Construction of Drug–Polymer Thermodynamic Phase Diagrams Using Flory–Huggins Interaction Theory: Identifying the Relevance of Temperature and Drug Weight Fraction to Phase Separation within Solid Dispersions

Unravelling the interactions between small molecules and liposomal bilayers via molecular dynamics and thermodynamic modelling

Lipid-based drug delivery systems hold immense promise in addressing critical medical needs, from cancer and neurodegenerative diseases to infectious diseases. By encapsulating active pharmaceutical ingredients - ranging from small molecule drugs to proteins and nucleic acids - these nanocarriers enhance treatment efficacy and safety. However, their commercial success faces hurdles, such as the lack of a systematic design approach and the issues related to scalability and reproducibility. This work aims to provide insights into the drug-phospholipid interaction by combining molecular dynamic simulations and thermodynamic modelling techniques. In particular, we have made a connection between the structural properties of the drug-phospholipid system and the physicochemical performance of the drug-loaded liposomal nanoformulations. We have considered two prototypical drugs, felodipine (FEL) and naproxen (NPX), and one model hydrogenated soy phosphatidylcholine (HSPC) bilayer membrane. Molecular dynamic simulations revealed which regions within the phospholipid bilayers are most and least favoured by the drug molecules. NPX tends to reside at the water-phospholipid interface and is characterized by a lower free energy barrier for bilayer membrane permeation. Meanwhile, FEL prefers to sit within the hydrophobic tails of the phospholipids and is characterized by a higher free energy barrier for membrane permeation. Flory-Huggins thermodynamic modelling, small angle X-ray scattering, dynamic light scattering, TEM, and drug release studies of these liposomal nanoformulations confirmed this drug-phospholipid structural difference. The naproxen-phospholipid system has a lower free energy barrier for permeation, higher drug miscibility with the bilayer, larger liposomal nanoparticle size, and faster drug release in the aqueous medium than felodipine. We suggest that this combination of molecular dynamics and thermodynamics approach may offer a new tool for designing and developing lipid-based nanocarriers for unmet medical applications.

Implications of Low-concentration Polymer on the Physical Stability of Glassy Griseofulvin: Role of the Segmental Mobility

Crystallization of amorphous pharmaceutical solids are widely reported to be affected by the addition of polymer, while the underlying mechanism require deep study. Herein, crystal growth behaviors of glassy griseofulvin (GSF) doped with various 1% w/w polymer were systematically studied. From the molecular structure, GSF cannot form the hydrogen bonding interactions with the selected polymer poly(vinyl acetate), polyvinyl pyrrolidone (PVP), 60:40 vinyl pyrrolidone-vinyl acetate copolymer (PVP/VA 64), and poly(ethylene oxide) (PEO). 1% w/w polymer exhibited weak or no detectable effects on the glass transition temperature (Tg) of GSF. However, crystal growth rates of GSF was altered from 4.27-fold increase to 2.57-fold decrease at 8 ℃ below Tg of GSF. Interestingly, the ability to accelerate and inhibit the growth rates of GSF crystals correlated well with Tg of polymer, indicating the controlling role of segmental mobility of polymer. Moreover, ring-banded growth of GSF was observed in the polymer-doped systems. Normal compact bulk and ring-banded crystals of GSF were both characterized as the thermodynamically stable form I. More importantly, formation of ring-banded crystals of GSF can significantly weaken the inhibitory effects of polymer on the crystallization of glassy GSF.

Development of Ternary Amorphous Solid Dispersions Manufactured by Hot-Melt Extrusion and Spray-Drying─Comparison of In Vitro and In Vivo Performance

Producing amorphous solid dispersions (ASDs) by hot-melt extrusion (HME) is favorable from an economic and ecological perspective but also limited to thermostable active pharmaceutical ingredients (APIs). A potential technology shift from spray-drying to hot-melt extrusion at later stages of drug product development is a desirable goal, however bearing the risk of insufficient comparability of the in vitro and in vivo performance of the final dosage form. Hot-melt extrusion was performed using API/polymer/surfactant mixtures with hydroxypropyl methylcellulose acetate succinate (HPMCAS) as the polymer and evaluated regarding the extrudability of binary and ternary amorphous solid dispersions (ASDs). Additionally, spray-dried ASDs were produced, and solid-state properties were compared to the melt-extruded ASDs. Tablets were manufactured of a ternary ASD lead candidate comparing their in vitro dissolution and in vivo performance. The extrudability of HPMCAS was improved by adding a surfactant as plasticizer, thereby lowering the high melt-viscosity. d-α-Tocopheryl polyethylene glycol succinate (TPGS) as surfactant showed the most similar solid-state properties between spray-dried and extruded ASDs compared to those of poloxamer 188 and sodium dodecyl sulfate. The addition of TPGS, however, barely affected API/polymer interactions. The in vitro dissolution experiment and in vivo dog study revealed a higher drug release of tablets manufactured from the spray-dried ASD compared to the melt-extruded ASD; this was attributed to the different particle size. We could further demonstrate that the drug release can be controlled by adjusting the particle size of melt-extruded ASDs leading to a similar release profile compared to tablets containing the spray-dried dispersion, which confirmed the feasibility of a technology shift from spray-drying to HME upon drug product development.

Solvent Content Controlling Strategy for Cocrystallizable Polyesters Enables a Stress-Free Two-Way Shape Memory Effect with Wider Service Temperatures

It is challenging to enhance the stress-free two-way shape memory (stress-free TWSM) effect to obtain a wide range of response temperatures. Herein, a polycaprolactone (PCL)/poly(ω-pentadecalactone) (PPDL) is photocured under UV light irradiation in the solvent of 1,1,2-trichloroethane (TCA), to obtain a series of cross-linked polyesters (CPES). Controlling solvent content (SC) which is removed after the polymerization allows the yielded CPES to perform a regulatable thermodynamic and stress-free TWSM properties. High SC is beneficial to reduce the degree of chain overlap (C/C* ) of PPDL chain segments in the PCL-based CPES network, then causes the cocrystallization of PCL and PPDL and yielding an additional melting-transitions (Tm ). An enhanced stress-free TWSM is obtained in high SC samples (CPES-15-90), reflected in the attainment of a wide range of response temperature, which means a wider service temperature. The enhancement is reflected in higher reversible strain of high SC samples compared with the samples prepared with low SC when varying high trigger temperature (Thigh ). Even at high Thigh , the high SC sample still has reversible strain. Therefore, controlling SC strategy for photocuring copolyester not only provides a new preparation approach for high-performance shape memory (SM) polymers, but also offers new condensed polymer structure to explore.

Material-Sparing Feasibility Screening for Hot Melt Extrusion

Hot melt extrusion (HME) offers a high-throughput process to manufacture amorphous solid dispersions. A variety of experimental and model-based approaches exist to predict API solubility in polymer melts, but these methods are typically aimed at determining the thermodynamic solubility and do not take into account kinetics of dissolution or the associated degradation of the API during thermal processing, both of which are critical considerations in generating a successful amorphous solid dispersion by HME. This work aims to develop a material-sparing approach for screening manufacturability of a given pharmaceutical API by HME using physically relevant time, temperature, and shear. Piroxicam, ritonavir, and phenytoin were used as model APIs with PVP VA64 as the dispersion polymer. We present a screening flowchart, aided by a simple custom device, that allows rapid formulation screening to predict both achievable API loadings and expected degradation from an HME process. This method has good correlation to processing with a micro compounder, a common HME screening industry standard, but only requires 200 mg of API or less.

