Multiaxial Mechanical Properties Research Articles

Multiaxial mechanical properties of additive manufactured titanium gyroid

Multiaxial mechanical properties of additive manufactured titanium gyroid

Generalized strategy to construct multifunctional inorganic nanomaterials/silicone rubber composite aerogels: Taking CNTs as an example for smart sensing

The structure and characteristics of carbon nanotubes (CNTs) aerogel (CNTA) make it capable of only compression, lacking the necessary toughness, flexural, and tensile properties. These limitations restrict its application. To overcome these obstacles, this study employed an interface modification and the Pickering emulsion strategy, using water-soluble CNTs as the continuous phase while silicone rubber (SR) as the dispersed phase, to successfully achieve the organic–inorganic combination and prepare the SR-CNTs composite aerogel (SRC). Benefiting from the synergistic effect of the “soft-hard” phase combination of SR (soft) and CNTs (hard), SRC exhibited good conductivity (1.23 S/m) and superior multi-axial mechanical properties such as compression (90 %), bending (360°), twisting (360°), and stretching (110 %), making it broad prospects in the field of flexible sensing. Importantly, the strategy employed in this study offers an innovative approach for a transition from low-dimensional nanomaterials to three-dimensional macroscopic overall structures. This approach effectively addresses common issues in traditional aerogel materials, such as mechanical brittleness and structural instability, which also allows for functionalization and customization, opening up new possibilities for the research and application of high-performance aerogels.

Measurement Capability of Rubber's Multiaxial Mechanical Properties by Compression Testing

Measurement Capability of Rubber's Multiaxial Mechanical Properties by Compression Testing

Effects of aggregate types and softening effect on multiaxial mechanical properties of lightweight aggregate concrete

Softening effect refers to the inherent property of porous media materials of having their strength decrease over time under water saturation compared with that under dry condition. Typical porous media materials, such as ceramsite and ceramsite-based concrete, exhibit a softening effect. This study investigated the softening effect of shale ceramsite (SC) and different types of lightweight aggregate concrete (LWACs). Mix ratios of LC30 all-lightweight shale ceramsite concrete (also known as all-lightweight concrete, ALWC) whose SC and shale pottery (SP) were selectively or simultaneously replaced with limestone gravel (LSG) and river sand (RS) with the same volume fraction, respectively, were prepared for comparison with gravel lightweight concrete (GLWC), sand lightweight concrete (SLWC) and hybrid aggregate lightweight concrete (HALWC) were formed. The four kinds of LWACs (ALWC, GLWC, SLWC and HALWC) were cast into their corresponding specification and size specimens and demoulded after indoor curing for 24 h, with their target ages (7–180 d) maintained under standard and hydrostatic curing. Then, the strength and initial elastic modulus under uniaxial stress, ultimate compressive strength and stress–strain curves under triaxial stress of the specimens were tested to analyse the influence of aggregate types and curing methods on the mechanical properties and softening effect of LWACs. According to the test results, the cube compression, prism compression, splitting tensile, conventional triaxial compression and elastic modulus decreased after 180 d of hydrostatic curing; the experimental age of the conventional triaxial compression test was after 90 d. ALWC demonstrated the most evident decrease, followed by SLWC, HALWC and GLWC. The trend indicates that normal aggregates can significantly improve the softening effect of LWACs. The failure modes of the triaxial compression specimens changed from splitting failure to shear failure, and a plastic platform phenomenon was apparent on the stress–strain curves, with their descending section appearing gentler than those in the uniaxial compression test with the increase in confining pressure. The relationship between ultimate compressive strength and confining pressure of the LWACs can be accurately described by the Mohr–Coulomb single-parameter failure criterion, Hsieh–Ting–Chen four-parameter failure criterion and Willam–Warnke five-parameter failure criterion. However, the three failure criteria demonstrated application limitations based on meridian equation and deviatoric plane analysis. The extension trend of the compression meridian of the LWACs after 90 d of hydrostatic curing was generally the same, and the types of aggregates exerted a minimal effect on the meridian and deviatoric plane limit trace. The softening effect of LWACs was mainly caused by the softening effect of the SC itself and the influence of pore water on the matrix concrete.

Experimental Study and Theoretical Analysis on the Compression-Shear Multiaxial Mechanical Properties of Recycled Concrete.

