viscoelasticity
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Evaluation of viscoelastic properties of four pharmaceutical fillers of different chemical structure using a stress relaxation test is described. The obtained values express not only the elasticity and plasticity of the material, but also describe the processes inside the compressed material. For each of the fillers tested, three modules of elasticity and three modules of plasticity were calculated. Different modules were found in the polymeric and crystalline fillers. Dehydrated dicalcium phosphate possesses a high module of plasticity comparable to that of microcrystalline cellulose. The strength of dicalcium phosphate tablets is very low in comparison to those from microcrystalline cellulose.
This study is devoted to the degradation pathway (bio, photo degradation and photo/bio) of Poly(Lactic acid) PLA polymers by means of melt viscoelasticity. A comparison was made between three PLA polymers with different microstructures (L, D stereoisomers). Biodegradability was determined during composting by burying the polymer films in compost at 58 °C. Melt viscoelasticity was used to assess the molecular evolution of the materials during the composting process. Viscoelastic data were plotted in the complex plane. We used this methodology to check the kinetics of the molecular weight decrease during the initial stages of the degradation, through the evolution of Newtonian viscosity. After a few days in compost, the Newtonian viscosity decreased sharply, meaning that macromolecular chain scissions began at the beginning of the experiments. However, a double molar mass distribution was also observed on Cole⁻Cole plots, indicating that there is also a chain recombination mechanism competing with the chain scission mechanism. PLA hydrolysis was observed by infra-red spectroscopy, where acid characteristic peaks appeared and became more intense during experiments, confirming hydrolytic activity during the first step of biodegradation. During UV ageing, polymer materials undergo a deep molecular evolution. After photo-degradation, lower viscosities were measured during biodegradation, but no significant differences in composting were found.
Understanding the mechanics of the respiratory system is crucial for optimizing ventilator settings and ensuring patient safety. While simple models of the respiratory system typically consider only flow resistance and lung compliance, lung tissue resistance is usually neglected. This study investigated the effect of lung tissue viscoelasticity on delivered mechanical power in a physical model of the respiratory system and the possibility of distinguishing tissue resistance from airway resistance using proximal pressure measured at the airway opening. Three different configurations of a passive physical model of the respiratory system representing different mechanical properties (Tissue resistance model, Airway resistance model, and No-resistance model) were tested. The same volume-controlled ventilation and parameters were set for each configuration, with only the inspiratory flow rates being adjusted. Pressure and flow were measured with a Datex-Ohmeda S/5 vital signs monitor (Datex-Ohmeda, Madison, WI, USA). Tissue resistance was intentionally tuned so that peak pressures and delivered mechanical energy measured at airway opening were similar in Tissue and Airway Resistance models. However, measurements inside the artificial lung revealed significant differences, with Tissue resistance model yielding up to 20% higher values for delivered mechanical energy. The results indicate the need to revise current methods of calculating mechanical power delivery, which do not distinguish between tissue resistance and airway flow resistance, making it difficult to evaluate and interpret the significance of mechanical power delivery in terms of lung ventilation protectivity.
Mechanical behavior of biological structures under dynamic loading generally depends on elastic as well as viscous properties of biological materials. The significance of "viscous" parameters in real situations remains to be elucidated. Behavior of rheological models consisting of a combination of inertial body and two Voigt's bodies were described mathematically with respect to inverse problem solution, and behavior in impulse and harmonic loadings was analyzed. Samples of walls of porcine and human aorta thoracica in transverse direction and samples of human bone (caput femoris, substantia compacta) were measured. Deformation responses of human skin in vivo were also measured. Values of elastic moduli of porcine aorta walls were in the interval from 10(2)kPa to 10(3) kPa, values of viscous coefficients were in the interval from 10(2) Pa.s to 10(3) Pa.s. The value of shear stress moduli of human caput femoris, substantia compacta range from 52.7 to 161.1 MPa, and viscous coefficients were in the interval from 27.3 to 98.9 kPa.s. The role of viscous coefficients is significant for relatively high loading frequencies - in our materials above 8 Hz in aorta walls and 5 Hz for bones. In bones, the viscosity reduced maximum deformation corresponding to short rectangular stress.
- MeSH
- aorta thoracica fyziologie MeSH
- biologické modely MeSH
- dospělí MeSH
- fyziologie kůže * MeSH
- kosti a kostní tkáň fyziologie MeSH
- lidé středního věku MeSH
- lidé MeSH
- mechanický stres MeSH
- pružnost MeSH
- reologie MeSH
- senioři MeSH
- Sus scrofa MeSH
- tlak MeSH
- točivý moment MeSH
- viskozita MeSH
- zvířata MeSH
- Check Tag
- dospělí MeSH
- lidé středního věku MeSH
- lidé MeSH
- mužské pohlaví MeSH
- senioři MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Hyaluronová kyselina je endogenní molekula, která má v medicíně několikero využití. V ortopedii se používá především intraartikulárně v terapii osteoartrózy kolenního kloubu. Tento článek je profilem zdravotnického prostředku Durolane, podává přehled farmakokinetiky hyaluronové kyseliny po intraartikulární aplikaci, přehled mechanismů působení, všímá si bezpečnosti intraartikulárně aplikované hyaluronové kyseliny a dokládá evidenci účinků a současná klinická doporučení.
Hyaluronic acid is an endogenous molecule that has several uses in medicine. In orthopaedics, it is mainly used in the form of intra‑articular injections for the treatment of osteoarthritis of the knee. This article presents the profile of Durolane, provides an overview of the pharmacokinetics of intra‑articular hyaluronic acid administration, an overview of the mechanisms of action, the safety of intra‑articular hyaluronic acid administration and reviews the current scientific evidence of effects and clinical recommendations.
- MeSH
- antiflogistika aplikace a dávkování chemie farmakokinetika farmakologie škodlivé účinky MeSH
- artróza kolenních kloubů farmakoterapie MeSH
- injekce intraartikulární MeSH
- klinická studie jako téma MeSH
- kyselina hyaluronová * aplikace a dávkování chemie farmakokinetika farmakologie škodlivé účinky MeSH
- lidé MeSH
- viskoelastické látky MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- přehledy MeSH
