Levan-based nanocarrier system for peptide and protein drug delivery: Optimization and influence of experimental parameters on the nanoparticle characteristics

Expanding the horizons of levan: from microbial biosynthesis to applications and advanced detection methods

Levan, a β-(2,6)-linked fructose polymer, exhibits diverse properties that impart versatility, rendering it a highly sought-after biopolymer with various industrial applications. Levan can be produced by various microorganisms using sucrose, food industry byproducts and agricultural wastes. Microbial levan represents the most potent cost-effective process for commercial-scale levan production. This study reviews the optimization of levan production by understanding its biosynthesis, physicochemical properties and the fermentation process. In addition, genetic and protein engineering for its increased production and emerging methods for its detection are introduced and discussed. All of these comprehensive studies could serve as powerful tools to optimize levan production and broaden its applications across various industries.

Electrosprayable Levan-Coated Nanoclusters and Ultrasound-Responsive Drug Delivery for Cancer Therapy

In this study, we synthesized levan shell hydrophobic silica nanoclusters encapsulating doxorubicin (L-HSi-Dox) and evaluated their potential as ultrasound-responsive drug delivery systems for cancer treatment. L-HSi-Dox nanoclusters were successfully fabricated by integrating a hydrophobic silica nanoparticle-doxorubicin complex as the core and an amphiphilic levan carbohydrate polymer as the shell by using an electrospray technique. Characterization analyses confirmed the stability, size, and composition of the nanoclusters. In particular, the nanoclusters exhibited a controlled release of Dox under aqueous conditions, demonstrating their potential as efficient drug carriers. The levanic groups of the nanoclusters enhanced the targeted delivery of Dox to specific cancer cells. Furthermore, the synergism between the nanoclusters and ultrasound effectively reduced cell viability and induced cell death, particularly in the GLUT5-overexpressing MDA-MB-231 cells. In a tumor xenograft mouse model, treatment with the nanoclusters and ultrasound significantly reduced the tumor volume and weight without affecting the body weight. Collectively, these results highlight the potential of the L-HSi-Dox nanoclusters and ultrasound as promising drug delivery systems with an enhanced therapeutic efficacy for biomedical applications.

Insights into the heterogeneity of levan polymers synthesized by levansucrase Bs-SacB from Bacillus subtilis 168

Levan is an enzymatically synthesized fructose polymer with widely reported structural heterogeneity depending on the producing levansucrase, the reaction conditions employed for its synthesis and the characterization techniques. We studied here the specific properties of levan produced by recombinant levansucrase from B. subtilis 168 (Bs-SacB), often characterized as a bimodal distribution, that is, a mixture of low and high molecular weight levan. We found significant differences between both levans in terms of the already reported molecular weight, size and morphology using different analytical methods. The low molecular weight levan consists of a non-uniform polymer ranging from 50 to 230 kDa, synthesized through a non-processive mechanism that can spontaneously form spherical nanoparticles in the reaction medium. In contrast, high molecular weight levan is a uniform polymer, most probably synthesized through a processive mechanism, with an average molecular weight of 30,750 kDa and a poorly defined nano-structure. This is the first report exploring differences in morphology between low and high molecular weight levans. Our findings demonstrate that only the low molecular weight levan forms spherical nanoparticles in the reaction medium and that high molecular weight levan is mainly composed of a 33,000 kDa fraction with a microgel behavior.

