scholarly journals Hindfoot Bone Viscoelasticity and Stress Relaxation

2019 ◽  
Vol 4 (4) ◽  
pp. 2473011419S0040
Author(s):  
Michelle M. Son ◽  
L. Daniel Latt
Keyword(s):  
Stress Relaxation ◽  
Testing Machine ◽  
Peak Load ◽  
Distal Tibia ◽  
Compressive Load ◽  
Compressive Force ◽  
Test Machine ◽  
Trabecular Thickness ◽  
Time Period ◽  
Time Periods

Category: Ankle, Ankle Arthritis, Basic Sciences/Biologics, Hindfoot Introduction/Purpose: Hindfoot arthrodeses have a non-union rate as high as 40%. Compression at the arthrodesis site plays a key role in stimulating bone growth leading to successful fusion. The ability to obtain and maintain compression depends not only on the surgical technique and the hardware which develop the compressive force but also on the response of the bone to compression. Bone, like other musculoskeletal tissues, is viscoelastic meaning that it has properties of both fluids and solids. Because bone is viscoelastic, it experiences stress relaxation (decrease in compressive force over time). The rate and magnitude of such stress relaxation is unknown. Our primary objective was to quantify stress relaxation of the hindfoot bones when subjected to a fixed compression displacement as would be done during arthrodesis. Methods: 10 human cadaveric bone cylinders measuring 10 mm in both diameter and height were cut from the articular surfaces of the talus, calcaneus, and distal tibia using a disposable cylindrical osteochondral harvester (OATS, Arthrex inc, Naples, FL). Each bone cylinder sample included subchondral and trabecular bone, and articular cartilage was removed during preparation. Each sample was scanned with a micro-computed tomography (uCT) scanner (Biomedical Micro CT Scanner, Scanco Medical, Switzerland) to quantify bone volume/total volume ratio (BV/TV), trabecular thickness, trabecular separation, trabecular number, and connectivity density. Each specimen was submerged in a saline bath and compressed by 1 mm at a strain rate of 1mm/sec using a material testing machine (System 810, MTS Systems, Eden Prairie, MN), and load data was gathered by an Interface load cell. Displacement was held constant for 3 hours, after which each sample was removed from the test machine and immediately rescanned with the uCT scanner. Results: The ensemble load curve of the ten samples displayed uniform exponential decay. After the initial load was placed on the bone, a steep, negative load velocity was apparent. Rapid decay occurred within the first 3 minutes, after which the load plateaued, holding constant over the subsequent 3 hours of compression. The average peak load was 515.53 N (SD: 254.58 N). The average percent load loss was 65.77% over 30 minutes (SD: 20.95%). Discrete time periods (B1, B2, B3, B4) were established corresponding to 0-3 min, 3-10 min, 10-20 min, and 20-30 min, respectively. Time periods B1, B2, B3, and B4 demonstrated an average percent load loss per time period of 43.35% (SD: 10.09%), 13.80% (SD: 14.77%), 18.65% (SD: 24.97%) and 7.95% (SD: 13.37%), respectively. Conclusion: Our data suggest that a significant percentage of compressive load placed across a bone is lost within the first 3 minutes as compared to any subsequent time period. Moreover, approximately 65.77% of the compressive load is lost over the first 30 minutes. These data suggest that when performing arthrodesis with compressive hardware, the majority of the initially applied compressive load may dissipate over the first 3-30 minutes, which may contribute to nonunion. Thus, a re-tightening of screws after 5-30 minutes or the use of a continuous compressive device may help to maintain compression at the arthrodesis site throughout healing.

scholarly journals Viscoelastic Properties of the Hindfoot Bones

2018 ◽  
Vol 3 (3) ◽  
pp. 2473011418S0045
Author(s):  
Michelle Son ◽  
Brent Munroe
Keyword(s):  
Stress Relaxation ◽  
Exponential Decay ◽  
Viscoelastic Properties ◽  
Peak Load ◽  
Distal Tibia ◽  
Bony Union ◽  
Load Relaxation ◽  
Trabecular Thickness ◽  
Trabecular Separation ◽  
Trabecular Number

Category: Hindfoot Introduction/Purpose: Obtaining and maintaining compression at an arthrodesis site is a key factor in achieving successful bony union. Bones, like other collagen containing tissues, are known to exhibit viscoelastic properties that may lead to stress relaxation at the arthrodesis site. The viscoelastic properties of the hindfoot bones when subjected to compression (as occurs during fusion surgery) are not known. The objective of this study was to quantify the viscoelastic properties of hindfoot bones under compression by measuring the time course of stress relaxation. Methods: 19 cadaveric human bone cubes 10 mm on each side consisting of trabecular and subchondral bone were cut from the hindfoot bones including the talus, calcaneus, and distal tibia. Each cube was scanned with micro computed tomography (µCT) to quantify bone volume/total volume ratio (BV/TV), trabecular thickness, trabecular separation, trabecular number, and connectivity density. Each specimen was then immersed in a saline bath and compressed 1 mm at a strain rate of 1 mm/s using an MTS machine (Fig 1). This compressed position was then held for 3 hours while the load was recorded. Following the compression test, each specimen was re-scanned with µCT. Results: Two distinct patterns of load relaxation were found. The first consisted of a uniform exponential decay. The second had a similar exponential decay but included a plateau occurring between 1-6 minutes. This second pattern was reflected in the average fractional load relaxation graph (Fig 2). The average peak load was 24.14 kg (SD ± 15.07 kg) and average end relaxation was 2.93 kg (SD ± 3.81 kg). The average time to achieve 95% decay in total load was 34.7 min (SD ± 29.1 min) although removing some outliers, it decreased to 24.9 min (SD ± 18.4 min) which is more representative of the overall data. Averages of BV/TV, trabecular thickness, and trabecular separation increased after stress relaxation while average connectivity density and trabecular number decreased. Conclusion: These data suggest that, due to the viscoelastic properties of bone, approximately 95% of an applied compressive load generated by a fixed displacement is lost within the first 30 minutes. Applied clinically, these findings may have a significant impact on the optimal surgical technique used for osteosynthesis and arthrodesis. Specifically, these data call into question whether the compression applied during surgery can be maintained throughout the healing phase without the application of continuous compression via an external fixator or internal continuous compression device. At minimum, these data suggest that lag or compression screws should be retightened prior to wound closure.

scholarly journals Evaluating the Hardness Characteristics of Hail through Compressive Strength Measurements

2015 ◽  
Vol 32 (11) ◽  
pp. 2100-2113 ◽  
Author(s):  
Ian M. Giammanco ◽  
Tanya M. Brown ◽  
Rosemarie G. Grant ◽  
Douglas L. Dewey ◽  
Jon D. Hodel ◽  
...  
Keyword(s):  
Compressive Stress ◽  
Field Measurement ◽  
Testing Machine ◽  
Impact Resistance ◽  
Compressive Load ◽  
Compressive Force ◽  
Measurement Device ◽  
Cross Sectional ◽  
Pass Filter ◽  
Low Pass Filter

AbstractThroughout historical literature anecdotal or visual observations have been used to describe the hardness property of hailstones (e.g., hard, soft, slushy). A unique field measurement device was designed and built to apply a compressive force to the point of fracture on hailstones in the field. The device uses a pistol-grip clamp to apply a compressive load to a hailstone and integrates a fast-response load cell and associated data acquisition components to measure the applied force through the point of fracture. The strain rate applied to the stone is fast enough to produce a brittle failure, and the peak compressive force is appropriately scaled by the cross-sectional area to produce a compressive stress value. When compared to an Instron universal testing machine (UTM), the field measurement device exhibited a low bias induced by measurement hardware sampling limits. When a low-pass filter was applied to the Instron data to replicate the hardware properties of the field measurement device, good agreement was found for compressive force tests performed on laboratory ice spheres, and it was clear the device was capturing a relative measure of strength. The mean compressive stress for natural hail was similar to that of pure ice spheres, but individual thunderstorm events exhibited variability. Laboratory ice spheres also showed significant variability, which argues for large sample sizes when testing any material for impact resistance.

