Depth Dependent In-Plane Shear Properties of the Corneal Stroma

2010 ◽  
Author(s):  
Steven Petsche ◽  
Peter Pinsky ◽  
Dimitri Chernyak ◽  
Jaime Martiz
Keyword(s):  
Shear Modulus ◽  
Patient Outcomes ◽  
Surgical Procedures ◽  
Refractive Surgery ◽  
Corneal Stroma ◽  
Shear Stiffness ◽  
Biomechanical Properties ◽  
Human Cornea ◽  
Plane Shear ◽  
Biomechanical Response

The popularity of refractive surgery to correct the vision of individuals with hyperopia or myopia is increasing. These procedures alter the tissue of the human cornea to cause a change in curvature (refractive power) of the cornea. Radial keratotomy, photorefractive keratectomy, LASIK, and LASEK are all types of refractive surgery. The outcomes of refractive surgical procedures must depend significantly on the biomechanical response of the tissue and therefore on the biomechanical properties of the cornea, or more specifically the corneal stroma which makes up 90% of the tissue. The missing link between computer models of these procedures and predicting patient outcomes is the biomechanical properties of the tissue, including shear modulus. This study aims to characterize the in-plane shear modulus of the corneal stroma through the depth by mechanical testing. Scant data, if any, exists about the shear stiffness and no data includes depth dependence. The stroma consists of sheets of collagenous lamellae in which fibrils are maintained at uniform spacing by glycoaminoglycan molecules. Studies have shown increased interweaving of the lamellae in the anterior third of the stroma compared to the central and posterior thirds [1]. Figure 1 shows the distinct interweaving in the anterior third [2]. It is hypothesized that more interweaving lamellae increases the in-plane shear stiffness. The shear modulus of the full cornea, as well as individual thirds, is examined in this study.

scholarly journals Influence of laminate direction and glue area on in-plane shear modulus of cross-laminated timber

2020 ◽  
Vol 2 (12) ◽  
Author(s):  
Jonas Turesson ◽  
Zahra Sharifi ◽  
Sven Berg ◽  
Mats Ekevad
Keyword(s):  
Finite Element ◽  
Shear Modulus ◽  
Compression Test ◽  
Contact Area ◽  
Tall Buildings ◽  
Shear Stiffness ◽  
Finite Element Simulations ◽  
Plane Shear ◽  
Cross Laminated Timber ◽  
Diagonal Compression

AbstractThe use of cross-laminated timber (CLT) in constructing tall buildings has increased. So, it has become crucial to get a higher in-plane stiffness in CLT panels. One way of increasing the shear modulus, G, for CLT panels can be by alternating the layers to other angles than the traditional 0° and 90°. The diagonal compression test can be used to measure the shear stiffness from which G is calculated. A general equation for calculating the G value for the CLT panels tested in the diagonal compression test was established and verified by tests, finite element simulations and external data. The equation was created from finite element simulations of full-scale CLT walls. By this equation, the influence on the G value was a factor of 2.8 and 2.0 by alternating the main laminate direction of the mid layer from the traditional 90° to 45° and 30°, respectively. From practical tests, these increases were measured to 2.9 and 1.8, respectively. Another influence on the G value was studied by the reduction of the glue area between the layers. It was shown that the pattern of the contact area was more important than the size of the contact area.

scholarly journals Comparison of Theoretical and Laboratory Out-of-Plane Shear Stiffness Values of Cross Laminated Timber Panels

Buildings ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 146 ◽  
Author(s):  
Jan Niederwestberg ◽  
Jianhui Zhou ◽  
Ying-Hei Chui
Keyword(s):  
Shear Modulus ◽  
Cross Section ◽  
Single Layer ◽  
Beam Theory ◽  
Shear Stiffness ◽  
Plane Shear ◽  
Shear Moduli ◽  
Cross Laminated Timber ◽  
Highly Sensitive ◽  
Out Of Plane

The lay-up of cross laminated timber (CLT) leads to significant differences in properties over its cross-section. Particularly the out-of-plane shear behavior of CLT is affected by the changes in shear moduli over the cross-section. Results from laboratory shear tests are used to evaluate the shear stiffness of 3- and 5-layer CLT panels in their major and minor strength direction. The results are compared to calculated shear stiffness values on evaluated single-layer properties as well as commonly used property ratios using the Timoshenko beam theory and the shear analogy method. Differences between the two calculation approaches are pointed out. The shear stiffness is highly sensitive to the ratio of the shear modulus parallel to the grain to the shear modulus perpendicular to the grain. The stiffness values determined from two test measurements are compared with the calculated results. The level of agreement is dependent on the number of layers in CLT and the property axis of the CLT panels.

