How a Single Cell Sense its Mechanical Environment?

The extracellular matrix (ECM) is essential for regulating cell behavior and tissue function [1]. Local ECM structure and mechanics are increasingly recognized as important mechanical effectors of cell responses and tissue regeneration [2]. This is illustrated by the fact that either the rigidity of ECM [3] or local tension regulate cellular mechanotransduction pathways, and their dysregulation results in many different types of diseases [4,5]. It was speculated that cell contractions, generated by the cross-bridging interaction of actin and myosin II motors, maintain a tensional homeostasis in response to mechanical disturbance. The question is what is exactly the tensional homeostasis, if any

Contribution of Fiber Undulation to Mechanics of Three-Dimensional Collagen-I Gel

The collagen-I gel is extensively used as a scaffold material in tissue engineering due to its ability to mimic the extracellular matrix (ECM). In this study, the mechanics of collagen-I gel is investigated using a numerical model of three-dimensional collagen network. The resulted mechanical behavior was validated against the published experimental data. Results illustrated that fiber alignment was dominated in the low strain region, and its transition to stretching dominated phenomena at higher strain led to the strain stiffening of collagen gel. The collagen undulation at the microscopic level was found to delay the initiation of strain stiffenin

How a Single Cell Sense its Mechanical Environment?

The extracellular matrix (ECM) is essential for regulating cell behavior and tissue function [1]. Local ECM structure and mechanics are increasingly recognized as important mechanical effectors of cell responses and tissue regeneration [2]. This is illustrated by the fact that either the rigidity of ECM [3] or local tension regulate cellular mechanotransduction pathways, and their dysregulation results in many different types of diseases [4,5]. It was speculated that cell contractions, generated by the cross-bridging interaction of actin and myosin II motors, maintain a tensional homeostasis in response to mechanical disturbance. The question is what is exactly the tensional homeostasis, if any

Contribution of Fiber Undulation to Mechanics of Three-Dimensional Collagen-I Gel

The collagen-I gel is extensively used as a scaffold material in tissue engineering due to its ability to mimic the extracellular matrix (ECM). In this study, the mechanics of collagen-I gel is investigated using a numerical model of three-dimensional collagen network. The resulted mechanical behavior was validated against the published experimental data. Results illustrated that fiber alignment was dominated in the low strain region, and its transition to stretching dominated phenomena at higher strain led to the strain stiffening of collagen gel. The collagen undulation at the microscopic level was found to delay the initiation of strain stiffenin

Controllable energy absorption of double sided corrugated tubes under axial crushing

To maximize the controllable energy absorption of corrugation troughs as observed in the single sided corrugated (SSC) tube, we proposed and tested a new structure design, i.e., double-sided corrugated (DSC) tube made of Al 6060-T6 aluminum alloy or CF1263 carbon/epoxy composite. Finite element models were developed to test the mechanical advantage of the DSC tube in comparison with both SSC and classical straight (S) tubes under axial crushing. Results have shown that the total absorbed energy of the DSC aluminum tube with 14 corrugations was 330% and 32% higher than that of the SSC tube with 14 corrugations and the S-tube, respectively. The initiation and progression of the crushing process for different tube configurations were characterized, leading to the mechanism of energy absorption. Plastic deformation in terms of PPEQ is the key parameter correlating with the energy absorption capacity. To overcome the lower specific absorbed energy (SAE) in the DSC tube compared to that in the S-tube, the CF1263 carbon/epoxy composite laminate was adopted and the corresponding SAE was 5.9 times higher than that of the aluminum one. Moreover, the influence of the number of corrugations on the crushing behaviors of the DSC tube was also inspected. A minimal straight tube section was suggested for a controllable smooth crushing behavior regardless of its advantage in SAE. This work might shed light on designing future thin-walled energy absorber devices with better control of crushing behaviors for minimal injuries and damages

Controllable energy absorption of double sided corrugated tubes under axial crushing

To maximize the controllable energy absorption of corrugation troughs as observed in the single sided corrugated (SSC) tube, we proposed and tested a new structure design, i.e., double-sided corrugated (DSC) tube made of Al 6060-T6 aluminum alloy or CF1263 carbon/epoxy composite. Finite element models were developed to test the mechanical advantage of the DSC tube in comparison with both SSC and classical straight (S) tubes under axial crushing. Results have shown that the total absorbed energy of the DSC aluminum tube with 14 corrugations was 330% and 32% higher than that of the SSC tube with 14 corrugations and the S-tube, respectively. The initiation and progression of the crushing process for different tube configurations were characterized, leading to the mechanism of energy absorption. Plastic deformation in terms of PPEQ is the key parameter correlating with the energy absorption capacity. To overcome the lower specific absorbed energy (SAE) in the DSC tube compared to that in the S-tube, the CF1263 carbon/epoxy composite laminate was adopted and the corresponding SAE was 5.9 times higher than that of the aluminum one. Moreover, the influence of the number of corrugations on the crushing behaviors of the DSC tube was also inspected. A minimal straight tube section was suggested for a controllable smooth crushing behavior regardless of its advantage in SAE. This work might shed light on designing future thin-walled energy absorber devices with better control of crushing behaviors for minimal injuries and damages

