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Effect of Solute Structure on Transport of Radiotracers
Published in Lelio G. Colombetti, Biological Transport of Radiotracers, 2020
In simple diffusion it is not structure but size which determines the diffusion rate. The diffusion coefficient is inversely proportional to the radius of the diffusing molecule, or approximately to the cube root of the molecular weight. For larger molecules, the diffusion coefficient is dependent upon the movement of the solvent molecules and is more closely related to the square root of the molecular weight.
Clinical Applications of IVIM MRI to the Nervous System
Published in Denis Le Bihan, Mami Iima, Christian Federau, Eric E. Sigmund, Intravoxel Incoherent Motion (IVIM) MRI, 2018
Intravoxel incoherent motion (IVIM) refers to translational movements within a given voxel, which result in a distribution in position during measurement time [1] and can be measured using appropriate encoding gradients. The main application of this method was found to be the measurement of the restriction of thermal diffusion through the biological environment, using the concept of apparent diffusion coefficient. In particular, the observation that acute brain ischemia lesions [2] show a restriction in diffusion compared to normal parenchyma has been a tremendous breakthrough in the diagnosis and management of this disease.
Gastrointestinal Tract as a Major Route of Pharmaceutical Administration
Published in Shayne C. Gad, Toxicology of the Gastrointestinal Tract, 2018
where F is the flux, D is the diffusion constant for the substance that is diffusing in the specific solvent, and ∂C(x, t)/∂x is the concentration gradient. The diffusion constant of a substance is also referred to as ‘diffusion coefficient’ and it is expressed in units of length2/time, such as µm2/hour. The negative sign [−] on the right side of the equation indicates that the substances flow in the direction of lower concentration.
Tailoring and optimization of a honey-based nanoemulgel loaded with an itraconazole–thyme oil nanoemulsion for oral candidiasis
Published in Drug Delivery, 2023
Amal M. Sindi, Waleed Y. Rizg, Muhammad Khalid Khan, Hala M. Alkhalidi, Waleed S. Alharbi, Fahad Y. Sabei, Eman Alfayez, Hanaa Alkharobi, Mohammed Korayem, Mohammed Majrashi, Majed Alharbi, Mohammed Alissa, Awaji Y. Safhi, Abdulmajeed M. Jali, Khaled M. Hosny
At regular intervals, precise aliquots were automatically removed, and the previously described HPLC method was used to quantify the ItZ content. A graph was made to show how long it took for the ItZ to penetrate the Q per cm2 of the membrane; this finding let researchers better understand how the drug was dispersed throughout the mucosa. From the acquired diffusion data, significant parameters such as the Jss (steady-state flow), Pc (permeability coefficient), EF (enhancement factor), and D (diffusion coefficient) were determined. Plots were made of the comparative dissemination patterns for various formulations. The following equation (2) was used to determine the percentage of ItZ that penetrated the membrane and the overall amount of ItZ distributed throughout the receptor chamber (Hosny et al., 2021):
Ectoine gel transdermal formulation as a novel therapeutic approach in melanoma using 3D printed microneedles
Published in Pharmaceutical Development and Technology, 2022
Sammar A. Bayoumi, Aya M. Dawaba, Ahmed Mansour, Zeinab AlKasaby Zalat, Amal A. Ammar
When compared to passive permeation trials, a significant increase in ectoine permeability was seen following MN application to the skin (p < 0.05) (Figure 6). When compared to passive penetrated amount, notable increases in the cumulative amount of ectoine permeated over the course of 24 h were seen with various batch treatments. Other permeation measures, such as permeability and diffusion coefficient values, showed a similar pattern (Table 6). When MNS was applied compared to passive treatment, a substantial decrease in lag time was seen (p < 0.05). When compared to passive trials, Uppuluri et al. noted in 2017 that 1.5 mm polymeric MN application resulted in approximately 4.2-fold increases in the rizatriptan steady-state flow values, which is consistent with our results (Uppuluri et al. 2017).
Nanocubosomal based in situ gel loaded with natamycin for ocular fungal diseases: development, optimization, in-vitro, and in-vivo assessment
Published in Drug Delivery, 2021
Khaled M. Hosny, Waleed Y. Rizg, Hala M. Alkhalidi, Walaa A. Abualsunun, Rana B. Bakhaidar, Alshaimaa M. Almehmady, Adel F. Alghaith, Sultan Alshehri, Amani M. El Sisi
The studies were conducted in triplicate with F1 (optimized NT-Cub dispersed in Carbopol 934 in situ gel base), F2 (optimized NT-Cub dispersed in phosphate buffer pH 5.5), NT suspension, and commercial NT (2%) suspension samples. This study aimed to assess the influence of cubosomes in the release behavior and corneal permeation parameters of NT from these samples. The study complied with the ethical principles of the Egyptian Research Institute of Ophthalmology for animal use in experiments. The corneal dissection of albino rabbits was carried out following the reported procedure (Alharbi & Hosny, 2020). The study samples (corresponding to 50 mg drug) were placed in the donor compartment of the diffusion cell, containing phosphate buffer pH 7.4 (7 mL) in the receptor chamber, fitted with the excised rabbit cornea as the barrier membrane. The ex vivo permeation samples were withdrawn, then the permeated NT content was determined by HPLC at 303 nm using a C18 column and mobile phase prepared with 4 mg/mL ammonium acetate solution: acetonitrile: tetrahydrofuran in a ratio of 76:24:5. The cumulative amount permeated per unit area was estimated from the withdrawn samples. The diffusion parameters, such as diffusion coefficient (D), permeability coefficient (Pc), and steady-state flux (Jss), were also determined (Alhakamy & Hosny, 2019). The relative permeation rate (RPR) and enhancement factor (EF) were calculated using Equations (2) and (3), respectively: