Particulate bioaerogels for respiratory drug delivery

The bioaerogel microparticles have been recently developed for respiratory drug delivery and attract fast increasing interests. These highly porous microparticles have ultralow density and hence possess much reduced aerodynamic diameter, which favour them with greatly enhanced dispersibility and improved aerosolisation behaviour. The adjustable particle geometric dimensions by varying preparation methods and controlling operation parameters make it possible to fabricate bioaerogel microparticles with accurate sizes for efficient delivery to the targeted regions of respiratory tract (i.e. intranasal and pulmonary). Additionally, the technical process can provide bioaerogel microparticles with the opportunities of accommodating polar, weak polar and non-polar drugs at sufficient amount to satisfy clinical needs, and the adsorbed drugs are primarily in the amorphous form that potentially can facilitate drug dissolution and improve bioavailability. Finally, the nature of biopolymers can further offer additional advantageous characteristics of improved mucoadhesion, sustained drug release and subsequently elongated time for continuous treatment on-site. These fascinating features strongly support bioaerogel microparticles to become a novel platform for effective delivery of a wide range of drugs to the targeted respiratory regions, with increased drug residence time on-site, sustained drug release, constant treatment for local and systemic diseases and anticipated better-quality of therapeutic effects.

Low-temperature superelastic, anisotropic, silane-crosslinked sodium alginate aerogel for thermal insulation

Bio-aerogels have attracted much attention owing to their remarkable properties, but their brittle and poor elasticity has limited their further applications. Here, we propose a strategy of in-situ silanization crosslinking combined with unidirectional freeze casting (SUFC) to prepare superelastic sodium alginate (SA) aerogels. The resulting aerogel was ultra-light (0.048 g/cm3), high porosity (96.86 %), and self-extinguishing from fire. Aerogels exhibited anisotropic properties, such as low-temperature elasticity (500 g compression at -70 °C 10-cycle, 99.6 % recovery), exceptional fatigue resistance (100-cycle at 50 % strain), and excellent thermal insulation (0.0696 W·m-1·K-1). Thus, the SUFC strategy provides considerable freedom for constructing multi-material, lamellar/honeycomb structured alginate-based aerogels, which pave the way to thermal insulation development at low temperatures.

Low-adhesion and low-swelling hydrogel based on alginate and carbonated water to prevent temporary dilation of wound sites

Hydrogel-based wound dressings have been developed for rapid wound healing; however, their adhesive properties have not been adequately investigated. Excessive adhesion to the skin causes wound expansion and pain when hydrogels absorb exudates and swell at wound sites. Herein, we developed a low-adhesion and low-swelling hydrogel dressing using alginate, which is non-adhesive to cells and skin tissue, CaCO3, and carbonated water. The alginate/CaCO3 solution rapidly formed a hydrogel upon the addition of carbonated water, and the CO2 in the hydrogel diffused into the atmosphere, preventing acidification and obtaining a pH value suitable for wound healing. Remarkably, the skin adhesion and swelling of the hydrogel were 11.9- to 16.5-fold and 1.9-fold lower, respectively, than those of clinical low-adhesion hydrogel dressings. In vivo wound-healing tests in mice demonstrated its therapeutic efficacy, and the prepared hydrogel prevented temporary wound dilation during early healing. These results illustrate the importance of controlling skin adhesion and swelling in wound dressings and demonstrate the potential clinical applications of this wound-friendly hydrogel dressing.

