Scanning probe microscopy in the field of drug delivery

Advanced structural characterisation of pharmaceuticals using nano-thermal analysis (nano-TA)

The production of drug delivery systems fabricated at the nano scale comes with the challenges of identifying reliable characterisation tools, especially for solid dosage forms. A full understanding of physicochemical properties of solid-state systems at a high spatial resolution is essential to monitor their manufacturability, processability, performance (dissolution) and stability. Nano-thermal analysis (nano-TA), a hybrid of atomic force microscopy (AFM) and thermal analysis, has emerged as a solution to address the need for complete characterisation of samples with surface heterogeneity. Nano-TA provides not only physical information using conventional AFM but also the thermal behaviour of these systems as an additional chemical dimension. In this review, the principles and techniques of nano-TA are discussed with emphasis on recent pharmaceutical applications. Building on nano-TA, the combination of this approach with infrared spectroscopic analysis is briefly introduced. The challenges and considerations for future development of nano-TA characterisation are also outlined.

Flexibility in Drug Product Development: A Perspective

The process of bringing a drug to market involves innumerable decisions to refine a concept into a final product. The final product goes through extensive research and development to meet the target product profile and to obtain a product that is manufacturable at scale. Historically, this process often feels inflexible and linear, as ideas and development paths are eliminated early on to allow focus on the workstream with the highest probability of success. Carrying multiple options early in development is both time-consuming and resource-intensive. Similarly, changing development pathways after significant investment carries a high "penalty of change" (PoC), which makes pivoting to a new concept late in development inhibitory. Can drug product (DP) development be made more flexible? The authors believe that combining a nonlinear DP development approach, leveraging state-of-the art data sciences, and using emerging process and measurement technologies will offer enhanced flexibility and should become the new normal. Through the use of iterative DP evaluation, "smart" clinical studies, artificial intelligence, novel characterization techniques, automation, and data collection/modeling/interpretation, it should be possible to significantly reduce the PoC during development. In this Perspective, a review of ideas/techniques along with supporting technologies that can be applied at each stage of DP development is shared. It is further discussed how these contribute to an improved and flexible DP development through the acceleration of the iterative build-measure-learn cycle in laboratories and clinical trials.

Physical stability of amorphous pharmaceutical solids: Nucleation, crystal growth, phase separation and effects of the polymers

Compared to their crystalline forms, amorphous pharmaceutical solids present marvelous potential and advantages for effectively improving the oral bioavailability of poorly water-soluble drugs. A central issue in developing amorphous pharmaceutical solids is the stability against crystallization, which is particularly important for maintaining their advantages in solubility and dissolution rate. This review provides a comprehensive overview of recent studies focusing on the physical stability of amorphous pharmaceutical solids affected by nucleation, crystal growth, phase separation and the addition of polymers. Moreover, we highlight the novel technologies and theories in the field of amorphous pharmaceutical solids. Meanwhile, the challenges and strategies in maintaining the physical stability of amorphous pharmaceutical solids are also discussed. With a better understanding of physical stability, the more robust amorphous pharmaceutical formulations with desired pharmaceutical performance would be easier to achieve.

Morphology and microstructural analysis of bioactive-loaded micro/nanocarriers via microscopy techniques; CLSM/SEM/TEM/AFM

Efficient characterization of the physicochemical attributes of bioactive-loaded micro/nano-vehicles is crucial for the successful product development. The introduction of outstanding science-based strategies and techniques makes it possible to realize how the characteristics of the formulation ingredients affect the structural and (bio)functional properties of the final bioactive-loaded carriers. The important points to be solved, at a microscopic level, are investigating how the features of the formulation ingredients affect the morphology, surface, size, dispersity, as well as the particulate interactions within bioactive-comprising nano/micro-delivery systems. This review presents a detailed description concerning the application of advanced microscopy techniques, i.e., confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) in characterizing the attributes of nano/microcarriers for the efficient delivery of bioactive compounds. Furthermore, the fundamental principles of these approaches, instrumentation, specific applications, and the strategy to choose the most proper technique for different carriers has been discussed.

