Synthesis and characterization of crosslinked gellan/PVA nanofibers for tissue engineering application

Silver nanoparticles loaded triple-layered cellulose-acetate based multifunctional dressing for wound healing

Chronic wounds present considerable challenges which delay their effective healing. Currently, there are several biomaterial-based wound dressings available for healing diverse wound types. However, most of commercial wound dressings are too expensive to be affordable to the patients belonging to the middle and lower socioeconomic strata of the society. Thus, in this investigation affordable triple layered nanofibrous bandages were fabricated using the layer-by-layer approach. Here, the topmost layer comprised of a hydrophilic poly vinyl alcohol layer, cross-linked with citric acid. The middle layer comprising of cellulose acetate was loaded with silver nanoparticles as an antibacterial agent, while the lowermost layer was fabricated using hydrophobic polycaprolactone. The triple-layered nanofibrous bandages having a nano-topography, exhibited a smooth, uniform and bead-free morphology, with the nanofiber diameter ranging between 200 and 300 nm. The nanofibers demonstrated excellent wettability, slow in vitro degradation, controlled release of nano‑silver and potent antibacterial activity against Gram-negative (E.coli) and Gram-positive (S. aureus) bacteria. The fabricated bandages had excellent mechanical strength upto 12.72 ± 0.790 M. Pa, which was suitable for biomedical and tissue engineering applications. The bandage demonstrated excellent in vitro hemocompatibility and biocompatibility. In vivo excisional wound contraction, along with H and E and Masson's Trichrome staining further confirmed the potential of the nanofibrous bandage for full-thickness wound healing. Pre-clinical investigations thus indicated the possibility of further evaluating the triple-layered nanofibrous dressing in clinical settings.

Thermally Stabilised Poly(vinyl alcohol) Nanofibrous Materials Produced by Scalable Electrospinning: Applications in Tissue Engineering

Electrospinning is a widely employed manufacturing platform for tissue engineering applications because it produces structures that closely mimic the extracellular matrix. Herein, we demonstrate the potential of poly(vinyl alcohol) (PVA) electrospun nanofibers as scaffolds for tissue engineering. Nanofibers were created by needleless direct current electrospinning from PVA with two different degrees of hydrolysis (DH), namely 98% and 99% and subsequently heat treated at 180 °C for up to 16 h to render them insoluble in aqueous environments without the use of toxic cross-linking agents. Despite the small differences in the PVA chemical structure, the changes in the material properties were substantial. The higher degree of hydrolysis resulted in non-woven supports with thinner fibres (285 ± 81 nm c.f. 399 ± 153 nm) that were mechanically stronger by 62% (±11%) and almost twice as more crystalline than those from 98% hydrolysed PVA. Although prolonged heat treatment (16 h) did not influence fibre morphology, it reduced the crystallinity and tensile strength for both sets of materials. All samples demonstrated a lack or very low degree of haemolysis (<5%), and there were no notable changes in their anticoagulant activity (≤3%). Thrombus formation, on the other hand, increased by 82% (±18%) for the 98% hydrolysed samples and by 71% (±10%) for the 99% hydrolysed samples, with heat treatment up to 16 h, as a direct consequence of the preservation of the fibrous morphology. 3T3 mouse fibroblasts showed the best proliferation on scaffolds that were thermally stabilised for 4 and 8 h. Overall these scaffolds show potential as 'greener' alternatives to other electrospun tissue engineering materials, especially in cases where they may be used as delivery vectors for heat tolerant additives.

Frontier in gellan gum-based microcapsules obtained by emulsification: Core-shell structure, interaction mechanism, intervention strategies

As a translucent functional gel with biodegradability, non-toxicity and acid resistance, gellan gum has been widely used in probiotic packaging, drug delivery, wound dressing, metal ion adsorption and other fields in recent years. Because of its remarkable gelation characteristics, gellan gum is suitable as the shell material of microcapsules to encapsulate functional substances, by which the functional components can improve stability and achieve delayed release. In recent years, many academically or commercially reliable products have rapidly emerged, but there is still a lack of relevant reports on in-depth research and systematic summaries regarding the process of microcapsule formation and its corresponding mechanisms. To address this challenge, this review focuses on the formation process and applications of gellan gum-based microcapsules, and details the commonly used preparation methods in microcapsule production. Additionally, it explores the impact of factors such as ion types, ion strength, temperature, pH, and others present in the solution on the performance of the microcapsules. On this basis, it summarizes and analyzes the prospects of gellan gum-based microcapsule products. The comprehensive insights from this review are expected to provide inspiration and design ideas for researchers.