Investigation of Gelation Techniques for the Fabrication of Cellulose Aerogels

Because of the pronounced degradation of the environment, there has been an escalated demand for the fabrication of eco-friendly and highly efficient products derived from renewable sources. Cellulose aerogels have attracted significant interest attributable to their structural characteristics coupled with biodegradability and biocompatibility. The features of the molecular structure of cellulose allow for the use of various methods in the production of gels. For instance, the presence of hydroxyl groups on the cellulose surface allows for chemical crosslinking via etherification reactions. On the other hand, cellulose gel can be procured by modulating the solvent power of the solvent. In this study, we investigate the impact of the gelation methodology on the structural attributes of aerogels. We present methodologies for aerogel synthesis employing three distinct gelation techniques: chemical crosslinking, cryotropic gelation, and CO2-induced gelation. The outcomes encompass data derived from helium pycnometry, Fourier-transform infrared spectroscopy, nitrogen porosimetry, and scanning electron microscopy. The resultant specimens exhibited a mesoporous fibrous structure. It was discerned that specimens generated through cryotropic gelation and CO2-induced gelation manifested higher porosity (93-95%) and specific surface areas (199-413 m2/g) in contrast to those produced via chemical crosslinking (porosity 72-95% and specific surface area 25-133 m2/g). Hence, this research underscores the feasibility of producing cellulose-based aerogels with enhanced characteristics, circumventing the necessity of employing toxic cross-linking agents. The process of gel formation through chemical crosslinking enables the creation of gels with enhanced mechanical properties and a more resilient structure. Two alternative methodologies prove particularly advantageous in applications necessitating biocompatibility and high porosity. Notably, CO2-induced gelation has not been hitherto addressed in the literature as a means to produce cellulose gels. The distinctive feature of this approach resides in the ability to combine the stages of obtaining an aerogel in one apparatus.

Hyaluronic Acid Aerogels Made Via Freeze-Thaw-Induced Gelation

The biodegradability, biocompatibility, and bioactivity of hyaluronic acid (HA), a natural polysaccharide, combined with the low density, high porosity, and high specific surface area of aerogels attract interest for biomedical applications such as wound dressings. In this work, physically cross-linked HA aerogels were prepared via the freeze-thaw (FT) induced gelation method, solvent exchange, and drying with supercritical CO2. The morphology and properties of HA aerogels (volume shrinkage, density, and specific surface area) were investigated as a function of several process parameters: HA concentration, solution pH, number of FT cycles, and type of nonsolvent used during solvent exchange. We demonstrate that the HA solution pH plays a key role in the aerogel formation, as not all conditions result in materials with high specific surface area. HA aerogels were of low density (<0.2 g/cm3), high specific surface area (up to 600 m2/g), and high porosity (≥90%). Scanning electron microscopy pictures revealed that HA aerogels present a porous structure with meso- and small macropores. The results show that HA aerogels are promising biomaterials with tunable properties and internal structure that offer high potential as, e.g., wound dressings.

State of Innovation in Alginate-Based Materials

This review article presents past and current alginate-based materials in each application, showing the widest range of alginate's usage and development in the past and in recent years. The first segment emphasizes the unique characteristics of alginates and their origin. The second segment sets alginates according to their application based on their features and limitations. Alginate is a polysaccharide and generally occurs as water-soluble sodium alginate. It constitutes hydrophilic and anionic polysaccharides originally extracted from natural brown algae and bacteria. Due to its promising properties, such as gelling, moisture retention, and film-forming, it can be used in environmental protection, cosmetics, medicine, tissue engineering, and the food industry. The comparison of publications with alginate-based products in the field of environmental protection, medicine, food, and cosmetics in scientific articles showed that the greatest number was assigned to the environmental field (30,767) and medicine (24,279), whereas fewer publications were available in cosmetic (5692) and food industries (24,334). Data are provided from the Google Scholar database (including abstract, title, and keywords), accessed in May 2023. In this review, various materials based on alginate are described, showing detailed information on modified composites and their possible usage. Alginate's application in water remediation and its significant value are highlighted. In this study, existing knowledge is compared, and this paper concludes with its future prospects.

In vivo tests of a novel wound dressing based on agar aerogel

Aerogels, especially bio-based ones, present a promising option for wound dressing; specifically, because of their low toxicity, high stability, bio-compatibility, and good biological performance. In this study, agar aerogel was prepared and evaluated as novel wound dressing material in an in vivo rat study. Agar hydrogel was prepared by thermal gelation, after that the water inside the gel was exchanged with ethanol, and finally the alcogel was dried by supercritical CO₂. The textural and rheological properties of the prepared aerogel were characterized, showing that the prepared agar aerogels possess high porosity (97-98 %), high surface area (250-330 m²g^-1) as well as good mechanical properties and easiness of removal from the wound site. The results of the in vivo experiments macroscopically demonstrate the tissue compatibility of the aerogels in dorsal interscapular injured rat tissue and a shorter wound healing time comparable to that of gauze-treated animals. The histological analysis underpins the reorganisation and healing of the tissue for the injured skin of rats treated with agar aerogel wound dressing within the studied time frame.

