Determining Thermal Conductivity of Small Molecule Amorphous Drugs with Modulated Differential Scanning Calorimetry and Vacuum Molding Sample Preparation

Thermal conductivity is a material specific property, which influences many aspects of pharmaceutical development, such as processing, modelling, analysis, and the development of novel formulation approaches. We have presented a method to measure thermal conductivity of small molecule organic glasses, based on a vacuum molding sample preparation technique combined with modulated differential scanning calorimetry. The method is applied to the two amorphous model compounds indomethacin and celecoxib. The measured values of below 0.2 W/m °C indicate very low thermal conductivity of the amorphous compounds, within the range of organic liquids and low conducting polymers.

Tailor-made solvents for pharmaceutical use? Experimental and computational approach for determining solubility in deep eutectic solvents (DES)

A deep eutectic solvent (DES) is a mixture of two or more chemicals that interact via hydrogen bonding and has a melting point far below that of the individual components. DESs have been proposed as alternative solvents for poorly soluble active pharmaceutical ingredients (API). In this study, the solvation capacities of six deep eutectic solvents were compared to water and three conventional pharmaceutical solvents (PEG 300, ethanol and glycerol) for 11 APIs. The experimentally determined solubilities were compared to computational solubilities predicted by the Conductor-like Screening Model for Real Solvents (COSMO-RS). While the conventional pharmaceutical solvents PEG 300 and ethanol were the best solvents for the majority of the studied APIs, API-DES combinations were identified, which exceeded the API solubility found in the conventional pharmaceutical solvents. Furthermore, it was also possible to obtain high solubilities in the DESs relative to water, suggesting DESs to be potential solvents for poorly water soluble APIs. In addition, the relative increase in solubility found in the experimental data could be well predicted ab initio using COSMO-RS. Hence, COSMO-RS may in the future be used to reduce the experimental screening of potential DESs for a given API.

Amino acids as stabilizers for spray-dried simvastatin powder for inhalation

BACKGROUND

The use of amino acids as excipients is a promising approach to improve the physical stability and powder dispersibility of spray-dried powders for inhalation.

OBJECTIVES

The aim of this study was to investigate the stabilizing effect of different amino acids on spray-dried amorphous powders for inhalation using simvastatin (SV) as a model compound.

METHODS

Two hydrophobic amino acids (leucine, LEU and tryptophan, TRP), and one hydrophilic amino acid (lysine, LYS) were spray dried from 1% (w/v) solutions with SV at a molar ratio of 1:1 into dry powders for inhalation. Scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to characterize the morphology, solid form and potential intermolecular interactions of the spray-dried powders. X-ray photoelectron spectroscopy (XPS) was used to analyse the chemical composition of the surface of the particles. The physical stability of the dry powders was examined upon storage in controlled conditions. A Next generation impactor (NGI) was applied to assess the in vitro aerosol performance of the powders.

RESULTS

XRPD and DSC results confirmed that the spray-dried SV-LEU was composed of crystalline LEU and amorphous SV, the spray-dried SV-LYS was co-amorphous, and the spray-dried SV-TRP was an amorphous system with two phases. XPS analyses revealed that the surface of the spray-dried SV-LEU particles were LEU rich, indicating surface-enrichment of LEU in these particles. In contrast, an almost even distribution of TRP and SV at the surface of spray-dried SV-TRP was observed. FTIR results indicated no intermolecular interaction between SV and the amino acids used in the present study. The three spray-dried samples were physically stable after eight months storage in a desiccator (12% RH, ca. 22 °C). Nevertheless, spray-dried SV-LEU exhibited the best storage stability as compared to the other two spray-dried samples when the samples were stored at 60% RH, 25 °C. Both, the spray-dried SV-LEU and SV-TRP exhibited higher fine particle fractions than the spray-dried SV-LYS.

CONCLUSION

Both the spray-dried SV-LEU and SV-TRP exhibited better aerosol performance and storage stability compared to the spray-dried SV-LYS. Compared to TRP, LEU exhibited better protection of spray-dried amorphous SV from re-crystallization, which could be attributed to the formation of a LEU crystalline shell covering SV upon the spray drying process.