Fucoidan loaded PVA/Dextran blend electrospun nanofibers for the effective wound healing

Chronic wounds have become a serious global health issue. In this study, we investigated the effect of increasing fucoidan (FD) concentration on the characteristics of nanofibers and their wound healing potential at in vitro as well as in vivo level. The results showed that increasing FD content (0.25 to 1 %) led to an significant increase in nanofiber diameter (487.7 ± 125.39 to 627.9 ± 149.78 nm), entrapment efficiency (64.26 ± 2.6 to 94.9 ± 3.1 %), and water uptake abilities (436.5 ± 1.2 to 679.7 ± 11.3 %). However, the in vitro biodegradation profile decreased with an increase in FD concentration. Water vapor transmission rate analysis showed that it was within the standard range for all FD concentrations. Nanofibers with 1 % PVA/DX/FD exhibited slow-release behavior, suggesting prolonged FD availability at the wound site. In vivo studies in rats with full-thickness wounds demonstrated that applying 1 % FD-enriched PVA/DEX nanofibers significantly (p < 0.0001) improved mean wound area closure. These findings suggest that FD-enriched nanofibers have immense potential as a wound dressing material in future if explored further.

New polyvinyl alcohol/gellan gum-based bioplastics with guava and chickpea extracts for food packaging

Plastic is a fossil-based synthetic polymer that has become an essential material in our daily life. Plastic pollution resulting from the accumulation of plastic objects has become problematic for our environment. Bioplastic can be a biodegradable environmentally friendly alternative for the synthetic plastic. In this paper, bioplastics based on polyvinyl alcohol (PVA)/gellan gum (GG) blend have been produced in three different compositions and their chemical structure, mechanical, morphological and thermal properties have been studied. Glycerol has been used as a plasticizer. To add extra features to the PVA/GG bioplastic, Psidium guajava (guava) leaves, GL, and chickpea, CP, extracts have been added to the PVA/GG (30/70) blend. Water and aqueous ethanol have been used in the extraction of GL and CP, respectively. The addition of the plant's extracts enhanced the tensile properties of the PVA/GG bioplastic. Weathering acceleration tests have been carried out to examine the degradation of the prepared bioplastics. Cytotoxicity studies revealed that the prepared bioplastic is safe to be used in food packaging applications. Water and oxygen permeability for the new PVA/GG bioplastic have also been studied. The addition of the plant extracts (GL and CP extracts) increased the oxygen and water permeability to different extents. Bioplastic life cycle assessment (LCA) and CO2 emissions in comparison to fossil-based plastic have been investigated. From all the results, PVA/GG based bioplastic proved to be a degradable, safe and effective alternative for fossil-based plastics in food packaging applications.

Study on electrospinning of wheat gluten: A review

Electrospinning has attracted extensive attention among various nanofabrication technologies owing to its ability to produce nanofiber structures with unique properties, such as high specific surface area and porosity, as well as tunable fiber morphology and mechanical properties. The most representative spinning raw materials include natural polymers and synthetic polymers. Owing to the sustainable development strategies, more and more researchers focus on natural polymers. Among natural polymers, wheat gluten (WG) nanofibers have recently attracted much attention owing to its high specific surface area, superior biocompatibility, and unique viscoelasticity. This review summarizes the composition and characteristics of WG, the physical and chemical indicators of a WG electrospinning solution, the main influencing factors in the WG electrospinning process and a characterizations of WG nanofibers. Finally, the review also outlines the applications of WG nanofibers in drug release, biological scaffold, and active food packaging.

Polymer Colloids: Current Challenges, Emerging Applications, and New Developments

Polymer colloids are complex materials that have the potential to be used in a vast array of applications. One of the main reasons for their continued growth in commercial use is the water-based emulsion polymerization process through which they are generally synthesized. This technique is not only highly efficient from an industrial point of view but also extremely versatile and permits the large-scale production of colloidal particles with controllable properties. In this perspective, we seek to highlight the central challenges in the synthesis and use of polymer colloids, with respect to both existing and emerging applications. We first address the challenges in the current production and application of polymer colloids, with a particular focus on the transition toward sustainable feedstocks and reduced environmental impact in their primary commercial applications. Later, we highlight the features that allow novel polymer colloids to be designed and applied in emerging application areas. Finally, we present recent approaches that have used the unique colloidal nature in unconventional processing techniques.

