Fracture mechanics and failure of soft materials
In addition to the deformation behavior of soft biological tissues, biomedical and elastomeric materials we investigate their failure behavior, in particular with regard to physiological function and medical contexts. Our research in this field began with studies on the failure of the fetal membranes, which are unique in the sense that failure of these tissues at term is part of their physiological function, while preterm failure can be associated with severe consequences for the newborn [1,2]. We have analyzed the performance of sealing strategies after surgical interventions [3,4], and analyzed the effect of hydration, osmolarity and exposure to CO2, which are conditions relevant in prenatal surgery [5].
We determine classical metrics of non-linear fracture mechanics such as the characteristic energy for tearing of biomedical materials [6], but for soft biological tissues, the significance of these metrics has limits [7]. Therefore, we also use dedicated testing equipment to define and quantify alternative measures such as the "defect tolerance" of materials [7,8], i.e. the property of tolerating the presence of a hole, cut or tear without a substantial reduction of the ultimate strength. As another example, we have recently revisited the suture retention test, a standard test to quantify a material's resistance to the pull-out of medical sutures, and considered it from a fracture mechanics perspective [8,9].
Our experimental fracture mechanics investigations are complemented by theoretical analysis, model development and computational studies, to refine the experimental techniques but also to rationalize the observed behavior [7, 10].
[1] Bürzle W. Mechanical characterization and modeling of human fetal membrane tissue. ETH Diss. Nr. 21784 (2014).
[2] Perrini M., Bürzle W., Haller C., Ochsenbein-Kölble N., Deprest J., Zimmermann R., Mazza E., Ehrbar M. (2013) Contractions, a risk for premature rupture of fetal membranes: A new protocol with cyclic biaxial tension. Med. Eng. Phys. 35, 846-851. DOI: 10.1016/j.medengphy.2012.08.014
[3] Kivelio A., Dekoninck P., Perrini M., Brubaker C.E., Messersmith P.B., Mazza E., Deprest J., Zimmermann R., Ehrbar M., Ochsenbein-Koelble, N. (2014) Mussel mimetic tissue adhesive for fetal membrane repair: initial in vivo investigation in rabbits. Eur. J. Obst. Gyn. Rep. Biol. 171, 240-245. DOI: 10.1016/j.ejogrb.2013.09.003
[4] Haller C.M., Buerzle W., Kivelio A., Perrini M., Brubaker C.E., Gubeli R.J., Mallik A.S., Weber W., Messersmith P.B., Mazza E., Ochsenbein-Koelble N., Zimmermann R., Ehrbar, M. (2012). Mussel-mimetic tissue adhesive for fetal membrane repair: an ex vivo evaluation. Acta Biomater. 8(12), 4365-4370. DOI: 10.1016/j.actbio.2012.07.047
[5] Bircher K., Merluzzi R., Wahlsten A., Spiess D., Simões-Wüst A.P., Ochsenbein-Kölble N., Zimmermann R., Deprest J. Mazza, E. (2020) Influence of osmolarity and hydration on the tear resistance of the human amniotic membrane. J Biomech 98, 109419. DOI: 10.1016/j.jbiomech.2019.109419
[6] Bernardi L., Hopf R., Sibilio D., Ferrari A., Ehret A.E., Mazza E. (2017) On the cyclic deformation behavior, fracture properties and cytotoxicity of silicone-based elastomers for biomedical applications. Polym. Test. 60, 117-123. DOI: 10.1016/j.polymertesting.2017.03.018
[7] Bircher K., Zündel M., Pensalfini M., Ehret A.E., Mazza E. (2019) Tear resistance of soft collagenous tissues. Nat. Commun. 10, 792. DOI: 10.1038/s41467-019-08723-y
[8] Bircher K., Ehret A.E., Spiess D., Ehrbar M., Simões-Wüst A. P., Ochsenbein-Kölble N., Zimmermann R., Mazza E. (2019) On the defect tolerance of fetal membranes. Interface Focus 9, 20190010. DOI: 10.1098/rsfs.2019.0010
[9] Pensalfini M. Meneghello S., Lintas V., Bircher K. Ehret A.E. Mazza E. (2018) The suture retention test, revisited and revised. J. Mech. Behav Biomed. Mater. 77, 711-717. DOI: 10.1016/j.jmbbm.2017.08.021
[10] Bernardi L., Mazza E., Ehret A.E. (2018) The effect of clamping conditions on tearing energy estimation for highly stretchable materials. Eng. Frac. Mech. 188, 300-308. DOI: 10.1016/j.engfracmech.2017.08.035