Enantiospecific crystallisation behaviour of malic acid in mechanochemical reactions with vinpocetine

We report an intriguing example of enantioselectivity in the formation of new multicomponent crystalline solid containing vinpocetine and malic acid. Several experimental data sets confirmed that the multicomponent system presents a clear enantiospecific crystallisation behaviour both in the solid-state and in solution: only the system consisting of vinpocetine and L-malic acid produces a free-flowing solid consisting of a new crystalline form, while the experiments with D-malic acid produced an amorphous and often deliquescent material. The new vinpocetine-L-malic system crystallizes in the monoclinic space group of P21 and in a 1:1 M ratio, where the two molecules are linked through intermolecular hydrogen bonds in the asymmetric unit. The vinpocetine-DL-malic system was partially crystalline (with also traces of unreacted vinpocetine) with diffraction peaks corresponding to those of vinpocetine-L-malic acid. Solid-state NMR experiments revealed strong ionic interactions in all the three systems. However, while vinpocetine-L-malic acid system was a pure and crystalline phase, in the other two systems the presence of unreacted vinpocetine was always detected. This resulted in a significant worsening of the dissolution profile with respect to vinpocetine-L-malic pure crystalline salt, whose dissolution kinetics appeared superior.

Sweeteners Show a Plasticizing Effect on PVP K30-A Solution for the Hot-Melt Extrusion of Fixed-Dose Amorphous Curcumin-Hesperetin Solid Dispersions

The co-administration of curcumin and hesperetin might be beneficial in terms of neuroprotective activity; therefore, in this study, we attempted to develop a fixed-dose formulation comprising these two compounds in an amorphous state. The aim of obtaining an amorphous state was to overcome the limitations of the low solubility of the active compounds. First, we assessed the possibility of using popular sweeteners (erythritol, xylitol, and sorbitol) as plasticizers to reduce the glass transition temperature of PVP K30 to prepare the polymer-excipient blends, which allowed the preparation of amorphous solid dispersions via hot-melt extrusion at a temperature below the original glass transition of PVP K30. Erythritol proved to be the superior plasticizer. Then, we focused on the development of fixed-dose amorphous solid dispersions of curcumin and hesperetin. Powder X-ray diffraction and thermal analysis confirmed the amorphous character of dispersions, whereas infrared spectroscopy helped to assess the presence of intermolecular interactions. The amorphous state of the produced dispersions was maintained for 6 months, as shown in a stability study. Pharmaceutical parameters such as dissolution rate, solubility, and in vitro permeability through artificial membranes were evaluated. The best improvement in these features was noted for the dispersion, which contained 15% of the total content of the active compounds with erythritol used as the plasticizer.

Amorphous Solid Forms of Ranolazine and Tryptophan and Their Relaxation to Metastable Polymorphs

Different methods were explored for the amorphization of ranolazine, a sparingly soluble anti-anginal drug, such as mechanochemistry, quench-cooling, and solvent evaporation from solutions. Amorphous phases, with Tg values lower than room temperature, were obtained by cryo-milling and quench-cooling. New forms of ranolazine, named II and III, were identified from the relaxation of the ranolazine amorphous phase produced by cryo-milling, which takes place within several hours after grinding. At room temperature, these metastable polymorphs relax to the lower energy polymorph I, whose crystal structure was solved in this work for the first time. A binary co-amorphous mixture of ranolazine and tryptophan was produced, with three important advantages: higher glass transition temperature, increased kinetic stability preventing relaxation of the amorphous to crystalline phases for at least two months, and improved aqueous solubility. Concomitantly, the thermal behavior of amorphous tryptophan obtained by cryo-milling was studied by DSC. Depending on experimental conditions, it was possible to observe relaxation directly to the lower energy form or by an intermediate metastable crystalline phase and the serendipitous production of the neutral form of this amino acid in the pure solid phase.

