur the biomimetic fabrication of high-performance MBSMs.

Facile synthesis of low toxicity iron oxide/TiO2 nanocomposites with hyperthermic and photo-oxidation properties

The present study aimed to assess the feasibility of developing low-cost multipurpose iron oxide/TiO2 nanocomposites (NCs) for use in combined antitumor therapies and water treatment applications. Larger size (≈ 100 nm) iron oxide nanoparticles (IONPs) formed magnetic core-TiO2 shell structures at high Fe/Ti ratios and solid dispersions of IONPs embedded in TiO2 matrices when the Fe/Ti ratio was low. When the size of the iron phase was comparable to the size of the crystallized TiO2 nanoparticles (≈ 10 nm), the obtained nanocomposites consisted of randomly mixed aggregates of TiO2 and IONPs. The best inductive heating and ROS photogeneration properties were shown by the NCs synthesized at 400 °C which contained the minimum amount of α-Fe2O3 and sufficiently crystallized anatase TiO2. Their cytocompatibility was assessed on cultured human and murine fibroblast cells and analyzed in relation to the adsorption of bovine serum albumin from the culture medium onto their surface. The tested nanocomposites showed excellent cytocompatibility to human fibroblast cells. The results also indicated that the environment (i.e. phosphate buffer or culture medium) used to disperse the nanomaterials prior to performing the viability tests can have a significant impact on their cytotoxicity.

Polymeric Hydrogels as Mesenchymal Stem Cell Secretome Delivery System in Biomedical Applications

Secretomes of mesenchymal stem cells (MSCs) have been successfully studied in preclinical models for several biomedical applications, including tissue engineering, drug delivery, and cancer therapy. Hydrogels are known to imitate a three-dimensional extracellular matrix to offer a friendly environment for stem cells; therefore, hydrogels can be used as scaffolds for tissue construction, to control the distribution of bioactive compounds in tissues, and as a secretome-producing MSC culture media. The administration of a polymeric hydrogel-based MSC secretome has been shown to overcome the fast clearance of the target tissue. In vitro studies confirm the bioactivity of the secretome encapsulated in the gel, allowing for a controlled and sustained release process. The findings reveal that the feasibility of polymeric hydrogels as MSC -secretome delivery systems had a positive influence on the pace of tissue and organ regeneration, as well as an enhanced secretome production. In this review, we discuss the widely used polymeric hydrogels and their advantages as MSC secretome delivery systems in biomedical applications.

Using small-angle scattering to guide functional magnetic nanoparticle design

Magnetic nanoparticles offer unique potential for various technological, biomedical, or environmental applications thanks to the size-, shape- and material-dependent tunability of their magnetic properties. To optimize particles for a specific application, it is crucial to interrelate their performance with their structural and magnetic properties. This review presents the advantages of small-angle X-ray and neutron scattering techniques for achieving a detailed multiscale characterization of magnetic nanoparticles and their ensembles in a mesoscopic size range from 1 to a few hundred nanometers with nanometer resolution. Both X-rays and neutrons allow the ensemble-averaged determination of structural properties, such as particle morphology or particle arrangement in multilayers and 3D assemblies. Additionally, the magnetic scattering contributions enable retrieving the internal magnetization profile of the nanoparticles as well as the inter-particle moment correlations caused by interactions within dense assemblies. Most measurements are used to determine the time-averaged ensemble properties, in addition advanced small-angle scattering techniques exist that allow accessing particle and spin dynamics on various timescales. In this review, we focus on conventional small-angle X-ray and neutron scattering (SAXS and SANS), X-ray and neutron reflectometry, gracing-incidence SAXS and SANS, X-ray resonant magnetic scattering, and neutron spin-echo spectroscopy techniques. For each technique, we provide a general overview, present the latest scientific results, and discuss its strengths as well as sample requirements. Finally, we give our perspectives on how future small-angle scattering experiments, especially in combination with micromagnetic simulations, could help to optimize the performance of magnetic nanoparticles for specific applications.

