Applications of Fourier transform infrared spectroscopic imaging to tablet dissolution and drug release

Optimization of mid-infrared noninvasive blood-glucose prediction model by support vector regression coupled with different spectral features

Mid-infrared spectral analysis of glucose in subcutaneous interstitial fluid has been widely employed as a noninvasive alternative to the standard blood-glucose detection requiring blood-sampling via skin-puncturing, but improving the confidence level of such a replacement remains highly desirable. Here, we show that with an innovative metric of attributes in measurements and data-management, a high accuracy in correlating the test results of our improved spectral analysis to those of the standard detection is accomplished. First, our comparative laser speckle contrast imaging of subcutaneous interstitial fluid in fingertips, thenar and hypothenar reveal that spectral measurements from hypothenar, with an attenuated total reflection Fourier transform infrared spectrometer, give much stronger signals than the stereotype measurements from fingertips. Second, we demonstrate that discriminative selection of the spectral locations and ranges, to minimize spectral interference and maximize signal-to-noise, are critically important. The optimal band is pinned at that between 1000 ± 3 cm-1 and1040 ± 3 cm-1. Third, we propose an individual exclusive prediction model by adopting the support vector regression analysis of the spectral data from four subjects. The average predicted coefficient of determination, root mean square error and mean absolute error of four subjects are 0.97, 0.21 mmol/L, 0.17 mmol/L, respectively, and the average probability of being in Zone A of the Clark error grid is 100.00 %. Additionally, we demonstrate with the Bland and Altman plot that our proposed model has the highest consistency with portable blood glucose meter detection method.

Application of shadowgraph imaging (SGI) particle characterisation data to interpret the impact of varying test conditions on power dissolution and to develop an automated agglomeration identification method (AIM) in the USP flow through apparatus

The aims of this work were 1) to explore the application of shadowgraph imaging (SGI) as a real time monitoring tool to characterize ibuprofen particle behaviour during dissolution testing under various conditions in the USP 4 flow-through apparatus and 2) to investigate the potential to develop an SGI-based automated agglomeration identification method (AIM) for real time agglomerate detection during dissolution testing. The effect of surfactant addition, changes in the drug mass and flow rate, the use of sieved and un-sieved powder fractions, and the use of different drug crystal habits were investigated. Videos at every sampling time point during dissolution were taken and analysed by SGI. The AIM was developed to characterize agglomerates based on two criteria - size and solidity. All detections were confirmed by manual video observation and a reference agglomerate data set. The method was validated under new dissolution conditions with un-sieved particles. Characterisation of particle dispersion behaviour by SGI enabled interpretation of the impact of dissolution test conditions. Higher numbers of early detections reflected greater dissolution rates with increased surfactant concentration, using sieved fraction or plate-shaped crystals, but was impacted by drug mass tested. An AIM was successfully developed and applied to detect agglomerates during dissolution, suggesting potential, with appropriate method development, for application in quality control.

IR-EcoSpectra: Exploring sustainable ex situ and in situ FTIR applications for green chemical and pharmaceutical analysis

In various industries, particularly in the chemical and pharmaceutical fields, Fourier transform infrared spectroscopy (FTIR) spectroscopy provides a unique capacity to detect and characterise complex chemicals while minimising environmental damage by minimal waste generation and reducing the need for extensive sample preparation or use of harmful reagents. This review showcases the versatility of ex situ and in situ FTIR applications for substance identification, analysis, and dynamic monitoring. Ex situ FTIR spectroscopy's accuracy in identifying impurities, monitoring crystallisation processes, and regulating medication release patterns improves product quality, safety, and efficacy. Furthermore, its quantification capabilities enable more effective drug development, dosage procedures, and quality control practices, all of which are consistent with green analytical principles. On the other hand, in situ FTIR spectroscopy appears to be a novel tool for the real-time investigation of molecular changes during reactions and processes, allowing for the monitoring of drug release kinetics, crystallisation dynamics, and surface contacts, as well as providing vital insights into material behaviour. The combination of ex situ FTIR precision and in situ FTIR dynamic capabilities gives a comprehensive analytical framework for developing green practices, quality control, and innovation in the chemical and pharmaceutical industries. This review presents the wide range of applications of ex situ and in situ FTIR spectroscopy in chemical, pharmaceutical and medical fields as an analytical green chemistry tool. However, further study is required to fully realise FTIR's potential and develop new applications that improve sustainability in these areas.

Analysis of the Dissolution Behavior of Theophylline and Its Cocrystal Using ATR-FTIR Spectroscopic Imaging

Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic imaging is a powerful tool to visualize the distribution of components, and it has been used to analyze drug release from tablets. In this work, ATR-FTIR spectroscopic imaging was applied for observing the dissolution of molecular crystals from tablet compacts. The IR spectra provided chemically specific information about the transformation of crystal structures during the dissolution experiments. Theophylline (TPL) anhydrate and its cocrystals were used as model systems of molecular crystals. The IR spectra during the dissolution of TPL revealed information about the crystal structure of TPL, which transformed from anhydrate to monohydrate in water. During a dissolution test of a model cocrystal system, it was suggested that an active pharmaceutical ingredient (API) and a coformer were dissolved in water simultaneously. The IR spectra that were acquired during the dissolution of a cocrystal tablet showed new spectral bands attributed to the API after 5 min. This suggested that the precipitation of API was observed during the dissolution experiment. Measurements from ATR-FTIR spectroscopic imaging can visualize the drug release from the tablet and determine the transformation of molecular crystals during their dissolution. These results will have an impact on clarifying the dissolution mechanism of molecular crystals.