The Impact of Roof Pitch and Ceiling Insulation on Cooling Load of Naturally-Ventilated Attics

A 2D unsteady computational fluid dynamics (CFD) model is employed to simulate buoyancy-driven turbulent ventilation in attics with different pitch values and ceiling insulation levels under summer conditions. The impacts of roof pitch and ceiling insulation on the cooling load of gable-roof residential buildings are investigated based on the simulation of turbulent air flow and natural convection heat transfer in attic spaces with roof pitches from 3/12 to 18/12 combined with ceiling insulation levels from R-1.2 to R-40. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the investigated variations of roof pitch and ceiling insulation. Furthermore, it is predicted that the ceiling insulation plays a control role on the attic cooling load and that an increase of roof pitch from 3/12 to 8/12 results in a decrease in the cooling load by around 9% in the investigated cases. The results suggest that the increase of roof pitch alone, without changing other design parameters, has limited impact on attics cooling load and airflow pattern. The research results also suggest both the predicted ventilating mass flow rate and attic cooling load can be satisfactorily correlated by simple relationships in terms of appropriately defined Rayleigh and Nusselt numbers

Effects of Arterial Strain and Stress in the Prediction of Restenosis Risk: Computer Modeling of Stent Trials

Purpose — In-stenting restenosis is one of the major complications after stenting. Clinical trials of various stent designs have reported different restenosis rates. However, quantitative correlation between stent features and restenosis statistics is scant. In this work, it is hypothesized that stress concentrations on arterial wall caused artery injury, which initiates restenosis. The goal is to assess the correlation between stent-induced arterial stress and strain and the documented restenosis rates. Methods — Six commercially available stents, including balloon-expandable stents and self-expanding stents, were virtually implanted into the arteries through finite element method. The resulted peak Von Mises stress, principal stress, principal logarithm strain, as well as percentage of intimal area with abnormal higher stress were monitored. Results — Positive correlation between arterial stress and strain after stent implantations and the documented restenosis rates from the corresponding clinical trials was found regardless of stent types. No statistical significant difference was observed for various stress or strain parameters serving as indicators of artery injury. Conclusions — In-stent restenosis are less likely to occur as arterial mechanics are least altered by stent implantations. Optimization of stent designs to minimize the stent-induced arterial stresses and strains can reduce the arterial injury, and thus reduce the occurrence of restenosis. This work improved our understanding of the stent-lesion interactions that regulate arterial mechanics and demonstrated that arterial stress and strain could predict the risk of instent restenosis

Case Study of Quantifying Energy Loss through Ceiling-Attic Recessed Lighting Fixtures through 3D Numerical Simulation

Abstract Air leakage through recessed lighting fixtures has been identified as a common issue that causes extra energy consumption in residential buildings. However, few quantitative studies in this area were found. As such, a preliminary assessment of the magnitude of this type of energy loss was conducted by using three-dimensional (3D) transient computational fluid dynamics (CFD) models. A hypothetical layout of recessed lighting fixtures was designed with boundary conditions of four different seasons, which were obtained from recorded roof/attic temperature data sets. The results of the study indicate that leakage of recessed lighting fixtures could be a significant channel of energy loss in such attic-related residential buildings, especially in the summer and winter

Case Study of Quantifying Energy Loss through Ceiling-Attic Recessed Lighting Fixtures through 3D Numerical Simulation

Air leakage through improperly installed recessed lighting fixtures has been identified as a common issue causing extra energy consumption of residential buildings. However, little quantitative study was found in this area. In this paper, a preliminary evaluation of the magnitude of such energy loss was conducted by numerical simulations using 3 dimensional transient computational fluid dynamics (CFD) model. A typical layout of recessed lighting fixtures was used in this case study with boundary conditions in four different seasons, which were obtained from past measured roof/attic temperature data sets. The results of the numerical simulations indicate that leakage of recessed lighting fixtures could be a very significant channel of energy loss in attic related residential buildings, especially in summer and winter time