182 research outputs found
Evaluation of In vitro and In vivo Performance of Granisetron In situ Forming Implants: Effect of Sterilization, Storage Condition and Degradation
Purpose: To investigate the effect of various solvent systems and gamma irradiation on the in vitro and in vivo performance of granisetron HCl injectable phase-sensitive in situ forming implants (ISFIs).Methods: ISFIs were prepared by mixing and sterilized by gamma irradiation. Effect of solvent system was studied. Injectability, polymer degradation and stability studies (4 and 25 oC for 4 months), viscositymeasurements, as well as in vitro and in vivo (in rabbits) drug release, and also histological examinations for biocompatibility studies (in rabbits and rats) were carried out.Results: ISFIs showed good injectability from 20-gauge needle and their in vitro drug release increased in the following rank order of solvent/solvent combinations: dimethylsulphoxide (DMSO) > DMSO:prophylenecarbonate (PC) > DMSO:triacetin(TA) > DMSO:benzylbenzoate (BB). DMSO:PC incorporating ISFI gave zero order (r2 = 0.9503) drug release for 21 days; application of gamma irradiation accelerated drug release with a difference factor (f1) of 53 but zero order release (r2 = 9690) was maintained. Following test results for DMSO:PC including ISFI as decrease in molecular weight of polymer was descriptive for drug release behavior and sterilization effect, additionally dynamic viscosities decreased in line with polymer degradation and all forms of this ISFI showed plastic flow(fresh, irradiated, aged at 4 and 25 oC for 4 months). In vivo performance showed steady state plasma drug concentrations between 2 to 21 days with value of 0.55 ± 0.03 ìg/ml and biocompatibility was confirmed by histological results obtained at specific stages of tissue reactions, and also by lack of fibrous capsule formation.Conclusion: An ISFI for long-term antiemetic therapy achieved in this preliminary study is promising and, therefore, further investigations are required.Keywords: Implant, Poly(DL-lactide-co-glycolide), Granisetron, Gamma irradiation, Sterilization, Degradation, Viscosity, Stability, Pharmacokinetic, Biocompatibility
Injectable In Situ Forming Microparticles: A Novel Drug Delivery System
Pharmaceutical formulation research has recently been focusing on delivery systems which provide long therapeutic effects and reduced side effects, and involving simplified production stages and facilitated application process. In situ forming microparticle (ISM) systems, one of the latest approach in this field, offer a new encapsulation technique and meet the objectives stated above. Factors such as the carrier used to form the multiparticles, amount and type of drug and the vehicle type can be taken as the main performance criteria for these systems. Ongoing studies have shown that this new multiparticulate drug delivery system is suitable for achieving new implant delivery system with low risk of dose-dumping, capable of being modulated to exhibit varying release patterns, reproducible, easily applicable and welltolerated compared with classically surgical implants.Keywords: Injectable, In situ forming, Microparticle system, Controlled drug delivery
Nanoscale tribology of graphene grown by chemical vapor deposition and transferred onto silicon oxide substrates
We present a comprehensive nanoscale tribological characterization of single-layer graphene grown by chemical vapor deposition (CVD) and transferred onto silicon oxide (SiO2) substrates. Specifically, the nanotribological properties of graphene samples are studied via atomic force microscopy (AFM) under ambient conditions using calibrated probes, by measuring the evolution of friction force with increasing normal load. The effect of using different probes and post-transfer cleaning procedures on frictional behavior is evaluated. A new method of quantifying lubrication performance based on measured friction coefficient ratios of graphene and SiO2 is introduced. A comparison of lubrication properties with mechanically-exfoliated graphene is performed. Results indicate that CVD-grown graphene constitutes a very good solid lubricant on SiO2, reducing friction coefficients by ∼ 90% for all investigated samples. Finally, the effect of wrinkles associated with CVD-grown graphene on measured friction values is quantitatively analyzed, with results revealing a substantial increase in friction on these structural defects. © 2016 Materials Research Society
Advanced atomic force microscopy techniques
Cataloged from PDF version of article.Although its conceptual approach is as simple as the technique used in record players already introduced in the 19th century, the invention of the atomic force microscope (AFM) in 1986 by Binnig, Quate, and Gerber was a milestone for nanotechnology. The scanning tunneling microscope (STM), introduced some years earlier, had already achieved atomic resolution, but is limited to conductive surfaces. Since its operational principle is based on the detection of the forces acting between tip and sample, this restriction does not exist for the AFM. Consequently, atomic force microscopy quickly became the standard tool for nanometer-scale imaging of all types of surfaces in all environments. True atomic resolution was first achieved in the 1990s. The most convincing results, however, were restricted to the so-called noncontact mode in vacuum for a long time, but recent technical developments overcame this limitation, and atomic-resolution imaging is now also a standard in liquids.
