Mechanical characterization of soft biological tissue is becoming more and more prevalent. Despite the growing use of planar biaxial testing for soft tissue characterization, testing conditions and subsequent data analysis have not been standardized and vary widely. This also influences the quality of the result of the parameter fitting. Moreover, the testing conditions and data analysis are often not or incompletely reported, which impedes the proper comparison of parameters obtained from different studies. With a focus on planar biaxial tests using rakes, this paper investigates varying testing conditions and varying data analysis methods and their effect on the quality of the parameter fitting results. By means of a series of finite element simulations, aspects such as number of rakes, rakes׳ width, loading protocol, constitutive model, material stiffness and anisotropy are evaluated based on the degree of homogeneity of the stress field, and on the correlation between the experimentally obtained stress and the stress derived from the constitutive model. When calculating the aforementioned stresses, different definitions of the section width and deformation gradient are used in literature, each of which are looked into. Apart from this degree of homogeneity and correlation, also the effect on the quality of the parameter fitting result is evaluated. The results show that inhomogeneities can be reduced to a minimum for wise choices of testing conditions and analysis methods, but never completely eliminated. Therefore, a new parameter optimization procedure is proposed that corrects for the inhomogeneities in the stress field and induces significant improvements to the fitting results. Recommendations are made for best practice in rake-based planar biaxial testing of soft biological tissues and subsequent parameter fitting, and guidelines are formulated for reporting thereof in publications.

Stress-stretch curves of planar biaxial tests of healthy aortic tissue ( ) Average stress in a fiber family at time , see Equation 23 Undeformed collagen fiber orientation vector Deviatoric part of a constituent-specific right Cauchy-Green tensor, see Equation 3

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Cardiac surgeries may expose pulmonary arterial tissue to systemic conditions, potentially resulting in failure of that tissue. our goal was to quantitatively assess pulmonary artery adaptation due to changes in mechanical environment. In 17 sheep, we placed a pulmonary autograft in aortic position, with or without macroporous mesh reinforcement. It was exposed to systemic conditions for 6 months. All sheep underwent 3 ECG-gated MRI's. Explanted tissue was subjected to mechanical and histological analysis. Results showed progressive dilatation of the unreinforced autograft, while reinforced autografts stabilized after two months. Some unreinforced pulmonary autograft samples displayed more aorta-like mechanical behavior with increased collagen deposition. the mechanical behavior of reinforced autografts was dominated by the mesh. the decrease in media thickness and loss of vascular smooth muscle cells was more pronounced in reinforced than in unreinforced autografts. In conclusion, altering the mechanical environment of a pulmonary artery causes changes in its mechano-biological properties.

Objective To describe effects of non‐ablative erbium‐doped:yttrium‐aluminium‐garnet (Er:YAG) laser on vaginal atrophy induced by iatrogenic menopause in the ewe. Design Animal experimental, randomised, sham and estrogen‐treatment controlled study with blinding for primary outcome. Setting KU Leuven, Belgium. Sample Twenty‐four ewes. Methods Menopause was surgically induced, after which the ewes were randomised to three groups receiving vaginal Er:YAG laser application three times, with a 1‐month interval; three sham manipulations with a 1‐month interval; or estrogen replacement and sham manipulations. At given intervals, ewes were clinically examined and vaginal wall biopsies were taken. Vaginal compliance was determined by passive biomechanical testing from explants taken at autopsy. Main outcome measures Vaginal epithelial thickness (primary), composition of the lamina propria (collagen, elastin, glycogen and vessel content), vaginal compliance, clinical signs. Results Animals exposed to Er:YAG laser application and sham manipulation, but not to estrogens, displayed a significant and comparable increase in vaginal epithelial thickness between baseline and 7 days after the third application (69% and 67%, respectively, both P < 0.0008). In laser‐treated ewes, temporary vaginal discharge and limited thermal injury were observed. Estrogen‐substituted ewes displayed a more prominent increase in epithelial thickness (202%; P < 0.0001) and higher vaginal compliance (P < 0.05). None of the interventions induced changes in the lamina propria. Conclusions Vaginal Er:YAG laser has comparable effect to sham manipulation in menopausal ewes. Tweetable abstract Vaginal Er:YAG laser has comparable effect to sham manipulation in menopausal ewes #LASER #GSM #RCT.