Eudragit® FS Microparticles Containing Bacteriophages, Prepared by Spray-Drying for Oral Administration

Phage therapy is recognized to be a promising alternative to fight antibiotic-resistant infections. In the quest for oral dosage forms containing bacteriophages, the utilization of colonic-release Eudragit^® derivatives has shown potential in shielding bacteriophages from the challenges encountered within the gastrointestinal tract, such as fluctuating pH levels and the presence of digestive enzymes. Consequently, this study aimed to develop targeted oral delivery systems for bacteriophages, specifically focusing on colon delivery and employing Eudragit^® FS30D as the excipient. The bacteriophage model used was LUZ19. An optimized formulation was established to not only preserve the activity of LUZ19 during the manufacturing process but also ensure its protection from highly acidic conditions. Flowability assessments were conducted for both capsule filling and tableting processes. Furthermore, the viability of the bacteriophages remained unaffected by the tableting process. Additionally, the release of LUZ19 from the developed system was evaluated using the Simulator of the Human Intestinal Microbial Ecosystem (SHIME^®) model. Finally, stability studies demonstrated that the powder remained stable for at least 6 months when stored at +5 °C.

Effect of Plasticization on Stretching Stability of Poly(Vinyl Alcohol) Films: A Case Study Using Glycerol and Water

Adding small molecular plasticizers is the most common route to tailor the stretchability of poly(vinyl alcohol) (PVA). However, how the plasticization along with the nature of the plasticizer governs the structural homogeneity during stretching remains an open question to answer. Herein, two representative plasticizers, glycerol (GLY) and water, are chosen to endow the PVA films with ductility. It is found that large strain cavitations cause obvious stress whitening in the PVA/H₂ O films; on the contrary, most of the PVA/GLY films maintain transparent undergoing tensile deformation. Through a combination of experimental inspections and molecular dynamic simulation, it is revealed that partial water molecules that behave as free water will aggregate into microdomains, which serve as mechanical defects responsible for yielding voids. Whereas, the GLY plasticizer homogeneously disperses at a molecular level and interacts with PVA chains through strong hydrogen bonds. More interestingly, it is illustrated that the dispersion and bound states of plasticizers are closely related to the mechanical character of the plasticized PVA films. These findings offer new insight into the working mechanism of plasticization on the structural stability during stretching, and guide the design of PVA/plasticizer system to obtain excellent comprehensive mechanics.

Mechanistic study of the solubilization effect of basic amino acids on a poorly water-soluble drug

Amino acids have shown promising abilities to form complexes with poorly water-soluble drugs and improve their physicochemical properties for a better dissolution profile through molecular interactions. Salt formation via ionization between acidic drugs and basic amino acids is known as the major contributor to solubility enhancement. However, the mechanism of solubility enhancement due to non-ionic interactions, which is less pH-dependent, remains unclear. The aim of this study is to evaluate non-ionic interactions between a model acidic drug, indomethacin (IND), and basic amino acids, arginine, lysine and histidine, in water. At low concentrations of amino acids, IND-arginine and IND-lysine complexes have shown a linear relationship (A_L-type phase solubility diagram) between IND solubility and amino acid concentration, producing ∼1 : 1 stoichiometry of drug-amino acid complexes as expected due to the strong electrostatic interactions. However, IND-histidine complexes have shown a nonlinear relationship with lower improvement in IND solubility due to the weaker electrostatic interactions when compared to arginine and lysine. Interestingly, the results have also shown that at high arginine concentrations, the linearity was lost between IND solubility and amino acid concentration with a negative diversion from linearity, following the type-A_N phase solubility. This is indicative that the electrostatic interaction is being interrupted by non-electrostatic interactions, as seen with histidine. The IND-lysine complex, on the other hand, showed a complex curvature phase solubility diagram (type B_S) as lysine self-assembles and polymerizes at higher concentrations. The freeze-dried drug-amino acid solids were further characterized using thermal analysis and infrared spectroscopy, with results showing the involvement of weak non-ionic interactions. This study shows that the solubility improvement of an insoluble drug in the presence of basic amino acids was due to both non-ionic and ionic interactions.