Methylene blue removal from aqueous solutions using a biochar/gellan gum hydrogel composite: Effect of agitation mode on sorption kinetics

Hydrogel membranes are prepared by casting a mixture of gellan gum (associated with PVA) and biochar produced from a local Egyptian plant. The mesoporous material is characterized by a specific surface area close to 134 m² g^-1, a residue of 28 % (at 800 °C), and a pH_PZC close to 6.43. After grinding, the material is tested for Methylene Blue sorption at pH 10.5: sorption capacity reaches 1.70 mmol MB g^-1 (synergistic effect of the precursors). The sorption isotherms are fitted by both Langmuir and Sips eqs. MB sorption increases with temperature: the sorption is endothermic (∆H°: 12.9 kJ mol^-1), with positive entropy (∆S°: 125 J mol^-1 K^-1). Uptake kinetics are controlled by agitation speed (optimum ≈200 rpm) and resistance to intraparticle diffusion. The profiles are strongly affected by the mode of agitation: the equilibrium time (≈180 min) is reduced to 20-30 min under sonication (especially at frequency: 80 kHz). The mode of agitation controls the best fitting equation: pseudo-first order rate agitation for mechanical agitation contrary to pseudo-second order rate under sonication. The sorption of MB is poorly affected by ionic strength (loss <6 % in 45 g L^-1 NaCl solution). Desorption (faster than sorption) is completely achieved using 0.7 M HCl solution. At the sixth recycling, the loss in sorption is close to 5 % (≈ decrease in desorption efficiency). The process is successfully applied for the treatment of MB-spiked industrial solution: the color index decreases by >97 % with a sorbent dose close to 1 g L^-1; a higher dose is required for maximum reduction of the COD (60 % at 3 g L^-1).

Progress and opportunities in Gellan gum-based materials: A review of preparation, characterization and emerging applications

Gellan gum, a microbial exopolysaccharide, is biodegradable and has potential to fill several key roles in many fields from food to pharmacy, biomedicine and tissue engineering. In order to improve the physicochemical and biological properties of gellan gum, some researchers take advantage of numerous hydroxyl groups and the free carboxyl present in each repeating unit. As a result, design and development of gellan-based materials have advanced significantly. The goal of this review is to provide a summary of the most recent, high-quality research trends that have used gellan gum as a polymeric component in the design of numerous cutting-edge materials with applications in various fields.

Ionotropic Gelation and Chemical Crosslinking as Methods for Fabrication of Modified-Release Gellan Gum-Based Drug Delivery Systems

Hydrogels have a tridimensional structure. They have the ability to absorb a significant amount of water or other natural or simulated fluids that cause their swelling albeit without losing their structure. Their properties can be exploited for encapsulation and modified targeted drug release. Among the numerous natural polymers suitable for obtaining hydrogels, gellan gum is one gaining much interest. It is a gelling agent with many unique features, and furthermore, it is non-toxic, biocompatible, and biodegradable. Its ability to react with oppositely charged molecules results in the forming of structured physical materials (films, beads, hydrogels, nanoparticles). The properties of obtained hydrogels can be modified by chemical crosslinking, which improves the three-dimensional structure of the gellan hydrogel. In the current review, an overview of gellan gum hydrogels and their properties will be presented as well as the mechanisms of ionotropic gelation or chemical crosslinking. Methods of producing gellan hydrogels and their possible applications related to improved release, bioavailability, and therapeutic activity were described.

Gellan Gum in Wound Dressing Scaffolds

Several factors, such as bacterial infections, underlying conditions, malnutrition, obesity, ageing, and smoking are the most common issues that cause a delayed process of wound healing. Developing wound dressings that promote an accelerated wound healing process and skin regeneration is crucial. The properties of wound dressings that make them suitable for the acceleration of the wound healing process include good antibacterial efficacy, excellent biocompatibility, and non-toxicity, the ability to provide a moist environment, stimulating cell migration and adhesion, and providing gaseous permeation. Biopolymers have demonstrated features appropriate for the development of effective wound dressing scaffolds. Gellan gum is one of the biopolymers that has attracted great attention in biomedical applications. The wound dressing materials fabricated from gellan gum possess outstanding properties when compared to traditional dressings, such as good biocompatibility, biodegradability, non-toxicity, renewability, and stable nature. This biopolymer has been broadly employed for the development of wound dressing scaffolds in different forms. This review discusses the physicochemical and biological properties of gellan gum-based scaffolds in the management of wounds.

