Automation Potential of a New, Rapid, Microscopy-Based Method for Screening Drug-Polymer Solubility.

For the pharmaceutical industry, the preformulation screening of the compatibility of drug and polymeric excipients can often be time-consuming because of the use of trial-and-error approaches. This is also the case for selecting highly effective polymeric excipients for forming molecular dispersions in order to improve the dissolution and subsequent bio-availability of a poorly soluble drug. Previously, we developed a new thermal imaging-based rapid screening method, thermal analysis by structure characterization (TASC), which can rapidly detect the melting point depression of a crystalline drug in the presence of a polymeric material. In this study, we used melting point depression as an indicator of drug solubility in a polymer and further explored the potential of using the TASC method to rapidly screen and identify polymers in which a drug is likely to have high solubility. Here, we used a data bank of 5 model drugs and 10 different pharmaceutical grade polymers to validate the screening potential of TASC. The data indicated that TASC could provide significant improvement in the screening speed and reduce the materials used without compromising the sensitivity of detection. It should be highlighted that the current method is a screening method rather than a method that provides absolute measurement of the degree of solubility of a drug in a polymer. The results of this study confirmed that the TASC results of each drug-polymer pair could be used in data matrices to indicate the presence of significant interaction and solubility of the drug in the polymer. This forms the foundation for automating the screening process using artificial intelligence.

A novel micro-photogrammetric instrument for visualizing in 3D small objects applied to the quantitative study of the dissolution behavior of a pharmaceutical dosage form.

The work presented here proposes an innovative approach to 3D chemical mapping of solid formulations by microphotogrammetry. We present details of a novel microphotogrammetry apparatus and the first results for the application of photogrammetry to the dissolution analysis of solid pharmaceutical dosage forms. Unlike other forms of optical imaging, microphotogrammetry allows a true 3D model to be constructed that includes direct observation of the sides of the sample rather than only top-down topographic imaging. Volume and structural changes are assessed quantitatively and related to chemical analysis by high performance liquid chromatography. The recently introduced method of chemical identification by dissolution analysis, or chemical imaging by dissolution analysis, is employed for the first time to obtain tomographic images of the dissolution process.

Novel Thermal Imaging Method for Rapid Screening of Drug-Polymer Miscibility for Solid Dispersion Based Formulation Development.

This study aimed to develop a rapid, simple, and inexpensive screening method for selecting the best polymeric candidates possessing high active pharmaceutical ingredient (API) miscibility during the early stages of formulation development of solid dispersion based pharmaceutical products. A new thermal imaging based method, thermal analysis by structural characterization (TASC), was used as a thermoptometric tool in conjunction with data analysis software to detect the melting point depression and postmelting dissolution of felodipine particles screened over thin spin-coated films of ten polymers commonly used in the pharmaceutical field. On the polymeric substrates the drug showed different degrees of melting point reduction, reflecting their different levels of polymer-drug miscibility. Using TASC to detect melting point depression is significantly (20-40 times) faster than the conventional DSC method without loss of the sensitivity of detection. The quantity of the material required for the screening is less than 1/1000th of the material used in conventional DSC tests, which significantly reduce the material wastage. Isothermal TASC tests and IR imaging confirmed the occurrence of thermal dissolution of the drug in the polymer for more miscible pairs. The real-time stability tests validate the accuracy of the polymer-drug miscibility screening results. These results demonstrate TASC as a promising screening tool for rapidly selecting the polymeric excipients for pharmaceutical formulations development.

Characterization of Heterogeneity and Spatial Distribution of Phases in Complex Solid Dispersions by Thermal Analysis by Structural Characterization and X-ray Micro Computed Tomography.