Beyond pushing the resolution limit to the picometer range, the invention of the AFM triggered the development of a growing number of new scanning probe methods and approaches, ranging from an expansion of the properties that can be mapped to the active manipulation of surfaces and small particles. Practically every month, reports on the growing capabilities of AFMs appear. Nearly every physical effect that influences the tip–sample interaction has been used to improve existing modes and to develop new ones. For example, many recently presented techniques include the excitation of higher cantilever oscillation modes; it is amazing in how many ways the shaking of a simple cantilever can improve our knowledge about the tip–sample interaction. Another direction is high-speed atomic force microscopy, which is one of the eminent challenges that need to be solved in order to allow the in situ observation of biological processes. Data acquisition times have already reached the millisecond range, enabling the visualization of the dynamic behavior of biological molecules and cells. Other recent accomplishments include imaging of organic molecules with unprecedented resolution, full three-dimensional mapping of surface force fields, and the imaging and discrimination of individual chemical bonds.
The development of advanced techniques is the focus of this Thematic Series, following the Thematic Series “Scanning probe microscopy and related techniques” edited by Ernst Meyer and the Thematic Series “Noncontact atomic force microscopy” edited by Udo Schwarz. The articles that are part of the series demonstrate that, despite its 25 years of history, the AFM is still far from reaching its limits, and today’s developments are far-reaching. As the number of research groups utilizing advanced atomic force microscopy techniques increases with each passing year, the technical improvements, data-acquisition approaches, analysis procedures, user friendliness, and application areas of the technique further diversify. With this Thematic Series, it is our intention to stimulate these improvements.
We thank all authors for contributing their excellent work to this series. Furthermore, we acknowledge all referees for their promptly provided reports keeping the publication times short and attractive for contributors. Finally, we are grateful to the open access policy of the Beilstein Journal of Nanotechnology providing the ground for unrestricted discussions on advanced atomic force microscopy techniques.
Thilo Glatzel, Hendrik Hölscher, Thomas Schimmel, Mehmet Z. Baykara, Udo D. Schwarz and Ricardo Garcia
December 201
Probing three-dimensional surfaces force fields with atomic resolution: Measurement strategies, limitations, and artifact reduction
Cataloged from PDF version of article.Noncontact atomic force microscopy (NC-AFM) is being increasingly used to measure the interaction force between an atomically sharp probe tip and surfaces of interest, as a function of the three spatial dimensions, with picometer and piconewton accuracy. Since the results of such measurements may be affected by piezo nonlinearities, thermal and electronic drift, tip asymmetries, and elastic deformation of the tip apex, these effects need to be considered during image interpretation.
In this paper, we analyze their impact on the acquired data, compare different methods to record atomic-resolution surface force fields, and determine the approaches that suffer the least from the associated artifacts. The related discussion underscores the idea that since force fields recorded by using NC-AFM always reflect the properties of both the sample and the probe tip, efforts to reduce unwanted effects of the tip on recorded data are indispensable for the extraction of detailed information about the atomic-scale properties of the surface
Injectable in situ forming microparticles: A novel drug delivery system
Pharmaceutical formulation research has recently been focusing on delivery systems which provide long therapeutic effects and reduced side effects, and involving simplified production stages and facilitated application process. In situ forming microparticle (ISM) systems, one of the latest approach in this field, offer a new encapsulation technique and meet the objectives stated above. Factors such as the carrier used to form the multiparticles, amount and type of drug and the vehicle type can be taken as the main performance criteria for these systems. Ongoing studies have shown that this new multiparticulate drug delivery system is suitable for achieving new implant delivery system with low risk of dose-dumping, capable of being modulated to exhibit varying release patterns, reproducible, easily applicable and welltolerated compared with classically surgical implants. © Pharmacotherapy Group
Exploring atomic-scale lateral forces in the attractive regime: a case study on graphite (0001)
