Novel lignin–chitosan–PVA composite hydrogel for wound dressing

Unilateral Silver-Loaded Silk Fibroin Difunctional Membranes as Antibacterial Wound Dressings

Silk fibroin (SF) has been widely used as wound dressings due to its good biocompatibility. To enhance the antibacterial properties of the dressings, silver (Ag) is often added. However, an overdose of Ag may cause cytotoxicity and inhibit wound healing. Therefore, this study aimed to develop a two-layered membrane to reduce cytotoxicity while maintaining the antibacterial properties of Ag through a simplified layer-by-layer technique. The membranes comprised an Ag-rich SF layer (Ag-SF) and a pure SF layer. The unilateral Ag-loaded membranes showed efficient antibacterial properties at doses above 0.06 mg/mL Ag, and the antibacterial properties were comparable on both sides. In contrast, the SF sides of the membranes showed lower cytotoxicity than the Ag-SF sides of the membranes. Further studies on the thickness ratio of Ag-SF/SF layers revealed that Ag0.12-SF/SF membranes with a ratio of 1:3 had high cytocompatibility on the SF sides while holding a strong antibacterial property. Besides, the SF sides of the Ag0.12-SF/SF1:3 membranes promoted the expression levels of collagen I and transforming growth factor-β mRNA in human foreskin fibroblasts. The SF sides of the Ag0.12-SF/SF1:3 membranes significantly promoted the healing of infected wounds in vivo. Therefore, unilateral loading with the simplified layer-by-layer preparation technique provided an effective method to balance the cytotoxicity and the antibacterial property of Ag-loaded materials and thus form a broader therapeutic window for Ag applications. The unilateral Ag-loaded silk fibroin difunctional membranes have the potential to be further preclinically explored as wound dressings.

Hyaluronic Acid-Based Scaffolds as Potential Bioactive Wound Dressings

The negative factors that result in delayed and prolonged wound healing process include microbial pathogens, excess wound exudates, underlying conditions, smoking, obesity, etc. Most of the currently used wound dressings demonstrate an inadequate capacity to treat wounds resulting from the factors mentioned above. The commonly used wound dressings include hydrogels, films, hydrocolloids, foams, fibers, sponges, dermal patches, bandages, etc. These wound dressings can be loaded with various types of bioactive agents (e.g., antibiotics, nanoparticles, anti-inflammatory drugs, etc.) to improve their therapeutic outcomes. Biopolymers offer interesting properties suitable for the design of wound dressings. This review article will be based on hyaluronic-acid-based scaffolds loaded with therapeutic agents for the treatment of wounds.

Investigation of the biological activity, mechanical properties and wound healing application of a novel scaffold based on lignin-agarose hydrogel and silk fibroin embedded zinc chromite nanoparticles

Given the important aspects of wound healing approaches, in this work, an innovative biocompatible nanobiocomposite scaffold was designed and prepared based on cross-linked lignin-agarose hydrogel, extracted silk fibroin solution, and zinc chromite (ZnCr2O4) nanoparticles. Considering the cell viability technique, red blood cell hemolysis in addition to anti-biofilm assays, it was determined that after three days, the toxicity of the cross-linked lignin-agarose/SF/ZnCr2O4 nanobiocomposite was less than 13%. Moreover, the small hemolytic effect (1.67%) and high level of prevention in forming a P. aeruginosa biofilm with low OD value (0.18) showed signs of considerable hemocompatibility and antibacterial activity. Besides, according to an in vivo assay study, the wounds of mice treated with the cross-linked lignin-agarose/SF/ZnCr2O4 nanobiocomposite scaffold were almost completely healed in five days. Aside from these biological tests, the structural features were evaluated by FT-IR, EDX, FE-SEM, and TG analyses, as well as swelling ratio, rheological, and compressive mechanical study tests. Additionally, it was concluded that adding silk fibroin and ZnCr2O4 nanoparticles could enhance the mechanical tensile properties of cross-linked lignin-agarose hydrogel, and also an elastic network was characterized for this designed nanobiocomposite.

