Hierarchical construction of a mechanically stable peptide-graphene oxide hybrid hydrogel for drug delivery and pulsatile triggered release in vivo

Recent advances of self-assembling peptide-based hydrogels for biomedical applications

Peptide-based hydrogels have been proven to be preeminent biomedical materials due to their high water content, tunable mechanical stability, great biocompatibility and excellent injectability. The ability of peptide-based hydrogels to provide extracellular matrix-mimicking environments opens up opportunities for their biomedical applications in fields such as drug delivery, tissue engineering, and wound healing. In this review, we first describe several methods commonly used for the fabrication of robust peptide-based hydrogels, including spontaneous hydrogelation, enzyme-controlled hydrogelation and cross-linking-enhanced hydrogelation. We then introduce some representative studies on their applications in drug delivery and antitumor therapy, antimicrobial and wound healing materials, and 3D bioprinting and tissue engineering. We hope that this review facilitates the advances of hydrogels in biomedical applications.

Biomarkers-based Biosensing and Bioimaging with Graphene for Cancer Diagnosis

At the onset of cancer, specific biomarkers get elevated or modified in body fluids or tissues. Early diagnosis of these biomarkers can greatly improve the survival rate or facilitate effective treatment with different modalities. Potential nanomaterial-based biosensing and bioimaging are the main techniques in nanodiagnostics because of their ultra-high selectivity and sensitivity. Emerging graphene, including two dimensional (2D) graphene films, three dimensional (3D) graphene architectures and graphene hybrids (GHs) nanostructures, are attracting increasing interests in the field of biosensing and bioimaging. Due to their remarkable optical, electronic, and thermal properties; chemical and mechanical stability; large surface area; and good biocompatibility, graphene-based nanomaterials are applicable alternatives as versatile platforms to detect biomarkers at the early stage of cancer. Moreover, currently, extensive applications of graphene-based biosensing and bioimaging has resulted in promising prospects in cancer diagnosis. We also hope this review will provide critical insights to inspire more exciting researches to address the current remaining problems in this field.

Supramolecular Hydrogel Based on Chlorambucil and Peptide Drug for Cancer Combination Therapy

Supramolecular hydrogels of self-assembling peptide-drug conjugates have been considered as effective self-delivery drug systems for cancer therapy in recent years. Here, a novel self-assembling peptide-based supramolecular hydrogel was developed by simultaneously conjugating small-molecule drug chlorambucil (CRB) and peptide drug tyroservatide (YSV) to the self-assembling peptide. The resulting hydrogel with a nanofiber structure showed enhanced stability against proteinase K degradation and an improved cellular uptake performance in comparison with the free molecules. As a consequence, it exhibited enhanced antitumor efficiency both in vitro and in vivo with favorable biocompatibility. This biocompatible self-delivery drug system could not only significantly improve the delivery efficiency of the small-molecule drugs but also adequately synergize the antitumor effect of CRB and YSV, inspiring the design of new strategies of cancer combination therapy.

Graphene and Graphene-Based Materials in Biomedical Applications

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Nanobiotechnology has huge potential in the field of regenerative medicine. One of the main drivers has been the development of novel nanomaterials. One developing class of materials is graphene and its derivatives recognized for their novel properties present on the nanoscale. In particular, graphene and graphene-based nanomaterials have been shown to have excellent electrical, mechanical, optical and thermal properties. Due to these unique properties coupled with the ability to tune their biocompatibility, these nanomaterials have been propelled for various applications. Most recently, these two-dimensional nanomaterials have been widely recognized for their utility in biomedical research. In this review, a brief overview of the strategies to synthesize graphene and its derivatives are discussed. Next, the biocompatibility profile of these nanomaterials as a precursor to their biomedical application is reviewed. Finally, recent applications of graphene-based nanomaterials in various biomedical fields including tissue engineering, drug and gene delivery, biosensing and bioimaging as well as other biorelated studies are highlighted.

NIR light-responsive short peptide/2D NbSe2 nanosheets composite hydrogel with controlled-release capacity

The design of light-responsive peptide hydrogels with controllable drug release characteristics is still a challenge.

Biomedical Applications of Graphene-Based Structures

Graphene and graphene oxide (GO) structures and their reduced forms, e.g., GO paper and partially or fully reduced three-dimensional (3D) aerogels, are at the forefront of materials design for extensive biomedical applications that allow for the proliferation and differentiation/maturation of cells, drug delivery, and anticancer therapies. Various viability tests that have been conducted in vitro on human cells and in vivo on mice reveal very promising results, which make graphene-based materials suitable for real-life applications. In this review, we will give an overview of the latest studies that utilize graphene-based structures and their composites in biological applications and show how the biomimetic behavior of these materials can be a step forward in bridging the gap between nature and synthetically designed graphene-based nanomaterials.

Protein-Engineered Biomaterials for Cancer Theranostics

Proteins are an important class of biomaterials promising a variety of applications such as drug delivery, and imaging or therapy, owing to their biodegradability, biocompatibility, as well as inherent biological activities acting as enzymes, recognizing molecules, or therapeutics by themselves. Over the few past decades, different types of proteins with desired properties have been widely explored for biomedical applications. Many therapeutic proteins have now entered clinical use. This review therefore summarizes various strategies in the engineering of biomaterials for delivery of therapeutic proteins, as well as the recent development of protein-based biomaterials for cancer theranostics.

Nanocomposite Hydrogels: Advances in Nanofillers Used for Nanomedicine

The ongoing progress in the development of hydrogel technology has led to the emergence of materials with unique features and applications in medicine. The innovations behind the invention of nanocomposite hydrogels include new approaches towards synthesizing and modifying the hydrogels using diverse nanofillers synergistically with conventional polymeric hydrogel matrices. The present review focuses on the unique features of various important nanofillers used to develop nanocomposite hydrogels and the ongoing development of newly hydrogel systems designed using these nanofillers. This article gives an insight in the advancement of nanocomposite hydrogels for nanomedicine.

Light-responsive Drug Delivery Systems

Materials that interact with light and subsequently change their physicochemical properties are of great interest for drug delivery. The human body is semitransparent to light of the near-infrared (NIR) region, which makes it possible to use light as an external stimulus to trigger drug release. In this chapter, we review light-triggered drug release systems of both photochemical and photothermal mechanisms. We explore recent literature on a variety of light-responsive materials for drug delivery, including organic, inorganic, and hybrid systems, which collectively embody the strategies for synergizing light responsiveness for controlled drug release/activation with other drug delivery techniques.

Designing Peptide/Graphene Hybrid Hydrogels through Fine-Tuning of Molecular Interactions

A recent strategy that has emerged for the design of increasingly functional hydrogels is the incorporation of nanofillers in order to exploit their specific properties to either modify the performance of the hydrogel or add functionality. The emergence of carbon nanomaterials in particular has provided great opportunity for the use of graphene derivatives (GDs) in biomedical applications. The key challenge when designing hybrid materials is the understanding of the molecular interactions between the matrix (peptide nanofibers) and the nanofiller (here GDs) and how these affect the final properties of the bulk material. For the purpose of this work, three gelling β-sheet-forming, self-assembling peptides with varying physiochemical properties and five GDs with varying surface chemistries were chosen to formulate novel hybrid hydrogels. First the peptide hydrogels and the GDs were characterized; subsequently, the molecular interaction between peptides nanofibers and GDs were probed before formulating and mechanically characterizing the hybrid hydrogels. We show how the interplay between electrostatic interactions, which can be attractive or repulsive, and hydrophobic (and π-π in the case of peptide containing phenylalanine) interactions, which are always attractive, play a key role on the final properties of the hybrid hydrogels. The shear modulus of the hydrid hydrogels is shown to be related to the strength of fiber adhesion to the flakes, the overall hydrophobicity of the peptides, as well as the type of fibrillar network formed. Finally, the cytotoxicity of the hybrid hydrogel formed at pH 6 was also investigated by encapsulating and culturing human mesemchymal stem cells (hMSC) over 14 days. This work clearly shows how interactions between peptides and GDs can be used to tailor the mechanical properties of the resulting hydrogels, allowing the incorporation of GD nanofillers in a controlled way and opening the possibility to exploit their intrinsic properties to design novel hybrid peptide hydrogels for biomedical applications.

Mechanically robust dual responsive water dispersible-graphene based conductive elastomeric hydrogel for tunable pulsatile drug release

Nanohybrid hydrogels based on pristine graphene with enhanced toughness and dual responsive drug delivery feature is opening a new era for smart materials. Here pristine graphene hydrogels are synthesized by in situ free radical polymerization where graphene platelets are the nanobuiliding blocks to withstand external stress and shows reversible ductility. Such uniqueness is a mere reflection of rubber-like elasticity on the hydrogels. These nanobuilding blocks serve also the extensive physisorption which enhances the physical crosslinking inside the gel matrix. Besides the pH-responsive drug release features, these hydrogels are also implemented as a pulsatile drug delivery device. The electric responsive drug release behaviours are noticed and hypothesized by the formation of conducting network in the polyelectrolytic hydrogel matrix. The hydrogels are also tested as good biocompatibility and feasible cell-attachment during live-dead cell adhesion study. The drug release characteristics can also be tuned by adjusting the conducting filler loading into the gel matrix. As of our knowledge, this type of hydrogels with rubber-like consistency, high mechanical property, tunable and dual responsive drug delivery feature and very good human cell compatible is the first to report.

Nanocomposite thin films for triggerable drug delivery

INTRODUCTION

Traditional drug release systems normally rely on a passive delivery of therapeutic compounds, which can be partially programmed, prior to injection or implantation, through variations in the material composition. With this strategy, the drug release kinetics cannot be remotely modified and thus adapted to changing therapeutic needs. To overcome this issue, drug delivery systems able to respond to external stimuli are highly desirable, as they allow a high level of temporal and spatial control over drug release kinetics, in an operator-dependent fashion.

AREAS COVERED

On-demand drug delivery systems actually represent a frontier in this field and are attracting an increasing interest at both research and industrial level. Stimuli-responsive thin films, enabled by nanofillers, hold a tremendous potential in the field of triggerable drug delivery systems. The inclusion of responsive elements in homogeneous or heterogeneous thin film-shaped polymeric matrices strengthens and/or adds intriguing properties to conventional (bare) materials in film shape.

EXPERT OPINION

This Expert Opinion review aims to discuss the approaches currently pursued to achieve an effective on-demand drug delivery, through nanocomposite thin films. Different triggering mechanisms allowing a fine control on drug delivery are described, together with current challenges and possible future applications in therapy and surgery.

Inhibiting pulmonary metastasis of breast cancer based on dual-targeting graphene oxide with high stability and drug loading capacity

In this study, heparin and polyethyleneimine-folic acid modified graphene oxide was designed and synthesized as a dual-targeting biomaterial to load doxorubicin (DOX@GPFH) with high loading capacity for enhanced cellular uptake. GDC0941, a phosphatidylinositide 3-kinase/Akt phosphorylation inhibitor, was selected to enhance anti-metastasis effect of DOX@GPFH via down-regulating expression of matrix metalloproteinase. Modified with heparin, the stability of DOX@GPFH was significantly enhanced and the drug loading ratio increased largely from 64.4% to 125.1%. The inhibition rates of the mixture of DOX@GPFH and GDC0941 in vitro by wound healing, cell migration and invasion assays were 61.2%±13.9%, 81.0%±3.6% and 76.8%±5.2%, respectively, while the tumor and the pulmonary anti-metastasis rates tested in vivo were 77.0%±7.6% and 73.7%±9.6%, respectively. Our findings illustrated an effective approach for developing dual-targeting graphene oxide with high drug loading for pulmonary anti-metastasis of breast cancer.

Fabrication of macroporous reduced graphene oxide composite aerogels reinforced with chitosan for high bilirubin adsorption

Numerous adsorbents have been reported for the removal of bilirubin, which is a well-known endogenous toxin. Three-dimensional graphene sponges and aerogels have been fully studied in the adsorption field but little in hemoperfusion especially for bilirubin adsorption. In this study, macroporous reduced graphene oxide (GO) aerogels were fabricated by a chemical reduction method. Besides, chitosan was introduced in the aerogels during the reduction process to improve their mechanical properties. The graphene oxide composite aerogels reinforced with chitosan (rGO/CS) were investigated using scanning electron microscopy (SEM), Fourier Transform Infrared Spectrometry (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET). Furthermore, the mechanical properties test showed the reinforced mechanical strength of the rGO/CS aerogels. The adsorption performance of the aerogels for bilirubin was studied in detail, showing a high adsorption capacity (458.9 mg g-1) and a fast adsorption rate. Moreover, the low hemolysis ratio and negligible anticoagulant activity of rGO/CS aerogels suggested good blood compatibility. The mesoporous structure of the aerogels can provide good mechanical strength, and the macroporous structure of the rGO/CS aerogels shows a good adsorption capacity, which would have potential applications in bilirubin adsorption.

Hydrogels for Hydrophobic Drug Delivery. Classification, Synthesis and Applications

Hydrogels have been shown to be very useful in the field of drug delivery due to their high biocompatibility and ability to sustain delivery. Therefore, the tuning of their properties should be the focus of study to optimise their potential. Hydrogels have been generally limited to the delivery of hydrophilic drugs. However, as many of the new drugs coming to market are hydrophobic in nature, new approaches for integrating hydrophobic drugs into hydrogels should be developed. This article discusses the possible new ways to incorporate hydrophobic drugs within hydrogel structures that have been developed through research. This review describes hydrogel-based systems for hydrophobic compound delivery included in the literature. The section covers all the main types of hydrogels, including physical hydrogels and chemical hydrogels. Additionally, reported applications of these hydrogels are described in the subsequent sections.

Designing isometrical gel precursors to identify the gelation pathway for nickel-selective metallohydrogels

Two novel multi-responsive metallohydrogels, namely, 2-PF-Ni and 3-PF-Ni, were successfully constructed from phenylalanine derivatives. The 2-PF gelator shows specific responses to Ni²⁺; particularly, 2-PF-Ni is lavender colored, which has been rarely reported among hydrogels triggered by Ni²⁺. 3-PF-Ni is light green and exhibits perfect thixotropy. This paper provides insights into the gelation mechanisms of these two metallogels.

Hierarchically porous graphene for batteries and supercapacitors

Hierarchical porous graphene based materials are explored for their application as electrochemical storage devices due to their large specific surface area, high electrical and thermal conductivity, and excellent specific capacity.

Homogenous graphene oxide-peptide nanofiber hybrid hydrogel as biomimetic polysaccharide hydrolase

Cellulose, an impressive potential sustainable fuel, is difficult to hydrolyze because of the protection of β-1,4-glycosidic bonds through the tight hydrogen bonding network. In this study, homogenous graphene oxide (GO)-peptide nanofiber hybrid hydrogels (GO-PNFs) were designed as a β-glycosyl hydrolase mimetic to achieve efficient degradation of cellobiose and cellopentaose. For comparison, free peptides, graphene oxide mixed with free peptides (GO-peptdies) and self-assembled peptide nanofibers (PNFs) were also studied for their activity as a hydrolase mimetics for degradation of cellobiose. Among these materials, GO-PNFs showed the highest hydrolysis activity. Transmission electron microscopy, atomic force microscopy, fluorescence analysis, circular dichroism spectroscopies, X-ray diffraction, Raman spectra and computational modeling were used to interpret the difference in activity mechanism in these artificially designed enzymes. These investigations suggested that high catalytic performance of GO-PNFs toward cellobiose and cellopentaose hydrolysis could be attributed to the formation of nanofiber structures of peptides, optimal molecular conformation and less steric hindrance to access the substrate. More importantly, GO not only served as a platform for attaching PNFs, but also created a hydrophobic microenvironment and facilitated proton transfer, an essential step in catalytic hydrolysis, thus enhancing catalytic activity. All these provided insights into the potential use of peptides and GO hybrid composite nanoenzymes in efficient cellulose hydrolysis.

Designed graphene-peptide nanocomposites for biosensor applications: A review

The modification of graphene with biomacromolecules like DNA, protein, peptide, and others extends the potential applications of graphene materials in various fields. The bound biomacromolecules could improve the biocompatibility and bio-recognition ability of graphene-based nanocomposites, therefore could greatly enhance their biosensing performances on both selectivity and sensitivity. In this review, we presented a comprehensive introduction and discussion on recent advance in the synthesis and biosensor applications of graphene-peptide nanocomposites. The biofunctionalization of graphene with specifically designed peptides, and the synthesis strategies of graphene-peptide (monomer, nanofibrils, and nanotubes) nanocomposites were demonstrated. On the other hand, the fabrication of graphene-peptide nanocomposite based biosensor architectures for electrochemical, fluorescent, electronic, and spectroscopic biosensing were further presented. This review includes nearly all the studies on the fabrication and applications of graphene-peptide based biosensors recently, which will promote the future developments of graphene-based biosensors in biomedical detection and environmental analysis.

Mussel-Inspired Adhesive and Tough Hydrogel Based on Nanoclay Confined Dopamine Polymerization

Adhesive hydrogels are attractive biomaterials for various applications, such as electronic skin, wound dressing, and wearable devices. However, fabricating a hydrogel with both adequate adhesiveness and excellent mechanical properties remains a challenge. Inspired by the adhesion mechanism of mussels, we used a two-step process to develop an adhesive and tough polydopamine-clay-polyacrylamide (PDA-clay-PAM) hydrogel. Dopamine was intercalated into clay nanosheets and limitedly oxidized between the layers, resulting in PDA-intercalated clay nanosheets containing free catechol groups. Acrylamide monomers were then added and in situ polymerized to form the hydrogel. Unlike previous single-use adhesive hydrogels, our hydrogel showed repeatable and durable adhesiveness. It adhered directly on human skin without causing an inflammatory response and was easily removed without causing damage. The adhesiveness of this hydrogel was attributed to the presence of enough free catechol groups in the hydrogel, which were created by controlling the oxidation process of the PDA in the confined nanolayers of clay. This mimicked the adhesion mechanism of the mussels, which maintain a high concentration of catechol groups in the confined nanospace of their byssal plaque. The hydrogel also displayed superior toughness, which resulted from nanoreinforcement by clay and PDA-induced cooperative interactions with the hydrogel networks. Moreover, the hydrogel favored cell attachment and proliferation, owning to the high cell affinity of PDA. Rat full-thickness skin defect experiments demonstrated that the hydrogel was an excellent dressing. This free-standing, adhesive, tough, and biocompatible hydrogel may be more convenient for surgical applications than adhesives that involve in situ gelation and extra agents.

Nanocomposite Hydrogels and Their Applications in Tissue Engineering

Nanocomposite (NC) hydrogels, organic-inorganic hybrid materials, are of great interest as artificial three-dimensional (3D) biomaterials for biomedical applications. NC hydrogels are prepared in water by chemically or physically cross-linking organic polymers with nanomaterials (NMs). The incorporation of hard inorganic NMs into the soft organic polymer matrix enhances the physical, chemical, and biological properties of NC hydrogels. Therefore, NC hydrogels are excellent candidates for artificial 3D biomaterials, particularly in tissue engineering applications, where they can mimic the chemical, mechanical, electrical, and biological properties of native tissues. A wide range of functional NMs and synthetic or natural organic polymers have been used to design new NC hydrogels with novel properties and tailored functionalities for biomedical uses. Each of these approaches can improve the development of NC hydrogels and, thus, provide advanced 3D biomaterials for biomedical applications.

Design, fabrication, and biomedical applications of bioinspired peptide–inorganic nanomaterial hybrids

We presented the design, composition, and typical biomedical applications of bioinspired peptide–inorganic nanomaterial hybrids.

Construction of poly(dopamine) doped oligopeptide hydrogel

Incorporation of poly(dopamine) (PDA) into the native oligopeptide hydrogel not only improve the rigidity but also endow the hydrogel with efficient free radical scavenging ability.

When biomolecules meet graphene: from molecular level interactions to material design and applications

Graphene-based materials have attracted increasing attention due to their atomically-thick two-dimensional structures, high conductivity, excellent mechanical properties, and large specific surface areas. The combination of biomolecules with graphene-based materials offers a promising method to fabricate novel graphene-biomolecule hybrid nanomaterials with unique functions in biology, medicine, nanotechnology, and materials science. In this review, we focus on a summarization of the recent studies in functionalizing graphene-based materials using different biomolecules, such as DNA, peptides, proteins, enzymes, carbohydrates, and viruses. The different interactions between graphene and biomolecules at the molecular level are demonstrated and discussed in detail. In addition, the potential applications of the created graphene-biomolecule nanohybrids in drug delivery, cancer treatment, tissue engineering, biosensors, bioimaging, energy materials, and other nanotechnological applications are presented. This review will be helpful to know the modification of graphene with biomolecules, understand the interactions between graphene and biomolecules at the molecular level, and design functional graphene-based nanomaterials with unique properties for various applications.

Calcium-Ion-Triggered Co-assembly of Peptide and Polysaccharide into a Hybrid Hydrogel for Drug Delivery

We report a new approach to constructing a peptide-polysaccharide hybrid hydrogel via the calcium-ion-triggered co-assembly of fluorenylmethyloxycarbonyl-diphenylalanine (Fmoc-FF) peptide and alginate. Calcium ions triggered the self-assembly of Fmoc-FF peptide into nanofibers with diameter of about 30 nm. Meanwhile, alginate was rapidly crosslinked by the calcium ions, leading to the formation of stable hybrid hydrogel beads. Compared to alginate or Fmoc-FF hydrogel alone, the hybrid Fmoc-FF/alginate hydrogel had much better stability in both water and a phosphate-buffered solution (PBS), probably because of the synergistic effect of noncovalent and ionic interactions. Furthermore, docetaxel was chosen as a drug model, and it was encapsulated by hydrogel beads to study the in vitro release behavior. The sustained and controlled docetaxel release was obtained by varying the concentration ratio between Fmoc-FF peptide and alginate.

Hydrogels with smart systems for delivery of hydrophobic drugs

INTRODUCTION

Smart hydrogel systems present opportunities to not only provide hydrophobic molecule encapsulation capability but to also respond to specific delivery routes. Areas covered: An overview of the design principles, preparation methods and applications of hydrogel systems for delivery of hydrophobic drugs is given. It begins with a summary of the advantages of hydrogels as delivery vehicles over other approaches, particularly macromolecular nanocarriers, before proceeding to address the design and preparation strategies and chemistry involved, with a particular focus on the introduction of hydrophobic domains into (naturally) hydrophilic hydrogels. Finally, the applications in different delivery routes are discussed. Expert opinion: Modifications to conventional hydrogels can endow them with the capability to carry hydrophobic drugs but other functions as well, such as the improved mechanical stability, which is important for long-term in vivo residence and/or self-healing properties useful for injectable delivery pathways. These modifications harness hydrophobic-hydrophobic forces, physical interactions and inclusion complexes. The lack of in-depth understanding of these interactions, currently limits more delicate and application-oriented designs. Increased efforts are needed in (i) understanding the interplay of gel formation and simultaneous drug loading; (ii) improving hydrogel systems with respect to their biosafety; and (iii) control over release mechanism and profile.

Heteropoly acids triggered self-assembly of cationic peptides into photo- and electro-chromic gels

A series of cationic peptides with alternating lysines and hydrophobic residues were designed and synthesized. These kinds of short peptides with protonated lysines can complex with anionic heteropoly acids (HPAs) to form a stable gel in water/ethanol mixed solution. Circular dichroism spectroscopy showed that the short peptides adopted a mixed conformation (β-sheet and random-coil) within the gel matrix. Scanning and transmission electron microscopy revealed that the heteropoly acids, acting as nanosized cross-linkers, first initiated the self-assembly of the cationic peptides into spherical nanostructures. Then these nanospheres accumulated with each other through hydrogen bonds and hydrophobic interactions to form large sheet-like assemblies, which further interconnected with each other forming continuous 3D network structures. Fourier-transform infrared spectroscopy showed that the structural integrity of the HPAs was maintained during the gelation process. The resultant hybrid gels showed reversible photo- and elecrtro-chromic properties. X-ray photoelectron spectroscopy revealed that the hybrid gels, capable of persistent and reversible changes of their colour, are attributed to the intervalence charge-transfer transition of the HPAs. Reversible information writing and erasing were demonstrated through a repeated photo-lithograph or electric stimuli without significant loss of the gel performance.

Electroresponsive Supramolecular Graphene Oxide Hydrogels for Active Bacteria Adsorption and Removal

Bacteria contamination in drinking water and medical products can cause severe health problems. However, currently available sterilization methods, mainly based on the size-exclusion mechanism, are typically slow and require the entire contaminated water to pass through the filter. Here, we present an electroresponsive hydrogel based approach for bacteria adsorption and removal. We successfully engineered a series of graphene oxide hydrogels using redox-active ruthenium complexes as noncovalent cross-linkers. The resulting hydrogels can reversibly switch their physical properties in response to the applied electric field along with the changes of oxidation states of the ruthenium ions. The hydrogels display strong bacteria adsorbing capability. A hydrogel of 1 cm(3) can adsorb a maximum of 1 × 10(8) E. coli. The adsorbed bacteria in the hydrogels can then be inactivated by a high voltage electric pulse and removed from the hydrogels subsequently. Owing to the high bacteria removal rate, reusability, and low production cost, these hydrogels represent promising candidates for the emergent sterilization of medical products or large-scale purification of drinking water.

