Deliquescence-Induced Caking in Binary Powder Blends

Evaluation of Time Consolidation Effect of Pharmaceutical Powders

PURPOSE

We aim to perform a systematic study of the time consolidation effect, i.e. the reduction of powder flowability resulting from at-rest storage, on a diverse array of pharmaceutical powders under different stress, humidity, and length of time.

METHODS

A ring shear cell-based methodology was employed. An instantaneous flow function was obtained, followed immediately by at-rest consolidation at precisely controlled humidity, stress, and duration. The consolidated powder was then subjected to shear-cell measurement. The difference in flowability between the immediate and consolidated specimens were attributed to the time consolidation effect.

RESULTS

Among the six excipients tested, three exhibited time consolidation at varying extents. Citric acid and starch underwent time consolidation only at high relative humidity (RH = 75%), promoted by vapor condensation and liquid bridge formation. For both materials, the flowability decreased with time, and the extent of time consolidation was not sensitive to the stress applied (0.4-2 kPa). Importantly, mannitol was found to time consolidate under both 50% and 75% RH. Given time, mannitol formed cake, giving rise to flow function below unity. Inverse gas chromatography analysis indicated that mannitol possesses high total surface energy among known pharmaceutical powders.

CONCLUSION

While time consolidation is prevalent among pharmaceutical powders, most can be mitigated by controlling the RH to below 75%. Notably, for materials possessing high surface energy, such as mannitol, time consolidation could occur at ambient humidity. Therefore, it is desirable to consider in-depth time consolidation evaluation for high surface energy powders, e.g. those subjected to milling or of amorphous nature.

The safety of nanomaterials in food production and packaging

Nanotechnology involves developing, characterising, and applying structures ranging in size from 1 to 100 nm. As a key advanced technology, it has contributed to a substantial impact across engineering, medicine, agriculture and food. With regards to their application in food, nanomaterials posses the ability to lead the quantitative and qualitative development of high-quality, healthier, and safer foods by outperforming traditional food processing technologies for increasing shelf life and preventing contaminations. Although rapid progress has been made in nanotechnology in food products, the toxicity of nanoparticles and nanomaterials is not very well known. As a result, nanomaterials are potentially toxic, therefore, considering the constantly increasing employment in food science, they need to be further characterised, and their use must be better regulated. We may face a crisis of nanotoxicity if the molecular mechanisms by which nanoparticles and nanomaterials interact with food and within living organisms is not fully understood. Food safety can be guaranteed only if we are thoroughly aware of nanomaterial properties and potential toxicity. Therefore, it is urgently necessary to have in the food sector a regulatory system capable of managing nanofood risks and nanotechnology, considering the health effects of food processing techniques based on nanotechnology. This present review discusses the impact and role nanotechnology play in food science. The specific application of Nanomaterials in food science, their advantages and disadvantages, the potential risk for human health and the analysis to detect nanocomponents are also highlighted.

Investigating the Influence of Excipients on the Stability of Levothyroxine Sodium Pentahydrate

A range of tablet excipients were evaluated for their influence on the physical form and chemical stability of levothyroxine sodium pentahydrate (LSP; C₁₅H₁₀I₄NNaO₄·5H₂O). LSP-excipient binary powder blends were stored under two conditions: (a) in hermetically sealed containers at 40 °C and (b) at 40 °C/75% RH. By use of synchrotron X-ray diffractometry, the disappearance of LSP could be quantified and the appearance of crystalline levothyroxine (free acid) could be identified. Under hermetically sealed conditions (40 °C) hygroscopic excipients such as povidone induced partial dehydration of LSP to form levothyroxine sodium monohydrate. When stored at 40 °C/75% RH, acidic excipients induced measurable disproportionation of LSP resulting in the formation of levothyroxine (free acid). HPLC analyses of drug-excipient mixtures revealed that lactose monohydrate, microcrystalline cellulose, and croscarmellose sodium caused pronounced chemical decomposition of LSP. On the other hand, magnesium stearate, sodium stearyl fumarate, and alkaline pH modifiers did not affect the physical and chemical stability of the API following storage at 40 °C/75% RH. HPLC, being a solution based technique, revealed chemical decomposition of the API, but the technique was insensitive to physical transformations. Excipient properties such as hygroscopicity and microenvironmental acidity were identified to be critical determinants of both physical and chemical stability of LSP in a drug product. For drugs exhibiting both physical and chemical transformations, simultaneous solid-state and solution based analyses will enable comprehensive stability evaluation.

