Papers by Keyword: Degradation

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Authors: Luca Giordano, Giuseppe Mancini, Francesco Tondolo
Abstract: Bond between steel and concrete in reinforced concrete structures plays a fundamental role. The stress transfer mechanism depends on the condition of the contact surface between the two materials, the mechanical characteristics of concrete near the rebar and on the available level of confinement. Corrosion of reinforcing bars in concrete structures modifies those three factors. Because of corrosion, on the rebar surface a granular oxide layer is present and with its expansion it generates a significant radial pressure; consequently tensile stresses grow till cracking of the concrete cover with a subsequent reduction of the confinement effect. Moreover the presence of a mechanical action modifies the resisting mechanism producing an increasing damage. In this study, a model is presented for the numerical simulation of experimental tests on r.c. ties subjected to mechanical action; furthermore some considerations on reinforced concrete ties subjected also to corrosion effect are reported. From those analyses it is possible to estimate a modified bond-slip law between the reinforcing bars and the concrete, in order to take into account the level of damage.
349
Authors: Maria Elisa Rodrigues Coimbra, Carlos Nelson Elias, Paulo Guilherme Coelho
Abstract: The objective of this study was to physico/chemically characterize a commercially available and a newly developed Bioglass and also to evaluate their degradation properties. Materials and Method: Two bioresorbable glasses were utilized, a bioglass synthesized at Chemical Engineering College (University of São Paulo, Lorena, São Paulo) (BG1), and the other bioglass utilized was Biogran (BG2) (3i Implant Innovations, Brazil). Particles size distribution histograms were developed for both materials, and then they were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) before and after immersion in simulated body fluid (SBF) for 30, 60, and 90 days. Results: The particle size distribution showed that the mean particle diameters at 10%, 50%, and 90% of the total volume were 17.65, 66.18, and 114.71 µm for BG1, and 354.54, 437.5, 525.00 µm for BG2. SEM images of BG1 showed that the as-received material had a rough surface and as the time of degradation elapsed, this surface became smooth. The images of BG2 showed that the as-received material also had a rough surface, and after immersion in SBF, the material’s crystalline content/morphology could be observed. The X-ray diffraction recorded that BG1 showed a silica peak, not seen at BG2. FTIR revealed that both bioglasses were of similar composition, except for the CO3-carbonate minor peak, present at the BG2 sample. Conclusions: 1. The particle size distribution showed a polydispersed pattern for both materials. 2. The material suffered degradation, and the decomposition increased as a function of immersion in SBF. 3. Both bioglasses had similar composition.
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Authors: Yan Mei Chen, Ting Fei Xi, Yu Dong Zheng, Yi Zao Wan
Abstract: The nanocomposite of nano-hydroxyapatite/bacterial cellulose (nHA/BC) obtained by depositing in simulated body fluid (SBF), incorporating their excellent mechanical and biological properties, is expected to have potential applications in bone tissue engineering. However, the biological response evaluation of biomaterials is required to provide useful information to improve their design and application. In this article, the in vitro cytotoxicity of composites nHA/BC as well as its degradation residues was studied. Scanning electron microscopy (SEM) was used to observe the morphology of original materials and their degradation residues. The degree of degradation was evalued by measuring the concentration of reducing sugar (glucose) by ultraviolet spectrophotometer. Bone-forming osteoblasts (OB) and infinite culture cell line L929 fibroblasts were used to measure the cytotocixity of materials with MTT assay. Both kinds of cells in infusion proliferate greatly in a normal form and their relative growth rate (RGR) exceeds by 75%, which shows the cytotoxicity of materials is graded as 0~1, according to the national standard. Nevertheless, bone-forming OB cells, as a kind of target cells, are more susceptive on the cytotoxicity than infinite culture fibroblast cells L929. The results suggest the nanocomposite of nHA/BC without cytotoxicity is greatly promising as a kind of scaffold materials for bone tissue engineering and tissue functional cells are more suited to evaluate the cytotoxicity of biomedical materials.
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Authors: Cheng Long Liu, Jiang Jiang, Meng Wang, Yue Ji Wang, Paul K Chu, Wei Jiu Huang
Abstract: Successful application of magnesium alloys as degradable load-bearing implants is determined by their biological performance especially degradation and corrosion behavior in the human body. Three magnesium alloys, namely WE43, ZK60, and AZ91 are investigated in this work. The in vitro degradation behavior, cytotoxicity, and genotoxicity are evaluated by corrosion tests, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and micronuclei tests, respectively. Immersion tests indicate that the ZK60 alloy has the best corrosion resistance and lowest corrosion rate in Hank’s solution, followed by AZ91 alloy and WE43 alloy in that order. The MTT results obtained from the three magnesium alloys after 7 days of immersion indicate good cellular viability. However, excessively high aluminum and magnesium concentrations have a negative influence on the genetic stability.
2008
Authors: Naznin Sultana, Min Wang
Abstract: Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) was used to make composite scaffolds for bone tissue engineering in our previous studies. To control the degradation rate and process of composite scaffolds, PHBV was blended with poly(L-lactic acid) (PLLA), which has a much higher degradation rate than PHBV, and PHBV/PLLA blends were used as polymer matrices for composite scaffolds. Composite scaffolds based on these blends and containing nano-sized hydroxyapatite (nHA) were fabricated using an emulsion freezing / freeze-drying technique. Non-porous films of PHBV/PLLA blends were prepared using the solvent casting method. In vitro degradation tests of non-porous PHBV/PLLA blends and porous composite scaffolds were conducted by immersing samples in phosphate buffered saline (PBS) for various periods of time. It was found that the composition of polymer blends affected water uptake of films and scaffolds. For PHBV/PLLA-based scaffolds, the incorporated nHA particles also significantly increased water uptake within the initial immersion time. Both PHBV/PLLA blends and composite scaffolds underwent rapid weight losses within the first few weeks. The degradation of composite scaffolds arose from the dissolution of nHA particles and degradation of the PLLA component of polymer blends. Composite scaffolds exhibited enhanced adsorption of bovine serum albumin (BSA), a model protein, in the current study.
