In situ reduction of silver nanoparticles in the lignin based hydrogel for enhanced antibacterial application

Lignosulfonate-doped polyaniline-reinforced poly(vinyl alcohol) hydrogels as highly sensitive, antimicrobial, and UV-resistant multifunctional sensors

Flexible wearable strain sensors exist the advantages of high resolution, lightweight, wide measurement range, which have unlimited potential in fields such as soft robotics, electronic skin, and artificial intelligence. However, current flexible sensors based on hydrogels still have some defects, including poor mechanical properties, self-adhesive properties and bacteriostatic properties. In this study, A conductive hydrogel Sodium Ligninsulfonate (LGS)@PANI-Ag-poly(vinyl alcohol) (PVA) hydrogels consisting of lignosulfonate-doped polyaniline (LGS@PANI), silver nitrate, and PVA interactions were designed and prepared for sensing applications. Here, the abundant reactive functional groups of lignosulfonates not only improve the electrochemical and electrical conductivity of polyaniline, thereby increasing its potential for sensing and capacitor applications, but also provide excellent mechanical properties (0.71 MPa), self-adhesion (81.27 J/m2) and ultraviolet (UV) resistance (UV inhibition close to 100 %) to the hydrogel. In addition, the hydrogel exhibited rich multifunctional properties, including tensile strain resistance (up to 397 %), antimicrobial properties (up to 100 % inhibition of Escherichia coli and Staphylococcus aureus), high sensitivity (gauge factor, GF = 4.18), and a rapid response time (100 ms). The LGS@PANI-Ag-PVA hydrogels showed potential for wearable sensors that monitor various biosignals from the human body, as well as human-computer interaction, artificial intelligence and other diverse fields.

Trends in sustainable chitosan-based hydrogel technology for circular biomedical engineering: A review

Eco-friendly materials have emerged in biomedical engineering, driving major advances in chitosan-based hydrogels. These hydrogels offer a promising green alternative to conventional polymers due to their non-toxicity, biodegradability, biocompatibility, environmental friendliness, affordability, and easy accessibility. Known for their remarkable properties such as drug encapsulation, delivery capabilities, biosensing, functional scaffolding, and antimicrobial behavior, chitosan hydrogels are at the forefront of biomedical research. This paper explores the fabrication and modification methods of chitosan hydrogels for diverse applications, highlighting their role in advancing climate-neutral healthcare technologies. It reviews significant scientific advancements and trends chitosan hydrogels focusing on cancer diagnosis, drug delivery, and wound care. Additionally, it addresses current challenges and green synthesis practices that support a circular economy, enhancing biomedical sustainability. By providing an in-depth analysis of the latest evidence on climate-neutral management, this review aims to facilitate informed decision-making and foster the development of sustainable strategies leveraging chitosan hydrogel technology. The insights from this comprehensive examination are pivotal for steering future research and applications in sustainable biomedical solutions.

Navigating Antibacterial Frontiers: A Panoramic Exploration of Antibacterial Landscapes, Resistance Mechanisms, and Emerging Therapeutic Strategies

The development of effective antibacterial solutions has become paramount in maintaining global health in this era of increasing bacterial threats and rampant antibiotic resistance. Traditional antibiotics have played a significant role in combating bacterial infections throughout history. However, the emergence of novel resistant strains necessitates constant innovation in antibacterial research. We have analyzed the data on antibacterials from the CAS Content Collection, the largest human-curated collection of published scientific knowledge, which has proven valuable for quantitative analysis of global scientific knowledge. Our analysis focuses on mining the CAS Content Collection data for recent publications (since 2012). This article aims to explore the intricate landscape of antibacterial research while reviewing the advancement from traditional antibiotics to novel and emerging antibacterial strategies. By delving into the resistance mechanisms, this paper highlights the need to find alternate strategies to address the growing concern.

Enhancing the anti-biofouling property of solar evaporator through the synergistic antibacterial effect of lignin and nano silver

Solar desalination is an effective solution to address the global water scarcity issue. However, biofouling poses a significant challenge for solar evaporators due to the presence of bacteria in seawater. In this study, an anti-biofouling evaporator was constructed using the synergistic antibacterial effect of lignin and silver nanoparticles (AgNPs). The AgNPs were easily synthesized using lignin as reductant under mild reaction conditions. Subsequently, the Lignin-AgNPs solution was integrated into polyacrylamide hydrogel (PAAm) without any purification steps, resulting in the formation of Lignin/AgNPs-PAAm (LAg-PAAm). Under the combined action of AgNPs and the hydroquinone groups present in oxidized lignin, LAg-PAAm achieved over 99 % disinfection efficiency within 1 h, effectively preventing biofilm formation in pore channels of solar evaporators. The anti-biofouling solar evaporator demonstrated an evaporation rate of 1.85 kg m-2 h-1 under 1 sun irradiation, and maintained stable performance for >30 days due to its high efficient bactericidal effect. Furthermore, it also exhibited exceptional salt-rejection capability attributed to its superior hydrophilicity.

Synthetic and biopolymers-based antimicrobial hybrid hydrogels: a focused review

The constantly accelerating occurrence of microbial infections and their antibiotic resistance has spurred advancement in the field of material sciences and has guided the development of novel materials with anti-bacterial properties. To address the clinical exigencies, the material of choice should be biodegradable, biocompatible, and able to offer prolonged antibacterial effects. As an attractive option, hydrogels have been explored globally as a potent biomaterial platform that can furnish essential antibacterial attributes owing to its three-dimensional (3D) hydrophilic polymeric network, adequate biocompatibility, and cellular adhesion. The current review focuses on the utilization of different antimicrobial hydrogels based on their sources (natural and synthetic). Further, the review also highlights the strategies for the generation of hydrogels with their advantages and disadvantages and their applications in different biomedical fields. Finally, the prospects in the development of hydrogels-based antimicrobial biomaterials are discussed along with some key challenges encountered during their development and clinical translation.