Stability Challenges of Amorphous Solid Dispersions of Drugs: A Critical Review on Mechanistic Aspects

The most common drawback of the existing and novel drug molecules is their low bioavailability because of their low solubility. One of the most important approaches to enhance the bioavailability in the enteral route for poorly hydrophilic molecules is amorphous solid dispersion (ASD). The solubility of compounds in amorphous form is comparatively high because of the availability of free energy produced during formulation. This free energy results in the change of crystalline nature of the prepared ASD to the stable crystalline form leading to the reduced solubility of the product. Due to the intrinsic chemical and physical uncertainty and the restricted knowledge about the interactions of active molecules with the carriers making, this ASD is a challenging task. This review focused on strategies to stabilize ASD by considering the various theories explaining the free-energy concept, physical interactions, and thermal properties. This review also highlighted molecular modeling and machine learning computational advancement to stabilize ASD.

The step-wise dissolution method: An efficient DSC-based protocol for verification of predicted API-polymer compatibility

The development of an amorphous solid dispersion (ASD) is a promising strategy for improving the low bioavailability of many poorly water-soluble active pharmaceutical ingredients (APIs). The construction of a temperature-composition (T-C) phase diagram for an API-polymer combination is imperative as it can provide critical information that is essential for formulating stable ASDs. However, the currently followed differential scanning calorimetry (DSC)-based strategies for API solubility determination in a polymer at elevated temperatures are inefficient and, on occasions, unreliable, which may lead to an inaccurate prediction at lower temperatures of interest (i.e., T = 25 °C). Recently, we proposed a novel DSC-based protocol called the "step-wise dissolution" (S-WD) method, which is both cost- and time-effective. The objective of this study was to test the applicability of the S-WD method regarding expeditious verification of the purely-predicted API-polymer compatibility via the perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state (EOS). Fifteen API-polymer T-C phase diagrams were reliably constructed, with three distinct API-polymer case types being identified regarding the approach used for the S-WD method. Overall, the PC-SAFT EOS provided satisfactory qualitative descriptions of the API-polymer compatibility, but not necessarily accurate quantitative predictions of the API solubility in the polymer at T = 25 °C. The S-WD method was subsequently modified and an optimal protocol was proposed, which can significantly reduce the required experimental effort.

Drug-excipient compatibility studies in formulation development: A case study with benznidazole and monoglycerides

Monoglycerides (MGs) such as glycerol monolaurate (GML) and glycerol monostearate (GMS) have been used as excipients in oral formulations because of their emulsifying effect as well as their ability to inhibit the precipitation and intestinal efflux of drugs. Excipient-drug compatibility studies, however, have been underexplored. In this study, benznidazole (BNZ) was selected as a drug model due to the difficulty in improving its solubility and because of the potential impact on public health (it is the only drug currently used to treat Chagas disease). The effect of different processing conditions (maceration, ball milling, and melting) on the physical-chemistry properties of BNZ/MGs mixtures was investigated to guide the rational development of new solid formulations. GML was more effective in improving the solubility of BNZ, which could be due to its more malleable structure, less hydrophobic nature, and greater interaction with BNZ. The formation of hydrogen bonds between the imidazole group of BNZ and the polar region of GML was confirmed by spectroscopy analyses (IR, 1H NMR). The higher the monoglyceride content in the mixture, the higher the BNZ solubility. Regardless of the method of processing the mixture, the drug was found to be crystalline. Polarized light microscopy analysis showed the presence of spherulites. Overall, these findings suggest that preparation methods of BNZ:MGs formulations that involve thermal or/and mechanical treatment have a low impact on the solid properties of the material, and this allows for the production of formulations with reproducible performance.

Advances in the development of amorphous solid dispersions: The role of polymeric carriers

Amorphous solid dispersion (ASD) is one of the most effective approaches for delivering poorly soluble drugs. In ASDs, polymeric materials serve as the carriers in which the drugs are dispersed at the molecular level. To prepare the solid dispersions, there are many polymers with various physicochemical and thermochemical characteristics available for use in ASD formulations. Polymer selection is of great importance because it influences the stability, solubility and dissolution rates, manufacturing process, and bioavailability of the ASD. This review article provides a comprehensive overview of ASDs from the perspectives of physicochemical characteristics of polymers, formulation designs and preparation methods. Furthermore, considerations of safety and regulatory requirements along with the studies recommended for characterizing and evaluating polymeric carriers are briefly discussed.

Selection of appropriate dapsone and poly(1-vinylpyrrolidone-co-vinyl acetate) ratios for the preparation of amorphous solid dispersions

Drug-polymer miscibility is a critical requirement for the efficient design and development of amorphous solid dispersions. The objective of the current study was to determine the miscibility between dapsone (DAP) and poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP-VA) through theoretical and experimental approaches, including the use of a thermodynamic phase diagram and Gibbs free energy of mixing. In the theoretical study, the difference in the solubility parameter between the DAP and PVP-VA was 2.74, the interaction parameter was 0.50, and the distance between the drug and polymer in the Bagley plot was 2.60. Hence, all these theoretical parameters favour the miscibility between DAP and PVP-VA. Melting point depression study (through thermal analysis) and Flory-Huggins theory were utilized for the practical determination of drug-polymer miscibility, where the interaction parameter was positive, suggesting limited miscibility. The obtained thermodynamic phase diagram and Gibbs free energy of mixing plot can provide an indication for the selection of appropriate drug-polymer ratios in stable and metastable zones and the optimum processing temperature required for the preparation of amorphous solid dispersions.

Investigating the physicochemical properties of solid dispersions based on semicrystalline carriers: A case study with ketoprofen

Hydrophilic semicrystalline carriers represent an alternative to amorphous polymers due to their low melting temperature, useful for the production of solid dispersions (SDs) by melting-based technologies. This research aims to compare SDs of ketoprofen (KET) and three different semicrystalline carriers (PEG, Poloxamer and Gelucire) regarding miscibility, phase behavior, molecular interactions and stability. KET was chosen owing to its low solubility and high glass forming ability. Estimation of drug-excipient miscibility was performed by Flory-Huggins theory. Negative Gibbs free energy indicated a spontaneous mixing of KET with the three carriers and miscibility in the order PEG > Poloxamer > Gelucire. SDs up to 40 % w/w of drug were produced by melting process at a temperature below KET melting point. Characterization of SDs was performed by differential scanning calorimetry, polarized light microscopy and powder X-ray diffraction. In case of PEG and Poloxamer, the drug incorporation did not affect carrier crystallinity, while KET was in the amorphous state. Differently, KET retarded the crystallization of Gelucire and at high drug loadings the SDs were amorphous and semisolid. FT-IR analysis revealed a strong interaction between KET and the three carriers. Finally, PEG-based SDs above 20 % KET loading displayed drug crystallization after 6 months of storage; while Poloxamer and Gelucire-based SDs showed KET crystallization only at 40 % KET. Due to its less hydrophilic character and limited water uptake, Gelucire showed the best stability among the three excipients.