Physicochemical Properties of Egg-Box-Mediated Hydrogels with Transiently Decreased pH Employing Carbonated Water

Anionic polysaccharides, including low-methoxy (LM) pectin, are extensively used in biomaterial applications owing to their safety, biocompatibility, and feasibility in constructing supramolecular assemblies by forming egg-box structures with divalent cations. Mixing an LM pectin solution with CaCO₃ spontaneously forms a hydrogel. The gelation behavior can be controlled by adding an acidic compound to change the solubility of CaCO₃. CO₂ is used as the acidic agent and can be easily removed after gelation, thereby reducing the acidity of the final hydrogel. However, CO₂ addition has been controlled under varied thermodynamical conditions; therefore, specific CO₂ effects on gelation are not necessarily visualized. To evaluate the CO₂ impact on the final hydrogel, which would be extended to control hydrogel properties further, we utilized carbonated water to supply CO₂ into the gelation mixture without changing its thermodynamic conditions. The addition of the carbonated water accelerated gelation and significantly increased the mechanical strength, promoting cross-linking. However, the CO₂ volatilized into the atmosphere, and the final hydrogel became more alkaline than that without the carbonated water, probably because a considerable amount of the carboxy group was consumed for cross-linking. Moreover, when aerogels were prepared from the hydrogels with carbonated water, they exhibited highly ordered networks of elongated porosity in scanning electron microscopy, proposing an intrinsic structural change by CO₂ in the carbonated water. We also controlled the pH and strength of the final hydrogels by changing the CO₂ amounts in the carbonated water added, thereby validating the significant effect of CO₂ on hydrogel properties and the feasibility of using carbonated water.

Trends and challenges in the development of bio-based barrier coating materials for paper/cardboard food packaging; a review

Currently, petroleum-based synthetic plastics are used as a key barrier material in the paper-based packaging of several food and nonfood goods. This widespread usage of plastic as a barrier lining is not only harmful to human and marine health, but it is also polluting the ecosystem. Researchers and food manufacturers are focused on biobased alternatives because of its numerous advantages, including biodegradability, biocompatibility, non-toxicity, and structural flexibility. When used alone or in composites/multilayers, these biobased alternatives provide strong barrier qualities against grease, oxygen, microbes, air, and water. According to the most recent literature reports, biobased polymers for barrier coatings are having difficulty breaking into the business. Technological breakthroughs in the field of bioplastic production and application are rapidly evolving, proffering new options for academics and industry to collaborate and develop sustainable packaging solutions. Existing techniques, such as multilayer coating of nanocomposites, can be improved further by designing them in a more systematic manner to attain the best barrier qualities. Modified nanocellulose, lignin nanoparticles, and bio-polyester are among the most promising future candidates for nanocomposite-based packaging films with high barrier qualities. In this review, the state-of-art and research advancements made in biobased polymeric alternatives such as paper and board barrier coating are summarized. Finally, the existing limitations and potential future development prospects for these biobased polymers as barrier materials are reviewed.

Polylactide-Grafted Metal-Alginate Aerogels

Τhis work describes the synthesis of PLA-grafted M-alginate (g-M-alginate; M: Ca²⁺, Co²⁺, Ni²⁺, Cu²⁺) aerogels. DL-lactide (LA) was attached on the surface of preformed M-alginate beads and was polymerized, using stannous octoate as catalyst and the –OH groups of the alginate backbone as initiators/points of attachment. The material properties of g-M-alginate aerogels were not affected much by grafting, because the linear PLA chains grew on the M-alginate framework like a brush and did not bridge their points of attachment as in polyurea-crosslinked M-alginate aerogels. Thus, all g-M-alginate aerogels retained the fibrous morphology of their parent M-alginate aerogels, and they were lightweight (bulk densities up to 0.24 g cm⁻³), macroporous/mesoporous materials with high porosities (up to 96% v/v). The BET surface areas were in the range of 154–542 m² g⁻¹, depending on the metal, the nature of the alginate framework and the PLA content. The latter was found at about 15% w/w for Ca- and Ni-based materials and at about 29% w/w for Co- and Cu-based materials. Overall, we have demonstrated a new methodology for the functionalization of alginate aerogels that opens the way to the synthesis of polylactide-crosslinked alginate aerogels with the use of multifunctional monomers.

Alginate/κ-carrageenan oral microcapsules loaded with Agaricus bisporus polysaccharides MH751906 for natural killer cells mediated colon cancer immunotherapy

The current study explores the effect of the extracted novel Mushroom polysaccharides and its formulation onto Alginate (Alg.)/kappa carrageenan microcapsules to exert immunotherapeutic effect upon activating gut resident natural killer cells (NK) against colon cancer. The extracted polysaccharides of Agaricus bisporus MH751906 was microcapsulated in Alg/κ-carrageenan microcapsules as an oral delivery system for colon cancer. The microcapsule is characterized by SEM, FTIR, Raman and TGA; and showed a superior acidic stability, controlled release, and thermal stability at high temperature with higher hydrogel swelling rate in colon-mimicking pH. Upon activation of human NK cells with microcapsules (^ANK cells), a significant increase in CD16⁺CD56⁺ NK cell populations were recorded. These activated NK cells showed 74.09% cytotoxic effects against human colon cancer Caco-2 cells where majority of cancer cell populations arrested at G0/G1 phase leading to apoptosis. The apoptotic molecular mechanism induced by ^ANK cells on Caco-2 treated cells is through down regulations of both BCL2 and TGF surviving genes and up regulation in IkappaB-α gene expression. Therefore, this novel polysaccharides-alginate/κ-carrageenan microcapsules can be used as an oral targeted delivery system for colon cancer immunotherapy.

Alginate-Based Smart Materials and Their Application: Recent Advances and Perspectives

Nature produces materials using available molecular building blocks following a bottom-up approach. These materials are formed with great precision and flexibility in a controlled manner. This approach offers the inspiration for manufacturing new artificial materials and devices. Synthetic artificial materials can find many important applications ranging from personalized therapeutics to solutions for environmental problems. Among these materials, responsive synthetic materials are capable of changing their structure and/or properties in response to external stimuli, and hence are termed "smart" materials. Herein, this review focuses on alginate-based smart materials and their stimuli-responsive preparation, fragmentation, and applications in diverse fields from drug delivery and tissue engineering to water purification and environmental remediation. In the first part of this report, we review stimuli-induced preparation of alginate-based materials. Stimuli-triggered decomposition of alginate materials in a controlled fashion is documented in the second part, followed by the application of smart alginate materials in diverse fields. Because of their biocompatibility, easy accessibility, and simple techniques of material formation, alginates can provide solutions for several present and future problems of humankind. However, new research is needed for novel alginate-based materials with new functionalities and well-defined properties for targeted applications.

Cellulose-Based Hydrogels and Aerogels Embedded with Silver Nanoparticles: Preparation and Characterization

The paper presents the preparation and characterization of novel composite materials based on microcrystalline cellulose (MCC) with silver nanoparticles (Ag NPs) in powder and gel forms. We use a promising synthetic conception to form the novel composite biomaterials. At first MCC was modified with colloidal solution of Ag NPs in isopropyl alcohol prepared via metal vapor synthesis. Then Ag-containing MCC powder was used as precursor for further preparation of the gels. The hydrogels were prepared by dissolving pristine MCC and MCC-based composite at low temperatures in aqueous alkali solution and gelation at elevated temperature. To prepare aerogels the drying in supercritical carbon dioxide was implemented. The as-prepared cellulose composites were characterized in terms of morphology, structure, and phase composition. Since many functional properties, including biological activity, in metal-composites are determined by the nature of the metal-to-polymer matrix interaction, the electronic state of the metal was carefully studied. The studied cellulose-based materials containing biologically active Ag NPs may be of interest for use as wound healing or water-purification materials.

Polysaccharide-based aerogels for thermal insulation and superinsulation: An overview

To reduce energy losses due to the insufficient thermal insulation is one of the current "hot" topics. Various commercial porous materials are used with the best conductivity around 0.03-0.04 W/(m·K). Aerogels are the only known materials with "intrinsic" thermal superinsulating properties, i.e. with thermal conductivity below that of air in ambient conditions (0.025 W/(m·K)). The classical thermal superinsulating aerogels are based on silica and some synthetic polymers, with conductivity 0.014-0.018 W/(m·K). Aerogels based on natural polymers are new materials created at the beginning of the 21st century. Can bio-aerogels possess thermal superinsulating properties? What are the bottlenecks in the development of bio-aerogels as new high-performance thermal insulationing materials? We try to answer these questions by analyzing thermal conductivity of bio-aerogels reported in literature.