Stress Relaxation of NR and NBR: Comparison of Measured Data with Reduced Variables Estimates

1984 ◽  
Vol 57 (2) ◽  
pp. 254-264 ◽  
Author(s):  
U. Meier ◽  
J. Kuster ◽  
J. F. Mandell
Keyword(s):  
Stress Relaxation ◽  
Compressive Stress ◽  
Measured Data ◽  
Time Span ◽  
Chemical Stress ◽  
Time Period ◽  
Long Time ◽  
Time Periods ◽  
Good Agreement

Abstract The application of reduced variables has been tested in long-time compressive stress relaxation at 293 K over a time period of 16 years for NR and NBR. The results show that within this time span there is good agreement with predicted data from reduced variables. However, the results indicate that over much longer time periods (approx. 20 to 50 years) disagreement is to be expected due to dominance of chemical stress relaxation for surface to volume ratios in the range of 0.6/mm.

scholarly journals Comparative Evaluation of Fracture Resistance of Endodontically Treated Teeth Restored with Resin Fiber Post and Stainless Steel Post: An In Vitro Study

2015 ◽  
Vol 03 (02) ◽  
pp. 080-084
Author(s):  
Vijay Singh ◽  
Poonam Bogra ◽  
Saurabh Gupta ◽  
Navneet Kukreja ◽  
Neha Gupta
Keyword(s):  
Stainless Steel ◽  
Fracture Resistance ◽  
Testing Machine ◽  
Compressive Force ◽  
Control Group ◽  
Fiber Post ◽  
Endodontically Treated Teeth ◽  
Group I ◽  
Significant Difference

AbstractFracture resistance of endodontically treated teeth restored with post. Aims: This study aims to compare the fracture resistance of endodontically treated teeth restored with resin fiber and stainless steel post. Commercially available prefabricated resin fiber post(Dentsply Maillefer Easy Post), prefabricated stainless steel post(Coltene/Whaledent Parapost) were used. Methods and Material: Forty five maxillary central incisors were obturated and divided into 3 groups: Control Group (Group I) without any post (n = 15), Resin Fiber Post Group (Group II) (n = 15) and Stainless Steel Post Group (Group III) (n = 15). In all Groups except control group, post space was prepared; a post was cemented, and a core build-up was provided. All the specimens were subjected to compressive force under a universal testing machine until fracture. Statistical analysis used: The results were analyzed using the variable analysis test (ANOVA). Results: One-way analysis of variance revealed significant difference among test groups. The control group demonstrated highest fracture resistance (925.2183 N), followed by the resin fiber post group (486.7265 N) and stainless steel post group (423.539N). Conclusions: Teeth restored with resin fiber post showed higher fracture resistance values than prefabricated stainless steel post.

scholarly journals Longitudinal birth cohort study finds that life-course frailty associates with later-life heart size and function

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Constantin-Cristian Topriceanu ◽  
James C. Moon ◽  
Rebecca Hardy ◽  
Nishi Chaturvedi ◽  
Alun D. Hughes ◽  
...  
Keyword(s):  
Life Course ◽  
Birth Cohort ◽  
Left Ventricular ◽  
Step Change ◽  
Deficit Accumulation ◽  
Cardiac Phenotype ◽  
Time Period ◽  
Time Periods ◽  
The Life Course ◽  
Health Deficit