Inhomogeneous Phase Significantly Reduces Oral Bioavailability of Felodipine/PVPVA Amorphous Solid Dispersion

Inhomogeneity is a key factor that significantly influences the dissolution behavior of amorphous solid dispersion (ASD). However, the underlying mechanisms of the effects of inhomogeneous phase on the dissolution characteristics as well as the bioavailability of ASDs are still unclear. In this study, two types of felodipine/PVPVA based ASDs with 30 wt % drug loading but different homogeneity were prepared: homogeneous "30 wt % ASD" prepared by spray drying, as well as inhomogeneous "30 wt % PM" prepared by physically mixing the sprayed dried 70 wt % ASD with PVPVA. We aimed to investigate (1) drug-polymer interaction mechanism and "apparent" interaction strength within the two ASDs and (2) dissolution mechanism as well as in vivo performance of the two ASDs. DSC thermogram revealing a single T_g in 30 wt % ASD confirmed its homogeneous phase. ¹H NMR, FT-IR, and DVS studies collectively proved that strong hydrogen bonding interactions formed between felodipine and PVPVA in ASDs. Moreover, homogeneous "30 wt % ASD" has more numbers of interacting drug-polymer pairs, and thus exhibits stronger "apparent" interaction strength comparing with that of inhomogeneous "30 wt % PM". Unexpectedly,in the in vitro dissolution studies, inhomogeneous "30 wt % PM" showed much faster dissolution and also generated drug concentration ∼4.4 times higher than that of homogeneous "30 wt % ASD". However, drug precipitate recrystallized much slower in homogeneous "30 wt % ASD", presumably because much more polymer coprecipitated with amorphous drug in this system, which helps inhibiting drug crystallization. Surprisingly, homogeneous "30 wt % ASD" showed a significantly higher bioavailability in the in vivo pharmacokinetic studies, with the maximum plasma concentrations (C_max) and the area under the curve (AUC) values of about 2.7 and 2.3 times higher than those of inhomogeneous "30 wt % PM". The above findings indicated that the amorphous state of drug precipitate contributes significantly to increase bioavailability of ASDs, while traditional in vitro dissolution studies, for instance, if we only compare the dissolved drug in solution or the capability of an ASD to generate supersaturation, are inadequate to predict in vivo performance of ASDs. In conclusion, the phase behavior of ASDs directly impact the formation of drug-polymer interaction, which controls not only drug supersaturation in solution but also drug crystallization in precipitate, and ultimately affect the in vivo performance of ASDs.

Development of a multiparticulate drug delivery system for in situ amorphisation

In the current study, the concept of multiparticulate drug delivery systems (MDDS) was applied to tablets intended for the amorphisation of supersaturated granular ASDs in situ, i.e. amorphisation by microwave irradiation within the final dosage form. The MDDS concept was hypothesised to ensure geometric and structural stability of the dosage form and to improve the in vitro disintegration and dissolution characteristics. Granules were prepared in two sizes (small and large) containing the crystalline drug celecoxib (CCX) and polyvinylpyrrolidone/vinyl acetate copolymer (PVP/VA) at a 50 % w/w drug load as well as sodium dihydrogen phosphate monohydrate as the microwave absorbing excipient. The granules were subsequently embedded in an extra-granular tablet phase composed of either the filler microcrystalline cellulose (MCC) or mannitol (MAN), as well as the disintegrant crospovidone and the lubricant magnesium stearate. The tensile strength and disintegration time were investigated prior to and after 10 min of microwave irradiation (800 and 1000 W) and the formed ASDs were characterised by X-ray powder diffraction and modulated differential scanning calorimetry. Additionally, the internal structure was elucidated by X-ray micro-Computed Tomography (XµCT) and, finally, the dissolution performance of selected tablets was investigated. The MDDS tablets displayed no geometrical changes after microwave irradiation, however, the tensile strength and disintegration time increased. Complete amorphisation of CCX was achieved only for the MCC-based tablets at a power input of 1000 W, while MAN-based tablets displayed partial amorphisation independent of power input. The complete amorphisation of CCX was associated with the fusion of individual ASD granules within the tablets, which impacted the subsequent disintegration and dissolution performance. For these tablets, supersaturation was only observed after 60 min. On the other hand, the partially amorphised MDDS tablets displayed complete disintegration during the dissolution experiments, resulting in a fast onset of supersaturation within 5 min and an approx. 3.5-fold degree of supersaturation within the experimental timeframe (3 h). Overall, the MDDS concept was shown to potentially be a feasible dosage form for in situ amorphisation, however, there is still room for improvement to obtain a fully amorphous and disintegrating system.

Amorphous Solid Dispersions: Role of the Polymer and Its Importance in Physical Stability and In Vitro Performance

Amorphous solid dispersions stabilized by one or more polymer(s) have been widely used for delivering amorphous drugs with poor water solubilities, and they have gained great market success. Polymer selection is important for preparing robust amorphous solid dispersions, and considerations should be given as to how the critical attributes of a polymer can enhance the physical stability, and the in vitro and in vivo performances of a drug. This article provides a comprehensive overview for recent developments in the understanding the role of polymers in amorphous solid dispersions from the aspects of nucleation, crystal growth, overall crystallization, miscibility, phase separation, dissolution, and supersaturation. The critical properties of polymers affecting the physical stability and the in vitro performance of amorphous solid dispersions are also highlighted. Moreover, a perspective regarding the current research gaps and novel research directions for better understanding the role of the polymer is provided. This review will provide guidance for the rational design of polymer-based amorphous pharmaceutical solids with desired physicochemical properties from the perspective of physical stability and in vitro performance.

Supersaturated amorphous solid dispersions of celecoxib prepared by in situ microwave irradiation

This study investigated the ability of in situ amorphization using microwave irradiation in order to prepare highly supersaturated ASDs, i.e. ASDs with drug loads higher than the saturation solubility in the polymer at ambient temperature. For this purpose, compacts containing the crystalline drug celecoxib (CCX) and polyvinylpyrrolidone (PVP), polyvinylpyrrolidone-vinyl acetate copolymer (PVP/VA), or polyvinyl acetate (PVAc), were prepared at drug loads between 30-90 % w/w. Sodium dihydrogen phosphate (NaH₂PO₄) monohydrate was included in all compacts, as a source of water, to facilitate the dielectric heating of the compacts upon dehydration during microwave irradiation. After processing, the samples were analysed towards their solid state using X-ray powder diffraction (XRPD) and modulated differential scanning calorimetry (mDSC). Complete amorphisation of CCX was achieved across all the investigated polymers and with a maximal drug load of 90, 80, and 50 % w/w in PVP, PVP/VA, and PVAc, respectively. These drug loads corresponded to a 2.3-, 2.4-, and 10.0-fold supersaturation in the investigated polymers at ambient temperature. However, dissolution experiments with the in situ prepared ASDs in fasted state simulated intestinal fluid (FaSSIF), showed a lower initial drug release (0-2 hours) compared to equivalent physical mixtures of crystalline CCX and polymers or crystalline CCX alone. The lower drug release rate was explained by the fusion of individual drug and polymer particles during microwave irradiation and, subsequently, a lack of disintegration of the monolithic ASDs. Nevertheless, supersaturation of CCX in FaSSIF was achieved with the in situ amorphised ASDs with PVP and PVP/VA, albeit only after 3-24 h. Overall, the present study confirmed that it is feasible to prepare supersaturated ASDs in situ. However, in the current experimental setup, the monolithic nature of the resulting ASDs is considered a limiting factor in the practical applicability of this preparation method, due to limited disintegration and the associated negative effect on the drug release.