Moisture sorption behaviors, water activity-temperature relationships, and physical stability traits of spices, herbs, and seasoning blends containing crystalline and amorphous ingredients

Spices, herbs, and seasoning blends containing both crystalline and amorphous ingredients are common throughout the food industry but may exhibit unwanted clumping or caking during storage. Crystalline and amorphous ingredients are known to respond differently to increases in relative humidity (RH) and temperature. The aim of this study was to better characterize what happens to moisture sorption behaviors, water-solid interactions, and physical stability when crystalline and amorphous ingredients are co-formulated in seasoning blends. Spices, herbs, and seasoning blends, 25 in total, were studied individually and in blends of increasing complexity (binary, ternary, and quaternary) with sucrose, salt, and maltodextrin. The effects of increasing temperature and RH on moisture content, moisture sorption profiles, water activity (a_w), glass transition temperature (T_g), including Gordon-Taylor modeling, physical appearance, and degree of clumping were measured. Crossover points, the temperature at which the a_w of the amorphous ingredient(s) and the deliquescence RH of the crystalline ingredient(s) in a blend intersect, were also calculated. Caking was observed when storage conditions (RH and/or temperature) exceeded the T_g of a blend or the deliquescence RH of a crystalline ingredient in the blend. When amorphous and crystalline ingredients were blended, synergistic moisture sorption and increased caking was observed. When multiple crystalline ingredients were present, mutual deliquescence further increased the sensitivity of the blend to moisture. When environmental conditions exceeded the crossover temperature, degree of caking increased, and physical appearance was altered due to the induced deliquescence of the crystalline ingredient(s) by the a_w of the amorphous ingredient(s). In general, as complexity of blends increased, sensitivity to moisture also increased, and physical stability of the blends decreased. The results of this study provide valuable information for increasing the physical stability of complex seasoning blends based on moisture sorption behaviors.

Desiccant Films Made of Low-Density Polyethylene with Dispersed Silica Gel-Water Vapor Absorption, Permeability (H2O, N2, O2, CO2), and Mechanical Properties

Silica gel is a well-known desiccant. Through dispersion of silica gel in a polymer, films can be made that absorb and desorb water vapor. The water vapor absorption becomes reversible by exposing such films to a water vapor pressure below that of the water vapor pressure during absorption, or by heating the film. The intention of this study was to achieve a better understanding about the water vapor absorption, permeability (H2O, N2, O2, CO2), and mechanical properties of films with dispersed silica gel. Low-density polyethylene (PE-LD) monolayer films with a nominal silica gel concentration of 0.2, 0.4, and 0.6 g dispersed silica gel per 1 g film (PE-LD) were prepared and they absorbed up to 0.08 g water vapor per 1 g of film. The water vapor absorption as a function of time was described by using effective diffusion coefficients. The steady state (effective) water vapor permeation coefficients of the films with dispersed silica gel were a factor of 2 to 14 (8.4 to 60.2·10-12 mg·cm·(cm²·s·Pa)-1, 23 °C) higher than for pure PE-LD films (4.3·10-12 mg·cm·(cm²·s·Pa)-1, 23 °C). On the other hand, the steady state gas permeabilities for N2, O2, and CO2 were reduced to around one-third of the pure PE-LD films. An important result is that (effective) water vapor permeation coefficients calculated from results of sorption and measured by permeation experiments yielded similar values. It has been found that it is possible to describe the sorption and diffusion behavior of water by knowing the permeability coefficient and the sorption capacity of the film (Peff.≈Seff.·Deff.). The tensile stress changed only slightly (values between 10 and 14 N mm-²), while the tensile strain at break was reduced with higher nominal silica gel concentration from 318 length-% (pure PE-LD film) to 5 length-% (PE-LD with 0.6 g dispersed silica gel per 1 g film).

Water-solid interactions in amorphous maltodextrin-crystalline sucrose binary mixtures

Amorphous and crystalline solids are commonly found together in a variety of pharmaceutical and food products. In this study, the influence of co-formulation of amorphous maltodextrins (MDs) and crystalline sucrose (S) on moisture sorption, deliquescence, and glass transition (Tg) properties of powder blends was investigated. Individual components and binary mixtures of four different molecular weight MDs with sucrose in 1:1 w/w ratios were exposed to various relative humidity (RH) environments and their equilibrium and dynamic moisture contents were monitored. The deliquescence point (RH0) and dissolution behavior of sucrose alone and in blends was also monitored by polarized light microscopy and second harmonic generation imaging. In S:MD blends, the deliquescence RH of sucrose was lower than the RH0 of sucrose alone, and synergistic moisture sorption also occurred at RHs lower than the RH0. Intimate contact of sucrose crystals with the amorphous MDs resulted in complete dissolution of sucrose at RH < RH0. When blends were stored at conditions exceeding the Tg of the individual MDs (25 °C and 60%, 49% and 34%RH for MD21, MD29 and MD40, respectively), the Tg of the blends was lower than that of individual MDs. Thus, co-formulation of amorphous MDs with crystalline sucrose sensitizes the blend to moisture, potentially leading to deleterious changes in the formulation if storage conditions are not adequately controlled.

