Oliver Walker

Abstract

Mechanical properties of porous lattice materials can be tuned by the structure. Thus, the effect of the unit cell design on the mechanical properties is of special interest. However, studies often lack an in-depth investigation of the underlying mechanisms. Additionally, inhomogeneous bulk material properties and structural deviations introduced during manufacturing are often neglected. Here, the impact of the pore shape on Young's modulus, initial peak stress, and energy absorbance of lattice materials is investigated. Structural deviations of 3D-printed lattice materials from the computer-aided design (CAD) are examined, and analyze how they affect the mechanical properties. For comparability, the porosity, overall dimensions, and unit cell size of the lattice material are kept constant. Flexible lattice materials assembled of 3 × 3 × 3 unit cells are 3D-printed (stereolithography). Mechanical properties are determined through uniaxial compression tests and finite element modeling (FEM). Deviations between CAD and 3D-printed lattice materials are analyzed using micro-computed tomography (µ-CT). Combining µ-CT with FEM revealed the impact of these deviations on the mechanical properties. It is found that the mechanical properties depend indeed on the pore shape. Furthermore, a pyramidal shape along the printing direction and displaced or deformed pores are observed in the 3D-printed lattice materials, all of which result in reduced mechanical properties.

Abstract

Magnesium and its alloys are suitable materials for biodegradable biomedical implants such as cardiovascular stents. Here we introduce an innovative composite polyelectrolyte multilayer/wax coating applied to commercial coronary Mg-based stents serving as a barrier layer effectively retarding corrosion. This hydrophobic coating, build by layer-by-layer technology, appeared very thin, smooth, homogeneous, strongly adherent and completely covering the surface of the Mg-stent. In-vitro degradation tests showed greater resistance to degradation of coated Mg-stents compared to uncoated and passivated ones. Cytocompatibility studies proved that Mg-stent coated with the composite coating was non-cytotoxic and improved fibroblast cell viability compared to the uncoated Mg-stent.

Abstract

In the context of rare earth element extraction using solid-liquid process, hybrid materials having specific functional group were largely studied. However, there is a lack of in situ characterization method to understand how the functional group behaves when interacts with the rare earth element. Here, we propose a new experimental method to understand the interaction between immobilized functional group and REE in aqueous media using a well-characterized model system coupled to surface analyses. Model system was prepared by grafting diglycolamide functionalized silane on planar silica substrate. In order to have a clear description of the morphology and the structure of the model system, the silane grafting process was characterized using contact angle measurement, X-Ray Reflectivity, peak force measurements by Atomic Force Microscopy and in situ analysis by Fourier Transformed Infrared Spectroscopy in Attenuated Total Reflection. Afterwards, the behavior of the grafted molecules was investigated in neodymium aqueous solution at various pH by in situ infrared spectroscopy and hard X-ray reflectivity characterizations. Here, we highlight that the complexation of Nd3+ by the diglycolamide function is correlated with its dehydration and a modification of the molecule configuration.