scholarly journals In vivo measurement of shear modulus of the human cornea using optical coherence elastography

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Antoine Ramier ◽  
Amira M. Eltony ◽  
YiTong Chen ◽  
Fatima Clouser ◽  
Judith S. Birkenfeld ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Rayleigh Wave ◽  
Wave Speed ◽  
Critical Role ◽  
Shear Stiffness ◽  
Human Cornea ◽  
Optical Coherence ◽  
In Vivo Measurement ◽  
Rayleigh Wave Speed

Abstract Corneal stiffness plays a critical role in shaping the cornea with respect to intraocular pressure and physical interventions. However, it remains difficult to measure the mechanical properties noninvasively. Here, we report the first measurement of shear modulus in human corneas in vivo using optical coherence elastography (OCE) based on surface elastic waves. In a pilot study of 12 healthy subjects aged between 25 and 67, the Rayleigh-wave speed was 7.86 ± 0.75 m/s, corresponding to a shear modulus of 72 ± 14 kPa. Our data reveal two unexpected trends: no correlation was found between the wave speed and IOP between 13–18 mmHg, and shear modulus decreases with age (− 0.32 ± 0.17 m/s per decade). We propose that shear stiffness is governed by the interfibrillar matrix, whereas tensile strength is dominated by collagen fibrils. Rayleigh-wave OCE may prove useful for clinical diagnosis, refractive surgeries, and treatment monitoring.

scholarly journals The corneal biomechanical changes after SMILE and LASIK refractive surgery were compared based on finite element analysis

2021 ◽  
Vol 271 ◽  
pp. 03045
Author(s):  
Yinyu Song ◽  
Lihua Fang ◽  
Ruirui Du ◽  
Luchao Lin ◽  
Xingming Tao
Keyword(s):  
Finite Element ◽  
Refractive Surgery ◽  
Three Dimensional ◽  
Element Model ◽  
Biomechanical Properties ◽  
Stress And Strain ◽  
Wavefront Aberration ◽  
Human Cornea ◽  
Element Analysis ◽  
Wavefront Aberrations

The three-dimensional (3D) finite element model of human eye was established, and the intraocular pressure (IOP) was loaded to simulate refractive surgery. The biomechanical properties of human cornea after SMILE and LASIK surgery were studied from the stress, strain and induced wavefront aberration. Our results showed that SMILE had less impact on the biomechanics, having less stress and strain changes than LASIK. However, the stress and strain of the cornea increased with the increase of the diopter and were concentrated in the central region. We also investigated the changes in wavefront aberrations of the cornea after surgery, and the results indicated that the defocus and vertical commotion were significantly affected by SMILE and LASIK surgery, while the remaining aberrations were approximately unchanged. In conclusion, both SMILE and LASIK sergury procedures changed the postoperative corneal biomechanics, but SMILE had less impact on the biomechanics of corneal.

scholarly journals In-plane shear modulus of cross-laminated timber by diagonal compression test

BioResources ◽  
2019 ◽  
Vol 14 (3) ◽  
pp. 5559-5572 ◽  
Author(s):  
Sven Berg ◽  
Jonas Turesson ◽  
Mats Ekevad ◽  
Anders Björnfot
Keyword(s):  
Shear Modulus ◽  
Compression Test ◽  
Pure Shear ◽  
Shear Stiffness ◽  
Least Square ◽  
Compression Tests ◽  
Plane Shear ◽  
Cross Laminated Timber ◽  
Fe Simulations ◽  
Diagonal Compression

Cross-laminated timber (CLT) is an engineered wood material that is used in the construction industry, e.g., for floors, walls, and beams. In cases where CLT-elements are used as shear walls, the in-plane-stiffness is an important property. For non-edge glued CLT, in-plane shear stiffness is lower than for edge-glued CLT. To evaluate the non-edge glued CLT panel’s in-plane shear modulus, the diagonal compression test and finite element (FE) simulation was used. FE-models with both isotropic and orthotropic material models were used to calculate the shear stiffness. The FE models using pure shear loads were used as a reference to determine the correct value of the shear modulus. To verify the FE simulations, diagonal compression tests were conducted on 30 CLT samples. A calibration formula was derived using the least square method for calculation of shear modulus. The formula gave accurate results. The results showed that FE simulations can reproduce the same shear stiffness as tests of non-edge glued 3-layer and 5-layer CLT panels.