Lignin - A green material for antibacterial application - A review

Lignin's antibacterial properties have become increasingly relevant due to the rise of microbial infectious diseases and antibiotic resistance. Lignin is capable of interacting electrostatically with bacteria and contains polyphenols that cause damage to their cell walls. These features make lignin a desirable material to exhibit antibacterial behavior. Therefore, lignin in antibacterial applications offers a novel approach to address the growing need for sustainable and effective antibacterial materials. Recent research has explored the incorporation of lignin in various biomedical applications, such as wound dressings, implants, and drug delivery systems, highlighting their potential as a sustainable alternative to synthetic antibacterial agents. Furthermore, the development of lignin-based nanomaterials with enhanced antimicrobial activity is an active area of research that holds great promise for the future. In this review, we have provided a summary of how lignin can be incorporated into different forms, such as composite and non-composite synthesis of antibacterial agents and their performances. The challenges and future considerations are also discussed in this review article.

Lignin derivatives-based hydrogels for biomedical applications

Recently, numerous studies have been conducted on renewable polymers derived from different natural sources, exploring their suitability for diverse biomedical applications. Lignin as one of the main components of lignocellulosic has garnered significant attention as a promising alternative to petroleum-based polymers. This interest is primarily due to its cost-effectiveness, biocompatibility, eco-friendly nature, as well as its antioxidant and antimicrobial properties. These characteristics could be more beneficial when incorporating lignin into the formulation of value-added products. Although lignin has a chemical structure that is suitable for various applications, these characteristics require modifications to guarantee that the resultant materials display the desired biological, chemical, and physical properties when applied in the creation of biodegradable hydrogels, particularly for biomedical purposes. This study delineates the recent modification approaches that have been employed in the creation of lignin-based hydrogels. These strategies encompass both chemical and physical interactions with other polymers. Additionally, this review encompasses an examination of the current applications of lignin hydrogels, spanning their use as scaffolds for tissue engineering, carriers for pharmaceuticals, materials for wound dressings and biosensors, and elements in flexible and wearable electronics. Finally, we delve into the challenges and constraints associated with these materials, discuss the necessary steps required to attain the appropriate properties for the development of innovative lignin-based hydrogels, and derive conclusions based on the presented findings.

Antibacterial mechanism of lignin and lignin-based antimicrobial materials in different fields

The control of microbial infection transmission often relies on the utilization of synthetic and metal-based antimicrobial agents. However, their non-biodegradability and inadequate disposal practices lead to significant environmental contamination. To address this concern, the quest for natural alternatives has gained paramount importance. Lignin, a widely available renewable aromatic compound, emerges as a promising candidate owing to its inherent phenolic moiety, which lends itself well to acting as a natural antimicrobial agent either independently or in combination with other agents. This article provides a comprehensive account of the structure and primary classes of lignin. Additionally, it elucidates the antimicrobial mechanism of lignin, the factors influencing its efficacy, and the methods employed for its detection. Moreover, it describes the progress made in developing the antimicrobial capacity of lignin in different areas. In conclusion, this paper not only outlines the current state of research on the antimicrobial function of lignin, but also identifies challenges and future possibilities for enhancing its antimicrobial properties. This work holds great significance in the ongoing endeavor to contribute to high-impact research on natural alternatives for controlling infections and fostering environmentally conscious practices.

Mechanistic insights into the cinnamaldehyde modification of lignin for sustainable anti-fungal reagent

The limited anti-fungal activity of enzymatic hydrolysis lignin (EHL) has been a challenge in its direct application as a bamboo preservative. To address this issue, the cinnamaldehyde modification of EHL was carried out to introduce anti-fungal structures into the lignin matrix, effectively enhancing its anti-fungal activity. The results demonstrated that the minimal inhibitory concentrations of the modified lignin (EHL-DC) against Aspergillus niger significantly improved from 16 mg/mL to 1 mg/mL, with comparable enhancements in anti-fungal activity against other fungi. As a result of the modification, the EHL-DC is more prone to interact with fungal cell membranes, contributing to a roughened, shrunken hyphal surface and a decrease in mycelial biomass. Multiple characterization methods were employed to better grapple with the EHL-DC chemical changes. The nitrogen content increased from 2.3 % to 8.3 %, and alterations in elemental compositions further support the proposed reaction mechanism and its role in enhancing EHL's anti-fungal activity. This study offers novel insights into the high-value utilization of enzymatic hydrolysis lignin based on green chemistry principles.

Preparation and properties of lignin-based dual network hydrogel and its application in sensing

Ionic conductive hydrogels prepared from various biological macromolecules are ideal materials for the manufacture of human motion sensors from the perspective of resource regeneration and environmental sustainability. However, it is now difficult to develop conductive hydrogels including excellent self-healing and mechanical properties, mainly due to their inherent trade-off between dynamic cross-linked healing and stable cross-linked mechanical strength. In this work, alkali lignin-Polyvinyl alcohol-polyacrylic acid double network conductive hydrogels with high mechanical strength and good self-healing properties were prepared. We formed the primary network structure by hydrogen bonding interaction between polyvinyl alcohol, alkali lignin and polyacrylic acid, and the secondary network structure by coordination interaction with polyacrylic acid through the addition of Fe3+. The added lignin acts as a dynamic linkage bridge in a porous network mediated by multiple ligand bonds, imparting superior mechanical properties to the hydrogels. The relationships between the alkali lignin and iron ion dosage and the comprehensive properties of hydrogels (adhesion, antibacterial, self-healing, electrical conductivity and mechanical properties) were studied in detail. On this basis, the hydrogels explored the role of lignin in the regulation of hydrogels properties and revealed the self-healing and conductive mechanism.

