396 research outputs found
Mechanics and drug release from poroviscoelastic hydrogels: Experiments and modeling
No full textHydrogels are peculiar soft materials formed by a 3D polymeric network surrounded by water molecules. In these systems the mechanical and the chemical energy are well balanced and an applied external stimulus (mechanical or chemical) can cause a distinctive response, where the contributions of the mechanics and the mass transport are combined to form a “poroviscoelastic” behavior. In this work the poroviscoelastic behavior of the agarose gels has been investigated, from the experimental and modeling points of view, by applications of external mechanical stimuli. The pure gel, brought in the non-equilibrium condition, showed that the combined effect of mechanical viscoelasticity and water transport were essential to reach the new equilibrium condition. Furthermore, the agarose gel loaded with a model drug, theophylline, showed that the mechanical stimulus can enhance the drug release from the system by stretching the polymeric chains, modifying the mesh size and therefore the drug diffusion coefficient
Spatial structuring and life history connectivity of Antarctic silverfish along the southern continental shelf of the Weddell Sea
No full textABSTRACT: A multi-disciplinary approach was employed to examine a physical-biological population hypothesis for a critical forage species, the Antarctic silverfish Pleuragramma antarctica. Caccavo et al. (2018; Sci Rep 8:17856) had shown strong gene flow along the westward Antarctic Slope Current, in addition to spatially recurring length modes that provided evidence for episodic connectivity. In this paper, otolith nucleus chemistry from a subset of fish collected in the southern Weddell Sea as part of a hydrographic survey of the Filchner Trough system was used to test between connectivity scenarios. Nucleus chemistry, which reflects environmental exposure during early life, showed significant spatial structuring despite homogeneity in microsatellite allele frequencies. Mg:Ca and Sr:Ca differentiated length modes, and Mg:Ca showed significant contrasts between Atka Bay, Halley Bay, and Filchner Trough. Physical-biological mechanisms may help reconcile structuring shown by otolith chemistry, length, and abundance data with prior evidence of gene flow. Such mechanisms include self-recruitment shaped by circulation associated with the Filchner Trough, fluctuations in mixing between immigrant and locally recruited fish, and feeding opportunities between inflowing Modified Warm Deep Water and outflowing Ice Shelf Water. The results illustrate how comparisons between multi-disciplinary techniques based on integrated sampling designs that incorporate hydrography can enhance understanding of population structure and connectivity around the Southern Ocean
An overview on the mathematical modeling of hydrogels’ behavior for drug delivery systems
No full textHydrogels-based systems (HBSs) for drug delivery are nowadays extensively used and the interest in modeling their behavior is dramatically increasing. In this review a critical overview on the modeling approaches is given, quantitatively and qualitatively analyzing the publications on the subject, the trend of the publications per year and the type of modeling approaches. It was found that, despite the drug release fitting models (i.e. Higuchi's equation) are the most abundant, their use for HBSs is decreasing in the last years and luckily, considering the limiting assumption on which they were built, they will be confined to simple mathematical fitting equations. Within the mechanistic models the “multi-component” with the swelling approximation (mass transport only) and with the mechanics (fully coupled) are experiencing the highest growth rate, with much more interest toward the last one that, in the next years could be able to provide a first principles model. Statistical models, especially based on the response surface methodology, are rapidly spreading in the scientific community mainly thanks to their ability to be predictive, regardless of the phenomenology, in the analyzed design space with very low efforts. Neural Networks models for HBSs, in countertrend with their use in the pharmaceutical industry, have never take off preferring less data demanding statistical models
Swelling Behavior of Anionic Hydrogels: Experiments and Modeling
No full textPolyelectrolyte hydrogels are smart materials whose swelling behavior is governed by ionizable groups on their polymeric chains, making them sensitive to pH and ionic strength. This study combined experiments and modeling to characterize anionic hydrogels. Mechanical tests and gravimetric analyses were performed to track hydrogel mass over time and at a steady state under varying pH and salt concentrations. The swelling ratio exhibited a bell-shaped curve with pH, reaching 120 in pure water, and decreased with increasing salt concentrations. Transient regimes showed slower swelling (similar to 40 h) under pH stimulation compared to faster deswelling (similar to 20 h) induced by salt. A fully coupled model integrating mass transport and solid mechanics was developed, with solvent diffusivity as the sole adjustable parameter in transient simulations. In conclusion, this study combined experiments and modeling to uncover complex mechanisms in PE behavior under two external stimuli, providing insights essential for designing advanced hydrogels
Hydrogels: Experimental characterization and mathematical modelling of their mechanical and diffusive behaviour
No full textHydrogels are materials widely used in countless applications, particularly in the biomedical, pharmaceutical, and nutraceutical fields, because of their biocompatibility and their mechanical and transport properties. Several approaches are known to evaluate their properties, but only a few approaches are under development to mathematically describe their behaviour, in terms of how the materials answer to mechanical stimuli and how incorporated active substances are released. In this review, the main properties of hydrogels are summarized and the structure-property relationships are investigated (i.e. how the macromolecular structure influences the properties of macroscopic samples made of hydrogels). A selection criterion is proposed based on the comparison of three characteristic times: relaxation time, diffusion time, and process time. Then, the most common experimental methods to investigate the hydrogel properties are summarized, along with the state-of-the-art of mathematical modelling, with reference to the mechanical and transport properties of hydrogels, with particular attention to the viscoelastic and poroelastic behaviours. Last but not least, some case histories which can be classified as viscoelastic, poroelastic, or poroviscoelastic behaviours are presented
PoroViscoElastic model to describe hydrogels’ behavior
No full textHydrogels are three-dimensional, cross-linked hydrophilic polymeric network able of absorb large amount of water. The mechanics of these systems is strictly coupled with the water transport resulting in the peculiar behavior known as poroviscoelasticy. This can be considered as sum of the viscoelastic behavior of the polymeric network and the poroelastic behavior caused by the water movement within the hydrogel. In this work a 3D monophasic model able to depict the poroviscoelastic behavior of these systems, within the field of nonlinear solid mechanics, is developed. The mass and momentum balances equations, supported by constitutive equations from non-equilibrium thermodynamics and by initial and boundary conditions, is implemented through the weak formulation in a commercial FEM-based software. A parametric study is performed in order to assess the relative importance of the model parameters on hydrogels’ behavior
[Evaluation of various parameters of platelet function in subjects with type II diabetes mellitus. Methodologic study of the changes in PF4 and beta-TG]
No full textModeling the modified drug release from curved shape drug delivery systems â Dome Matrix®
No full textThe controlled drug release from hydrogel-based drug delivery systems is a topic of large interest for research in pharmacology. The mathematical modeling of the behavior of these systems is a tool of emerging relevance, since the simulations can be of use in the design of novel systems, in particular for complex shaped tablets. In this work a model, previously developed, was applied to complex-shaped oral drug delivery systems based on hydrogels (Dome Matrix®). Furthermore, the model was successfully adopted in the description of drug release from partially accessible Dome Matrix® systems (systems with some surfaces coated). In these simulations, the erosion rate was used as a fitting parameter, and its dependence upon the surface area/volume ratio and upon the local fluid dynamics was discussed. The model parameters were determined by comparison with the drug release profile from a cylindrical tablet, then the model was successfully used for the prediction of the drug release from a Dome Matrix® system, for simple module configuration and for module assembled (void and piled) configurations. It was also demonstrated that, given the same initial S/V ratio, the drug release is independent upon the shape of the tablets but it is only influenced by the S/V evolution. The model reveals itself able to describe the observed phenomena, and thus it can be of use for the design of oral drug delivery systems, even if complex shaped
- …