Imaging techniques for studying solid dosage formulation: Principles and applications

Classic methods for evaluating the disintegration and dissolution kinetics of solid dosage forms are no longer sufficient to meet the growing demands in the pharmaceutical field. Hence, scientists have turned to imaging techniques and computer technology to develop innovative visualization methods. These methods allow for a visual understanding of the disintegration or dissolution process and offer valuable insights into the drug release kinetics. This article aims to provide an overview of the commonly used imaging techniques and their applications in studying the disintegration or dissolution of solid dosage forms. Therefore, imaging presents a novel and alternative approach to understanding the mechanisms of disintegration and dissolution in the formulation study of solid dosages.

Advances in ATR-FTIR Spectroscopic Imaging for the Analysis of Tablet Dissolution and Drug Release

One of the major challenges in the development of effective pharmaceutical formulations for oral administration is the poor solubility of active pharmaceutical ingredients. For this reason, the dissolution process and drug release from solid oral dosage forms, such as tablets, is usually thoroughly studied in order to understand the dissolution behaviour under various conditions and optimize the formulation accordingly. Standard dissolution tests used in the pharmaceutical industry provide information on the amount of drug released over time; however, these do not allow for a detailed analysis of the underlying chemical and physical mechanisms of tablet dissolution. FTIR spectroscopic imaging, by contrast, does offer the ability to study these processes with high spatial and chemical specificity. As such, the method allows us to see the chemical and physical processes which occur inside the tablet as it dissolves. In this review, the power of ATR-FTIR spectroscopic imaging is demonstrated by presenting a number of successful applications of this chemical imaging technique to dissolution and drug release studies for a range of different pharmaceutical formulations and study conditions. Understanding these processes is essential for the development of effective oral dosage forms and optimization of pharmaceutical formulations.

Kinetics of Water-Induced Amorphous Phase Separation in Amorphous Solid Dispersions via Raman Mapping

The poor bioavailability of an active pharmaceutical ingredient (API) can be enhanced by dissolving it in a polymeric matrix. This formulation strategy is commonly known as amorphous solid dispersion (ASD). API crystallization and/or amorphous phase separation can be detrimental to the bioavailability. Our previous work (Pharmaceutics 2022, 14(9), 1904) provided analysis of the thermodynamics underpinning the collapse of ritonavir (RIT) release from RIT/poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA) ASDs due to water-induced amorphous phase separation. This work aimed for the first time to quantify the kinetics of water-induced amorphous phase separation in ASDs and the compositions of the two evolving amorphous phases. Investigations were performed via confocal Raman spectroscopy, and spectra were evaluated using so-called Indirect Hard Modeling. The kinetics of amorphous phase separation were quantified for 20 wt% and 25 wt% drug load (DL) RIT/PVPVA ASDs at 25 °C and 94% relative humidity (RH). The in situ measured compositions of the evolving phases showed excellent agreement with the ternary phase diagram of the RIT/PVPVA/water system predicted by PC-SAFT in our previous study (Pharmaceutics 2022, 14(9), 1904).

Research progress on the application of spectral imaging technology in pharmaceutical tablet analysis

Tablet as a traditional dosage form in pharmacy has the advantages of accurate dosage, ideal dissolution and bioavailability, convenient to carry and transport. The most concerned tablet quality attributes include active pharmaceutical ingredient (API) contents and polymorphic forms, components distribution, hardness, density, coating state, dissolution behavior, etc., which greatly affect the bioavailability and consistency of tablet final products. In the pharmaceutical industry, there are usually industry standard methods to analyze the tablet quality attributes. However, these methods are generally time-consuming and laborious, and lack a comprehensive understanding of the properties of tablets, such as spatial information. In recent years, spectral imaging technology makes up for the shortcomings of traditional tablet analysis methods because it provides non-contact and rich information in time and space. As a promising technology to replace the traditional tablet analysis methods, it has attracted more and more attention. The present paper briefly describes a series of spectral imaging techniques and their applications in tablet analysis. Finally, the possible application prospect of this technology and the deficiencies that need to be improved were also prospected.

Glass fiber (GF)/polypropylene (PP) composite studied by Raman disrelation mapping

Disrelation mapping was applied to Raman imaging data for the first time to investigate submolecular-level variations that occurred at the interface between glass fiber (GF) and polypropylene (PP). Disrelation maps constructed with Raman spectra provided spatial as well as spectral information, which are not readily accessible from hypercubic data. For example, patterns that appeared in the disrelation maps showed the predominant development of a long helix band (1002 cm^-1) at the interface between the GF and PP, rather than a short helix band (974 cm^-1). The development of the disrelation intensity was observed inside the sample as well as at the surface. These results clearly reveal that the GF or compatibilizer works intrinsically as a nucleating agent to induce additional development of the crystalline structure of the PP, which eventually makes the polymer system harder but more brittle.