Water-solids interactions: deliquescence

Deliquescence is a first order phase transition from solid to solution that occurs at a relative humidity (RH) that is characteristic to the solid ingredient. In blends containing more than one component with deliquescent behavior, the RH of the solid-solution transition will be lowered, leading to some level of dissolution at relatively low RH conditions. Dissolution arising as a result of deliquescence will impact the chemical and physical stability of complex food systems. Because chemical reactions occur much more readily in solution, deliquescence will enhance the degradation of labile food ingredients. RH fluctuations will lead to cycles of deliquescence and efflorescence (crystallization), which will contribute to particle agglomeration and caking. This review addresses the phenomenon of deliquescence, the significance of deliquescence to the food industry, measurement techniques, the kinetics and thermodynamics of deliquescence, the behavior of mixtures of deliquescent salts (including phase diagrams and thermodynamics of binary systems), and consequences of deliquescence on chemical and physical stability of powdered food and nutritional ingredient blends.

Transformation pathways of cocrystal hydrates when coformer modulates water activity

An important attribute of cocrystals is that their properties can be tailored to meet required solubility and stability specifications. But before such practical uses can be realized, a better understanding of the factors that dictate co-crystal behavior is needed. This study attempts to explain the phase behavior of anhydrous/hydrated cocrystals when the coformer modulates both water activity and co-crystal solubility. Stability dependence on solution composition and water activity was studied for theophylline-citric acid (THP-CTA) anhydrous and hydrated cocrystals by both suspension and vapor equilibration methods. Eutectic points and associated water activities were measured by suspension equilibration methods to determine stability regions and phase diagrams. The critical water activity for the anhydrous-hydrate co-crystal was found to be 0.8. It is shown that (a) both water and coformer activities determine phase stability, and (b) excipients that alter water activity can profoundly affect the hydrate/anhydrous eutectic points and phase stability. Vapor phase stability studies demonstrate that cocrystals of highly water soluble coformers, such as citric acid, are predisposed to conversions due to moisture uptake and deliquescence of the coformer. The presence of such coformers as trace level impurities with co-crystal will alter hygroscopic behavior and stability.

Kinetics of moisture-induced hydrolysis in powder blends stored at and below the deliquescence relative humidity: investigation of sucrose-citric acid mixtures

Previous studies have shown that deliquescent organic compounds frequently exhibit chemical instability when stored in environmental conditions above their deliquescence relative humidity (RH). The goal of the current study was to investigate the effect of atmospheric moisture on the long-term chemical stability of crystalline sucrose-citric acid mixtures following storage at RHs at and below the mutual deliquescence relative humidity (MDRH). Interestingly, it was found that sucrose hydrolysis can occur below the MDRH of 64% and was observed for samples stored at 54% RH. However, hydrolysis was not seen for samples stored at 33 or 43% RH. The rate of sucrose hydrolysis could be modeled by taking into account the rate and extent of moisture uptake, which in turn was dependent on the composition of the powder and the storage RH. A reaction mechanism initiated by capillary condensation and involving additional deliquescence lowering by the degradation products formed as a result of sucrose hydrolysis (glucose and fructose) was proposed.

Mechanisms by which moisture generates cocrystals

The purpose of this study is to determine the mechanisms by which moisture can generate cocrystals when solid particles of cocrystal reactants are exposed to deliquescent conditions (when moisture sorption forms an aqueous solution). It is based on the hypothesis that cocrystallization behavior during water uptake can be derived from solution chemistry using models that describe cocrystal solubility and reaction crystallization of molecular complexes. Cocrystal systems were selected with active pharmaceutical ingredients (APIs) that form hydrates and include carbamazepine, caffeine, and theophylline. Moisture uptake and crystallization behavior were studied by gravimetric vapor sorption, X-ray powder diffraction, and on-line Raman spectroscopy. Results indicate that moisture uptake generates cocrystals of carbamazepine-nicotinamide, carbamazepine-saccharin, and caffeine or theophylline with dicarboxylic acid ligands (oxalic acid, maleic acid, glutaric acid, and malonic acid) when solid mixtures with cocrystal reactants deliquesce. Microscopy studies revealed that the transformation mechanism to cocrystal involves (1) moisture uptake, (2) dissolution of reactants, and (3) cocrystal nucleation and growth. Studies of solid blends of reactants in a macro scale show that the rate and extent of cocrystal formation are a function of relative humidity, moisture uptake, deliquescent material, and dissolution rates of reactants. It is shown that the interplay between moisture uptake and dissolution determines the liquid phase composition, supersaturation, and cocrystal formation rates. Differences in the behavior of deliquescent additives (sucrose and fructose) are associated with moisture uptake and composition of the deliquesced solution. Our results show that deliquescence can transform API to cocrystal or reverse the reaction given the right conditions. Key indicators of cocrystal formation and stability are (1) moisture uptake, (2) cocrystal aqueous solubility, (3) solubility and dissolution of cocrystal reactants, and (4) transition concentration.