scholarly journals A Nanoindentation Approach for Time-Dependent Evaluation of Surface Free Energy in Micro- and Nano-Structured Titanium

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 287
Author(s):  
Serena De Santis ◽  
Edoardo Rossi ◽  
Marco Sebastiani ◽  
Simona Sennato ◽  
Edoardo Bemporad ◽  
...  
Keyword(s):  
Tissue Engineering ◽  
Free Energy ◽  
High Resolution ◽  
Sample Preparation ◽  
Surface Free Energy ◽  
Time Dependent ◽  
Long Term Stability ◽  
Titanium Surfaces ◽  
Non Destructive

Surface free energy (SFE) of titanium surfaces plays a significant role in tissue engineering, as it affects the effectiveness and long-term stability of both active coatings and functionalization and the establishment of strong bonds to the newly growing bone. A new contact–mechanics methodology based on high-resolution non-destructive elastic contacting nanoindentation is applied here to study SFE of micro- and nano-structured titanium surfaces, right after their preparation and as a function of exposure to air. The effectiveness of different surface treatments in enhancing SFE is assessed. A time-dependent decay of SFE within a few hours is observed, with kinetics related to the sample preparation. The fast, non-destructive method adopted allowed for SFE measurements in very hydrophilic conditions, establishing a reliable comparison between surfaces with different properties.

scholarly journals Novel blood protein based scaffolds for cardiovascular tissue engineering

2016 ◽  
Vol 2 (1) ◽  
pp. 5-9 ◽  
Author(s):  
Antonia I. Kuhn ◽  
Marc Müller ◽  
Sara Knigge ◽  
Birgit Glasmacher
Keyword(s):  
Tissue Engineering ◽  
Fibre Diameter ◽  
Final Concentration ◽  
Blood Protein ◽  
Cross Linking ◽  
Blood Proteins ◽  
Cardiovascular Tissue ◽  
Long Term Stability ◽  
Cardiovascular Tissue Engineering

AbstractA major challenge in cardiovascular tissue engineering is the fabrication of scaffolds, which provide appropriate morphological and mechanical properties while avoiding undesirable immune reactions. In this study electrospinning was used to fabricate scaffolds out of blood proteins for cardiovascular tissue engineering. Lyophilised porcine plasma was dissolved in deionised water at a final concentration of 7.5% m/v and blended with 3.7% m/v PEO. Electrospinning resulted in homogeneous fibre morphologies with a mean fibre diameter of 151 nm, which could be adapted to create macroscopic shapes (mats, tubes). Cross-linking with glutaraldehyde vapour improved the long-term stability of protein based scaffolds in comparison to untreated scaffolds, resulting in a mass loss of 41% and 96% after 28 days of incubation in aqueous solution, respectively.

Structural characterization of free-standing gallium arsenide coiled membranes produced by micromachining

1999 ◽  
Vol 32 (1) ◽  
pp. 60-64
Author(s):  
Krishan Lal ◽  
S. Niranjana N. Goswami ◽  
J. Miao ◽  
H. L. Hartnagel
Keyword(s):  
High Resolution ◽  
Beam Width ◽  
Thin Strip ◽  
X Ray Diffraction ◽  
Free Standing ◽  
X Ray ◽  
Long Term Stability ◽  
Diffraction Peaks

High-resolution X-ray diffraction techniques have been employed successfully to evaluate crystalline quality and long-term stability of coiled membranes. The process of fabrication involves photolithography, implantation by 2 MeV N^{2+} ions inn-type GaAs substrates, followed by selective etching. A five-crystal X-ray diffractometer was employed in (+, −, +) setting with an Mo Kα1exploring beam for high-resolution X-ray diffractometry and topography experiments. The exploring-beam width was reduced to illuminate different segments of the coiled membrane. Diffraction curves recorded from the bulk crystal surrounding the sensor had a half width of 26 arcseconds, whereas the half widths from sensor segments were in the range ∼58 to ∼166 arcseconds. Different segments (particularly vertical ones) were identified from the observed angular separations between different diffraction peaks as well as from the shape of the diffraction peaks. It was found that different segments of the sensor were tilted with respect to one another and the tilt angles were in the range 15–212 arcseconds. High-resolution X-ray diffraction topographs recorded from (5\bar 11) and (400) diffracting planes revealed that the sides of the trough below the membrane created by etching are not vertical, but tapered. Also, there is a thin strip of crystal freely hanging over the tapered regions as a result of underetching. The surface of the cavity is uneven. The structural perfection of different membrane segments could also be ascertained from the contrast in topographs.

