Search results for "Biophysical Phenomena"
showing 10 items of 47 documents
Three-dimensional cardiac computational modelling: methods, features and applications
2015
[EN] The combination of computational models and biophysical simulations can help to interpret an array of experimental data and contribute to the understanding, diagnosis and treatment of complex diseases such as cardiac arrhythmias. For this reason, three-dimensional (3D) cardiac computational modelling is currently a rising field of research. The advance of medical imaging technology over the last decades has allowed the evolution from generic to patient-specific 3D cardiac models that faithfully represent the anatomy and different cardiac features of a given alive subject. Here we analyse sixty representative 3D cardiac computational models developed and published during the last fifty …
An easy-to-use model for O2 supply to red muscle. Validity of assumptions, sensitivity to errors in data
1995
An easy-to-use capillary cylinder model of O2 supply to muscle is presented that considers all those factors that are known to be most important for realistic results: (1) red blood cell (RBC) O2 unloading along the capillary, (2) effects of the particulate nature of blood, (3) free and hemoglobin-facilitated O2 diffusion and reaction kinetics inside RBCs, (4) free and myoglobin-facilitated O2 diffusion inside the muscle cell, and (5) carrier-free region separating RBC and tissue. In a first approach, a highly simplified yet reasonably accurate treatment of the complex three-dimensional oxygen diffusion field in and next to capillaries is employed. As an alternative, a more realistic descri…
Denaturing for Nanoarchitectonics: Local and Periodic UV-Laser Photodeactivation of Protein Biolayers to Create Functional Patterns for Biosensing
2022
[EN] The nanostructuration of biolayers has become a paradigm for exploiting nanoscopic light-matter phenomena for biosensing, among other biomedical purposes. In this work, we present a photopatterning method to create periodic structures of biomacromolecules based on a local and periodic mild denaturation of protein biolayers mediated by UV-laser irradiation. These nanostructures are constituted by a periodic modulation of the protein activity, so they are free of topographic and compositional changes along the pattern. Herein, we introduce the approach, explore the patterning parameters, characterize the resulting structures, and assess their overall homogeneity. This UV-based patterning…
Pulmonary surfactant protein C containing lipid films at the air-water interface as a model for the surface of lung alveoli.
1995
The pulmonary surfactant lines as a complex monolayer of lipids and proteins the alveolar epithelial surface. The monolayer dynamically adapts the surface tension of this interface to the varying surface areas during inhalation and exhalation. Its presence in the alveoli is thus a prerequisite for a proper lung function. The lipid moiety represents about 90% of the surfactant and contains mainly dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG). The surfactant proteins involved in the surface tension adaption are called SP-A, SP-B and SP-C. The aim of the present investigation is to analyse the properties of monolayer films made from pure SP-C and from mixtures of DPPC, DP…
Validation of a biophysical drug absorption model by the PATQSAR system
1999
Absorption rate constants (in situ rat gut technique) and in vitro antibacterial activities of twenty fluoroquinolones have been evaluated. A biophysical model that relates the absorption of the compounds with their lipophilicity was fitted. The model considers the absorption process from the intestinal lumen as the sum of two resistances in series: aqueous diffusional barrier and lipoidal membrane. Even if partitioning into the membrane and membrane diffusion are both enhanced for lipophilic compounds, the absorption rate constant is limited by the aqueous diffusion. To estimate the influence of structural modifications on each property and to establish the role of lipophilicity in control…
Mechanisms of Adaptation from a Multiple to a Single Step Recovery Strategy following Repeated Exposure to Forward Loss of Balance in Older Adults
2012
When released from an initial, static, forward lean angle and instructed to recover with a single step, some older adults are able to meet the task requirements, whereas others either stumble or fall. The purpose of the present study was to use the concept of margin of stability (MoS) to investigate balance recovery responses in the anterior-posterior direction exhibited by older single steppers, multiple steppers and those that are able to adapt from multiple to single steps following exposure to repeated forward loss of balance. One hundred and fifty-one healthy, community dwelling, older adults, aged 65-80 years, participated in the study. Participants performed four trials of the balanc…
Biophysical Models as an Approach To Study Passive Absorption in Drug Development: 6-Fluoroquinolones
1995
A preliminary study attempting to assess and explain the intestinal absorption of a series of antibacterial 7-piperazinyl-6-fluoroquinolones is presented. The synthesis, n-octanol partition coefficients, intrinsic rat gut in situ absorption rate constants, and in vitro antibacterial activity data found for these homologous compounds are described. A fluorimetric, reverse-phase HPLC method was performed for the quantification of the quinolones in absorption and partition samples. Equations based on two classic biophysical absorption models are given for predicting the intrinsic absorption features of the series according to the partition data or merely single structural parameters. In situ a…
Synthetic nanopores with fixed charges: An electrodiffusion model for ionic transport
2003
Synthetic nanopores with fixed charges exhibit ionic equilibrium and transport properties that resemble those displayed by biological ion channels. We present an electrodiffusion model based on the Nernst-Planck flux equations, which allows for a qualitative description of the steady state ionic transport through a nanopore when the membrane fixed charges and all mobile carriers (including the water ions) are properly taken into account. In particular, we study the current-voltage curve, the electrical conductance, the reversal potential (a measure of the nanopore ionic selectivity), as well as the flux inhibition by protons and divalent cations in the nanopore. The model clearly shows how …
Response charactterization of ammonium tartrate solid state pellets for ESR dosimetry with radiotherapeutic photon and electron beams.
2001
Solid state pellets (1 mm thick) for electron spin resonance (ESR) dosimetry were made using ammonium tartrate as the radiation-sensitive substance. Their behaviour was experimentally investigated as a function of dose with 60Co gamma rays. The calibration function obtained permits measurements of absorbed dose in the 2-50 Gy range, with a combined uncertainty of +/-4%. The lowest detectable dose was about 0.5 Gy. These properties are comparable with or even better than those of ESR dosimeters made from other materials. The time stability of the ESR signal of ammonium tartrate dosimeters at different storage conditions after irradiation was studied. A rather complex behaviour was observed, …
Advanced microscopy analysis of the micro-nanoscale architecture of human menisci
2019
AbstractThe complex inhomogeneous architecture of the human meniscal tissue at the micro and nano scale in the absence of artefacts introduced by sample treatments has not yet been fully revealed. The knowledge of the internal structure organization is essential to understand the mechanical functionality of the meniscus and its relationship with the tissue’s complex structure. In this work, we investigated human meniscal tissue structure using up-to-date non-invasive imaging techniques, based on multiphoton fluorescence and quantitative second harmonic generation microscopy complemented with Environmental Scanning Electron Microscopy measurements. Observations on 50 meniscal samples extract…