A universal strategy for the fabrication of single-photon and multiphoton NIR nanoparticles by loading organic dyes into water-soluble polymer nanosponges

The development of optical organic nanoparticles (NPs) is desirable and widely studied. However, most organic dyes are water-insoluble such that the derivatization and modification of these dyes are difficult. Herein, we demonstrated a simple platform for the fabrication of organic NPs designed with emissive properties by loading ten different organic dyes (molar masses of 479.1-1081.7 g/mol) into water-soluble polymer nanosponges composed of poly(styrene-alt-maleic acid) (PSMA). The result showed a substantial improvement over the loading of commercial dyes (3.7-50% loading) while preventing their spontaneous aggregation in aqueous solutions. This packaging strategy includes our newly synthesized organic dyes (> 85% loading) designed for OPVs (242), DSSCs (YI-1, YI-3, YI-8), and OLEDs (ADF-1-3, and DTDPTID) applications. These low-cytotoxicity organic NPs exhibited tunable fluorescence from visible to near-infrared (NIR) emission for cellular imaging and biological tracking in vivo. Moreover, PSMA NPs loaded with designed NIR-dyes were fabricated, and photodynamic therapy with these dye-loaded PSMA NPs for the photolysis of cancer cells was achieved when coupled with 808 nm laser excitation. Indeed, our work demonstrates a facile approach for increasing the biocompatibility and stability of organic dyes by loading them into water-soluble polymer-based carriers, providing a new perspective of organic optoelectronic materials in biomedical theranostic applications.

A Hot-Melt Extrusion Risk Assessment Classification System for Amorphous Solid Dispersion Formulation Development

Several literature publications have described the potential application of active pharmaceutical ingredient (API)–polymer phase diagrams to identify appropriate temperature ranges for processing amorphous solid dispersion (ASD) formulations via the hot-melt extrusion (HME) technique. However, systematic investigations and reliable applications of the phase diagram as a risk assessment tool for HME are non-existent. Accordingly, within AbbVie, an HME risk classification system (HCS) based on API–polymer phase diagrams has been developed as a material-sparing tool for the early risk assessment of especially high melting temperature APIs, which are typically considered unsuitable for HME. The essence of the HCS is to provide an API risk categorization framework for the development of ASDs via the HME process. The proposed classification system is based on the recognition that the manufacture of crystal-free ASD using the HME process fundamentally depends on the ability of the melt temperature to reach the API’s thermodynamic solubility temperature or above. Furthermore, we explored the API–polymer phase diagram as a simple tool for process design space selection pertaining to API or polymer thermal degradation regions and glass transition temperature-related dissolution kinetics limitations. Application of the HCS was demonstrated via HME experiments with two high melting temperature APIs, sulfamerazine and telmisartan, with the polymers Copovidone and Soluplus. Analysis of the resulting ASDs in terms of the residual crystallinity and degradation showed excellent agreement with the preassigned HCS class. Within AbbVie, the HCS concept has been successfully applied to more than 60 different APIs over the last 8 years as a robust validated risk assessment and quality-by-design (QbD) tool for the development of HME ASDs.

Use of Flory-Huggins Interaction Parameter and Contact Angle Values to Predict the Suitability of the Drug-Polymer System for the Production and Stability of Nanosuspensions

PURPOSE

Use of Flory-Huggins interaction parameter and contact angle values to predict the suitability of the drug-polymer system for the production and stability of nanosuspensions.

MATERIAL AND METHODS

Melting point depression of the drug was measured using differential scanning calorimetry. Interaction parameter, χ, was calculated using the melting point depression data to elucidate the drug-polymer interaction strength to predict the suitability of the drug-polymer system for the production and stability of nanosuspensions. Contact angle of the drug films were measured with purified water and 0.1%w/w polymer solutions to predict polymer's suitability for the production and stability of nanosuspension. Nanosuspensions were manufactured to validate the application of the melting point depression approach along with surface property information.

RESULTS

All three polymers, HPMC, Soluplus®, and poloxamer exhibited a negative interaction parameter with naproxen and budesonide. Higher negative interaction parameter values for the naproxen-polymer system indicated stronger drug-polymer interactions, while smaller negative interaction parameter values for the budesonide-polymer system indicated weaker drug-polymer interactions. Interaction parameter was not obtained for fenofibrate with HPMC and Soluplus®, and similarly, no interaction parameter was obtained for carvedilol with HPMC, most likely due to weaker drug-polymer interactions. All three polymers provided lower equilibrium contact angle values when compared to purified water, indicating an affinity for polymers.

CONCLUSIONS

Successful production and stability of several nanosuspensions were correlated with Flory-Huggins's interaction parameter and contact angle values. In the absence of melting point depression, contact angle values can also be used predict the agglomeration tendencies as we have shown for this study.

Amorphous Solid Dispersions: Utilization and Challenges in Preclinical Drug Development within AstraZeneca

The poor aqueous solubility of many active pharmaceutical ingredients (APIs) dominates much of the early drug development portfolio and poses a major challenge in pharmaceutical development. Polymer-based amorphous solid dispersions (ASDs) are becoming increasingly common and offer a promising formulation strategy to tackle the solubility and oral absorption issues of these APIs. This review discusses the design, manufacture, and utilisation of ASD formulations in preclinical drug development, with a key focus on the pre-formulation assessments and workflows employed at AstraZeneca.

Pharmaceutical profiling and molecular dynamics simulations reveal crystallization effects in amorphous formulations

Robust and reliable in vivo performance of medicines based on amorphous solid dispersions (ASDs) depend on maintenance of physical stability and efficient supersaturation. However, molecular drivers of these two kinetic processes are poorly understood. Here we used molecular dynamics (MD) simulations coupled with experimental assessments to explore supersaturation, nucleation, and crystal growth. The effect of drug loading on physical stability and supersaturation potential was highly drug specific. Storage under humid conditions influenced crystallization, but also resulted in morphological changes and particle fusion. This led to increased particle size, which significantly reduced dissolution rate. MD simulations identified the importance of nano-compartmentalization in the crystallization rate of the ASDs. Nucleation during storage did not inherently compromise the ASD. Rather, the poorer performance resulted from a combination of properties of the compound, nanostructures formed in the formulation, and crystallization.