Developing Novel Fabrication and Optimisation Strategies on Aggregation-Induced Emission Nanoprobe/Polyvinyl Alcohol Hydrogels for Bio-Applications

The current study describes a new technology, effective for readily preparing a fluorescent (FL) nanoprobe-based on hyperbranched polymer (HB) and aggregation-induced emission (AIE) fluorogen with high brightness to ultimately develop FL hydrogels. We prepared the AIE nanoprobe using a microfluidic platform to mix hyperbranched polymers (HB, generations 2, 3, and 4) with AIE (TPE-2BA) under shear stress and different rotation speeds (0-5 K RPM) and explored the FL properties of the AIE nanoprobe. Our results reveal that the use of HB generation 4 exhibits 30-times higher FL intensity compared to the AIE alone and is significantly brighter and more stable compared to those that are prepared using HB generations 3 and 2. In contrast to traditional methods, which are expensive and time-consuming and involve polymerization and post-functionalization to develop FL hyperbranched molecules, our proposed method offers a one-step method to prepare an AIE-HB nanoprobe with excellent FL characteristics. We employed the nanoprobe to fabricate fluorescent injectable bioadhesive gel and a hydrogel microchip based on polyvinyl alcohol (PVA). The addition of borax (50 mM) to the PVA + AIE nanoprobe results in the development of an injectable bioadhesive fluorescent gel with the ability to control AIEgen release for 300 min. When borax concentration increases two times (100 mM), the adhesion stress is more than two times bigger (7.1 mN/mm2) compared to that of gel alone (3.4 mN/mm2). Excellent dimensional stability and cell viability of the fluorescent microchip, along with its enhanced mechanical properties, proposes its potential applications in mechanobiology and understanding the impact of microstructure in cell studies.

Magnetic correlations of iron oxide nanoparticles as probed by polarized SANS in stretched magnetic nanoparticle-elastomer composites

We have investigated the magnetic correlations among 7 nm iron oxide nanoparticles embedded in stretched silicone elastomers using polarized Small Angle Neutron Scattering (SANS). The magnetic nanoparticle (MNP)-elastomer composite can be stretched during experiments, and macroscopic deformations cause rearrangement of the iron oxide particles on the nanoscale. Polarized neutrons can be used to nondestructively probe the arrangement of magnetic nanoparticles before and after stretching, so that the relationship between applied stress and nanoscale magnetization can be interrogated. We find that stretching the MNP-elastomer composite past a certain threshold dramatically changes the structural and magnetic morphology of the system. The unstretched sample is modeled well by ~40 nm clusters of ~7 nm particles arranged in a hard sphere packing with a "volume fraction" parameter of 0.3. After the sample is stretched 3× its original size, however, the scattering data can be modeled by smaller, 16 nm clusters with a higher volume fraction of 0.4. We suggest that the effect can be understood by considering a stretching transformation on FCC-like crystallites of iron oxide nanoparticles embedded in an elastomeric medium.

A Heterostructured FeNi Hydroxide for Effective Electrocatalytic Oxygen Evolution

Hydrogen production technology by water splitting has been heralded as an effective means to alleviate the envisioned energy crisis. However, the overall efficiency of water splitting is limited by the effectiveness of the anodic oxygen evolution reaction (OER) due to the high energy barrier of the 4e⁻ process. The key to addressing this challenge is the development of high-performing catalysts. Transition-metal hydroxides with high intrinsic activity and stability have been widely studied for this purpose. Herein, we report a gelatin-induced structure-directing strategy for the preparation of a butterfly-like FeNi/Ni heterostructure (FeNi/Ni HS) with excellent catalytic performance. The electronic interactions between Ni²⁺ and Fe³⁺ are evident both in the mixed-metal “torso” region and at the “torso/wing” interface with increasing Ni³⁺ as a result of electron transfer from Ni²⁺ to Fe³⁺ mediated by the oxo bridge. The amount of Ni³⁺ also increases in the “wings”, which is believed to be a consequence of charge balancing between Ni and O ions due to the presence of Ni vacancies upon formation of the heterostructure. The high-valence Ni³⁺ with enhanced Lewis acidity helps strengthen the binding with OH⁻ to afford oxygen-containing intermediates, thus accelerating the OER process. Direct evidence of FeNi/Ni HS facilitating the formation of the Ni–OOH intermediate was provided by in situ Raman studies; the intermediate was produced at lower oxidation potentials than when Ni₂(CO₃)(OH)₂ was used as the reference. The Co congener (FeCo/Co HS), prepared in a similar fashion, also showed excellent catalytic performance.

