Microstructural investigation to the controlled release kinetics of monolith osmotic pump tablets via synchrotron radiation X-ray microtomography

Modelling the controlled drug release of push-pull osmotic pump tablets using DEM

The push-pull osmotic pump tablet is a promising drug delivery approach, offering advantages over traditional dosage forms in achieving consistent and predictable drug release rates. In the current study, the drug release process of push-pull osmotic pump tablets is modelled for the first time using the discrete element method (DEM) incorporated with a microscopic diffusion-induced swelling model. The effects of dosage and formulation design, such as delivery orifice size, drug-to-polymer ratio, tablet surface curvature, friction between particles and cohesion of polymer particles, on the drug release performance are systematically analysed. Numerical results reveal that an enlarged delivery orifice significantly increases both the total drug release and the drug release rate. Moreover, the larger the swellable particle component in the tablet, the higher the drug release rate. Furthermore, the tablet surface curvature is found to affect the drug release profile, i.e. the final drug release percentage increases with the increasing tablet surface curvature. It is also found that the drug release rate could be controlled by adjusting the inter-particle friction and the cohesion of polymer particles in the formulation. This DEM study offers valuable insights into the mechanisms governing drug release in push-pull osmotic pump tablets.

Wurster Technology-Assisted Step-by-Step Engineering of Multi-layered Pellets (Sprinkles): Microscopy, Micro-CT, and e-Tongue-Based Analysis

The advancement in the formulation and characterization techniques have paved the path for development of new as well as modification of existing dosage forms. The present work explores the role of micro-computed tomography (micro-CT) as advanced characterization technique for multi-layered-coated pellets to ascertain the quality of coated pellets. The work further explored in-house e-tongue technique for understanding palatability of formulation in early stages of development thus by reducing clinical taste evaluation time. The developed multi-layered-coated pellets were characterized using microscopy (optical and electron microscopy). The obtained results demonstrated formation of spherical-shaped pellets with uniform coating. The uniform coating was further confirmed by results obtained from scanning electron microscopy (SEM) and cross-sectional SEM analysis, which showed visible difference in pellet surface before and after multi-layered coating. The micro-CT results confirmed the visible demarcation of layers (drug and polymer, i.e., hydroxypropyl methylcellulose (HPMC) and eudragit (EPO)) along with uniform thickness of various layering. The dissolution study of developed pellets suggested the role of layering EPO on drug release from pellets. The e-tongue analysis proved to be an excellent tool for early prediction of taste masking of drug via multi-layered pellets and can serve as potential platform for taste masking with high specificity. The overall results suggest the suitability of developed multi-layered platform as efficient dosage form (sprinkle) in pediatric/geriatric product development.

Advances in Structure Pharmaceutics from Discovery to Evaluation and Design

Drug delivery systems (DDSs) play an important role in delivering active pharmaceutical ingredients (APIs) to targeted sites with a predesigned release pattern. The chemical and biological properties of APIs and excipients have been extensively studied for their contribution to DDS quality and effectiveness; however, the structural characteristics of DDSs have not been adequately explored. Structure pharmaceutics involves the study of the structure of DDSs, especially the three-dimensional (3D) structures, and its interaction with the physiological and pathological structure of organisms, possibly influencing their release kinetics and targeting abilities. A systematic overview of the structures of a variety of dosage forms, such as tablets, granules, pellets, microspheres, powders, and nanoparticles, is presented. Moreover, the influence of structures on the release and targeting capability of DDSs has also been discussed, especially the in vitro and in vivo release correlation and the structure-based organ- and tumor-targeting capabilities of particles with different structures. Additionally, an in-depth discussion is provided regarding the application of structural strategies in the DDSs design and evaluation. Furthermore, some of the most frequently used characterization techniques in structure pharmaceutics are briefly described along with their potential future applications.