Sustainable Biomass Lignin-Based Hydrogels: A Review on Properties, Formulation, and Biomedical Applications

Different techniques have been developed to overcome the recalcitrant nature of lignocellulosic biomass and extract lignin biopolymer. Lignin has gained considerable interest owing to its attractive properties. These properties may be more beneficial when including lignin in the preparation of highly desired value-added products, including hydrogels. Lignin biopolymer, as one of the three major components of lignocellulosic biomaterials, has attracted significant interest in the biomedical field due to its biocompatibility, biodegradability, and antioxidant and antimicrobial activities. Its valorization by developing new hydrogels has increased in recent years. Furthermore, lignin-based hydrogels have shown great potential for various biomedical applications, and their copolymerization with other polymers and biopolymers further expands their possibilities. In this regard, lignin-based hydrogels can be synthesized by a variety of methods, including but not limited to interpenetrating polymer networks and polymerization, crosslinking copolymerization, crosslinking grafted lignin and monomers, atom transfer radical polymerization, and reversible addition-fragmentation transfer polymerization. As an example, the crosslinking mechanism of lignin-chitosan-poly(vinyl alcohol) (PVA) hydrogel involves active groups of lignin such as hydroxyl, carboxyl, and sulfonic groups that can form hydrogen bonds (with groups in the chemical structures of chitosan and/or PVA) and ionic bonds (with groups in the chemical structures of chitosan and/or PVA). The aim of this review paper is to provide a comprehensive overview of lignin-based hydrogels and their applications, focusing on the preparation and properties of lignin-based hydrogels and the biomedical applications of these hydrogels. In addition, we explore their potential in wound healing, drug delivery systems, and 3D bioprinting, showcasing the unique properties of lignin-based hydrogels that enable their successful utilization in these areas. Finally, we discuss future trends in the field and draw conclusions based on the findings presented.

Lignins as Promising Renewable Biopolymers and Bioactive Compounds for High-Performance Materials

The recycling of biomass into high-value-added materials requires important developments in research and technology to create a sustainable circular economy. Lignin, as a component of biomass, is a multipurpose aromatic polymer with a significant potential to be used as a renewable bioresource in many fields in which it acts both as promising biopolymer and bioactive compound. This comprehensive review gives brief insights into the recent research and technological trends on the potential of lignin development and utilization. It is divided into ten main sections, starting with an outlook on its diversity; main properties and possibilities to be used as a raw material for fuels, aromatic chemicals, plastics, or thermoset substitutes; and new developments in the use of lignin as a bioactive compound and in nanoparticles, hydrogels, 3D-printing-based lignin biomaterials, new sustainable biomaterials, and energy production and storage. In each section are presented recent developments in the preparation of lignin-based biomaterials, especially the green approaches to obtaining nanoparticles, hydrogels, and multifunctional materials as blends and bio(nano)composites; most suitable lignin type for each category of the envisaged products; main properties of the obtained lignin-based materials, etc. Different application categories of lignin within various sectors, which could provide completely sustainable energy conversion, such as in agriculture and environment protection, food packaging, biomedicine, and cosmetics, are also described. The medical and therapeutic potential of lignin-derived materials is evidenced in applications such as antimicrobial, antiviral, and antitumor agents; carriers for drug delivery systems with controlled/targeting drug release; tissue engineering and wound healing; and coatings, natural sunscreen, and surfactants. Lignin is mainly used for fuel, and, recently, studies highlighted more sustainable bioenergy production technologies, such as the supercapacitor electrode, photocatalysts, and photovoltaics.

Multidrug-Resistant Pathogens in Burn Wound, Prevention, Diagnosis, and Therapeutic Approaches (Conventional Antimicrobials and Nanoparticles)

Multidrug-resistant pathogens are one of the common causes of death in burn patients and have a high risk of nosocomial infections, especially pneumonia, urinary tract infections, and cellulitis. The role of prolonged hospitalization and empirical antibiotics administration in developing multidrug-resistant pathogens is undeniable. In the early days of admitting burn patients, Gram-positive bacteria were the dominant isolates with a more sensitive antibiotic pattern. However, the emergence of Gram-negative bacteria that are more resistant later occurs. Trustworthy guideline administration in burn wards is one of the strategies to prevent multidrug-resistant pathogens. Also, a multidisciplinary therapeutic approach is an effective way to avoid antibiotic resistance that involves infectious disease specialists, pharmacists, and burn surgeons. However, the emerging resistance to conventional antimicrobial approaches (such as systemic antibiotic exposure, traditional wound dressing, and topical antibiotic ointments) among burn patients has challenged the treatment of multidrug-resistant infections, and using nanoparticles is a suitable alternative. In this review article, we will discuss different aspects of multidrug-resistant pathogens in burn wounds, emphasizing the full role of these pathogens in burn wounds and discussing the application of nanotechnology in dealing with them. Also, some advances in various types of nanomaterials, including metallic nanoparticles, liposomes, hydrogels, carbon quantum dots, and solid lipid nanoparticles in burn wound healing, will be explained.

