Exploring in-vivo infrared spectroscopy for nail-based diabetes screening.

Diabetes screening is traditionally complex, inefficient, and reliant on invasive sampling. This study evaluates near-infrared spectroscopy for non-invasive detection of glycated keratin in nails in vivo. Glycation of keratin, prevalent in tissues like nails and skin, is a key indicator of T2DM risk. In this study involving 200 participants (100 with diabetes, 100 without), NIR's efficacy was compared against a point-of-care HbA1c analyzer. Results showed a specificity of 92.9% in diabetes risk assessment. This study highlights the proposed NIR system potential as a simple, reliable tool for early diabetes screening and risk management in various healthcare settings.

The role of terahertz polariton absorption in the characterization of crystalline iron sulfate hydrates.

Iron sulfate compounds have been used extensively to produce iron gall ink, a widely used writing ink in the western world from the 12th-20th centuries. Iron gall ink is well known to corrode writing supports, so detection of iron species is important for the preservation of historical artwork and documents. Iron(ii) sulfate readily changes hydration states and oxidizes in ambient conditions, forming compounds that contribute to this deterioration. In this study, five forms of iron sulfate are characterized by terahertz spectroscopy and solid-state density functional theory (DFT). The results have revealed that the room temperature spectra of FeSO4·7H2O and FeSO4·4H2O are remarkably similar, differing by only a single absorption feature. The identifying terahertz spectra provide an unambiguous metric to determine the relative concentrations of the most common hydrates FeSO4·7H2O and FeSO4·4H2O in a mixed sample. Complete spectral assignments of these species were accomplished by quantum mechanical simulations, with the exception being a single anomalous feature at approximately 40 cm(-1) in the heptahydrate. This peak is believed to be due to polariton absorption, brought about by the particular coordination structure of FeSO4·7H2O that results in a greater charge separation relative to the other iron sulfate crystals.

Assignment of the terahertz spectra of crystalline copper sulfate and its hydrates via solid-state density functional theory.

Terahertz (THz) vibrational spectroscopy is a promising tool for the nondestructive and potentially noninvasive characterization of historical objects, which can provide information on the materials used for their production as well as identify and monitor their chemical degradation. Copper sulfate (CuSO4) has drawn interest due to its inclusion in the preparation of iron gall inks found in historical artwork and documents. Copper sulfate rapidly forms hydrates which contribute to the formulation of these ink species and may influence their corrosive nature. In this study, copper sulfate has been studied using a combination of THz time-domain spectroscopy, powder X-ray diffraction (PXRD), and solid-state density functional theory (DFT) in order to better understand the spectral absorbances in the THz region. The results have revealed that the THz spectrum of commercially available "anhydrous" copper sulfate results from the presence of not only the anhydrous form but also the monohydrate (CuSO4·H2O) and trihydrate (CuSO4·3H2O) forms. Complete assignment of the experimental spectrum was achieved through a comparison of density functionals and extensive investigation of the influence of basis set polarization functions on the bonding interactions, lattice parameters, and low-frequency motions in these crystalline solids.

Systematic study of terahertz time-domain spectra of historically informed black inks.

The potential of terahertz-time domain spectroscopy (THz-TDS) as a diagnostic tool for studies of inks in historical documents is investigated in this paper. Transmission mode THz-TDS was performed on historically informed model writing and drawing inks. Carbon black, bistre and sepia inks show featureless spectra between 5 and 75 cm(-1) (0.15-2.25 THz); however, their analysis still provided useful information on the interaction of terahertz radiation with amorphous materials. On the other hand, THz-TDS can be used to distinguish different iron gall inks with respect to the amount of iron(II) sulfate contained, as sharp spectral features are observed for inks containing different ratios of iron(II) sulfate to tannic or gallic acid. Additionally, copper sulfate was found to modify the structure of iron(II) precipitate. Furthermore, Principal Component Analysis (PCA) applied to THz-TDS spectra, highlights changes in iron gall inks during thermal degradation, during which a decrease in the sharp spectral bands associated with iron(II) sulfate is observed. ATR-FTIR spectroscopy combined with THz-TDS of dynamically heated ink samples indicate that this phenomenon is due to dehydration of iron(II) sulfate heptahydrate. While this research demonstrates the potential of THz-TDS to improve monitoring of the chemical state of historical documents, the outcomes go beyond the heritage field, as it also helps to develop the theoretical knowledge on interactions between terahertz radiation and matter, particularly in studies of long-range symmetry (polymorphism) in complex molecular structures and the role played by the surrounding matrix, and also indicates the potential of THz-TDS for the optimization of contrast in terahertz imaging.

Evaluating the effect of coating equipment on tablet film quality using terahertz pulsed imaging.