Chitosan modifications for adsorption of pollutants - A review

In recent times, research interest into the development of biodegradable, cost-effective and environmental friendly adsorbents with favourable properties for adsorption of pollutants is a challenge. Modification of chitosan via different physical and chemical methods have gained attention as a promising approach for removing organic (such as dyes and pharmaceuticals) and inorganic (such as metal/metal ions) pollutants from aqueous medium. In this regard, researchers have reported grafting and cross-linking approach among others as a potentially useful method for chitosan's modification for improved adsorption efficiency with respect to pollutant uptake. This article reviews the trend in chitosan modification, with regards to the summary of some recently published works on modification of chitosan and their adsorption application in pollutants (metal ion, dyes and pharmaceuticals) removal from aqueous medium. The review uniquely highlights some common cross-linkers and grafting procedures for chitosan modification, their influence on structure and adsorption capacity of modified-chitosan with respect to pollutants removal. Findings revealed that the performance of modified chitosan for adsorption of pollutants depends largely on the modification method adopted, materials used for the modification and adsorption experimental conditions. Cross-linking is commonly utilized for improving the chemical and mechanical stabilities of chitosan but usually decreases adsorption capacity of chitosan/modified-chitosan for adsorption of pollutants. However, literature survey revealed that adsorption capacity of cross-linked chitosan based materials have been enhanced in recently published works either by grafting, incorporation of solid adsorbents (e.g metals, clays and activated carbon) or combination of both prior to cross-linking.

Investigations on the impact of the introduction of the Aloe vera into the hydrogel matrix on cytotoxic and hydrophilic properties of these systems considered as potential wound dressings

In the paper, synthesis of chitosan-based hydrogels modified with Aloe vera juice is presented. The novelty of the research was a combination of hydrogel materials with properties beneficial in viewpoint of their use as modern wound dressings and Aloe vera juice supporting the wound healing process. Hydrogels have been obtained via UV radiation. The impact of the amount of the crosslinking agent as well as the introduction of the Aloe vera juice into the hydrogel matrix has been determined. Performed measurements involved analysis of the swelling ability, characteristics of the surface roughness, determining the release profile of Aloe vera and the contact angles of hydrogels. Furthermore, the analysis of the dehydration process of the polymer membrane, investigations on the cytotoxicity of hydrogels via MTT reduction assay and the neutral red uptake assay as well as the studies on the pro-inflammatory activity have also been performed. It was proved that the addition of Aloe vera juice improves the hydrophilic properties of the materials (e.g. contact angle changed from 82.5° to 73.0°). Next, the use of 25% more of the crosslinker resulted even in the increase of the contact angle by 86%. Modified hydrogels showed higher swelling properties even by 15% than unmodified materials. Furthermore, obtained hydrogels show an ability to release Aloe vera - after 5 h approx. 80% of this additive has been released in an acidic environment. Tested materials do not exhibit cytotoxic properties, the addition of Aloe vera results in an improvement of the viability of L929 murine fibroblasts and, importantly, these materials show lower pro-inflammatory activity than the positive control. Performed investigations allow to state that obtained materials show a great application potential.

Lignin: Drug/Gene Delivery and Tissue Engineering Applications

Lignin is an abundant renewable natural biopolymer. Moreover, a significant development in lignin pretreatment and processing technologies has opened a new window to explore lignin and lignin-based bionanomaterials. In the last decade, lignin has been widely explored in different applications such as drug and gene delivery, tissue engineering, food science, water purification, biofuels, environmental, pharmaceuticals, nutraceutical, catalysis, and other interesting low-value-added energy applications. The complex nature and antioxidant, antimicrobial, and biocompatibility of lignin attracted its use in various biomedical applications because of ease of functionalization, availability of diverse functional sites, tunable physicochemical and mechanical properties. In addition to it, its diverse properties such as reactivity towards oxygen radical, metal chelation, renewable nature, biodegradability, favorable interaction with cells, nature to mimic the extracellular environment, and ease of nanoparticles preparation make it a very interesting material for biomedical use. Tremendous progress has been made in drug delivery and tissue engineering in recent years. However, still, it remains challenging to identify an ideal and compatible nanomaterial for biomedical applications. In this review, recent progress of lignin towards biomedical applications especially in drug delivery and in tissue engineering along with challenges, future possibilities have been comprehensively reviewed.