Theoretical and experimental validation of praziquantel with different polymers for selection of an appropriate matrix for hot-melt extrusion

The selection of an appropriate matrix for the preparation of amorphous extrudate in hot-melt extrusion (HME) deals with the study of various solid-state properties of drugs and polymers. Therefore, it is necessary to have an appropriate knowledge of drug-polymer miscibility, the interaction between the drug-polymer on mixing, and Gibb's free thermal energy of mixing to screen polymers through thermodynamic phase diagrams, to be suitable amorphous matrix system for HME. Here, we evaluated the possibility of three different polymers, namely, Eudragit®EPO, polyvinyl alcohol (PVA), Kollicoat®IR (KIR) with Praziquantel (PZQ), with proper validation of the Flory-Huggins theory and construction of the phase diagram using the melting point depression approach to determine a suitable matrix for HME. The solubility parameter theoretical calculation approach was used as a preliminary study to validate the miscibility of PZQ with three different polymers. Theoretical and experimental validation studies using the Flory-Huggins interaction parameter value using the melting point depression approach and the effect of PZQ loading on the interaction parameter were systematically validated to predict thermodynamic phase diagrams and Gibbs free energy of mixing for screening these polymers for the preparation of amorphous extrudate. Using the phase diagram, the thermal processing temperature for the HME was determined using a T-φ phase diagram to obtain an appropriate matrix. The obtained extrudates were further validated through physical appearance, microscopic structure, thermal and functional group characterizations, followed by the PZQ assay. Thus, considering the solid-state properties, the processing parameters of HME were selected to obtain stable extrudates and an appropriate matrix for PZQ loading.

The effects of protein charge patterning on complex coacervation

The complex coacervation of proteins with other macromolecules has applications in protein encapsulation and delivery and for determining the function of cellular coacervates. Theoretical or empirical predictions for protein coacervates would enable the design of these coacervates with tunable and predictable structure-function relationships; unfortunately, no such theories exist. To help establish predictive models, the impact of protein-specific parameters on complex coacervation were probed in this study. The complex coacervation of sequence-specific, polypeptide-tagged, GFP variants and a strong synthetic polyelectrolyte was used to evaluate the effects of protein charge patterning on phase behavior. Phase portraits for the protein coacervates demonstrated that charge patterning dictates the protein's binodal phase boundary. Protein concentrations over 100 mg mL-1 were achieved in the coacervate phase, with concentrations dependent on the tag polypeptide sequence covalently attached to the globular protein domain. In addition to shifting the binodal phase boundary, polypeptide charge patterning provided entropic advantages over isotropically patterned proteins. Together, these results show that modest changes of only a few amino acids in the tag polypeptide sequence alter the coacervation thermodynamics and can be used to tune the phase behavior of polypeptides or proteins of interest.

Continuous manufacture of hydroxychloroquine sulfate drug products via hot melt extrusion technology to meet increased demand during a global pandemic: From bench to pilot scale

During pandemics and global crises, drug shortages become critical as a result of increased demand, shortages in personnel and lockdown restrictions that disrupt the supply chain. The pharmaceutical industry is therefore moving towards continuous manufacturing instead of conventional batch manufacturing involving numerous steps, that normally occur at different sites. In order to validate the use of large-scale industrial processes, feasibility studies need to be performed using small-scale laboratory equipment. To that end, the scale-up of a continuous process and its effect on the critical quality attributes (CQAs) of the end product were investigated in this work. Hydroxychloroquine Sulphate (HCQS) was used as the model drug, Soluplus® as a model polymeric carrier and both horizontal and vertical twin screw extruders used to undertake this hot melt extrusion (HME) study. Seven formulations were processed using a small-scale horizontal extruder and a pilot-scale vertical extruder at various drug loadings, temperature profiles and screw speeds. When utilising a horizontal extruder, formulations with the highest drug load and processed at the lowest screw speed and temperature had the highest crystallinity with higher drug release rates. Upon scale-up to a vertical extruder, the crystallinity of the HCQS was significantly reduced, with less variation in both crystallinity and release profile across the different extrudates. This study demonstrates improved robustness with the pilot-scale vertical extruder compared to lab-scale horizontal extruder. The reduced variation with the vertical extruder will allow for short increases in production rate, with minimum impact on the CQAs of the final product enabling high-performance continuous manufacturing with minimum waste of raw materials. Finally, this research provides valuable information for the pharmaceutical industry in accessing continuous technologies for the manufacture of pharmaceutical products, allowing for efficient utilisation of resources upon scale-up and mass production during global pandemics and drug shortages.

Hot-Melt Extrusion: a Roadmap for Product Development

Hot-melt extrusion has found extensive application as a feasible pharmaceutical technological option over recent years. HME applications include solubility enhancement, taste masking, and sustained drug release. As bioavailability enhancement is a hot topic of today's science, one of the main applications of HME is centered on amorphous solid dispersions. This review describes the most significant aspects of HME technology and its use to prepare solid dispersions as a drug formulation strategy to enhance the solubility of poorly soluble drugs. It also addresses molecular and thermodynamic features critical for the physicochemical properties of these systems, mainly in what concerns miscibility and physical stability. Moreover, the importance of applying the Quality by Design philosophy in drug development is also discussed, as well as process analytical technologies in pharmaceutical HME monitoring, under the current standards of product development and regulatory guidance. Graphical Abstract.

Considerations for the selection of co-formers in the preparation of co-amorphous formulations

Co-amorphous drug delivery systems are evolving as a credible alternative to amorphous solid dispersions technology. In Co-amorphous systems (CAMs), a drug is stabilized in amorphous form using small molecular weight compounds called as co-formers. A wide variety of small molecular weight co-formers have been leveraged in the preparation of CAMs. The stability and supersaturation potential of prepared co-amorphous phases largely depend on the type of co-former employed in the CAMs. However, the rationality behind the co-former selection in co-amorphous systems is poorly understood and scarcely compiled in the literature. There are various facets to the rational selection of co-former for CAMs. In this context, the present review compiles various factors affecting the co-former selection. The factors have been broadly classified under Thermodynamic, Kinetic and Pharmacokinetic-Pharmacologically relevant parameters. In particular, the importance of Glass transition, Miscibility, Liquid-Liquid phase separation (LLPS), Crystallization inhibition has been deliberated in detail.

Specific mechanical energy - An essential parameter in the processing of amorphous solid dispersions

Specific mechanical energy (SME) is a frequently overlooked but essential parameter of hot-melt extrusion (HME). It can determine whether an amorphous solid dispersion (ASD) can be successfully processed. A minimum combination of thermal input and SME is required to convert a crystalline active pharmaceutical product (API) into its amorphous form. A maximum combination is allowed before it or the carrier polymer chemically degrades. This has important implications on design space. SME input during HME provides information on the totality of the effect of various independent processing parameters such as screw speed, feed rate, and complex viscosity. If only these independent processing parameters are considered separately instead of SME, then important information would be lost regarding the interaction of these parameters and their ability to affect ASD formulation. A complete understanding of the HME process requires an analysis of SME. This paper provides a review of SME use in the pharmaceutical processing of ASDs, the importance of SME in terms of a variety of formulation qualities, and novel future uses of SME. Theoretical background is discussed, along with the relative importance of thermal and mechanical input on various nonsolvent ASD processing methods.