In situ wet pharmaceutical granulation captured using synchrotron radiation based dynamic micro-CT

Synchrotron radiation based dynamic micro-computed tomography (micro-CT) is a powerful technique available at synchrotron light sources for investigating evolving microstructures. Wet granulation is the most widely used method of producing pharmaceutical granules, precursors to products like capsules and tablets. Granule microstructures are known to influence product performance, so this is an area for potential application of dynamic CT. Here, lactose monohydrate (LMH) was used as a representative powder to demonstrate dynamic CT capabilities. Wet granulation of LMH has been observed to occur on the order of several seconds, which is too fast for lab-based CT scanners to capture the changing internal structures. The superior X-ray photon flux from synchrotron light sources makes sub-second data acquisition possible and well suited for analysis of the wet-granulation process. Moreover, synchrotron radiation based imaging is non-destructive, does not require altering the sample in any way, and can enhance image contrast with phase-retrieval algorithms. Dynamic CT can bring insights to wet granulation, an area of research previously only studied via 2D and/or ex situ techniques. Through efficient data-processing strategies, dynamic CT can provide quantitative analysis of how the internal microstructure of an LMH granule evolves during the earliest moments of wet granulation. Here, the results revealed granule consolidation, the evolving porosity, and the influence of aggregates on granule porosity.

Development of Flow-Through Cell Dissolution Method for In Situ Visualization of Dissolution Processes in Solid Dosage Forms Using X-ray μCT

Visualization of the dynamic behavior of pharmaceutical dosage forms during the dissolution process offers a better understanding of the drug release mechanism, enabling the design of customized dosage forms. In this study, an X-ray tomography-based approach is proposed to monitor and analyze the dynamics of the structure at the pore scale level during the dissolution process. A flow-through cell dissolution apparatus was developed, capable of mimicking the standard in vitro dissolution process, which can be easily positioned in an X-ray tomography setup. The method was utilized to study the dissolution of a Capa^® (polycaprolactone)-based sustained-release 3D printed tablet. The impact of the flow rate on the active pharmaceutical ingredient (API) release rate was studied and 16 mL/min was selected as a suitable flow rate. Furthermore, cesium chloride (CsCl) was used as a contrast agent to increase the contrast between the sample and the dissolution medium. Data obtained with this novel technique were in a good agreement with the released drug rate acquired by the standard in vitro dissolution test (the similarity factor (f2) = 77%). Finally, the proposed approach allowed visualizing the internal structure of the sample, as well as real-time tracking of solution ingress into the product.

Redefinition to bilayer osmotic pump tablets as subterranean river system within mini-earth via three-dimensional structure mechanism

Defining and visualizing the three-dimensional (3D) structures of pharmaceuticals provides a new and important tool to elucidate the phenomenal behavior and underlying mechanisms of drug delivery systems. The mechanism of drug release from complex structured dosage forms, such as bilayer osmotic pump tablets, has not been investigated widely for most solid 3D structures. In this study, bilayer osmotic pump tablets undergoing dissolution, as well as after dissolution in a desiccated solid state were examined, and visualized by synchrotron radiation micro-computed tomography (SR-μCT). In situ formed 3D structures at different in vitro drug release states were characterized comprehensively. A distinct movement pattern of NaCl crystals from the push layer to the drug layer was observed, beneath the semi-permeable coating in the desiccated tablet samples. The 3D structures at different dissolution time revealed that the pushing upsurge in the bilayer osmotic pump tablet was directed via peripheral "roadways". Typically, different regions of the osmotic front, infiltration region, and dormant region were classified in the push layer during the dissolution of drug from tablet samples. According to the observed 3D microstructures, a "subterranean river model" for the drug release mechanism has been defined to explain the drug release mechanism.

Bridging the structure gap between pellets in artificial dissolution media and in gastro-intestinal tract in rats

Changes in structure of oral solid dosage forms (OSDF) elementally determine the drug release and its therapeutic effects. In this research, synchrotron radiation X-ray micro-computed tomography was utilized to visualize the 3D structure of enteric coated pellets recovered from the gastrointestinal tract of rats. The structures of pellets in solid state and in vitro compendium media were measured. Pellets in vivo underwent morphological and structural changes which differed significantly from those in vitro compendium media. Thus, optimizations of the dissolution media were performed to mimic the appropriate in vivo conditions by introducing pepsin and glass microspheres in media. The sphericity, pellet volume, pore volume and porosity of the in vivo esomeprazole magnesium pellets in stomach for 2 h were recorded 0.47, 1.55 × 10⁸ μm³, 0.44 × 10⁸ μm³ and 27.6%, respectively. After adding pepsin and glass microspheres, the above parameters in vitro reached to 0.44, 1.64 × 10⁸ μm³, 0.38 × 10⁸ μm³ and 23.0%, respectively. Omeprazole magnesium pellets behaved similarly. The structural features of pellets between in vitro media and in vivo condition were bridged successfully in terms of 3D structures to ensure better design, characterization and quality control of advanced OSDF.