Traversing the diverse avenues of exopolysaccharides-based nanocarriers in the management of cancer

Exopolysaccharides are unique polymers generated by living organisms such as algae, fungi and bacteria to protect them from environmental factors. After a fermentative process, these polymers are extracted from the medium culture. Exopolysaccharides have been explored for their anti-viral, anti-bacterial, anti-tumor, and immunomodulatory effects. Specifically, they have acquired massive attention in novel drug delivery strategies owing to their indispensable properties like biocompatibility, biodegradability, and lack of irritation. Exopolysaccharides such as dextran, alginate, hyaluronic acid, pullulan, xanthan gum, gellan gum, levan, curdlan, cellulose, chitosan, mauran, and schizophyllan exhibited excellent drug carrier properties. Specific exopolysaccharides, such as levan, chitosan, and curdlan, have demonstrated significant antitumor activity. Moreover, chitosan, hyaluronic acid and pullulan can be employed as targeting ligands decorated on nanoplatforms for effective active tumor targeting. This review shields light on the classification, unique characteristics, antitumor activities and nanocarrier properties of exopolysaccharides. In addition, in vitro human cell line experiments and preclinical studies associated with exopolysaccharide-based nanocarriers have also been highlighted.

Recent Developments and Applications of Microbial Levan, A Versatile Polysaccharide-Based Biopolymer

Polysaccharides are essential components with diverse functions in living organisms and find widespread applications in various industries. They serve as food additives, stabilizers, thickeners, and fat substitutes in the food industry, while also contributing to dietary fiber for improved digestion and gut health. Plant-based polysaccharides are utilized in paper, textiles, wound dressings, biodegradable packaging, and tissue regeneration. Polysaccharides play a crucial role in medicine, pharmacy, and cosmetology, as well as in the production of biofuels and biomaterials. Among microbial biopolymers, microbial levan, a fructose polysaccharide, holds significant promise due to its high productivity and chemical diversity. Levan exhibits a wide range of properties, including film-forming ability, biodegradability, non-toxicity, self-aggregation, encapsulation, controlled release capacity, water retention, immunomodulatory and prebiotic activity, antimicrobial and anticancer activity, as well as high biocompatibility. These exceptional properties position levan as an attractive candidate for nature-based materials in food production, modern cosmetology, medicine, and pharmacy. Advancing the understanding of microbial polymers and reducing production costs is crucial to the future development of these fields. By further exploring the potential of microbial biopolymers, particularly levan, we can unlock new opportunities for sustainable materials and innovative applications that benefit various industries and contribute to advancements in healthcare, environmental conservation, and biotechnology.

Exopolysaccharides Producing Bacteria: A Review

Bacterial exopolysaccharides (EPS) are essential natural biopolymers used in different areas including biomedicine, food, cosmetic, petroleum, and pharmaceuticals and also in environmental remediation. The interest in them is primarily due to their unique structure and properties such as biocompatibility, biodegradability, higher purity, hydrophilic nature, anti-inflammatory, antioxidant, anti-cancer, antibacterial, and immune-modulating and prebiotic activities. The present review summarizes the current research progress on bacterial EPSs including their properties, biological functions, and promising applications in the various fields of science, industry, medicine, and technology, as well as characteristics and the isolation sources of EPSs-producing bacterial strains. This review provides an overview of the latest advances in the study of such important industrial exopolysaccharides as xanthan, bacterial cellulose, and levan. Finally, current study limitations and future directions are discussed.

Exploring the potential of Halomonas levan and its derivatives as active ingredients in cosmeceutical and skin regenerating formulations

Demand on natural products that contain biological ingredients mimicking growth factors and cytokines made natural polysaccharides popular in pharmaceutical and cosmetic industries. Levan is the β-(2-6) linked, nontoxic, biocompatible, water-soluble, film former fructan polymer that has diverse applications in pharmacy and cosmeceutical industries with its moisturizing, whitening, anti-irritant, anti-aging and slimming activities. Driven by the limited reports on few structurally similar levan polymers, this study presents the first systematic investigation on the effects of structurally different extremophilic Halomonas levan polysaccharides on human skin epidermis cells. In-vitro experiments with microbially produced linear Halomonas levan (HL), its hydrolyzed, (hHL) and sulfonated (ShHL) derivatives as well as enzymatically produced branched levan (EL) revealed increased keratinocyte and fibroblast proliferation (113-118 %), improved skin barrier function through induced expressions of involucrin (2.0 and 6.43 fold changes for HL and EL) and filaggrin (1.74 and 3.89 fold changes for hHL and ShHL) genes and increased type I collagen (2.63 for ShHL) and hyaluronan synthase 3 (1.41 for HL) gene expressions together with fast wound healing ability within 24 h (100 %, HL) on 2D wound models clearly showed that HL and its derivatives have high potential to be used as natural active ingredients in cosmeceutical and skin regenerating formulations.