Encapsulation of AgNPs in a Lignin Isocyanate Film: Characterization and Antimicrobial Properties

Lignin isolated from agricultural residues is a promising alternative for petroleum-based polymers as feedstocks in development of antimicrobial materials. A polymer blend based on silver nanoparticles and lignin-toluene diisocyanate film (AgNPs-Lg-TDIs) was generated from organosolv lignin and silver nanoparticles (AgNPs). Lignin was isolated from Parthenium hysterophorus using acidified methanol and used to synthesize lignin capped silver nanoparticles. Lignin-toluene diisocyanate film (Lg-TDI) was prepared by treating lignin (Lg) with toluene diisocyanate (TDI) followed by solvent casting to form films. Functional groups present and thermal properties of the films were evaluated using Fourier-transform infrared spectrophotometry (FT-IR), thermal gravimetry (TGA), and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM), UV-visible spectrophotometry (UV-Vis), and Powder X-ray diffractometry (XRD) were used to assess the morphology, optical properties, and crystallinity of the films. Embedding AgNPs in the Lg-TDI films increased the thermal stability and the residual ash during thermal analysis, and the presence of powder diffraction peaks at 2θ = 20, 38, 44, 55, and 58⁰ in the films correspond to lignin and silver crystal planes (111). SEM micrographs of the films revealed the presence of AgNPs in the TDI matrix with variable sizes of between 50 to 250 nm. The doped films had a UV radiation cut-off at 400 nm as compared to that of undoped films, but they did not exhibit significant antimicrobial activity against selected microorganisms.

Recent advances in pharmaceutical and biotechnological applications of lignin-based materials

Lignin, a versatile and abundant biomass-derived polymer, possesses a wide array of properties that makes it a promising material for biotechnological applications. Lignin holds immense potential in the biotechnology and pharmaceutical field due to its biocompatibility, high carbon content, low toxicity, ability to be converted into composites, thermal stability, antioxidant, UV-protectant, and antibiotic activity. Notably, lignin is an environmental friendly alternative to synthetic plastic and fossil-based materials because of its inherent biodegradability, safety, and sustainability potential. The most important findings related to the use of lignin and lignin-based materials are reported in this review, providing an overview of the methods and techniques used for their manufacturing and modification. Additionally, it emphasizes on recent research and the current state of applications of lignin-based materials in the biomedical and pharmaceutical fields and also highlights the challenges and opportunities that need to be overcome to fully realize the potential of lignin biopolymer. An in-depth discussion of recent developments in lignin-based material applications, including drug delivery, tissue engineering, wound dressing, pharmaceutical excipients, biosensors, medical devices, and several other biotechnological applications, is provided in this review article.

Designing Lignin-Based Biomaterials as Carriers of Bioactive Molecules

There is a need to develop circular and sustainable economies by utilizing sustainable, green, and renewable resources in high-tech industrial fields especially in the pharmaceutical industry. In the last decade, many derivatives of food and agricultural waste have gained considerable attention due to their abundance, renewability, biocompatibility, environmental amiability, and remarkable biological features. Particularly, lignin, which has been used as a low-grade burning fuel in the past, recently attracted a lot of attention for biomedical applications because of its antioxidant, anti-UV, and antimicrobial properties. Moreover, lignin has abundant phenolic, aliphatic hydroxyl groups, and other chemically reactive sites, making it a desirable biomaterial for drug delivery applications. In this review, we provide an overview of designing different forms of lignin-based biomaterials, including hydrogels, cryogels, electrospun scaffolds, and three-dimensional (3D) printed structures and how they have been used for bioactive compound delivery. We highlight various design criteria and parameters that influence the properties of each type of lignin-based biomaterial and corelate them to various drug delivery applications. In addition, we provide a critical analysis, including the advantages and challenges encountered by each biomaterial fabrication strategy. Finally, we highlight the prospects and future directions associated with the application of lignin-based biomaterials in the pharmaceutical field. We expect that this review will cover the most recent and important developments in this field and serve as a steppingstone for the next generation of pharmaceutical research.

Nanomaterials-Based Wound Dressing for Advanced Management of Infected Wound

The effective prevention and treatment of bacterial infections is imperative to wound repair and the improvement of patient outcomes. In recent years, nanomaterials have been extensively applied in infection control and wound healing due to their special physiochemical and biological properties. Incorporating antibacterial nanomaterials into wound dressing has been associated with improved biosafety and enhanced treatment outcomes compared to naked nanomaterials. In this review, we discuss progress in the application of nanomaterial-based wound dressings for advanced management of infected wounds. Focus is given to antibacterial therapy as well as the all-in-one detection and treatment of bacterial infections. Notably, we highlight progress in the use of nanoparticles with intrinsic antibacterial performances, such as metals and metal oxide nanoparticles that are capable of killing bacteria and reducing the drug-resistance of bacteria through multiple antimicrobial mechanisms. In addition, we discuss nanomaterials that have been proven to be ideal drug carriers for the delivery and release of antimicrobials either in passive or in stimuli-responsive manners. Focus is given to nanomaterials with the ability to kill bacteria based on the photo-triggered heat (photothermal therapy) or ROS (photodynamic therapy), due to their unparalleled advantages in infection control. Moreover, we highlight examples of intelligent nanomaterial-based wound dressings that can detect bacterial infections in-situ while providing timely antibacterial therapy for enhanced management of infected wounds. Finally, we highlight challenges associated with the current nanomaterial-based wound dressings and provide further perspectives for future improvement of wound healing.

Antimicrobial Natural Hydrogels in Biomedicine: Properties, Applications, and Challenges-A Concise Review

Natural hydrogels are widely used as biomedical materials in many areas, including drug delivery, tissue scaffolds, and particularly wound dressings, where they can act as an antimicrobial factor lowering the risk of microbial infections, which are serious health problems, especially with respect to wound healing. In this review article, a number of promising strategies in the development of hydrogels with biocidal properties, particularly those originating from natural polymers, are briefly summarized and concisely discussed. Common strategies to design and fabricate hydrogels with intrinsic or stimuli-triggered antibacterial activity are exemplified, and the mechanisms lying behind these properties are also discussed. Finally, practical antibacterial applications are also considered while discussing the current challenges and perspectives.