In this study, terahertz pulsed imaging (TPI) was employed to investigate the effect of the coating equipment (fluid bed and drum coater) on the structure of the applied film coating and subsequent dissolution behaviour. Six tablets from every batch coated with the same delayed release coating formulation under recommended process conditions (provided by the coating polymer supplier) were mapped individually to evaluate the effect of coating device on critical coating characteristics (coating thickness, surface morphology and density). Although the traditional coating quality parameter (weight gain) indicated no differences between both batches, TPI analysis revealed a lower mean coating thickness (CT) for tablets coated in the drum coater compared to fluid bed coated tablets (p<0.05). Moreover, drum coated tablets showed a more pronounced CT variation between the two sides and the centre band of the biconvex tablets, with the CT around the centre band being 22.5% thinner than the top and bottom sides for the drum coated tablets and 12.5% thinner for fluid bed coated tablets. The TPI analysis suggested a denser coating for the drum coated tablets. Dissolution testing confirmed that the film coating density was the drug release governing factor, with faster drug release for tablets coated in the fluid bed coater (98 ± 4% after 6h) compared to drum coated tablets (72 ± 6% after 6h). Overall, TPI investigation revealed substantial differences in the applied film coating quality between tablets coated in the two coaters, which in turn correlated with the subsequent dissolution performance.

Coating and Density Distribution Analysis of Commercial Ciprofloxacin Hydrochloride Monohydrate Tablets by Terahertz Pulsed Spectroscopy and Imaging.

Terahertz pulsed spectroscopy was used to qualitatively detect ciprofloxacin hydrochloride monohydrate (CPFX·HCl·H(2)O) in tablets, and terahertz pulsed imaging (TPI) was used to scrutinize not only the coating state but also the density distribution of tablets produced by several manufacturers. TPI was also used to evaluate distinguishability among these tablets. The same waveform, which is a unique terahertz absorption spectrum derived from pure CPFX·HCl·H(2)O, was observed in all of the crushed tablets and in pure CPFX·HCl·H(2)O. TPI can provide information about the physical states of coated tablets. Information about the uniformity of parameters such as a coating thickness and density can be obtained. In this study, the authors investigated the coating thickness distributions of film-coated CPFX·HCl·H(2)O from four different manufacturers. Unique terahertz images of the density distributions in these commercial tablets were obtained. Moreover, B-scan (depth) images show the status of the coating layer in each tablet and the density map inside the tablets. These features would reflect differences resulting from different tablet-manufacturing processes.

Investigating dissolution performance critical areas on coated tablets: a case study using terahertz pulsed imaging.

During the process development of coated tablets, knowledge on the formation and the location of film coating 'weak spots' is a key factor to the success of the process and the resulting product batch. It is understood that the performance of the product batch may be greatly limited, and often compromised, by weak spots on the tablet film coat. This study uses circular, biconvex tablets to investigate the ability of terahertz pulsed imaging (TPI) to identify the affected areas on the tablet film coat that are critical for dissolution performance. From the TPI analysis we determined that the tablet central band exhibited the thinnest film coating, lowest coating density and highest surface roughness and thus was the performance limiting area of the film coating. Dissolution tests confirmed that the film coating on the tablet central band was indeed dissolution rate determining, with a faster mean dissolution time (MDT) of 7.4 h in comparison to 10.4 h for the convex top/bottom surface. TPI, as a nondestructive analytical technique, showed potential to be employed as a process analytical tool to probe film coating weak spots during film coating development and to assess the effect on the subsequent dissolution performance.

Terahertz pulsed imaging, a novel process analytical tool to investigate the coating characteristics of push-pull osmotic systems.

The aim of this study was to investigate coating characteristics of push-pull osmotic systems (PPOS) using three-dimensional terahertz pulsed imaging (3D-TPI) and to detect physical alterations potentially impacting the drug release. The terahertz time-domain reflection signal was used to obtain information on both the spatial distribution of the coating thickness and the coating internal physical mapping. The results showed that (i) the thickness distribution of PPOS coating can be non-destructively analysed using 3D-TPI and (ii) internal physical alterations impacting the drug release kinetics were detectable by using the terahertz time-domain signal. Based on the results, the potential benefits of implementing 3D-TPI as quality control analytical tool were discussed.

Effects of film coating thickness and drug layer uniformity on in vitro drug release from sustained-release coated pellets: a case study using terahertz pulsed imaging.