Levan nanoparticles with intrinsic CD44-targeting ability for tumor-targeted drug delivery

Existing anticancer therapeutics exhibit short half-lives, non-specificity, and severe side effects. To address this, active-targeting nanoparticles have been developed; however, the complex fabrication procedures, scale-up, and low reproducibility delay FDA approval, particularly for functionalized nanoparticles. We developed levan nanoparticles via simple one-pot nanoprecipitation for specific anticancer drug delivery. Levan is a plant polysaccharide which has a binding affinity to CD44 receptors and amphiphilicity. The nanoparticles are self-assembled and enable active-targeting without chemical modifications. The paclitaxel-loaded levan nanoparticles (PTX@LevNP) demonstrated a sustained PTX release and long-term stability. The LevNP can bind CD44 receptors on cancer cells, and PTX@LevNP showed enhanced anticancer activity in CD44-positive cells (SCC7 cells). In SCC7 tumor-bearing mice, the accumulation of LevNP in tumor tissue was 3.7 times higher than that of the free-dye, resulting in improved anticancer efficacy of PTX@LevNP. This new strategy using levan can produce nanoparticles for effective cancer treatment without complex fabrication procedures.

Microbial Exopolysaccharide Composites in Biomedicine and Healthcare: Trends and Advances

Microbial exopolysaccharides (EPSs), e.g., xanthan, dextran, gellan, curdlan, etc., have significant applications in several industries (pharma, food, textiles, petroleum, etc.) due to their biocompatibility, nontoxicity, and functional characteristics. However, biodegradability, poor cell adhesion, mineralization, and lower enzyme activity are some other factors that might hinder commercial applications in healthcare practices. Some EPSs lack biological activities that make them prone to degradation in ex vivo, as well as in vivo environments. The blending of EPSs with other natural and synthetic polymers can improve the structural, functional, and physiological characteristics, and make the composites suitable for a diverse range of applications. In comparison to EPS, composites have more mechanical strength, porosity, and stress-bearing capacity, along with a higher cell adhesion rate, and mineralization that is required for tissue engineering. Composites have a better possibility for biomedical and healthcare applications and are used for 2D and 3D scaffold fabrication, drug carrying and delivery, wound healing, tissue regeneration, and engineering. However, the commercialization of these products still needs in-depth research, considering commercial aspects such as stability within ex vivo and in vivo environments, the presence of biological fluids and enzymes, degradation profile, and interaction within living systems. The opportunities and potential applications are diverse, but more elaborative research is needed to address the challenges. In the current article, efforts have been made to summarize the recent advancements in applications of exopolysaccharide composites with natural and synthetic components, with special consideration of pharma and healthcare applications.

Dual-functional carboxymethyl levan-based protein carrier for cosmeceutical application of human epidermal growth factor

Human epidermal growth factor (hEGF) has been a subject of extensive research as its wide range of physiological functions has many potential applications. However, due to the low stability of hEGF, its physiological effect is easily lost under conditions of use. To compensate for this, we developed a stable delivery system using levan-based nanoparticles. The entrapment yield of various tested proteins was significantly improved by employing carboxymethyl levan (CML) instead of levan; the entrapment yield of the CML-hEGF nanoparticles was 84.1 %. The size and zeta potential of the nanoparticles were identified as 199.9 ± 3.87 nm and -19.1 mV, respectively, using scanning electron microscopy (SEM) and particle size analysis. Dual biological functions of the nanoparticles (skin regeneration and moisturizing) were identified through collagen synthesis activity and aquaporin 3 expression level analysis. Stability of the prepared nanoparticles was also investigated via cell proliferation activity comparison under mimicked physiological conditions. The CML-hEGF nanoparticles maintained cell proliferation activity over 100 % for 6 weeks, while free hEGF was almost inactivated within 2 weeks. Taken together, our results indicate that the CML-based hEGF nanoparticles can be used in pharma- and cosmeceutical applications, guaranteeing a high entrapment capability, functionality, and stability.

Effects of stirring speed ladder on the acid-promoted refolding of rice glutelin

The effects of stirring speed (0, 250, 500, 750, 1000, 1250, and 1500 rpm) on the rice glutelin hydrocolloids (1 %, w/v) during the acidified process were investigated. As the stirring speed was increased to 750 rpm, the hydration diameter of the rice glutelin was significantly decreased, but higher stirring speeds had no significant effect on size. The highest and lowest solubility were recorded for the samples treated at 750 and 0 rpm stirring speeds, respectively. The surface hydrophobicity and molecular weight increased first and then decreased, both the minimum value was recorded at 750 rpm sample. The principal component analysis (PCA) was employed to detect patterns between changes in various properties (solubility, particle size, β-sheet content, surface hydrophobicity, and ζ-potential) and stirring treatment. To conclude, the various properties of rice glutelin refold during acidification are drastically affected by employing different stirring speeds. Choosing a suitable stirring speed is important for quality control in protein hydrocolloid production.

UV and Chemically Induced Halomonas smyrnensis Mutants for Enhanced Levan Productivity

Halomonas smyrnensis AAD6^T is a moderately halophilic bacterium proven to be a powerful biotechnological tool with its ability to accumulate valuable biopolymers such as levan and poly(3-hydroxybutyrate) (PHB). Levan is a fructose homopolymer with β-2,6 fructofuranosidic linkages on the polymer backbone, and its distinctive applications in various industries such as food, pharmaceutical, medical, and chemical have been well-defined. On the other hand, PHB is a promising raw material to produce biodegradable plastics. Although it was shown in our previous studies that H. smyrnensis AAD6^T exhibits one of the highest conversion yields of sucrose to levan reported to date, novel strategies are required to overcome high costs of levan production. In this study, we aimed at increasing levan productivity of H. smyrnensis AAD6^T cultures using random mutagenesis techniques combined (i.e., ethyl methanesulfate treatment and/or ultraviolet irradiation). After several consecutive treatments, mutant strains BAE2, BAE5 and BAE6 were selected as efficient levan producers, as BAE2 standing out as the most efficient one not only in sucrose utilization and levan production rates, but also in final PHB concentrations. The mutants' whole genome sequences were analysed to determine the mutations occurred. Several mutations in genes related to central carbon metabolism and osmoregulation were found. Our results suggest that random mutagenesis can be a facile and efficient strategy to enhance the performance of extremophiles in adverse conditions.

The anticancer activity of doxorubicin-loaded levan-functionalized gold nanoparticles synthesized by laser ablation

Here, gold nanoparticles (AuNPs) were synthesized upon exposure to nano-pulsed Nd-YAG laser irradiation in de-ionized water (PLAL) and functionalized with levan polysaccharide for assessing the anticancer efficacy of doxorubicin (DOX)-conjugated levan-capped AuNPs complexes to MCF-7 breast cancer cells. According to the physicochemical test results, the increments in levan amount enhanced the colloidal stability and the drug encapsulation efficiency (DEE) significantly. For the 10L-AuNP group having the highest levan amount (10 mg/mL levan), DEE was calculated as 92.21 ± 0.56%. The lean levan, uncapped AuNPs, and 10L-AuNP were found non-cytotoxic (>80% cell viability) in the studied concentrations with 48 h MTT assays. At higher DOX loadings (25, 50, and 100 μg/mL) of 10L-AuNP, the cell viability reduced significantly compared to free DOX. Overall, these nanoparticle complexes could be proposed as potent drug delivery vehicles for cancer drugs such as DOX, as well as other drugs in the prospective studies.