PURPOSE: This study investigated the effect of drug-excipient miscibility on the heterogeneity and spatial distribution of phase separation in pharmaceutical solid dispersions at a micron-scale using two novel and complementary characterization techniques, thermal analysis by structural characterization (TASC) and X-ray micro-computed tomography (XµCT) in conjunction with conventional characterization methods. METHOD: Complex dispersions containing felodipine, TPGS, PEG and PEO were prepared using hot melt extrusion-injection moulding. The phase separation behavior of the samples was characterized using TASC and XµCT in conjunction with conventional thermal, microscopic and spectroscopic techniques. The in vitro drug release study was performed to demonstrate the impact of phase separation on dissolution of the dispersions. RESULTS: The conventional characterization results indicated the phase separating nature of the carrier materials in the patches and the presence of crystalline drug in the patches with the highest drug loading (30% w/w). TASC and XµCT where used to provide insight into the spatial configuration of the separate phases. TASC enabled assessment of the increased heterogeneity of the dispersions with increasing the drug loading. XµCT allowed the visualization of the accumulation of phase separated (crystalline) drug clusters at the interface of air pockets in the patches with highest drug loading which led to poor dissolution performance. Semi-quantitative assessment of the phase separated drug clusters in the patches were attempted using XµCT. CONCLUSION: TASC and XµCT can provide unique information regarding the phase separation behavior of solid dispersions which can be closely associated with important product quality indicators such as heterogeneity and microstructure.

Thermal Analysis by Structural Characterization as a Method for Assessing Heterogeneity in Complex Solid Pharmaceutical Dosage Forms.

Characterizing inter- and intrasample heterogeneity of solid and semisolid pharmaceutical products is important both for rational design of dosage forms and subsequent quality control during manufacture; however, most pharmaceutical products are multicomponent formulations that are challenging in this regard. Thermal analysis, in particular differential scanning calorimetry, is commonly used to obtain structural information, such as degree of crystallinity, or identify the presence of a particular polymorph, but the results are an average over the whole sample; it cannot directly provide information about the spatial distribution of phases. This study demonstrates the use of a new thermo-optical technique, thermal analysis by structural characterization (TASC), that can provide spatially resolved information on thermal transitions by applying a novel algorithm to images acquired by hot stage microscopy. We determined that TASC can be a low cost, relatively rapid method of characterizing heterogeneity and other aspects of structure. In the examples studied, it was found that high heating rates enabled screening times of 3-5 min per sample. In addition, this study demonstrated the higher sensitivity of TASC for detecting the metastable form of polyethylene glycol (PEG) compared to conventional differential scanning calorimetry (DSC). This preliminary work suggests that TASC will be a worthwhile additional tool for characterizing a broad range of materials.

The development of thermal nanoprobe methods as a means of characterizing and mapping plasticizer incorporation into ethylcellulose films.

PURPOSE: The phase composition and distribution of ethylcellulose (EC) films containing varying amounts of the plasticizer fractionated coconut oil (FCO) were studied using a novel combination of thermal and mapping approaches. METHODS: The thermal and thermomechanical properties of films containing up to 30% FCO were characterized using modulated temperature differential scanning calorimetry (MTDSC) and dynamic mechanical analysis (DMA). Film surfaces were mapped using atomic force microscopy (AFM; topographic and pulsed force modes) and the composition of specific regions identified using nanothermal probes. RESULTS: Clear evidence of distinct conjugate phases was obtained for the 20-30% FCO/EC film systems. We suggest a model whereby the composition of the distinct phases may be estimated via consideration of the glass transition temperatures observed using DSC and DMA. By combining pulsed force AFM and nano-thermal analysis we demonstrate that it is possible to map the two separated phases. In particular, the use of thermal probes allowed identification of the distinct regions via localized thermomechanical analysis, whereby nanoscale probe penetration is measured as a function of temperature. CONCLUSION: The study has indicated that by using thermal and imaging techniques in conjunction it is possible to both identify and map distinct regions in binary films.

Thermal scanning probe microscopy in the development of pharmaceuticals.

