a-package-established-analytical-tools-to-investigate-solid-state

A Package of Established Analytical Tools to Investigate the Solid-State Alteration of Lipid-Based Excipients

Lipid-based excipients (LBEs) are low-toxic, biocompatible, and natural-based, and their application supports the sustainability of pharmaceutical ...

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The purpose of this work was to investigate the influence of residual water in freeze-dried protein powders on the dissolution behavior of the solid-state proteins. To that end, six freeze-dried fibrinogen powder lots were stored at four levels of relative humidity and analyzed with regard to the particle size and shape, the specific surface area, the solid state of protein and the inner surface. Furthermore, the dissolution behavior of the powders was investigated. We clearly identified differences in the specific surface area, specific inner surface area, crystallinity, particle size and shape, which we were able to correlate to the dissolution behavior. These differences were triggered due to the different levels of residual moisture during two weeks of storage. Thus, we were able to show that the storage conditions have significant impact on the processing of pharmaceutical protein materials. 

The influence of residual water on the solid-state properties of freeze-dried fibrinogen.

Although lipid excipients are of increasing interest for development of taste-masked and modified release formulations, the drug release instability and the lack of mechanistic understanding in that regard still prevent their larger-scale application. In this work, we investigated the physical stability of a binary (tripalmitin/polysorbate 65) lipid coating formulation with a known stable polymorphism. The coating composition was characterized using DSC to construct the phase diagram of binary system and polarized light microscopy to display the microstructure organization. The water uptake and the erosion of slabs cast from the coating formulations were investigated post-production and after storage. Subsequently, N-acetylcysteine particles were coated with the selected formulations and the drug release stability was investigated. Additionally, microstructure characterization was performed via SEM and X-ray diffraction. The drug release instability was explained by polysorbate 65 and tripalmitin phase growth during storage, especially at 40°C, suggesting that polysorbate 65 can leak out of tripalmitin spherulitic structures, creating lipophilic and impermeable tripalmitin regions. The growth of polysorbate 65 phase leads to larger hydrophilic channels with reduced tortuosity. This work indicates that for obtaining stable drug release profiles from advanced lipid formulations, microphase separation should be prevented during storage.

Microphase separation in solid lipid dosage forms as the cause of drug release instability.

Self-emulsifying drug delivery systems (SEDDS), often intended for oral delivery, are normally explored in biorelevant aqueous media. The high complexity of these multi-component systems leaves the understanding of self-emulsification poor, hindering formulation rationalization. In this work, we aimed to fill this gap by studying the effects of glycerol on the self-emulsification of a ternary component formulation made of 20% w/w Tween 80, 15% w/w Span 80, and 65% w/w Captex 300 Low C6. The behavior of SEDDS in pure water and a binary mixture of water and glycerol (58.8% w/w) were investigated by optical microscopy, SAXS (small angle X-ray scattering), dynamic light scattering, and surface tension measurements. The presence of glycerol, at 58.8% w/w, altered the self-emulsification behavior by suppressing the formation of lamellar structures observed in the presence of water, reducing the droplet mean diameter from 0.2 to 0.1 μm and changing the mechanism of self-emulsification. As co-surfactant, glycerol may intercalate within the polyoxyethylene chains of the surfactant at the palisade layer, increasing the interface flexibility and expanding it. Since no free water is available at the investigated glycerol concentration, glycerol, which is also a co-solvent, may additionally modify long-range interactions by reducing Van-der-Waals attractions or giving rise to repulsive surface-solvent mediated forces of entropic origin. These effects could be exploited to rationalize SEDDS formulations, widening their use within the pharmaceutical industry.

Self-emulsification of Lipidic Drug Delivery System in Pure Water and in Concentrated Glycerol Solution.

The effect of different irradiation doses on the structure and activity of lyophilized powders of Hen Egg-White Lysozyme (HEWL) and alcohol dehydrogenase (ADH) was investigated using these substances as models for robust and sensitive proteins, respectively. Three doses were selected to cover the ranges of radio-sterilization (25kGy), treatment of blood products (25Gy) and annual background radiation dose (approximately 2mGy). The results offer an initial screening of different irradiation doses and support the development of X-ray imaging methods as non-destructive process analytical technology (PAT) tools for detecting the visible particulate matters in such products.

Effect of Technically Relevant X-Ray Doses on the Structure and Function of Alcohol Dehydrogenase and Hen Egg-White Lysozyme.