Emerging Role of Hydrogels in Drug Delivery Systems, Tissue Engineering and Wound Management

The popularity of hydrogels as biomaterials lies in their tunable physical properties, ability to encapsulate small molecules and macromolecular drugs, water holding capacity, flexibility, and controllable degradability. Functionalization strategies to overcome the deficiencies of conventional hydrogels and expand the role of advanced hydrogels such as DNA hydrogels are extensively discussed in this review. Different types of cross-linking techniques, materials utilized, procedures, advantages, and disadvantages covering hydrogels are tabulated. The application of hydrogels, particularly in buccal, oral, vaginal, and transdermal drug delivery systems, are described. The review also focuses on composite hydrogels with enhanced properties that are being developed to meet the diverse demand of wound dressing materials. The unique advantages of hydrogel nanoparticles in targeted and intracellular delivery of various therapeutic agents are explained. Furthermore, different types of hydrogel-based materials utilized for tissue engineering applications and fabrication of contact lens are discussed. The article also provides an overview of selected examples of commercial products launched particularly in the area of oral and ocular drug delivery systems and wound dressing materials. Hydrogels can be prepared with a wide variety of properties, achieving biostable, bioresorbable, and biodegradable polymer matrices, whose mechanical properties and degree of swelling are tailored with a specific application. These unique features give them a promising future in the fields of drug delivery systems and applied biomedicine.

Synergistic effect of silane cross-linker (APTEOS) on PVA/gelatin blend films for packaging applications

The objective of this work is to fabricate hydrogel films which are biodegradable and also fit for packaging applications. The hydrogel films were prepared by the reaction of polyvinyl alcohol and gelatin with and without 3-aminopropyltriethoxysilane (APTEOS) cross-linker. The hydrogel films were then characterized by FTIR spectroscopy, degree of swelling, TGA, SEM analysis and mechanical testing. The FTIR spectra of the hydrogel films confirmed the presence of both polymers and hydrogen bonding between them. TGA analysis confirmed the increase in thermal stability with the increase of cross-linker amount. SEM analysis confirmed the increase in uniformity of structure with the increase of cross-linker amount. The increase in cross-linker amount resulted in decrease of degree of swelling and increase of tensile strength. The biodegradability of hydrogel films was evaluated by performing soil burial test and found to be decreased with the increase of cross-linker amount. In order to balance the tensile strength and biodegradability, the optimum amount of cross-linker was determined which resulted in the formation of the best performing film. Finally, our best performing film was compared with other hydrogel films reported in the literature. Hence, the hydrogel films cross-linked with APTEOS are biodegradable, having high tensile strength and suitable for packaging purpose.

Rational Design of Smart Hydrogels for Biomedical Applications

Hydrogels are polymeric three-dimensional network structures with high water content. Due to their superior biocompatibility and low toxicity, hydrogels play a significant role in the biomedical fields. Hydrogels are categorized by the composition from natural polymers to synthetic polymers. To meet the complicated situation in the biomedical applications, suitable host–guest supramolecular interactions are rationally selected. This review will have an introduction of hydrogel classification based on the formulation molecules, and then a discussion over the rational design of the intelligent hydrogel to the environmental stimuli such as temperature, irradiation, pH, and targeted biomolecules. Further, the applications of rationally designed smart hydrogels in the biomedical field will be presented, such as tissue repair, drug delivery, and cancer therapy. Finally, the perspectives and the challenges of smart hydrogels will be outlined.

Chitosan-Based Functional Materials for Skin Wound Repair: Mechanisms and Applications

Skin wounds not only cause physical pain for patients but also are an economic burden for society. It is necessary to seek out an efficient approach to promote skin repair. Hydrogels are considered effective wound dressings. They possess many unique properties like biocompatibility, biodegradability, high water uptake and retention etc., so that they are promising candidate materials for wound healing. Chitosan is a polymeric biomaterial obtained by the deacetylation of chitin. With the properties of easy acquisition, antibacterial and hemostatic activity, and the ability to promote skin regeneration, hydrogel-like functional wound dressings (represented by chitosan and its derivatives) have received extensive attentions for their effectiveness and mechanisms in promoting skin wound repair. In this review, we extensively discussed the mechanisms with which chitosan-based functional materials promote hemostasis, anti-inflammation, proliferation of granulation in wound repair. We also provided the latest information about the applications of such materials in wound treatment. In addition, we summarized the methods to enhance the advantages and maintain the intrinsic nature of chitosan via incorporating other chemical components, active biomolecules and other substances into the hydrogels.

Effects of chitosan-collagen dressing on wound healing in vitro and in vivo assays

The present study was designed to fabricate a new chitosan-collagen sponge (CCS) for potential wound dressing applications. CCS was fabricated by a 3.0% chitosan mixture with a 1.0% type I collagen (7:3(w/w)) through freeze-drying. Then the dressing was prepared to evaluate its properties through a series of tests. The new-made dressing demonstrated its safety toward NIH3T3 cells. Furthermore, the CCS showed the significant surround inhibition zone than empty controls inoculated by E. coli and S. aureus. Moreover, the moisture rates of CCS were increased more rapidly than the collagen and blank sponge groups. The results revealed that the CCS had the characteristics of nontoxicity, biocompatibility, good antibacterial activity, and water retention. We used a full-thickness excisional wound healing model to evaluate the in vivo efficacy of the new dressing. The results showed remarkable healing at 14th day post-operation compared with injuries treated with collagen only as a negative control in addition to chitosan only. Our results suggest that the chitosan-collagen wound dressing were identified as a new promising candidate for further wound application.

A 3D Bioprinted Material That Recapitulates the Perivascular Bone Marrow Structure for Sustained Hematopoietic and Cancer Models

Translational medicine requires facile experimental systems to replicate the dynamic biological systems of diseases. Drug approval continues to lag, partly due to incongruencies in the research pipeline that traditionally involve 2D models, which could be improved with 3D models. The bone marrow (BM) poses challenges to harvest as an intact organ, making it difficult to study disease processes such as breast cancer (BC) survival in BM, and to effective evaluation of drug response in BM. Furthermore, it is a challenge to develop 3D BM structures due to its weak physical properties, and complex hierarchical structure and cellular landscape. To address this, we leveraged 3D bioprinting to create a BM structure with varied methylcellulose (M): alginate (A) ratios. We selected hydrogels containing 4% (w/v) M and 2% (w/v) A, which recapitulates rheological and ultrastructural features of the BM while maintaining stability in culture. This hydrogel sustained the culture of two key primary BM microenvironmental cells found at the perivascular region, mesenchymal stem cells and endothelial cells. More importantly, the scaffold showed evidence of cell autonomous dedifferentiation of BC cells to cancer stem cell properties. This scaffold could be the platform to create BM models for various diseases and also for drug screening.

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.

Gene therapy in wound healing using nanotechnology

Wound healing is a complex and highly regulated process that is susceptible to a variety of failures leading to delayed wound healing or chronic wounds. This is becoming an increasingly global burden on the healthcare system. Treatment of wounds has evolved considerably to overcome barriers to wound healing especially within the field of regenerative medicine that focuses on the replacement of tissues or organs. Improved understanding of the pathophysiology of wound healing has enabled current advances in technology to allow better optimization of microenvironment within wounds. This approach may help tackle wounds that are difficult to treat and help reduce the global burden of the disease. This article provides an overview of the physiology in wound healing and the application of gene therapy using nanotechnology in the management of wounds.

Chitosan and Cellulose-Based Hydrogels for Wound Management

Wound management remains a challenge worldwide, although there are several developed wound dressing materials for the management of acute and chronic wounds. The wound dressings that are currently used include hydrogels, films, wafers, nanofibers, foams, topical formulations, transdermal patches, sponges, and bandages. Hydrogels exhibit unique features which make them suitable wound dressings such as providing a moist environment for wound healing, exhibiting high moisture content, or creating a barrier against bacterial infections, and are suitable for the management of exuding and granulating wounds. Biopolymers have been utilized for their development due to their non-toxic, biodegradable, and biocompatible properties. Hydrogels have been prepared from biopolymers such as cellulose and chitosan by crosslinking with selected synthetic polymers resulting in improved mechanical, biological, and physicochemical properties. They were useful by accelerating wound re-epithelialization and also mimic skin structure, inducing skin regeneration. Loading antibacterial agents into them prevented bacterial invasion of wounds. This review article is focused on hydrogels formulated from two biopolymers-chitosan and cellulose-for improved wound management.

Additive manufacturing of the core template for the fabrication of an artificial blood vessel: the relationship between the extruded deposition diameter and the filament/nozzle transition ratio

An artificial blood vessel with a tubular structure was additively manufactured via fused deposition modeling (FDM) starting from a single strand of polyvinyl alcohol (PVA) filament coated with a specific thickness of biocompatible polydimethylsiloxane (PDMS), followed by removal of the inner core via hydrogen peroxide leaching under sonication. In particular, we examined the relationship between the extruded deposition diameter and the filament migration speed/nozzle control speed (referred to as the filament/nozzle transition ratio), which is almost independent of the extruded deposition flow rate due to the weak die-swelling and memory effects of the extruded PVA arising from its intrinsically low viscoelasticity. The chemical stability of the PDMS during sonication in the hydrogen peroxide solution was then determined by spectroscopic techniques. The PDMS displayed no mechanical degradation in the hydrogen peroxide solution, resulting in similar fracture elongation and yield strength to those of the pristine specimen without the leaching treatment. As a further advantage, the inside surface of the PDMS was smooth regardless of the hydrogen peroxide leaching under sonication. The potential application of the as-developed scaffold in soft tissue engineering (particularly that involving vascular tissue regeneration) was demonstrated by the successful transplantation of the artificial blood vessel in a right-hand surgical replica used in a clinical simulation.