Numerical Investigation on Factors Influencing the Time-Dependent Stability of the Rock Slopes with Weak Structure Planes

2013 ◽  
Vol 353-356 ◽  
pp. 177-182
Author(s):  
Lian Chong Li ◽  
Shao Hua Li
Keyword(s):  
Rock Mass ◽  
Rock Slope ◽  
Failure Time ◽  
Time Dependent ◽  
Catastrophic Failure ◽  
Long Term Stability ◽  
Stability Of Slopes ◽  
Factors Influencing ◽  
Weak Structure

Under the combined effects of various external factors, such as temperature, seepage, alternate wetting and drying and so on, the mechanical properties of rock mass are susceptible to be deteriorated, and its strength characteristics are significantly degraded with time. The mesoscopic damage accumulated inside the rock, contributing the rock slope instability with weak structure planes, generate the time-dependent deformation, and eventually lead to the slope failure. Given the time-dependent deformation of the rock, numerical simulations are conducted to investigate the key factors influencing the long-term stability of slopes. Numerical results show that the catastrophic failure time of slopes is linear to its cohesion, and the bigger cohesion and friction angle increase catastrophic failure time, i.e., the stability of rock slope increase. In addition, the configuration of the intact rock bridge can also influence the time-dependent slope stability. Slope height can significantly affect the slope stability and the maximum horizontal displacement. Differences in rock mass storage environment play an important role in the long-term stability of slopes.

THE ENERGY OF ALPHA PARTICLES FROM U234, U238, AND Th232

1957 ◽  
Vol 35 (3) ◽  
pp. 258-270 ◽  
Author(s):  
B. G. Harvey ◽  
H. G. Jackson ◽  
T. A. Eastwood ◽  
G. C. Hanna
Keyword(s):  
Standard Deviation ◽  
High Resolution ◽  
Ionization Chamber ◽  
Pulse Generator ◽  
Low Noise ◽  
Alpha Particles ◽  
Pulse Rise Time ◽  
Long Term Stability ◽  
Two Parameter

The α-particle energies of U234, U238, and Th232 have been measured with a grid ionization chamber. The electronic equipment was designed to provide low noise, high resolution, and good long term stability. Ra226, Em222, Po218, Po214, and Po210 were used as energy standards. An investigation was made of the corrections to the measurements due to variation in pulse rise-time, source thickness, and imperfect shielding of the collector by the grid. It was found that the experimentally observed resolution was satisfactorily accounted for by the combination of these factors and the noise and ionization straggling.Alpha particle pulse heights were measured in terms of the output of a precision pulse generator. The corrected pulse heights were related to the energies of the standard sources by a two-parameter least squares calculation; the standard deviation was never greater than 5 kev. On extrapolating to zero ionization the line so obtained intercepted the energy axis at 83 kev. The α-particle energies deduced using this line were: U234 4.768 ± 0.003, U238 4.195 ± 0.005, Th232 4.007 ± 0.005 Mev.

scholarly journals Design Study of Steel Fibre Reinforced Concrete Shaft Lining for Swelling Ground in Toronto, Canada

2021 ◽  
Vol 11 (8) ◽  
pp. 3490
Author(s):  
Min Seong Kim ◽  
Sean Seungwon Lee
Keyword(s):  
Reinforced Concrete ◽  
Steel Fibre ◽  
Time Dependent ◽  
Fibre Reinforced Concrete ◽  
Swelling Behaviour ◽  
Steel Fibre Reinforced Concrete ◽  
Long Term Stability ◽  
Shaft Lining ◽  
Installation Time