Antibacterial and hemostatic capacities of cellulose nanocrystalline-reinforced poly(vinyl alcohol) electrospun mats doped with Tiger 17 and pexiganan peptides for prospective wound healing applications

Infection is a major issue in chronic wound care. Different dressings have been developed to prevent microbial propagation, but an effective, all-in-one (cytocompatible, antimicrobial and promoter of healing) solution is still to be uncovered. In this research, polyvinyl alcohol (PVA) nanofibrous mats reinforced with cellulose nanocrystal (CNC), at 10 and 20% v/v ratios, were produced by electrospinning, crosslinked with glutaraldehyde vapor and doped with specialized peptides. Crosslinking increased the mats' fiber diameters but maintained their bead-free morphology. Miscibility between polymers was confirmed by Fourier-transform infrared spectroscopy and thermal evaluations. Despite the incorporation of CNC having reduced the mats' mechanical performance, it improved the mats' surface energy and its structural stability over time. Pexiganan with an extra cysteine group was functionalized onto the mats via hydroxyl- polyethylene glycol 2-maleimide, while Tiger 17 was physisorbed to preserve its cyclic conformation. Antimicrobial assessments demonstrated the peptide-doped mat's effectiveness against Staphylococcus aureus and Pseudomonas aeruginosa; pexiganan contributed mostly for such outcome. Tiger 17 showed excellent capacity in accelerating clotting. Cytocompatibility evaluations attested to these mats' safety. C90/10 PVA/CNC mats were deemed the most effective from the tested group and, thus, a potentially effective option for chronic wound treatments.

Cross-Linking Agents for Electrospinning-Based Bone Tissue Engineering

Electrospun nanofibers are promising bone tissue scaffolds that support bone healing due to the body’s structural similarity to the extracellular matrix (ECM). However, the insufficient mechanical properties often limit their potential in bone tissue regeneration. Cross-linking agents that chemically interconnect as-spun electrospun nanofibers are a simple but effective strategy for improving electrospun nanofibers’ mechanical, biological, and degradation properties. To improve the mechanical characteristic of the nanofibrous bone scaffolds, two of the most common types of cross-linking agents are used to chemically crosslink electrospun nanofibers: synthetic and natural. Glutaraldehyde (GTA) is a typical synthetic agent for electrospun nanofibers, while genipin (GP) is a natural cross-linking agent isolated from gardenia fruit extracts. GP has gradually gained attention since GP has superior biocompatibility to synthetic ones. In recent studies, much more progress has been made in utilizing crosslinking strategies, including citric acid (CA), a natural cross-linking agent. This review summarizes both cross-linking agents commonly used to improve electrospun-based scaffolds in bone tissue engineering, explains recent progress, and attempts to expand the potential of this straightforward method for electrospinning-based bone tissue engineering.

Green nanofiber mat from HLM-PVA-Pectin (Hibiscus leaves mucilage-polyvinyl alcohol-pectin) polymeric blend using electrospinning technique as a novel material in wound-healing process

The present work is focused on fabrication of novel nanofiber (NF) mat as wound-healing scaffold using blends of novel combination of Hibiscus rosa-sinensis leaves mucilage (HLM)-Polyvinyl alcohol (PVA)-Pectin, which was never reported previously. Different ratios of the polymeric blends were electrospun by setting different parameters to achieve best possible electrospun nanofiber mat which was later crosslinked by glutaraldehyde vapor. The optimized formulation of nanofiber mat was characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The crosslinked sample was evaluated for its efficacy in wound healing using Swiss albino mice model, where rapid healing of excised wound was observed with faster epithelization in test mice group than control mice within a period of 8 days. The hemolysis test with optimized crosslinked nanofiber mat CrNF(S7-CL) indicated it to be hemo-compatible. There were no traces of optimized CrNF(S7-CL) when placed under the skin hypodermis in test mice groups revealing its biodegradable nature. The degradation pattern of CrNF(S7-CL) in soil reflects its eco-friendly behavior. Thus, the prepared nanofiber grade CrNF(S7-CL) can be considered as a novel material for faster wound healing and can also be explored for other biomedical applications.

Synthesis, characterization, and antimicrobial properties of novel dual drug loaded electrospun mat for wound dressing applications

Wound healing properties of some herbs have been known for decades. Recently, electrospun mats have been used as a wound dressing material due to the high surface area of fiber and ease of incorporation of drug into the fiber matrix. In this aspect, the incorporation of herbal extracts in electrospun matrix could provide synergistic effect for wound healing. In the present work, extracts from Cissus quadrangularis (CQ) and Galinsoga parviflora Cav (GP) were loaded into the PVA solution in different proportions. These solutions were used to produce nanofibrous mat in electrospinning and the characteristics of the mat were analyzed. The morphology of the fiber was analyzed using scanning electron microscope (SEM), the presence of functional groups was identified using Fourier transform infrared spectroscopy (FTIR). The result of drug release shows that the GP extract loaded PVA nanofibrous mat has sustained drug release of 28% after 8 h of incubation compared to CQ loaded PVA nanofibrous mat. This trend follows as the concentration of GP increases in the mixture. The antimicrobial efficiency of the prepared mat was evaluated against both Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus. The prepared nanofibrous mat has shown excellent antibacterial activity, cell viability, hemocompatibility, and sufficient tensile properties which indicates that it could be a promising biomaterial for wound dressing application.