Applications of Microbial Exopolysaccharides in the Food Industry

Exopolysaccharides (EPSs) are high molecular weight polysaccharides secreted by microorganisms in the surrounding environment. In addition to the favorable benefits of these compounds for microorganisms, including microbial cell protection, they are used in various food, pharmaceutical, and cosmetic industries. Investigating the functional and health-promoting characteristics of microbial EPS, identifying the isolation method of these valuable compounds, and their applications in the food industry are the objectives of this study. EPS are used in food industries as thickeners, gelling agents, viscosifiers, and film formers. The antioxidative, anticancer, prebiotic, and cholesterol-lowering effects of some of these compounds make it possible to use them in functional food production.

Synergistic enzyme cocktail between levansucrase and inulosucrase for superb levan-type fructooligosaccharide synthesis

Inulosucrase (ISC) and levansucrase (LSC) utilise sucrose and produce inulin- and levan-type fructans, respectively. This study aims to propose a new strategy to improve levan-type fructooligosaccharide (L-FOS) production. The effect of ISC/ LSC -mixed reaction was elucidated on L-FOS production. The presence of ISC in the LSC reaction significantly leads to the higher production of L-FOSs as the main products. Furthermore, the different ratios between ISC and LSC affected the distribution of L-FOSs. A greater amount of ISC compared to LSC promoted the synthesis of short-chain L-FOSs. Conversely, when LSC was increased, the synthesis of longer-chain L-FOSs was enhanced. The addition of trisaccharide mixtures obtained from either a single ISC or LSC reaction could enhance L-FOSs synthesis in the LSC reaction. Analysis of these trisaccharides revealed that most species of the oligosaccharides were similar, with 1-kestose being the major one. The supplement of only 1-kestose in the LSC reaction showed similar results to those of the reaction in the presence of trisaccharide mixtures. Moreover, the results were supported by molecular dynamics simulations. This work not only provides an improvement in L-FOS production but also revealed and supported some insights into the mechanism of fructansucrases.

Levan enhanced the NF-κB suppression activity of an oral nano PLGA-curcumin formulation in breast cancer treatment

Chemoresistance (CR) is one of the reasons why chemotherapy agents like Gemcitabine (GMC) remain insufficient in healing breast cancer. Activation of Nuclear Factor-kappa B (NF-κB) during chemotherapy is known as an important factor in the development of CR. The hydrophobic polyphenol curcumin is shown to inhibit NF-κB and hence CR. The aim of this work was to increase the poor bioavailability of curcumin by loading it into the nano-micelles made of Poly (Lactide-co-Glycolide) (PLGA) and levan, where levan as a natural fructose homopolymer makes the nano-micelle more stable and increases its uptake using the fructose moieties. In this study, a PLGA-levan-curcumin formulation (PLC) was designed and characterized. The size was measured as 154.16 ± 1.45 nm with a 67.68% encapsulation efficiency (EE%). The incorporation between the components was approved. Levan made the nano-micelles stable for at least three months, increased their uptake, and led to a 10,000-fold increase in the solubility of curcumin. The enhanced bioavailability of curcumin reduced the NF-κB levels elevated by GMC, both in vitro and in vivo. The PLC showed a complete tumor treatment, while GMC only showed a rate of 52%. These point to the great potential of the PLC to be used simultaneously with chemotherapy.

Synthesis and characterization of levan hydrogels and their use for resveratrol release

Considering the need for systematic studies on levan based hydrogels to widen their use in drug delivery systems and biomedical applications, this study is mainly focused on the synthesis and comprehensive characterization as well as drug release properties of hydrogels based on Halomonas levan (HL) and its chemical derivatives. For this, hydrolyzed and phosphonated HL derivatives were chemically synthesized and then cross-linked with 1,4-Butanediol diglycidyl ether (BDDE) and the obtained hydrogels were characterized in terms of their swelling, adhesivity, and rheological properties. Both native and phosphonated HL hydrogels retained their rigid gel like structure with increasing shear stress levels and tack test analysis showed superior adhesive properties of the phosphonated HL hydrogels. Moreover, hydrogels were loaded with resveratrol and entrapment and release studies as well as cell culture studies with human keratinocytes were performed. Biocompatible and adhesive features of the hydrogels confirmed their suitability for tissue engineering and drug delivery applications.