AbstractA frailty index (FI) counts health deficit accumulation. Besides traditional risk factors, it is unknown whether the health deficit burden is related to the appearance of cardiovascular disease. In order to answer this question, the same multidimensional FI looking at 45-health deficits was serially calculated per participant at 4 time periods (0–16, 19–44, 45–54 and 60–64 years) using data from the 1946 Medical Research Council (MRC) British National Survey of Health and Development (NSHD)—the world’s longest running longitudinal birth cohort with continuous follow-up. From these the mean and total FI for the life-course, and the step change in deficit accumulation from one time period to another was derived. Echocardiographic data at 60–64 years provided: ejection fraction (EF), left ventricular mass indexed to body surface area (LVmassi, BSA), myocardial contraction fraction indexed to BSA (MCFi) and E/e′. Generalized linear models assessed the association between FIs and echocardiographic parameters after adjustment for relevant covariates. 1375 participants were included. For each single new deficit accumulated at any one of the 4 time periods, LVmassi increased by 0.91–1.44% (p < 0.013), while MCFi decreased by 0.6–1.02% (p < 0.05). A unit increase in FI at age 45–54 and 60–64, decreased EF by 11–12% (p < 0.013). A single health deficit step change occurring between 60 and 64 years and one of the earlier time periods, translated into higher odds (2.1–78.5, p < 0.020) of elevated LV filling pressure. Thus, the accumulation of health deficits at any time period of the life-course associates with a maladaptive cardiac phenotype in older age, dominated by myocardial hypertrophy and poorer function.

scholarly journals Comorbid disease burden among MS patients 1968–2012: A Swedish register–based cohort study

2020 ◽  
pp. 135245852091049 ◽  
Author(s):  
Kelsi A Smith ◽  
Sarah Burkill ◽  
Ayako Hiyoshi ◽  
Tomas Olsson ◽  
Shahram Bahmanyar ◽  
...  
Keyword(s):  
General Population ◽  
Age Groups ◽  
Comorbid Disease ◽  
Hazard Ratios ◽  
Time Period ◽  
Younger Age ◽  
Cardiovascular Depression ◽  
Prevalence Prevalence ◽  
Time Periods ◽  
Prevalence Ratios

Background: People with multiple sclerosis (pwMS) have increased comorbid disease (CMD) risk. Most previous studies have not considered overall CMD burden. Objective: To describe lifetime CMD burden among pwMS. Methods: PwMS identified using Swedish registers between 1968 and 2012 ( n = 25,476) were matched by sex, age, and county of residence with general-population comparators ( n = 251,170). Prevalence, prevalence ratios (PRs), survival functions, and hazard ratios by MS status, age, and time period compared seven CMD: autoimmune, cardiovascular, depression, diabetes, respiratory, renal, and seizures. Results: The magnitude of the PRs for each CMD and age group decreased across time, with higher PRs in earlier time periods. Before 1990, younger age groups had higher PRs, and after 1990, older age groups had higher PRs. Male pwMS had higher burden compared with females. Overall, renal, respiratory, and seizures had the highest PRs. Before 2001, 50% of pwMS received a first/additional CMD diagnosis 20 years prior to people without MS, which reduced to 4 years after 2001. PwMS had four times higher rates of first/additional diagnoses in earlier time periods, which reduced to less than two times higher in recent time periods compared to people without MS. Conclusion: Swedish pwMS have increased CMD burden compared with the general population, but this has reduced over time.

Photoelastic Analysis on Different Retention Methods of Implant-Supported Prosthesis

2015 ◽  
Vol 41 (3) ◽  
pp. 258-263 ◽  
Author(s):  
Angélica Castro Pimentel ◽  
Marcello Roberto Manzi ◽  
Cristiane Ibanhês Polo ◽  
Claudio Luiz Sendyk ◽  
Maria da Graça Naclério-Homem ◽  
...  
Keyword(s):  
Stress Distribution ◽  
Axial Load ◽  
Testing Machine ◽  
Compressive Load ◽  
Lower Intensity ◽  
Photoelasticity Method ◽  
Universal Testing ◽  
Isochromatic Fringes ◽  
Photoelastic Analysis ◽  
Compressive Axial Load

The aim of this study was to evaluate the stress distribution of different retention systems (screwed, cemented, and mixed) in 5-unit implant-supported fixed partial dentures through the photoelasticity method. Twenty standardized titanium suprastructures were manufactured, of which 5 were screw retained, 5 were cement retained, and 10 were mixed (with an alternating sequence of abutments), each supported by 5 external hexagon (4.0 mm × 11.5 mm) implants. A circular polariscope was used, and an axial compressive load of 100 N was applied on a universal testing machine. The results were photographed and qualitatively analyzed. We observed the formation of isochromatic fringes as a result of the stresses generated around the implant after installation of the different suprastructures and after the application of a compressive axial load of 100 N. We conclude that a lack of passive adaptation was observed in all suprastructures with the formation of low-magnitude stress in some implants. When cemented and mixed suprastructures were subjected to a compressive load, they displayed lower levels of stress distribution and lower intensity fringes compared to the screwed prosthesis.