Expedited Investigation of Powder Caking Aided by Rapid 3D Prototyping of Testing Devices

Powder caking can dramatically affect powder handling and downstream production processes. Understanding the key factors that contribute to bulk powder caking is crucial. This article introduces the Hirschberg caking device (HCD), which is a 3D-printed device allowing for parallel testing of powder caking in a cylindrical geometry. In the HCD setup, the powder sample is stored in controlled conditions in the sample holder. On removal of the sample holder, the caked powder will remain in the shape determined by the sample geometry while the remaining powder will fall down. Caking indices can be calculated based on image analysis and weight measurement. The results obtained for the caking of lactose monohydrate with the HCD were in good agreement with the results obtained by a ring shear tester. In addition, a strain tester was used to measure the strength of the formed cakes. Using this approach, critical storage conditions and the required concentration of a given anticaking agent (talc) for lactose monohydrate could be identified. This work demonstrates the potential of rapid prototyping in powder characterization by introducing a fast and affordable approach for exploring and trouble-shooting powder caking.

Correction to: Quantification of Inkjet-Printed Pharmaceuticals on Porous Substrates Using Raman Spectroscopy and Near-Infrared Spectroscopy

Mohammed Al-Sharabi's affiliation was incorrect at the time of publishing. The updated affiliation appears below.

Quantification of Inkjet-Printed Pharmaceuticals on Porous Substrates Using Raman Spectroscopy and Near-Infrared Spectroscopy

The use of inkjet printing for pharmaceutical manufacturing is gaining interest for production of personalized dosage forms tailored to specific patients. As part of the manufacturing, it is imperative to ensure that the correct dose is printed. The aim of this study was to use inkjet printing for manufacturing of personalized dosage forms combined with the use of near-infrared (NIR) and Raman spectroscopy as complementary analytical techniques for active pharmaceutical ingredient (API) quantification of the inkjet-printed dosage forms. Three APIs, propranolol (0.5-4.1 mg), montelukast (2.1-12.1 mg), and haloperidol (0.6-4.1 mg) were inkjet printed in 1 cm² areas on a porous substrate. The printed doses were non-destructively analyzed by transmission NIR and Raman spectroscopy (both transmission and backscatter). X-ray computed microtomography (μ-CT) analysis was undertaken for porosity measurements of the substrate. The API content was confirmed using high-performance liquid chromatography (HPLC), and the content in the dosage forms was modeled from the NIR and Raman spectra using partial least squares regression (PLS). HPLC analysis revealed a linear correlation of the number of layers printed to the API content. The resulting PLS models for both NIR and Raman had R² values between 0.95 and 0.99. The best predictive model was obtained using NIR, followed by Raman spectroscopy. μ-CT revealed the substrate to be highly porous and optimal for inkjet printing. In conclusion, NIR and Raman spectroscopic techniques could be used complementary as fast API quantification tools for inkjet-printed medicines.

Exploring the chemical space for freeze-drying excipients

Commonly, a limited number of generally accepted bulking agents and lyoprotectants are used for freeze-drying; predominantly mannitol, glycine, sucrose and trehalose. The purpose of this study was to combine a theoretical approach using molecular descriptors with a large scale experimental screening to evaluate the suitability of a broad range of excipients for freeze-drying. A large selection of sugars, polyols and amino acids was characterized by modulated differential scanning calorimetry (mDSC) and X-ray powder diffraction (XRPD) after well-plate based freeze-drying. The calculated molecular descriptors were investigated with both hierarchical cluster analysis and principal component analysis. A clear clustering of the excipients according to the size-related and weight-related descriptors was observed; however other relevant descriptors could also be identified. From a practical perspective, a trend was observed with regard to a higher likelihood for amorphisation and a higher glass transition temperature of the maximally freeze-concentrated solution with increasing molecular size. A translation of the molecular descriptors on pharmaceutical performance was more successful for lyoprotectants than for bulking agents. Additionally, in the course of the experimental screening, several new potential bulking agents and lyoprotectants were identified.