The use of X-ray microtomography to investigate the microstructure of pharmaceutical tablets: Potentials and comparison to common physical methods

Within this study, tablets microstructure was investigated by X-ray microtomgraphy. The aim was to gain information about their microstructure, and thus, derive deeper interpretation of tablet properties (mechanical strength, component distribution) and qualified property functions. Challenges in image processing are discussed for the correct identification of solids and voids. Furthermore, XMT measurements are critically compared with complementary physical methods for characterizing active pharmaceutical ingredient (API) content and porosity and its distribution (mercury porosimetry, calculated tablet porosity, Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM)). The derived porosity by XMT is generally lower than the calculated porosity based on geometrical data due to the resolution of the XMT in relation to the pore sizes in tablets. With rising compactions stress and API concentration, deviations between the actual and the calculated API decrease. XMT showed that API clusters are present for all tablets containing >1 wt% of ibuprofen. The 3D orientation of the components is assessable by deriving cord lengths along all dimensions of the tablets. An increasing compaction stress leads to rising cord lengths, showing higher connectivity of the respective material. Its lesser extent in the z-direction illustrates the anisotropy of the compaction process. Additionally, cracks in the fabric are identified in tablets without visible macroscopic damage. Finally, the application of XMT provides valuable structural insights if its limitations are taken into account and its strengths are fostered by advanced pre- and post-processing.

Dynamic structure model of polyelectrolyte complex based controlled-release matrix tablets visualized by synchrotron radiation micro-computed tomography

Hydrophilic matrix tablets are the most commonly used dosage forms to fabricate oral controlled-release systems. It is highly desirable to design delivery system with novel mechanism to achieve sustained drug release through a simplified preparation process. The chitosan-anionic polymers based matrix tablets is assumed to produce self-assembly in the gastrointestinal tract, then transferring into film-coated tablets from original matrix type. But its dynamic behavior during dissolution process and the on-going internal microstructural changes during drug release were still in the dark. In this study, by using synchrotron radiation X-ray micro-tomography (SR-μCT) with phase contrast imaging, the micro-structure characteristics of chitosan-λ-carrageenan (CS-λ-CG) matrix based tablets during the dissolution were successfully elucidated for the first time. The qualitative and quantitative analyses of intensity distribution distinguished a hydrated CS-λ-CG layer from a solid core. Visualization based on 3D models provided quantitative details on the micro-structural characteristics of hydration dynamics. After CS-λ-CG matrix tablets were immersed in simulated gastric fluid (SGF) pH 1.2 medium for 0.5-2.0 h, the hydrated layer transformed into a gel layer and a solid swollen layer. The erosion front, swelling front, and solvent penetration front were also defined from the distinguishable micro-structures. More importantly, once the matrix tablet was transferred from SGF to the simulated intestinal fluid (SIF) pH 6.8 medium, a new layer with the enhanced strength and compactness in comparison to common gels was formed on the surface of tablets. The temporal and spatial variation of 3D models further provided direct evidence for this cross-linking behavior, the new layer was composed of CS-λ-CG polyelectrolyte complexes (PEC) which subsequently dominated release mechanisms. In summary, the phase contrast SR-μCT technique was utilized to investigate the hydration dynamics of CS-λ-CG matrix tablets which was supposed to provide a novel drug release mechanism. Based on the structure feature obtained from the high contrast image, different hydration region was distinguished and the cross-linked film was identified and visualized directly for the first time.