Recycled concrete, which is formed by replacing coarse aggregates in ordinary concrete with recycled aggregates (RA), is of great significance for the secondary utilization of waste building resources. In civil engineering, concrete structures are sometimes subjected to a compression–shear multiaxial stress state. Therefore, research on the compression–shear multiaxial mechanical properties of recycled concrete plays an important role in engineering practice. To explore the effect of RA replacement rate on the compression–shear properties of recycled concrete, an experimental study was carried out using a compression–shear testing machine and considering five RA replacement rates and five axial compression ratios. Consequently, the failure modes and mechanical property parameters under different working conditions were obtained and were used to analyze the effects of RA replacement rate and axial compression ratio on the shear stress of recycled concrete. Eventually, the following conclusions were reached: With the growth of axial compression ratio, the shear cracks exhibit a developing trend along the oblique direction, and the friction traces on the shear surface are gradually deepened. As the replacement rate increases, the number of shear cracks is gradually increased, accompanied by increasing broken fragments falling off from the shear interface. Since the action of the axial compression ratio can effectively improve the mechanical bite force and friction on the shear interface of recycled concrete, as the axial compression ratio increases, the shear stress is gradually increased. On the other hand, due to the initial damage of RA and its weak adhesion with cement mortar, the shear stress is gradually reduced with the increase of RA replacement rate. Meanwhile, the increase in shear stress shows a gradually decreasing trend with the growth of axial compression ratio. Specifically, for the RA replacement rates of 0% and 100%, the shear stress increased by 4.06 times and 3.21 times, respectively, under the influence of the axial compression ratio. Under different axial compression ratios, the shear stress was reduced by 43~46%, due to the increase of RA replacement rate. In addition, based on the octahedral stress space and the principal stress space, a compression–shear multiaxial failure criterion and shear stress calculation model for recycled concrete were proposed, by considering the effect of the RA replacement rate. The outcomes of this research are of great significance for engineering applications and the development of recycled concrete.

Mechanical properties of silk plain‐weft knitted scaffolds for bladder tissue engineering applications

AbstractAppropriate mechanical properties in both longitudinal and circumferential directions are an important requirement for the scaffold aimed at tissue engineering of the human urinary bladder. In this research, three weft‐knitted silk fibroin scaffolds with stitch densities of 138, 182, and 245 loops/cm2 were fabricated and studied for potential use in bladder regeneration applications. It was shown that the porosity and surface porosity of the scaffolds increased as stitch density decreased. Moreover, increasing the stitch density assisted with decreasing the very big pore size of the weft‐knitted scaffolds. The uniaxial mechanical properties of the degummed scaffolds (namely strength and loading–unloading behavior), as well as multiaxial mechanical properties (providing the clinically relevant assessment conditions), were studied. We further studied the effect of cell culturing on the uniaxial mechanical properties of the scaffolds. It was observed that the cell‐cultured scaffold represented more strength and strain than the control scaffold after 6 weeks in culture. This study demonstrated that all three studied scaffolds demonstrate low stiffness (high compliance) along with high strength and high strains. Furthermore, comparing the uniaxial properties of weft‐knitted scaffolds with those of porcine bladder confirms that all three types of silk fibroin weft‐knitted scaffolds resemble bladder. However, the scaffold with a stitch density of 182 loops/cm2 more closely simulated the porcine bladder, which is believed to be similar to the human bladder. Therefore, this scaffold can be a potential candidate for bladder tissue engineering studies.

Multimodality Imaging-Based Characterization of Regional Material Properties in a Murine Model of Aortic Dissection

Chronic infusion of angiotensin-II in atheroprone (ApoE−/−) mice provides a reproducible model of dissection in the suprarenal abdominal aorta, often with a false lumen and intramural thrombus that thickens the wall. Such lesions exhibit complex morphologies, with different regions characterized by localized changes in wall composition, microstructure, and properties. We sought to quantify the multiaxial mechanical properties of murine dissecting aneurysm samples by combining in vitro extension-distension data with full-field multimodality measurements of wall strain and thickness to inform an inverse material characterization using the virtual fields method. A key advance is the use of a digital volume correlation approach that allows for characterization of properties not only along and around the lesion, but also across its wall. Specifically, deformations are measured at the adventitial surface by tracking motions of a speckle pattern using a custom panoramic digital image correlation technique while deformations throughout the wall and thrombus are inferred from optical coherence tomography. These measurements are registered and combined in 3D to reconstruct the reference geometry and compute the 3D finite strain fields in response to pressurization. Results reveal dramatic regional variations in material stiffness and strain energy, which reflect local changes in constituent area fractions obtained from histology but emphasize the complexity of lesion morphology and damage within the dissected wall. This is the first point-wise biomechanical characterization of such complex, heterogeneous arterial segments. Because matrix remodeling is critical to the formation and growth of these lesions, we submit that quantification of regional material properties will increase the understanding of pathological mechanical mechanisms underlying aortic dissection.