Imaging of dehydration in particulate matter using Raman line-focus microscopy

Crystalline solids can incorporate water molecules into their crystal lattice causing a dramatic impact on their properties. This explains the increasing interest in understanding the dehydration pathways of these solids. However, the classical thermal analytical techniques cannot spatially resolve the dehydration pathway of organic hydrates at the single particle level. We have developed a new method for imaging the dehydration of organic hydrates using Raman line-focus microscopy during heating of a particle. Based on this approach, we propose a new metastable intermediate of theophylline monohydrate during the three-step dehydration process of this system and further, we visualize the complex nature of the three-step dehydration pathway of nitrofurantoin monohydrate to its stable anhydrous form. A Raman line-focus mapping option was applied for fast simultaneous mapping of differently sized and shaped particles of nitrofurantoin monohydrate, revealing the appearance of multiple solid-state forms and the non-uniformity of this particle system during the complex dehydration process. This method provides an in-depth understanding of phase transformations and can be used to explain practical industrial challenges related to variations in the quality of particulate materials.

The Use of 3D Printed Molds to Cast Tablets with a Designed Disintegration Profile

Development of new product design principles is crucial for obtaining pharmaceutical products with controlled functionality. Four different molds were designed using a computer-aided design (CAD) software and 3D printed with polylactic acid (PLA). A hydroxypropyl methylcellulose (HPMC) and polyethylene glycol (PEG)-based formulation containing indomethacin as the active pharmaceutical ingredient (API) was casted into the molds. Each mold produced a tablet that was designed to disintegrate into a defined number of sections (2, 4, and 6). This was achieved by incorporating break lines (regions that were significantly thinner than the remainder of the tablet) to control the disintegration process. Disintegration and drug release from these designed tablets was contrasted with a casted tablet without break lines. Disintegration studies confirmed that the casted tablets disintegrated according to their design. Drug-release studies meanwhile demonstrated that tablets with a greater number of sections released the API at a faster rate than those with fewer sections; for example, the 6-sectioned tablet released the API at twice the rate of the tablet without any break lines. It is expected that by using this concept, it would be possible to produce tablets with a designed disintegration profile, which could potentially allow the tailoring of the drug release.

Stability of lysozyme incorporated into electrospun fibrous mats for wound healing

In this study, we investigated the feasibility of incorporating protein drugs into electrospun fibrous mats (EFMs) for wound healing using lysozyme as a model drug. Lysozyme nanoparticles (Lyso- NPs) were first obtained by electrospray. Lysozyme solutions were prepared with a binary solvent mixture of ethanol (EtOH)-water (H₂O) at varied volume ratios. Subsequently, Lyso-NPs were suspended in poly(lactic-co-glycolic acid) (PLGA) solutions using trifluoroethanol (TFE) as a solvent. Lyso-NPs loaded EFMs were obtained by electrospinning of the aforementioned suspensions, and the bioactivity of lysozyme in the EFMs was investigated using fluorescence-based assay kit. The electrosprayed Lyso-NPs were spherical with barely altered bioactivity as compared to the untreated raw material when using EtOH- H₂O (30:70, v/v) as the solvent. After the subsequent electrospinning process, more than 90% of the bioactivity of lysozyme was retained compared to the raw material. The cytotoxicity of the produced EFMs was evaluated by thiazolyl blue tetrazolium bromide (MTT) study and the proliferation and distribution of mouse fibroblast cells (L929) growing on EFMs were investigated using 4,6-diamidino-2-phenylindol dihydrochloride (DAPI) for nucleic acid staining. Nearly negligible cytotoxicity of all the EFMs was observed according to the MTT study. Furthermore, it was observed that the L929 cells grew well on the Lyso-EFMs, especially those with the modification of polyethylene glycol (PEG) that was added to improve the hydrophilicity of EFMs. This study demonstrated that the electrospray/electrospinning processes are suitable for loading biomacromolecules to produce functionalized wound dressings to promote wound healing.

Determining short-lived solid forms during phase transformations using molecular dynamics

We demonstrate that elusive high-energy metastable crystal structures can be determined from molecular dynamics simulations.

