Solid nanofoams based on cellulose nanofibers and indomethacin-the effect of processing parameters and drug content on material structure

Recent advances in nanomaterial-stabilized pickering foam: Mechanism, classification, properties, and applications

Pickering foam is a type of foam stabilized by solid particles known as Pickering stabilizers. These solid stabilizers adsorb at the liquid-gas interface, providing superior stability to the foam. Because of its high stability, controllability, versatility, and minimal environmental impact, nanomaterial-stabilized Pickering foam has opened up new possibilities and development prospects for foam applications. This review provides an overview of the current state of development of Pickering foam stabilized by a wide range of nanomaterials, including cellulose nanomaterials, chitin nanomaterials, silica nanoparticles, protein nanoparticles, clay mineral, carbon nanotubes, calcium carbonate nanoparticles, MXene, and graphene oxide nanosheets. Particularly, the preparation and surface modification methods of various nanoparticles, the fundamental properties of nanomaterial-stabilized Pickering foam, and the synergistic effects between nanoparticles and surfactants, functional polymers, and other additives are systematically introduced. In addition, the latest progress in the application of nanomaterial-stabilized Pickering foam in the oil industry, food industry, porous functional material, and foam flotation field is highlighted. Finally, the future prospects of nanomaterial-stabilized Pickering foam in different fields, along with directions for further research and development directions, are outlined.

Effect of Powdered Cellulose Nanofiber with Different Particle Sizes on the Physical Properties of Tablets Manufactured via Direct Compression

Direct compression is a tableting technique that involves a few steps in non-demanding manufacturing conditions. High strength and rapid disintegration of tablet formulations were previously achieved through the addition of cellulose nanofibers (CNFs), which have recently attracted attention as a high-performance biomass material. However, CNF addition results in greater variation in tablet weight and drug content, potentially due to differences in particle size between CNF and other additives. Herein, we used pulverized CNF to evaluate the effect of CNF particle size on the variation in tablet weight and drug content. Tablet formulations consisted of CNF with different particle sizes (approximately 100 µm [CNF100] and 300 µm [CNF300], at 0, 10, 30, or 50%), lactose hydrate, acetaminophen, and magnesium stearate. Ten powder formulations with different particle sizes and CNF concentrations were prepared; thereafter, the tablets were produced using a rotary tableting press with a compression force of 10 kN. The variation in weight and drug content as well as the tensile strength, friability, disintegration time, and drug dissolution of tablets were evaluated. CNF100 addition to the tablets reduced the weight and drug content variation to a greater extent than CNF300 addition. Using CNF300, we produced tablets of sufficient strength and short disintegration time. These properties were also achieved with CNF100 addition. Our findings suggest that adding CNF of small particle size to the tablet formulation can reduce the variation in weight and drug content while maintaining high strength and short disintegration time.

Orally Disintegrating Tablet Manufacture via Direct Powder Compression Using Cellulose Nanofiber as a Functional Additive

In recent years, orally disintegrating (OD) tablets have been continuously improved to increase efficacy. Herein, we focused on the benefits of cellulose nanofiber (CNF), a highly functional material, in OD tablet manufacturing. We studied its effects on the physical properties of tablets during manufacture. The analyzed tablet formulations included different content CNF (0-50%; 6 preparations), lactose hydrate, acetaminophen, and magnesium stearate (Mg-St). We measured the angles of repose and evaluated the flowability of the powder. Tablets were prepared on a tabletop and rotary tableting presses, whereafter their weight, drug content, hardness, friability, and disintegration time were evaluated. Although CNF addition slightly reduced powder flowability, continuous tableting was feasible via direct powder compression. Tablet hardness (~40 N) was comparable between CNF-containing (20%) tablets and those prepared with crystalline cellulose under 10 kN compression force. Disintegration time (~30 s) was similar between CNF-supplemented tablets and those supplemented with low-substituted hydroxypropyl cellulose, crospovidone, or croscarmellose sodium. At higher CNF fractions, tablet hardness increased, while friability decreased. Adding ≥30% CNF prolonged the tablet disintegration time. To set the optimized manufacturing condition for ensuring the desired tablet physical properties, we created contour plots for evaluating the effects of CNF concentration and compression force on hardness and disintegration time. A CNF concentration of 10-20% and a compression force of 12-13 kN would allow for the preparation of tablets with a hardness ≥30 N and a disintegration time ≤60 s. Altogether, addition of CNF to the OD tablet formulation for direct powder compression enhanced hardness and disintegration.