The ability to characterize the physical and chemical properties of dosage forms is crucial to a more complete understanding of how vehicles for drug delivery behave and therefore how effective they are. Spatially resolved characterization that enables the visualization of properties on the nanoscale is particularly powerful. The usefulness of scanning probe microscopy (SPM) in the field of drug delivery is becoming increasingly well established and the use of thermal probes offers new capabilities thus enabling SPM to provide more and sometimes unique information. One type of measurement enabled by thermal probes is determining transition temperatures by means of local thermal analysis. The ability to identify and characterize materials in this way has found applications in characterizing a wide range of dosage forms. A complimentary thermal probe technique is photothermal infrared microspectroscopy (PTMS). PTMS offers a variety of advantages over more conventional approaches including the ability analyze compacts without the need for thin sections. It is also able to achieve sub-micron spatial resolution. Thermal probe techniques can characterize pharmaceutical dosage forms in terms of their physical properties and their chemical composition.

Physicochemical properties of the amorphous drug, cast films, and spray dried powders to predict formulation probability of success for solid dispersions: etravirine.

Solid dispersion technology represents an enabling approach to formulate poorly water-soluble drugs. While providing for a potentially increased oral bioavailability secondary to an increased drug dissolution rate, amorphous dispersions can be limited by their physical stability. The ability to assess formulation risk in this regard early in development programs can not only help in guiding development strategies but can also point to critical design elements in the configuration of the dosage form. Based on experience with a recently approved solid dispersion-based product, Intelence® (etravirine), a three part strategy is suggested to predict early formulate-ability of these systems. The components include an assessment of the amorphous form, a study of binary drug/carrier cast films and the evaluation of a powder of the drug and polymer processed in a manner relevant to the intended final dosage form. A variety of thermoanalytical, spectroscopic, and spectrophotometric approaches were applied to study the prepared materials. The data suggest a correlation between the glass forming ability and stability of the amorphous drug and the nature of the final formulation. Cast films can provide early information on miscibility and stabilization and assessment of processed powders can help define requirements and identify issues with potential final formulations.

Characterisation and prediction of phase separation in hot-melt extruded solid dispersions: a thermal, microscopic and NMR relaxometry study.

PURPOSE: To develop novel analytical approaches for identifying both miscibility and phase separation in hot-melt extruded formulations. METHODS: Felodipine-Eudragit E PO solid dispersions were prepared using hot-melt extrusion. The fresh and aged formulations were characterised using scanning electron microscopy, differential scanning calorimetry, heat capacity (C(p)) measurements using modulated temperature DSC and nuclear magnetic resonance relaxometry. RESULTS: The solubility of the drug in polymer was predicted as being < or =10% w/w using a novel model proposed in this study. Freshly prepared HME formulations were found to show no evidence for phase separation despite drug loadings greatly in excess of this figure. Conventional DSC showed limitations in directly detecting phase separation. However, a novel use of C(p) measurements indicated that extensive phase separation into crystalline domains was present in all aged samples, a conclusion supported by SEM studies. The NMR relaxometry study confirmed the existence of phase separation in all aged formulations and also allowed the estimation of separated domains sizes in different formulations. CONCLUSIONS: This study has presented a series of novel approaches for the identification, quantification and prediction of phase separation in HME formulations. Supersaturation of drug in the polymer caused the phase separation of the aged felodipine-Eudragit E PO formulations.

Compositional analysis of metal chelating materials using near-field photothermal Fourier transform infrared microspectroscopy.

Photothermal-Fourier transform-infrared (PT-FT-IR) microspectroscopy employs a thermal probe mounted in a scanning probe microscope (SPM). By placement of the tip of the probe on the surface of a solid sample, it can obtain localized IR spectra of a wide range of samples. A second mode of analysis is also available; a sample can be taken from the selected location using a technique called thermally assisted nanosampling (TAN), then a spectrum can be obtained of the nanosample while the probe is remote from the surface. We report a novel method of local compositional analysis that combines both of these types of measurement; a reagent is attached to the tip using TAN, then the reagent is placed in contact with analyte. IR spectroscopy can then be used to analyze any interaction between the reagent and surface it is placed in contact with. All of these modes of analysis were illustrated using a metal chelating agent. In the surface mode, changes to a solid bead of a chelating resin were measured using standard PT-FT-IR. In the nanosampling mode of analysis, a particle of a chelating polymer was attached to the tip of the probe using TAN and this was placed in contact with a concentrated calcium solution. Strong spectral changes were observed that mirrored those found when exposing the surface bound chelating resin bead to a solution of the same ion. A semiquantitative simulation of the PT spectrum for a chelating resin bead was achieved using a thermal diffusion model derived from photoacoustic spectroscopy indicating that semiquantitative or quantitative measurements will be possible in such a system.