Revisiting lignin: a tour through its structural features, characterization methods and applications

A pedagogical overview of the main extraction procedures and structural features, characterization methods and state-of-the-art applications.

Biorefinery Approach for Aerogels

According to the International Energy Agency, biorefinery is "the sustainable processing of biomass into a spectrum of marketable bio-based products (chemicals, materials) and bioenergy (fuels, power, heat)". In this review, we survey how the biorefinery approach can be applied to highly porous and nanostructured materials, namely aerogels. Historically, aerogels were first developed using inorganic matter. Subsequently, synthetic polymers were also employed. At the beginning of the 21st century, new aerogels were created based on biomass. Which sources of biomass can be used to make aerogels and how? This review answers these questions, paying special attention to bio-aerogels' environmental and biomedical applications. The article is a result of fruitful exchanges in the frame of the European project COST Action "CA 18125 AERoGELS: Advanced Engineering and Research of aeroGels for Environment and Life Sciences".

Ca-Zn-Ag Alginate Aerogels for Wound Healing Applications: Swelling Behavior in Simulated Human Body Fluids and Effect on Macrophages

Chronic non-healing wounds represent a substantial economic burden to healthcare systems and cause a considerable reduction in quality of life for those affected. Approximately 0.5-2% of the population in developed countries are projected to experience a chronic wound in their lifetime, necessitating further developments in the area of wound care materials. The use of aerogels for wound healing applications has increased due to their high exudate absorbency and ability to incorporate therapeutic substances, amongst them trace metals, to promote wound-healing. This study evaluates the swelling behavior of Ca-Zn-Ag-loaded alginate aerogels and their metal release upon incubation in human sweat or wound fluid substitutes. All aerogels show excellent liquid uptake from any of the formulas and high liquid holding capacities. Calcium is only marginally released into the swelling solvents, thus remaining as alginate bridging component aiding the absorption and fast transfer of liquids into the aerogel network. The zinc transfer quota is similar to those observed for common wound dressings in human and animal injury models. With respect to the immune regulatory function of zinc, cell culture studies show a high availability and anti-inflammatory activity of aerogel released Zn-species in RAW 264.7 macrophages. For silver, the balance between antibacterial effectiveness versus cytotoxicity remains a significant challenge for which the alginate aerogels need to be improved in the future. An increased knowledge of the transformations that alginate aerogels undergo in the course of the fabrication as well as during wound fluid exposure is necessary when aiming to create advanced, tissue-compatible aerogel products.

Long-term antibacterial composite via alginate aerogel sustained release of antibiotics and Cu used for bone tissue bacteria infection

Bone related-bacterial diseases including wound infections and osteomyelitis (OM) remain a serious problem accompanied with amputation in most severe cases. In this work, we report an exceptional effective antibacterial alginate aerogel, which consists of tigecycline (TGC) and octahedral Cu crystal as an organo-inorganic synergy platform for antibacterial and local infection therapy applications. The alginate aerogel could greatly prolong the release of copper ions and maintain effective antibacterial concentration over 18 days. The result of in-vitro experiments demonstrated that the alginate aerogel has an exceptional effective function on antibacterial activity. Cytotoxicity tests indicated that the alginate aerogel has low biological toxicity (average cell viability >75%). These remarkable results suggested that the alginate aerogel exhibits great potential for the treatment of OM, and has a prosperous future of application in bone tissue engineering.