Over length quantification of the multiaxial mechanical properties of the ascending, descending and abdominal aorta using Digital Image Correlation.

In this paper, we hypothesize that the biaxial mechanical properties of the aorta may be dependent on arterial location. To demonstrate any possible position-related difference, our study analyzed and compared the biaxial mechanical properties of the ascending thoracic aorta, descending thoracic aorta and infrarenal abdominal aorta stemming from the same porcine subjects, and reported values of constitutive parameters for well-known strain energy functions, showing how these mechanical properties are affected by location along the aorta. When comparing ascending thoracic aorta, descending thoracic aorta and infrarenal abdominal aorta, abdominal tissues were found to be stiffer and highly anisotropic. We found that the aorta changed from a more isotropic to a more anisotropic tissue and became progressively less compliant and stiffer with the distance to the heart. We observed substantial differences in the anisotropy parameter between aortic samples where abdominal samples were more anisotropic and nonlinear than the thoracic samples. The phenomenological model was not able to capture the passive biaxial properties of each specific porcine aorta over a wide range of biaxial deformations, showing the best prediction root mean square error ε=0.2621 for ascending thoracic samples and, especially, the worst for the infrarenal abdominal samples ε=0.3780. The micro-structured model with Bingham orientation density function was able to better predict biaxial deformations (ε=0.1372 for ascending thoracic aorta samples). The root mean square error of the micro-structural model and the micro-structured model with von Mises orientation density function were similar for all positions.

Changes in pelvic organ prolapse mesh mechanical properties following implantation in rats

Pelvic organ prolapse (POP) is a multifactorial disease that manifests as the herniation of the pelvic organs into the vagina. Surgical methods for prolapse repair involve the use of a synthetic polypropylene mesh. The use of this mesh has led to significantly higher anatomical success rates compared with native tissue repairs, and therefore, despite recent warnings by the Food and Drug Administration regarding the use of vaginal mesh, the number of POP mesh surgeries has increased over the last few years. However, mesh implantation is associated with higher postsurgery complications, including pain and erosion, with higher consecutive rates of reoperation when placed vaginally. Little is known on how the mechanical properties of the implanted mesh itself change in vivo. It is assumed that the mechanical properties of these meshes remain unchanged, with any differences in mechanical properties of the formed mesh-tissue complex attributed to the attached tissue alone. It is likely that any changes in mesh mechanical properties that do occur in vivo will have an impact on the biomechanical properties of the formed mesh-tissue complex. The objective of the study was to assess changes in the multiaxial mechanical properties of synthetic clinical prolapse meshes implanted abdominally for up to 90 days, using a rat model. Another objective of the study was to assess the biomechanical properties of the formed mesh-tissue complex following implantation. Three nondegradable polypropylene clinical synthetic mesh types for prolapse repair (Gynemesh PS, Polyform Lite, and Restorelle) and a partially degradable polypropylene/polyglecaprone mesh (UltraPro) were mechanically assessed before and after implantation (n = 5/ mesh type) in Sprague Dawley rats for 30 (Gynemesh PS, Polyform Lite, and Restorelle) and 90 (UltraPro and Polyform Lite) days. Stiffness and permanent extension following cyclic loading, and breaking load, of the preimplanted mesh types, explanted mesh-tissue complexes, and explanted meshes were assessed using a multi-axial (ball-burst) method. The 4 clinical meshes varied from each other in weight, thickness, porosity, and pore size and showed significant differences in stiffness and breaking load before implantation. Following 30 days of implantation, the mechanical properties of some mesh types altered, with significant decreases in mesh stiffness and breaking load, and increased permanent extension. After 90 days these changes were more obvious, with significant decreases in stiffness and breaking load and increased permanent extension. Similar biomechanical properties of formed mesh-tissue complexes were observed for mesh types of different preimplant stiffness and structure after 90 days implantation. This is the first study to report on intrinsic changes in the mechanical properties of implanted meshes and how these changes have an impact on the estimated tissue contribution of the formed mesh-tissue complex. Decreased mesh stiffness, strength, and increased permanent extension following 90 days of implantation increase the biomechanical contribution of the attached tissue of the formed mesh-tissue complex more than previously thought. This needs to be considered when using meshes for prolapse repair.