Film coating thickness and terahertz electric field peak strength (TEFPS) were determined using terahertz pulsed imaging (TPI) and employed for the analysis of sustained-release coated pellets (theophylline layered sugar cores coated with Kollicoat SR:Kollicoat IR polymer blends). The effects of coating thickness, drug layer uniformity and optional curing were investigated using eight batches of pellets. Ten pellets from each batch were imaged with TPI to analyse the coating morphology (depicted in TEFPS) and thickness prior to release measurements. The results showed TEFPS values of 15.8% and 14.5% for pellets with a smooth drug layer coated at 8.2 and 12.5% (w/w) polymer weight-gain, respectively. Whereas 6.7% was derived for pellets with a coarse drug layer coated at both weight-gains. Although there were major differences in TEFPS, the resulting drug release kinetics were very similar. It was also shown that a 36 microm coating thickness difference was not drug release rate determining. These results suggested that drug release for the pellets studied was not predominately governed by drug diffusion through the polymeric film coating but probably to a large extent limited by drug solubility. TPI proved to be highly suitable to detect non-homogeneities in the drug layer and polymeric film coating.

Monitoring the film coating unit operation and predicting drug dissolution using terahertz pulsed imaging.

Understanding the coating unit operation is imperative to improve product quality and reduce output risks for coated solid dosage forms. Three batches of sustained-release tablets coated with the same process parameters (pan speed, spray rate, etc.) were subjected to terahertz pulsed imaging (TPI) analysis followed by dissolution testing. Mean dissolution times (MDT) from conventional dissolution testing were correlated with terahertz waveforms, which yielded a multivariate, partial least squares regression (PLS) model with an R(2) of 0.92 for the calibration set and 0.91 for the validation set. This two-component, PLS model was built from batch I that was coated in the same environmental conditions (air temperature, humidity, etc.) to that of batch II but at different environmental conditions from batch III. The MDTs of batch II was predicted in a nondestructive manner with the developed PLS model and the accuracy of the predicted values were subsequently validated with conventional dissolution testing and found to be in good agreement. The terahertz PLS model was also shown to be sensitive to changes in the coating conditions, successfully identifying the larger coating variability in batch III. In this study, we demonstrated that TPI in conjunction with PLS analysis could be employed to assist with film coating process understanding and provide predictions on drug dissolution.

Terahertz pulsed imaging as an analytical tool for sustained-release tablet film coating.

The ability of terahertz pulsed imaging (TPI) to be employed as an analytical tool for monitoring a film coating unit operation and to assess the success of a subsequent process scale-up was explored in this study. As part of a process scale-up development, a total of 190 sustained-release tablets were sampled at 10% increments of the amount of polymer applied, from a lab-scale and a pilot-scale coating run. These tablets were subjected to TPI analysis, followed by dissolution testing. Information on tablet film coating layer thickness and variations in coating density were extracted using TPI. It was found that both terahertz parameters were more sensitive and informative to product quality when compared with measuring the amount of polymer applied. For monitoring the film coating unit operation, coating layer thickness showed a strong influence on the dissolution behaviour for both the lab-scale and the pilot-scale batches. An R(2) of 0.89, root mean square error (RMSE)=0.22 h (MDT range=3.21-5.48 h) and an R(2) of 0.92, RMSE=0.23 h (MDT range=5.43-8.12 h) were derived from the lab-scale and pilot-scale, respectively. The scale-up process led to significant changes in MDT between the lab-scale and pilot-scale. These changes in MDT could be explained by the differences observed in the film coating density on samples with similar amount of polymer applied between the lab and the pilot-scale. Overall, TPI demonstrated potential to be employed as an analytical tool to help refine the coating unit operation and the scale-up procedure.

Pulsed terahertz attenuated total reflection spectroscopy.

Pulsed terahertz attenuated total reflection (ATR) spectra of solid materials and liquids covering the 10 cm(-1) to 120 cm(-1) (0.3 THz to 3.6 THz) region of the electromagnetic spectrum are recorded using a terahertz pulsed spectrometer and silicon ATR modules. Pulsed terahertz ATR measurements are completed nondestructively using small amounts of sample (typically 1 mg for solids) and no sample preparation. Many terahertz analyses can be run in rapid sequence, minimizing the analysis time.

Applications of terahertz pulsed imaging to sustained-release tablet film coating quality assessment and dissolution performance.

The potential of terahertz pulsed imaging (TPI) to predict the dissolution performance in sustained-release tablets was investigated in this study. Batches of coated tablets with similar weight gain during the coating process at the lab and pilot scales were subjected to non-destructive imaging by TPI and subsequently analysed by dissolution testing. The results from the dissolution tests revealed significant differences in the product performance between the lab and pilot scales (Student t-test, P<0.05). The model-independent dissolution parameters in the pilot scale showed a prolonged mean dissolution time. This indicated that the pharmaceutical active ingredient was released at a slower rate in the pilot compared to the lab scale. While weight gain measurements (the traditional coating quality parameter), failed to provide an early indication of the product functional performance; terahertz parameters (terahertz electric field peak strength and coating layer thickness) provided insight into the subsequent dissolution behaviour. Correlations between terahertz parameters and dissolution were much stronger than correlations between weight gain and dissolution; with the R(2) value for terahertz correlations typically around 0.84 as opposed to 0.07 for weight gain correlations. This study presents the initial finding of correlations between terahertz parameters for assessing the coating quality to the dissolution performance of the coated tablet. The contributing factors for these particular correlations are also discussed.