Visualising liquid transport through coated pharmaceutical tablets using Terahertz pulsed imaging

Dissolution of pharmaceutical tablets is a complex process, especially for coated tablets where layered structures form an additional barrier for liquid transport into the porous tablet matrix. A better understanding of the role of the coating structure in the mass transport processes that govern drug release, starting with the wetting of the coating layer by the dissolution medium, can benefit the formulation design and optimisation of the production. For this study, terahertz pulsed imaging was used to investigate how dissolution medium can penetrate coated tablets. In order to focus on the fundamental process, the model system for this proof-of-principle study consisted of tablet cores made from pure microcrystalline cellulose compacted to a defined porosity coated with Opadry II, a PVA-based immediate release coating blend. The coating was applied to a single side of flat-faced tablets using vacuum compression moulding. It was possible to resolve the hydration of the coating layer and the subsequent liquid ingress into the dry tablet core. The analysis revealed a discontinuity in density at the interface between coating and core, where coating polymer could enter the pore space at the immediate surface of the tablet cores during the coating process. This structure affected the liquid transport of the dissolution medium into the core. We found evidence for the formation of a gel layer upon hydration of the coating polymer. The porosity of the tablet core impacted the quality of coating and thus affected its dissolution performance (r =  0.6932 for the effective liquid penetration rate RP_eff and the core porosity). This study established a methodology and can facilitate a more in-depth understanding of the role of coating on tablet dissolution.

Analysis of Over-Granulated Particles using Near-Infrared Chemical Imaging and Attenuated Total Reflectance-Infrared Techniques

To elucidate the previously described mechanism of segregation caused by over-granulation, we analyzed over-granulated particles using the techniques of near-infrared chemical imaging (NIR-CI) and attenuated total reflectance infrared (ATR-IR). The same area of over-granulated particles was measured using both techniques. The distributions of the active ingredient, ethenzamide, and other additives in the over-granulated particles were compared. As ATR-IR chemical imaging easily identifies components and has higher spatial resolution than NIR-CI, it permitted a clearer observation of the distribution of ingredients, particularly in fine cornstarch particles. Using both techniques, segregation of components were observed as previously reported. Although lactose was barely observed in the ethenzamide-enriched regions, ethenzamide and cornstarch were observed in lactose-enriched regions. This suggests that only lactose aggregated and segregated from the other compounds during the process of granulation. Hydrophilic lactose aggregation is supposedly caused by the behavior of water during granulation. In conclusion, ATR-IR chemical imaging is an excellent analytical technique for obtaining the detailed distribution of components. Furthermore, fusion of ATR-IR chemical imaging and NIR-CI is a useful tool for understanding drug manufacturing processes and may be applicable to pharmaceutical manufacturing and quality control.

Raman mapping-based non-destructive dissolution prediction of sustained-release tablets

In this paper, the applicability of Raman chemical imaging for the non-destructive prediction of the in vitro dissolution profile of sustained-release tablets is demonstrated for the first time. Raman chemical maps contain a plethora of information about the spatial distribution and the particle size of the components, compression force and even polymorphism. With proper data analysis techniques, this can be converted into simple numerical information which can be used as input in a machine learning model. In our work, sustained-release tablets using hydroxypropyl methylcellulose (HPMC) as matrix polymer are prepared, the concentration and particle size of this component varied between samples. Chemical maps of HPMC are converted into histograms with two different methods, an approach based on discretizing concentration values and a wavelet analysis technique. These histograms are then subjected to Principal Component Analysis, the score value of the first two principal components was found to represent HPMC content and particle size. These values are used as input in Artificial Neural Networks which are trained to predict the dissolution profile of the tablets. As a result, accurate predictions were obtained for the test tablets (the average f₂ similarity value is higher than 59 with both methods). The presented methodology lays the foundations of the analysis of far more extensive datasets acquired with the emerging fast Raman imaging technology.

A Review of Optical Imaging Technologies for Microfluidics

Microfluidics can precisely control and manipulate micro-scale fluids, and are also known as lab-on-a-chip or micro total analysis systems. Microfluidics have huge application potential in biology, chemistry, and medicine, among other fields. Coupled with a suitable detection system, the detection and analysis of small-volume and low-concentration samples can be completed. This paper reviews an optical imaging system combined with microfluidics, including bright-field microscopy, chemiluminescence imaging, spectrum-based microscopy imaging, and fluorescence-based microscopy imaging. At the end of the article, we summarize the advantages and disadvantages of each imaging technology.

Fourier Transform Infrared Imaging Analysis of Interactions Between Polypropylene Grafted with Maleic Anhydride and Silica Spheres Using Two-Trace Two-Dimensional Correlation Mapping

A technique for analyzing infrared imaging data based on two-trace two-dimensional (2T2D) correlation analysis is presented to extract pertinent information underlying spectroscopic imaging data. In 2T2D correlation mapping, each spectrum in hyperspectral data is individually compared with a reference spectrum to generate 2T2D asynchronous correlation intensity at the x- and y-coordinates on a 2T2D correlation map. Asynchronous correlation intensity develops only when the signal contribution from a certain species becomes even more significant in the sample spectrum compared with the reference spectrum. This feature can be advantageously utilized to examine molecular interaction or an intermediate form of the component present in a system of interest. 2T2D correlation mapping is examined using Fourier transform infrared imaging data of polymer composites based on polypropylene grafted with maleic anhydride melt-mixed with silica spheres. Infrared images derived by using conventional visualization based on a single wavenumber (i.e., 1713 cm^-1) are dominated with the overwhelming infrared absorbance induced by the normal maleic anhydride species, making the identification of subtle but pertinent changes in the composite system difficult. A 2T2D correlation map derived from the maleic anhydride/silica spheres composite developed a significant asynchronous correlation intensity between the infrared bands at 1695 and 1713 cm^-1 around a specific region on the map where the maleic anhydride and silica spheres coexist. On the other hand, such a correlation pattern becomes less acute when the silica spheres is modified with the octadecyldimethyl group to prevent the hydrogen bonding with the maleic anhydride. It thus revealed that the silanol groups on the surface of the silica spheres substantially interact with the maleic anhydride via the development of the hydrogen bonding.

