Wyniki wyszukiwania - BazTech

1

A micromechanical approach to numerical modeling of yielding of open-cell porous structures under compressive loads

Hedayati R., Sadighi M.

Journal of Theoretical and Applied Mechanics

|

2016

|

Vol. 54 nr 3

769--781

EN

Today, interconnected open-cell porous structures made of titanium and its alloys are replacing the prevalent solid metals used in bone substitute implants. The advent of additive manufacturing techniques has enabled manufacturing of open-cell structures with arbitrary micro-structural geometry. In this paper, rhombic dodecahedron structures manufactured using SLM technique and tested by Amin Yavari et al. (2014) are investigated numerically using ANSYS and LS-DYNA finite element codes for the modeling of the elastic and postyielding behavior of the lattice structure, respectively. Implementing a micro-mechanical approach to the numerical modeling of the yielding behavior of open-cell porous materials is the main contribution of this work.One of the advantages of micro-mechanical modeling of an open-cell structure is that, in contrast to the macro-mechanical finite element modeling, it is not necessary to obtain several material constants for different foam material models through heavy experimental tests. The results of the study showed that considering the irregularity in defining the cross-sections of the struts decreases both the yielding stress and densification strain of the numerical structure to the values obtained from the experimental tests. Moreover, the stress-strain curve of the irregular structure was much smoother in two points of yielding and densification, which is also observable in experimental plots. Considering the irregularity in the structure also decreased the elastic modulus of the lattice structure by about 20-30%. The post-densification modulus was more influenced by irregularity as it was decreased by more than 50%. In summary, it was demonstrated that using beam elements with variable cross-sections for constructing open-cell biomaterials could result in numerical results sufficiently close to the experimental data.

2

Atomic layer deposition of TiO2 onto porous biomaterials

Dobrzański L. A., Dobrzańska-Danikiewicz A. D., Szindler M., Achtelik-Franczak A., Pakieła W.

Archives of Materials Science and Engineering

|

2015

|

Vol. 75, nr 1

5--11

EN

Purpose: The aim of this article was to investigate the possibility of uniform coverage of porous biomaterials with a thin film of titanium oxide deposited using the atomic layer deposition method (ALD) Design/methodology/approach: The porous biomaterials were prepared by Selective Laser Melting (SLM) from Ti powder. The TiO2 thin films were prepared with use of atomic layer deposition method. The changes in surface topography was observed by the atomic force microscope AFM XE-100 and scanning electron microscope SEM. The measurement of thickness performed using spectroscopic ellipsometer. Findings: Results and their analysis have confirmed show that the atomic layer deposition (ALD) method allows the deposition of homogenous and uniform thin films of TiO2 with the desired geometric characteristics onto porous Ti biomaterials. Practical implications: The combination of porous substrate made from titanium which has good mechanical properties with a biocompatible titanium oxide provides practical possibilities of use for example in dental engineering. Originality/value: The combination of porous substrate made from titanium which has good mechanical properties with a biocompatible titanium oxide provides practical possibilities of use for example in dental engineering.

3

The novel semi-biodegradable interpenetrating polymer networks based on urethane-dimethacrylate and epoxy-polyester components as alternative biomaterials

Barszczewska-Rybarek I., Jaszcz K., Jurczyk S., Chladek G

Acta of Bioengineering and Biomechanics

|

2015

|

Vol. 17, no. 3

13--22

EN

Purpose: This paper presents the pilot study aimed at the development of new full interpenetrating polymer networks based on urethane-dimethacrylate and biodegradable epoxy-polyester as the proposition of new biomaterials with gradually emerging porosity. Methods: The urethane-dimethacrylate monomer was obtained from 4,4’-methylenebis(phenyl isocyanate) and tetraethylene glycol monomethacrylate. The redox-initiating system was employed for its radical polymerization. The epoxy-polyester was produced by oxidation of the polyester, synthesized from succinic anhydride and allyl glicydyl ether. It was cured in a step-growth process with biogenic, aliphatic amine – spermidine. The mixtures of both monomers with adequate curing agents were room temperature polymerized. The hardened materials were characterized for damping behavior and dynamic modulus, hardness, water sorption, the course of hydrolytic degradation as well as the morphology – before and during the degradation process. Results: The cured materials revealed the nonporous, dense morphology. In the hydrolytic environment, the epoxy-polyester network degraded and the porous urethane-dimethacrylate scaffold remained. The epoxy-polyester appeared to prevent the urethane-dimethacrylate from attaining a high degree of conversion, even if the polymerization rate and the molecular mobility of the latter one are higher than those of the epoxy-polyester. The most homogeneous material with the best physico-mechanical properties was obtained when the urethane-dimethacrylate content was smaller than the epoxy-polyester content, respectively 25 and 50 wt%. Conclusions: The system presented in this work could be useful in tissue engineering, where at the beginning of the tissue regeneration process it would meet the implant mechanical properties and then would deliver its porosity, facilitating the tissue regeneration process.