Constructing a self-healing injectable SABA/Borax/PDA@AgNPs hydrogel for synergistic low-temperature photothermal antibacterial therapy

Infections caused by bacteria are one of the biggest challenges humans face around the world. Photothermal therapy (PTT) has been regarded as a promising strategy in combating pathogenic infection, however the high temperatures (55-65 °C) required during a single PTT process can induce injury to healthy tissues nearby. Combination therapy could overcome this problem by reducing the photothermal temperature. Here, we developed a self-healing and injectable hydrogel to realize low-temperature PTT (LT-PTT, ≤45 °C) for antisepsis with high-efficiency. The hybrid hydrogel is prepared by incorporating borax into a mixture of 3-aminophenylboronic acid grafted sodium alginate and nano-silver decorated polydopamine nanoparticles. Our results showed that the SABA/Borax/PDA@AgNPs hydrogel possesses satisfactory mechanical properties and self-healing capacity, and as a result, it can repair itself after being damaged mechanically, retaining its integrality and recovering its initial functionalities. Furthermore, through utilizing the photothermal property of polydopamine nanoparticles and broad-spectrum antibacterial activity of nano-silver, the hybrid hydrogel achieves excellent LT-PTT for sterilization both in vitro as well as in an in vivo mice skin wound model with no distinct injury to normal tissues. Overall, our prepared hydrogel is expected to be an excellent candidate for treating bacterial infections.

Green In Situ Synthesis of Silver Nanoparticles-Peptide Hydrogel Composites: Investigation of Their Antibacterial Activities

The present paper investigated the synthesis of peptide-based hydrogel composites containing photo-generated silver nanoparticles (AgNPs) obtained in the presence and absence of honey as tensile strength enhancer and hydrogel stabilizer. Fmoc-Phe and diphenylalanine (Phe2) were used as starting reagents for the hydrogelator synthesis via an enzymatic method. In particular, we developed an in situ one-pot approach for preparing AgNPs inside peptide hydrogels using a photochemical synthesis, without any toxic reducing agents, with reaction yields up to 30%. The structure and morphology of the nanohybrids were characterized with different techniques such as FESEM, UV-Vis, DLS, SAXS and XPS. Moreover, the antibacterial activity of these hybrid biomaterials was investigated on a laboratory strain and on a clinical isolate of Staphylococcus aureus. Results demonstrated that honey increased both swelling ability and also mechanical stability of the hydrogel. Finally, a higher antibacterial effect of AgNPs in the hybrid was observed in the presence of honey. In particular, AgNPs/hgel and AgNPs/hgel-honey showed an enhanced antibacterial activity (3.12 mg/L) compared to the free form of AgNPs, alone or in combination with honey (6.25 mg/L) for both S. aureus strains.

Antibacterial lignin-based nanoparticles and their use in composite materials

Lignin, one of the most abundant biopolymers on earth, has been traditionally considered a low-value by-product of the pulp and paper industries. This renewable raw material, besides being a source of valuable molecules for the chemical industry, also has antioxidant, UV-absorbing, and antibacterial properties in its macromolecular form. Moreover, lignin in the form of nanoparticles (LigNPs) presents advantages over bulk lignin, such as higher reactivity due to its larger surface-to-volume ratio. In view of the rapid surge of antimicrobial resistance (AMR), caused by the overuse of antibiotics, continuous development of novel antibacterial agents is needed. The use of LigNPs as antibacterial agents is a suitable alternative to conventional antibiotics for topical application or chemical disinfectants for surfaces and packaging. Besides, their multiple and unspecific targets in the bacterial cell may prevent the emergence of AMR. This review summarizes the latest developments in antibacterial nano-formulated lignin, both in dispersion and embedded in materials. The following roles of lignin in the formulation of antibacterial NPs have been analyzed: (i) an antibacterial active in nanoformulations, (ii) a reducing and capping agent for antimicrobial metals, and (iii) a carrier of other antibacterial agents. Finally, the review covers the inclusion of LigNPs in films, fibers, hydrogels, and foams, for obtaining antibacterial lignin-based nanocomposites for a variety of applications, including food packaging, wound healing, and medical coatings.

Redispersion of dried plant nanocellulose: A review

Nanocellulose has undergone substantial development as a high value-added cellulose product with broad applications. Dried products are advantageous to decrease transportation costs. However, dried nanocellulose has redispersion challenges when rewetting. In this work, drying techniques, factors affecting redispersibility, and strategies improving the nanocellulose redispersibility are comprehensively reviewed. Hydrogen bonds of nanocellulose are unavoidably developed during drying, leading to inferior redispersibility of dried nanocellulose, even hornification. Drying processes of nanocellulose are discussed first. Then, factors affecting redispersibility are discussed. Following that, strategies improving the nanocellulose redispersibility are analyzed and their advantages and disadvantages are highlighted. Surface charge modification and steric hindrance concept are two main pathways to overcome the redispersion challenge, which are mainly carried out by chemical modification, additive incorporation and non-cellulosic component preservation. Despite several advancements having been achieved, new approaches for enhancing the nanocellulose redispersibility are still required to promote the industrial-scale applications of nanocellulose in various domains.

From residue to resource: new insights into the synthesis of functionalized lignin micro/nanospheres by self-assembly technology for waste resource utilization

Among the most abundant biopolymers in the biosphere, lignin is a renewable aromatic compound that represents an untapped opportunity to create new biological products. However, the complex interlacing structures of cellulose, hemicellulose and lignin, as well as the unique properties of lignin, limit the utilization of value-added lignin. Lignin-based nanomaterials open the door for lignin applications in environmental pollutant remediation, biofuel production, biomedicine, and other fields. Herein, we present various factors influencing the formation of micro-nanospheres by self-assembly techniques through a review of previous literature, and emphasize the simple and green synthesis of lignin micro/nanospheres (LMNPs) under non-modified conditions. More importantly, we discuss the mechanism of the formation of nanospheres. Considering the heterogeneity of lignin and the polarity of different solvents, we propose that self-assembly techniques should focus more on the influence brought by lignin itself or the solvent, so that the external conditions can be controlled to prepare LMNPs, which can be used in specific fields. A brief overview of the contribution of lignin-based nanomaterials in various fields is also presented. This review could provide insight for the development of lignin-based nanomaterials.