Perspectives on infrared spectroscopic imaging from cancer diagnostics to process analysis

This perspective paper discusses the recent and potential developments in the application of infrared spectroscopic imaging, with a focus on Fourier transform infrared (FTIR) spectroscopic imaging. The current state-of-the-art has been briefly reported, that includes recent trends and advances in applications of FTIR spectroscopic imaging to biomedical systems. Here, some new opportunities for research in the biomedical field, particularly for cancer diagnostics, and also in the engineering field of process analysis; as well as challenges in FTIR spectroscopic imaging are discussed. Current and future prospects that will bring spectroscopic imaging technologies to the frontier of advanced medical diagnostics and to process analytics in engineering applications will be outlined in this opinion paper.

Application of percolation threshold to disintegration and dissolution of ibuprofen tablets with different microcrystalline cellulose grades

The study presented was conducted to determine whether a percolation threshold value, previously determined for ibuprofen/microcrystalline cellulose (MCC) blends using percolation theory and compression data (Queiroz et al., 2019), could translate to tablet disintegration and dissolution data. The influence of MCC grade (air stream dried versus spray dried) on tablet disintegration and dissolution was also investigated. Complementary to conventional disintegration and dissolution testing, Raman imaging determined drug distribution within tablets, and in-line particle video microscopy (PVM) and focused-beam reflectance measurement (FBRM) monitored tablet disintegration. Tablets were prepared containing 0-30% w/w ibuprofen. Raman imaging confirmed the percolation threshold by quantifying the number and equivalent circular diameters of ibuprofen domains on tablet surfaces. Across the percolation threshold, a step change in dissolution behaviour occurred, and tablets containing air stream dried MCC showed slower disintegration rates compared to tablets containing spray dried MCC. Dissolution measurements confirmed experimentally a percolation threshold in agreement with that determined using percolation theory and compression data. An increase in drug domains, due to cluster formation, and less efficient tablet disintegration contributed to slower ibuprofen dissolution above the percolation threshold. Slower dissolution was measured for tablets containing air stream dried compared to spray dried MCC.

Biomolecular and bioanalytical applications of infrared spectroscopy - A review

Infrared (IR; or mid-infrared, MIR; 4000-400 cm^-1; 2500-25,000 nm) spectroscopy has become one of the most powerful and versatile tools at the disposal of modern bioscience. Because of its high molecular specificity, applicability to wide variety of samples, rapid measurement and non-invasivity, IR spectroscopy forms a potent approach to elucidate qualitative and quantitative information from various kinds of biological material. For these reasons, it became an established bioanalytical technique with diverse applications. This work aims to be a comprehensive and critical review of the recent accomplishments in the field of biomolecular and bioanalytical IR spectroscopy. That progress is presented on a wider background, with fundamental characteristics, the basic principles of the technique outlined, and its scientific capability directly compared with other methods being used in similar fields (e.g. near-infrared, Raman, fluorescence). The article aims to present a complete examination of the topic, as it touches the background phenomena, instrumentation, spectra processing and data analytical methods, spectra interpretation and related information. To suit this goal, the article includes a tutorial information essential to obtain a thorough perspective of bio-related applications of the reviewed methodologies. The importance of the fundamental factors to the final performance and applicability of IR spectroscopy in various areas of bioscience is explained. This information is interpreted in critical way, with aim to gain deep understanding why IR spectroscopy finds extraordinarily intensive use in this remarkably diverse and dynamic field of research and utility. The major focus is placed on the diversity of the applications in which IR biospectroscopy has been established so far and those onto which it is expanding nowadays. This includes qualitative and quantitative analytical spectroscopy, spectral imaging, medical diagnosis, monitoring of biophysical processes, and studies of physicochemical properties and dynamics of biomolecules. The application potential of IR spectroscopy in light of the current accomplishments and the future prospects is critically evaluated and its significance in the progress of bioscience is comprehensively presented.

Applications of Fourier transform infrared spectroscopy to pharmaceutical preparations

Introduction: Various pharmaceutical preparations are widely used for clinical treatment. Elucidation of the mechanisms of drug release and evaluation of drug efficacy in biological samples are important in drug design and drug quality control.Areas covered: This review classifies recent applications of Fourier transform infrared (FTIR) spectroscopy in the field of medicine to comprehend drug release and diffusion. Drug release is affected by many factors of preparations, such as drug delivery system and microstructure polymorphism. The applications of FTIR imaging and nano-FTIR technique in biological samples lay a foundation for studying drug mechanism in vivo.Expert opinion: FTIR spectroscopy meets the research needs on preparations to understand the processes and mechanisms underlying drug release. The combination of attenuated total reflectance-FTIR imaging and nano-FTIR accompanied by chemometrics is a potent tool to overcome the deficiency of conventional infrared detection. FTIR shows an enormous potential in drug characterization, drug quality control, and bio-sample detection.

