Hydroxypropylmethylcellulose (HPMC) as emulsifier for submicron emulsions: influence of molecular weight and substitution type on the droplet size after high-pressure homogenization

Impact of colloidal drug-rich droplet size and amorphous solubility on drug membrane permeability: A comprehensive analysis

This study aimed to investigate the impact of amorphous solubility and colloidal drug-rich droplets on drug absorption. The amorphous solubility of cilnidipine (CND) in AS-HF grade of hypromellose acetate succinate (HPMC-AS) solution was significantly reduced compared to that in non-polymer solution due to AS-HF partitioning into the CND-rich phase. In contrast, AS-LF grade of HPMC-AS has minimal effect on the amorphous solubility. The size of colloidal CND-rich droplets formed in the CND-supersaturated solution was less than 100 nm in the presence of AS-HF, while 200-450 nm in the presence of AS-LF. When the CND concentrations were near the amorphous solubility, CND membrane flux was reduced in the presence of AS-HF due to the decrease in the amorphous solubility of CND. However, the CND flux increased with the increase in CND-rich droplets, especially in the AS-HF solution. The size reduction of the CND-rich droplets led to their effective diffusion into the unstirred water layer, enhancing CND flux. In higher CND concentration regions, the CND flux became higher in the AS-HF solution than in the AS-LF solution. Thus, it is essential to elucidate the drug concentration-dependent impact of the colloidal drug-rich droplets on the drug absorption performance to optimize supersaturating formulations.

Polysaccharides as wall materials in spray-dried microencapsulation of bioactive compounds: Physicochemical properties and characterization

Natural bioactive compounds (BCs) are types of chemicals found in plants and certain foods that promote good health, however they are sensitive to processing and environmental conditions. Microencapsulation by spray drying is a widely used and cost-effective approach to create a coating layer to surround and protect BCs and control their release, enabling the production of high functional products/ingredients with extended shelf life. In this process, wall materials determine protection efficiency, and physical properties, bioavailability, and storage stability of microencapsulated products. Therefore, an understanding of physicochemical properties of wall materials is essential for the successful and effective spray-dried microencapsulation process. Typically, polysaccharide-based wall materials are generated from more sustainable sources and have a wider range of physicochemical properties and applications compared to their protein-based counterparts. In this review, we highlight the essential physicochemical properties of polysaccharide-based wall materials for spray-dried microencapsulation of BCs including solubility, thermal stability, and emulsifying properties, rheological and film forming properties. We provide further insight into possibilities for the chemical structure modification of native wall materials and their controlled release behaviors. Finally, we summarize the most recent studies involving polysaccharide biopolymers as wall materials and/or emulsifiers in spray-dried microencapsulation of BCs.

Formation mechanism of amorphous drug nanoparticles using the antisolvent precipitation method elucidated by varying the preparation temperature

The present study focuses on the effect of the preparation temperature on the physicochemical properties of amorphous drug nanoparticles to clarify their formation mechanism. Amorphous glibenclamide (GLB) nanoparticles were prepared at 4-40 °C using two antisolvent precipitation methods. In method A, N,N-dimethylformamide (DMF) solution of GLB was added to an aqueous solution containing hydroxypropyl methylcellulose (HPMC) to obtain nano-A suspensions. In method B, nano-B suspensions were obtained by adding DMF solution containing both GLB and HPMC into water. When the preparation temperature was above 25 °C, nano-A and nano-B showed similar HPMC compositions. However, nano-B contained a large amount of HPMC compared to nano-A at temperatures below 20 °C. The glassy nature of the nanoparticle cores restricts the diffusion of HPMC from amorphous GLB nanoparticles to the aqueous phase, indicating that the glass transition temperature (T_g) of neat amorphous GLB (73 °C) would be considerably decreased owing to the nanosizing and water sorption of amorphous GLB. The physical stability of amorphous GLB nanoparticles was improved with increased HPMC in the nanoparticles. Thus, setting the preparation temperature by considering the T_g of the antisolvent-saturated amorphous drug nanoparticles is essential to develop stable amorphous drug nanoparticles.

Hydrophobic interactions control the self-assembly of DNA and cellulose

Desoxyribosenucleic acid, DNA, and cellulose molecules self-assemble in aqueous systems. This aggregation is the basis of the important functions of these biological macromolecules. Both DNA and cellulose have significant polar and nonpolar parts and there is a delicate balance between hydrophilic and hydrophobic interactions. The hydrophilic interactions related to net charges have been thoroughly studied and are well understood. On the other hand, the detailed roles of hydrogen bonding and hydrophobic interactions have remained controversial. It is found that the contributions of hydrophobic interactions in driving important processes, like the double-helix formation of DNA and the aqueous dissolution of cellulose, are dominating whereas the net contribution from hydrogen bonding is small. In reviewing the roles of different interactions for DNA and cellulose it is useful to compare with the self-assembly features of surfactants, the simplest case of amphiphilic molecules. Pertinent information on the amphiphilic character of cellulose and DNA can be obtained from the association with surfactants, as well as on modifying the hydrophobic interactions by additives.

Development and Characterization of Potential Ocular Mucoadhesive Nano Lipid Carriers Using Full Factorial Design

Generally, topically applied eye drops have low bioavailability due to short residence time and low penetration of the drug. The aim of the present study was to incorporate dexamethasone (DXM) into nano lipid carriers (NLC), which contain mucoadhesive polymer, in order to increase the bioavailability of the drug. A 2³ factorial experimental design was applied, in which the three factors were the polymer, the DXM, and the emulsifier concentrations. The samples were analyzed for particle size, zeta potential, polydispersity index, and Span value. The significant factors were identified. The biocompatibility of the formulations was evaluated with human corneal toxicity tests and immunoassay analysis. The possible increase in bioavailability was analyzed by means of mucoadhesivity, in vitro drug diffusion, and different penetration tests, such as in vitro cornea PAMPA model, human corneal cell penetration, and ex vivo porcine corneal penetration using Raman mapping. The results indicated that DXM can be incorporated in stable mucoadhesive NLC systems, which are non-toxic and do not have any harmful effect on cell junctions. Mucoadhesive NLCs can create a depot on the surface of the cornea, which can predict improved bioavailability.

Development and evaluation of Classical and Pickering emulsions containing crude or fractionated extracts of Libidibia ferrea pods

Objective: The development of medicinal plants for clinical use represents an important direction in biomedical research, despite the technological difficulties.Significance: The aim of this study was to compare pharmaceutical characteristics and in vitro release of Classical and Pickering emulsions containing crude or fractionated extracts of Libidibia ferrea.Methods: After evaluating the extract's solubility in formulation, a dispersion of hydroxypropyl methylcellulose (HPMC) was prepared in water. For Pickering emulsions, the aqueous phase was HPMC and the oil phase was Miglyol^® 812; for Classical emulsions, water with Tween^® 20 and Miglyol^® 812 with Span^® 80 were used for aqueous and oil phases, respectively. Crude or fractionated extracts were added to the aqueous phase (5% w/v). Both phases were heated (40 °C); then, the oil phase was poured into the aqueous phase and homogenized using an Ultra-Turrax. Emulsions were characterized for 90 days by pH, polyphenol content, phytomarker content, macroscopic characteristics, droplet size, and zeta potential.Results: These formulations displayed satisfactory stability for 90 days when stored at 25 °C. Regarding the investigation of rheological properties, Pickering emulsions displayed higher viscosity with lesser deformation than Classical emulsions. Moreover, the emulsions displayed similar in vitro release behavior.Conclusion: Based on the results of present study, the Pickering emulsions were obtainable and displayed higher stability than Classical emulsions. Additionally, maintenance of system integrity points to promising systems for delivery of active pharmaceutical ingredients in the internal phase, despite the complex chemical mixture added to the external phase.