Recent advances of novel technologies for quality consistency assessment of natural herbal medicines and preparations

Quality consistency is one of the basic attributes of medicines, but it is also a difficult problem that natural medicines and their preparations must face. The complex chemical composition and comprehensive pharmacological action of natural medicines make it difficult to simply apply the commonly used evaluation methods in chemical drugs. It is thus urgent to explore the novel evaluation methods suitable for the characteristics of natural medicines. With the rapid development of analytical techniques and the deepening understanding of the quality of natural herbs, increasing numbers of researchers have proposed many new ideas and technologies. This review mainly focuses on the basic principles, technical characteristics and application examples of the chemical evaluation, biological evaluation methods and their combination in quality consistency evaluation of natural herbs. On the bases of chemical evaluation and clinical efficacy, new methods reflecting their pharmacodynamic mechanism and safety characteristics will be developed, and gradually towards accurate quality control, to achieve the goal of quality consistency. We hope that this manuscript can provide new ideas and technical references for the quality consistency of natural drugs and their preparations, thus better guarantee their clinical efficacy and safety, and better promote industrial development.

Multi-dimensional visualization for the morphology of lubricant stearic acid particles and their distribution in tablets

The shapes of particles and their distribution in tablets, controlled by pretreatment and tableting process, determine the pharmaceutical performance of excipient like lubricant. This study aims to provide deeper insights to the relationship of the morphology and spatial distribution of stearic acid (SA) with the lubrication efficiency, as well as the resulting tablet property. Unmodified SA particles as flat sheet-like particles were firstly reprocessed by emulsification in hot water to obtain the reprocessed SA particles with spherical morphology. The three-dimensional (3D) information of SA particles in tablets was detected by a quantitative and non-invasive 3D structure elucidation technique, namely, synchrotron radiation X-ray micro-computed tomography (SR-µCT). SA particles in glipizide tablets prepared by using unmodified SA (GUT), reprocessed SA (GRT), as well as reference listed drug (RLD) of glipizide tablets were analyzed by SR-µCT. The results showed that the reprocessed SA with better flowability contributed to similarity of breaking forces between that of GRT and RLD. SA particles in GRT were very similar to those in RLD with uniform morphology and particle size, while SA particles in GUT were not evenly distributed. These findings not only demonstrated the feasibility of SR-µCT as a new method in revealing the morphology and spatial distribution of excipient in drug delivery system, but also deepened insights of solid dosage form design into a new scale by powder engineering.

Optimization of taste-masking on ibuprofen microspheres with selected structure features

The microsphere was a primary particulate system for taste-masking with unique structural features defined by production process. In this article, ibuprofen lipid microspheres of octadecanol and glycerin monostearate were prepared to mask the undesirable taste of ibuprofen via three kinds of spray congealing processes, namely, air-cooling, water-cooling and citric acid solution-cooling. The stereoscopic and internal structures of ibuprofen microspheres were quantitatively analyzed by synchrotron radiation X-ray micro-computed tomography (SR-µCT) to establish the relationship between the preparation process and microsphere architectures. It was found that the microstructure and morphology of the microspheres were significantly influenced by preparation processes as the primary factors to determine the release profiles and taste-masking effects. The sphericity of ibuprofen microspheres congealed in citric acid solution was higher than that of other two and its morphology was more regular than that being congealed in air or distilled water, and the contact angles between congealing media and melted ibuprofen in octadecanol and glycerin monostearate well demonstrated the structure differences among microspheres of three processes which controlled the release characteristics of the microspheres. The structure parameters like porosity, sphericity, and radius ratio from quantitative analysis were correlated well with drug release behaviors. The results demonstrated that the exterior morphology and internal structure of microspheres had considerable influences on the drug release behaviors as well as taste-masking effects.