Multiaxial mechanical properties of plain recycled aggregate concrete

Multiaxial tests were performed on 150 mm × 150 mm × 150 mm cubic specimens of three strength grades of plain structural recycled aggregate concrete (RAC) at different stress ratios using a large static–dynamic true triaxial machine. Friction-reducing pads (two layers of plastic membrane with lubricants) were placed between the compressive loading plate and the specimens. The tensile loading planes of the concrete samples were processed by an attrition machine and then the samples were glued to the loading plate. The characteristic failure modes of the specimens and the crack directions were observed. The three principal static strengths in the corresponding stress state were measured. The influence of the stress ratios, stress states and strength grade on the triaxial strengths of RAC was also analysed. The experimental results showed that ratio of triaxial failure strength σ3f to the corresponding uniaxial compressive strength fc for the three strength grades of RAC was higher than that of conventional concrete (CC), especially under triaxial compression; moreover, it is dependent on the strength grade of RAC, the stress states and stress ratios; however, the differences of tensile–compressive ratios between the RAC and CC are not significant. On this basis, a new failure criterion with the six parameters is proposed for plain RAC under multiaxial stress states. It provides the experimental foundations for strength analysis of RAC structures subject to complex loads.

Interferometric laser measurement of multi-axial mechanical properties exhibited by carbon nanotubes

Interferometric optical experiments for measuring changes in fringe irradiance patterns dependent on optical and mechanical responses associated to carbon nanotubes are reported. Thin solid films conformed by multiwall carbon nanotubes were prepared by an aerosol pyrolysis method. A Michelson optical interferometer with a highly stable 488nm wavelength was employed for evaluating the studied sample. According to the interferometric results, the strain of the carbon nanotubes presented a nonlinear behavior resulting from applied multiaxial forces. On the other hand, for further investigating the effect of the variation of the mechanical properties and the optical characteristics of the tubes, nonlinear optical experiments were performed when the sample was exposed to a mechanical action. The third order nonlinear optical response was explored with the assistance of the second harmonic provided by a Nd:YAG laser system in a two-wave mixing configuration. Potential applications for mechano-optical modulation by nanosystems based on carbon nanotubes are contemplated.

Multiaxial mechanical properties and constitutive modeling of human adipose tissue: A basis for preoperative simulations in plastic and reconstructive surgery

A preoperative simulation of soft tissue deformations during plastic and reconstructive surgery is desirable to support the surgeon’s planning and to improve surgical outcomes. The current development of constitutive adipose tissue models, for the implementation in multilayer computational frameworks for the simulation of human soft tissue deformations, has proved difficult because knowledge of the required mechanical parameters of fat tissue is limited. Therefore, for the first time, human abdominal adipose tissues were mechanically investigated by biaxial tensile and triaxial shear tests. The results of this study suggest that human abdominal adipose tissues under quasi-static and dynamic multiaxial loadings can be characterized as a nonlinear, anisotropic and viscoelastic soft biological material. The nonlinear and anisotropic features are consequences of the material’s collagenous microstructure. The aligned collagenous septa observed in histological investigations causes the anisotropy of the tissue. A hyperelastic model used in this study was appropriate to represent the quasi-static multiaxial mechanical behavior of fat tissue. The constitutive parameters are intended to serve as a basis for soft tissue simulations using the finite element method, which is an apparent method for obtaining promising results in the field of plastic and reconstructive surgery.

Triaxial T–C–C behavior of air-entrained concrete after freeze–thaw cycles

Abstract This paper presents results of triaxial tensile–compressive–compressive (T–C–C) tests on air-entrained concrete with uniaxial compressive strength of 25.64 MPa before and after 100, 200, 300, 400 cycles of freeze–thaw. The strength, failure mode and the direction of the crack of air-entrained concrete specimens under T–C–C were observed and measured, respectively. The influence of number of freeze–thaw cycles and stress ratio on the T–C–C strength was analyzed, respectively. Based on the experimental data, a failure criterion with the number of freeze–thaw cycles and stress ratio parameters under T–C–C stress states is proposed. The formulated failure criteria for air-entrained concrete can be used, e.g., in finite-element simulations. The decrease in strength by acting a compressive–tensile stress state related to the uniaxial compressive strength should be considered and this study is helpful to reveal the multiaxial mechanical properties of air-entrained structure enduring freeze–thaw cycles.