Polymer Type Impacts Amorphous Solubility and Drug-Rich Phase Colloidal Stability: A Mechanistic Study Using Nuclear Magnetic Resonance Spectroscopy

The polymer used in an amorphous solid dispersion (ASD) formulation plays a critical role in dosage form performance. Herein, drug-polymer interactions in aqueous solution were evaluated in order to better understand the dispersion stability of the colloidal drug-rich phase generated when the amorphous solubility is exceeded. The amorphous solubility (S_a,IBP) of ibuprofen (IBP) decreased when hypromellose (HPMC) or polyvinylpyrrolidone/vinyl acetate (PVP-VA) were present in solution. Solution nuclear magnetic resonance (NMR) spectroscopy revealed that a large amount of HPMC and PVP-VA distributed into the IBP-rich phase. The mixing of HPMC and PVP-VA with the IBP-rich phase led to the decreased S_a,IBP. In contrast, the charged amino methacrylate copolymer (Eudragit E PO, EUD-E) showed minimal mixing with the IBP-rich phase; however, this polymer did lead to solubilization of IBP in the bulk aqueous phase. Although the IBP-rich phase generated by dissolving IBP at concentrations above S_a,IBP rapidly coarsened followed by creaming in the absence of polymer, all of the polymers stabilized the IBP dispersion to some extent. The droplet size of the IBP-rich phase immediately after formation was around 300 nm in HPMC and PVP-VA solutions, and around 800 nm in the EUD-E solution. The mixing of the former two polymers with the drug-rich phase is thought to account for the smaller droplet size. Despite a smaller initial size, the dispersion stability of the IBP-rich droplets was relatively poor in the presence of PVP-VA. In contrast, the coalescence of the IBP-rich droplets was effectively suppressed by the steric repulsion and electrostatic repulsion derived from adsorbed HPMC and EUD-E, respectively. The present study highlights the complex effects of a polymer on the drug amorphous solubility and colloidal stability, which should be considered when optimizing ASD formulations with the goal of maximizing drug absorption.

Effects of Molecular Weight and Guluronic Acid/Mannuronic Acid Ratio on the Rheological Behavior and Stabilizing Property of Sodium Alginate

The aim of this study was to prepare sodium alginates (SAs) with different molecular weight and G/M ratio, and characterize their rheological behaviors and emulsifying properties. The result of Fourier transform infrared (FTIR) showed that the chemical bonds among the β-d-mannuronic acid- (M-), α-l-guluronic acid- (G-), and MG-sequential blocks in the SA chains were not changed significantly by acid treatment. Meanwhile, the molecular weight and G/M ratio of the SA exhibited drastic variation after acid modification. The result of rheological analysis suggesting that the apparent viscosity of SA reduced from 30 to 16.4 mPa.s with the increase of shear rate, reveals that SA solution belongs to pseudoplastic liquid. Also, the apparent viscosity of acid-modified SA solution dropped rapidly with the decrease of the molecular weight. The properties of emulsions stabilized by SA, SA-Ms, and commercial SAs were evaluated via the interface tensiometry and determination of the zeta potential, droplet size, creaming index (CI), and Turbiscan stability index (TSI). Compared with the SA-stabilized emulsion, the interfacial tension of the emulsion stabilized by SA-M increased with the decrease of the molecular weight reduced at the similar M/G ratio. The decrease in zeta potential and the increase in TSI of the emulsion were observed with the decrease of molecular weight, indicating that molecular weight plays an important role on the emulsifying ability of SA. In addition, the SA with low G/M ratio can form emulsions with stable and fine droplets.

Emulsion Formation and Stabilization by Biomolecules: The Leading Role of Cellulose

Emulsion stabilization by native cellulose has been mainly hampered because of its insolubility in water. Chemical modification is normally needed to obtain water-soluble cellulose derivatives. These modified celluloses have been widely used for a range of applications by the food, cosmetic, pharmaceutic, paint and construction industries. In most cases, the modified celluloses are used as rheology modifiers (thickeners) or as emulsifying agents. In the last decade, the structural features of cellulose have been revisited, with particular focus on its structural anisotropy (amphiphilicity) and the molecular interactions leading to its resistance to dissolution. The amphiphilic behavior of native cellulose is evidenced by its capacity to adsorb at the interface between oil and aqueous solvent solutions, thus being capable of stabilizing emulsions. In this overview, the fundamentals of emulsion formation and stabilization by biomolecules are briefly revisited before different aspects around the emerging role of cellulose as emulsion stabilizer are addressed in detail. Particular focus is given to systems stabilized by native cellulose, either molecularly-dissolved or not (Pickering-like effect).