Hydrogen-bond-dominated mechanical stretchability in PVA films: from phenomenological to numerical insights

Hydrogen bonds (H-bonds) in poly(vinyl alcohol) (PVA) play a crucial role in macroscopic mechanical properties, particularly for stretchability. However, there is still some ambiguity about the quantitative dependence of H-bond interactions on the mechanical performance, mainly attributed to the difficulty in the discrimination of various H-bond types. Herein, small molecular chemicals as plasticizers were incorporated into the PVA matrix to tailor the H-bonding interactions. By altering the PVA molecular weight, plasticizer type and loading, both the stretchability and H-bond content were regulated on a large scale. By a combination of DMA, IR spectroscopy, MD simulation and solid-state ¹³C-NMR, every sort of H-bond in PVA was assigned, and their relative fractions were ascertained quantitatively. After correlating the elongation ratio with the relative fraction of the different types of H-bonding interaction, it was found that all the pairs of elongation vs. intermolecular H-bond content derived from different series of PVA/plasticizer films could be plotted into a master curve and exhibited good linearity, indicating that intermolecular H-bonds dominate the mechanical stretchability in PVA films. Our efforts contribute towards an in-depth understanding of performance optimization induced by H-bond manipulation from empirical, phenomenological aspects to intrinsic, numerical insights.

A Design of Experiment Approach to Optimize Spray-Dried Powders Containing Pseudomonas aeruginosaPodoviridae and Myoviridae Bacteriophages

In the present study, we evaluated the effect of spray-drying formulations and operating parameters of a laboratory-scale spray-dryer on the characteristics of spray-dried powders containing two Pseudomonas aeruginosa bacteriophages exhibiting different morphotypes: a podovirus (LUZ19) and a myovirus (14-1). We optimized the production process for bacteriophage-loaded powders, with an emphasis on long-term storage under ICH (international conference on harmonization) conditions. D-trehalose-/L-isoleucine-containing bacteriophage mixtures were spray-dried from aqueous solutions using a Büchi Mini Spray-dryer B-290 (Flawil, Switzerland). A response surface methodology was used for the optimization of the spray-drying process, with the following as-evaluated parameters: Inlet temperature, spray gas flow rate, and the D-trehalose/L-isoleucine ratio. The dried powders were characterized in terms of yield, residual moisture content, and bacteriophage lytic activity. L-isoleucine has demonstrated a positive impact on the activity of LUZ19, but a negative impact on 14-1. We observed a negligible impact of the inlet temperature and a positive correlation of the spray gas flow rate with bacteriophage activity. After optimization, we were able to obtain dry powder preparations of both bacteriophages, which were stable for a minimum of one year under different ICH storage conditions (up to and including 40 °C and 75% relative humidity).

Combining crystalline and polymeric excipients in API solid dispersions - Opportunity or risk?

Amorphous solid dispersions (ASDs) are often metastable against crystallization of the active pharmaceutical ingredient (API) and thus might undergo unwanted changes during storage. The crystallization tendency of ASDs is influenced by the API crystallization driving force (CDF) and the mobility of the molecules in the ASD. Low molecular weight-excipients are known to stabilize amorphous APIs in so-called co-amorphous formulations. Due to their success in stabilizing co-amorphous APIs, low-molecular weight excipients might also enhance the stability of polymeric ASDs. In this work, we investigated the potential of combined low-molecular weight excipient/polymer formulations with in-silico tools and validated the predictions with long-term stability tests of the most promising excipient/polymer combinations. The considered critical quality attributes for the ASDs were the occurrence of amorphous phase separation, API CDF, and molecular mobility in the ASD. As an example, carbamazepine/polyvinylpyrrolidone ASDs were investigated combined with the excipients fructose, lactose, sucrose, trehalose, saccharin, tryptophan, and urea. Although all excipients had a negative impact on the ASD stability, saccharin still turned out to be the most promising one. Long-term stability studies with ASDs containing either saccharin or tryptophan verified -in agreement to the predictions- that API crystallization occurred faster than in the reference ASDs without additional excipient. This work showed that the addition of crystalline excipients to polymeric ASDs might not only offer opportunities but might also bear risks for the long-term stability of the ASD, even though the crystalline excipient stabilizes the polymer-free API. Consequently, excipients should be evaluated based on the thermodynamic phase behavior of the individual mixture of API/polymer/excipient, rather than based on pure-component properties of the excipient only. In-silico predictions proposed in this work remarkably decrease the number of screening tests for identifying suitable formulation excipients.

