Browsing by Author "Nolvi, Anton"
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Item Elastic and fracture properties of free-standing amorphous ALD Al2O3 thin films measured with bulge test(IOP PUBLISHING LTD, 2018-04) Rontu, Ville; Nolvi, