First successful design of semi-IPN hydrogel–silver nanocomposites: A facile approach for antibacterial application

Hydrogel Loaded with Components for Therapeutic Applications in Hypertrophic Scars and Keloids

Hypertrophic scars and keloids are common fibroproliferative diseases following injury. Patients with pathologic scars suffer from impaired quality of life and psychological health due to appearance disfiguration, itch, pain, and movement disorders. Recently, the advancement of hydrogels in biomedical fields has brought a variety of novel materials, methods and therapeutic targets for treating hypertrophic scars and keloids, which exhibit broad prospects. This review has summarized current research on hydrogels and loaded components used in preventing and treating hypertrophic scars and keloids. These hydrogels attenuate keloid and hypertrophic scar formation and progression by loading organic chemicals, drugs, or bioactive molecules (such as growth factors, genes, proteins/peptides, and stem cells/exosomes). Among them, smart hydrogels (a very promising method for loading many types of bioactive components) are currently favoured by researchers. In addition, combining hydrogels and current therapy (such as laser or radiation therapy, etc.) could improve the treatment of hypertrophic scars and keloids. Then, the difficulties and limitations of the current research and possible suggestions for improvement are listed. Moreover, we also propose novel strategies for facilitating the construction of target multifunctional hydrogels in the future.

Biopolymer-Based Composite Hydrogels Embedding Small Silver Nanoparticles for Advanced Antimicrobial Applications: Experimental and Theoretical Insights

In this work, we report a two-step methodology for the synthesis of small silver nanoparticles embedded into hydrogels based on chitosan (CS) and hydroxypropyl methylcellulose (HPMC) biopolymers. This method uses d-glucose as an external green reducing agent and purified water as a solvent, leading to an eco-friendly, cost-effective, and biocompatible process for the synthesis of silver nanocomposite hydrogels. Their characterization comprises ultraviolet-visible spectroscopy, Fourier-transform infrared spectra, differential scanning calorimetry, scanning electron microscopy with energy-dispersive spectroscopy, and transmission electron microscopy assays. Moreover, the structural stability of the hydrogels was investigated through sequential swelling-deswelling cycles. The nanomaterials showed good mechanical properties in terms of their structural stability and revealed prominent antibacterial properties due to the reduced-size particles that promote their use as new advanced antimicrobial agents, an advantage compared to conventional particles in aqueous suspension that lose stability and effectiveness. Finally, theoretical analyses provided insights into the possible interactions, charge transfer, and stabilization process of nanoclusters mediated by the high-electron-density groups belonging to CS and HPMC, revealing their unique structural properties in the preparation of nano-scaled materials.

Application of Red Onion Peel Extract for Green Synthesis of Silver Nanoparticles in Hydrogels Exhibiting Antimicrobial Properties

UV-initiated green synthesis of metal nanoparticles by using plant extracts as photoreducing agents is of particular interest since it is an environmentally friendly, easy-to-maintain, and cost-effective method. Plant molecules that act as reducing agents are assembled in a highly controlled way which makes them suitable for metal nanoparticle synthesis. Depending on the plant species, their application for green synthesis of metal nanoparticles for diverse applications may contribute to the mediation/reduction in organic waste amounts, thus enabling the implementation of the circular economy concept. In this work, UV-initiated green synthesis of Ag nanoparticles in hydrogels and hydrogel's thin films containing gelatin (matrix), red onion peel extract of different concentrations, water, and a small amount of 1 M AgNO₃ have been investigated and characterized using UV-Vis spectroscopy, SEM and EDS analysis, XRD technique, performing swelling experiments and antimicrobial tests using bacteria (Staphylococcus aureus, Acinetobacter baumannii, Pseudomonas aeruginosa), yeasts (Candida parapsilosis, Candida albicans) and microscopic fungi (Aspergillus flavus, Aspergillus fumigatus). It was found that the antimicrobial effectiveness of the silver-enriched red onion peel extract-gelatin films was higher at lower AgNO₃ concentrations as compared to those usually used in the commercially available antimicrobial products. The enhancement of the antimicrobial effectiveness was analyzed and discussed, assuming the synergy between photoreducing agent (red onion peel extract) and silver nitrate (AgNO₃) in the initial gel solutions leading to the intensification of Ag nanoparticles production.

Recent developments of polysaccharide based superabsorbent nanocomposite for organic dye contamination removal from wastewater - A review

One of the main problems with water pollution is dye contamination of rivers, industrial effluents, and water sources. It has endangered the world's sources of drinking water. Several remediation strategies have been carefully developed and tested to minimize this ominous picture. Due to their appealing practical and financial benefits, adsorption methods in particular are often listed as one of the most popular solutions to remediate dye-contaminated water. Biopolymer-based hydrogel nanocomposites are a cutting-edge class of materials with a wide range of applications that are effective in removing organic dyes from the environment. Since the incorporation of various materials into hydrogel matrices generated composite materials with distinct characteristics, these unique materials were often alluded to as ideal adsorbents. The fundamental emphasis of the conceptual and critical review of the literature in this research is the significant potential of hydrogel nanocomposites (HNCs) to remediate dye-contaminated water (especially for articles from the previous five years). The review also provides knowledge for the development of biopolymer-based HNCs, prospects, and opportunities for future research. It is also focused on optimum conditions for dye adsorption processes along with their adsorption kinetics and isotherm models. In summary, the information gained in this review research may contribute to a strengthened scientific rationale for the practical and efficient application of these novel adsorbent materials.

Synthesis of Hydrogels and Their Progress in Environmental Remediation and Antimicrobial Application

As a kind of efficient adsorptive material, hydrogel has a wide application prospect within different fields, owing to its unique 3D network structures composed of polymers. In this paper, different synthetic strategies, crosslinking methods and their corresponding limitations and outstanding contributions of applications in the fields of removing environmental pollutants are reviewed to further provide a prospective view of their applications in water resources sustainability. Furthermore, the applications within the biomedical field, especially in wound dressing, are also reviewed in this paper, mainly due to their unique water retention ability, antibacterial ability, and good biocompatibility. Finally, the development direction of hydrogels in the fields of environmental remediation and biomedicine were summarized and prospected.

Engineering Hydrogels for the Development of Three-Dimensional In Vitro Models

The superiority of in vitro 3D cultures over conventional 2D cell cultures is well recognized by the scientific community for its relevance in mimicking the native tissue architecture and functionality. The recent paradigm shift in the field of tissue engineering toward the development of 3D in vitro models can be realized with its myriad of applications, including drug screening, developing alternative diagnostics, and regenerative medicine. Hydrogels are considered the most suitable biomaterial for developing an in vitro model owing to their similarity in features to the extracellular microenvironment of native tissue. In this review article, recent progress in the use of hydrogel-based biomaterial for the development of 3D in vitro biomimetic tissue models is highlighted. Discussions of hydrogel sources and the latest hybrid system with different combinations of biopolymers are also presented. The hydrogel crosslinking mechanism and design consideration are summarized, followed by different types of available hydrogel module systems along with recent microfabrication technologies. We also present the latest developments in engineering hydrogel-based 3D in vitro models targeting specific tissues. Finally, we discuss the challenges surrounding current in vitro platforms and 3D models in the light of future perspectives for an improved biomimetic in vitro organ system.

From prevention to diagnosis and treatment: Biomedical applications of metal nanoparticle-hydrogel composites

Recent advances in biomaterials integrate metal nanoparticles with hydrogels to generate composite materials that exhibit new or improved properties. By precisely controlling the composition, arrangement and interactions of their constituents, these hybrid materials facilitate biomedical applications through myriad approaches. In this work we seek to highlight three popular frameworks for designing metal nanoparticle-hydrogel hybrid materials for biomedical applications. In the first approach, the properties of metal nanoparticles are incorporated into a hydrogel matrix such that the composite is selectively responsive to stimuli such as light and magnetic flux, enabling precisely activated therapeutics and self-healing biomaterials. The second approach mediates the dynamic reorganization of metal nanoparticles based on environment-directed changes in hydrogel structure, leading to chemosensing, microbial and viral detection, and drug-delivery capabilities. In the third approach, the hydrogel matrix spatially arranges metal nanoparticles to produce metamaterials or passively enhance nanoparticle properties to generate improved substrates for biomedical applications including tissue engineering and wound healing. This article reviews the construction, properties and biomedical applications of metal nanoparticle-hydrogel composites, with a focus on how they help to prevent, diagnose and treat diseases. Discussion includes how the composites lead to new or improved properties, how current biomedical research leverages these properties and the emerging directions in this growing field.

A dual stimuli responsive natural polymer based superabsorbent hydrogel engineered through a novel cross-linker

An intelligent dual stimuli (pH and thermo) responsive, highly porous grafted SPI hydrogel.

RETRACTED: A review on biomacromolecular hydrogel classification and its applications

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief and Author. The work included substantial parts copied without attribution from a prior work by Varaprasad et al (2017): https://doi.org/10.1016/j.msec.2017.05.096

Preparation of Cellulose Nanocrystal-Reinforced Physical Hydrogels for Actuator Application

In the present investigation, we prepared cellulose nanocrystal (CNC)-reinforced polyvinyl alcohol-cellulose (PVA-Cell) physical hydrogels using a simple blending method for actuator application. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and the surface and cross-section were studied by scanning electron microscopy. CNCs were well dispersed in the PVA-Cell hydrogel. In the preparation process, surface hydroxyl groups of the CNC and PVA-Cell matrix hydroxyl groups were interacted to produce uniform dispersion of CNCs in the hydrogels. Swelling behavior and compression studies revealed that the increase of the CNCs reinforced the crosslinking. The actuation test of the prepared hydrogels showed that the displacement linearly increased with the voltage, and the immense output displacement was observed at low CNC concentration. The prepared hydrogels are applicable for soft robot actuators and active lens.

In-situ stabilization of silver nanoparticles in polymer hydrogels for enhanced catalytic reduction of macro and micro pollutants

The in-situ stabilization of Ag nanoparticles is carried out by the use of reducing agent and synthesized three different types of hydrogen (anionic, cationic, and neutral) template. The morphology, constitution and thermal stability of the synthesized pure and Ag-entrapped hybrid hydrogels were efficiently confirmed using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). The prepared hybrid hydrogels were used in the decolorization of methylene blue (MB) and azo dyes congo red (CR), methyl Orange (MO), and reduction of 4-nitrophenol (4-NP) and nitrobenzene (NB) by an electron donor NaBH4. The kinetics of the reduction reaction was also assessed to determine the activation parameters. The hybrid hydrogen catalysts were recovered by filtration and used continuously up to six times with 98% conversion of pollutants without substantial loss in catalytic activity. It was observed that these types of hydrogel systems can be used for the conversion of pollutants from waste water into useful products.

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.

Synthesis of physically crosslinked PVA/Chitosan loaded silver nanoparticles hydrogels with tunable mechanical properties and antibacterial effects

Limitation of antibacterial activity, low water vapour, oxygen permeation and mechanical strength are the disadvantages of existing wound dressings. The present research is focused on synthesis of Polyvinyl alcohol (PVA) and Chitosan (CH) hydrogels using freeze thaw process. The formation of AgNPs and PVA/CH hydrogels was confirmed by UV spectroscopy, particle size, morphology, spectral analysis, swelling studies, and in-vitro drug release studies. The particle size of AgNPs was found to be in the range of 20-35 nm with an intense peak at 430 nm. The results of spectral peaks showed that PVA/CH blend maintains characteristics peak of -OH and -NH in the spectrum with higher intensity. The morphology and tensile strength of hydrogels showed a wrinkled surface with an increase in force and extension values from 0.49 to 11.15 N and 45 to 129 mm, respectively. A controlled release of 84.3% (28 h) of Ocimum sanctum extract was noticed from hydrogel discs which scavenges 69.2% of free radicals as compared to raw extract 82.5% (16 h) which scavenges 63.1% of free radicals, respectively. The results of zone of inhibition (ZOI) against gram +ve and gram -ve bacteria was found to be 9.3 mm and 6.3 mm, respectively.

Preparation of Silver/Chitosan Nanofluids Using Selected Plant Extracts: Characterization and Antimicrobial Studies Against Gram-Positive and Gram-Negative Bacteria

Chitosan/silver nanofluids were prepared using Phoenix dactylifera (DPLE) or Rumex vesicarius (HEL) extracts as the reducing agent, characterized using Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis), X-ray diffraction (XRD), and transmission electron microscope (TEM). The antimicrobial effect of the nanofluids against Gram positive, Bacillus licheniformis, Staphylococcus haemolyticus, Bacillus cereus, and Micrococcus luteus, and Gram-negative Pseudomonas aeruginosa, Pseudomonas citronellolis, and Escherichia coli bacteria has been studied. The nanoparticles were polydispersed in the chitosan matrix and are highly stable. The zeta potential of the silver nanoparticles in DPLE- and HEL-mediated composites is +46 mV and +56 mV, respectively. The FTIR results reveal that the free carboxylate groups in the plant biomaterial took part in stabilization process. HEL is a stronger reducing agent than DPLE and nanoparticles generated with HEL are smaller (8.0-36 nm) than those produced with DPLE (10-43 nm). DPLE- and HEL-mediated composites effectively inhibit the growth of the studied bacteria but HEL-mediated composite exhibited higher effect. The higher antimicrobial activity of HEL-mediated composite is linked to the smaller nanoparticles. The foregoing results indicate that HEL extract can be used in the green production of potential antimicrobial chitosan/silver nanofluids for biomedical and packaging applications.

Implantable antimicrobial biomaterials for local drug delivery in bone infection models

Increased use of implantable biomedical devices demonstrates their potential in treating a wide variety of ailments and disorders in bone trauma and orthopaedic, reconstructive, and craniofacial applications. However, the number of cases involving implant failure or malfunction due to bacterial infection have also increased in recent years. Implanted devices can facilitate the growth of bacteria as these micro-organisms have the potential to adhere to the implant and grow and develop to form biofilms. In an effort to better understand and mitigate these occurrences, biomaterials containing antimicrobial agents that can be released or presented within the local microenvironment have become an important area of research. In this review, we discuss critical factors that regulate antimicrobial therapy to sites of bone infection, such as key biomolecular considerations and platforms for delivery, as well as current in vivo models and current advances in the field. STATEMENT OF SIGNIFICANCE: This review outlines the important factors that are taken into consideration for the development of biomaterials for local delivery of therapeutics to the site of bone infections. An overview of important criteria for development of this model (such as type of bone defect, antimicrobial therapeutic, and delivery vehicle) are provided, along with current research that utilizes these considerations. Additionally, this review highlights recent clinical trials that have utilized antimicrobial therapeutics for treatment of osteomyelitis.

Rational Design of Microfabricated Electroconductive Hydrogels for Biomedical Applications

Electroconductive hydrogels (ECHs) are highly hydrated 3D networks generated through the incorporation of conductive polymers, nanoparticles, and other conductive materials into polymeric hydrogels. ECHs combine several advantageous properties of inherently conductive materials with the highly tunable physical and biochemical properties of hydrogels. Recently, the development of biocompatible ECHs has been investigated for various biomedical applications, such as tissue engineering, drug delivery, biosensors, flexible electronics, and other implantable medical devices. Several methods for the synthesis of ECHs have been reported, which include the incorporation of electrically conductive materials such as gold and silver nanoparticles, graphene, and carbon nanotubes, as well as various conductive polymers (CPs), such as polyaniline, polypyrrole, and poly(3,4-ethylenedioxyythiophene) into hydrogel networks. Theses electroconductive composite hydrogels can be used as scaffolds with high swellability, tunable mechanical properties, and the capability to support cell growth both in vitro and in vivo. Furthermore, recent advancements in microfabrication techniques such as three dimensional (3D) bioprinting, micropatterning, and electrospinning have led to the development of ECHs with biomimetic microarchitectures that reproduce the characteristics of the native extracellular matrix (ECM). In addition, smart ECHs with controlled structures and healing properties have also been engineered into devices with prolonged half-lives and increased durability. The combination of sophisticated synthesis chemistries and modern microfabrication techniques have led to engineer smart ECHs with advanced architectures, geometries, and functionalities that are being increasingly used in drug delivery systems, biosensors, tissue engineering, and soft electronics. In this review, we will summarize different strategies to synthesize conductive biomaterials. We will also discuss the advanced microfabrication techniques used to fabricate ECHs with complex 3D architectures, as well as various biomedical applications of microfabricated ECHs.