4

Surface treatment of porous Ti13Nb13Zr alloy for biomedical applications

Serbiński W., Zieliński A., Seramak T., Ossowska A., Sobieszczyk S., Supernak M., Majkowska B.

Inżynieria Materiałowa

|

2012

|

Vol. 33, nr 1

6--12

EN

The porous Ti13Zr13Nb alloy intended for load-bearing implants has been investigated. The alloy powder was obtained by plasma jet spraying a solid alloy sheet. Then the alloy granules were sintered by employing powder metallurgy, with and without a space holder, resulting in specimens demonstrating an open porous structure with a porosity up to 68% and mean pore size ranging between 30 and 150 μm. Further thermal, chemical and/or electrochemical oxidation caused increased corrosion resistance and the appearance of nanotubular titania layers after anodization, with nanotubes up to 2 μm in length and 80÷120 nm in diameter. The nanotubular layers were finally coated with deposits of hydroxyapatite obtained by using biomimetic or chemical (Alternate Immersion and biomimetic) methods. In conclusion, the employed surface techniques allow substantial improvement of the chemical stability, corrosion resistance, biocompatibility and bioactivity of the investigated titanium based biomaterial.

PL

Przeprowadzono badania materiału porowatego, przeznaczonego na implanty ortopedyczne, wytworzonego metodą metalurgii proszków ze stopu Ti13Zr13Nb. Proszki z badanego stopu uzyskano metodą rozpylania plazmowego. Były one następnie spiekane bez lub z użyciem porogenu. Otrzymano próbki o otwartej porowatej strukturze, stopniu porowatości do 68% i średniej wielkości porów w przedziale od 30 do 150 mikrometrów. Obróbka próbek porowatych – utlenianie termiczne, chemiczne i/lub elektrochemiczne spowodowało otrzymanie krystalicznych lub nanorurkowych warstw tlenkowych, składających się z nanorurek o długości do 2 μm i średnicy 80÷120 nm oraz zwiększenie ich odporności na korozję. Nanorurkowe warstwy tlenkowe zostały następnie pokryte hydroksyapatytem metodą biomimetyczną lub chemiczną (przemiennego zanurzenia). Podsumowując, zastosowane techniki obróbki powierzchniowej pozwalają na znaczną poprawę stabilności chemicznej, odporności korozyjnej, biozgodności i aktywności biologicznej biomateriałów o osnowie tytanu.

5

The influence of temperature and pore size on cell growth and proliferation on hydroxyapatite scaffolds

Soukup D., Bacakova M., Pabst W., Gregorova E., Bacakova L.

Engineering of Biomaterials

|

2012

|

Vol. 15, no. 116-117 spec. iss.