AK, Ramakrishna S, Amirul AAA. Surface Characterization and Physiochemical Evaluation of P(3HB-co-4HB)-Collagen Peptide Scaffolds with Silver Sulfadiazine as Antimicrobial Agent for Potential Infection-Resistance Biomaterial

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] is a bacterial derived biopolymer widely known for its unique physical and mechanical properties to be used in biomedical application. In this study, antimicrobial agent silver sulfadiazine (SSD) coat/collagen peptide coat-P(3HB-co-4HB) (SCCC) and SSD blend/collagen peptide coat-P(3HB-co-4HB) scaffolds (SBCC) were fabricated using a green salt leaching technique combined with freeze-drying. This was then followed by the incorporation of collagen peptides at various concentrations (2.5-12.5 wt.%) to P(3HB-co-4HB) using collagen-coating. As a result, two types of P(3HB-co-4HB) scaffolds were fabricated, including SCCC and SBCC scaffolds. The increasing concentrations of collagen peptides from 2.5 wt.% to 12.5 wt.% exhibited a decline in their porosity. The wettability and hydrophilicity increased as the concentration of collagen peptides in the scaffolds increased. In terms of the cytotoxic results, MTS assay demonstrated the L929 fibroblast scaffolds adhered well to the fabricated scaffolds. The 10 wt.% collagen peptides coated SCCC and SBCC scaffolds displayed highest cell proliferation rate. The antimicrobial analysis of the fabricated scaffolds exhibited 100% inhibition towards various pathogenic microorganisms. However, the SCCC scaffold exhibited 100% inhibition between 12 and 24 h, but the SBCC scaffolds with SSD impregnated in the scaffold had controlled release of the antimicrobial agent. Thus, this study will elucidate the surface interface-cell interactions of the SSD-P(3HB-co-4HB)-collagen peptide scaffolds and controlled release of SSD, antimicrobial agent.

Green Electrospinning of Polymer Latexes: A Systematic Study of the Effect of Latex Properties on Fiber Morphology

Green electrospinning is a relatively new promising technology in which a polymer (latex) can be spun from an aqueous dispersion with the help of a template polymer. This method is a green, clean and safe technology that is able to spin hydrophobic polymers using water as an electrospinning medium. In this article, a systematic study that investigates the influence of the template polymer molar mass, the total solids content of the initial dispersion and the particle/template ratio is presented. Furthermore, the influence of the surfactant used to stabilize the polymer particles, the surface functionality of the polymer particles and the use of a bimodal particle size distribution on the final fiber morphology is studied for the first time. In green electrospinning, the viscosity of the initial complex blend depends on the amount and molar mass of the template polymer but also on the total solids content of the dispersion to be spun. Thus, both parameters must be carefully taken into account in order to fine-tune the final fiber morphology. Additionally, the particle packing and the surface chemistry of the polymer particles also play an important role in the obtained nanofibers quality.

An asymmetric electrospun membrane for the controlled release of ciprofloxacin and FGF-2: Evaluation of antimicrobial and chemoattractant properties

Here, an asymmetric double-layer membrane has been designed and fabricated by electrospinning as a tool for a potential wound healing application. A hydrophobic layer has been produced by using a polyurethane-polycaprolactone (PU-PCL) copolymer and loaded with the antibacterial ciprofloxacin whereas an ion responsive hydrophilic layer has been produced by using an octyl derivative of gellan gum (GG-C₈) and polyvinyl alcohol (PVA) and loaded with the growth factor FGF-2. This study investigated how the properties of this asymmetric membrane loaded with actives, were influenced by the ionotropic crosslinking of the hydrophilic layer. In particular, the treatment in DPBS and the crosslinking in CaCl₂ 0.1 or 1 M of the hydrophilic layer affected the release profile of the bioactive molecules allowing to modulate both the antimicrobial effect, as assayed by logarithmic reduction of the Staphylococcus aureus viable count, and the chemoattractant properties on NIH 3 T3 cell line, as assayed by scratch test and cell chemoattraction assay.

Lignin-mediated in-situ synthesis of CuO nanoparticles on cellulose nanofibers: A potential wound dressing material

Herein we present our research on the synthesis of CuO nanoparticles on the surface of electrospun cellulose (CE) nanofibers using alkali lignin as a reducing agent. Fascinatingly, CA nanofibers were deacetalized during alkali lignin treatment, which was verified by FTIR-ATR spectra. The morphology of the produced nanofibers was observed with SEM and TEM. The presence of CuO nanoparticles was verified by EDX, XRD, and XPS. The Cu/CE nanofibers showed low thermal stability. MVTR values of 2100-1900 g/m²/day are adequate for the transport of air and moisture from the wound surface. The Cu/CE showed faster release (80%) of copper ions to aqueous environment within 24 h and seemed to advance towards plateau for the next five days. The Cu/CE nanofibrous mats exhibited excellent antibacterial efficacy against both gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) bacteria. NIH3T3 fibroblast cells have excellent migrating and proliferating ability on our prepared nanofibrous mats. The presence of bound alkali lignin on the surface of nanofibers added a benefit of antioxidant activity. These findings revealed that such type of nanofibrous mats could be used as a potential wound dressing material.