scholarly journals Comparison of Theoretical and Laboratory Out-of-Plane Shear Stiffness Values of Cross Laminated Timber Panels

2018 ◽  
Author(s):  
Jan Niederwestberg ◽  
Jianhui Zhou ◽  
Ying-Hei Chui
Keyword(s):  
Shear Modulus ◽  
Cross Section ◽  
Single Layer ◽  
Beam Theory ◽  
Shear Stiffness ◽  
Plane Shear ◽  
Shear Moduli ◽  
Cross Laminated Timber ◽  
Highly Sensitive ◽  
Out Of Plane

The lay-up of cross laminated timber (CLT) leads to significant differences in properties over its cross-section. Particularly the out-of-plane shear behavior of CLT is effected by the changes in shear moduli over the cross-section. Results from laboratory shear tests are used to evaluate the shear stiffness of 3- and 5-layer CLT panels in their major and minor strength direction. The results are compared to calculated shear stiffness values on evaluated single-layer properties as well as commonly used property ratios using the Timoshenko beam theory and the shear analogy method. Differences between the two calculation approaches are pointed out. The shear stiffness is highly sensitive to the ratio of the shear modulus parallel to the grain to the shear modulus perpendicular to the grain. The stiffness values determined from two test measurements are compared with the calculated results. The level of agreement is dependent on the number of layers in CLT and the property axis of the CLT panels.

Microporous Polysaccharide Hemosphere Absorbable Hemostat (AristaAH®) in Re-Operative Cardiac Surgical Procedures

2012 ◽  
Vol 9 (2) ◽  
pp. 96-98
Author(s):  
Brian A Bruckner ◽  
Matthias Loebe
Keyword(s):  
Patient Outcomes ◽  
Surgical Procedures ◽  
Systematic Approach ◽  
Surgical Intervention ◽  
Transfusion Requirement ◽  
Cardiac Surgical Procedures ◽  
Platelet Inhibitors ◽  
Hemostatic Agents ◽  
Surgical Field ◽  
Improve Patient

Patients undergoing re-operative cardiac surgical procedures present a great challenge with regard to obtaining hemostasis in the surgical field. Adhesions are ever-present and these patients are often on oral anti-coagulants and platelet inhibitors. As part of a well-planned surgical intervention, a systematic approach to hemostasis should be employed to decrease blood transfusion requirement and improve patient outcomes. Topical hemostatic agents can be a great help to the surgeon in achieving surgical field hemostasis and are increasingly being employed. Our approach, to these difficult patients, includes the systematic and planned use of AristaAH, which is a novel hemostatic agent whose use has proven safe and efficacious in our patient population.

scholarly journals Moulding hydrodynamic 2D-crystals upon parametric Faraday waves in shear-functionalized water surfaces

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mikheil Kharbedia ◽  
Niccolò Caselli ◽  
Diego Herráez-Aguilar ◽  
Horacio López-Menéndez ◽  
Eduardo Enciso ◽  
...  
Keyword(s):  
Soft Matter ◽  
Shear Stiffness ◽  
External Control ◽  
Faraday Waves ◽  
Plane Shear ◽  
Unit Cell Size ◽  
Ordering Transitions ◽  
Water Surfaces ◽  
Ordering Transition ◽  
Surface Rigidity

AbstractFaraday waves, or surface waves oscillating at half of the natural frequency when a liquid is vertically vibrated, are archetypes of ordering transitions on liquid surfaces. Although unbounded Faraday waves patterns sustained upon bulk frictional stresses have been reported in highly viscous fluids, the role of surface rigidity has not been investigated so far. Here, we demonstrate that dynamically frozen Faraday waves—that we call 2D-hydrodynamic crystals—do appear as ordered patterns of nonlinear gravity-capillary modes in water surfaces functionalized with soluble (bio)surfactants endowing in-plane shear stiffness. The phase coherence in conjunction with the increased surface rigidity bears the Faraday waves ordering transition, upon which the hydrodynamic crystals were reversibly molded under parametric control of their degree of order, unit cell size and symmetry. The hydrodynamic crystals here discovered could be exploited in touchless strategies of soft matter and biological scaffolding ameliorated under external control of Faraday waves coherence.

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