Understanding of the bone remodelling process has considerably increased during the last 20 years. Since the ability to simulate (and predict) the effects of bone remodelling offers substantial insights, several models have been proposed to describe this phenomenon. The strength of the presented model is that it includes biochemical control factors (e.g., the necessity of cell-to-cell contact, which is mediated by the RANKL-RANK-OPG chain during osteoclastogenesis) and mechanical stimulation, the governing equations are derived from interaction kinetics (e.g., mass is preserved in running reactions), and the parameters are measurable. Behaviour of the model is in accordance with experimental and clinical observations, such as the role of dynamic loading, the inhibitory effect of dynamic loading on osteoclastogenesis, the observation that polykaryon osteoclasts are activated and formed by a direct cell-to-cell contact, and the correct concentrations of osteoblasts, osteoclasts, and osteocytes. The model does not yet describe the bone remodelling process in complete detail, but the implemented simplifications describe the key features and further details of control mechanisms may be added.

• MeSH
• biologické modely * MeSH
• kostní denzita fyziologie   MeSH
• lidé MeSH
• ligand RANK fyziologie   MeSH
• mechanický stres MeSH
• osteogeneze fyziologie   MeSH
• osteoklasty fyziologie   MeSH
• osteoprotegerin fyziologie   MeSH
• protein RANK fyziologie   MeSH
• remodelace kosti fyziologie   MeSH
• signální transdukce fyziologie   MeSH
• termodynamika * MeSH
• zatížení muskuloskeletálního systému fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ligand RANK MeSH
• osteoprotegerin MeSH
• protein RANK MeSH
• TNFRSF11A protein, human MeSH Prohlížeč
• TNFSF11 protein, human MeSH Prohlížeč

Lattice dynamics and stability of four fcc crystals (Al, Ir, Pt and Au) under isotropic (hydrostatic) tensile loading are studied from first principles using the linear response method and the harmonic approximation. The results reveal that, contrary to former expectations, strengths of all the studied crystals are limited by instabilities related to soft phonons with finite or vanishing wavevectors. The critical strains associated with such instabilities are remarkably lower than those related to the volumetric instability. On the other hand, the corresponding reduction of the tensile strength is by 20% at the most. An analysis of elastic stability conditions is also performed and the results obtained by means of both approaches are compared.

• MeSH
• anizotropie MeSH
• chemické modely * MeSH
• kovy chemie   MeSH
• krystalizace * MeSH
• mechanický stres MeSH
• pevnost v tahu MeSH
• počítačová simulace MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• kovy MeSH

The mechanical behavior of eggshell was determined in terms of average rupture force and corresponding deformation. For the experiment, we selected goose eggs (Anser anser f. domestica). Samples of eggs were compressed along their x-axis and z-axis. The effect of the loading orientation can be described in terms of the eggshell contour curvature. Two different experimental methods were used: compression between two plates (loading rates up to 5 mm/s) and the Hopkinson split pressure bar technique. This second method enables achieving loading rates up to about 17 m/s. The response of goose eggs to this high loading rate was characterized also by simultaneous measurement of the eggshell surface displacements using a laser vibrometer and by the measurement of both circumferential and meridian strains.

• Klíčová slova
• Compression, Dynamic loading, Eggs, HSPB technique, Rupture force,
• MeSH
• husy MeSH
• mechanické jevy * MeSH
• mechanický stres MeSH
• ovum * MeSH
• pevnost v tlaku MeSH
• testování materiálů metody   MeSH
• tlak MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

This case study describes the experimental determination of displacements and stresses on a composite model of a pelvis that was modified to represent a healthy intact pelvic ring. The modified model was stressed statically up to 1750 N to simulate standing on one leg and also cyclically to model walking. For two different model settings in the loading machine the values of displacements and stresses at the pelvic ring were determined. The two different settings correspond to two different loading vectors applied on the pelvic ring, boundary conditions and degrees of freedom. The experimentally determined values of displacements in both settings are very similar and in accordance with the knowledge on the behaviour of a real human pelvis. The modified model is thus suitable for testing of newly developed implants for pelvis treatment and experimental determination of displacements and stresses in pelvic ring which are caused by application of implants.