In Situ Measurement Methods for the CO2-Induced Gelation of Biopolymer Systems

This work presents two novel methods to investigate in situ the carbon dioxide (CO₂)-induced gelation of biopolymer-based solutions. The CO₂-induced gelation is performed in a viewing cell at room temperature under CO₂ pressure (20 to 60 bar), whereby calcium precursors are used as cross-linkers. The novel methods allow the in situ optical observation and evaluation of the gelation process via the change in turbidity due to dissolution of dispersed calcium carbonate (CaCO₃) particles and in situ pH measurements. The combination of both methods enables the determination of the gelation direction, gelation rate, and the pH value in spatial and temporal resolution. The optical gelation front and pH front both propagate equally from top to bottom through the sample solutions, indicating a direct link between a decrease in the pH value and the dissolution of the CaCO₃ particles. Close-to-vertical movement of both gelation front and pH front suggests almost one dimensional diffusion of CO₂ from the contact surface (gel–CO₂) to the bottom of the sample. The gelation rate increases with the increase in CO₂ pressure. However, the increase in solution viscosity and the formation of a gel layer result in a strong decrease in the gelation rate due to a hindrance of CO₂ diffusion. Released carbonate ions from CaCO₃ dissolution directly influence the reaction equilibrium between CO₂ and water and therefore the change in pH value of the solution. Increasing the CaCO₃ concentrations up to the solubility results in lower gelation rates.

Structures, properties and application of alginic acid: A review

Alginic acid is a natural polysaccharide, which has been widely concerned and applied due to its excellent water solubility, film formation, biodegradability and biocompatibility. This paper briefly describes the source, properties, structure and application of sodium alginate by summarizing and analyzing the current literature. This paper reviews the application of sodium alginate in the fields of food industry, catalyst, health, water treatment, packaging, immobilized cells, and looks forward to its application prospects.

Large, Rapid Swelling of High-cis Polydicyclopentadiene Aerogels Suitable for Solvent-Responsive Actuators

High-cis polydicyclopentadiene (PDCPD) aerogels were synthesized using ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) with a relatively air-stable ditungsten catalytic system, Na[W₂(-Cl)₃Cl₄(THF)₂]·(THF)₃ (W₂; (W ³ W)⁶⁺, a΄²e΄⁴), and norbornadiene (NBD)as a co-initiator. These aerogels are compared in terms of chemical structure and material properties with literature PDCPD aerogels obtained using well-established Ru-based alkylidenes as catalysts. The use of NBD as a co-initiator enhances the degree of crosslinking versus the more frequently used phenylacetylene (PA), yielding materials with a controlled molecular structure that would persist solvent swelling. Indeed, those PDCPD aerogels absorb selected organic solvents (e.g., chloroform, tetrahydrofuran) and swell rapidly, in some cases up to 4 times their original volume within 10 min, thus showing their potential for applications in chemical sensors and solvent-responsive actuators. The advantage of aerogels versus xerogels or dense polymers for these applications is their open porosity, which provides rapid access of the solvent to their interior, thus decreasing the diffusion distance inside the polymer itself, which in turn accelerates the response to the solvents of interest.

Polyurea-crosslinked biopolymer aerogel beads

Polyurea-crosslinked calcium alginate and chitosan aerogel beads: novel fibrous biopolymer-based aerogels.

κ-Carrageenan/Sodium alginate double-network hydrogel with enhanced mechanical properties, anti-swelling, and adsorption capacity

The abuse of antibiotics is becoming increasingly serious, particularly in offshore aquaculture areas. Double-network polymer gel has good prospects for environmental application for the removal of antibiotics. In this work, κ-Carrageenan/Sodium Alginate (κ-car/SA) double-network hydrogels were designed and synthesized with enhanced mechanical properties, anti-swelling, and adsorption capacity. It was found that the intermolecular interaction and viscosity tend to increase with the increasing concentration of κ-carrageenan. The swelling degree of the composite hydrogel in NaCl solution presented a decreasing trend with the increase of carrageenan. SA can effectively improve the mechanical properties of κ-carrageenan composite gel and enhance its compressive resistance and elasticity. Ciprofloxacin (CIP) was used as the model pollutant for testing the adsorption performance. The results show that the Langmuir-Freundlich isotherm model is more suitable for fitting the adsorption isotherm data of CIP on gel beads, which indicates that κ-car/SA hydrogels have heterogeneous surface and different binding sites. κ-car/SA composite double-network hydrogels exhibit excellent adsorption properties for CIP (229 mg/g). The optimal adsorption capacity of κ-car/SA composite hydrogels was obtained at pH 4, and the adsorption capacity of the hydrogels increased with increasing ion concentration. FTIR spectroscopy and the Zeta potential test analyses showed that the adsorption mechanism may be explained by hydrogen bonding and the electrostatic interactions between κ-car/SA composite hydrogels and CIP. The formation of the new double-network hydrogel provided good properties and development potential for the adsorption of antibiotic in water.