Solid crystal suspension of Efavirenz using hot melt extrusion: Exploring the role of crystalline polyols in improving solubility and dissolution rate

Poor aqueous solubility of drugs has emerged as a major issue for pharmaceutical scientists from many decades. The current study explores the manufacture and development of a thermodynamically stabilized solid crystal suspension (SCS) of poorly water soluble drug efavirenz via hot melt extrusion. Efavirenz is a non-nucleoside reverse transcriptase inhibitor and belongs to BCS class II. The SCS was prepared using pearlitol and xylitol as a crystalline carrier. The drug-excipient blend was processed by hot melt extrusion with up to 50% (w/w) drug loading. Physico-chemical characterization of the SCS conducted via a scanning electron microscopy, differential scanning calorimetry and hot stage microscopy confirmed that SCS are in crystalline state. Similarly, X-ray powder diffraction analysis revealed highly crystalline existence of pure drug, crystalline carriers and developed SCS. The FTIR chemical imaging analysis of SCS formulations showed a homogeneous drug distribution within respective crystalline carriers while an advanced chemical analysis via atomic force microscopy and Raman analysis complemented the foregoing findings. The developed SCS1 formulation showed up to 81 fold increase in the solubility and 4.1 fold increase in the dissolution rate of the drug compared to that of the bulk substance. Surprisingly, the developed SCS formulation remained stable for a period of more than one year at accelerated conditions inferred from dissolution studies. It can be concluded that the SCS approach can be used as an alternative contemporary technique to enhance the dissolution rates of many other poorly water-soluble drugs by means of thermal HME processing.

Hot melt extrusion based solid solution approach: Exploring polymer comparison, physicochemical characterization and in-vivo evaluation

The objective of this study was to develop solid solution (SSL) using hot-melt extrusion as a continuous manufacturing method. Powder blends of artesunate (ARS) a water insoluble drug with either Soluplus (SOL) or Kollidon VA64 (VA64) and additives in the form of surfactants or plasticizers were extruded to manufacture extrudes. The incorporation of surfactant or plasticizers facilitates smooth extrusion processing of the drug-excipient blend which directly reduced the residence time to form extrudes and works as parameter to control flow of the drug-excipients melt inside the extruder barrel. Differential scanning calorimetry (DSC) and X-ray diffraction (TXRD) analysis revealed the existence of the drug within the extrudes in amorphous state. Scanning electron microscopy (SEM), Raman spectroscopy (RS), Raman imaging (RI) and Atomic force microscopy (AFM) analytical characterization were carry out on the SSL formulations showed a homogeneous drug distribution within the extrudes. (2)D NMR and (1)H NMR studies were undertaken to reveal the possible drug-excipient interactions. The SSL produced via continuous HME processing showed significantly faster release of ARS compared to the pure drug substance. It is observed that F1 SSL (soluplus based) have 66.44 times higher AUC(0-72) and 16.60 times higher Cmax than pure ARS. Also K1 SSL (Kollidon VA64 based) have 62.20 times higher AUC(0-72) and 13.40 times higher Cmax than pure ARS.

Development of hot melt co-formulated antimalarial solid dispersion system in fixed dose form (ARLUMELT): Evaluating amorphous state and in vivo performance