Novel Micro- and Nanocellulose-Based Delivery Systems for Liposoluble Compounds

Poor aqueous solubility of bioactive compounds is becoming a pronounced challenge in the development of bioactive formulations. Numerous liposoluble compounds have very interesting biological activities, but their low water solubility, stability, and bioavailability restrict their applications. To overcome these limitations there is a need to use enabling delivering strategies, which often demand new carrier materials. Cellulose and its micro- and nanostructures are promising carriers with unique features. In this context, this review describes the fast-growing field of micro- and nanocellulose based delivery systems with a focus on the release of liposoluble bioactive compounds. The state of research on this field is reviewed in this article, which also covers the chemistry, preparation, properties, and applications of micro- and nanocellulose based delivery systems. Although there are promising perspectives for introducing these materials into various fields, aspects of safety and toxicity must be revealed and are discussed in this review. The impact of gastrointestinal conditions on the systems and on the bioavailability of the bioactive compounds are also addressed in this review. This article helps to unveil the whole panorama of micro- and nanocellulose as delivery systems for liposoluble compounds, showing that these represent a great promise in a wide range of applications.

Foams as unique drug delivery systems

Foams are multiphase systems found throughout nature. We meet them equally often in our everyday life, starting with the foam in the morning espresso, where the foam should constitute 10% of the drink or in a glass of beer and ending with the evening bath with foam. These multiphase systems consist mainly of gas, which is separated by liquid or solid lamellae. The lamellae have a very large surface area and a small thickness, which results in their low stability. The foams in pharmaceutics are known for a long time as protective or therapeutic preparations for topical use. However, the physicochemical structure of both solid and liquid foams offers multiple fields of application in the modern therapy. For instance, owing to the unique structure, foams can be also used for parenteral use in the form of implants serving as a drug carrier and at the same time, a scaffold for regenerating the tissue. Foams can also be used orally in the form of controlled drug delivery systems that are potentially useful for sustained or targeted drug delivery. The article describes the unique advantages and features of foams that make them useful in modern pharmacotherapy.

Nanocelluloses: Sources, Pretreatment, Isolations, Modification, and Its Application as the Drug Carriers

The 'Back-to-nature' concept has currently been adopted intensively in various industries, especially the pharmaceutical industry. In the past few decades, the overuse of synthetic chemicals has caused severe damage to the environment and ecosystem. One class of natural materials developed to substitute artificial chemicals in the pharmaceutical industries is the natural polymers, including cellulose and its derivatives. The development of nanocelluloses as nanocarriers in drug delivery systems has reached an advanced stage. Cellulose nanofiber (CNF), nanocrystal cellulose (NCC), and bacterial nanocellulose (BC) are the most common nanocellulose used as nanocarriers in drug delivery systems. Modification and functionalization using various processes and chemicals have been carried out to increase the adsorption and drug delivery performance of nanocellulose. Nanocellulose may be attached to the drug by physical interaction or chemical functionalization for covalent drug binding. Current development of nanocarrier formulations such as surfactant nanocellulose, ultra-lightweight porous materials, hydrogel, polyelectrolytes, and inorganic hybridizations has advanced to enable the construction of stimuli-responsive and specific recognition characteristics. Thus, an opportunity has emerged to develop a new generation of nanocellulose-based carriers that can modulate the drug conveyance for diverse drug characteristics. This review provides insights into selecting appropriate nanocellulose-based hybrid materials and the available modification routes to achieve satisfactory carrier performance and briefly discusses the essential criteria to achieve high-quality nanocellulose.

Recent Advances in Fiber-Hydrogel Composites for Wound Healing and Drug Delivery Systems

In the last decades, much research has been done to fasten wound healing and target-direct drug delivery. Hydrogel-based scaffolds have been a recurrent solution in both cases, with some reaching already the market, even though their mechanical stability remains a challenge. To overcome this limitation, reinforcement of hydrogels with fibers has been explored. The structural resemblance of fiber-hydrogel composites to natural tissues has been a driving force for the optimization and exploration of these systems in biomedicine. Indeed, the combination of hydrogel-forming techniques and fiber spinning approaches has been crucial in the development of scaffolding systems with improved mechanical strength and medicinal properties. In this review, a comprehensive overview of the recently developed fiber-hydrogel composite strategies for wound healing and drug delivery is provided. The methodologies employed in fiber and hydrogel formation are also highlighted, together with the most compatible polymer combinations, as well as drug incorporation approaches creating stimuli-sensitive and triggered drug release towards an enhanced host response.

Floating Photocatalysts for Effluent Refinement Based on Stable Pickering Cellulose Foams and Graphitic Carbon Nitride (g-C3N4)

The transfer of heterogeneous photocatalysis applications from the laboratory to real-life aqueous systems is challenging due to the higher density of photocatalysts compared to water, light attenuation effects in water, complicated recovery protocols, and metal pollution from metal-based photocatalysts. In this work, we overcome these obstacles by developing a buoyant Pickering photocatalyst carrier based on green cellulose nanofibers (CNFs) derived from wood. The air bubbles in the carrier were stable because the particle surfactants provided thermodynamic stability and the derived photocatalytic foams floated on water throughout the test period (4 weeks). A metal-free semiconductor photocatalyst, g-C3N4, was facilely embedded inside the foam by mixing the photocatalyst with the air-bubble suspension followed by casting and drying to produce solid foams. When tested under mild irradiation conditions (visible light, low energy LEDs) and no agitation, almost three times more dye was removed after 6 h for the floating g-C3N4-CNF nanocomposite foam, compared to the pure g-C3N4 powder residing on the bottom of a ca. 2 cm-high water pillar. The buoyancy and physicochemical properties of the carrier material were imperative to render escalated oxygenation, high photon utilization, and faster dye degradation. The reported assembly protocol is facile, general, and provides a new strategy for assembling green floating foams that can potentially carry a number of different photocatalysts.