Ultrasensitive Microstring Resonators for Solid State Thermomechanical Analysis of Small and Large Molecules

Thermal analysis plays an important role in both industrial and fundamental research and is widely used to study thermal characteristics of a variety of materials. However, despite considerable effort using different techniques, research struggles to resolve the physicochemical nature of many thermal transitions such as amorphous relaxations or structural changes in proteins. To overcome the limitations in sensitivity of conventional techniques and to gain new insight into the thermal and mechanical properties of small- and large-molecule samples, we have developed an instrumental analysis technique using resonating low-stress silicon nitride microstrings. With a simple sample deposition method and postprocess data analysis, we are able to perform rapid thermal analysis of direct instrumental triplicate samples with only pico- to nanograms of material. Utilizing this method, we present the first measurement of amorphous alpha and beta relaxation, as well as liquid crystalline transitions and decomposition of small-molecule samples deposited onto a microstring resonator. Furthermore, sensitive measurements of the glass transition of polymers and yet unresolved thermal responses of proteins below their apparent denaturation temperature, which seem to include the true solid state glass transition of pure protein, are reported. Where applicable, thermal events detected with the setup were in good agreement with conventional techniques such as differential scanning calorimetry and dynamic mechanical analysis. The sensitive detection of even subtle thermal transitions highlights further possibilities and applications of resonating microstrings in instrumental physicochemical analysis.

On-line rheological characterization of semi-solid formulations

The rheological profile of a semi-solid product is a critical quality attribute. To monitor changes of this attribute during manufacturing, it would be beneficial to measure the rheological parameters in an on-line or in-line mode and implement this as a part of a control strategy for manufacturing of semi-solids. None of the process analytical technology (PAT) tools for measuring the rheological parameters have yet been widely accepted in the pharmaceutical area, as most of the equipment can only measure viscosity. Therefore, an automated system based on the measurement of pressure difference across both a topology optimized channel and a tube geometry (capillary viscometer) was investigated. The Pressure Difference Apparatus (PDA) can sample from the bulk intermediate/product stream and press the sample through the apparatus at different flow rates to yield a frequency sweep (G' and G″) and a flow curve (viscosity). A calibration model was successfully prepared and verified with hydroxyethyl cellulose gels with polymer content varying from 1.0 to 1.5% (w/w) resulting in gels of different viscosities. The calibration model was used on-line during manufacturing of a gel and manufacturing changes related to dilution of the product were clearly reflected in the batch evolution profiles. The measurements with the PDA reflected the shear rate and frequency ranges relevant for manufacturing and thereby complemented the rheology measurements obtained with a standard rheometer with real time data.

Roadmap to 3D-Printed Oral Pharmaceutical Dosage Forms: Feedstock Filament Properties and Characterization for Fused Deposition Modeling

Application of additive manufacturing techniques (3D printing) for mass-customized products has boomed in the recent years. In pharmaceutical industry and research, the interest has grown particularly with the future scenario of more personalized medicinal products. Understanding a broad range of material properties and process behavior of the drug-excipient combinations is necessary for successful 3D printing of dosage forms. This commentary reviews recent 3D-printing studies by fused deposition modeling (FDM) technique in pharmaceutical sciences, extending into the fields of polymer processing and rapid prototyping, where more in-depth studies on the feedstock material properties, modeling, and simulation of the FDM process have been performed. A case study of a model oral dosage form from custom-prepared indomethacin-polycaprolactone feedstock filament was used as an example in the pharmaceutical context. The printability was assessed in the different process steps: preparation of customized filaments for FDM, filament feeding, deposition, and solidification. These were linked with the rheological, thermal, and mechanical properties and their characterization, relevant for understanding the printability of drug products by FDM.