3D Bioprinting of Lignocellulosic Biomaterials

The interest in bioprinting of sustainable biomaterials is rapidly growing, and lignocellulosic biomaterials have a unique role in this development. Lignocellulosic materials are biocompatible and possess tunable mechanical properties, and therefore promising for use in the field of 3D-printed biomaterials. This review aims to spotlight the recent progress on the application of different lignocellulosic materials (cellulose, hemicellulose, and lignin) from various sources (wood, bacteria, and fungi) in different forms (including nanocrystals and nanofibers in 3D bioprinting). Their crystallinity, leading to water insolubility and the presence of suspended nanostructures, makes these polymers stand out among hydrogel-forming biomaterials. These unique structures give rise to favorable properties such as high ink viscosity and strength and toughness of the final hydrogel, even when used at low concentrations. In this review, the application of lignocellulosic polymers with other components in inks is reported for 3D bioprinting and identified supercritical CO₂ as a potential sterilization method for 3D-printed cellulosic materials. This review also focuses on the areas of potential development by highlighting the opportunities and unmet challenges such as the need for standardization of the production, biocompatibility, and biodegradability of the cellulosic materials that underscore the direction of future research into the 3D biofabrication of cellulose-based biomaterials.

Antioxidant and antibacterial polyelectrolyte wound dressing based on chitosan/hyaluronan/phosphatidylcholine dihydroquercetin

Antioxidant and antimicrobial wound dressings are the most favorable for acute and chronic wounds treatment. Herein, we formulated a multifunctional polyelectrolyte wound dressing membrane on the basis of chitosan (Ch) and hyaluronan (HA) enhanced by phosphatidylcholine dihydroquercetin (PCDQ). Physicochemical properties and microstructures of fabricated films were investigated adopting Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Furthermore, water uptakes, wettability profiles, surface roughness, and mechanical characteristics of the developed membranes were studied. The developed wound dressing revealed free radical scavenging potency, hemocompatibility with a tendency to enhance blood clotting. Furthermore, incorporation of PCDQ significantly promoted the antibacterial and anti-inflammatory activities of Ch/HA/PCDQ. Moreover, Ch/HA/PCDQ films exhibited cellular compatibility towards mouse fibroblast cells. The capability of Ch/HA/PCDQ to promote wound healing was evaluated using adult Wistar albino female rats. The in vivo findings demonstrated that Ch/HA/PCDQ films significantly ameliorated mouse full-thickness wounds as evidenced by a reduction in the wound area. Moreover, histological examinations of wounds dressed with Ch/HA/PCDQ illustrated a prominent re-epithelialization compared with wounds handled with the cotton gauze and Ch/HA dressings, exposing the efficiency of PCDQ. These findings emphasized that a Ch/HA/PCDQ membrane has outstanding potential for wound healing and skin regeneration.

Regenerative Wound Dressings for Skin Cancer

Skin cancer is considered the most prevalent cancer type globally, with a continuously increasing prevalence and mortality growth rate. Additionally, the high risk of recurrence makes skin cancer treatment among the most expensive of all cancers, with average costs estimated to double within 5 years. Although tumor excision is the most effective approach among the available strategies, surgical interventions could be disfiguring, requiring additional skin grafts for covering the defects. In this context, post-surgery management should involve the application of wound dressings for promoting skin regeneration and preventing tumor recurrence and microbial infections, which still represents a considerable clinical challenge. Therefore, this paper aims to provide an up-to-date overview regarding the current status of regenerative wound dressings for skin cancer therapy. Specifically, the recent discoveries in natural biocompounds as anti-cancer agents for skin cancer treatment and the most intensively studied biomaterials for bioactive wound dressing development will be described.

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.