A versatile fluorescent biosensor based on target-responsive graphene oxide hydrogel for antibiotic detection

A fluorescent sensing platform based on graphene oxide (GO) hydrogel was developed through a fast and facile gelation, immersion and fluorescence determination process, in which the adenosine and aptamer worked as the co-crosslinkers to connect the GO sheets and then form the three-dimensional (3D) macrostructures. The as-prepared hydrogel showed high mechanical strength and thermal stability. The optimal hydrogel had a linear response for oxytetracycline (OTC) of 25-1000μg/L and a limit of quantitation (LOQ) of 25μg/L. Moreover, together with the high affinity of the aptamer for its target, this assay exhibited excellent sensitivity and selectivity. According to its design principle, the as-designed hydrogel was also tested to possess the generic detection function for other molecules by simply replacing its recognition element, which is expected to lay a foundation to realize the assembly of functionalized hierarchical graphene-based materials for practical applications in analytical field.

Applications and toxicity of graphene family nanomaterials and their composites

Graphene has attracted much attention of scientific community due to its enormous potential in different fields, including medical sciences, agriculture, food safety, cancer research, and tissue engineering. The potential for widespread human exposure raises safety concerns about graphene and its derivatives, referred to as graphene family nanomaterials (GFNs). Due to their unique chemical and physical properties, graphene and its derivatives have found important places in their respective application fields, yet they are being found to have cytotoxic and genotoxic effects too. Since the discovery of graphene, a number of researches are being conducted to find out the toxic potential of GFNs to different cell and animal models, finding their suitability for being used in new and varied innovative fields. This paper presents a systematic review of the research done on GFNs and gives an insight into the mode and action of these nanosized moieties. The paper also emphasizes on the recent and up-to-date developments in research on GFNs and their nanocomposites for their toxic effects.

Aqueous compatible boron nitride nanosheets for high-performance hydrogels

Hexagonal boron nitride nanosheets (BNNSs) possess ultimate thermal and chemical stabilities and mechanical strengths. However, the unmodified BNNSs are hydrophobic and insoluble in water, which hinders their use in many technological areas requiring aqueous compatibility. In this work, h-BN was treated with molten citric acid to produce aqueous dispersible boron nitride sheets (ca-BNNSs). The resultant ca-BNNSs were used to fabricate ca-BNNS/polyacrylamide (i.e., BNNS2.5/PAAm) nanocomposite hydrogels, targeting high water retentivity and flexibility. The BNNS2.5/PAAm hydrogel (initially swollen in water) largely remained swollen (water content ∼94 wt%) even after one-year storage under ambient conditions. Importantly, the swollen BNNS2.5/PAAm hydrogel (water content ∼95 wt%) was highly flexible. Its elongation and compressive strength exceeded 10,000% and 8 MPa at 97% strain, respectively. Moreover, the aforementioned hydrogel recovered upon the removal of compression force, without obvious damage. The substantially improved water retentivity and flexibility revealed that BNNSs can serve as a promising new platform in the development of high-performance hydrogels.

3D graphene oxide supramolecular hybrid hydrogel with well-ordered interior microstructure prepared by a host–guest inclusion-induced self-assembly strategy

A three-dimensional self-assembly strategy for constructing graphene oxide hybrid supramolecular hydrogel with regular porous structure was developed.

Controlling the width of nanosheets by peptide length in peptoid–peptide biohybrid hydrogels

The width of self-assembling nanosheets could be controlled by the variation of peptide length.

Physically cross-linked pH-responsive chitosan-based hydrogels with enhanced mechanical performance for controlled drug delivery

A novel physically cross-linked pH-responsive hydrogel with enhanced mechanical performance was prepared from chitosan, acrylic acid and (2-dimethylamino) ethyl methacrylate via in situ free radical polymerization for controlled drug delivery.

Controlling the resolution and duration of pulsatile release from injectable magnetic ‘plum-pudding’ nanocomposite hydrogels

Injectable hydrogel nanocomposites with entrapped SPIONs, thermosensitive microgels, and model drugs generate heat when an alternating magnetic field is applied, causing the microgels to deswell and create pore space to promote enhanced drug release.

Supramolecular nanofibers of self-assembling peptides and DDP to inhibit cancer cell growth

The addition of cis-dichlorodiamineplatinum(ii) to a taxol-peptide amphiphile results in hydrogelations.