Analytical and Computational Methods for the Determination of Drug-Polymer Solubility and Miscibility

In the pharmaceutical industry, poorly water-soluble drugs require enabling technologies to increase apparent solubility in the biological environment. Amorphous solid dispersion (ASD) has emerged as an attractive strategy that has been used to market more than 20 oral pharmaceutical products. The amorphous form is inherently unstable and exhibits phase separation and crystallization during shelf life storage. Polymers stabilize the amorphous drug by antiplasticization, reducing molecular mobility, reducing chemical potential of drug, and increasing glass transition temperature in ASD. Here, drug-polymer miscibility is an important contributor to the physical stability of ASDs. The current Review discusses the basics of drug-polymer interactions with the major focus on the methods for the evaluation of solubility and miscibility of the drug in the polymer. Methods for the evaluation of drug-polymer solubility and miscibility have been classified as thermal, spectroscopic, microscopic, solid-liquid equilibrium-based, rheological, and computational methods. Thermal methods have been commonly used to determine the solubility of the drug in the polymer, while other methods provide qualitative information about drug-polymer miscibility. Despite advancements, the majority of these methods are still inadequate to provide the value of drug-polymer miscibility at room temperature. There is still a need for methods that can accurately determine drug-polymer miscibility at pharmaceutically relevant temperatures.

Amorphous Salts Solid Dispersions of Celecoxib: Enhanced Biopharmaceutical Performance and Physical Stability

Numerous amorphous solid dispersion (ASD) formulations of celecoxib (CEL) have been attempted for enhancing the solubility, dissolution rate, and in vivo pharmacokinetics via high drug loading, polymer combination, or by surfactant addition. However, physical stability for long-term shelf life and desired in vivo pharmacokinetics remains elusive. Therefore, newer formulation strategies are always warranted to address poor aqueous solubility and oral bioavailability with extended shelf life. The present investigation elaborates a combined strategy of amorphization and salt formation for CEL, providing the benefits of enhanced solubility, dissolution rate, in vivo pharmacokinetics, and physical stability. We generated amorphous salts solid dispersion (ASSD) formulations of CEL via an in situ acid-base reaction involving counterions (Na⁺ and K⁺) and a polymer (Soluplus) using the spray-drying technique. The generated CEL-Na and CEL-K salts were homogeneously and molecularly dispersed in the matrix of Soluplus polymer. The characterization of generated ASSDs by differential scanning calorimetry revealed a much higher glass-transition temperature (T_g) than the pure amorphous CEL, confirming the salt formation of CEL in solid dispersions. The micro-Raman and proton nuclear magnetic resonance spectroscopy further confirmed the formation of salt at the -S═O position in the CEL molecules. CEL-Na-Soluplus ASSD exhibited a synergistic enhancement in the aqueous solubility (332.82-fold) and in vivo pharmacokinetics (9.83-fold enhancement in the blood plasma concentration) than the crystalline CEL. Furthermore, ASSD formulations were physically stable for nearly 1 year (352 days) in long-term stability studies at ambient conditions. Hence, we concluded that the ASSD is a promising strategy for CEL in improving the physicochemical properties and biopharmaceutical performance.

Utilizing Laser Activation of Photothermal Plasmonic Nanoparticles to Induce On-Demand Drug Amorphization inside a Tablet

Poor aqueous drug solubility represents a major challenge in oral drug delivery. A novel approach to overcome this challenge is drug amorphization inside a tablet, that is, on-demand drug amorphization. The amorphous form is a thermodynamically instable, disordered solid-state with increased dissolution rate and solubility compared to its crystalline counterpart. During on-demand drug amorphization, the drug molecularly disperses into a polymer to form an amorphous solid at elevated temperatures inside a tablet. This study investigates, for the first time, the utilization of photothermal plasmonic nanoparticles for on-demand drug amorphization as a new pharmaceutical application. For this, near-IR photothermal plasmonic nanoparticles were tableted together with a crystalline drug (celecoxib) and a polymer (polyvinylpyrrolidone). The tablets were subjected to a near-IR laser at different intensities and durations to study the rate of drug amorphization under each condition. During laser irradiation, the plasmonic nanoparticles homogeneously heated the tablet. The temperature was directly related to the rate and degree of amorphization. Exposure times as low as 180 s at 1.12 W cm^-2 laser intensity with only 0.25 wt % plasmonic nanoparticles and up to 50 wt % drug load resulted in complete drug amorphization. Therefore, near-IR photothermal plasmonic nanoparticles are promising excipients for on-demand drug amorphization with laser irradiation.

Solubilizing temperature of crystalline drug in polymer carrier: A rheological investigation on a posaconazole-copovidone system with low drug load

Measuring the solubility of a crystalline active pharmaceutical ingredient (API) in a polymer-rich system is challenging due to the high viscosity of the polymer which kinetically impedes reaching the solubility equilibrium. In this study, a rheological approach of determining the solubilizing temperature of a crystalline API in a polymeric carrier has been developed. To validate the method, a model physical mixture of crystalline posaconazole and copovidone with a relatively low API load (25 wt%) was utilized. First, a comparison between conventional differential scanning calorimetry (DSC) and a rheological temperature ramp was conducted to illustrate that the rheological method could capture the melting point depression behavior similarly to the more well-known DSC technique. Second, to further understand the dissolution process of the crystalline posaconazole into the copovidone carrier and precisely measure the solubilizing temperature, a series of isothermal rheological time sweeps were carried out at various temperatures selected based on the rheological temperature sweep. Because the dissolved API molecule imparted a plasticizing effect to the polymeric carrier, the complex viscosity of the API-polymer system decreased gradually over time and correlated well to an exponential decay function. Moreover, dependent on the applied temperature, the API-polymer system eventually accomplished distinct equilibrium states (complex viscosities) within different time frames. The obtained time constants at different temperatures were fitted to the Arrhenius equation, allowing the determination of the activation energy of the mixing process. The results indicated that once the processing temperature exceeded a critical point below the melting point of the crystalline API, the API-polymer solubilization process switched from a surface dominated dispersive mechanism to a molecular-level solubilization mode, manifested by the significantly increased activation energy. To the best of our knowledge, the currently developed rheological approach was the first successful measurement of the solubilizing temperature of a crystalline drug in a polymer-rich system.