Study on Multi-Axial Mechanical Properties of a Polyurethane Foam and Experimental Verification

In order to investigate the multi-axial mechanical properties of a kind of PU (polyurethane) foam, some experiments in different loading conditions including uni-axial tension, uni-axial compression, hydrostatic compression and three-point bending were conducted. It is shown that the hydrostatic component influences yield behavior of PU foam, the yield strength and degree of strain hardening in hydrostatic compression exceed those for uni-axial compression. In terms of the differential hardening constitutive model, the evolution of PU foam yield surface and plastic hardening laws were fitted from experimental data. A finite element method was applied to analyze the quasi-static responses of the PU foam sandwich beam subjected to three-point bending, and good agreement was observed between experimental load-displacement responses and computational predictions, which validated the multi-axial loading methods and stress-strain constitutive model parameters. Moreover, effects of two foam models applied to uni-axial loading and multi-axial loading conditions were analyzed and compared with three-point bending tests and simulations. It is found that the multi-axial constitutive model can bring more accurate prediction whose parameters are obtained from the tests above mentioned.

Multiaxial tensile–compressive strengths and failure criterion of plain high-performance concrete before and after high temperatures

Multiaxial tensile–compressive tests were performed on 100 mm × 100 mm × 100 mm cubic specimens of plain high-performance concrete (HPC) at all kinds of stress ratios after exposure to normal and high temperatures of 20, 200, 300, 400, 500, and 600 °C, using a large static–dynamic true triaxial machine. Friction-reducing pads were three layers of plastic membrane with glycerine in-between for the compressive loading plane; the tensile loading planes of concrete samples were processed by attrition machine, and then the samples were glued-up with the loading plate with structural glue. The failure mode characteristic of specimens and the direction of the crack were observed and described, respectively. The three principally static strengths in the corresponding stress state were measured. The influence of the temperatures, stress ratios, and stress states on the triaxial strengths of HPC after exposure to high temperatures were also analyzed respectively. The experimental results showed that the uniaxial compressive strength of plain HPC after exposure to high temperatures does not decrease completely with the increase in temperature, the ratios of the triaxial to its uniaxial compressive strength depend on brittleness–stiffness of HPC after different high temperatures besides the stress states and stress ratios. On this basis, the formula of a new failure criterion with the temperature parameters under multiaxial tensile–compressive stress states for plain HPC is proposed. This study is helpful to reveal the multiaxial mechanical properties of HPC structure enduring high temperatures, and provides the experimental and theory foundations (testing data and correlated formula) for fire-resistant structural design, and for structural safety assessment and maintenance after fire.

Tensile properties and fiber alignment of human supraspinatus tendon in the transverse direction demonstrate inhomogeneity, nonlinearity, and regional isotropy

A recent study (Lake et al., 2009); reported the properties of human supraspinatus tendon (SST) tested along the predominant fiber direction. The SST was found to have a relatively disperse distribution of collagen fibers, which may represent an adaptation to multiaxial loads imposed by the complex loading environment of the rotator cuff. However, the multiaxial mechanical properties of human SST remain unknown. The objective of this study, therefore, was to evaluate the mechanical properties, fiber alignment, change in alignment with applied load, and structure–function relationships of SST in transverse testing. Samples from six SST locations were tested in uniaxial tension with samples oriented transverse to the tendon long-axis. Polarized light imaging was used to quantify collagen fiber alignment and change in alignment under applied load. The mechanical properties of samples taken near the tendon–bone insertion were much greater on the bursal surface compared to the joint surface (e.g., bursal moduli 15–30 times greater than joint; p<0.001). In fact, the transverse moduli values of the bursal samples were very similar to values obtained from samples tested along the tendon long-axis (Lake et al., 2009). This key and unexpected finding suggests planar mechanical isotropy for bursal surface samples near the insertion, which may be due to complex in vivo loading. Organizationally, fiber distributions became less aligned along the tendon long-axis in the toe-region of the stress–strain response. Alignment changes occurred to a slightly lesser degree in the linear-region, suggesting that movement of collagen fibers may play a role in mechanical nonlinearity. Transverse mechanical properties were significantly correlated with fiber alignment (e.g., for linear-region modulus rs=0.74, p<0.0001), demonstrating strong structure–function relationships. These results greatly enhance current understanding of the properties of human SST and provide clinicians and scientists with vital information in attempting to treat or replace this complex tissue.