The Influence of Management Innovation and Technological Innovation on Organization Performance. A Mediating Role of Sustainability

Organizations have several objectives, including competitiveness, high profit and long-term survival. However, sustainability has become a diligent act of business and non-business organizations because it moves organizations toward superior performance. Sustainability does not come itself; it requires enough resources and capabilities. Extant studies have examined the factors that influence sustainability, but have rarely touched on innovation in this perspective. The present study examines the influence of management innovation and technological innovation on organization performance with the mediating role of sustainability. To test the model, we applied structural equation modeling in the analysis of a moment structures (AMOS) on the empirical evidence collected from 304 Pakistani CEOs and top managers. The results indicate that management innovation and technological innovation significantly positively contribute to sustainability and organization performance. Sustainability plays a partial mediating role between management innovation and organization performance and also a partial mediating role between technological innovation and organization performance. We recommend CEOs and top managers to give due attention to management innovation and technological innovation to enhance sustainability and survive the long run. Implications are discussed.

HIFU induced particles redistribution in polymer matrix via synchrotron radiation X-ray microtomography

High-intensity Focused Ultrasound (HIFU) was used to stimulate the embedded copper sulfate (CuSO₄) particles to release from the crosslinked poly (methyl methacrylate-co-butyl acrylate) copolymer solid matrix. In order to better understand the ultrasound release mechanism for drug/polymer delivery systems, the synchrotron radiation X-ray computed microtomography (SR-CT) was used to non-destructively investigate the structure of drug/polymer delivery systems after different HIFU treatment time. For the first time, we clearly demonstrate that ultrasonic waves can overcome the constraints of the polymer chain and drive the filler to move from the strong region to the weak region in the solid polymer matrix, thus resulting in a change in distribution of the filler in solid polymers. This result also demonstrates that SR-CT is a powerful technique which can be used to quantitatively study the 3D structure of fillers/polymers composite as it can take a broader and overall view than the conventional localized two-dimensional analysis method such as SEM, TEM.

In situ 3D topographic and shape analysis by synchrotron radiation X-ray microtomography for crystal form identification in polymorphic mixtures

Polymorphism denotes the existence of more than one crystal structure of a substance, and great practical and theoretical interest for the chemical and pharmaceutical industries. In many cases, it is challenging to produce a pure crystal form and establish a sensitive detection method for the identification of crystal form in a mixture of polymorphs. In this study, an accurate and sensitive method based on synchrotron radiation X-ray computed microtomography (SR-μCT) was devised to identify the polymorphs of clopidogrel bisulphate (CLP). After 3D reconstruction, crystal particles were extracted and dozens of structural parameters were calculated. Whilst, the particle shapes of the two crystal forms were all irregular, the surface of CLP II was found to be rougher than CLP I. In order to classify the crystal form based on the quantitative morphological property of particles, Volume Bias Percentage based on Surface Smoothing (VBP) was defined and a new method based on VBP was successfully developed, with a total matching rate of 99.91% for 4544 particles and a lowest detectable limit of 1%. More important for the mixtures in solid pharmaceutical formulations, the interference of excipients can be avoided, a feature cannot achieved by other available analytical methods.

Visualization and quantification of deformation behavior of clopidogrel bisulfate polymorphs during tableting

The deformation behavior of particles under pressure dominates the mechanical properties of solid dosage forms. In this study, the in situ 3D deformation of two polymorphs (I and II) of clopidogrel bisulfate (CLP) was determined to illustrate pressure distribution profiles within the tablet by the deformation of the crystalline particles for the first time. Synchrotron radiation X-ray computed microtomography (SR-μCT) was utilized to visualize and quantify the morphology of thousands crystalline particles of CLP I and CLP II before and after compression. As a result, the deformation was examined across scale dimensions from microns to the size of the final dosage form. Three dimensional parameters such as volume, sphericity, oblate and prolate of individual particle and distributions were computed and analyzed for quantitative comparison to CLP I and CLP II. The different degrees of deformation under the same compression conditions of CLP I and CLP II were observed and characterized quantitatively. The map of deformation degrees within the tablet illustrated the heterogeneous pressure distribution in various regions of the compacted tablet. In conclusion, the polymorph deformation behaviors demonstrated by SR-μCT quantitative structure analysis deepen understanding of tableting across dimensions from microns to millimeters for the macrostrcuture of tablet.