Fiber-Array-Based Raman Hyperspectral Imaging for Simultaneous, Chemically-Selective Monitoring of Particle Size and Shape of Active Ingredients in Analgesic Tablets

The particle shape, size and distribution of active pharmaceutical ingredients (API) are relevant quality indicators of pharmaceutical tablets due to their high impact on the manufacturing process. Furthermore, the bioavailability of the APIs from the dosage form depends largely on these characteristics. Routinely, particle size and shape are only analyzed in the powder form, without regard to the effect of the formulation procedure on the particle characteristics. The monitoring of these parameters improves the understanding of the process; therefore, higher quality and better control over the biopharmaceutical profile can be ensured. A new fiber-array-based Raman hyperspectral imaging technique is presented for direct simultaneous in-situ monitoring of three different active pharmaceutical ingredients- acetylsalicylic acid, acetaminophen and caffeine- in analgesic tablets. This novel method enables a chemically selective, noninvasive assessment of the distribution of the active ingredients down to 1 µm spatial resolution. The occurrence of spherical and needle-like particles, as well as agglomerations and the respective particle size ranges, were rapidly determined for two commercially available analgesic tablet types. Subtle differences were observed in comparison between these two tablets. Higher amounts of acetaminophen were visible, more needle-shaped and bigger acetylsalicylic acid particles, and a higher incidence of bigger agglomerations were found in one of the analgesic tablets.

Quantitative analysis of glycated albumin in serum based on ATR-FTIR spectrum combined with SiPLS and SVM

A rapid quantitative analysis model for determining the glycated albumin (GA) content based on Attenuated total reflectance (ATR)-Fourier transform infrared spectroscopy (FTIR) combining with linear SiPLS and nonlinear SVM has been developed. Firstly, the real GA content in human serum was determined by GA enzymatic method, meanwhile, the ATR-FTIR spectra of serum samples from the population of health examination were obtained. The spectral data of the whole spectra mid-infrared region (4000-600 cm^-1) and GA's characteristic region (1800-800 cm^-1) were used as the research object of quantitative analysis. Secondly, several preprocessing steps including first derivative, second derivative, variable standardization and spectral normalization, were performed. Lastly, quantitative analysis regression models were established by using SiPLS and SVM respectively. The SiPLS modeling results are as follows: root mean square error of cross validation (RMSECV_T) = 0.523 g/L, calibration coefficient (R_C) = 0.937, Root Mean Square Error of Prediction (RMSEP_T) = 0.787 g/L, and prediction coefficient (R_P) = 0.938. The SVM modeling results are as follows: RMSECV_T = 0.0048 g/L, R_C = 0.998, RMSEP_T = 0.442 g/L, and R_p = 0.916. The results indicated that the model performance was improved significantly after preprocessing and optimization of characteristic regions. While modeling performance of nonlinear SVM was considerably better than that of linear SiPLS. Hence, the quantitative analysis model for GA in human serum based on ATR-FTIR combined with SiPLS and SVM is effective. And it does not need sample preprocessing while being characterized by simple operations and high time efficiency, providing a rapid and accurate method for GA content determination.

Recent advances in the applications of vibrational spectroscopic imaging and mapping to pharmaceutical formulations

Vibrational spectroscopic imaging and mapping approaches have continued in their development and applications for the analysis of pharmaceutical formulations. Obtaining spatially resolved chemical information about the distribution of different components within pharmaceutical formulations is integral for improving the understanding and quality of final drug products. This review aims to summarise some key advances of these technologies over recent years, primarily since 2010. An overview of FTIR, NIR, terahertz spectroscopic imaging and Raman mapping will be presented to give a perspective of the current state-of-the-art of these techniques for studying pharmaceutical samples. This will include their application to reveal spatial information of components that reveals molecular insight of polymorphic or structural changes, behaviour of formulations during dissolution experiments, uniformity of materials and detection of counterfeit products. Furthermore, new advancements will be presented that demonstrate the continuing novel applications of spectroscopic imaging and mapping, namely in FTIR spectroscopy, for studies of microfluidic devices. Whilst much of the recently developed work has been reported by academic groups, examples of the potential impacts of utilising these imaging and mapping technologies to support industrial applications have also been reviewed.

An Application for the Quantitative Analysis of Pharmaceutical Tablets Using a Rapid Switching System Between a Near-Infrared Spectrometer and a Portable Near-Infrared Imaging System Equipped with Fiber Optics

We present a rapid switching system between a newly developed near-infrared (NIR) spectrometer and its imaging system to select the spot size of a diffuse reflectance (DR) probe. In a previous study, we developed a portable NIR imaging system, known as D-NIRs, which has significant advantages over other systems. Its high speed, high spectral resolution, and portability are particularly useful in the process of monitoring pharmaceutical tablets. However, the spectral accuracies relating to the changes in the formulation of the pharmaceutical tablets have not been fully discussed. Therefore, we improved the rapid optical switching system and present a new model of D-NIRs (ND-NIRs) here. This system can automatically switch the optical paths of the DR and NIR imaging probes, greatly contributing to the simultaneous measurement of both the imaging and spot. The NIR spectra of the model tablets, including 0-10% ascorbic acid, were measured and simultaneous NIR images of the tablets were obtained. The predicted results using spot sizes for the DR probe of 1 and 5 mm diameter, resulted in concentrations of R2 = 0.79 and 0.94, with root mean square errors (RMSE) of 1.78 and 0.89, respectively. For tablets with a high concentration of ascorbic acid, the NIR imaging results showed inhomogeneity in concentration. However, the predicted values for the low concentration samples appeared higher than the known concentration of the tablets, although the homogeneity of the concentration was confirmed. In addition, the optimal spot size using NIR imaging data was estimated to be 5-7 mm. The results obtained in this study show that the spot size of the fiber probe, attached to a spectrometer, is important in developing a highly reliable model to determine the component concentration of a tablet.

Infrared spectroscopy and spectroscopic imaging in forensic science

Infrared spectroscopy and spectroscopic imaging, are robust, label free and inherently non-destructive methods with a high chemical specificity and sensitivity that are frequently employed in forensic science research and practices. This review aims to discuss the applications and recent developments of these methodologies in this field. Furthermore, the use of recently emerged Fourier transform infrared (FT-IR) spectroscopic imaging in transmission, external reflection and Attenuated Total Reflection (ATR) modes are summarised with relevance and potential for forensic science applications. This spectroscopic imaging approach provides the opportunity to obtain the chemical composition of fingermarks and information about possible contaminants deposited at a crime scene. Research that demonstrates the great potential of these techniques for analysis of fingerprint residues, explosive materials and counterfeit drugs will be reviewed. The implications of this research for the examination of different materials are considered, along with an outlook of possible future research avenues for the application of vibrational spectroscopic methods to the analysis of forensic samples.

UV imaging in pharmaceutical analysis

UV imaging provides spatially and temporally resolved absorbance measurements, which are highly useful in pharmaceutical analysis. Commercial UV imaging instrumentation was originally developed as a detector for separation sciences, but the main use is in the area of in vitro dissolution and release testing studies. The review covers the basic principles of the technology and summarizes the main applications in relation to intrinsic dissolution rate determination, excipient compatibility studies and in vitro release characterization of drug substances and vehicles intended for parenteral administration. UV imaging has potential for providing new insights to drug dissolution and release processes in formulation development by real-time monitoring of swelling, precipitation, diffusion and partitioning phenomena. Limitations of current instrumentation are discussed and a perspective to new developments and opportunities given as new instrumentation is emerging.

Fourier Transform Infrared (FT-IR) Spectroscopic Imaging Analysis of Partially Miscible PMMA-PEG Blends Using Two-Dimensional Disrelation Mapping

A novel technique called disrelation spectroscopic imaging describes the process of identifying an area where a coordinated or out-of-phase change in pattern of spectral absorbance occurs. Disrelation mapping can be viewed as a spatial filter based on the well-established two-dimensional (2D) correlation function to highlight specific areas where disrelated variation occurs between ν₁ and ν₂. Disrelation intensity develops only if the spectral absorbance measured at ν₁ and ν₂ vary out of phase with each other within a specific spatial area. The disrelation mapping locates regions where absorbance varies in a dissimilar manner because of the contribution from species of different physical or chemical origins. Consequently, it becomes possible to probe onset of molecular interactions or presence of intermediate forms between components, which is not fully detected by the conventional visualizations based on a single wavenumber. Data analysis using disrelation mapping applied to Fourier transform infrared (FT-IR) spectroscopic images is presented in this study. Data sets of FT-IR spectroscopic images of blends of poly(methyl methacrylate) (PMMA) and polyethylene glycol (PEG) were subjected to the disrelation mapping. It was found that the disrelation intensity between 1730 and 1714 cm^-1 becomes especially acute around the spatial boundary between PMMA and PEG domains within the studied blend sample. Thus the band at 1730 cm^-1 most likely represents the C=O stretching mode of the C=O···H-O species due to the intermolecular hydrogen bonding between PMMA and PEG. The appearance of such disrelation is more noticeable in the PEG-rich region, for the PEG with low molecular weight. Consequently, it suggests that the blends of PMMA and PEG are partially miscible at the molecular level and these intermolecular interactions are affected by the quantity of the terminal -OH groups of the PEG.

Protein hydration in living cells probed by Fourier transform infrared (FT-IR) spectroscopic imaging

FT-IR spectra of a HEK cell were analyzed with 2D disrelation mapping to reveal molecular states of water and protein hydration.

Application of UV Imaging in Formulation Development

Efficient drug delivery is dependent on the drug substance dissolving in the body fluids, being released from dosage forms and transported to the site of action. A fundamental understanding of the interplay between the physicochemical properties of the active compound and pharmaceutical excipients defining formulation behavior after exposure to the aqueous environments and pharmaceutical performance is critical in pharmaceutical development, manufacturing and quality control of drugs. UV imaging has been explored as a tool for qualitative and quantitative characterization of drug dissolution and release with the characteristic feature of providing real-time visualization of the solution phase drug transport in the vicinity of the formulation. Events occurring during drug dissolution and release, such as polymer swelling, drug precipitation/recrystallization, or solvent-mediated phase transitions related to the structural properties of the drug substance or formulation can be monitored. UV imaging is a non-intrusive and simple-to-operate analytical technique which holds potential for providing a mechanistic foundation for formulation development. This review aims to cover applications of UV imaging in the early and late phase pharmaceutical development with a special focus on the relation between structural properties and performance. Potential areas of future advancement and application are also discussed.