Microstructural evolution during multiaxial deformation of pseudoelastic NiTi studied by first-principles-based micromechanical modeling

The deformation behavior of pseudoelastic NiTi shape memory alloys under multiaxial loading conditions is influenced by the evolution of anisotropic martensitic microstructures. We use structural data and elastic constants of B19’ martensite calculated from first principles in a micromechanical model to simulate uni- and biaxial experiments with complex strain paths. The microstructural evolution in terms of volume fractions of different martensite variants and the effect of their elastic anisotropy are investigated in detail. The calculated macroscopic stress–strain data are in good agreement with experimental results reported. The simulations elucidate the relative importance of elastic and inelastic deformation mechanisms (twinning, detwinning and reorientation) for the multiaxial mechanical properties of NiTi. They provide a clear picture of the interplay between phase transformation, evolution of martensitic microstructures and macroscopic mechanical behavior. It is demonstrated that apparently small changes of variant volume fractions in twinned microstructures can significantly affect macroscopic stress states.

Altered Multiaxial Mechanical Properties of the Porcine Anterior Lens Capsule Cultured in High Glucose

Hyperglycemia can alter the mechanical properties of tissues through the formation of advanced glycation endproducts in matrix proteins that have long half-lives. We used a custom experimental system and subdomain finite element method to quantify alterations in the regional multiaxial mechanical properties of porcine lens capsules that were cultured for 8 or 14 weeks in high glucose versus control media. Findings revealed that high glucose significantly stiffened the capsules in both the circumferential and the meridional directions, but it did not affect the known regional variations in anisotropy. Such information could be important in the design of both improved clinical procedures and intraocular implants for diabetic patients.

Multiaxial Mechanical Behavior of Human Saccular Aneurysms

Intracranial saccular aneurysms are focal dilatations of the arterial wall that usually occur in or near the circle of Willis. Two-to-five percent of the population in the western world likely harbors such an aneurysm, rupture of which is the leading cause of nontraumatic subarachnoid hemorrhage. It is widely thought that these lesions rupture when wall stress exceeds wall strength. Given that aneurysms experience multiaxial stress and strain fields in vivo, there is a pressing need for data on their multiaxial mechanical properties. In this paper, we report the first multiaxial data on human saccular aneurysms. Lesions were obtained at autopsy, cannulated, and subjected to cyclic pressurization using a triplane video-based experimental system. The latter recorded the pressures and associated motions of multiple markers that were affixed to the surface of the lesion. Finally, a new sub-domain inverse finite element method was used to estimate the best-fit material parameters in a Fung-type pseudostrain energy function. It was found that the lesions were much stiffer than previously thought, which in turn will affect significantly any estimation of wall stress. There remains a need, however, to collect data on additional specimens, to evaluate different descriptors of the multiaxial behavior, and to correlate these findings with direct measures of the underlying histology.

Orthotropic mechanical properties of chemically treated bovine pericardium.

To facilitate bioprosthetic heart valve design, especially in the use of novel antimineralization chemical technologies, a thorough understanding of the multiaxial mechanical properties of chemically treated bovine pericardium (BP) is needed. In this study, we utilized a small angle light scattering based tissue pre-sorting procedure to select BP specimens with a high degree of structural uniformity. Both conventional glutaraldehyde (GL) and photo-oxidation (PO) chemical treatment groups were studied, with untreated tissue used as the control group. A second set of GL and PO groups was prepared by prestretching them along the preferred fiber direction during the chemical treatment. An extensive biaxial test protocol was used and the resulting stress-strain data fitted to an exponential strain energy function. The high structural uniformity resulted in both a consistent mechanical response and low variability in the material constants. For free fixed tissues, the strain energy per unit volume for GL treated BP was approximately 2.8 times that of PO treated BP at an equibiaxial Green's strain level of 0.16. Pre-stretched tissues exhibited a profound increase in both stiffness and the degree of anisotropy, with the GL treatment demonstrating a greater effect. Thus, structural control leads to an improved understanding of chemically treated BP mechanical properties. Judicious use of this knowledge can facilitate the design and enhanced long-term performance of bioprosthetic heart valves.