China
Africa
Explore chapters and articles related to this topic
Combination of Microneedles with Other Methods
Published in Boris Stoeber, Raja K Sivamani, Howard I. Maibach, Microneedling in Clinical Practice, 2020
McAllister et al. published a first report on delivery of latex nanospheres through skin using microneedles (43). Molecules of different radii such as calcein, insulin, BSA, and nanospheres were evaluated in this in vitro study using solid microneedles. Human cadaver epidermis was pretreated with microneedles. Without microporation, there were no detectable levels of any of the above-mentioned molecules. With pretreatment, molecular diffusion on the order of 0.001–0.01 cm/h was seen depending on the molecular radius of the molecule. Highest diffusion was seen for calcein and the lowest for nanospheres. Mechanism of permeation of the nanoparticles was evaluated using mathematical modeling. It supported the theory that diffusion happens through the water-filled channels created in the skin by microneedles.
Biomedical Imaging Magnetic Resonance Imaging
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
Diffusion is a “random walk” of molecules in a medium. In biological tissues, microstructures, cellular composition, and heterogeneity can substantially affect water molecular diffusion processes spatially and temporally. Measuring water diffusion is a viable way to probe tissue microstructures at a spatial scale much smaller than the voxel size (Le Bihan 2007). MRI signals are sensitive to diffusion, which provides an excellent window to study various aspects of tissue structures and the micro-environment. In the presence of a diffusion-weighting gradient, the MRI signal can be attenuated differently among tissues, introducing diffusion contrast to the image (Le Bihan 2007). The degree of attenuation depends on diffusion coefficient and an experimentally controllable parameter, known as the b-value (units: s/mm2). The resultant diffusion-weighted images can be used to infer cellular density, fiber orientations, brain structural connectivity, tissue heterogeneity, and even the axonal diameter using various diffusion models (Tang and Zhou 2019).
Introduction to IVIM MRI
Published in Denis Le Bihan, Mami Iima, Christian Federau, Eric E. Sigmund, Intravoxel Incoherent Motion (IVIM) MRI, 2018
Molecular diffusion is just one type of IVIM. Due to their thermal energy all molecules move, colliding against each other. Each collision results in a change in the motion direction of each molecule, and the overall process is well described by a random walk, as first realized by Einstein. For liquid water the average of individual molecular displacement between two “collisions,” l, in 3D space, is in the 10th of a nanometer range while mean “velocity” (a concept more valid for a gas phase than a liquid phase), v, is around 100 m/s, which correspond to a diffusion coefficient, D, around 10–9 m²/s based on Einstein equation (D = lv/6) [6]. Diffusion refers to the random movement of individual molecules, but on a statistical basis, taking into account billions of molecules, each one diffusing on its own, this movement translates into an overall probability displacement along one spatial direction that obeys a Gaussian distribution. For water at body temperature the average diffusion distance is 17 μm during a time interval of 50 ms, a perfect scale to explore the microstructure of biological tissues in vivo (Fig. 1.1).
Updated insight into the characterization of nano-emulsions
Published in Expert Opinion on Drug Delivery, 2023
Xinyue Wang, Halina Anton, Thierry Vandamme, Nicolas Anton
Besides its common use for chemical characterization, in recent years, NMR was also used in NE characterization. This method reveals information on the arrangement of surfactants and co-surfactant on the oil-water interface by the modification of their chemical shift. Xie et al. chose 1H and 13C NMR as the major approach to identify the functional groups on the droplet’s interface, through following the variation of the peak intensity and comparing formulations with different interfacial composition [92]. Another NMR-based technology, so-called pulsed field gradient NMR (PFG-NMR), can be used to determine the particle size and size distribution for single and double emulsions [20]. This technique analyzes the reduction of the molecular diffusion, when they are confined in the discrete phase – i.e. emulsion droplets – in comparison to those located in the interfacial region. Analyzing when the diffusion becomes restricted provides an estimation of the droplet size. Beyond the information in size, PFG-NMR allows the fine characterization of assembled states and structures, level of sedimentation, or creaming of emulsions [93]. Figure 10 illustrates the size determination of the droplet suspension by PFG-NMR, showing that this technique is less affected by light scattering and permits to track the diffusion properties of individual components in turbid and concentrated samples, by measuring their characteristic spectra (inherently chemically selective).
Hydroxypropyl chitosan nail lacquer of ciclopirox-PLGA nanocapsules for augmented in vitro nail plate absorption and onychomycosis treatment
Published in Drug Delivery, 2022
Eman Yahya Gaballah, Thanaa Mohammed Borg, Elham Abdelmonem Mohamed
In vitro release profiles of CIX from the optimized NCs (F3) and its HPCH nail lacquer in phosphate buffers of pHs 5.8 and 7.4 in comparison with the free drug in both solution and dispersion forms are illustrated in Figure 4(A and B, respectively). At both media, a rapid release during the first 4 hours was followed by a sustained release till 24 h. Similar results were reported for PLGA-NCs (Maribel et al., 2019). The initial fast release could be attributed to the desorption of the drug on NCs surface. The sustained release phase may be owing to the drug encapsulated in the oil core that was protected by PLGA coat as indicated by TEM examination (Flores et al., 2017). Therapeutic drug concentrations can be attained due to the rapid drug release, while the sustained drug release could maintain these concentrations (Mohamed et al., 2018). As well, the drug gradual release may lead to the reduction in the application frequency enhancing the patient compliance. In vitro release of CIX from both formulations during the rapid and sustained release phases can be explained by first order model (Table 2(A and B)). Fickian diffusion mechanism (n < 0.45) in which the release is assumed to occur by the molecular diffusion of the drug due to a chemical potential gradient, was found to describe the drug release during the two phases from F3 and its lacquer at the two media (Singhvi & Singh, 2011).
Antibiotics adsorption from aqueous solutions using carbon nanotubes: a systematic review
Published in Toxin Reviews, 2020
Seyyed Alireza Mousavi, Hosna Janjani
Pollutant and adsorbent behavior varies by temperature. In a study, it has been showed low-temperature affected hydrophobic compounds more than hydrophilic compounds (Nam et al. 2014). In Ncibi et al study, increasing temperature from 15 to 45 °C has increased the adsorption capacity for MWCNTs (from 170 to 342 mg, respectively), while, an increase in adsorption was registered between 15 and 35 °C, for SWCNTs and DWCNTs and adsorption has decreased at higher temperatures (45 °C). This decreases has been related to decreasing the viscosity of the solution containing the nanotubes. But to range of 35 °C adsorption increases has been due to deagglomeration of nanotubes that helps to create of new adsorption sites. Increasing temperature will decrease the viscosity of solution and also can enhance the rate of molecular diffusion. So at higher temperatures due to much more dissociation, and broken down of pore structure, adsorption will decrease (Ncibi et al. 2015).