UV-initiated crosslinking of electrospun chitosan/poly(ethylene oxide) nanofibers doped with ZnO-nanoparticles: development of antibacterial nanofibrous hydrogel

UV-initiated crosslinking of electrospun poly(ethylene) oxide (PEO)/chitosan (CS) nanofibers doped with zinc oxide nanoparticles (ZnO-NPs) was performed using pentaerythritol triaclyrate (PETA) as the photoinitiator and crosslinker agent. The influence of the addition of PETA to the PEO/CS diameter and crosslinking of nanofibers was evaluated. The effect of irradiation time on the morphology and swelling properties of the crosslinked nanofibers were investigated. For ZnO-NPs, the minimum inhibitory concentrations were found at 1 mg/mL, and the minimum bactericidal concentrations at 2 mg/mL for all the strains tested. The nanofibrous hydrogel antibacterial effect was tested. This material enters the realm of fibrous hydrogels which have potential use in several applications as in the biomedical area.

SUPPLEMENTARY MATERIAL

The supplementary material for this article can be found at 10.1557/mrc.2020.74.

Titanium nitride nanoparticle embedded membrane for photothermal membrane distillation

To meet the increasing worldwide need for freshwater, it has become critical to exploit non-potable saline water. Solar membrane distillation (MD) is a promising desalination technique, which does not require conventional energy and can reduce the cost of water production. We developed a cost-effective and high-efficiency photothermal membrane that employs TiN nanoparticles as an absorber of sunlight and energy converter. Due to a strong photothermal effect, the solar energy efficiency significantly improved. With optimal membrane and MD operating conditions, we obtained an MD flux of 0.940 kg/m²∙h and a solar efficiency of 64.1% under 1.0 kW/m² solar irradiation. Compared with a bare poly(vinylidene fluoride) (PVDF) membrane, 65.8% more pure water was produced. Furthermore, the temperature polarization encountered in the conventional MD process was relieved on account of the unique interfacial heating of the photothermal coating, which also contributed to the high solar efficiency. In addition, the membrane was quite stable and the permeate water was of a high, potable quality. The as-prepared photothermal membrane demonstrated a good performance and application prospects for solar MD.

Microbial Exopolysaccharides as Drug Carriers

Microbial exopolysaccharides are peculiar polymers that are produced by living organisms and protect them against environmental factors. These polymers are industrially recovered from the medium culture after performing a fermentative process. These materials are biocompatible and biodegradable, possessing specific and beneficial properties for biomedical drug delivery systems. They can have antitumor activity, they can produce hydrogels with different characteristics due to their molecular structure and functional groups, and they can even produce nanoparticles via a self-assembly phenomenon. This review studies the potential use of exopolysaccharides as carriers for drug delivery systems, covering their versatility and their vast possibilities to produce particles, fibers, scaffolds, hydrogels, and aerogels with different strategies and methodologies. Moreover, the main properties of exopolysaccharides are explained, providing information to achieve an adequate carrier selection depending on the final application.

Three Dimensional Quercetin-Functionalized Patterned Scaffold: Development, Characterization, and In Vitro Assessment for Neural Tissue Engineering

Regeneration of injured neuronal areas is a big challenge owing to the complex structure and function of the nervous system along with the limited regeneration capacity of neural cells. Recent reports show that patterned and functionalized scaffolds could control neural cell directional growth. In this study, aligned nanofibers (ANFs) were fabricated using a versatile and cost-effective approach, electrospinning, and further processed to make a patterned hybrid scaffold (HANF). The patterned scaffold had circular rings of ANFs reinforced in a biocompatible gellan-gelatin hydrogel matrix to provide adequate mechanical strength and contact guidance for adhesion and growth of neural cells in vitro. Quercetin was loaded into the nanofibrous scaffold to provide a functional agent that supported regeneration of neural cells. The reinforced ANFs enhanced the mechanical strength of the scaffold and provided a cylindrical nerve conduit structure to support neuronal cell growth. The influence of scaffold topology on cell behavior was assessed in in vitro cell culture conditions that revealed that the functionalized patterned scaffolds favored directed neurite cell growth/extension with favored cell culture morphology and showed no cytotoxicity toward neural cells. The results ultimately indicated that the fabricated scaffold has potential for guiding nerve tissue growth and can be used as nerve regeneration scaffolds.