Cataloged from PDF version of article.A non-contact atomic force microscopy-based method has been used to map the static lateral forces exerted on an atomically sharp Pt/Ir probe tip by a graphite surface. With measurements carried out at low temperatures and in the attractive regime, where the atomic sharpness of the tip can be maintained over extended time periods, the method allows the quantification and directional analysis of lateral forces with piconewton and picometer resolution as a function of both the in-plane tip position and the vertical tip-sample distance, without limitations due to a finite contact area or to stick-slip-related sudden jumps of tip apex atoms. After reviewing the measurement principle, the data obtained in this case study are utilized to illustrate the unique insight that the method offers. In particular, the local lateral forces that are expected to determine frictional resistance in the attractive regime are found to depend linearly on the normal force for small tip-sample distances
Understanding Scanning Tunneling Microscopy Contrast Mechanisms on Metal Oxides: A Case Study
Cataloged from PDF version of article.A comprehensive analysis of contrast formation
mechanisms in scanning tunneling microscopy (STM) experiments on
a metal oxide surface is presented with the oxygen-induced
(2√2
√2)R45 missing row reconstruction of the Cu(100) surface
as a model system. Density functional theory and electronic
transport calculations were combined to simulate the STM imaging
behavior of pure and oxygen-contaminated metal tips with structurally
and chemically different apexes while systematically varying
bias voltage and tip sample distance. The resulting multiparameter
database of computed images was used to conduct an extensive comparison with experimental data. Excellent agreement was attained for a large
number of cases, suggesting that the assumed model tips reproduce most of the commonly encountered contrast-determining effects. Specifically, we find
that depending on the bias voltage polarity, copper-terminated tips allow selective imaging of two structurally distinct surface Cu sites, while oxygenterminated
tips show complex contrasts with pronounced asymmetry and tip sample distance dependence. Considering the structural and chemical
stability of the tips reveals that the copper-terminated apexes tend to react with surface oxygen at small tip sample distances. In contrast, oxygenterminated
tips are considerably more stable, allowing exclusive surface oxygen imaging at small tip sample distances. Our results provide a conclusive
understanding of fundamental STM imaging mechanisms, thereby providing guidelines for experimentalists to achieve chemically selective imaging by
properly selecting imaging parameters
Genetically-Tunable Mechanical Properties of Bacterial Functional Amyloid Nanofibers
Bacterial biofilms are highly ordered, complex, dynamic material systems including cells, carbohydrates, and proteins. They are known to be resistant against chemical, physical, and biological disturbances. These superior properties make them promising candidates for next generation biomaterials. Here we investigated the morphological and mechanical properties (in terms of Young’s modulus) of genetically-engineered bacterial amyloid nanofibers of Escherichia coli (E. coli) by imaging and force spectroscopy conducted via atomic force microscopy (AFM). In particular, we tuned the expression and biochemical properties of the major and minor biofilm proteins of E. coli (CsgA and CsgB, respectively). Using appropriate mutants, amyloid nanofibers constituting biofilm backbones are formed with different combinations of CsgA and CsgB, as well as the optional addition of tagging sequences. AFM imaging and force spectroscopy are used to probe the morphology and measure the Young’s moduli of biofilm protein nanofibers as a function of protein composition. The obtained results reveal that genetically-controlled secretion of biofilm protein components may lead to the rational tuning of Young’s moduli of biofilms as promising candidates at the bionano interface. © 2017 American Chemical Society
Simultaneous measurement of multiple independent atomic-scale Interactions using scanning probe microscopy: data interpretation and the effect of cross-talk
Cataloged from PDF version of article.In high-resolution scanning probe microscopy, it is becoming increasingly common to simultaneously record multiple channels representing different tip-sample interactions to collect complementary information about the sample surface. A popular choice involves simultaneous scanning tunneling microscopy (STM) and noncontact atomic force microscopy (NC-AFM) measurements, which are thought to reflect the chemical and electronic properties of the sample surface. With surface-oxidized Cu(100) as an example, we investigate whether atomic-scale information on chemical interactions can be reliably extracted from frequency shift maps obtained while using the tunneling current as the feedback parameter. Ab initio calculations of interaction forces between specific tip apexes and the surface are utilized to compare experiments with theoretical expectations. The examination reveals that constant-current operation may induce a noticeable influence of topography-feedback-induced cross-talk on the frequency shift data, resulting in misleading interpretations of local chemical interactions on the surface. Consequently, the need to apply methods such as 3D-AFM is emphasized when accurate conclusions about both the local charge density near the Fermi level, as provided by the STM channel, and the site-specific strength of tip-sample interactions (NC-AFM channel) are desired. We conclude by generalizing to the case where multiple atomic-scale interactions are being probed while only one of them is kept constant
- …