The paper deals with the application of combined nondestructive method for assessment of compressive strength of calcium silicate bricks. In this case, it is a combination of the rebound hammer method and ultrasonic pulse method. Calibration relationships for determining compressive strength of calcium silicate bricks obtained from nondestructive parameter testing for the combined method as well as for the L-type Schmidt rebound hammer and ultrasonic pulse method are quoted here. Calibration relationships are known for their close correlation and are applicable in practice. The highest correlation between parameters from nondestructive measurement and predicted compressive strength is obtained using the SonReb combined nondestructive method. Combined nondestructive SonReb method was proved applicable for determination of compressive strength of calcium silicate bricks at checking tests in a production plant and for evaluation of bricks built in existing masonry structures.

• MeSH
• algoritmy MeSH
• chemické modely MeSH
• kalibrace MeSH
• konstrukční materiály normy   MeSH
• pevnost v tlaku * MeSH
• počítačová simulace MeSH
• reprodukovatelnost výsledků MeSH
• silikáty chemie   MeSH
• sloučeniny vápníku chemie   MeSH
• testování materiálů metody   MeSH
• ultrazvuk MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

V práci byla hodnocena pevnost tablet v tahu ze suchého pojiva Prosolv SMCC 90 a vliv tří koncentrací mazadla stearanu horečnatého na pevnost tablet z této látky. Výsledky byly srovnávány se stejným hodnocením u Avicelu PH 102. Testované koncenti-ace stearanu byly 0,4; 0,8 a 1,2 %. Tablety byly lisovány třemi lisovacími silami (3; 3,5 a 4 kN). Na základě získaných výsledků lze konstatovat, že samotný Prosolv SMCC 90 poskytuje při stejných lisovacích silách pevnější výlisky než Avicel PH 102. Z hlediska snížení pevnosti výlisků přídavkem stearanu horečnatého je suché pojivo Prosolv SMCC 90 mnohem méně citiivé než Avicel PH 102. U Avicelu PH 102 je výrazné snížení pevnosti zaznamenáno přídavkem 0,4 % stearanu horečnatého, což u Prosolvu SMCC 90 zaznamenáno nebylo. Významnější snížení pevnosti výlisků vykazuje tato látka až u koncentrace stearanu 0,8 %. Nejvyšší použitá koncentrace stearanu 1,2 % snižuje pevnost tablet z Prosolvu SMCC 90 u lisovacích sil 3,5 a 4 kN dvakrát méně než pevnost výlisků z Avicelu PH 102.

The present paper evaluated the tensile strength of tablets made from the dry binder Prosolv SMCC 90 and the influence of three concentrations of the lubricant magnesium stearate on the tensile strength of tablets manufactured firom this material. The results were compared with the same evaluation in Avicel PH102. The tested concentrations of the stearate were 0.4,0.8 and 1.2 %. The tablets were compressed by three press powers (3, 3.5, and 4 kN). On the basis of obtained results it can be stated that under the same press powers Prosolv SMCC 90 alone yields stronger compacts than Avicel PH 102. From the viewpoint of decreased strength of compacts by adding magnesium stearate, the dry binder Prosolv SMCC 90 is much less sensitive than Avicel PH 102. In Avicel PH 102 a marked decrease in tensile strength was recorded with an addition of 0.4 %, which was not observed with Prosolv SMCC 90. Amore significant decrease in the strength of compacts was shown by the substance not until a stearate concentration of 0.8 %. The highest employed stearate concentration of 1.2 % decreases the tensile strength of tablets made from Prosolv SMCC 90 in the press powers of 3.5 and 4 kN two times less than the tensile strength of the compacts from Avicel PH 102.

• Klíčová slova
• PROSOLV SMCC 90, AVICEL PH 102,
• MeSH
• farmaceutické pomocné látky MeSH
• pevnost v tahu účinky léků   MeSH
• stearany farmakologie   MeSH
• tablety normy   terapeutické užití   MeSH
• techniky in vitro MeSH

V práci byla hodnocena pevnost výlisků z mikrokrystalické celulózy dvou typů používaných jakosuchá pojiva v technologii přímého lisování tablet, a to Avicelu PH 102 a Avicelu PH 301. Dále bylhodnocen vliv tří koncentrací mazadla stearanu hořečnatého (0,4; 0,8; 1,2 %) na pevnost tabletz těchto látek. Tablety byly lisovány třemi lisovacími silami (3; 3,5 a 4 kN). Na základě získanýchvýsledků lze konstatovat, že Avicel PH 102 poskytuje při stejných lisovacích silách pevnější výliskynež Avicel PH 301. Dále bylo zjištěno, že koncentrace stearanu hořečnatého 0,4 % markantněsnižuje pevnost tablet v tahu z Avicelu PH 102, další markantnější snížení je u koncentrace 1,2 %.Snížení pevnosti výlisků z Avicelu PH 301 stearanem hořečnatým není tak výrazné jako u tabletz Avicelu PH 102 a u koncentrací stearanu 0,4 % a 1,2 % není oproti předcházejícím koncentracímrozdíl v pevnosti tak významný.

The paper evaluated the strength of compacts made of microcrystaUine cellulose of two types used as dry binders in the technology of direct compression of tablets, i.e. Avicel PH 102 and Avicel PH 301. The effect of three concentrations of the lubricant magnesium stearate (0.4; 0.8; 1.2 %) on the strength of tablets made from these substances was also evaluated. Tables were compressed using three forces of compression (3; 3.5, and 4 kN). On the basis of the obtained results it can be concluded that Avicel PH 102 provides, under identical forces of compression, stronger compacts than Avicel PH 301 does. It has been further found that a magnesium stearate concentration of 0.4 markedly decreases the tensile strength of Avicel PH 102 tablets, and another marked decrease is observed with a concentration of 1.2 %. The decrease in the tensUe strength of Avicel PH 301 compacts due to magnesium stearate is not so marked as in Avicel PH 102 tablets, and with stearate concentrations of 0.4 % and 1.2 % the difference in strength is not of such importance in comparison with the previous concentrations.

• Klíčová slova
• AVICEL PH 102, AVICEL PH 301,
• MeSH
• celulosa MeSH
• farmaceutické pomocné látky MeSH
• pevnost v tahu MeSH
• příprava léků metody   MeSH
• stearany MeSH
• tablety MeSH

The resistance of goose (Anser anser f. domestica) eggs to damage was determined by measuring the average rupture force, specific deformation and rupture energy during their compression at different compression speeds (0.0167, 0.167, 0.334, 1.67, 6.68 and 13.36 mm/s). Eggs have been loaded between their poles (along X axis) and in the equator plane (Z axis). The greatest amount of force required to break the eggs was required when eggs were loaded along the X axis and the least compression force was required along the Z axis. This effect of the loading orientation can be described in terms of the eggshell contour curvature. The rate sensitivity of the eggshell rupture force is higher than that observed for the Japanese quail's eggs.

• MeSH
• biomechanika MeSH
• husy * MeSH
• pevnost v tlaku * MeSH
• povrchové vlastnosti MeSH
• testování materiálů * MeSH
• vaječná skořápka MeSH
• vejce * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

PURPOSE: Investigation of trabecular bone strength and compaction is important for fracture risk prediction. At 1-2% compressive strain, trabecular bone undergoes strain softening, which may lead to numerical instabilities and mesh dependency in classical local damage-plastic models. The aim of this work is to improve our continuum damage-plastic model of bone by reducing the influence of finite element mesh size under large compression. METHODOLOGY: This spurious numerical phenomenon may be circumvented by incorporating the nonlocal effect of cumulated plastic strain into the constitutive law. To this end, an over-nonlocal implicit gradient model of bone is developed and implemented into the finite element software ABAQUS using a user element subroutine. The ability of the model to detect the regions of bone failure is tested against experimental stepwise loading data of 16 human trabecular bone biopsies. FINDINGS: The numerical outcomes of the nonlocal model revealed reduction of finite element mesh dependency compared with the local damage-plastic model. Furthermore, it helped reduce the computational costs of large-strain compression simulations. ORIGINALITY: To the best of our knowledge, the proposed model is the first to predict the failure and densification of trabecular bone up to large compression independently of finite element mesh size. The current development enables the analysis of trabecular bone compaction as in osteoporotic fractures and implant migration, where large deformation of bone plays a key role.

• MeSH
• algoritmy MeSH
• biologické modely * MeSH
• biomechanika fyziologie   MeSH
• fraktury kostí MeSH
• kosti a kostní tkáň fyziologie   MeSH
• lidé MeSH
• pevnost v tlaku fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem 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.

• 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

Osteoporosis-related vertebral body fractures involve large compressive strains of trabecular bone. The small strain mechanical properties of the trabecular bone such as the elastic modulus or ultimate strength can be estimated using the volume fraction and a second order fabric tensor, but it remains unclear if similar estimations may be extended to large strain properties. Accordingly, the aim of this work is to identify the role of volume fraction and especially fabric in the large strain compressive behavior of human trabecular bone from various anatomical locations. Trabecular bone biopsies were extracted from human T12 vertebrae (n=31), distal radii (n=43), femoral head (n=44), and calcanei (n=30), scanned using microcomputed tomography to quantify bone volume fraction (BV/TV) and the fabric tensor (M), and tested either in unconfined or confined compression up to very large strains (∼70%). The mechanical parameters of the resulting stress-strain curves were analyzed using regression models to examine the respective influence of BV/TV and fabric eigenvalues. The compressive stress-strain curves demonstrated linear elasticity, yielding with hardening up to an ultimate stress, softening toward a minimum stress, and a steady rehardening followed by a rapid densification. For the pooled experiments, the average minimum stress was 1.89 ± 1.77 MPa, while the corresponding mean strain was 7.15 ± 1.84%. The minimum stress showed a weaker dependence with fabric as the elastic modulus or ultimate strength. For the confined experiments, the stress at a logarithmic strain of 1.2 was 8.08 ± 7.91 MPa, and the dissipated energy density was 5.67 ± 4.42 MPa. The latter variable was strongly related to the volume fraction (R(2)=0.83) but the correlation improved only marginally with the inclusion of fabric (R(2)=0.84). The influence of fabric on the mechanical properties of human trabecular bone decreases with increasing strain, while the role of volume fraction remains important. In particular, the ratio of the minimum versus the maximum stress, i.e., the relative amount of softening, decreases strongly with fabric, while the dissipated energy density is dominated by the volume fraction. The collected results will prove to be useful for modeling the softening and densification of the trabecular bone using the finite element method.

• MeSH
• biologické modely MeSH
• biomechanika MeSH
• biomedicínské inženýrství MeSH
• hlavice femuru fyziologie   MeSH
• hrudní obratle fyziologie   MeSH
• kosti a kostní tkáň anatomie a histologie   fyziologie   radiografie   MeSH
• lidé středního věku MeSH
• lidé MeSH
• mechanický stres MeSH
• modul pružnosti MeSH
• patní kost fyziologie   MeSH
• pevnost v tlaku MeSH
• radius fyziologie   MeSH
• regresní analýza MeSH
• rentgenová mikrotomografie MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• techniky in vitro MeSH
• zobrazování trojrozměrné MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

We synthesized Fe foams using water suspensions of micrometric Fe2O3 powder by reducing and sintering the sublimated Fe oxide green body to Fe under 5% H2/Ar gas. The resultant Fe foam showed aligned lamellar macropores replicating the ice dendrites. The compressive behavior and deformation mechanism of the synthesized Fe foam were studied using an acoustic emission (AE) method, with which we detected sudden localized structural changes in the Fe foam material. The evolution of the deformation mechanism was elucidated using the adaptive sequential k-means (ASK) algorithm; specifically, the plastic deformation of the cell struts was followed by localized cell collapse, which eventually led to fracturing of the cell walls. For potential biomedical applications, the corrosion and biocompatibility characteristics of the two synthesized Fe foams with different porosities (50% vs. 44%) were examined and compared. Despite its larger porosity, the superior corrosion behavior of the Fe foam with 50% porosity can be attributed to its larger pore size and smaller microscopic surface area. Based on the cytotoxicity tests for the extracts of the foams, the Fe foam with 44% porosity showed better cytocompatibility than that with 50% porosity.

• MeSH
• akustika * MeSH
• biokompatibilní materiály chemie   toxicita   MeSH
• buněčné linie MeSH
• difrakce rentgenového záření MeSH
• elektrochemie metody   MeSH
• fibroblasty MeSH
• koroze MeSH
• myši MeSH
• pevnost v tlaku MeSH
• poréznost MeSH
• testování materiálů MeSH
• viskoelastické látky chemie   MeSH
• železité sloučeniny chemie   MeSH
• železo chemie   toxicita   MeSH
• zvířata MeSH
• Check Tag
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