A butterfly-like FeNi/Ni HS featuring a “torso” of Ni-doped FeOOH and two “wings” of Ni₂(CO₃)(OH)₂ showed excellent activity in electrocatalytic oxygen evolution reaction attributable to the increase of higher-valance Ni³⁺ in the heterostructure.

Magnetic Properties of Collagen-Chitosan Hybrid Materials with Immobilized Superparamagnetic Iron Oxide Nanoparticles (SPIONs)

The paper presents results of our studies on hybrid materials based on polymers of natural origin containing superparamagnetic iron oxide nanoparticles (SPIONs). Such nanoparticles, coated with the chitosan derivative, were immobilized in a chitosan-collagen hydrogel matrix by crosslinking with genipin. Three types of biopolymer matrices of different collagen-to-chitosan ratios were studied. A thorough magnetic characterization was performed, including magnetic susceptibility, magnetization, and hysteresis loop measurements in a temperature range of 4 K to 300 K and a magnetic field induction up to 8 Tesla. The effect of SPION immobilization and material composition on the magnetic properties of the hybrids was investigated. The results showed that hybrid materials with covalently bounded SPIONs preserved the superparamagnetic character of SPIONs and exhibited promising magnetic properties, which are important for their potential applications.

Magnetic Properties of Iron Oxide Nanoparticles Do Not Essentially Contribute to Ferrogel Biocompatibility

Two series of composite polyacrylamide (PAAm) gels with embedded superparamagnetic Fe₂O₃ or diamagnetic Al₂O₃ nanoparticles were synthesized, aiming to study the direct contribution of the magnetic interactions to the ferrogel biocompatibility. The proliferative activity was estimated for the case of human dermal fibroblast culture grown onto the surfaces of these types of substrates. Spherical non-agglomerated nanoparticles (NPs) of 20-40 nm in diameter were prepared by laser target evaporation (LTE) electrophysical technique. The concentration of the NPs in gel was fixed at 0.0, 0.3, 0.6, or 1.2 wt.%. Mechanical, electrical, and magnetic properties of composite gels were characterized by the dependence of Young's modulus, electrical potential, magnetization measurements on the content of embedded NPs. The fibroblast monolayer density grown onto the surface of composite substrates was considered as an indicator of the material biocompatibility after 96 h of incubation. Regardless of the superparamagnetic or diamagnetic nature of nanoparticles, the increase in their concentration in the PAAm composite provided a parallel increase in the cell culture proliferation when grown onto the surface of composite substrates. The effects of cell interaction with the nanostructured surface of composites are discussed in order to explain the results.

Graphene-based hybrid materials as promising scaffolds for peripheral nerve regeneration

Peripheral nerve injury (PNI) is a serious clinical health problem caused by the damage of peripheral nerves which results in neurological deficits and permanent disability. There are several factors that may cause PNI such as localized damage (car accident, trauma, electrical injury) and outbreak of the systemic diseases (autoimmune or diabetes). While various diagnostic procedures including X-ray, magnetic resonance imaging (MRI), as well as other type of examinations such as electromyography or nerve conduction studies have been efficiently developed, a full recovery in patients with PNI is in many cases deficient or incomplete. This is the reason why additional therapeutic strategies should be explored to favor a complete rehabilitation in order to get appropriate nerve injury regeneration. The use of biomaterials acting as scaffolds opens an interesting approach in regenerative medicine and tissue engineering applications due to their ability to guide the growth of new tissues, adhesion and proliferation of cells including the expression of bioactive signals. This review discusses the preparation and therapeutic strategies describing in vitro and in vivo experiments using graphene-based materials in the context of PNI and their ability to promote nerve tissue regeneration.