Enhanced Solubility and Bioavailability of Dolutegravir by Solid Dispersion Method: In Vitro and In Vivo Evaluation-a Potential Approach for HIV Therapy

Being a candidate of BCS class II, dolutegravir (DTG), a recently approved antiretroviral drug, possesses solubility issues. The current research was aimed to improve the solubility of the DTG and thereby enhance its efficacy using the solid dispersion technique. In due course, the miscibility study of the drug was performed with different polymers, where Poloxamer 407 (P407) was found suitable to move forward. The solid dispersion of DTG and P407 was formulated using solvent evaporation technique with a 1:1 proportion of drug and polymer, where the solid-state characterization was performed using differential scanning calorimetry, Fourier transform infrared spectroscopy and X-ray diffraction. No physicochemical interaction was found between the DTG and P407 in the fabricated solid dispersion; however, crystalline state of the drug was changed to amorphous as evident from the X-ray diffractogram. A rapid release of DTG was observed from the solid dispersion (>95%), which is highly significant (p<0.05) as compared to pure drug (11.40%), physical mixture (20.07%) and marketed preparation of DTG (35.30%). The drug release from the formulated solid dispersion followed Weibull model kinetics. Finally, the rapid drug release from the solid dispersion formulation revealed increased C_max (14.56 μg/mL) when compared to the physical mixture (4.12 μg/mL) and pure drug (3.45 μg/mL). This was further reflected by improved bioavailability of DTG (AUC: 105.99±10.07 μg/h/mL) in the experimental Wistar rats when compared to the AUC of animals administered with physical mixture (54.45±6.58 μg/h/mL) and pure drug (49.27±6.16 μg/h/mL). Therefore, it could be concluded that the dissolution profile and simultaneously the bioavailability of DTG could be enhanced by means of the solid dispersion platform using the hydrophilic polymer, P407, which could be projected towards improved efficacy of the drug in HIV/AIDS.

How can we improve the physical stability of co-amorphous system containing flutamide and bicalutamide? The case of ternary amorphous solid dispersions

The article describes the preparation and characterization of binary mixtures of two antiandrogens used in prostate cancer treatment, i.e. flutamide (FL) and bicalutamide (BIC), as well as their ternary mixtures with either poly(methyl methacrylate-co-ethyl acrylate) (MMA/EA) or polyvinylpyrrolidone (PVP). The samples were converted into amorphous form to improve their water solubility and dissolution rate. Broadband dielectric spectroscopy and differential scanning calorimetry revealed that FL-BIC (65%) (w/w) does not tend to crystallize from the supercooled liquid state. We made the assumption that the drug-to-drug weight ratio should be maintained as in the case of monotherapy so we decided to investigate the system containing FL and BIC in 15:1 (w/w) ratio with 30% additive of polymers as stabilizers. Our research has shown that only in the case of the FL-BIC-PVP mixture the crystallization has been completely inhibited, both in glassy and supercooled liquid state, which was confirmed by X-ray diffraction studies. In addition, we performed solubility and dissolution rate tests, which showed a significant improvement in solubility of ternary system as compared to its crystalline counterpart. Enhanced physical stability and water solubility of the amorphous ternary system makes it promising for further studies.

Comparative Study of DSC-Based Protocols for API-Polymer Solubility Determination

Knowledge of the active pharmaceutical ingredient (API) solubility in a polymer is imperative for successful amorphous solid dispersion design and formulation but acquiring this information at storage temperature is challenging. Various solubility determination methods have been established, which utilize differential scanning calorimetry (DSC). In this work, three commonly used DSC-based protocols [i.e., melting point depression (MPD), recrystallization, and zero-enthalpy extrapolation (Z-EE)] and a method that we have developed called "step-wise dissolution" (S-WD) were analyzed. For temperature-composition phase diagram construction, two glass-transition temperature equations (i.e., those of Gordon-Taylor and Kwei) and three solid-liquid equilibrium curve modeling approaches [i.e., the Flory-Huggins model, an empirical equation, and the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EOS)] were considered. Indomethacin (IND) and Kollidon 12 PF (PVP K12) were selected as the API and polymer, respectively. An annealing time investigation revealed that the IND-PVP K12 dissolution process was remarkably faster than demixing, which contradicted previously published statements. Thus, the recrystallization method overestimated the solubility of IND in PVP K12 when a 2-h time of annealing was set as the benchmark. Likewise, the MPD and Z-EE methods overestimated the API solubility because of unreliable IND melting endotherm evaluation at lower API loadings and a relatively slow heating rate, respectively. When the experimental results obtained using the S-WD method (in conjunction with the Kwei equation) were applied to the PC-SAFT EOS, which was regarded as the most reliable combination, the predicted IND solubility in PVP K12 at T = 25 °C was approximately 40 wt %. When applicable, the S-WD method offers the advantage of using a limited number of DSC sample pans and API-polymer physical mixture compositions, which is both cost- and time-effective.

Application of Thermodynamic Phase Diagrams and Gibbs Free Energy of Mixing for Screening of Polymers for Their Use in Amorphous Solid Dispersion Formulation of a Non-Glass-Forming Drug

The objective of the present investigations was to assess the use of thermodynamic phase diagrams and the Gibbs free energy of mixing, ΔG_mix, for the screening of the polymeric carriers by determining the ideal drug-loading for an amorphous solid dispersion formulation and optimum processing temperature for the hot-melt extrusion of a non-glass-forming drug. Mefenamic acid (MFA) was used as a model non-glass-forming drug and four chemically distinct polymers with close values of the solubility parameters, viz. Kollidon® VA64, Soluplus®, Pluronic® F68, and Eudragit® EPO, were used as carriers. The thermodynamic phase diagrams were constructed using the melting point depression data, Flory-Huggins theory, and Gordan-Taylor equation. The Gibbs free energy of mixing was estimated using the values of the drug-polymer interaction parameter, χ, and Flory-Huggins theory. The rank order miscibility of MFA in the four polymeric carriers estimated based on the difference in the values of their solubility parameters, Δδ, did not correlate well with the thermodynamic phase diagrams and Gibbs free energy plots. The study highlights the limitation of using the solubility parameter method in screening the polymeric carriers for poorly glass-forming drugs and reiterates the applicability of thermodynamic phase diagrams and Gibbs free energy plots in determining the ideal drug-loading and optimum processing temperature for hot-melt extrusion.

Evaluation of rivaroxaban amorphous solid dispersions physical stability via molecular mobility studies and molecular simulations

The present study evaluates the effect of molecular mobility and molecular interactions in the physical stability of rivaroxaban (RIV) - soluplus® (SOL) amorphous solid dispersions (ASDs). Initially, the use of Adam-Gibbs approach revealed that RIV's molecular mobility (below its glass transition temperature) is significantly reduced in the presence of SOL, while the use of ATR-FTIR spectroscopy showed the formation of hydrogen bonds (HBs) between the two ASD components, indicating that these two mechanisms can be considered as responsible for system's physical stability. Contrary to previously published reports, the utilization of ATR-FTIR spectroscopy in the present study was able to clarify, for the first time, the type of intermolecular interactions formed within the examined ASD system, while the presence of a separate drug-rich amorphous phase (significantly increasing as the content of the drug increases) was also identified. Furthermore, in order to gain an insight into the intermolecular interactions responsible for drug's amorphous phase separation, molecular dynamics (MD) simulation models were utilized as realistic representations of the actual systems. Analysis of the obtained trajectories showed that the formation of strong intermolecular HBs between RIV's secondary amide proton and its three carbonyl oxygens (originating from the οxazolidone, oxomorpholin and carboxamide part of the drug molecule) as well as the significant reduction of the available HB acceptors in SOL due to copolymer's chain shrinkage, were responsible for the formation of a separate drug-rich amorphous phase within the ASD.