The structure degradation and strength changes of calcium phosphate scaffolds after long-term exposure to an acidic environment simulating the osteoclastic activity were determined and compared. Sintered calcium phosphate scaffolds with different phase structures were prepared with a similar cellular pore structure and an open porosity of over 80%. Due to microstructural features the biphasic calcium phosphate (BCP) scaffolds had a higher compressive strength of 1.7 MPa compared with the hydroxyapatite (HA) and β-tricalcium phosphate (TCP) scaffolds, which exhibited a similar strength of 1.2 MPa. After exposure to an acidic buffer solution of pH = 5.5, the strength of the HA scaffolds did not change over 14 days. On the other hand, the strength of the TCP scaffolds decreased steeply in the first 2 days and reached a negligible value of 0.09 MPa after 14 days. The strength of the BCP scaffolds showed a steady decrease with a reasonable value of 0.5 MPa after 14 days. The mass loss, phase composition and microstructural changes of the scaffolds during degradation in the acidic environment were investigated and a mechanism of scaffold degradation was proposed. The BCP scaffold showed the best cell response in the in vitro tests. The BCP scaffold structure with the highly soluble phase (α-TCP) embedded in a less soluble matrix (β-TCP/HA) exhibited a controllable degradation with a suitable strength stability and with beneficial biological behavior it represented the preferred calcium phosphate structure for a resorbable bone scaffold.

• MeSH
• buněčná adheze MeSH
• DNA metabolismus   MeSH
• fosforečnany vápenaté chemie   MeSH
• keramika chemie   MeSH
• koncentrace vodíkových iontů MeSH
• kosti a kostní tkáň fyziologie   MeSH
• lidé MeSH
• mezenchymální kmenové buňky cytologie   MeSH
• pevnost v tlaku MeSH
• poréznost MeSH
• tkáňové podpůrné struktury chemie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

Vivapur® je mikrokrystalická celulosa vyráběná německou firmou J. Rettenmeier & Söhne GmbH+Co. a typy Vivapur 102 a 12 mají prioritní využití jako suchá pojiva pro přímé lisování tablet. V této práci byla hodnocena pevnost tablet z těchto látek a její ovlivnění přídavkem mazadla stearanu horečnatého v souvislosti s jeho koncentrací a podmínkami mísícího procesu, konkrétně dobou a intenzitou míšení. Testované koncentrace stearanu byly 0,4 a 0,8 %, testované doby míšení 2,5; 5; 10 a 20 minut, intenzity míšení 17 a 34 ot./min. Citlivost suchých pojiv na přídavek stearanu byla hodnocena pomocí hodnot LSR („lubricant sensitivity ratio"). Výsledky prokázaly vyšší citlivost na přídavek mazadla u Vivapuru 12 než u Vivapuru 102. V první části práce zaměřené na vliv koncentrace stearanu na pevnost tablet byl Vivapur 102 porovnán také s Avicelem PH-102. Tablety ze samotného Vivapuru 102 byly pevnější než z AviceluPH-102. Koncentrace stearanu 0,8 % snížila výrazněji pojivovou kapacitu Vivapuru 102 než Avicelu PH-102. S prodlouženou dobou míšení a zvýšenou intenzitou míšení se stearanem klesala pevnost tablet z obou typů Vivapuru, prodloužená doba míšení měla výraznější vliv u Vivapuru 12 a zvýšená intenzita míšení u Vivapuru 102.

Vivapur® is microcrystalline cellulose manufactured by the German firm J. Rettenmeier & Söhne GmbH+Co. The types Vivapur 102 and 12 enjoy priority use as dry binders for direct tablet compression. The present paper evaluates tensile strength of tablets made from these substances and the effect of an addition of the lubricant magnesium stearate in connection with its concentration and the conditions of the process of mixing, particularly the period and intensity of mixing. The tested concentrations of stearate were 0.4 and 0.8 %, the tested periods of mixing being 2.5, 5, 10, and 20 minutes, intensities of mixing 17 and 34 rot./min. Sensitivity of dry binders to added stearate was evaluated by means of the LSR (lubricant sensitivity ratio) values. The results demonstrated higher sensitivity to an addition of the lubricant in Vivapur 12 than in Vivapur 102. In the first part of the paper focused on the effect of stearate concentration on tensile strength of tablets, Vivapur 102 was also compared with Avicel PH-102. Tablets from Vivapur 102 alone were stronger than those from Avicel PH-102. A concentration of stearate of 0.8 % decreased the binding capacity of Vivapur 102 more than that of Avicel PH-102. With a prolonged period of mixing and increased intensity of mixing with stearate, tensile strength of tablets from both Vivapur types was decresed, and a prolonged period of mixing exerted a more marked effect on Vivapur 12 and increased intensity of mixing, on Vivapur 102.

• MeSH
• celulosa MeSH
• farmaceutické pomocné látky MeSH
• příprava léků MeSH
• stearany MeSH
• tablety MeSH