In situ mechanical reinforcement of polymer hydrogels via metal-coordinated crosslink mineralization

Biological organic-inorganic materials remain a popular source of inspiration for bioinspired materials design and engineering. Inspired by the self-assembling metal-reinforced mussel holdfast threads, we tested if metal-coordinate polymer networks can be utilized as simple composite scaffolds for direct in situ crosslink mineralization. Starting with aqueous solutions of polymers end-functionalized with metal-coordinating ligands of catechol or histidine, here we show that inter-molecular metal-ion coordination complexes can serve as mineral nucleation sites, whereby significant mechanical reinforcement is achieved upon nanoscale particle growth directly at the metal-coordinate network crosslink sites.

Biological organic-inorganic materials, such as self-assembling metal-reinforced mussel holdfast threads, remain a popular source of inspiration for materials design and engineering. Here the authors show that metal-coordinate polymer networks can be utilized as simple composite scaffolds for direct in situ crosslink mineralization.

Composite Hydrogels in Three-Dimensional in vitro Models

3-dimensional (3D) in vitro models were developed in order to mimic the complexity of real organ/tissue in a dish. They offer new possibilities to model biological processes in more physiologically relevant ways which can be applied to a myriad of applications including drug development, toxicity screening and regenerative medicine. Hydrogels are the most relevant tissue-like matrices to support the development of 3D in vitro models since they are in many ways akin to the native extracellular matrix (ECM). For the purpose of further improving matrix relevance or to impart specific functionalities, composite hydrogels have attracted increasing attention. These could incorporate drugs to control cell fates, additional ECM elements to improve mechanical properties, biomolecules to improve biological activities or any combinations of the above. In this Review, recent developments in using composite hydrogels laden with cells as biomimetic tissue- or organ-like constructs, and as matrices for multi-cell type organoid cultures are highlighted. The latest composite hydrogel systems that contain nanomaterials, biological factors, and combinations of biopolymers (e.g., proteins and polysaccharide), such as Interpenetrating Networks (IPNs) and Soft Network Composites (SNCs) are also presented. While promising, challenges remain. These will be discussed in light of future perspectives toward encompassing diverse composite hydrogel platforms for an improved organ environment in vitro.

Design Principles for Aqueous Interactive Materials: Lessons from Small Molecules and Stimuli-Responsive Systems

Interactive materials are at the forefront of current materials research with few examples in the literature. Researchers are inspired by nature to develop materials that can modulate and adapt their behavior in accordance with their surroundings. Stimuli-responsive systems have been developed over the past decades which, although often described as "smart," lack the ability to act autonomously. Nevertheless, these systems attract attention on account of the resultant materials' ability to change their properties in a predicable manner. These materials find application in a plethora of areas including drug delivery, artificial muscles, etc. Stimuli-responsive materials are serving as the precursors for next-generation interactive materials. Interest in these systems has resulted in a library of well-developed chemical motifs; however, there is a fundamental gap between stimuli-responsive and interactive materials. In this perspective, current state-of-the-art stimuli-responsive materials are outlined with a specific emphasis on aqueous macroscopic interactive materials. Compartmentalization, critical for achieving interactivity, relies on hydrophobic, hydrophilic, supramolecular, and ionic interactions, which are commonly present in aqueous systems and enable complex self-assembly processes. Relevant examples of aqueous interactive materials that do exist are given, and design principles to realize the next generation of materials with embedded autonomous function are suggested.