127

EN

Porous biomaterials, especially synthetic porous ceramics, are of significant importance in bone tissue engineering, and there has been rapid growth in the medical use of these biomaterials over the last 50 years. The reason is that they are relatively easy to prepare and are available in unlimited supply, unlike the allografts and autografts that are used in clinical practice. Various hydroxyapatite (HAp) scaffolds can be prepared, using various pore-forming techniques and firing temperatures. The firing temperature significantly affects microstructural parameters such as total porosity, pore size, the interconnected pore network, and also the chemical and phase composition. Last but not least, it also affects the mechanical properties of the samples. Knowledge about these factors is therefore essential for designing a sample with the desired controlled microstructure and properties. In this work, uniaxial pressing has been used for preparing HAp disks from nanocrystalline HAp powder, using saccharose as a pore-forming agent. The highest porosity achieved (after partial sintering at 800°C) was in the range of 64.7-70.6%. The firing temperature significantly affects porosity, pore size, grain size and mechanical strength, whereas the dwell time has only a minor effect on these parameters. After firing, XRD confirmed more than 98.4% HAp in all cases. Mercury porosimetry confirmed the presence of nanosized interstitial voids for partially sintered materials and pore throat sizes of approximately 100μm (much smaller than the pore cavities), which is adequate for bone cell penetration and further ingrowth. After firing at 1200°C, the matrix is more or less fully sintered, and nanosized pores are absent or closed. The biological part of the paper summarizes the results from cell-seeding and cultivation experiments to determine the cell adhesion, proliferation, viability, mitochondrial activity and osteogenic cell differentiation on the scaffolds, and thus the biocompatibility and bioactivity of the scaffolds. The highest values for all these parameters, particularly the number of cells, were on HAp fired at 1200°C. The samples fired at 1200°C were prepared with various pore sizes (in the range of 100 - 800μm). We found that pore size has a non-significant effect on cell colonization, whereas the firing temperature has a major influence. All tested HAp samples showed a remarkable ability to adsorb proteins on their surfaces, namely albumin and fibronectin, and to promote cell adhesion. Some cytotoxic activity was observed on the samples fired at 800 and 1000°C. Possible reasons for this cytotoxicity have been discussed. However, it can be concluded that the HAp samples created in this study and fired at 1200°C hold great promise for bone tissue engineering.

6

Analiza procesów zachodzących podczas ściskania porowatej stali 316L do zastosowań biomedycznych

Grądzka-Dahlke M.

Eksploatacja i Niezawodność

|

2010

|

nr 4

16-22

PL

Porowate biomateriały metaliczne są atrakcyjnym materiałem implantacyjnym ze względu na większe od tradycyjnych stopów dopasowanie modułu sprężystości do kości oraz na możliwość przerastania porów tkanką kostną i zapewnienia właściwego mocowania implantu w kości. Materiałom tym stawiane są jednak wysokie wymagania, aby zagwarantować odpowiednią trwałość wszczepu. Wśród tych wymogów są m.in. właściwości mechaniczne, szczególnie wytrzymałość zmęczeniowa, a także właściwości magnetyczne. Wszystkie stosowane obecnie stopy implantacyjne (stale chromowo-niklowe, stopy kobaltu i stopy niklu) są paramagnetykami. Jednak na skutek cyklicznych obciążeń, którym poddawane są implanty podczas eksploatacji w organizmie w niektórych materiałach mogą zajść przemiany strukturalne, zmieniające także właściwości użytkowe biomateriałów. W pracy analizowano zmiany zmęczeniowe, zachodzące pod wpływem obciążeń cyklicznych w porowatych spiekach ze stali 316L, przeznaczonych na implanty biomedyczne oraz ich wpływ na właściwości magnetyczne materiałów. Na podstawie wyników badań można stwierdzić, że spieki porowate wykazują początkowe osłabienie, a następnie stabilizację zmęczeniową w badanym zakresie odkształceń. Badania magnetyczne pokazały, że wraz ze wzrostem stopnia odkształcenia rośnie wartość magnetyzacji spieków ze stali 316L, co może mieć wpływ na właściwości użytkowe tych materiałów.

EN

The porous metallic biomaterials are to be considered very attractive implant materials due to the matching of their elastic modulus to the bone as well as the possibility of bone tissue ingrowth into pores and assurance of good stabilization if implant. High requirements are set though to ensure proper durability. Among these are mechanical properties, especially fatigue strength and magnetic properties. All of recently used implant alloys (Cr-Ni steel, cobalt or titanium alloys) are paramagnetic. However, cyclic stress that implants must stand during exploitation, may cause structural as well as functional changes in biomaterials. In presented work, fatigue changes occurring during cyclic stresses in porous sinters of 316L steel were analyzed, as well as their influence on magnetic properties of investigated materials. The obtained results showed that initial weakening and then fatigue stabilization was observed in the whole range of analyzed strain. The magnetic research indicated magnetization increase as an effect of rising strain. This can affect functional properties of implant materials.