Density mapping and chemical component calibration development of four-component compacts via terahertz pulsed imaging.

The purpose of this research was to investigate suitable procedures for generating multivariate prediction vectors for quantitative composition and density analysis of intact solid oral dosage forms using terahertz pulsed imaging (TPI) spectroscopy. Both frequency- (absorbance and refractive index) and time-domain data are presented. A set of calibration and prediction samples were created according to a quaternary mixture design with five levels of compaction at each concentration design point. Calibration models were generated by partial least-squares, type II (PLS-2) regression of the TPI spectra against nominal composition and relative density reference measurements. Quantitative frequency-domain composition calibration models were created for all crystalline components (R(2)>0.90), but the calibration models for individual amorphous components (R(2)<0.76) did not perform as well in testing. Combining both amorphous components into a single component variable for regression resulted in lower error statistics and equally good predictions of crystalline components. A non-linear attenuation of time-domain spectra was observed as a function of compaction force, which corresponded to compact density predictions (R(2)=0.948). While refractive index spectra were sensitive to density (R(2)=0.937), the absorbance spectra were not. Surface density maps were prepared based on refractive index calibrations.

Delayed release tablet dissolution related to coating thickness by terahertz pulsed image mapping.

Delayed release dosage forms such as Asacol employ coatings that are engineered to breakdown and release the drug topically at the nominal pH of the lower intestinal tract. Asacol tablets were found to dissolve in an erratic fashion when they are dissolved in buffers below pH 7 which can occur naturally. In this study Terahertz pulsed imaging (TPI) was used to accurately map the coating thickness of a group of Asacol tablets that were subsequently dissolved using the USP method at pH 6.8. The mean dissolution times were found to correlate with the average coating thickness measured over all surfaces. Thickness values for a single randomly selected face did not correlate well with the dissolution results. The speed and ease of TPI mapping may make it an attractive replacement for wet dissolution testing both in product development and eventually for process analysis.

Relaxation and crystallization of amorphous carbamazepine studied by terahertz pulsed spectroscopy.

At the example of carbamazepine the crystallization of a small organic molecule from its amorphous phase was studied using in situ variable temperature terahertz pulsed spectroscopy (TPS). Even though terahertz spectra of disordered materials in the glassy state exhibit no distinct spectral features we demonstrate subtle changes in the spectra with increasing temperature and discuss the findings in respect to the density of vibrational states. The crystallization leads to distinct spectral features allowing the crystallization and subsequent polymorphic phase transition at higher temperatures to be studied in detail. It is possible to study both relaxation and crystallization processes by variable temperature TPS.

Terahertz pulsed spectroscopy and imaging in the pharmaceutical setting--a review.

Terahertz pulsed spectroscopy (TPS) and terahertz pulsed imaging (TPI) are two novel techniques for the physical characterization of pharmaceutical drug materials and final solid dosage forms, utilizing spectral information in the far infrared region of the electromagnetic spectrum. This review focuses on the development and performance of pharmaceutical applications of terahertz technology compared with other tools for physical characterization. TPS can be used to characterize crystalline properties of drugs and excipients. Different polymorphic forms of a drug can be readily distinguished and quantified. Recent developments towards a better understanding of the fundamental theory behind spectroscopy in the far infrared have been discussed. Applications for TPI include the measurement of coating thickness and uniformity in coated pharmaceutical tablets, structural imaging and 3D chemical imaging of solid dosage forms.

Analysis of coating structures and interfaces in solid oral dosage forms by three dimensional terahertz pulsed imaging.

Three dimensional terahertz pulsed imaging (TPI) was evaluated as a novel tool for the nondestructive characterization of different solid oral dosage forms. The time-domain reflection signal of coherent pulsed light in the far infrared was used to investigate film-coated tablets, sugar-coated tablets, multilayered controlled release tablets, and soft gelatin capsules. It is possible to determine the spatial and statistical distribution of coating thickness in single and multiple coated products using 3D TPI. The measurements are nondestructive even for layers buried underneath other coating structures. The internal structure of coating materials can be analyzed. As the terahertz signal penetrates up to 3 mm into the dosage form interfaces between layers in multilayered tablets can be investigated. In soft gelatin capsules it is possible to measure the thickness of the gelatin layer and to characterize the seal between the gelatin layers for quality control. TPI is a unique approach for the nondestructive characterization and quality control of solid dosage forms. The measurements are fast and fully automated with the potential for much wider application of the technique in the process analytical technology scheme.