Supercritical carbon dioxide techniques for processing microbial exopolysaccharides used in biomedical applications

Microbial exopolysaccharides are polymers that show a great potential for biomedical applications, such as tissue engineering applications and drug delivery, due to their biocompatibility, biodegradability and their gelling properties. These polysaccharides are obtained from a microorganism culture with a relatively straightforward downstream process thanks to their extracellular character, and can be processed to obtain aerogels, fibers and micro- or nano-particles with conventional techniques. However, these techniques present several disadvantages in that they involve time-consuming processes and the use of toxic solvents. Supercritical carbon dioxide techniques can overcome these drawbacks, but their use for processing microbial exopolysaccharides is not extended in the scientific community. This review describes the most frequently used exopolysaccharides in biomedical applications and how they can be obtained, as well as the different supercritical carbon dioxide techniques that can be used for processing them and their challenges. Specifically, high pressure shows a great potential to process and sterilize exopolysaccharide biomaterials for biomedical applications (e.g. tissue engineering or drug delivery systems) in spite of the disadvantage concerning the hydrophilicity of this type of polymers.

Effects of Heat Treatment and Tea Polyphenols on the Structure and Properties of Polyvinyl Alcohol Nanofiber Films for Food Packaging

In this study, biodegradable polyvinyl alcohol (PVA) was blended with natural antioxidant tea polyphenols (TPs) to produce PVA/TP nanofiber films by electrospinning. The effects of heat treatment and TP incorporation on the structural and physical properties of the films were then evaluated. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) revealed that the PVA/TP nanofiber film has a more compact structure and better morphology than PVA alone. In addition, the water resistance was enhanced, and the formation of hydrogen bonds between the TP and PVA molecules increased via the heat treatment. Furthermore, the mechanical, antioxygenic, and antibacterial properties of the nanofiber films were significantly improved (P < 0.05) owing to the incorporation of TP. In particular, when the mass ratio of the PVA/TP was 7:3, the elongation at break (EAB) of the film increased to 105.24% ± 2.87%, and the antioxidant value reached a maximum at 64.83% ± 5.21%. In addition, the antibacterial activity of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) increased to the maximum levels of 82.48% ± 2.12% and 86.25% ± 2.32%, respectively. In summary, our study produced a functional food packaging material that includes preservation with an acceptable bioactivity, ability to keep food fresh, and biodegradability.

Poly(Vinyl Alcohol)-Based Nanofibrous Electrospun Scaffolds for Tissue Engineering Applications

Tissue engineering (TE) holds an enormous potential to develop functional scaffolds resembling the structural organization of native tissues, to improve or replace biological functions and prevent organ transplantation. Amongst the many scaffolding techniques, electrospinning has gained widespread interest because of its outstanding features that enable the production of non-woven fibrous structures with a dimensional organization similar to the extracellular matrix. Various polymers can be electrospun in the form of three-dimensional scaffolds. However, very few are successfully processed using environmentally friendly solvents; poly(vinyl alcohol) (PVA) is one of those. PVA has been investigated for TE scaffolding production due to its excellent biocompatibility, biodegradability, chemo-thermal stability, mechanical performance and, most importantly, because of its ability to be dissolved in aqueous solutions. Here, a complete overview of the applications and recent advances in PVA-based electrospun nanofibrous scaffolds fabrication is provided. The most important achievements in bone, cartilage, skin, vascular, neural and corneal biomedicine, using PVA as a base substrate, are highlighted. Additionally, general concepts concerning the electrospinning technique, the stability of PVA when processed, and crosslinking alternatives to glutaraldehyde are as well reviewed.

Chemically and Thermally Crosslinked PVA-Based Membranes: Effect on Swelling and Transport Behavior

The novel poly(vinyl alcohol) (PVA)-based membranes were prepared using the two-step crosslinking approach: the chemical crosslinking of PVA using sulfosuccinic acid (SSA) (0-50 wt.%) and the thermal treatment (120-160 °C). The membrane composition and crosslinking temperature were optimized in terms of the mechanical and transport properties. The FTIR-ATR analysis revealed that the increase of the SSA concentration and crosslinking temperature resulted in the rise of the ester bond bands intensity due to the esterification reaction between PVA and SSA. As a consequence, the PVA-based membrane with 50 wt % SSA and crosslinked at 140 °C showed the reduced Young's modulus (from 1266.2 MPa to 1.4 MPa) and elongation at break (from 316% to 66%) in comparison with the pure PVA membrane. The studied swelling behavior of the obtained membranes revealed significantly higher water sorption than that in methanol and propal-2-ol whatever the crosslinking temperature. The performed studies provide a new way of tailoring the membrane physicochemical properties, in particular, the surface hydrophilicity. In addition, the obtained results are crucial for the design and elaboration of the polymer membranes for the pervaporative separation of the liquid-liquid mixtures, in particular, for the alcohol dehydration.