Biological Hydrogels Formed by Swollen Multilamellar Liposomes

The self-assembly of lecithin-bile salt mixtures in solutions has long been an important research topic, not only because they are both biosurfactants closely relevant to physiological functions but also for the potential biomedical applications. In this paper, we report an unusual biological hydrogel formed by mixing bile salts and lecithin at low bile salt/lecithin molar ratios (B0) in water. The gel can be prepared at a total lipid concentration as low as ∼15 wt %, and the solidlike property of the solutions was confirmed by dynamic rheological measurements. We used cryo-TEM and SAXS/SANS techniques to probe the self-assembled structure and clearly evidence that the gel is made up of jammed swollen multilamellar vesicles (liposomes), instead of typical fibrous networks found in conventional gels. A mechanism-based on the strong repulsion between bilayers due to the incorporation of negatively charged bile salts is proposed to explain the swelling of the liposomes. In addition to gel, a series of phases, including viscoelastic, gel-like, and low-viscosity fluids, can be created by increasing B0. Such a variety of phase behaviors are caused by the transformation of bilayers into cylindrical and spheroidal micelles upon the change of the effective molecular geometry with B0.

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.

Fabrication and Characterization of a Novel Anticancer Drug Delivery System: Salecan/Poly(methacrylic acid) Semi-interpenetrating Polymer Network Hydrogel

Salecan is a novel linear extracellular polysaccharide with a linear backbone of 1-3-linked glucopyranosyl units. Salecan is suitable for preparing hydrogels for biomedical applications due to its prominent physicochemical and biological profiles. In this contribution, a variety of innovative semi-interpenetrating polymer network (semi-IPN) hydrogels consisting of Salecan and poly(methacrylic acid) (PMAA) were developed via free radical polymerization for controlled drug delivery. The successful fabrication of the semi-IPNs was verified by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric (TGA) measurements. Scanning electron microscopy (SEM) and rheology analyses demonstrated that the morphological and mechanical behaviors of the resultant hydrogels were strongly affected by the contents of Salecan and cross-linker N,N'-methylenebis(acrylamide) (BIS). Moreover, the swelling properties of these hydrogels were systematically investigated, and the results indicated that they exhibited pH sensitivity. The drug delivery applications of such fabricated hydrogels were further evaluated from which doxorubicin (Dox) was chosen as a model drug for in vitro release and cell viability studies. It was found that the Dox release from the Dox-loaded hydrogels was significantly accelerated when the pH of the release media decreased from 7.4 to 5.0. Toxicity assays confirmed that the blank hydrogels had negligible toxicity to normal cells, whereas the Dox-loaded hydrogels remained high in cytotoxicity for A549 and HepG2 cancer cells. All of these attributes implied that the new proposed semi-IPNs serve as potential drug delivery platforms for cancer therapy.

Reduced Graphene Oxide-Based Silver Nanoparticle-Containing Composite Hydrogel as Highly Efficient Dye Catalysts for Wastewater Treatment

New reduced graphene oxide-based silver nanoparticle-containing composite hydrogels were successfully prepared in situ through the simultaneous reduction of GO and noble metal precursors within the GO gel matrix. The as-formed hydrogels are composed of a network structure of cross-linked nanosheets. The reported method is based on the in situ co-reduction of GO and silver acetate within the hydrogel matrix to form RGO-based composite gel. The stabilization of silver nanoparticles was also achieved simultaneously within the gel composite system. The as-formed silver nanoparticles were found to be homogeneously and uniformly dispersed on the surface of the RGO nanosheets within the composite gel. More importantly, this RGO-based silver nanoparticle-containing composite hydrogel matrix acts as a potential catalyst for removing organic dye pollutants from an aqueous environment. Interestingly, the as-prepared catalytic composite matrix structure can be conveniently separated from an aqueous environment after the reaction, suggesting the potentially large-scale applications of the reduced graphene oxide-based nanoparticle-containing composite hydrogels for organic dye removal and wastewater treatment.

Nanocomposite Hydrogels: 3D Polymer-Nanoparticle Synergies for On-Demand Drug Delivery

Considerable progress in the synthesis and technology of hydrogels makes these materials attractive structures for designing controlled-release drug delivery systems. In particular, this review highlights the latest advances in nanocomposite hydrogels as drug delivery vehicles. The inclusion/incorporation of nanoparticles in three-dimensional polymeric structures is an innovative means for obtaining multicomponent systems with diverse functionality within a hybrid hydrogel network. Nanoparticle-hydrogel combinations add synergistic benefits to the new 3D structures. Nanogels as carriers for cancer therapy and injectable gels with improved self-healing properties have also been described as new nanocomposite systems.