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Authors: Yong Tang Jia, Xiang Ying Zhu, Qing Qing Liu
Abstract: The ultrafine fibers of poly(ε-caprolactone) (PCL) composited with different Polyvinyl Pyrrolidone (PVP) content were successfully prepared by electrospinning method. The morphology, hydrophilicity and in vitro degradation behavior of samples were characterized by Scanning Electron Microscopy (SEM), water contact angle and weight loss rate. Pore size and distribution on the fibers changed with the increase of PVP content. The hydrophilicity of PCL membrane was improved by addition of PVP. When the content of PVP was 25% and 50%, the water contact angle approached zero. The degradation was essentially a dissolution process of PVP on the first 7days. Since large specific surface, high porosity and different crystallinity, percent degradation loss of electrospun fiber membranes were about 1 to 12 times higher than that of cast films.
1330
Authors: Maria Elisa Rodrigues Coimbra, Márcia Gouvea Bernardes, Carlos Nelson Elias, Paulo Guilherme Coelho
Abstract: This study evaluated the in vitro degradation of pellet, powder and plates of poly-L-DL-lactic acid (PLDLLA) after two processing methods. Part of the material was reduced to powder by cryogenic milling and part of it molded injected in plate form. The crystallinity was evaluated by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Gel Permeation Chromatography (GPC) before and after immersion in simulated body fluid for 30, 60, and 90 days. The glass transition temperature (Tg) of the pellets and the powder were 61.5°C, 66°C. The Tgs of the plates ranged from 59.55°C to 63.06°C. Their endothermic peaks were observed at 125°C and 120°C, which was not identified to the plates samples. The FTIR spectrum showed bands of amorphous and crystalline content. The XRD results showed a peak related to the crystalline content, and a wide reflection related to the amorphous content. The milling process increased the crystallinity and the molding injection decreased it.
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Authors: A. Adamus, J. Jozwiakowska, R.A. Wach, D. Suarez-Sandoval, K. Ruffieux, J.M. Rosiak
Abstract: Poly (L-lactic acid) (PLLA) and composite of PLLA with osteoconductiveβ-tricalcium phosphate fine powder (PLLA/TCP) compression moulded specimens were subjected to in vitro biodegradation up one year. Samples were investigated in terms of physical-chemical evaluation after several periods of incubationin simulated body fluid solution. Reduction in PLLA molecular weights occurred during thermal processing of compounding of the polymer with TCP. 3-point bending measurements revealed some decay in the flexural strength and increase in stiffness after incorporation of the inorganic particles into the polymer. Those parameters remained nearly stable during the biodegradation period despite constant drop of polymer molecular weight. Thermal properties of both kinds of samples did not changed significantly, however degree of crystallinity of PLLA matrix was increasing slowly in pure PLLA samples. Despite no mass loss,extent of surface deteriorationincreased steady during the incubation. Current study is intended to develop material for implants, mainly fusion cages targeted for spinal applications.
283
Authors: Yan Mei Chen, Ting Fei Xi, Yu Feng Zheng, Liang Zhou, Yi Zao Wan
Abstract: Nano-bacterial cellulose (nBC), secreted by Acetobacter xylinum, is expected to have potential applications in tissue engineering. In this paper, the in-vitro degradation performance and the corresponding mechanism of nBC immersed in phosphate buffer solution (PBS) for different time periods was investigated. The pH value variation of solution, material degradation, and the swelling and structural changes of nBC was analysed successively. The results indicate that water molecules attack the exposed nBC fibrils, weakening the bonding strength of inter- and intra-molecular chains and disconnecting partial C-O-C bonds. The disconnection of C-O-C bonds is considered the primary reason for the degradation of nBC large molecular chains after nBC is immersed in PBS. The present work is instructive for controlling the in-vivo degradation performance of nBC acting as bone tissue engineered scaffold materials.
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Authors: Hyung Seok Lee, Martin Domeij, Carl Mikael Zetterling, Mikael Östling
Abstract: 4H-SiC BJTs have been fabricated with varying geometrical designs. The maximum value of the current gain was about 30 at IC=85 mA, VCE=14 V and room temperature (RT) for a 20 μm emitter width structure. A collector-emitter voltage drop VCE of 2 V at a forward collector current 55 mA (JC = 128 A/cm2) was obtained and a specific on-resistance of 15.4 m2·cm2 was extracted at RT. Optimum emitter finger widths and base-contact implant distances were derived from measurement. The temperature dependent DC I-V characteristics of the BJTs have been studied resulting in 45 % reduction of the gain and 75 % increase of the on-resistance at 225 oC compared to RT. Forward-bias stress on SiC BJTs was investigated and about 20 % reduction of the initial current gain was found after 27.5 hours. Resistive switching measurements with packaged SiC BJTs were performed showing a resistive fast turn-on with a VCE fall-time of 90 ns. The results indicate that significantly faster switching can be obtained by actively controlling the base current.
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