Pharmaceutical Applications of Iron-Oxide Magnetic Nanoparticles

Advances of nanotechnology led to the development of nanoparticulate systems with many advantages due to their unique physicochemical properties. The use of iron-oxide magnetic nanoparticles (IOMNPs) in pharmaceutical areas increased in the last few decades. This article reviews the conceptual information about iron oxides, magnetic nanoparticles, methods of IOMNP synthesis, properties useful for pharmaceutical applications, advantages and disadvantages, strategies for nanoparticle assemblies, and uses in the production of drug delivery, hyperthermia, theranostics, photodynamic therapy, and as an antimicrobial. The encapsulation, coating, or dispersion of IOMNPs with biocompatible material(s) can avoid the aggregation, biodegradation, and alterations from the original state and also enable entrapping the bioactive agent on the particle via adsorption or covalent attachment. IOMNPs show great potential for target drug delivery, improving the therapy as a consequence of a higher drug effect using lower concentrations, thus reducing side effects and toxicity. Different methodologies allow IOMNP synthesis, resulting in different structures, sizes, dispersions, and surface modifications. These advantages support their utilization in pharmaceutical applications, and getting suitable drug release control on the target tissues could be beneficial in several clinical situations, such as infections, inflammations, and cancer. However, more toxicological clinical investigations about IOMNPs are necessary.

A review on versatile applications of blends and composites of CNC with natural and synthetic polymers with mathematical modeling

Cellulose is world's most abundant, renewable and recyclable polysaccharide on earth. Cellulose is composed of both amorphous and crystalline regions. Cellulose nanocrystals (CNCs) are extracted from crystalline region of cellulose. The most attractive feature of CNC is that it can be used as nanofiller to reinforce several synthetic and natural polymers. In this article, a comprehensive overview of modification of several natural and synthetic polymers using CNCs as reinforcer in respective polymer matrix is given. The immense activities of CNCs are successfully utilized to enhance the mechanical properties and to broaden the field of application of respective polymer. All the technical scientific issues have been discussed highlighting the recent advancement in biomedical and packaging field.

The Contribution of Magnetic Nanoparticles to Ferrogel Biophysical Properties

Iron oxide γ-Fe₂O₃ magnetic nanoparticles (MNPs) were fabricated by laser target evaporation technique (LTE) and their structure and magnetic properties were studied. Polyacrylamide (PAAm) gels with different cross-linking density of the polymer network and polyacrylamide-based ferrogel with embedded LTE MNPs (0.34 wt.%) were synthesized. Their adhesive and proliferative potential with respect to human dermal fibroblasts were studied. At the same value of Young modulus, the adhesive and proliferative activities of the human dermal fibroblasts on the surface of ferrogel were unexpectedly much higher in comparison with the surface of PAAm gel. Properties of PAAm-100 + γ-Fe₂O₃ MNPs composites were discussed with focus on creation of a new generation of drug delivery systems combined in multifunctional devices, including magnetic field assisted delivery, positioning, and biosensing. Although exact applications are still under development, the obtained results show a high potential of LTE MNPs to be applied for cellular technologies and tissue engineering. PAAm-100 ferrogel with very low concentration of γ-Fe₂O₃ MNPs results in significant improvement of the cells’ compatibility to the gel-based scaffold.

Mechanism of silica-lysozyme composite formation unravelled by in situ fast SAXS

A quantitative understanding of aggregation mechanisms leading to the formation of composites of inorganic nanoparticles (NPs) and proteins in aqueous media is of paramount interest for colloid chemistry. In particular, the interactions between silica (SiO2) NPs and lysozyme (LZM) have attracted attention, because LZM is well-known to adsorb strongly to silica NPs, while at the same time preserving its enzymatic activity. The inherent nature of the aggregation processes leading to NP-LZM composites involves structural changes at length scales from few to at least hundreds of nanometres but also time scales much smaller than one second. To unravel these we used in situ synchrotron-based small-angle X-ray scattering (SAXS) and followed the subtle interparticle interactions in solution at a time resolution of 50 ms/frame (20 fps). We show that if the size of silica NPs (ca. 5 nm diameter) is matched by the dimensions of LZM, the evolving scattering patterns contain a unique structure-factor contribution originating from the presence of LZM. We developed a scattering model and applied it to analyse this structure function, which allowed us to extract structural information on the deformation of lysozyme molecules during aggregation, as well as to derive the mechanisms of composite formation.