The analytical potential of X-ray small-angle scattering (SAXS) combined with simultaneous wide-angle diffraction (WAXS) has been explored on the example of three active pharmaceutical ingredients, (desvenlofaxine, simvastatin, and sulfamerazine, resp.) with the aim of identifying quantitative parameters obtained from SAXS that allow to describe the nano-structural characteristics of different amorphous forms and to monitor the processes of amorphisation and ageing. Cryo-milling, co-milling with polymer, melting and melt-quenching have been used for amorphisation of initially crystalline powders. In parallel to SAXS, the WAXS patterns have been obtained to fingerprint the crystalline state. The SAXS results demonstrate strong, systematic nanostructure variations in amorphous samples obtained by different milling conditions, or by melt-quenching. It has been found that the mean-square density fluctuation, directly obtained from the SAXS invariant, is a sensitive and robust parameter to characterize the degree of nano-heterogeneity, which is related to entropy and hence thermodynamic stability. The SAXS curves also allow estimates of amorphous domain sizes of different density. The propensity to recrystallize or to remain amorphous, respectively, upon ageing has been found to depend on the existence of domains in the starting amorphous materials.

Density fluctuations in amorphous pharmaceutical solids. Can SAXS help to predict stability?

Solvent-free hot melt coating (HMC) provides a safer and more economic process compared to the conventional solvent coating techniques. However, drug release instability and the lack of fundamental understanding on it are limiting factors for application of HMC for industrial productions. In this work, we investigated glyceryl dibehenate, glyceryl monostearate and behenoyl polyoxyl-8 glyceride as HMC materials. The microstructure and solid state alteration of lipids were studied via polarized light microscopy, DSC and powder x-ray diffraction. Microcapsules of N-acetylcysteine particles were provided with these excipients and stored under long term and accelerated conditions for 3 months. The feasibility of selected lipids as HMC excipients was confirmed. The drug release from freshly coated microcapsules was dictated by microstructure, solid state and HLB of lipid coating. Alterations in the release profiles after storage under accelerated conditions were correlated with time-dependent structural alterations of selected lipids. The faster drug release from glyceryl dibehenate and behenoyl polyoxyl-8 glyceride microcapsules was correlated with a low-melting small fraction composed by mixed phases in glyceryl dibehenate and the amorphous region of polyoxyl part in behenoyl polyoxyl-8 glyceride, respectively. The slower drug release from glyceryl dibehenate after storage was explained by the transition of lipid crystals to the β-form with dense crystalline structure. The gained information can be used to design effective tempering strategies for providing stable pharmaceutical products.

Correlation between the solid state of lipid coating and release profile of API from hot melt coated microcapsules.

The present study investigated the impact of solid-state disorders generated during milling on the chemical reactivity of simvastatin. An amorphous and a partially crystalline simvastatin powders were generated via cryomilling simvastatin crystals for either 90 or 10 min, respectively. The thoroughly characterized milled powders were stored at 40°C/75% RH, in open and closed containers. The effect of milling and storage conditions on physical stability was investigated using simultaneous small and wide-angle X-ray scattering and differential scanning calorimetry. The chemical degradation was evaluated using liquid chromatography-mass spectrometry. Compared with the fully amorphous state, the partially crystalline simvastatin crystallized to a lower extent in the expense of higher chemical degradation on open storage. The closely stored samples degraded to a lower extent and crystallized to a higher extent than the openly stored ones. However, the trends of the total crystallinity and degradation between amorphous and partially crystalline powders were similar. Small-angle X-ray scattering revealed that the partially crystalline simvastatin comprised a higher extent of nanoscale density heterogeneity than the fully amorphous powder. The overall results pointed toward the role of the remaining amorphous content and the nanoscale and mesoscale density heterogeneity on the chemical reactivity in the disordered simvastatin.

Solid-State Reactivity of Mechano-Activated Simvastatin: Atypical Relation to Powder Crystallinity.

Previously, we reported on the surfactant cetylpyridinium chloride (CPC) as a crosslinker of alginate for the formation of stable polyelectrolyte-surfactant-complex nanoparticles. Here, we evaluate this system for increased solubility of a poorly soluble drug. The aim was to use CPC for solubilisation of ibuprofen and to use the micellar associates formed for alginate complexation and nanoparticle formation. We acquired deeper insights into the entropy led interactions between alginate, CPC and ibuprofen. Stable nanoparticles were formed across limited surfactant-to-polyelectrolyte molar ratios, with ~150 nm hydrodynamic diameter, monodispersed distribution, and negative zeta potential (-40 mV), with 34% ibuprofen loading. Their structure was obtained using small-angle X-ray scattering, which indicated disordered micellar associates when ibuprofen was incorporated. This resulted in nanoparticles with a complex nanostructured composition, as shown by transmission electron microscopy. Drug release from ibuprofen-cetylpyridinium-alginate nanoparticles was not hindered by alginate, and was similar to the release kinetics from ibuprofen-CPC solubilisates. These innovative carriers developed as polyelectrolyte-surfactant complexes can be used for solubilisation of poorly soluble drugs, where the surfactant simultaneously increases the solubility of the drug at concentrations below its critical micellar concentration and crosslinks the polyelectrolyte to form nanoparticles.