An investigation into the crystallisation behaviour of an amorphous cryomilled pharmaceutical material above and below the glass transition temperature.

The aim of this study was to evaluate the glass transition and recrystallisation of a cryomilled drug, TMC125 (Etravirine), with particular emphasis on assessing the physical stability of the drug above and below the glass transition temperature. DSC (conventional, fast and modulated temperature) and variable temperature ATR-FTIR spectroscopy were employed to monitor the glass transition and crystallisation behaviour of the material. The isothermal crystallisation behaviour was investigated at temperatures below T(g). The humidity-induced crystallisation behaviour of the material was evaluated using dynamic vapour sorption (DVS). The glass transition (99 degrees C) was measured in isolation from the crystallisation process using fast DSC, while ATR-FTIR allowed identification of the polymorph formed on recrystallisation. At a heating rate of 0.2 degrees C/min, the onset temperature of the crystallisation exotherm (67 degrees C) was 32 degrees C below T(g). Evidence is presented for incomplete crystallisation under isothermal conditions. In conclusion, the study has ascertained the crystallisation profile of cryomilled Etravirine under both isothermal and scanning conditions, with the material showing marked physical instability below the measured T(g).

Mapping amorphous material on a partially crystalline surface: nanothermal analysis for simultaneous characterisation and imaging of lactose compacts.

The use of nanothermal analysis for mapping amorphous and crystalline lactose at a nanoscale is explored. Compressed tablets of amorphous and crystalline lactose (alone and mixed) were prepared and localised thermomechanical analysis (L-TMA) performed using micro- and nanothermal analysis in a addition to single point variable temperature pull-off force measurements. L-TMA was shown to be able to identify the different materials at a nanoscale via measurement of the thermal events associated with the amorphous and crystalline regions, while pull off force measurements showed that the adhesion of the amorphous material increased on approaching the T(g). Imaging was performed isothermally using topographic and pulsed force mode (PFM) measurements; both approaches were capable of discriminating two regions which L-TMA conformed to correspond to the two materials. In addition, force volume imaging (FVI) is suggested as a further approach to mapping the surfaces. We demonstrate that performing heated tip PFM measurements at a temperature close to the T(g) allows greater discrimination between the two regions. We therefore suggest that the nanothermal approach allows both characterisation and imaging of partially amorphous surfaces, and also demonstrate that heated tip imaging allows greater discrimination between crystalline and amorphous materials than is possible using ambient studies.

Thermal probe based analytical microscopy: thermal analysis and photothermal Fourier-transform infrared microspectroscopy together with thermally assisted nanosampling coupled with capillary electrophoresis.

In this study, we have demonstrated that a scanning probe microscope (SPM) can be used for thermally assisted nanosampling (TAN) with subsequent analysis by capillary electrophoresis (CE). Localized thermomechanical analysis (L-TMA) and photothermal Fourier-transform infrared (PT-FTIR) microspectroscopy can also be employed using the same probe, thus illustrating how a single instrument can carry out a number of different complementary analytical measurements. Benzoic acid and 4-hydroxybenzoic acid were manipulated with a heated Wollaston wire probe and successfully deposited onto the surface of a piece of CE capillary tubing. The deposited samples were then separated with CE. L-TMA and PT-FTIR were also used to characterize these materials. We have also demonstrated how a nanosample of a nonparticulate material can be taken and then deposited onto the surface of an inert matrix. TAN of a nonparticulate material was explored using polyethylene as the analyte and fluorene as the matrix. These examples show that thermal probe techniques provide a versatile "tool box" of modes of analysis with the potential to analyze a wide range of samples in a spatially resolved way.

Application of calorimetry, sub-ambient atomic force microscopy and dynamic mechanical analysis to the study of frozen aqueous trehalose solutions.

