Institute of Mechanical SystemsOpen OpportunitiesStudying the long-term diffusion of solutes in metals is crucial for a variety of present and futuristic engineering applications. This includes the design of safe and compact solid-state hydrogen reservoirs for automobile applications, designing corrosion-resistant materials for nuclear applications, and much more. The time scales involved in such mass diffusion processes for potential applications range from seconds to minutes. However, most state-of-the-art atomistic techniques can simulate an ensemble of atoms as large as some micrometers and for a real-time of some microseconds at best. Hence, the computational modeling of atomistic mass diffusion presents many challenges, which is why the design of these devices has relied on experiments. This project deals with an emerging class of atomistic simulation techniques based on statistical mechanics, which aims to track the relevant statistics of the ensemble rather than tracking all atomic positions and momenta. In such a statistical framework with multiple atomic species, every atomic site ceases to be a pure species and is instead identified by probabilities of finding different types of species at that site.
In order to introduce mass transport in such a setting, one needs to update the concentrations of different species at the atomic sites based on a phenomenological model, or by an atomistically informed master equation for the site probabilites. We are more interested in the latter approach, which involves computing the energy barriers and minimum energy pathways needed for atoms of different types to hop from one site to another. As this computation needs to be done for every possible atomic hop in the ensemble, the concentration update becomes computationally expensive. In this project, we plan to bypass this by employing graph neural networks (GNNs) to learn the hopping energy barriers as a function of local atomic environments and using a pre-trained GNN to update the site probabilities, which would enable us to reach higher time scales relevant for potential applications. - Engineering and Technology
- Master Thesis
| Unlike crystalline materials which are characterized by well ordered atomic arrangements of a clear repeated unit-cell, amorphous solids cannot be described by a tessellated representative volume element due to the disorder of their microstructures. One example of amorphous solids are metallic glasses that typically have high resistance to plastic deformations thanks to the absence of grain boundaries, yet their failure modes are rapid and catastrophic. Recently it was shown that a macroscale analogy can be achieved with truss metamaterials, as introduction of disorder can lead to similar characteristics to those exhibited by amorphous solids.
On our ongoing research we study reconfigurable truss metamaterials, whose members are modelled as "bendy-straws" which are characterized by local multistability. Namely, in 2D each constituent segment of every straw has four stable equilibria, which provide a straw-based truss metamaterial a myriad of multiaxial stable configurations. Thus, a careful design can lead to structures with different operative stable states, whose reconfigurations do not involve introducing plastic deformations. So far, we mainly focused on periodic straw-based structures, yet in inspiration of amorphous solids and the interesting behavior they introduce, we wish to expand this study to disordered arrangements. Such structures are expected to provide high resilience and damage tolerance. Moreover, since large deformations are manifested in post buckling rather than plastic deformations, instabilities such as shear bands which cause irreversible plastic deformations in metallic glasses and truss metamaterials, can in this case be leveraged for rapid reconfiguration. Thanks to this characteristic, studying disorder in reconfigurable structures lays the foundations for nondestructive experimentation of plastic phenomena. - Mechanical Engineering
- ETH Zurich (ETHZ), Master Thesis
| During pregnancy, the skin around the womb gets continuously stretched. The thickest layer of this skin, is the dermis, which consists mainly of collagen and fibroblasts. An established model of the dermis is the 3D culture of fibroblasts in collagen hydrogels. To now mimic the load situation of skin during pregnancy, a creep setup shall be established based on existing bioreactor systems (Wahlsten & Rütsche et al., 2022). The goal is to expose the cells in their viscoelastic matrix to a constant pressure followed by a tension-release. Observing the response of the cells to these mechanical stimuli over time will give new insights into the mechanobiology of skin cells. - Engineering and Technology, Medical and Health Sciences
- Master Thesis, Semester Project
| Skin is a multilayer tissue. The biggest layer of the human skin, the dermal layer, consists mainly of collagen and fibroblasts (skin cells). An established model of the dermis is the 3D culture of fibroblasts in collagen hydrogels. Stimulating these fibroblasts by applying equibiaxial strain to the gels has been shown to significantly enhance the cell’s proliferation (Wahlsten & Rütsche et al., 2022). These findings are of high importance for tissue engineering, but also highlight the need to study the mechanobiological response of fibroblasts to mechanical stimuli more in detail. Therefore, a 2D fibroblast cell culture system shall be established enabling to physiologically strain cells grown on a soft substrate. - Biology, Engineering and Technology, Medical and Health Sciences
- Master Thesis, Semester Project
| Skin is a multilayer tissue. The biggest layer of the human skin, the dermal layer, consists mainly of collagen and fibroblasts.
For applications like skin substitutes as chronic wound treatments, 3D cultures of fibroblasts have been developed. As shown in the figure attached, it was presented that human Dermal Fibroblasts cultured in 3D collagen hydrogels show an enhanced proliferation (increase in cell number by cell division) when exposed to mechanical stimulation in the form of cyclic strain (Wahlsten & Rütsche et al., 2022). This desired effect often comes with the downside of apoptosis (cell death), highlighting the need for a time-lapsed simultaneous study of proliferation and apoptosis in dynamic 3D culture of fibroblasts. - Biology, Engineering and Technology, Medical and Health Sciences
- Master Thesis, Semester Project
| This project involves the study of the effect of quasiperiodicity on the homogenized mechanical behavior of two-dimensional truss metamaterials, both in the linear regime as well as in the presence of large deformations and self-contact.
The student is expected to approach the problem computationally while also supporting an ongoing experimental campaign. With the support of the supervisors, they will design different quasiperiodic lattices, develop efficient numerical models and investigate the computational homogenization problem of these lattices. The student will also assist with compression experiments carried out on 3D-printed architectures. - Materials Engineering, Mechanical Engineering
- Bachelor Thesis, Collaboration, Master Thesis, Semester Project
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