• Klíčová slova
• Pelvic trauma, acetabulum, composite pelvic model, pubic symphysis, sacroiliac joint, stress and displacement in pelvis,
• MeSH
• biomechanika MeSH
• lidé MeSH
• pánev * MeSH
• pánevní kosti * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

Selective laser melting (SLM) is an additive technology that allows for the production of precisely designed complex structures for energy absorbing applications from a wide range of metallic materials. Geometrical imperfections of the SLM fabricated lattice structures, which form one of the many thin struts, can lead to a great difference in prediction of their behavior. This article deals with the prediction of lattice structure mechanical properties under dynamic loading using finite element method (FEA) with inclusion of geometrical imperfections of the SLM process. Such properties are necessary to know especially for the application of SLM fabricated lattice structures in automotive or aerospace industries. Four types of specimens from AlSi10Mg alloy powder material were manufactured using SLM for quasi-static mechanical testing and determination of lattice structure mechanical properties for the FEA material model, for optical measurement of geometrical accuracy, and for low-velocity impact testing using the impact tester with a flat indenter. Geometries of struts with elliptical and circular cross-sections were identified and tested using FEA. The results showed that, in the case of elliptical cross-section, a significantly better match was found (2% error in the Fmax) with the low-velocity impact experiments during the whole deformation process compared to the circular cross-section. The FEA numerical model will be used for future testing of geometry changes and its effect on mechanical properties.

• Klíčová slova
• ANSYS Workbench, aluminum alloy AlSi10Mg, energy absorption, finite element analysis (FEA), lattice structure, low-velocity impact, material model, numerical model,
• Publikační typ
• časopisecké články MeSH

Nanoparticles made of amphiphilic block copolymers comprising biodegradable core-forming blocks are very attractive for the preparation of drug-delivery systems with sustained release. Their therapeutic applications are, however, hindered by low values of the drug-loading content (DLC). The compatibility between the drug and the core-forming block of the copolymer is considered the most important factor affecting the DLC value. However, the molecular picture of the hydrophobic drug-copolymer interaction is still not fully recognized. Herein, we examined this complex issue using a range of experimental techniques in combination with atomistic molecular dynamics simulations. We performed an analysis of the interaction between itraconazole, a model hydrophobic drug, and a poly(ethylene glycol)-poly(lactide- co-glycolide) (PEG-PLGA) copolymer, a biodegradable copolymer commonly used for the preparation of drug-delivery systems. Our results clearly show that the limited capacity of the PEG-PLGA nanoparticles for the accumulation of hydrophobic drugs is due to the fact that the drug molecules are located only at the water-polymer interface, whereas the interior of the PLGA core remains empty. These findings can be useful in the rational design and development of amphiphilic copolymer-based drug-delivery systems.

• MeSH
• dynamický rozptyl světla MeSH
• hydrofobní a hydrofilní interakce MeSH
• itrakonazol chemie   metabolismus   MeSH
• nanočástice chemie   MeSH
• nosiče léků chemie   MeSH
• polyestery chemie   MeSH
• polyethylenglykoly chemie   MeSH
• simulace molekulární dynamiky MeSH
• voda chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• itrakonazol MeSH
• nosiče léků MeSH
• polyestery MeSH
• polyethylene glycol-poly(lactide-co-glycolide) MeSH Prohlížeč
• polyethylenglykoly MeSH
• voda MeSH

Polyurethane foams are one of the most common auxetic structures regarding energy absorption enhancement. This present study evaluates the result reliability of two different numerical approaches, the H-method and the P-method, to obtain the best convergence solution. A polymeric re-entrant cell is created with a beam element and the results of the two different methods are compared. Additionally, the numerical results compare well with the analytical solution. The results show that there is a good agreement between converged FE models and the analytical solution. Regarding the computational cost, the P-method is more efficient for simulating the re-entrant structure subjected to axial loading. During the second part of this study, the re-entrant cell is used for generating a polymeric auxetic cellular tube. The mesh convergence study is performed on the cellular structures using the H- and P- methods. The cellular tube is subjected to tensional and compressive loading, the module of elasticity and Poisson's ration to calculate different aspect ratios. A nonlinear analysis is performed to compare the dynamic response of a cellular tube versus a solid tube. The crashworthiness indicators are addressed and the results are compared with equivalent solid tubes. The results show that the auxetic cellular tubes have better responses against compressive loading. The primary outcome of this research is to assess a reliable FE approach for re-entrant structures under axial loading.