The aim of this study was to investigate the industrial feasibility of developing a co-formulated solid dispersion (SD) containing two antimalarial drugs artemether (ARTM) and lumefantrine (LUMF). Soluplus(®) (polyethyleneglycol-polyvinyl caprolactam-polyvinyl acetate grafted copolymer) was used as primary carrier matrices via hot-melt extrusion processing to improve solubility profile and the oral bioavailability of the combination. Based on the preliminary screening, the optimized quantities of PEG 400, Lutrol F127 and Lutrol F68 were incorporated as surfactant with soluplus in different ratios to improve extrudability, increase wettability and the melt viscosity of the HME process. Soluplus(®) was proved to successfully stabilize both the drugs inside its polymeric network during extrusion via forming a stable solid dispersion. Physicochemical properties of the APIs and the SDs characterized by thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), MDSC, FTIR spectroscopy and X-ray diffractometry (XRD) revealed the amorphous existence of the drug in all SDs developed. Molecular level morphology of solid dispersion characterized by using advanced physicochemical characterization techniques such as Raman spectroscopy, atomic force microscopy (AFM) and 2D NMR showed the transformation of the crystalline drugs to its stable amorphous state. All manufactured SDs retained their amorphicity even after a stability study conducted in accelerated condition over 6 months. The solubility and in vitro dissolution performance of both drugs in SD formulations was improved significantly when compared with pure drugs and marketed product while the in vivo studies revealed the same.The pharmacokinetic studies in rats revealed that the SD (AL1) shows a 44.12-65.24 folds increase in the AUC(0-72) and 42.87-172.61 folds increase in Cmax compared to that of pure drugs and a better bioavailability than that of commercial product.

X-ray radiation promotes the metastatic potential of tongue squamous cell carcinoma cells via modulation of biomechanical and cytoskeletal properties

This study investigated the metastatic potential of tongue squamous cell carcinoma (TSCC) cells after X-ray irradiation as well as radiation-induced changes in the biomechanical properties and cytoskeletal structure that are relevant to metastasis. Tca-8113 TSCC cells were X-ray-irradiated at increasing doses (0, 1, 2, or 4 Gy), and 24 h later, migration was evaluated with the wound healing and transwell migration assays, while invasion was assessed with the Matrigel invasion assay. Confocal and atomic force microscopy were used to examine changes in the structure of the actin cytoskeleton and Young's modulus (cell stiffness), respectively. X-ray radiation induced dose-dependent increases in invasive and migratory potentials of cells relative to unirradiated control cells (p < 0.05). The Young's modulus of irradiated cells was decreased by radiation exposure (p < 0.05), which was accompanied by alterations in the integrity and organization of the cytoskeletal network, as evidenced by a decrease in the signal intensity of actin fibers (p < 0.05). X-ray irradiation enhanced migration and invasiveness in Tca-8113 TSCC cells by altering their biomechanical properties and the organization of the actin cytoskeleton. A biomechanics-based analysis can provide an additional platform for assessing tumor response to radiation and optimization of cancer therapies.

The scanning ion conductance microscope for cellular physiology

The quest for nonoptical imaging methods that can surmount light diffraction limits resulted in the development of scanning probe microscopes. However, most of the existing methods are not quite suitable for studying biological samples. The scanning ion conductance microscope (SICM) bridges the gap between the resolution capabilities of atomic force microscope and scanning electron microscope and functional capabilities of conventional light microscope. A nanopipette mounted on a three-axis piezo-actuator, scans a sample of interest and ion current is measured between the pipette tip and the sample. The feedback control system always keeps a certain distance between the sample and the pipette so the pipette never touches the sample. At the same time pipette movement is recorded and this generates a three-dimensional topographical image of the sample surface. SICM represents an alternative to conventional high-resolution microscopy, especially in imaging topography of live biological samples. In addition, the nanopipette probe provides a host of added modalities, for example using the same pipette and feedback control for efficient approach and seal with the cell membrane for ion channel recording. SICM can be combined in one instrument with optical and fluorescent methods and allows drawing structure-function correlations. It can also be used for precise mechanical force measurements as well as vehicle to apply pressure with precision. This can be done on living cells and tissues for prolonged periods of time without them loosing viability. The SICM is a multifunctional instrument, and it is maturing rapidly and will open even more possibilities in the near future.