Application of X-ray micro-CT for micro-structural characterization of APCVD deposited SiC coatings on graphite conduit

SiC coatings are commonly used as oxidation protective materials in high-temperature applications. The operational performance of the coating depends on its microstructure and uniformity. This study explores the feasibility of applying tabletop X-ray micro-CT for the micro-structural characterization of SiC coating. The coating is deposited over the internal surface of pipe structured graphite fuel tube, which is a prototype of potential components of compact high-temperature reactor (CHTR). The coating is deposited using atmospheric pressure chemical vapor deposition (APCVD) and properties such as morphology, porosity, thickness variation are evaluated. Micro-structural differences in the coating caused by substrate distance from precursor inlet in a CVD reactor are also studied. The study finds micro-CT a potential tool for characterization of SiC coating during its future course of engineering. We show that depletion of reactants at larger distances causes development of larger pores in the coating, which affects its morphology, density and thickness.

Recent Advances in Solid-State Analysis of Pharmaceuticals

Current analytical techniques for characterizing solid-state pharmaceuticals include powder x-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, Raman spectroscopy, electron microscopy and nuclear magnetic resonance. Powder x-ray diffraction and differential scanning calorimetry are mainstream techniques but they lack spatial resolution. Scanning electron microscopy and micro-Raman spectroscopy provide good chemical and optical characterization but they are not capable of analysing very small nanoparticles. Transmission electron microscopy and nano-thermal analysis can provide explicit characterization of nanoparticles but they are invasive. Nuclear magnetic resonance offers good spatial resolution but its use is mainly limited by poor sensitivity and high costs. In view of the many challenges posed by existing methods, new and novel techniques are being continually researched and developed to cater to the growing number of solid formulations in the pipeline and in the market. Some of the recent advances attained in the solid-state analysis of pharmaceutical are summarized in this review article.

Quantification of swelling and erosion in the controlled release of a poorly water-soluble drug using synchrotron X-ray computed microtomography

The hydration layer plays a key role in the controlled drug release of gel-forming matrix tablets. For poorly water-soluble drugs, matrix erosion is considered as the rate limiting step for drug release. However, few investigations have reported on the quantification of the relative importance of swelling and erosion in the release of poorly soluble drugs, and three-dimensional (3D) structures of the hydration layer are poorly understood. Here, we employed synchrotron radiation X-ray computed microtomography with 9-μm resolution to investigate the hydration dynamics and to quantify the relative importance of swelling and erosion on felodipine release by a statistical model. The 3D structures of the hydration layer were revealed by the reconstructed 3D rendering of tablets. Twenty-three structural parameters related to the volume, the surface area (SA), and the specific surface area (SSA) for the hydration layer and the tablet core were calculated. Three dominating parameters, including SA and SSA of the hydration layer (SA hydration layer and SSA hydration layer ) and SA of the glassy core (SA glassy core ), were identified to establish the statistical model. The significance order of independent variables was SA hydration layer > SSA hydration layer > SA glassy core , which quantitatively indicated that the release of felodipine was dominated by a combination of erosion and swelling. The 3D reconstruction and structural parameter calculation methods in our study, which are not available from conventional methods, are efficient tools to quantify the relative importance of swelling and erosion in the controlled release of poorly soluble drugs from a structural point of view.

Fractal structure determines controlled release kinetics of monolithic osmotic pump tablets

Objectives

To calculate the fractal dimension values of felodipine osmotic pump tablets during drug dissolution and to characterize the mechanism of the controlled drug release kinetics through three-dimensional fractal data.

Methods

Three-dimensional fractal values of volume (Df,volume) and surface (Df,surface) of the tablet core were calculated based on the box counting method.

Key findings

During the process of release of felodipine, both Df,volume and Df,surface were within the range of 2–3 and then changed markedly after a period of 3.0 h release, corresponding to extensive changes in entire shape, interior porous channels and surface structure of the tablet core. The curve of Df,volume mirrored that for tablet volume, however the curve of Df,surface was quite different from that of the surface area. Results showed that values of Df,surface correlated well with the drug release rate. Df,surface was found to be an efficient fractal parameter that could be used to characterize the complex changes to the tablet core that take place during drug release.

Conclusions

The fractal dimension can be used as a quantitative indicator reflecting the drug release performance and be regarded as a key indicator for the quality control of oral controlled drug delivery systems.