The Combined Use of Imaging Approaches to Assess Drug Release from Multicomponent Solid Dispersions

Purpose

Imaging methods were used as tools to provide an understanding of phenomena that occur during dissolution experiments, and ultimately to select the best ratio of two polymers in a matrix in terms of enhancement of the dissolution rate and prevention of crystallization during dissolution.

Methods

Magnetic resonance imaging, ATR-FTIR spectroscopic imaging and Raman mapping have been used to study the release mechanism of a poorly water soluble drug, aprepitant, from multicomponent amorphous solid dispersions. Solid dispersions were prepared based on the combination of two selected polymers - Soluplus, as a solubilizer, and PVP, as a dissolution enhancer. Formulations were prepared in a ratio of Soluplus:PVP 1:10, 1:5, 1:3, and 1:1, in order to obtain favorable properties of the polymer carrier.

Results

The crystallization of aprepitant during dissolution has occurred to a varying degree in the polymer ratios 1:10, 1:5, and 1:3, but the increasing presence of Soluplus in the formulation delayed the onset of crystallization. The Soluplus:PVP 1:1 solid dispersion proved to be the best matrix studied, combining the abilities of both polymers in a synergistic manner.

Conclusions

Aprepitant dissolution rate has been significantly enhanced. This study highlights the benefits of combining imaging methods in order to understand the release process.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-016-2018-x) contains supplementary material, which is available to authorized users.

Performance characteristics of UV imaging instrumentation for diffusion, dissolution and release testing studies

UV imaging is capable of providing spatially and temporally resolved absorbance measurements, which is highly beneficial in drug diffusion, dissolution and release testing studies. For optimal planning and design of experiments, knowledge about the capabilities and limitations of the imaging system is required. The aim of this study was to characterize the performance of two commercially available UV imaging systems, the D100 and SDI. Lidocaine crystals, lidocaine containing solutions, and gels were applied in the practical assessment of the UV imaging systems. Dissolution of lidocaine from single crystals into phosphate buffer and 0.5% (w/v) agarose hydrogel at pH 7.4 was investigated to shed light on the importance of density gradients under dissolution conditions in the absence of convective flow. In addition, the resolution of the UV imaging systems was assessed by the use of grids. Resolution was found to be better in the vertical direction than the horizontal direction, consistent with the illumination geometry. The collimating lens in the SDI imaging system was shown to provide more uniform light intensity across the UV imaging area and resulted in better resolution as compared to the D100 imaging system (a system without a lens). Under optimal conditions, the resolution was determined to be 12.5 and 16.7 line pairs per mm (lp/mm) corresponding to line widths of 40μm and 30μm in the horizontal and vertical direction, respectively. Overall, the performance of the UV imaging systems was shown mainly to depend on collimation of light, the light path, the positioning of the object relative to the line of 100μm fibres which forms the light source, and the distance of the object from the sensor surface.

The Relationship Between the Evolution of an Internal Structure and Drug Dissolution from Controlled-Release Matrix Tablets

In the last decade, imaging has been introduced as a supplementary method to the dissolution tests, but a direct relationship of dissolution and imaging data has been almost completely overlooked. The purpose of this study was to assess the feasibility of relating magnetic resonance imaging (MRI) and dissolution data to elucidate dissolution profile features (i.e., kinetics, kinetics changes, and variability). Commercial, hydroxypropylmethyl cellulose-based quetiapine fumarate controlled-release matrix tablets were studied using the following two methods: (i) MRI inside the USP4 apparatus with subsequent machine learning-based image segmentation and (ii) dissolution testing with piecewise dissolution modeling. Obtained data were analyzed together using statistical data processing methods, including multiple linear regression. As a result, in this case, zeroth order release was found to be a consequence of internal structure evolution (interplay between region's areas-e.g., linear relationship between interface and core), which eventually resulted in core disappearance. Dry core disappearance had an impact on (i) changes in dissolution kinetics (from zeroth order to nonlinear) and (ii) an increase in variability of drug dissolution results. It can be concluded that it is feasible to parameterize changes in micro/meso morphology of hydrated, controlled release, swellable matrices using MRI to establish a causal relationship between the changes in morphology and drug dissolution. Presented results open new perspectives in practical application of combined MRI/dissolution to controlled-release drug products.

Attenuated total reflection-Fourier transform infrared spectroscopic imaging of pharmaceuticals in microfluidic devices

The poor aqueous solubility of many active pharmaceutical ingredients presents challenges for effective drug delivery. In this study, the combination of attenuated total reflection (ATR)-FTIR spectroscopic imaging with specifically designed polydimethylsiloxane microfluidic devices to study drug release from pharmaceutical formulations has been developed. First, the high-throughput analysis of the dissolution of micro-formulations studied under flowing conditions has been introduced using a model formulation of ibuprofen and polyethylene glycol. The behaviour and release of the drug was monitored in situ under different pH conditions. In contrast to the neutral solution, where both the drug and excipient dissolved at a similar rate, structural change from the molecularly dispersed to a crystalline form of ibuprofen was characterised in the obtained spectroscopic images and the corresponding ATR-FTIR spectra for the experiments carried out in the acidic medium. Further investigations into the behaviour of the drug after its release from formulations (i.e., dissolved drug) were also undertaken. Different solutions of sodium ibuprofen dissolved in a neutral medium were studied upon contact with acidic conditions. The phase transition from a dissolved species of sodium ibuprofen to the formation of solid crystalline ibuprofen was revealed in the microfluidic channels. This innovative approach could offer a promising platform for high-throughput analysis of a range of micro-formulations, which are of current interest due to the advent of 3D printed pharmaceutical and microparticulate delivery systems. Furthermore, the ability to study dissolved drug in solution under flowing conditions can be useful for the studies of the diffusion of drugs into tissues or live cells.