PURPOSE: Disaccharides such as trehalose are widely used as cryo-protectants to maintain the activity of proteinaceous drugs during freezing. One unresolved issue is the double transition that is observed very commonly in DSC experiments on disaccharide solutions in the frozen state; the assignment of these transitions remains disputed. Here we use calorimetry and two new techniques to shed light on the true nature of these transitions. METHODS: Modulated Temperature DSC (MTDSC), cryo atomic force microscopy (AFM) and a novel DMA technique were used to study these transitions. RESULTS: MTDSC identified the two transitions Tr1 and Tr2 at -35.4 and -27.9 degrees C respectively in the reversing heat flow signal, an exotherm and endotherm were observed in the non-reversing signal at circa -32 and -29 degrees C respectively. It is shown for the first time that AFM images can be obtained of a softening and melting sample without damaging it. A force modulation imaging technique showed a softening at Tr1 and a loss of ice crystals at Tr2. These observations were supported by the DMA results. CONCLUSIONS: The results indicate Tr1 is associated with a glass transition while Tr2 is associated with the onset of loss of crystallinity.

Evidence for non-thermal microwave effects using single and multimode hybrid conventional/microwave systems.

Clear evidence for the microwave effect has been observed during experiments in which a variety of materials have been heated using experimental systems that allowed both conventional and conventional-microwave hybrid heating. A hybrid single mode cavity has been used to investigate the microwave effect during phase changes in silver iodide, barium titanate and benzil, whilst a hybrid multimode cavity has been used to investigate the microwave effect during sintering and annealing of a range of ceramic materials with different dielectric properties. Although evidence for the microwave effect was not found in every case, where it was found the results could not be explained purely in terms of temperature gradients within the materials.

Calorimetric and spatial characterization of polymorphic transitions in caffeine using quasi-isothermal MTDSC and localized thermomechanical analysis.

We describe a novel integrated approach to the study of polymorphic transformation that includes quasi-isothermal modulated temperature differential scanning calorimetry (QI-MTDSC) and microthermal analysis (MTA), with a view to studying the thermal, kinetic and spatial characteristics of the process. Form II and I caffeine was prepared and conventional DSC and hot stage microscopy performed. The Form II to I transition at circa 413 K was associated with a change in crystal habit to needle shaped crystals. QI-MTDSC was used to measure the heat capacity of the system as a function of temperature, while MTA was able to spatially differentiate between the two polymorphs in compressed systems. We present a novel extension of the reduced temperature method whereby we apply it for the first time to linear rising temperature data corresponding to the transition; the analysis suggests a close approximation to Arrhenius behavior. We also describe a heat transfer model that allows calculation of the thermal gradients within a hermetically sealed pan for the first time. The combined approach has therefore allowed the characterization of the thermodynamics and kinetics of the transformation process as well as spatial identification of the distribution of the transformation in compressed systems.

The development of thermally assisted particle manipulation and thermal nanointeraction studies as a means of investigating drug-polymer interactions.

This investigation outlines the development of two novel techniques, thermally assisted particle manipulation and thermal nanointeraction studies, to examine the interaction between materials during heating. Dispersions of paracetamol in polyethylene glycol 6000 were prepared and studied using microthermal analysis in a range of modes. The localised thermomechanical analysis (L-TMA) responses showed intermediate responses compared to the pure materials. Thermally assisted particle manipulation was used to place a single particle of PEG on the paracetamol surface and the assembly analyzed using L-TMA as a function of position, with the intermediate response seen at the interface between the two materials. Thermal nanointeraction studies, whereby nanosampled PEG was heated in the immediate proximity of the paracetamol, indicated that the process was kinetically controlled and could be interpreted in terms of the molten PEG influencing the apparent melting of the paracetamol. Near-field photothermal IR was used to identify the nature of the material on the probe tip; we provide the first quantitative evaluation of the amount sampled when carrying out thermally assisted nanosampling (circa 500 fg). The investigation has therefore demonstrated that these methods maybe used as a novel approach to studying thermal interactions between pharmaceutical materials.