From Solute, Fluidic and Particulate Precursors to Complex Organizations of Matter

The organization of matter from its constitutive units recruits intermediate states with distinctive degrees of self-association and molecular order. Existing as clusters, droplets, gels as well as amorphous and crystalline nanoparticles, these precursor forms have fundamental contributions towards the composition and structure of inorganic and organic architectures. In this personal account, we show that the transitions from atoms, molecules or ionic species to superstructures of higher order are intertwined with the interfaces and interactions of precursor and intermediate states. Structural organizations distributed across different length scales are explained by the multistep nature of nucleation and crystallization, which can be guided towards functional hybrid materials by the strategic application of additives, templates and reaction environments. Thus, the non-classical pathways for material formation and growth offer conceptual frameworks for elucidating, inducing and directing fascinating material organizations of biogenic and synthetic origins.

Ionic Dependence of Gelatin Hydrogel Architecture Explored Using Small and Very Small Angle Neutron Scattering Technique

The hierarchical structure of gelatin hydrogels mimics a natural extracellular matrix and provides an optimized microenvironment for the growth of 3D structured tissue analogs. In the presence of metal ions, gelatin hydrogels exhibit various mechanical properties that are correlated with the molecular interactions and the hierarchical structure. The structure and structural response of gelatin hydrogels to variation of gelatin concentration, pH, or addition of metal ions are explored by small and very small angle neutron scattering over broad length scales. The measurements of the hydrogels reveal the existence of a two-level structure of colloid-like large clusters and a 3D cage-like gel network. In the presence of Fe³⁺ ions the hydrogels show a highly dense and stiff network, while Ca²⁺ ions have an opposite effect. The results provide important structural insight for improvement of the design of gelatin based hydrogels and are therefore suitable for various applications.

Development of Smart Optical Gels with Highly Magnetically Responsive Bicelles

Hydrogels delivering on-demand tailorable optical properties are formidable smart materials with promising perspectives in numerous fields, including the development of modern sensors and switches, the essential quality criterion being a defined and readily measured response to environmental changes. Lanthanide ion (Ln³⁺)-chelating bicelles are interesting building blocks for such materials because of their magnetic responsive nature. Imbedding these phospholipid-based nanodiscs in a magnetically aligned state in gelatin permits an orientation-dependent retardation of polarized light. The resulting tailorable anisotropy gives the gel a well-defined optical signature observed as a birefringence signal. These phenomena were only reported for a single bicelle-gelatin pair and required high magnetic field strengths of 8 T. Herein, we demonstrate the versatility and enhance the viability of this technology with a new generation of aminocholesterol (Chol-NH₂)-doped bicelles imbedded in two different types of gelatin. The highly magnetically responsive nature of the bicelles allowed to gel the anisotropy at commercially viable magnetic field strengths between 1 and 3 T. Thermoreversible gels with a unique optical signature were generated by exposing the system to various temperature conditions and external magnetic field strengths. The resulting optical properties were a signature of the gel's environmental history, effectively acting as a sensor. Solutions containing the bicelles simultaneously aligning parallel and perpendicular to the magnetic field directions were obtained by mixing samples chelating Tm³⁺ and Dy³⁺. These systems were successfully gelled, providing a material with two distinct temperature-dependent optical characteristics. The high degree of tunability in the magnetic response of the bicelles enables encryption of the gel's optical properties. The proposed gels are viable candidates for temperature tracking of sensitive goods and provide numerous perspectives for future development of tomorrow's smart materials and technologies.

Polymer architecture of magnetic gels: a review

In this review article, we provide an introduction to ferrogels, i.e. polymeric gels with embedded magnetic particles. Due to the interplay between magnetic and elastic properties of these materials, they are promising candidates for engineering and biomedical applications such as actuation and controlled drug release. Particular emphasis will be put on the polymer architecture of magnetic gels since it controls the degrees of freedom of the magnetic particles in the gel, and it is important for the particle-polymer coupling determining the mechanisms available for the gel deformation in magnetic fields. We report on the different polymer architectures that have been realized so far, and provide an overview of synthesis strategies and experimental techniques for the characterization of these materials. We further focus on theoretical and simulational studies carried out on magnetic gels, and highlight their contributions towards understanding the influence of the gels' polymer architecture.