Identifying the mechanisms of drug release from amorphous solid dispersions using MRI and ATR-FTIR spectroscopic imaging

The dissolution mechanism of a poorly aqueous soluble drug from amorphous solid dispersions was investigated using a combination of two imaging methods: attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic imaging and magnetic resonance imaging (MRI). The rates of elementary processes such as water penetration, polymer swelling, growth and erosion of gel layer, and the diffusion, release and in some cases precipitation of drug were evaluated by image analysis. The results from the imaging methods were compared with drug release profiles obtained by classical dissolution tests. The study was conducted using three polymeric excipients (soluplus, polyvinylpyrrolidone - PVP K30, hydroxypropylmethyl cellulose - HPMC 100M) alone and in combination with a poorly soluble drug, aprepitant. The imaging methods were complementary: ATR-FTIR imaging enabled a qualitative observation of all three components during the dissolution experiments, water, polymer and drug, including identifying structural changes from the amorphous form of drug to the crystalline form. The comparison of quantitative MRI data with drug release profiles enabled the different processes during dissolution to be established and the rate-limiting step to be identified, which - for the drug-polymer combinations investigated in this work - was the drug diffusion through the gel layer rather than water penetration into the tablet.

Fast drying and film formation of latex dispersions studied with FTIR spectroscopic imaging

Drying of thin latex films (∼20 μm) at high drying speeds (of the order of seconds) has been studied by fast chemical imaging. ATR-FTIR spectroscopic imaging combined with a fast "kinetic" mode was used to acquire spectral images without coaddition, enabling the amount of water and homogeneity of the drying film to be studied over time. Drying profiles, constructed from analyzing the water content in each image, show two stages of drying, a fast and a slow region. The formulation of latex dispersions affects the onset of slow drying and the volume fraction of water remaining at the onset of slow drying. In this work, the effect of physical properties, film thickness and glass transition temperature (Tg), were investigated, as well as the effect of monomer composition where two monomoers, 2-ethylhexyl acrylate and n-butyl acrylate, and the amount of hydrophilic comonomer, methyl methacrylate (MMA), were varied. It was found that thicker films produced slower overall drying and that the formulation with a Tg above the minimum film formation temperature did not dry evenly, exhibiting cracking. However, the drying kinetics of high and low Tg films were similar, highlighting the advantage of using a spatially-resolved spectroscopic approach. Formulations containing more MMA dried faster than those with less. This was due to the hydrophilicity of MMA and the increase in Tg of the dispersion from the addition of MMA. Overall, FTIR spectroscopic imaging was shown to be a suitable approach in measuring film drying at high speeds as both chemical changes and chemical distribution could be analyzed over time.

Microenvironmental pH measurement during sodium naproxenate dissolution in acidic medium by UV/vis imaging

Variable dissolution from sodium salts of drugs containing a carboxylic acid group after passing the acidic environment of the stomach may affect oral bioavailability. The aim of the present proof of concept study was to investigate pH effects in relation to the dissolution of sodium naproxenate in 0.01M hydrochloric acid. For this purpose a UV/vis imaging-based approach capable of measuring microenvironmental pH in the vicinity of the solid drug compact as well as monitoring drug dissolution was developed. Using a pH indicating dye real-time spatially resolved measurement of pH was achieved. Sodium naproxenate, can significantly alter the local pH of the dissolution medium, is eventually neutralized and precipitates as the acidic species naproxen. The developed approach is considered useful for detailed studies of pH dependent dissolution phenomena in dissolution testing.

Advances in nanocrystallography as a proteomic tool

In order to overcome the difficulties and hurdles too much often encountered in crystallizing a protein with the conventional techniques, our group has introduced the innovative Langmuir-Blodgett (LB)-based crystallization, as a major advance in the field of both structural and functional proteomics, thus pioneering the emerging field of the so-called nanocrystallography or nanobiocrystallography. This approach uniquely combines protein crystallography and nanotechnologies within an integrated, coherent framework that allows one to obtain highly stable protein crystals and to fully characterize them at a nano- and subnanoscale. A variety of experimental techniques and theoretical/semi-theoretical approaches, ranging from atomic force microscopy, circular dichroism, Raman spectroscopy and other spectroscopic methods, microbeam grazing-incidence small-angle X-ray scattering to in silico simulations, bioinformatics, and molecular dynamics, has been exploited in order to study the LB-films and to investigate the kinetics and the main features of LB-grown crystals. When compared to classical hanging-drop crystallization, LB technique appears strikingly superior and yields results comparable with crystallization in microgravity environments. Therefore, the achievement of LB-based crystallography can have a tremendous impact in the field of industrial and clinical/therapeutic applications, opening new perspectives for personalized medicine. These implications are envisaged and discussed in the present contribution.