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Modelling and Simulation of Nanosystems for Delivering Drugs to the Brain
Published in Carla Vitorino, Andreia Jorge, Alberto Pais, Nanoparticles for Brain Drug Delivery, 2021
Tânia F. G. G. Cova, Sandra C.C. Nunes
Kopelman and co-workers [70] synthetised different nanoparticles with tuneable drug release. The polymer matrix density of amine or carboxyl functionalised hydrogel nanoparticles, loaded with cisplatin, was varied. It was shown that the NPs displaying the loose matrix, released more cisplatin, with a rate faster than 30 times. The relation between matrix density and drug release kinetics was detailed through Monte Carlo simulations. In short, the model consists of a 2D square lattice with L x L sites. Drug particles are randomly placed on the lattice sites and are allowed to diffuse with time, taking steps only to adjacent sites. When a drug molecule reaches the perimeter of the matrix, it is permanently removed from the system. Some sites were blocked with the aim of hindering particle motion. This means that if a drug particle diffuses towards a blocked site it must go back and find an open site to diffuse into. Particle diffusion was simulated by selecting particles at random and moving them randomly to one of the nearest-neighbour sites. A particle is removed from the system when it migrated through one of the perimeter sites. The number of particles released from the system was monitored as a function of time, approximated by Monte Carlo steps. Drug release was evaluated for different obstacle sites concentrations and different matrix densities. A good agreement between simulation and experiment was obtained (see Fig. 4 in Ref. [70]).
Mathematical modeling of inhaled therapeutic aerosol deposition in the respiratory tract
Published in Anthony J. Hickey, Heidi M. Mansour, Inhalation Aerosols, 2019
Jeffry Schroeter, Bahman Asgharian, Julia Kimbell
Some of the highlighted findings from these modeling studies include that, for total deposition in the respiratory tract, the dependence on particle diameter predicts minimum deposition at a particle diameter in the 0.1–0.5 μm range. As particle diameter increases, deposition increases due to impactive deposition in the upper respiratory tract and large bronchi, and due to sedimentation in the smaller airways and pulmonary region. As particle diameter increases, the location of deposition shifts to more proximal regions of the respiratory tract where inertial impaction is the dominant deposition mechanism and flow rates are high. For particles smaller than 0.1 μm, the mechanism of particle diffusion becomes important, and the overall deposition increases with decreasing particle diameter. These modeling results have provided insights for pharmaceutical applications regarding shifts in particle deposition in the lung as breathing rate or particle size changes.
Modelling and analysis of skin pigmentation
Published in Ahmad Fadzil Mohamad Hani, Dileep Kumar, Optical Imaging for Biomedical and Clinical Applications, 2017
Ahmad Fadzil Mohamad Hani, Hermawan Nugroho, Norashikin Shamsudin, Suraiya H. Hussein
Diffusion is because of the deflection of light through impacts with molecules, particles or group of particles lessening the energy of the incident light at the same time. The diffusion procedure may be grouped into three: molecular diffusion, particle diffusion and surface/reflective–refractive diffusion [58–60]. Molecular scattering (Rayleigh scattering) happens when the wavelength of the light is larger than the size of the molecules/particles. Particle scattering (Mie scattering), meanwhile, happens when the wavelength of the incident light is comparable to the size of the molecules or particles. For some practical intent, the error in utilizing Rayleigh, rather than Mie theory, to small particles is less than 1% when the radius of the particle is smaller or equal to 0.03λ [59]. Moreover, reflective–refractive or geometrical optics diffusion happens when the size of the particles is much larger than the wavelength of incident light. This category of diffusion happens for a large portion of the internal diffusion in organic tissues, such as on human skin. It is fundamentally brought about by the arrangement of tissues, and the refractive differences, connected with the air-cell wall interfaces with respect to cells whose dimensions are quite larger compared to the wavelength of light. Due to its dependency on refractive differences, the variations across the spectrum are directly associated with the wavelength dependency of the refractive indices of the materials.
Vitreous Humor: Composition, Characteristics and Implication on Intravitreal Drug Delivery
Published in Current Eye Research, 2023
Deepakkumar Mishra, Shilpkala Gade, Katie Glover, Ravi Sheshala, Thakur Raghu Raj Singh
Diffusion of small and large molecules in a viscous medium like vitreous humor has been studied in detail. Highly concentrated protein solutions often show higher viscosity due to formation of protein clusters within the solution and this may lead to decreased translational diffusion of the protein.57 This if taken in perspective of intravitreal injections of anti-VEGF agents could present a challenging scenario. The monthly injection of anti-VEGF agents is done from highly concentrated solutions with concentrations of up to 25 mg/ml. This high local concentration of protein could promote clumping and delay the diffusion. The other factors that could affect the diffusion of macromolecules are charge, size and hydrophilic interaction of macromolecules within vitreous humor. In one instance, Käsdorf et al. (2015) showed that the nanoparticles often show decreased diffusion in the vitreous humour when compared with diffusion in water. It was observed that majority fraction of nanoparticles (up to 75%) showed slow and delayed diffusion in vitreous humour and only up to 25% showed particle diffusion similar to water by single particle tracking studies conducted using florescent microscopy. It was also observed that PEGylation of nanoparticles enhanced the diffusion fraction by up to 50%.41
Dyes adsorption properties of KOH-activated resorcinol-formaldehyde carbon gels -kinetic, isotherm and dynamic studies
Published in Toxin Reviews, 2022
Azrul Nurfaiz Mohd Faizal, Muhammad Abbas Ahmad Zaini
The Boyd’s model further elicits accurate understanding on the rate-limiting step and removal mechanisms by particle diffusion or film diffusion (Karthikeyan et al.2010). The time constant, B was used to determine the effective diffusion coefficient, Di (cm2/s). The film diffusion coefficient, Df holds a value between 10−6 to 10−8 cm2/s for film diffusion to be the actual slow step. Particle diffusion is the rate-limiting step for Dp in the range of 10−11 to 10−13 cm2/s (Michelson et al.1975, Karthikeyan et al.2010). The deviation from origin implies that the rate-limiting step is film diffusion with effective diffusion coefficient, Di = Df in the range of 8.67 × 10−9 to 1.01 × 10−8 cm2/s.
Improving the 6-Aminopenicillanic acid release process using vermiculite-alginate biocomposite bead on drug delivery system
Published in Drug Development and Industrial Pharmacy, 2021
Nona Soleimanpour moghadam, Amirreza Azadmehr, Ardeshir Hezarkhani
To better understand major limitations in the adsorption of 6-APA onto VMT-Alg, the intra-particle diffusion model was used. The plot of qt versus t1/2 showed a high value of R2 (Figure 9). The result indicated that intra-particle diffusion could be divided into three linear parts. Three parts are corresponded to three phases of surface diffusion, intra-particle diffusion, and ultimate adsorption equilibrium, respectively. The first section of the intra-particle diffusion model did not pass through the origin indicating that intra-particle diffusion was not the only rate-controlling step, but also affected by the boundary layer diffusion process. Fundamentally, the first step demonstrates the transfer of 6-APA from solution to the external surface of VMT-Alg through film diffusion and the second step is related to the thickness of the boundary layer which corresponds to the diffusion of the antibiotic into the organic spaces of VMT-Alg molecules via hydrophobic interaction. The slope of the first step was less than the second step which indicates internal layer diffusion is more effective than surface diffusion. It is necessary to mention that, the third subdued portion is the gradual adsorption stage, where intra-particle diffusion started to slow down due to the extremely low 6-APA concentration that remains in the solution. The results are similar to the adsorption of ciprofloxacin (a type of antibiotic) onto alginate [55].