Supramolecular nanogels based on gelatin-cyclodextrin-stabilized silver nanocomposites with antibacterial and anticancer properties

An effective method for reducing silver ions using gelatin (Gel) and 2-hydroxypropyl-β-cyclodextrin (HPCD) hydrogels, which stabilize silver at various concentrations is described. The formation of AgNPs in solution, as well as Gel-HPCD nanogels, is confirmed by the surface plasmon resonance (SPR) band at 420-440 nm in the UV-Vis spectrum. The resulting Gel-HPCD and Gel-HPCD/AgNPs composites are characterized using various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and thermogravimetric analysis (TGA). SEM images showed that the porous structure and the AgNPs are homogeneously dispersed throughout the Gel-HPCD/AgNP composites network. The AgNPs in the Gel-HPCD/AgNPs composite is crystalline, with spherical particles having an average size of 7.0 ± 2.5 nm, as determined by TEM. The Gel-HPCD/AgNPs composites are strongly effective against both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. The assembled antibacterial Gel-HPCD/AgNPs composites are also assessed for their cytotoxic and anticancer activities using HCT-116 cancer cells. The results suggest that Gel-HPCD/AgNPs composites could be used as effective therapeutics in the future in tissue engineering applications, as their bactericidal properties and low toxicity make them ideal for clinical use.

Next generation applications of lignin derived commodity products, their life cycle, techno-economics and societal analysis

The pulp and biorefining industries produce their waste as lignin, which is one of the most abundant renewable resources. So far, lignin has been remained severely underutilized and generally burnt in a boiler as a low-value fuel. To demonstrate lignin's potential as a value-added product, we will review market opportunities for lignin related applications by utilizing the thermo-chemical/biological depolymerization strategies (with or without catalysts) and their comparative evaluation. The application of lignin and its derived aromatics in various sectors such as cement industry, bitumen modifier, energy materials, agriculture, nanocomposite, biomedical, H2 source, biosensor and bioimaging have been summarized. This comprehensive review article also highlights the technical, economic, environmental, and socio-economic variable that affect the market value of lignin-derived by-products. The review shows the importance of lignin, and its derived products are a platform for future bioeconomy and sustainability.

How far is Lignin from being a biomedical material?

Lignin is a versatile biomass that possesses many different desirable properties such as antioxidant, antibacterial, anti-UV, and good biocompatibility. Natural lignin can be processed through several chemical processes. The processed lignin can be modified into functionalized lignin through chemical modifications to develop and enhance biomaterials. Thus, lignin is one of the prime candidate for various biomaterial applications such as drug and gene delivery, biosensors, bioimaging, 3D printing, tissue engineering, and dietary supplement additive. This review presents the potential of developing and utilizing lignin in the outlook of new and sustainable biomaterials. Thereafter, we also discuss on the challenges and outlook of utilizing lignin as a biomaterial.

Nano-silver functionalized polysaccharides as a platform for wound dressings: A review

The healing of defected skin tissue is a complex process, especially for chronic wounds. Poor healing of these wounds may cause extensive suffering and high cost for patients. Traditional wound dressings are typically designed for a single function and they cannot satisfy all requirements for the whole process of wound healing. Therefore, it is necessary to develop new types of wound dressings with multiple functions for wound healing. In particular, adding an antibacterial function has been shown to be of great benefit during tissue repair. Nano‑silver is widely used in wound treatment because of various advantages, such as its wide antibacterial spectrum and lower drug resistance. Therefore, wound dressings loaded with nano‑silver have attracted widespread attention in wound healing. Naturally derived polysaccharides hold great potential as wound dressings, because of their abundant availability, low prices and good biocompatibility. In this review, nano‑silver functionalized polysaccharide-based wound dressings are systematically reviewed, including their preparation methods, antibacterial performances and classification of nano‑silver wound dressings. Moreover, the toxicity of nano‑silver based wound dressings is discussed and the prospective research direction is elaborated. This review aims to provide readers with an overview of the latest developments in silver nanotechnology, and to provide a little guidance for the research of nano‑silver functionalized polysaccharide-based wound dressings.

Combined bactericidal process of lignin and silver in a hybrid nanoparticle on E. coli

Among multiple engineered nanoparticles that have been used in the bactericidal application, silver nanoparticles (Ag NPs) are the most explored bactericidal functional materials with their high efficiency and broad-spectrum bactericidal properties. However, environmental toxicology and lack of modifiability restrict their further development. In this study, a simple and economic method was established to fabricate lignin and silver hybrid nanoparticles (Lig-Ag NPs) with bactericidal ability. Afterwards, material characterization, bactericidal evaluation, and mechanism exploration were implemented to explore the properties of Lig-Ag NPs. The results indicated that Lig-Ag NPs not only demonstrated remarkable dispersity, uniformity, and encapsulation efficiency but also possessed approximated bactericidal ability on Escherichia coli and better durability compared with the same concentration of Ag NPs on E. coli. On the other hand, flow cytometry and transcriptomic analysis were used to further explore the bactericidal mechanism of Lig-Ag NPs. The results showed that oxidative stress was the possible leading bactericidal mechanism of Lig-Ag NPs. The formation approaches of reactive oxygen species production were various including the slow release of silver ion and generation of quinone/semi-quinone radicals on account of the combined effect of lignin and silver.

GRAPHICAL ABSTRACT

Lig-Ag NPs exhibited remarkable dispersity, uniformity, encapsulation efficiency, and possessed approximated bactericidal ability and better durability compared with Ag NPs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42114-022-00460-z.