• Klíčová slova
• axial loading, cellular structures, crashworthiness, finite element method, negative Poisson’s ratio,
• Publikační typ
• časopisecké články MeSH

Due to the internal structure of the knee joint, the ability to characterize and quantify the dynamic response of the meniscal tissue directly in vivo is highly problematic. The main purpose of this study was to investigate the behaviour of the meniscus under loading conditions. Four healthy young females were included. To obtain T2* values in the meniscus, the vTE sequence was used with 10 echoes ranging from 0.8 to 10.1 ms. Submilisecond first echo time is a great advantage of vTE sequence allowing for precise mapping of relatively short T2*. The two-parametric least squares fitting procedure was used to calculate T2* pixel-wise. A custom-made diamagnetic apparatus was developed to simulate stress conditions on the lower limb in a conventional MR scanner. vTE T2* was performed in five consecutive scans, 6:10 min apart. Three different compartments of the medial and lateral meniscus were segmented. The differences at the different time-points were calculated. A constant increase of T2* times after compression was statistically significant in the anterior horn of the medial meniscus. T2* mapping with variable echo time sequence might be a satisfactorily sensitive technique to detect the changes of meniscus physiology under loading conditions in vivo.

• Klíčová slova
• Loading, MRI, Meniscus, T2* changes, vTE,
• Publikační typ
• časopisecké články MeSH

Arabidopsis plants exposed to the antibiotic kanamycin (Kan) display altered metal homeostasis. Further, mutation of the WBC19 gene leads to increased sensitivity to kanamycin and changes in iron (Fe) and zinc (Zn) uptake. Here we propose a model that explain this surprising relationship between metal uptake and exposure to Kan. We first use knowledge about the metal uptake phenomenon to devise a transport and interaction diagram on which we base the construction of a dynamic compartment model. The model has three pathways for loading Fe and its chelators into the xylem. One pathway, involving an unknown transporter, loads Fe as a chelate with citrate (Ci) into the xylem. This transport step can be significantly inhibited by Kan. In parallel, FRD3 transports Ci into the xylem where it can chelate with free Fe. A third critical pathway involves WBC19, which transports metal-nicotianamine (NA), mainly as Fe-NA chelate, and possibly NA itself. To permit quantitative exploration and analysis, we use experimental time series data to parameterize this explanatory and predictive model. Its numerical analysis allows us to predict responses by a double mutant and explain the observed differences between data from wildtype, mutants and Kan inhibition experiments. Importantly, the model provides novel insights into metal homeostasis by permitting the reverse-engineering of mechanistic strategies with which the plant counteracts the effects of mutations and of the inhibition of iron transport by kanamycin.

• Klíčová slova
• FRD3, IREG1, WBC19, citrate, iron, kanamycin, nicotianamine, zinc,
• Publikační typ
• časopisecké články MeSH

Despite the increasing interest in pharmaceutical use of mesoporous silica, there is still only limited knowledge on mechanisms of pore loading and subsequent drug desorption and release. Hence the aim of this work was to address the mechanistic aspects of drug loading into the mesoporous silica pores and to minimise the risk of pore clogging. Hydrophilic solvents (polysorbate 20 and polyethylene glycol 200) with high dissolving capacity for the model drug celecoxib were studied for their surface tension as well as dynamic viscosity by considering hydration. As an innovation in liquisolid systems preparation, a rather simple drug loading method on a mesoporous carrier was introduced by using semi-volatile solvent mixtures. Fast liquid loading into the pores was achieved due to the lowered viscosity and surface tension of the whole solvent system. Drug release kinetics suggested that lipid-based formulations belonging to class IV of Lipid Formulation Classification System may exhibit a lower risk of incomplete desorption from a carrier. The utilisation of volatile solvents during preparation had no negative impact on the liquisolid systems' dissolution behaviour. All prepared formulations showed similar significantly faster dissolution profiles compared to the physical mixture. The novel approach has potential to promote liquisolid applications in pharmaceutics.

• Klíčová slova
• Drug loading, Liquisolid systems, Mesoporous silica, Poor solubility, Semi-volatile mixture, Syloid XDP,
• MeSH
• diferenciální skenovací kalorimetrie metody   MeSH
• farmaceutická chemie metody   MeSH
• farmaceutická technologie metody   MeSH
• hydrofobní a hydrofilní interakce MeSH
• kinetika MeSH
• léčivé přípravky chemie   MeSH
• lipidy chemie   MeSH
• nosiče léků chemie   MeSH
• oxid křemičitý chemie   MeSH
• polysorbáty chemie   MeSH
• propylenglykol chemie   MeSH
• rozpouštědla chemie   MeSH
• rozpustnost účinky léků   MeSH
• tablety chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• léčivé přípravky MeSH
• lipidy MeSH
• nosiče léků MeSH
• oxid křemičitý MeSH
• polysorbáty MeSH
• propylenglykol MeSH
• rozpouštědla MeSH
• tablety MeSH