Polyacrylamide Ferrogels with Magnetite or Strontium Hexaferrite: Next Step in the Development of Soft Biomimetic Matter for Biosensor Applications

Magnetic biosensors are an important part of biomedical applications of magnetic materials. As the living tissue is basically a "soft matter." this study addresses the development of ferrogels (FG) with micron sized magnetic particles of magnetite and strontium hexaferrite mimicking the living tissue. The basic composition of the FG comprised the polymeric network of polyacrylamide, synthesized by free radical polymerization of monomeric acrylamide (AAm) in water solution at three levels of concentration (1.1 M, 0.85 M and 0.58 M) to provide the FG with varying elasticity. To improve FG biocompatibility and to prevent the precipitation of the particles, polysaccharide thickeners-guar gum or xanthan gum were used. The content of magnetic particles in FG varied up to 5.2 wt % depending on the FG composition. The mechanical properties of FG and their deformation in a uniform magnetic field were comparatively analyzed. FG filled with strontium hexaferrite particles have larger Young's modulus value than FG filled with magnetite particles, most likely due to the specific features of the adhesion of the network's polymeric subchains on the surface of the particles. FG networks with xanthan are stronger and have higher modulus than the FG with guar. FG based on magnetite, contract in a magnetic field 0.42 T, whereas some FG based on strontium hexaferrite swell. Weak FG with the lowest concentration of AAm shows a much stronger response to a field, as the concentration of AAm governs the Young's modulus of ferrogel. A small magnetic field magnetoimpedance sensor prototype with Co_68.6Fe_3.9Mo_3.0Si_12.0B_12.5 rapidly quenched amorphous ribbon based element was designed aiming to develop a sensor working with a disposable stripe sensitive element. The proposed protocol allowed measurements of the concentration dependence of magnetic particles in gels using magnetoimpedance responses in the presence of magnetite and strontium hexaferrite ferrogels with xanthan. We have discussed the importance of magnetic history for the detection process and demonstrated the importance of remnant magnetization in the case of the gels with large magnetic particles.

Engineering magnetically responsive tropoelastin spongy-like hydrogels for soft tissue regeneration

Magnetic biomaterials are a key focus in medical research.

Nanostructure of Fully Injectable Hydrazone-Thiosuccinimide Interpenetrating Polymer Network Hydrogels Assessed by Small-Angle Neutron Scattering and dSTORM Single-Molecule Fluorescence Microscopy

Herein, we comprehensively investigate the internal morphology of fully injectable interpenetrating networks (IPNs) prepared via coextrusion of functionalized precursor polymer solutions based on thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and nonthermoresponsive poly(vinyl pyrrolidone) (PVP) by reactive mixing using kinetically orthogonal hydrazone and thiosuccinimide cross-linking mechanisms. Small-angle neutron scattering, probing both the full IPN as well as the individual constituent networks of the IPN using index-matching, suggests a partially mixed internal structure characterized by PNIPAM-rich domains entrapped in a clustered PVP-rich phase. This interpretation is supported by super-resolution fluorescence microscopy (direct stochastic optical reconstruction microscopy) measurements on the same gels on a different length scale, which show both the overall phase segregation typical of an IPN as well as moderate mixing of PNIPAM into the PVP-rich phase. Such a morphology is consistent with the kinetics of both gelation and phase separation in this in situ gelling system, in which gelation effectively traps a fraction of the PNIPAM in the PVP phase prior to full phase separation; by contrast, such interphase mixing is not observed in semi-IPN control hydrogels. This knowledge has significant potential for the design of an injectable hydrogel with internal morphologies optimized for particular biomedical applications.