Polyelectrolyte-surfactant-complex nanoparticles as a delivery platform for poorly soluble drugs: A case study of ibuprofen loaded cetylpyridinium-alginate system.

This article describes the designing of matrix tablets composed of polyethylene oxides (PEOs) with relative molecular masses of 1 × 106, 2 × 106, and 4 × 106. Percolation thresholds were determined for all of the selected PEO formulations (18, 16, and 12 %, m/m), taking into consideration excipients and tablet surface area which significantly increased the percolation threshold. Moreover, the robustness of the gel layer in PEO matrix tablets was evaluated by magnetic resonance imaging under various mechanical stresses (no flow, 12 mL min-1, and 64 mL-1 of medium flow). Correlations between the percolation threshold and gel thickness (R2 = 0.86), gel thickness and the erosion coefficient (R2 = 0.96) was detected. Furthermore, small-angle X-ray scattering of the selected PEOs detected differences in polymer molecular complexity at the nanoscale. Finally, the ratio of the heat of coalescence to the heat of fusion has confirmed the PEO molecular mass-dependent percolation threshold.

Polyethylene oxide matrix tablet swelling evolution: The impact of molecular mass and tablet composition.

The present study investigates the chemical composition governing the physical properties of mono- and diglycerides (MDGs) at the microstructural level, as a function of aging and lot-to-lot variability. The physical structure of the MDG plays a vital role in ameliorating the emulsion stability and is widely explored in diverse research horizons related to the pharmaceutical, cosmetic, and food industries. In an effort to understand the mechanism of emulsion stabilization, physical properties were extensively evaluated in selective commercial lots to determine if there is a correlation between the chemical composition of MDG and physical properties. The solid state of the MDG samples with different aging profiles was characterized using X-ray scattering, differential scanning calorimetry, attenuated total reflection-Fourier transform infrared spectroscopy, and NMR relaxometry. Moreover, the kinetic aspect of solid-state transformation was also evaluated via treating MDG samples with a heat-cool cycle. The chemical composition of MDGs was quantified using a quantitative NMR (qNMR) method. Interestingly, the X-ray scattering results demonstrated a change in the MDG polymorphic form and an increase in the %β content as a function of aging. The increase in the %β content led to the formation of rigid crystal structures of MDG, as evident from the NMR relaxometry. Chemical quantification of isomeric composition revealed chemical composition change as a potentially critical factor responsible for the altered physical structures of MDG with respect to aging and lot-to-lot variability. The findings correlated the solid-state transformation with the change in the chemical composition of the MDG as a combined effect of aging and lot-to-lot variability. This work serves as a basis to better understand the interdependency of the physicochemical properties of MDG. Furthermore, the present work can also be used as guidance for setting up the specifications of MDG, as per the required polymorphic form for a multitude of applications.

Interplay of Aging and Lot-to-Lot Variability on the Physical and Chemical Properties of Excipients: A Case Study of Mono- and Diglycerides.

Orally inhaled products (OIPs) are gaining increased attention, as pulmonary delivery is a preferred route for the treatment of various diseases. Yet, the field of inhalation biopharmaceutics is still in development phase. For a successful correlation between various in vitro data obtained during formulation characterization and in vivo performance, it is necessary to understand the impact of parameters such as solubility and dissolution of drugs. In this work, we used in vitro-in silico feedback-feedforward approach to gain a better insight into the biopharmaceutics behavior of inhaled Salbutamol Sulphate (SS) and Budesonide (BUD). The thorough characterization of the in vitro test media and the impact of different in vitro fluid components such as lipids and protein on the solubility of aforementioned drugs was studied. These results were subsequently used as an input into the developed in silico models to investigate potential PK parameter changes in vivo. Results revealed that media comprising lipids and albumin were the most biorelevant and impacted the solubility of BUD the most. On the contrary, no notable impact was seen in case of SS. The use of simple media such as phosphate buffer saline (PBS) might be sufficient to use in solubility studies of the highly soluble and permeable drugs. However, its use for the poorly soluble drugs is limited due to the greater potential for interactions within in vivo environment. The use of in silico tools showed that the model response varies, depending on the used media. Therefore, this work highlights the relevance of carefully selecting the media composition when investigating solubility and dissolution behavior, especially in the early phases of drug development and of poorly soluble drugs.

Impact of simulated lung fluid components on the solubility of inhaled drugs and predicted in vivo performance.