An overview of the analytical characterization of nanostructured drug delivery systems: towards green and sustainable pharmaceuticals: a review

The analytical characterization of drug delivery systems prepared by means of green manufacturing technologies using CO(2) as a processing fluid is here reviewed. The assessment of the performance of nanopharmaceuticals designed for controlled drug release may result in a complex analytical issue and multidisciplinary studies focused on the evaluation of physicochemical, morphological and textural properties of the products may be required. The determination of the drug content as well as the detection of impurities and solvent residues are often carried out by chromatography. Assays on solid state samples relying on X-ray, vibrational and nuclear magnetic resonance spectroscopies are of great interests to study the composition and structure of pharmaceutical forms. The morphology and size of particles are commonly checked by microscopy and complementary chemical information can be extracted in combination with spectroscopic accessories. Regarding the thermal behavior, calorimetric and thermogravimetric techniques are applied to assess the thermal transitions and stability of the samples. The evaluation of drug release profiles from the nanopharmaceuticals can be based on various experimental set-ups depending on the administration route to be considered. Kinetic curves showing the evolution of the drug concentration as a function of time in various physiological conditions (e.g., gastric, plasmatic or topical) are recorded commonly by UV-vis spectroscopy and/or chromatography. Representative examples are commented in detail to illustrate the characterization strategies.

Thermal scanning probe microscopy in the development of pharmaceuticals

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

Advanced microscopy techniques to assess solid-state properties of inhalation medicines

Efficient control and characterisation of the physico-chemical properties of active pharmaceutical ingredients (APIs) and excipients for orally inhaled drug products (OIDPs) are critical to successful product development. Control and reduction of risk require the introduction of a material science based approach to product development and the use of advanced analytical tools in understanding how the solid-state properties of the input materials influence structure and product functionality. The key issues to be addressed, at a microscopic scale, are understanding how the critical quality attributes of input materials influence surface, interfacial and particulate interactions within OIDPs. This review offers an in-depth discussion on the use of advanced microscopy techniques in characterising of the solid-state properties of particulate materials for OIDPs. The review covers the fundamental principles of the techniques, instrumentation types, data interpretation and specific applications in relation to the product development of OIDPs.

Atomic force microscopy-based screening of drug-excipient miscibility and stability of solid dispersions

PURPOSE

Development of a method to assess the drug/polymer miscibility and stability of solid dispersions using a melt-based mixing method.

METHODS

Amorphous fractured films are prepared and characterized with Raman Microscopy in combination with Atomic Force Microscopy to discriminate between homogenously and heterogeneously mixed drug/polymer combinations. The homogenous combinations are analyzed further for physical stability under stress conditions, such as increased humidity or temperature.

RESULTS

Combinations that have the potential to form a molecular disperse mixture are identified. Their potential to phase separate is determined through imaging at molecular length scales, which results in short observation time. De-mixing is quantified by phase separation analysis, and the drug/polymer combinations are ranked to identify the most stable combinations.

CONCLUSIONS

The presented results demonstrate that drug/polymer miscibility and stability of solid dispersions, with many mechanistic details, can be analyzed with Atomic Force Microscopy. The assay allows to identify well-miscible and stable combinations within hours or a few days.

Surface-mediated two-dimensional growth of the pharmaceutical carbamazepine

Scanning tunneling microscopy (STM) has become a staple surface microscopy technique for a number of research fields ranging from semiconductor research to heterogeneous catalysis. Pharmaceutical compounds, however, remain largely unstudied. Here we report the first STM study of carbamazepine (CBZ), an anti-epileptic drug, on Au(111) and Cu(111) surfaces. The analysis reveals that CBZ adopts unusual chiral molecular architectures on both metals. These previously unreported structures, which are strikingly different from CBZ packing arrangements observed in 3D crystal structures, indicate that the main molecular architecture is driven by a combination of CBZ intermolecular hydrogen bonding and metal-CBZ interactions. Comparison of the 2D molecular structures reveals large differences in local geometry and packing density that are dependent on the nature of the metal surface. These results have implications for the potential role of metal surfaces as heteronuclei or templating agents for controlling polymorph formation, which continues to be a problem for many compounds in the pharmaceutical industry including CBZ.