Tailoring of structured hydroxypropyl methylcellulose-stabilized emulsions for encapsulation of nobiletin: modification of the oil and aqueous phases

HPMC as emulsifier inhibited the migration of nobiletin crystals. The physical stability and digestion fate of nobiletin depended on the emulsion structure.

Influence of hydroxypropyl methylcellulose, methylcellulose, gelatin, poloxamer 407 and poloxamer 188 on the formation and stability of soybean oil-in-water emulsions

Macromolecules of polysaccharides, proteins and poloxamers have a hydrophobic portion and a hydrophilic one that can be used as emulsifiers. Parts of these emulsifiers are safe pharmaceutical excipients, which can replace the irritant low molecular weight surfactants to formulate emulsions for the pharmaceutical field. This project focused on preparing O/W emulsions stabilized with polymers for pharmaceuticals such as polysaccharides, proteins and poloxamers, including hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), gelatin, poloxamer 407 (F127) and poloxamer 188 (F68). Emulsion physical stability was assessed by centrifugation, autoclaving sterilization and droplet size measurements. The stabilization mechanisms of emulsions were determined by interfacial tension and rheological measurements. Results stated that the efficacy of these polymers for pharmaceuticals stabilized emulsions was sorted in the order: F127 > F68 > HPMC > MC > Gelatin.

Tear fluid-eye drops compatibility assessment using surface tension

OBJECTIVE

To evaluate the compatibility of commercially available eye drop surface tension with the tear film physiological range and to characterize commonly used ophthalmic excipients in terms of their surface activity under eye-biorelevant conditions.

SIGNIFICANCE

There are a number of quality requirements for the eye drops (e.g. tonicity, pH, viscosity, refractive index) that needs to comply with the physiological parameters of the eye surface. However, the adjustment of surface tension properties of the eye drops to the normal range of surface tension at the air/tear fluid interface (40-46 mN/m) has received rather less attention thus far. Yet, the surface tension at the air/tear fluid interface is of vital importance for the normal function of the eye surface.

METHODS

The surface tension compatibility of the isotonic aqueous solutions of commonly used ophthalmic excipients as well as 18 approved eye drops with the tear fluid have been evaluated using surface tension method.

RESULTS

Each ophthalmic ingredient including the preservatives, solubilizing agents and thickening agents can influence the surface tension of the final formulation. In case of complex ophthalmic formulations one should also consider the possible interactions among excipients and consequent impact on overall surface activity. Out of 18 evaluated eye drops, three samples were within, 12 samples were below and three samples were above the physiological range of the tear fluid surface tension.

CONCLUSIONS

Our results provide a rationale for clinical studies aiming to assess the correlation between the eye drops surface tension and the tear film (in)stability.

Influence of the Oil Phase and Topical Formulation on the Wound Healing Ability of a Birch Bark Dry Extract

Triterpenes from the outer bark of birch are known for various pharmacological effects including enhanced wound healing (WH). A birch bark dry extract (TE) obtained by accelerated solvent extraction showed the ability to form oleogels when it is suspended in oils. Consistency of the oleogels and the dissolved amount of triterpenes varies largely with the used oil. Here we wanted to know to what extent different oils and formulations (oleogel versus o/w emulsion) influence WH. Looking at the plain oils, medium-chain triglycerides (MCT) enhanced WH (ca. 1.4-fold), while e.g. castor oil (ca.0.3-fold) or light liquid paraffin (LLP; ca. 0.5-fold) significantly decreased WH. Concerning the respective oleogels, TE-MCT showed no improvement although the solubility of the TE was high. In contrast, the oleogel of sunflower oil which alone showed a slight tendency to impair WH, enhanced WH significantly (ca. 1.6-fold). These results can be explained by release experiments where the release rate of betulin, the main component of TE, from MCT oleogels was significantly lower than from sunflower oil oleogels. LLP impaired WH as plain oil and even though it released betulin comparable to sunflower oil it still results in an overall negative effect of the oleogel on WH. As a further formulation option also surfactant free o/w emulsions were prepared using MCT, sunflower oil and LLP as a nonpolar oil phase. Depending on the preparation method (suspension or oleogel method) the distribution of the TE varied markedly and affected also release kinetics. However, the released betulin was clearly below the values measured with the respective oleogels. Consequently, none of the emulsions showed a significantly positive effect on WH. In conclusion, our data show that the oil used as a vehicle influences wound healing not only by affecting the release of the extract, but also by having its own vehicle effect on wound healing. This is also of importance for other applications where drugs have to be applied in non-polar vehicles because these solvents likely influence the outcome of the experiment substantially.