Resveratrol-Loaded Levan Nanoparticles Produced by Electrohydrodynamic Atomization Technique

Considering the significant advances in nanostructured systems in various biomedical applications and the escalating need for levan-based nanoparticles as delivery systems, this study aimed to fabricate levan nanoparticles by the electrohydrodynamic atomization (EHDA) technique. The hydrolyzed derivative of levan polysaccharide from Halomonas smyrnensis halophilic bacteria, hydrolyzed Halomonas levan (hHL), was used. Nanoparticles were obtained by optimizing the EHDA parameters and then they were characterized in terms of morphology, molecular interactions, drug release and cell culture studies. The optimized hHL and resveratrol (RS)-loaded hHL nanoparticles were monodisperse and had smooth surfaces. The particle diameter size of hHL nanoparticles was 82.06 ± 15.33 nm. Additionally, release of RS from the fabricated hHL nanoparticles at different pH conditions were found to follow the first-order release model and hHL with higher RS loading showed a more gradual release. In vitro biocompatibility assay with human dermal fibroblast cell lines was performed and cell behavior on coated surfaces was observed. Nanoparticles were found to be safe for healthy cells. Consequently, the fabricated hHL-based nanoparticle system may have potential use in drug delivery systems for wound healing and tissue engineering applications and surfaces could be coated with these electrosprayed particles to improve cellular interaction.

A review of extracellular polysaccharides from extreme niches: An emerging natural source for the biotechnology. From the adverse to diverse!

Every year, new organisms that survive and colonize adverse environments are discovered and isolated. Those organisms, called extremophiles, are distributed throughout the world, both in aquatic and terrestrial environments, such as sulfurous marsh waters, hydrothermal springs, deep waters, volcanos, terrestrial hot springs, marine saltern, salt lakes, among others. According to the ecosystem inhabiting, extremophiles are categorized as thermophiles, psychrophiles, halophiles, acidophiles, alkalophilic, piezophiles, saccharophiles, metallophiles and polyextremophiles. They have developed chemical adaptation strategies that allow them to maintain their cellular integrity, altering physiology or improving repair capabilities; one of them is the biosynthesis of extracellular polysaccharides (EPS), which constitute a slime and hydrated matrix that keep the cells embedded, protecting from environmental stress (desiccation, salinity, temperature, radiation). EPS have gained interest; they are explored by their unique properties such as structural complexity, biodegradability, biological activities, and biocompatibility. Here, we present a review concerning the biosynthesis, characterization, and potential EPS applications produced by extremophile microorganisms, namely, thermophiles, halophiles, and psychrophiles. A bibliometric analysis was conducted, considering research articles published within the last two decades. Besides, an overview of the culture conditions used for extremophiles, the main properties and multiple potential applications of their EPS is also presented.

Polymer Based Bioadhesive Biomaterials for Medical Application-A Perspective of Redefining Healthcare System Management

This article deliberates about the importance of polymer-based bioadhesive biomaterials' medical application in healthcare and in redefining healthcare management. Nowadays, the application of bioadhesion in the health sector is one of the great interests for various researchers, due to recent advances in their formulation development. Actually, this area of study is considered as an active multidisciplinary research approach, where engineers, scientists (including chemists, physicists, biologists, and medical experts), material producers and manufacturers combine their knowledge in order to provide better healthcare. Moreover, while discussing the implications of value-based healthcare, it is necessary to mention that health comprises three main domains, namely, physical, mental, and social health, which not only prioritize the quality healthcare, but also enable us to measure the outcomes of medical interventions. In addition, this conceptual article provides an understanding of the consequences of the natural or synthetic polymer-based bioadhesion of biomaterials, and its significance for redefining healthcare management as a novel approach. Furthermore, the research assumptions highlight that the quality healthcare concept has recently become a burning topic, wherein healthcare service providers, private research institutes, government authorities, public service boards, associations and academics have taken the initiative to restructure the healthcare system to create value for patients and increase their satisfaction, and lead ultimately to a healthier society.