Antimicrobial hydrogels: promising materials for medical application

The rapid emergence of antibiotic resistance in pathogenic microbes is becoming an imminent global public health problem. Local application of antibiotics might be a solution. In local application, materials need to act as the drug delivery system. The drug delivery system should be biodegradable and prolonged antibacterial effect should be provided to satisfy clinical demand. Hydrogel is a promising material for local antibacterial application. Hydrogel refers to a kind of biomaterial synthesized by a water-soluble natural polymer or a synthesized polymer, which turns into gel according to the change in different signals such as temperature, ionic strength, pH, ultraviolet exposure etc. Because of its high hydrophilicity, unique three-dimensional network, fine biocompatibility and cell adhesion, hydrogel is one of the suitable biomaterials for drug delivery in antimicrobial areas. In this review, studies from the past 5 years were reviewed, and several types of antimicrobial hydrogels according to different ingredients, different preparations, different antimicrobial mechanisms, different antimicrobial agents they contained and different applications, were summarized. The hydrogels loaded with metal nanoparticles as a potential method to solve antibiotic resistance were highlighted. Finally, future prospects of development and application of antimicrobial hydrogels are suggested.

Controllable thermal and pH responsive behavior of PEG based hydrogels and applications for dye adsorption and release

A series of controllable thermal and pH dual-responsive copolymeric hydrogels (PMA) were prepared by a one-pot reaction with poly(ethylene glycol) methyl ether acrylate (PEGA), 2-methoxyethyl acrylate (MEA) and acroleic acid (AA). The hydrogels exhibited good mechanical properties and a sensitive response to pH and temperature. Besides, the Lower Critical Solution Temperature (LCST) of the hydrogels can be adjusted from 37 °C to 58 °C by changing the content of AA. The hydrogels also showed excellent selective adsorption properties. The maximum adsorption quantity of organic cationic dye brilliant green and methylene blue were 0.49 mg mg⁻¹ and 0.42 mg mg⁻¹ respectively, much better than previous reports. Furthermore, using the thermal and pH responsibility, the PMA hydrogels can release the adsorbed molecules with control. Nearly 95% of carriers could be released at pH 4.01 and 65 °C over 8 h. The regeneration ability makes the materials easy to reuse many times. Due to these properties, these dual-responsive hydrogels have great potential applications in various fields for adsorption, drug delivery, release and tissue engineering.

Controllable thermal and pH responsive hydrogels not only showed good stimuli-response and mechanical properties, but also have excellent adsorption properties.

Polymersome–hydrogel composites with combined quick and long-term antibacterial activities

Intrinsically antibacterial polymersomes loaded with antibiotics were incorporated into hydrogels, exhibiting quick and long-acting antibacterial activity.

Porous double network gels with high toughness, high stretchability and fast solvent-absorption

Using the freeze-drying method, we fabricated porous double network gels with high toughness, high stretchability and fast solvent-absorption. When the freezing temperature was -20 °C and the freezing time was 24 hours, pores with diameters around 300 μm could form in the gel. When the freezing temperature was lowered to -196 °C and the freezing time was reduced to 10 minutes, monodisperse pores with diameters around 15 μm could form in the gel. We found out that both porous gels fabricated under different conditions could absorb solvent much more and much faster than a nonporous gel. Furthermore, we found that the rupturing strain, stiffness and strength of the porous double network gels were all comparable to the nonporous double network gel when containing the same amount of solvent. The unique combination of the mechanical properties of the porous double network gels might motivate new explorations of gels in practical applications.

Dual-crosslinked poly(vinyl alcohol)/sodium alginate/silver nanocomposite beads - A promising antimicrobial material

In this paper, we report the immobilization of borate-stabilized silver nanoparticles (AgNPs) as nanofillers in dual-crosslinked polymers comprised of poly(vinyl alcohol) (PVA) and sodium alginate (SA) at different ratios. Ionic-crosslinking using Ca²⁺ ions and physical-crosslinking by freeze-thawing were used to entrap silver nanoparticles in the prepared PVA/SA/AgNPs nanocomposite beads. These polymeric nanocomposites were characterized by UV-Vis, XRD, FE-SEM, FT-IR, TGA, and using rheological and swelling properties. The antibacterial activities of these PVA/SA/AgNPs nanocomposites were evaluated against Escherichia coli O157: H7, which causes escherichiosis through contaminated food and water. The results obtained indicated that PVA/SA/AgNPs nanocomposite formed with a ratio 10/90 of PVA to SA (formulation F5) exhibited high bactericidal activity, with entrapment of AgNPs and had excellent rheological and thermal stabilities. Due to the low cost and effectiveness of these antimicrobial nanocomposites, they have potential as an active food-packaging material for food safety and to extend shelf-life of packaged foods.