Abstract Background Mechanical testing of soft materials requires specialized equipment. Unfortunately, commercial devices are expensive and, thus, prohibitive for many laboratories. Additionally, non-uniformity in device use across laboratories contributes to the reproducibility crisis in experimental mechanics. Finally, even expensive commercial devices are usually not adaptable and do not allow for customization, for example, to integrate in-situ imaging modalities into the test protocols. Objective Therefore, our objective was to develop a device that is accessible, customizable, and compatible with various imaging modalities. Methods We set out to develop a device capable of operating in biaxial, off-biaxial, and uniaxial modes under monotonic loading, cyclic testing, and stress relaxation. To this end, we combined a 3D printed device platform with off-the-shelf motors, load cells, and LabVIEW control. Results Our device is easy to use, relatively inexpensive ( $$\approx $$ ≈ $15,000), and fully customizable. To showcase the device, we first obtained equibiaxial stress-strain curves of rubber samples under large deformation. Additionally, we tracked in-plane strains via digital image correlation and through-thickness deformations via optical coherence tomography. In our second and third examples, we produced strip biaxial and biaxial stress-strain curves under repeated step and stress relaxation loading of PCL meshes and a tricuspid valve leaflet, respectively. Simultaneously, we imaged the microstructure of the materials via confocal and multiphoton microscopy. Conclusion In conclusion, we have designed a device that is accessible, customizable, and compatible with various imaging modalities. We hope that our technology enables other labs to conduct soft material tests and that it improves the reproducibility of soft material mechanical data.

The mechanics of the tricuspid valve are a critical determinant of its function and dysfunction. With millions suffering from tricuspid regurgitation, there is a pressing need to fill persistent knowledge gaps. A better understanding of the valve's mechanics is essential for improving repair strategies and biomaterial-based replacements. This study aimed to quantify the differences in strains within leaflets and between leaflets under both physiological and pathological loads. We mounted six whole porcine heart preparations in vitro and measured full-field leaflet strains using three-dimensional digital image correlation.We varied peak transvalvular pressures between 20, 50, and 80 mmHg and applied three levels of annular dilation (0%, 30%, and 60%). Strain data were transformed into leaflet-specific radial and circumferential components, and compared statistically using linear mixed-effects models. Leaflet strains exhibited significant within- and between-leaflet heterogeneity. Strain magnitude increased with pressure but not with annular dilation. Additionally, strains were directionally dependent. Furthermore, we found that anterior and posterior leaflet strains near the annulus, in the belly, and near the free edge did not differ significantly. In contrast, strains in the septal leaflet increased from the annulus to the free edge. These data provide spatially and directionally resolved strain maps of all three tricuspid valve leaflets in whole-heart preparations. By filling a critical knowledge gap, these findings may guide the design of biomaterials for valve repair and replacement.

Abstract Background The hole-drilling method, widely used to evaluate near-surface residual stresses, typically relies on strain gauge rosettes to measure surface deformations resulting from stress relaxation. However, this approach has several limitations, including a small number of discrete measurement points, the need for careful surface preparation, and sensitivity to misalignment between the rosette and the drilled hole. Objective To address these issues, the use of Digital Image Correlation (DIC), a full-field optical measurement technique, was investigated as a replacement for the strain gauge rosette within the hole-drilling method. Methods DIC was employed to measure strain and displacement fields around drilled holes in steel specimens subjected to various load levels, aiming to identify the minimum stress that could be accurately resolved. Several adjustments were made to both the hardware configuration and data processing procedures within the DIC setup to improve the accuracy of measured deformation. Results Accurate stress evaluation was achieved even at low stress levels, on the order of a few MPa, despite the relatively small strain magnitudes compared to the noise level. Conclusions The results obtained demonstrate that integrating DIC with the hole-drilling method offers a promising and effective alternative to traditional strain gauge-based residual stress measurement.