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.

Evaluation of the Potential Use of Levan Polysaccharide in Paper Conservation

Conservation of paper-based materials, namely, manuscripts, includes repair of tears, gap filling, consolidation, and fixation, which requires the use of adhesives. The adhesive in use for these purposes should be compatible with the chemical and physical properties of paper and should present good aging characteristics. In this study, we conducted a set of experiments with paper samples on which fructan-based biopolymer Halomonas levan (Hlevan) was applied for the first time and compared with glucan-based adhesive starch. Adhesive-applied samples were initially prepared by the application of different historical recipes of sizing and ink. Then, they underwent accelerated thermal aging. Chemical and physical changes of paper samples (crystallinity, pH, and color) were analyzed. Finally, Principal Component Analysis was performed to identify dominating factors affecting sample behavior with applied adhesives. This study demonstrates the aging characteristics of Hlevan on cellulose-based materials. The results showed that there is a color shift from blue to yellow for all samples after aging, but it is more pronounced for some samples with Hlevan. In addition, Hlevan is slightly less acidic than starch in all cases and acted as a plasticizer for a specific kind of sizing material. The methodology of this research is also efficacious in terms of understanding the interaction of paper media with the adhesives and their effects on aging.

Control of microbial biofilm formation as an approach for biomaterials synthesis

The search for new biomaterials with superior mechanical properties is the focus in the area of materials science. A promising pathway is drawing inspiration from nature to design and develop materials with enhanced properties. In this work, a novel strategy to produce functionalized supramolecular bionanomaterials from the microbial biofilm is reported. Tuneable biofilms with specific characteristics were obtained by controlling the culture condition of the microorganism. When the exopolysaccharide (EPS) production was desired the tryptone was the best nutritional component for the EPS production into the biofilm. However, for the expression of a high amount of amyloid protein the combination of peptone and glucose was the best nutritional choice. Each biofilm obtained showed its owner rheology properties. These properties were altered by the addition of extracellular DNA, which increased the viscosity of the biofilm and induced a viscoelastic hydrogel behavior. Besides, as a proof of concept of bionanomaterial, a novel supramolecular polymeric hybrid EPS-Amyloid protein (EPAP) was obtained from the biofilm and it was tested as a new natural functionalized support for enzyme immobilization. The results suggest that this technology could be used as a new concept to obtain biomaterials from biofilms by controlling the nutritional conditions of a microorganism. Understanding environmental factors affecting biofilm formation will help the development of methods for controlling biofilm production and therefore obtaining new biomaterials.

Levan-based nanostructured systems: An overview

Bacterial levan is a fructose homopolymer that offers great potential in biotechnological applications due to biocompatibility, biodegradability and non-toxicity. This biopolymer possesses diverse multifunctional features, which translates into a wide range of applicability, including in industry, consumer products, pharmaceuticals and biomedicine. Extensive research has identified great potential for its exploitation in human health. In addition, nanostructured systems have provided significant advances in the area of health, mainly with respect to disease diagnosis and treatment. While the functional properties of these natural polysaccharide-based polymers are desirable in these systems, research in this area has been limited to few natural polymers, such as chitosan, alginate and dextran, which obscures the true potential of levan in the production of nanostructured systems for biotechnological and medical applications. The present review considers the latest research in the field to focus on the use of levan as a promising biopolymer for the development of nanomaterials.