scholarly journals Effects of temperature and impactor nose diameter on the impact behavior of PA6 and PP thermoplastic composites

2018 ◽  
Vol 51 (1) ◽  
pp. 64-74 ◽  
Author(s):  
Akar Dogan ◽  
Yusuf Arman
Keyword(s):  
Load Capacity ◽  
Testing Machine ◽  
Polyamide 6 ◽  
Impact Testing ◽  
Impact Behavior ◽  
Thermoplastic Composites ◽  
Test Machine ◽  
Effects Of Temperature ◽  
Impact Energies ◽  
The Impact

In this study, the effects of temperature and impactor nose diameter on the impact behavior of woven glass-reinforced polyamide 6 (PA6) and polypropylene (PP) thermoplastic composites were investigated experimentally. Impact energies are chosen as 10, 30, 50, 70, 90, 110, 130, and 170 J. The thickness of composite materials is 4 mm. Impact tests were performed using a drop weight impact testing machine, CEAST-Fractovis Plus, and the load capacity of test machine is 22 kN. Hemispherical impactor nose diameter of 12, 7, and 20 mm were used as an impactor. The tests are conducted at room temperature (20°C and 75°C). As a result, the PP composites of the same thickness absorbed more energy than PA6 composites. The amount of absorbed energy of PP and PA6 composites decreased with temperature.

scholarly journals Visualizing Belief in Meritocracy, 1930–2010

2018 ◽  
Vol 4 ◽  
pp. 237802311881180 ◽  
Author(s):  
Jonathan J. B. Mijs
Keyword(s):  
Survey Data ◽  
Representative Sample ◽  
Western World ◽  
Birth Cohorts ◽  
Popular Belief ◽  
Time Period ◽  
Level Data ◽  
Two Measures ◽  
Time Periods ◽  
Over Time

In this figure I describe the long trend in popular belief in meritocracy across the Western world between 1930 and 2010. Studying trends in attitudes is limited by the paucity of survey data that can be compared across countries and over time. Here, I show how to complement survey waves with cohort-level data. Repeated surveys draw on a representative sample of the population to describe the typical beliefs held by citizens in a given country and period. Leveraging the fact that citizens surveyed in a given year were born in different time-periods allows for a comparison of beliefs across birth cohorts. The latter overlaps with the former, but considerably extends the time period covered by the data. Taken together, the two measures give a “triangulated” longitudinal record of popular belief in meritocracy. I find that in most countries, popular belief in meritocracy is (much) stronger for more recent periods and cohorts.

scholarly journals The Effects of Power Levels/Time Periods for Sputtering Cobalt onto Carbon Nanotubes/Graphene Composites and Cobalt Annealed on the Characteristics of Anode Materials for Lithium-Ion Batteries

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Chuen-Chang Lin ◽  
You-Lun Shen ◽  
An-Na Wu
Keyword(s):  
Carbon Nanotubes ◽  
Cobalt Oxide ◽  
Anode Materials ◽  
Specific Capacity ◽  
Rf Sputtering ◽  
Lithium Ion ◽  
Chemical Vapor ◽  
Electrochemical Stability ◽  
Time Period ◽  
Time Periods

Carbon nanotubes/graphene composites are directly grown on nickel foil without additional catalysts by chemical vapor deposition (CVD). Next, the cobalt is deposited on carbon nanotubes/graphene composites by radio frequency (RF) sputtering with different power levels and time periods. Then, the cobalt is transformed into cobalt oxide by annealing. A longer time period of sputtering leads to higher specific capacity. Furthermore, the electrochemical stability of cobalt oxide/carbon nanotubes/graphene composites is higher than that of cobalt oxide.

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