The Importance of Quantifying the Composition of the Amorphous Intermixed Phase in Organic Solar Cells

The relation of phase morphology and solid-state microstructure with organic photovoltaic (OPV) device performance has intensely been investigated over the last twenty years. While it has been established that a combination of donor:acceptor intermixing and presence of relatively phase-pure donor and acceptor domains is needed to get an optimum compromise between charge generation and charge transport/charge extraction, a quantitative picture of how much intermixing is needed is still lacking. This is mainly due to the difficulty in quantitatively analyzing the intermixed phase, which generally is amorphous. Here, fast scanning calorimetry, which allows measurement of device-relevant thin films (<200 nm thickness), is exploited to deduce the precise composition of the intermixed phase in bulk-heterojunction structures. The power of fast scanning calorimetry is illustrated by considering two polymer:fullerene model systems. Somewhat surprisingly, it is found that a relatively small fraction (<15 wt%) of an acceptor in the intermixed amorphous phase leads to efficient charge generation. In contrast, charge transport can only be sustained in blends with a significant amount of the acceptor in the intermixed phase (in this case: ≈58 wt%). This example shows that fast scanning calorimetry is an important tool for establishing a complete compositional characterization of organic bulk heterojunctions. Hence, it will be critical in advancing quantitative morphology-function models that allow for the rational design of these devices, and in delivering insights in, for example, solar cell degradation mechanisms via phase separation, especially for more complex high-performing systems such as nonfullerene acceptor:polymer bulk heterojunctions.

Myth or Truth: The Glass Forming Ability Class III Drugs Will Always Form Single-Phase Homogenous Amorphous Solid Dispersion Formulations

The physical stability of amorphous solid dispersions (ASD) of active pharmaceutical ingredients (APIs) of high glass forming ability (GFA class III) is generally expected to be high among the scientific community. In this study, the ASD of ten-selected class III APIs with the two polymers, PVPVA 64 and HPMC-E5, have been prepared by spray-drying, film-casting, and their amorphicity at T0 was investigated by modulated differential scanning calorimetry and powder X-ray diffraction. It was witnessed that only five out of ten APIs form good quality amorphous solid dispersions with no phase separation and zero crystalline content, immediately after the preparation and drying process. Hence, it was further established that the classification of an API as GFA class III does not guarantee the formulation of single phase amorphous solid dispersions.

Influence of mechanical and thermal energy on nifedipine amorphous solid dispersions prepared by hot melt extrusion: Preparation and physical stability

Hot melt extrusion (HME) has been used to prepare solid dispersions, especially molecularly dispersed amorphous solid dispersions (ASDs) for solubility enhancement purposes. The energy generated by the extruder in the form of mechanical and thermal output enables the dispersion and dissolution of crystalline drugs in polymeric carriers. However, the impact of this thermal and mechanical energy on ASD systems remains unclear. We selected a model ASD system containing nifedipine (NIF) and polyvinylpyrrolidone vinyl acetate (PVP/VA 64) to investigate how different types of energy input affect the preparation and physical stability of ASDs. Formulations were prepared using a Leistritz Nano-16 extruder, and we varied the screw design, barrel temperature, screw speed, and feed rate to control the mechanical and thermal energy input. Specific mechanical energy (SME) was calculated to quantitate the mechanical energy input, and the thermal energy was estimated using barrel temperature. We find that both mechanical and thermal energy inputs affect the conversion of crystalline NIF into an amorphous form, and they also affect the level of mixing and the degree of homogeneity in NIF ASDs. However, for small size extruders (e.g., Leistritz Nano-16), thermal energy is more efficient than mechanical energy in preparing NIF ASDs that have better stability.