Chemical and structural investigation of lipid nanoparticles: drug-lipid interaction and molecular distribution

Lipid nanoparticles are a promising alternative to existing carriers in chemical or drug delivery systems. A key challenge is to determine how chemicals are incorporated and distributed inside nanoparticles, which assists in controlling chemical retention and release characteristics. This study reports the chemical and structural investigation of gamma-oryzanol loading inside a model lipid nanoparticle drug delivery system composed of cetyl palmitate as solid lipid and Miglyol 812 as liquid lipid. The lipid nanoparticles were prepared by high pressure homogenization at varying liquid lipid content, in comparison with the gamma-oryzanol free systems. The size of the lipid nanoparticles, as measured by the photon correlation spectroscopy, was found to decrease with increased liquid lipid content from 200 to 160 nm. High-resolution proton nuclear magnetic resonance ((1)H-NMR) measurements of the medium chain triglyceride of the liquid lipid has confirmed successful incorporation of the liquid lipid in the lipid nanoparticles. Differential scanning calorimetric and powder x-ray diffraction measurements provide complementary results to the (1)H-NMR, whereby the crystallinity of the lipid nanoparticles diminishes with an increase in the liquid lipid content. For the distribution of gamma-oryzanol inside the lipid nanoparticles, the (1)H-NMR revealed that the chemical shifts of the liquid lipid in gamma-oryzanol loaded systems were found at rather higher field than those in gamma-oryzanol free systems, suggesting incorporation of gamma-oryzanol in the liquid lipid. In addition, the phase-separated structure was observed by atomic force microscopy for lipid nanoparticles with 0% liquid lipid, but not for lipid nanoparticles with 5 and 10% liquid lipid. Raman spectroscopic and mapping measurements further revealed preferential incorporation of gamma-oryzanol in the liquid part rather than the solid part of in the lipid nanoparticles. Simple models representing the distribution of gamma-oryzanol and lipids (solid and liquid) inside the lipid nanoparticle systems are proposed.

Atomic force microscope study of tumor cell membranes following treatment with anti-cancer drugs

Integrity of the cell membrane is a basic requirement for maintaining the biological characteristics of a cell. In this study, changes in the morphology and ultrastructure of HeLa (human cervical carcinoma), HepG2 (human hepatocellular liver carcinoma), and C6 (rat glioma) cells were studied by atomic force microscopy (AFM) both before and after treatment with the anti-cancer drugs, colchicine or cytarabine. In response to both drugs, the microstructure of the cell membrane of all three cell types displayed similar changes; that is, with increases in drug concentration and reaction time, the degree of morphological changes on the surface of cell membrane increased. These changes included increases in the fluctuation of the surface components of the cell membrane, increase in shrinkage, or even the appearance of pores. Cell viability was maintained, as determined by optical microscope observation of gross cell morphology and by MTT assay results. Analysis of the cell membrane root-mean-square (RMS) roughness showed that under the action of colchicine and cytarabine, RMS values for the cell membranes of all three tumor cell types were positively correlated to the drug concentration and reaction time. This research has great significance for the visual diagnosis of early stage apoptosis in tumor cells in response to anti-cancer drugs, as well as in the studies on the interaction between drugs and cells. The use of AFM can be a rapid and sensitive visual method for studying the interaction between cells and drug.

Following the surface response of caffeine cocrystals to controlled humidity storage by atomic force microscopy

Active pharmaceutical ingredient (API) stability in solid state tablet formulation is frequently a function of the relative humidity (RH) environment in which the drug is stored. Caffeine is one such problematic API. Previously reported caffeine cocrystals, however, were found to offer increased resistance to caffeine hydrate formation. Here we report on the use of atomic force microscopy (AFM) to image the surface of two caffeine cocrystal systems to look for differences between the surface and bulk response of the cocrystal to storage in controlled humidity environments. Bulk responses have previously been assessed by powder X-ray diffraction. With AFM, pinning sites were identified at step edges on caffeine/oxalic acid, with these sites leading to non-uniform step movement on going from ambient to 0% RH. At RH >75%, areas of fresh crystal growth were seen on the cocrystal surface. In the case of caffeine/malonic acid the cocrystals were observed to absorb water anisotropically after storage at 75% RH for 2 days, affecting the surface topography of the cocrystal. These results show that AFM expands on the data gathered by bulk analytical techniques, such as powder X-ray diffraction, by providing localised surface information. This surface information may be important for better predicting API stability in isolation and at a solid state API-excipient interface.