Methacrylated alkali lignin grafted P(Nipam-Co-AAc) copolymeric hydrogels: Tuning the mechanical and stimuli-responsive properties

The current study reports the preparation of lignin grafted temperature and pH responsive hydrogels through copolymerization of N-isopropylacrylamide, acrylic acid and varying amount of lignin methacrylate (LMA = 50, 100, 150 and 200 mg) as crosslinker adopting radical polymerization technique. Functional group and structural characterizations were carried out to confirm hydrogels synthesis and their network structure. The variation in pore size on addition of lignin revealed the tuning of pores as well as swelling capacity of the hydrogels by suitable amount of LMA. All LMA grafted hydrogels showed temperature responsive behavior and pH dependent sensitivity in swelling, with reduced equilibrium swelling capacity values compared to sample without lignin. In alkali medium at room temperature, the maximum swelling capacity with 48% higher retention was noticed, while a significant reduction in swelling was observed at 40 °C in all media. The addition of lignin still preserved the tensile strength up to 100 kPa and compressive load bearing ability up to 30 kPa in freeze dried state with adequate interfacial stress transfer. An increase in lignin concentration showed enhanced storage modulus (~two-fold increase), adequate loss modulus values and improved cell viability, which paves the way for possible biomedical applications.

Moxifloxacin and Sulfamethoxazole-Based Nanocarriers Exhibit Potent Antibacterial Activities

Antibiotic resistance is a major concern given the rapid emergence of multiple-drug-resistant bacteria compared to the discovery of novel antibacterials. An alternative strategy is enhancing the existing available drugs. Nanomedicine has emerged as an exciting area of research, showing promise in the enhanced development of existing antimicrobials. Herein, we synthesized nanocarriers and loaded these with available clinically approved drugs, namely Moxifloxacin and Sulfamethoxazole. Bactericidal activity against Gram-negative (Serratia marcescens, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Salmonella enterica) and Gram-positive (methicillin-resistant Staphylococcus aureus, Streptococcus pneumoniae, and Bacillus cereus) bacteria was investigated. To characterize the nanocarriers and their drug-loaded forms, Fourier-transform infrared spectroscopy, dynamic light scattering, and atomic force microscopy were utilized. Antibacterial assays and hemolysis assays were carried out. Moreover, lactate dehydrogenase assays were performed to determine cytotoxicity against human cells. The results depicted the successful formation of drug-nanocarrier complexes. The potent antibacterial activities of the drug-loaded nanocarriers were observed and were significantly enhanced in comparison to the drugs alone. Hemolysis and cytotoxicity assays revealed minimal or negligible cytotoxic effects against human red blood cells and human cells. Overall, metronidazole-based nanocarriers loaded with Moxifloxacin and Sulfamethoxazole showed enhanced bactericidal effects against multiple-drug-resistant bacteria compared with drugs alone, without affecting human cells. Our findings show that drug-loaded nanocarriers hold promise as potent chemotherapeutic drugs against multiple-drug-resistant bacteria.

Incorporation of Silver Nanoparticles in Hydrogel Matrices for Controlling Wound Infection

For centuries, silver has been recognized for its antibacterial properties. With the development of nanotechnology, silver nanoparticles (AgNPs) have garnered significant attention for their diverse uses in antimicrobial gel formulations, dressings for wound healing, orthopedic applications, medical catheters and instruments, implants, and contact lens coatings. A major focus has been determining AgNPs' physical, chemical, and biological characteristics and their potential to be incorporated in biocomposite materials, particularly hydrogel scaffolds, for burn and wound healing. Though AgNPs have been rigorously explored and extensively utilized in medical and nonmedical applications, important research is still needed to elucidate their antibacterial activity when incorporated in wound-healing scaffolds. In this review, we provide an up-to-date, 10-yr (2010-2019), comprehensive literature review on advancements in the understanding of AgNP characteristics, including the particles' preparation and mechanisms of activity, and we explore various hydrogel scaffolds for delivering AgNPs.

Silver Nanoparticles and Their Antibacterial Applications

Silver nanoparticles (AgNPs) have been imposed as an excellent antimicrobial agent being able to combat bacteria in vitro and in vivo causing infections. The antibacterial capacity of AgNPs covers Gram-negative and Gram-positive bacteria, including multidrug resistant strains. AgNPs exhibit multiple and simultaneous mechanisms of action and in combination with antibacterial agents as organic compounds or antibiotics it has shown synergistic effect against pathogens bacteria such as Escherichia coli and Staphylococcus aureus. The characteristics of silver nanoparticles make them suitable for their application in medical and healthcare products where they may treat infections or prevent them efficiently. With the urgent need for new efficient antibacterial agents, this review aims to establish factors affecting antibacterial and cytotoxic effects of silver nanoparticles, as well as to expose the advantages of using AgNPs as new antibacterial agents in combination with antibiotic, which will reduce the dosage needed and prevent secondary effects associated to both.

Carbon dots-releasing hydrogels with antibacterial activity, high biocompatibility, and fluorescence performance as candidate materials for wound healing

Antibacterial hydrogels have received attention for preventing infections and for their biomedical applications. However, traditional antibiotics-containing and metal nanoparticle-containing hydrogels often cause bacterial resistance, exhibit low biocompatibility, and lack real-time monitoring capability. Here, a fluorescent antibacterial hydrogel with antibacterial ability, excellent optical performance, and high biocompatibility was developed based on cationic carbon dots (CDs), pectin, and acrylic acid triggered construction of the hydrogel network by cross-linker. The antibacterial high-cationic CDs (+51.20 mV) were synthesized by a simple hydrothermal method and released from hydrogel in response to broken hydrogen bonds due to a change in the ambient environment caused by the growing bacteria. The hydrogel showed long-term potent broad-spectrum antibacterial ability (even drug-resistant bacteria) due to the bacterial membrane seriously damaged by the released CDs. The inhibitory capability of this hydrogel was 108.5-fold higher than the other hydrogel. After implantation or incubation with cells, no obvious cytotoxicity or tissue toxicity was observed for the antibacterial hydrogel. This hydrogel enhanced both the application of CDs in vivo and the biosafety of hydrogel. Furthermore, the multicolor fluorescence emission produced by CD provides a potential idea for the development of dual-function hydrogels with in situ monitoring and prevention of bacterial infections to treat wounds.