Hydrochlorothiazide (HCT) multiparticulate systems (MPS) were hot melt coated with the binary mixture of tripalmitin (PPP) and polysorbate 65 (PS 65) to gain an immediate release profile. Once, HCT MPS were produced with a constant ratio of PPP/PS 65 (90:10) at three different coating amounts (15, 25, and 60%) and once the PPP/PS 65 ratio was varied on 98:2 and 80:20, by keeping the coating amount at 60%. PS 65 induced the polymorphic transformation of PPP from the α-form to its most stable β-form right after the hot melt coating (HMC). A release alteration of HCT, either accelerated or decelerated, occurred after the storage under accelerated conditions. The effect of the API core on the lipid lamellar configuration, the thermal behavior of lipid coating, and the effect of PS 65 concentration on the crystal growth of PPP were investigated via X-ray diffraction and DSC. While a low amount of PS 65 was sufficient to promote crystal growth of PPP and resulted in a decelerated release of HCT from the coating, a higher PS 65 concentration favored phase separation of PPP and PS 65 and led to an accelerated release. The increase in PS 65 reinforced the molecular interaction with the lipophilic HCT, reflected in less crystal growth and decelerated release. The knowledge presented in this study supports understanding the instability of binary emulsifier-lipid coating systems, paving the way for developing robust HMC formulations.

Impact of polysorbate 65 on tripalmitin crystal growth and release stability of hot melt coated multiparticulate systems.

The impact of the crystallinity of organic solid materials on their tribocharging propensity is well reported. However, no unequivocal explanation about the potential underlying mechanism(s) could be found so far in the literature. This study reports the effect that different degrees of crystalline disorder has on the tribocharging propensity of a small molecular organic material, salbutamol sulfate (SS). Ball-milling was used to induce structural transformations in the crystalline structure of SS. Particles with different nanostructures were produced and analyzed for their solid-state, particle properties, and tribocharging. It was found that differences in the amorphous content among the processed particles and related moisture levels had an impact on powder tribocharging. A correlation between the latter and the nanostructural properties of the particles was also established. The presence of interfaces between nanodomains of different densities and shorter average lengths within the phases seems to lead to a mitigation of charge. This suggests that undetected, subtle nanostructural differences of materials can affect powder handling and processability by altering their tribocharging. The present findings demonstrate the nanostructural implications of powder triboelectrification, which can help toward the rational design of a wide variety of organic solids.

Article	Year
The influence of residual water on the solid-state properties of freeze-dried fibrinogen. European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V\| PubMed ID: 25617832	2015
Microphase separation in solid lipid dosage forms as the cause of drug release instability. International journal of pharmaceutics\| PubMed ID: 28007547	2017
Self-emulsification of Lipidic Drug Delivery System in Pure Water and in Concentrated Glycerol Solution. AAPS PharmSciTech\| PubMed ID: 28516413	2017
Effect of Technically Relevant X-Ray Doses on the Structure and Function of Alcohol Dehydrogenase and Hen Egg-White Lysozyme. Pharmaceutical research\| PubMed ID: 29736628	2018
Density fluctuations in amorphous pharmaceutical solids. Can SAXS help to predict stability? Colloids and surfaces. B, Biointerfaces\| PubMed ID: 29752132	2018
Correlation between the solid state of lipid coating and release profile of API from hot melt coated microcapsules. International journal of pharmaceutics\| PubMed ID: 31100383	2019
Solid-State Reactivity of Mechano-Activated Simvastatin: Atypical Relation to Powder Crystallinity. Journal of pharmaceutical sciences\| PubMed ID: 31173762	2019
Polyelectrolyte-surfactant-complex nanoparticles as a delivery platform for poorly soluble drugs: A case study of ibuprofen loaded cetylpyridinium-alginate system. International journal of pharmaceutics\| PubMed ID: 32147494	2020
Polyethylene oxide matrix tablet swelling evolution: The impact of molecular mass and tablet composition. Acta pharmaceutica (Zagreb, Croatia)\| PubMed ID: 33151172	2021
Interplay of Aging and Lot-to-Lot Variability on the Physical and Chemical Properties of Excipients: A Case Study of Mono- and Diglycerides. Molecular pharmaceutics\| PubMed ID: 33475378	2021
Impact of simulated lung fluid components on the solubility of inhaled drugs and predicted in vivo performance. International journal of pharmaceutics\| PubMed ID: 34274456	2021
Impact of polysorbate 65 on tripalmitin crystal growth and release stability of hot melt coated multiparticulate systems. International journal of pharmaceutics\| PubMed ID: 34363917	2021
Insights into the Impact of Nanostructural Properties on Powder Tribocharging: The Case of Milled Salbutamol Sulfate. Molecular pharmaceutics\| PubMed ID: 35044180	2022

Peter Laggner

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