Phase behavior of ASDs based on hydroxypropyl cellulose

Novel polymeric carriers for amorphous solid dispersions (ASDs) are highly demanded in pharmaceutical industry to improve the bioavailability of poorly-soluble drug candidates. Besides established polymer candidates, hydroxypropyl celluloses (HPC) comes more and more into the focus of ASD production since they have the availability to stabilize drug molecules in aqueous media against crystallization. The thermodynamic long-term stability of HPC ASDs with itraconazole and fenofibrate was predicted in this work with PC-SAFT and compared to three-months enduring long-term stability studies. The glass-transition temperature is a crucial attribute of a polymer, but in case of HPC hardly detectable by differential scanning calorimetry. By investigating the glass transition of HPC blends with a miscible polymer, we were for the first time able to estimate the HPC glass transition. Although both, fenofibrate and itraconazole reveal a very low crystalline solubility in HPC regardless of the HPC molecular weight, we observed that low-molecular weight HPC grades such as HPC-UL prevent fenofibrate crystallization for a longer period than the higher molecular weight HPC grades. As predicted, the ASDs with higher drug load underwent amorphous phase separation according to the differential scanning calorimetry thermograms. This work thus showed that it is possible to predict critical drug loads above which amorphous phase separation and/or crystallization occurs in HPC ASDs.

Connecting primitive phase separation to biotechnology, synthetic biology, and engineering

One aspect of the study of the origins of life focuses on how primitive chemistries assembled into the first cells on Earth and how these primitive cells evolved into modern cells. Membraneless droplets generated from liquid-liquid phase separation (LLPS) are one potential primitive cell-like compartment; current research in origins of life includes study of the structure, function, and evolution of such systems. However, the goal of primitive LLPS research is not simply curiosity or striving to understand one of life's biggest unanswered questions, but also the possibility to discover functions or structures useful for application in the modern day. Many applicational fields, including biotechnology, synthetic biology, and engineering, utilize similar phaseseparated structures to accomplish specific functions afforded by LLPS. Here, we briefly review LLPS applied to primitive compartment research and then present some examples of LLPS applied to biomolecule purification, drug delivery, artificial cell construction, waste and pollution management, and flavor encapsulation. Due to a significant focus on similar functions and structures, there appears to be much for origins of life researchers to learn from those working on LLPS in applicational fields, and vice versa, and we hope that such researchers can start meaningful cross-disciplinary collaborations in the future.

Amorphous Solid Dispersions of Felodipine and Nifedipine with Soluplus®: Drug-Polymer Miscibility and Intermolecular Interactions

The objective of this study was to investigate thermodynamic and kinetic miscibility for two structurally similar model compounds nifedipine (NIF) and felodipine (FEL) when formulated as amorphous solid dispersions (ASDs) with an amphiphilic polymer Soluplus®. Thermodynamic miscibility was studied via melting point depression approach for the two systems. The Flory Huggins theory was used to calculate the interaction parameter and generate the phase diagrams. It was shown that NIF was more miscible in Soluplus® than FEL. The nature of drug polymer interactions was studied by fourier transform infra-red spectroscopy (FTIR) and solid-state nuclear magnetic resonance spectroscopy (ssNMR). The data from spectroscopic analyses showed that both the drugs interacted with Soluplus® through hydrogen bonding interactions. Furthermore, ¹³C ssNMR data was used to get quantitative estimate of the extent of hydrogen bonding for ASDs samples. Proton relaxation measurements were carried out on ASDs in order to evaluate phase heterogeneity on two different length scales of mixing. The data suggested that better phase homogeneity in NIF:SOL systems especially for lower Soluplus® content ASDs on smaller domains. This could be explained by understanding the extent of hydrogen bonding interactions for these two systems. This study highlights the need to consider thermodynamic and kinetic mixing, when formulating ASDs with the goal of understanding phase mixing between drug and polymer.

Correlationship of Drug-Polymer Miscibility, Molecular Relaxation and Phase Behavior of Dipyridamole Amorphous Solid Dispersions

In present work, a correlationship among quantitative drug-polymer miscibility, molecular relaxation and phase behavior of the dipyridamole (DPD) amorphous solid dispersions (ASDs), prepared with co-povidone (CP), hydroxypropyl methylcellulose phthalate (HPMC P) and hydroxypropyl methylcellulose acetate succinate (HPMC AS) has been investigated. Miscibility predicted using melting point depression approach for DPD with CP, HPMC P and HPMC AS at 25 °C was 0.93% w/w, 0.55% w/w and 0.40% w/w, respectively. Stretched relaxation time (τ^β) for DPD ASDs, measured using modulated differential scanning calorimetry (MDSC) at common degree of undercooling, was in the order of DPD- CP > DPD-HPMC P > DPD-HPMC AS ASDs. Phase behavior of 12 months aged (25 ± 5 °C and 0% RH) spray dried 60% w/w ASDs was tracked using MDSC. Initial ASD samples had homogeneous phase revealed by single glass transition temperature (T_g) in the MDSC. MDSC study of aged ASDs revealed single-phase DPD-CP ASD, amorphous-amorphous and amorphous-crystalline phase separated DPD-HPMC P and DPD-HPMC AS ASDs, respectively. The results were supported by X-ray micro computed tomography and confocal laser scanning microscopy studies. This study demonstrated a profound influence of drug-polymer miscibility on molecular mobility and phase behavior of ASDs. This knowledge can help in designing "physical stable" ASDs.

Physical formulation approaches for improving aqueous solubility and bioavailability of ellagic acid: A review

Ellagic acid (EA) is a polyphenolic active compound with antimalarial and other promising therapeutic activities. However, its solubility and its permeability are both low (BCS IV). These properties greatly compromise its oral bioavailability and clinical utilizations. To overcome these limitations of the physicochemical parameters, several formulation approaches, including particle size reduction, amorphization and lipid-based formulations, have been used. Although these strategies have not yet led to a clinical application, some of them have resulted in significant improvements in the solubility and bioavailability of EA. This critical review reports and analyses the different formulation approaches used by scientists to improve both the biopharmaceutical properties and the clinical use of EA.

The Use of Glycerol as an Enabling Excipient for Microwave-Induced In Situ Drug Amorphization

Microwave-induced in situ amorphization is a promising approach to circumvent stability and manufacturing issues associated with amorphous solid dispersions (ASD). Using in situ amorphization, the crystalline state of the drug is converted into its amorphous form inside the dosage form, e.g. a compact, upon exposure to microwave radiation. The study aimed to investigate the feasibility of using glycerol as an enabling excipient in compacts prepared from mixtures of indomethacin and Soluplus®. Additionally, the possibility to form a supersaturated ASD upon exposure to microwave radiation due to elevated temperatures was investigated. It was found that glycerol i) acts as a dielectric heating source absorbing the microwaves, ii) plasticizes the polymer Soluplus® and iii) increases the solubility of the drug indomethacin in the polymer Soluplus®. Additionally, it was found that fully amorphous ASDs could be achieved with drug loadings below -, and slightly above the saturation solubility of indomethacin in the Soluplus®/glycerol mixtures, after exposure to 20 min of microwave radiation. Hence, glycerol was a feasible excipient for the microwave-induced in situ amorphization and allowed the preparation of a, at room temperature, supersaturated ASD, due to the elevated temperatures obtained during exposure to microwave radiation.