Recent developments towards performance-enhancing lignin-based polymers

This review examines recent strategies, challenges, and future opportunities in preparing high-performance polymeric materials from lignin and its derivable compounds.

Lignin-Inorganic Interfaces: Chemistry and Applications from Adsorbents to Catalysts and Energy Storage Materials

Lignin is one the most fascinating natural polymers due to its complex aromatic-aliphatic structure. Phenolic hydroxyl and carboxyl groups along with other functional groups provide technical lignins with reactivity and amphiphilic character. Many different lignins have been used as functional agents to facilitate the synthesis and stabilization of inorganic materials. Herein, the use of lignin in the synthesis and chemistry of inorganic materials in selected applications with relevance to sustainable energy and environmental fields is reviewed. In essence, the combination of lignin and inorganic materials creates an interface between soft and hard materials. In many cases it is either this interface or the external lignin surface that provides functionality to the hybrid and composite materials. This Minireview closes with an overview on future directions for this research field that bridges inorganic and lignin materials for a more sustainable future.

Lignin-Based Micro- and Nanomaterials and their Composites in Biomedical Applications

Lignin, as the most abundant aromatic renewable biopolymer in nature, has long been regarded as waste and simply discarded from the pulp and paper industry. In recent years, with many breakthroughs in lignin chemistry, pretreatment, and processing techniques, a lot of the inherent bioactivities of lignin, including antioxidant activities, antimicrobial activities, biocompatibilities, optical properties, and metal-ion chelating and redox activities, have been discovered and this has opened a new field not only for lignin-based materials but also for biomaterials. In this Review, the biological activities of lignin and drug/gene delivery and bioimaging applications of various types of lignin-based material are summarized. In addition, the challenges and limitations of lignin-based materials encountered during the development of biomedical applications are also discussed.

Synthesis of nanocomposite hydrogel based carboxymethyl starch/polyvinyl alcohol/nanosilver for biomedical materials

Treatment of infections using wound dressing integrated with multiple functions such as antibacterial activity, non-toxicity, and good mechanical properties has attracted much attention. In this study, carboxymethyl starch/polyvinyl alcohol/citric acid (CMS/PVA/CA) hydrogels containing silver nanoparticles (AgNPs) were prepared. The CMS, PVA and CA were used as polymer matrix and bio-based reducing agents for green synthesis of AgNPs. Silver nitrate (AgNO₃) concentrations of 50, 100, and 150 mM were used to obtain nanocomposite hydrogels containing different AgNPs concentrations (AgNPs-50, AgNPs-100 and AgNPs-150, respectively). The minimum inhibitory concentration against E. coli and S. aureus was observed in CMS/PVA/CA hydrogels containing AgNPs-50. Uniform dispersion of AgNPs-100 in the hydrogel provided the highest storage modulus at 56.4 kPa. AgNPs-loaded hydrogels showed low toxicity to human fibroblast cells indicating good biocompatibility. Incorporation of AgNPs demonstrated an enhancement in antibacterial properties and overall mechanical properties, which makes these nanocomposite hydrogels attractive as novel wound dressing materials.

Lignin to Materials: A Focused Review on Recent Novel Lignin Applications

In recent decades, advancements in lignin application include the synthesis of polymers, dyes, adhesives and fertilizers. There has recently been a shift from perceiving lignin as a waste product to viewing lignin as a potential raw material for valuable products. More recently, considerable attention has been placed in sectors, like the medical, electrochemical, and polymer sectors, where lignin can be significantly valorized. Despite some technical challenges in lignin recovery and depolymerization, lignin is viewed as a promising material due to it being biocompatible, cheap, and abundant in nature. In the medical sector, lignins can be used as wound dressings, pharmaceuticals, and drug delivery materials. They can also be used for electrochemical energy materials and 3D printing lignin–plastic composite materials. This review covers the recent research progress in lignin valorization, specifically focusing on medical, electrochemical, and 3D printing applications. The technoeconomic assessment of lignin application is also discussed.

Processing and modification of hydrogel and its application in emerging contaminant adsorption and in catalyst immobilization: a review

Due to the wonderful property of hydrogels, they can provide a platform for a wide range of applications. Recently, there is a growing research interest in the development of potential hydrogel adsorbents in wastewater treatment due to their adsorption ability toward aqueous pollutants. It is important to prepare such a hydrogel that possesses appropriate robustness, adsorption capacity, and adsorption efficiency to meet the need of water treatment. In order to improve the property of hydrogels, much effort has been made by researchers to modify hydrogels, among which incorporating inorganic components into the polymeric networks is the most common method, which can reduce the product cost and simplify the preparation procedure. Not only can hydrogel be applied as adsorbent, but it also can be used as matrix for catalyst immobilization. In this review, the key advancement on the preparation and modification of hydrogels is discussed, with special emphasis on the introduction of inorganic materials into polymeric networks and consequential changes in the properties of mechanical strength, swelling, and adsorption. Besides, hydrogels used as adsorbents for removal of dyes and inorganic pollutants have been widely explored, but their use for adsorbing emerging contaminants from aqueous solution has not received much attention. Thus, this review is mainly focused on hydrogels' application in removing emerging contaminants by adsorption. Furthermore, hydrogels can be also applied in immobilizing catalysts, such as enzyme and photocatalyst, to remove pollutants completely and avoid secondary pollution, so their progress as catalyst matrix is overviewed.