Modelling of Mechanical Behavior of Biopolymer Alginate Aerogels Using the Bonded-Particle Model

A novel mesoscale modelling approach for the investigation of mechanical properties of alginate aerogels is proposed. This method is based on the discrete element method and bonded-particle model. The nanostructure of aerogel is not directly considered, instead the highly porous structure of aerogels is represented on the mesoscale as a set of solid particles connected by solid bonds. To describe the rheological material behavior, a new elastic-plastic functional model for the solids bonds has been developed. This model has been derived based on the self-similarity principle for the material behavior on the macro and mesoscales. To analyze the effectiveness of the proposed method, the behavior of alginate aerogels with different crosslinking degrees (calcium content) was analyzed. The comparison between experimental and numerical results has shown that the proposed approach can be effectively used to predict the mechanical behavior of aerogels on the macroscale.

Review on the Production of Polysaccharide Aerogel Particles

A detailed study of the production of polysaccharide aerogel (bio-aerogel) particles from lab to pilot scale is surveyed in this article. An introduction to various droplets techniques available in the market is given and compared with the lab scale production of droplets using pipettes and syringes. An overview of the mechanisms of gelation of polysaccharide solutions together with non-solvent induced phase separation option is then discussed in the view of making wet particles. The main steps of particle recovery and solvent exchange are briefly described in order to pass through the final drying process. Various drying processes are overviewed and the importance of supercritical drying is highlighted. In addition, we present the characterization techniques to analyse the morphology and properties of the aerogels. The case studies of bio-aerogel (agar, alginate, cellulose, chitin, κ-carrageenan, pectin and starch) particles are reviewed. Potential applications of polysaccharide aerogel particles are briefly given. Finally, the conclusions summarize the prospects of the potential scale-up methods for producing bio-aerogel particles.

Synthesis of alginate-silica hybrid hydrogel for biocatalytic conversion by β-glucosidase in microreactor

The organic-inorganic hybrid materials have been used in different fields to immobilize biomolecules since they offer many advantages. The aim of this study was to optimize and characterize the alginate-silica hybrid hydrogel as a stable and injectable form for microfluidic systems using internal gelation method and increase the stability and activity of immobilized enzyme for biocatalytic conversions as well. Characterization was carried out by scanning electron microscopy, energy dispersive spectroscopy/mapping, Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, and Fourier-transform infrared spectroscopy analyses, and the shrinkages of monoliths were evaluated. Subsequent to optimizing the enzyme concentration (40 μg), hydrolytic conversion of 4-nitrophenyl β-d-glucopyranoside (pNPG) was performed to understand the behavior of the bioconversion in the microfluidic system. The yield was 94% which reached the equilibrium at 24 h indicating that the alginate-silica gel derived microsystem overcome some drawbacks of monolithic systems. Additionally, bioconversion of Ruscus aculeatus saponins was carried out at the same setup in order to obtain aglycon part, which has pharmaceutical significance. Although pure aglycon could not be achieved, an intermediate compound was obtained based on the HPLC analysis. The developed formulation can be utilized for various life science applications.

Bioinspired Synthesis of Monolithic and Layered Aerogels

Aerogels are the least dense and most porous materials known to man, with potential applications from lightweight superinsulators to smart energy materials. To date their use has been seriously hampered by their synthesis methods, which are laborious and expensive. Taking inspiration from the life cycle of the damselfly, a novel ambient pressure-drying approach is demonstrated in which instead of employing low-surface-tension organic solvents to prevent pore collapse during drying, sodium bicarbonate solution is used to generate pore-supporting carbon dioxide in situ, significantly reducing energy, time, and cost in aerogel production. The generic applicability of this readily scalable new approach is demonstrated through the production of granules, monoliths, and layered solids with a number of precursor materials.