The development of heated tip force-distance measurements as a novel approach to site-specific characterization of pharmaceutical materials.

The study describes the development of a novel approach to surface analysis whereby thermal probes are used to perform scanning probe microscopy pull-off force measurements as a function of tip rather than sample temperature. The initial impetus for the investigation was the study of a poorly understood phenomenon associated with microthermal analysis (MTA) whereby the thermal probe is pulled into the surface of a sample following temperature-induced softening. Localized thermomechanical analysis experiments were performed on a range of pharmaceutical materials using TA Instruments 2990 Microthermal Analyzer equipped with a TM Microscopes Explorer atomic force microscope. The system was then interfaced with a second instrument to allow simultaneous probe temperature control and pull-off force measurement. It was found that the pull-in effect is due to the adhesion of the probe to the material at elevated (softening) temperatures. However, it was also noted that for paracetamol tablets the pull-off force increased at temperatures well below the softening associated with melting. This behavior was ascribed to surface polymorphic changes caused by the compression process. The temperature-controlled pull-off force method therefore represents a novel and potentially widely applicable means of detecting surface changes that are not easily observed using isothermal pull-off force measurements or indeed standard MTA studies.

Nanoscale characterisation and imaging of partially amorphous materials using local thermomechanical analysis and heated tip AFM.

PURPOSE: The purpose is to investigate the use of thermal nanoprobes in thermomechanical and heated tip pulsed force modes as novel means of discriminating between amorphous and crystalline material on a sub-micron scale. MATERIALS AND METHODS: Indometacin powder was compressed and partially converted into amorphous material. Thermal nanoprobes were used to perform localised thermomechanical analysis (L-TMA) and heated tip pulsed force mode imaging as a function of temperature. RESULTS: L-TMA with submicron lateral spatial resolution and sub-100 nm depth penetration was achieved, allowing us to thermomechanically discriminate between amorphous and crystalline material at a nanoscale for the first time. The amorphous and crystalline regions were imaged as a function of temperature using heated tip pulsed force AFM and a resolution of circa 50 nm was achieved. We are also able to observe tip-induced recrystallisation of the amorphous material. DISCUSSION: The study demonstrates that we are able to discriminate and characterise amorphous and crystalline regions at a submicron scale of scrutiny. We have demonstrated the utility of two methods, L-TMA and heated tip pulsed force mode AFM, that allow us to respectively characterise and image adjacent amorphous and crystalline regions at a nanoscale. CONCLUSIONS: The study has demonstrated that thermal nanoprobes represent a novel method of characterising and imaging partially amorphous materials.

Two- and three-dimensional imaging of multicomponent systems using scanning thermal microscopy and localized thermomechanical analysis.

The aim of this study was to develop a novel approach to the spatial characterization of multicomponent samples, based on the emergent technique of microthermal analysis. More specifically, we present an assessment of the use of scanning thermal microscopy as a means of component mapping via thermal conductivity; we include a new statistical approach to data handling, which allows reduction of topographic effects. We also introduce a novel three-dimensional mapping technique based on localized thermomechanical analysis. Tablets of paracetamol and hyproxypropyl methylcellulose (HPMC) and 50:50 mixes of the two were prepared and the materials characterized in scanning and localized modes using a TA Instruments 2990 microthermal analyzer with a Thermomicroscopes Explorer AFM head and Wollaston wire thermal probe. L-TMA studies of the pure components indicated markedly differing thermal responses, with the paracetamol showing a sharp melting accompanied by a probe pull-in effect, while HPMC showed only thermal expansion over the temperature range studied. Thermal conductivity and topographic images indicated that two-dimensional differentiation between the components was possible in scanning mode. A means of delineating the relative contribution of the topographic and conductivity effects was developed based on a regression analysis of the thermal conductivity measurements on a set of terms representing the local surface curvature. The results of three-dimensional imaging using a grid of L-TMA measurements is presented. This technique utilized the distinct thermal responses of the two components to allow the probe to melt through the paracetamol down to the underlying HPMC. The advantages and limitations of this novel imaging method are discussed in the context of pharmaceutical and broader uses of the approach.