Quantification of Fragmentation of Pharmaceutical Materials After Tableting

Deformation is the material property that is a key for successful tablet formulation. Still, a quantitative method for assessing the change in particle size as a result of compression is lacking. The purpose of this study is to introduce a method for quantifying fragmentation after tableting. Different size fractions of dibasic calcium phosphate, microcrystalline cellulose, lactose, and starch were blended with magnesium stearate and compressed into tablets. The compressed particles were recovered from the tablets by manual grinding, which was possible by the addition of magnesium stearate. The recovered particles were subjected to scanning electron microscopy and particle size distribution (PSD) analysis. Fragmentation was quantified by characterizing the change in PSD. PSDs of the compressed samples with increasing compression pressures were analyzed, and more specifically, the particle sizes from the inflection point were used to generate a fragmentation profile. The fragmentation profiles of dibasic calcium phosphate and lactose showed extensive fragmentation during tableting; microcrystalline cellulose fragmented slightly, whereas starch did not fragment at all. The results furthermore showed that the mechanical strength of the tablet was highly dependent on fragmentation, as the mechanical strength did not start to increase before almost all fragmentation had occurred. Hence, by using this method, it is possible to quantify at which compression pressure and to which degree materials fragment during the tableting process.

Additive manufacturing of prototype elements with process interfaces for continuously operating manufacturing lines

Rapid prototyping based on in silico design and 3D printing enables fast customization of complex geometries to multiple needs. This study utilizes, additive manufacturing for rapid prototyping of elements for continuously operating mixing geometries including interfaces with process analytical technology (PAT) tools, to show that 3D printing can be used for prototyping of both parts of production line and PAT interfacing solution. An additional setup was designed for measuring the dynamic calibration samples for a semi-quantitative near infrared (NIR) spectroscopic model. The powder was filled in a small calibration chamber and in-line NIR spectra of calibration samples were collected from moving material while mimicking the powder flow dynamics in a typical continuous mixer. This dynamic powder mixing system was compared with a static powder calibration model where the NIR probe was placed at different positions on a static sample. Principal component analysis (PCA) revealed that the 3D printed device with dynamic measurement of the NIR spectra had more potential for quantitative analysis. With the prototype continuous mixer, two differently placed process interfaces for NIR spectroscopic monitoring of the powder mixing were evaluated. With this approach, the importance of positioning the process analytical tools to assess the blend uniformity could be demonstrated. It was also observed that with the longer mixing geometry, a better mixing result was achieved due to a larger hold up volume and increased residence time.

Insight into Nanoscale Network of Spray-Dried Polymeric Particles: Role of Polymer Molecular Conformation

Poly(lactic- co-glycolic acid) (PLGA) microparticles represent a promising formulation approach for providing steady pharmacokinetic/pharmacodynamic profiles of therapeutic drugs for a long period. Understanding and controlling the supramolecular structure of PLGA microparticles at a molecular level is a prerequisite for the rational design of well-controlled, reproducible sustained-release profiles. Herein, we reveal the role of PLGA molecular conformation in particle formation and drug release. The nanoscale network of PLGA microparticles spray-dried using the solvents with distinct polarities was investigated by using NMR and neutron scattering. By employing chemometric method, we further demonstrate the evolution of nanoscale networks in spray-dried PLGA microparticles upon water absorption. Our results indicate that PLGA molecules form more chain entanglements during spray drying when using the solvents with low polarity, where PLGA molecule adopts a more flexible, extended conformation, resulting in the network being more resistant to water absorption in spray-dried PLGA microparticles. This work underlines the role of PLGA molecular conformation in controlling formation and evolution of nanoscale network of spray-dried PLGA microparticles and will have important consequences in achieving customized drug release from the PLGA microparticles.

Analytical aspects of printed oral dosage forms

Printing technologies, both 2D and 3D, have gained considerable interest during the last years for manufacturing of personalized dosage forms, tailored to each patient. Here we review the research work on 2D printing techniques, mainly inkjet printing, for manufacturing of film-based oral dosage forms. We describe the different printing techniques and give an overview of film-based oral dosage forms produced using them. The main part of the review focuses on the non-destructive analytical methods used for evaluation of qualitative aspects of printed dosage forms, e.g., solid-state properties, as well as for quantification of the active pharmaceutical ingredient (API) in the printed dosage forms, with an emphasis on spectroscopic methods. Finally, the authors share their view on the future of printed dosage forms.