Antibacterial Hybrid Hydrogels

Bacterial infectious diseases and bacterial-infected environments have been threatening the health of human beings all over the world. In view of the increased bacteria resistance caused by overuse or improper use of antibiotics, antibacterial biomaterials are developed as the substitutes for antibiotics in some cases. Among them, antibacterial hydrogels are attracting more and more attention due to easy preparation process and diversity of structures by changing their chemical cross-linkers via covalent bonds or noncovalent physical interactions, which can endow them with various specific functions such as high toughness and stretchability, injectability, self-healing, tissue adhesiveness and rapid hemostasis, easy loading and controlled drug release, superior biocompatibility and antioxidation as well as good conductivity. In this review, the recent progress of antibacterial hydrogel including the fabrication methodologies, interior structures, performances, antibacterial mechanisms, and applications of various antibacterial hydrogels is summarized. According to the bacteria-killing modes of hydrogels, several representative hydrogels such as silver nanoparticles-based hydrogel, photoresponsive hydrogel including photothermal and photocatalytic, self-bacteria-killing hydrogel such as inherent antibacterial peptides and cationic polymers, and antibiotics-loading hydrogel are focused on. Furthermore, current challenges of antibacterial hydrogels are discussed and future perspectives in this field are also proposed.

Quantitative Insights into the Effects of Post-Cross-Linking on Physical Performance Improvement and Surface-Cracking Healing of a Hydrogel

We report a post-cross-linking protocol that can improve the mechanical properties, freezing resistance, and fracture energies of a covalent cross-linking hydrogel and can also enable its surface-cracking healing. We design a covalent cross-linking reaction based on 3-(methacryloylamino) propyl-trimethylammonium chloride (MPTC) and sodium acrylate (SA) to give rise to a PMPTC@PSA model hydrogel. After post-cross-linking treatment, the mechanical stress is improved by 9.0-fold, accompanied by a 3.5-fold improvement in elongation; the freezing resistance is increased by 2.5-fold, which is reflected by the stretchability improvement at -35 °C. In addition, the fracture energy increased from 266 to 4686 J/m², an ∼17-fold improvement. Importantly, a surface-cracking hydrogel can be healed through the post-cross-linking treatment that enables the healing efficiency to approach 100% in terms of mechanical modulus and >81% in terms of maximum mechanical stress. This protocol is expected to provide a new option for physical performance improvement and crack healing of hydrogels in soft actuator, sensing device, and robotic applications.

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.

Enhancement of UV absorbance and mechanical properties of chitosan films by the incorporation of solvolytically fractionated lignins

In this work, an effective sequential organic solvent extraction of kraft and organosolv lignins was carried out to separate lignin into more homogeneous fractions with specific properties. The selected solvents were ethyl acetate, ethanol, methanol, and acetone in that order. Fractions were analysed in terms of their yield, molecular weight, S/G ratio, and phenolic hydroxyl groups content. The incorporation of lignin fractions into the chitosan was aimed to increase the UV absorbance and the mechanical resistance of the chitosan films, which would provide good properties for applications in the packaging field. Films were analysed in terms of UV-vis absorption spectra, tensile strength, as well as colour changes. Results showed a significant increase in the absorbance of UV-A and UV-B with the addition of lignin fractions, mechanical properties showed an increase in the ultimate tensile strength in case of kraft fractions, while organosolv fractions do not affect tensile strength significantly.

Lignin-Based Hydrogels: Synthesis and Applications

Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin for the production of new materials with improved properties is currently considered as one of the main challenging issues, especially for the paper industry. Regarding its chemical structure, lignin is a crosslinked polymer that contains many functional hydrophilic and active groups, such as hydroxyls, carbonyls and methoxyls, which provides a great potential to be employed in the synthesis of biodegradable hydrogels, materials that are recognized for their interesting applicability in biomedicine, soil and water treatment, and agriculture, among others. This work describes the main methods for the preparation of lignin-based hydrogels reported in the last years, based on the chemical and/or physical interaction with polymers widely used in hydrogels formulations. Furthermore, herein are also reviewed the current applications of lignin hydrogels as stimuli-responsive materials, flexible supercapacitors, and wearable electronics for biomedical and water remediation applications.

Cellulose Nanofibers and Other Biopolymers for Biomedical Applications. A Review

Biopolymers are materials synthesised or derived from natural sources, such as plants, animals, microorganisms or any other living organism. The use of these polymers has grown significantly in recent years as industry shifts away from unsustainable fossil fuel resources and looks towards a softer and more sustainable environmental approach. This review article covers the main classes of biopolymers: Polysaccharides, proteins, microbial-derived and lignin. In addition, an overview of the leading biomedical applications of biopolymers is also provided, which includes tissue engineering, medical implants, wound dressings, and the delivery of bioactive molecules. The future clinical applications of biopolymers are vast, due to their inherent biocompatibility, biodegradability and low immunogenicity. All properties which their synthetic counterparts do not share.