Reinforced concrete (RC) is a widely used construction material around the world. RC has many advantages in terms of structural stability. However, the reinforcement of RC requires extensive labour costs. Steel fibre reinforced concrete (SFRC) has been widely studied to replace steel bars in concrete structures over the decades. However, most underground structures, such as tunnel lining, are usually designed using conventional RC for long-term stability due to unexpected geotechnical characteristics, such as directional and depth-dependent varied lateral pressure, earthquakes, groundwater, and time-dependent swelling behaviour. In this paper, an alternative design of shaft structure using SFRC, based on the original RC designed data in the Toronto region, was studied to evaluate the feasibility of SFRC replacing conventional RC. A key geological feature of the site is that the bedrock is comprised of Georgian Bay shale, which exhibits long-term time-dependent deformation (TDD). The capacities of RC and SFRC for the shaft lining were calculated based on the Canadian concrete design codes CSA A23.3 and RILEM TC 162-TDF, to assess the benefit of adding steel fibre, and several analytical solutions were used to calculate the applied load on the lining. A specialised TDD constitutive model in Fast Lagrangian Analysis of Continua (FLAC) 2D was developed to estimate whether the optimum installation time of the shaft lining, based on the geological reports, is appropriate under swelling behaviour, and evaluate the resultant long-term stability. The calculated hoop thrust and bending moment for several loading cases were within the capacity of the SFRC shaft lining. The numerical analysis demonstrated that the proposed lining installation time could be reduced, despite consideration of the long-term TDD behaviour.

scholarly journals Soft Devices for High-Resolution Neuro-Stimulation: The Interplay Between Low-Rigidity and Resolution

2021 ◽  
Vol 3 ◽  
Author(s):  
Ieva Vėbraitė ◽  
Yael Hanein
Keyword(s):  
High Resolution ◽  
State Of The Art ◽  
Neural Tissue ◽  
Great Promise ◽  
Low Resolution ◽  
Term Stability ◽  
Long Term Stability ◽  
Tremendous Progress ◽  
Technological Perspective

The field of neurostimulation has evolved over the last few decades from a crude, low-resolution approach to a highly sophisticated methodology entailing the use of state-of-the-art technologies. Neurostimulation has been tested for a growing number of neurological applications, demonstrating great promise and attracting growing attention in both academia and industry. Despite tremendous progress, long-term stability of the implants, their large dimensions, their rigidity and the methods of their introduction and anchoring to sensitive neural tissue remain challenging. The purpose of this review is to provide a concise introduction to the field of high-resolution neurostimulation from a technological perspective and to focus on opportunities stemming from developments in materials sciences and engineering to reduce device rigidity while optimizing electrode small dimensions. We discuss how these factors may contribute to smaller, lighter, softer and higher electrode density devices.

A Numerical Investigation on Time-Dependent Failure of Tunnels Based on the Long-Term Strength Characteristics of Rocks

2014 ◽  
Vol 580-583 ◽  
pp. 1315-1320
Author(s):  
Lian Chong Li ◽  
Meng Xing
Keyword(s):  
Numerical Model ◽  
Model Test ◽  
Failure Modes ◽  
Physical And Mechanical Properties ◽  
Time Dependent ◽  
Rock Mechanic ◽  
Long Term Stability ◽  
Numerical Experimentation ◽  
Accelerated Creep

How to establish the proper rheological model to describe and simulate the relationship between rock mechanic characteristics and time is one of the difficulties in the tunnel long-term stability analysis. In this paper, a numerical model to replicate the time-dependent deformation of rock mass was presented. In the model, the time-dependent deformation is described in terms of degradation of intrinsic physical and mechanical properties of rock and accumulation of mesoscopic damage inside the rock. Based on the model, uniaxial numerical experimentation and tunnel numerical model test are numerically constructed and investigated respectively. The model well reflects the initial creep, steady creep of rock and accelerated creep, which preliminary prove the validity of the proposed model. The results of the tunnel numerical model test show that the displacement curves from the numerical simulation were generally consistent with those from physical model tests. Furthermore, the macroscopic failure modes and local mesoscopic damage evolution of the tunnels were simulated.

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