Preparation of Lutein-Loaded PVA/Sodium Alginate Nanofibers and Investigation of Its Release Behavior

This investigation aims to study the characteristics and release properties of lutein-loaded polyvinyl alcohol/sodium alginate (PVA/SA) nanofibers prepared by electrospinning. In order to increase PVA/SA nanofibers' water-resistant ability for potential biomedical applications, the electrospun PVA/SA nanofibers were cross-linked with a mixture of glutaraldehyde and saturated boric acid solution at room temperature. The nanofibers were characterized using scanning electron microscopy (SEM) and X-ray diffractometer (XRD). Disintegration time and contact angle measurements testified the hydrophilicity change of the nanofibers before and after cross-linking. The lutein release from the nanofibers after cross-linking was measured by an ultraviolet absorption spectrophotometer, which showed sustained release up to 48 h and followed anomalous (non-Fickian) release mechanism as indicated by diffusion exponent value obtained from the Korsmeyer-Peppas equation. The results indicated that the prepared lutein-loaded PVA/SA nanofibers have great potential as a controlled release system.

One-pot reactive electrospinning of chitosan/PVA hydrogel nanofibers reinforced by halloysite nanotubes with enhanced fibroblast cell attachment for skin tissue regeneration

In this study, in situ glyoxal crosslinked chitosan/poly (vinyl alcohol) (PVA) hydrogel nanofibers reinforced with halloysite nanotubes (HNT) were prepared by the electrospinning method without needing post-treatment for stabilization of the nanofibers in aqueous media. FTIR spectroscopy approved the formation of acetal bonds between glyoxal and hydroxyl groups of PVA and chitosan. Morphological studies by SEM/EDX and TEM in accordance with XRD patterns proved that HNT was successfully incorporated into the crosslinked chitosan/PVA nanofibers. The crosslinked nanofibers were insoluble in water. Due to the hydrophilic nature of HNT, the swelling of the nanofibers was increased from 272% for crosslinked chitosan/PVA nanofibers to around 400% for the HNT reinforced nanocomposite nanofibers. Comparing to chitosan/PVA nanofibers, the tensile strength of the crosslinked nanocomposite nanofibers was increased to 2.4 and 3.5 fold by incorporation of 3 and 5% HNT, respectively. Presence of HNT in chitosan/PVA nanofibers reduced the contact angle with water and increased the hydrophilicity of HNT-reinforced nanofibers favoring the attachment of fibroblast cells. Cytotoxicity studies by AlamarBlue assay showed that presence of HNT increased the biocompatibility of the nanofibers. It was also concluded that glyoxal can be used safely for crosslinking of chitosan/PVA nanofibers without any cytotoxic effect for fibroblast cells. From the results of this work, HNT reinforced chitosan/PVA nanofibers crosslinked by glyoxal are introduced as promising nanomaterials for skin tissue regeneration.

Nanopharmaceuticals for wound healing - Lost in translation?

Today, many of the newly developed pharmaceuticals and medical devices take advantage of nanotechnology and with a rising incidence of chronic diseases such as diabetes and cardiovascular disease, the number of patients afflicted globally with non-healing wounds is growing. This has created a requirement for improved therapies and wound care. However, converting the strategies applied in early research into new products is still challenging. Many of them fail to comply with the market requirements. This review discusses the legal and scientific challenges in the design of nanomedicines for wound healing. Are they lost in translation or is there a new generation of therapeutics in the pipeline?

Recent trends on gellan gum blends with natural and synthetic polymers: A review

Gellan gum (GG), a linear negatively charged exopolysaccharide,is biodegradable and non-toxic in nature. It produces hard and translucent gel in the presence of metallic ions which is stable at low pH. However, GG has poor mechanical strength, poor stability in physiological conditions, high gelling temperature and small temperature window.Therefore,it is blended with different polymers such as agar, chitosan, cellulose, sodium alginate, starch, pectin, polyanaline, pullulan, polyvinyl chloride, and xanthan gum. In this article, a comprehensive overview of combination of GG with natural and synthetic polymers/compounds and their applications in biomedical field involving drug delivery system, insulin delivery, wound healing and gene therapy, is presented. It also describes the utilization of GG based materials in food and petroleum industry. All the technical scientific issues have been addressed; highlighting the recent advancement.