Thermal Superinsulating Materials Made from Nanofibrillated Cellulose-Stabilized Pickering Emulsions

Thermal superinsulating properties of biobased materials are investigated via the structuration of aerogels through a biphasic system. Highly stable Pickering emulsions are produced using TEMPO-oxidized cellulose nanofibrils (NFC) adsorbed at an oil/water interface. NFCs form an entangled system of clusters of droplets that lead to excellent mechanical properties. The emulsions produced are strong gels that are further used as template to form aerogels. The freeze-dried emulsions result in porous bioaerogels with extremely low densities (0.012-0.030 g/cm³). We describe a hierarchical morphology with three levels of porosity: an alveolar organization of larger macropores due to ice crystals, spherical smaller macropores induced by the emulsion template, and mesoporous domains localized at the pore walls level. The low-density bioaerogels have compression moduli as high as 1.5 MPa and can be deformed up to 60% strain before the structure collapse. NFC aerogels have thermal superinsulating properties; the lowest thermal conductivity obtained is 0.018 W/(m·K). In the context of the development of sustainable materials, we demonstrate that NFC-stabilized Pickering emulsions are excellent templates to produce fully biobased, mechanically strong thermal superinsulating materials.

Non-Conventional Methods for Gelation of Alginate

This review presents and critically evaluates recent advances in non-conventional gelation method of native alginate. A special focus is given to the following three methods: cryotropic gelation, non-solvent induced phase separation and carbon dioxide induced gelation. A few other gelation approaches are also briefly reviewed. Results are discussed in the context of subsequent freeze and supercritical drying. The methods are selected so as to provide the readers with a range of novel tools and tactics of pore engineering for alginate and other anionic polysaccharides.

Electrolyte and pH-sensitive amphiphilic alginate: synthesis, self-assembly and controlled release of acetamiprid

In this study, a pH-responsive amphiphilic alginate (Ugi-Alg) was synthesized via Ugi reaction without using a catalyst. The structure of Ugi-Alg was confirmed by FT-IR and ¹H NMR spectroscopy. Amphiphilic alginate can form micelles in an aqueous medium due to it's amphiphilic nature.. The impacts of Na⁺ concentration and pH on the micelle size were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The dynamic light scattering observations showed that micelle size increases with the decrease in Na⁺ concentration in aqueous solution. However, the micelle size decreases first and then increases as the pH value decreases from 5.3 to 2.0. Transmission electron microscopy confirmed that the mean size of micelles is 30–200 nm. In addition, a model hydrophobic pesticide (acetamiprid) was loaded in the micelles. The encapsulation efficiency and release behavior of micelles were studied, which could be controlled by Na⁺ concentration and pH. The results indicated that encapsulation efficiency of acetamiprid increases from 55% to 96% due to the increase in Na⁺ concentration from 0.01 M to 0.3 M. Moreover, with the decrease in pH from 5.3 to 2.0, encapsulation efficiency increases from 55% to 80%. Furthermore, the data of acetamiprid release kinetics could be well-fitted by the Weibull model.

Schematic of Ugi-Alg aggregation in aqueous solution of different NaCl concentrations and pH values.

Supercritical CO2 drying of alginate/zinc hydrogels: a green and facile route to prepare ZnO foam structures and ZnO nanoparticles

In the present study, we investigate a simple and effective synthetic protocol to produce zinc oxide foams by a facile solution-based method using alginate gelation. The influences of the zinc concentration and the drying process on the structural, textural and morphological properties of the synthesized ZnO nanomaterial were studied and discussed. The components of these nanomaterials were characterized by several techniques to demonstrate the effectiveness of the adopted synthetic route in controlling the growth of the ZnO nanoparticles. XRD analysis revealed that the as-prepared ZnO nanomaterial crystallizes in the hexagonal wurtzite structure. The room temperature photoluminescence (PL) spectra of ZnO show ultra-violet (UV) and visible emissions. SEM analysis revealed the porous texture of the prepared zinc oxide. TEM analysis confirmed the nano dimensions of the synthesized zinc oxide nanoparticles. A comparative study of conventional air drying versus supercritical drying was conducted to determine the influence of each mode of drying on the structural, textural and morphological as well as optical properties of the synthesized ZnO nanoparticles.

In the present study, we investigate a simple and effective synthetic protocol to produce zinc oxide foams by a facile solution-based method using alginate gelation.