Cellulose Nanofibers and Other Biopolymers for Biomedical Applications. A Review

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

Unravelling the Acoustic and Thermal Responses of Perfluorocarbon Liquid Droplets Stabilized with Cellulose Nanofibers

The attractive colloidal and physicochemical properties of cellulose nanofibers (CNFs) at interfaces have recently been exploited in the facile production of a number of environmentally benign materials, e.g. foams, emulsions, and capsules. Herein, these unique properties are exploited in a new type of CNF-stabilized perfluoropentane droplets produced via a straightforward and simple mixing protocol. Droplets with a comparatively narrow size distribution (ca. 1-5 μm in diameter) were fabricated, and their potential in the acoustic droplet vaporization process was evaluated. For this, the particle-stabilized droplets were assessed in three independent experimental examinations, namely temperature, acoustic, and ultrasonic standing wave tests. During the acoustic droplet vaporization (ADV) process, droplets were converted to gas-filled microbubbles, offering enhanced visualization by ultrasound. The acoustic pressure threshold of about 0.62 MPa was identified for the cellulose-stabilized droplets. A phase transition temperature of about 22 °C was observed, at which a significant fraction of larger droplets (above ca. 3 μm in diameter) were converted into bubbles, whereas a large part of the population of smaller droplets were stable up to higher temperatures (temperatures up to 45 °C tested). Moreover, under ultrasound standing wave conditions, droplets were relocated to antinodes demonstrating the behavior associated with the negative contrast particles. The combined results make the CNF-stabilized droplets interesting in cell-droplet interaction experiments and ultrasound imaging.

Amorphisation of Free Acid Ibuprofen and Other Profens in Mixtures with Nanocellulose: Dry Powder Formulation Strategy for Enhanced Solubility

The formulation of arylpropionic acid derivatives (profens), which are poorly soluble Biopharmaceutical Classification System (BCS) Type II drugs, has a strong impact on their therapeutic action. This article shows that heat-treated powder mixtures of free acid profens with high surface area Cladophora cellulose induces drug amorphization and results in enhanced solubility and bioavailability. Similar mixtures produced using conventional low surface area cellulose, i.e., microcrystalline cellulose, does not produce the same effect. The concept is thoroughly described and links the solid-state characterization data, such as differential scanning calorimetry, X-ray powder diffraction, and Fourier-transform infra-red spectroscopy, with in vitro dissolution in biorelevant media and in vivo pharmacokinetic analysis in rats. The concept is demonstrated for several substances from the profens group, including ibuprofen (main model drug), ketoprofen, flurbiprofen, and naproxen. The presented approach opens new ways to produce solid dosage forms of profen drugs in their free acidic form as alternatives to existing analogues, e.g., drug-salt conjugates or soft gel liquid capsules.

Toward Improved Understanding of the Interactions between Poorly Soluble Drugs and Cellulose Nanofibers

Cellulose nanofibers (CNFs) have interesting physicochemical and colloidal properties that have been recently exploited in novel drug-delivery systems for tailored release of poorly soluble drugs. The morphology and release kinetics of such drug-delivery systems heavily relied on the drug-CNF interactions; however, in-depth understanding of the interactions was lacking. Herein, the interactions between a poorly soluble model drug molecule, furosemide, and cationic cellulose nanofibers with two different degrees of substitution are studied by sorption experiments, Fourier transform infrared spectroscopy, and molecular dynamics (MD) simulation. Both MD simulations and experimental results confirmed the spontaneous sorption of drug onto CNF. Simulations further showed that adsorption occurred by the flat aryl ring of furosemide. The spontaneous sorption was commensurate with large entropy gains as a result of release of surface-bound water. Association between furosemide molecules furthermore enabled surface precipitation as indicated by both simulations and experiments. Finally, sorption was also found not to be driven by charge neutralization, between positive CNF surface charges and the furosemide negative charge, so that surface area is the single most important parameter determining the amount of sorbed drug. An optimized CNF-furosemide drug-delivery vehicle thus needs to have a maximized specific surface area irrespective of the surface charge with which it is achieved. The findings also provide important insights into the design principles of CNF-based filters suitable for removal of poorly soluble drugs from wastewater.