Colloidal stability and biological activity evaluation of microbial exopolysaccharide levan-capped gold nanoparticles

The main objectives of this study were to explore the suitability of the exopolysaccharide levan, biosynthesized by Bacillus subtilis, to aid in the formation of gold nanoparticles (AuNPs) and to investigate the colloidal stability and in vitro biological activity of this biopolymer-AuNPs complex. AuNPs (mainly spherical, 8-10 nm-sized, and monodispersed) were successfully synthesized in levan concentrations up to 0.5% w/v (L-AuNP0.5) while exposed to ultraviolet C (UVC) irradiation. The increase of levan quantity decreased the size of AuNPs according to Transmission Electron Microscopy (TEM) images and enhanced the colloidal stability significantly. The presence of L-AuNP0.5 at the highest treatment dose (1000 μg/mL) exhibited substantial cytotoxicity towards L-929 mouse fibroblasts for all incubation periods. Dose-dependent toxicity was observed for the first day while, after this threshold value, medium (100 μg/mL) and the lowest (10 μg/mL) treatment doses were non-cytotoxic during 7 days of incubation, implying dose and time-independent cell viabilities (> 95%) compared to the negative control (complete cell culture medium). There occurred a special surface interaction with cells and L-AuNP0.5, especially when the cells were subjected to deliberate starvation periods to increase L-AuNP0.5 internalization via passive and active endocytosis. Scanning Electron Microscopy (SEM) images showed high accumulation of L-AuNP0.5 around or inside the cell membrane after 7 days. Overall, this attribute (high uptake of L-AuNP0.5) could make them promising candidates for prospective cancer therapeutics or drug delivery systems by enabling the cell internalization of anticancer drugs.

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.

Efficient production of levan using a recombinant yeast Saccharomyces cerevisiae hypersecreting a bacterial levansucrase

Levan is a fructose polymer with diverse applications in the food and medical industries. In this study, levansucrase from Rahnella aquatilis (RaLsrA) was hyper-secreted using a Saccharomyces cerevisiae protein secretion system. An optimal secretion signal, a translation fusion partner (TFP) containing an N-terminal 98 amino acid domain from a mitochondrial inner membrane protein, UTH1, was employed to secrete approximately 50 U/mL of bioactive RaLsrA into culture media with 63% secretion efficiency by fed-batch fermentation. Although the purified RaLsrA was useful for enzymatic conversion of high-molecular-weight levan of approximately 3.75 × 10⁶ Da, recombinant yeast secreting RaLsrA could produce levan more efficiently by microbial fermentation. In a 50-L scale fermenter, 76-g/L levan was directly converted from 191-g/L sucrose by recombinant yeast cells, attaining an 80% conversion yield and 3.17-g/L/h productivity. Thus, we developed a cost-effective and industrially applicable production system for food-grade levan.

Preparation of a novel water-soluble gel from Erwinia amylovora levan

Less attention has been focused on the industrial applications of levan-type fructan than that of inulin. Levan-type fructan is a unique homopolysaccharide consisting of fructose residues with a β-(2, 6) linkage that possesses unique physiochemical properties such as low intrinsic viscosity. In this study, the recombinant levansucrase from Erwinia amylovora was used to efficiently produce levan from sucrose, and under optimised conditions, 195 g/L levan was produced from 500 g/L sucrose, with the highest conversion rate of 59%. The physicochemical properties of E. amylovora levan, such as surface morphology, thermal behaviour, rheology behaviour and texture analysis, were evaluated and compared with those of commercial gels, including xanthan, guar, carrageenan and Arabic gums. The produced E. amylovora levan showed a series of acceptable physicochemical properties, indicating a potential application for levan as a novel water-soluble micro gel. The conclusions of this study support the exploration of the use of more hydrogels in the food, medicinal and cosmetic industries.

An injectable and physical levan-based hydrogel as a dermal filler for soft tissue augmentation

A novel levan-based injectable hydrogel was developed as a dermal filler having better in vivo stability and efficacy compared to HA-based hydrogel.