Potential of chitosan-loaded nanoemulsions to control different Colletotrichum spp. and maintain quality of tropical fruits during cold storage

AIMS

To investigate the antifungal activity of conventional chitosan and chitosan-loaded nanoemulsions against anthracnose caused by Colletotrichum spp. isolated from different tropical fruits.

METHODS AND RESULTS

In vitro results illustrated that conventional chitosan onwards 1·5% concentration inhibited radial mycelial growth, conidial germination, sporulation and dry weight of mycelia for Colletotrichum musae (Berk. & Curt) Arx. isolated from banana, Colletotrichum gloeosporioides (Penz.) Penz and Sacc. isolated from papaya and dragon fruits. For further investigations, chitosan-loaded nanoemulsions were prepared, and chitosan at 2·0% concentration with 200 nm droplet size gave the best results in terms of all the in vitro parameters tested for C. musae and at the same concentration with 600 nm droplet size for both the isolates of C. gloeosporioides. However, the results obtained at 2·0% chitosan concentration with different droplet sizes were nonsignificantly different with 1·0 and 1·5% concentrations. Therefore, for in vivo studies, only 1·0% chitosan with different droplet sizes was used. In terms of fungicidal effects and maintaining postharvest quality of banana, papaya and dragon fruits, chitosan at 1·0% concentration with a droplet size of 200 nm in banana and 600 nm in papaya and dragon fruits showed the best results in delaying the onset of anthracnose and maintaining quality of all the fruits for up to 28 days of cold storage.

CONCLUSION

Chitosan used in a conventional form showed good results but not as effective as in the form of nanoemulsions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study suggest that instead of applying chitosan in a conventional form, chitosan in the form of nanoemulsions could be more effective as a biofungicide for controlling anthracnose of fresh fruits. Moreover, it could be cost-effective as the amount of chemical used is reduced when applied in the form of nanoemulsions.

Formulation development and optimization of a novel Cremophore EL-based nanoemulsion using ultrasound cavitation

In the present study, response surface methodology (RSM) based on central composite design (CCD) was employed to investigate the influence of main emulsion composition variables, namely drug loading, oil content, emulsifier content as well as the effect of the ultrasonic operating parameters such as pre-mixing time, ultrasonic amplitude, and irradiation time on the properties of aspirin-loaded nanoemulsions. The two main emulsion properties studied as response variables were: mean droplet size and polydispersity index. The ultimate goal of the present work was to determine the optimum level of the six independent variables in which an optimal aspirin nanoemulsion with desirable properties could be produced. The response surface analysis results clearly showed that the variability of two responses could be depicted as a linear function of the content of main emulsion compositions and ultrasonic processing variables. In the present investigation, it is evidently shown that ultrasound cavitation is a powerful yet promising approach in the controlled production of aspirin nanoemulsions with smaller average droplet size in a range of 200-300 nm and with a polydispersity index (PDI) of about 0.30. This study proved that the use of low frequency ultrasound is of considerable importance in the controlled production of pharmaceutical nanoemulsions in the drug delivery system.

Solid lipid nanoparticles produced through a coacervation method

Solid lipid nanoparticles (SLN) of fatty acids (FAs) were prepared with a new, solvent-free technique based on FAs precipitation from their sodium salt micelles in the presence of polymeric non-ionic surfactants: this technique was called 'coacervation'. Myristic, palmitic, stearic, arachidic and behenic acid were employed as lipid matrixes. Spherical shaped nanoparticles with mean diameters ranging from 250 to approximately 500 nm were obtained. Different aqueous acidifying solutions were used to precipitate various FAs from their sodium salt micellar solution. Good encapsulation efficiency of Nile Red, a lipophilic model dye, in stearic acid nanoparticles was obtained. The coacervation method seems to be a potentially suitable technique to prepare close to monodisperse nanoparticles for drug delivery purposes.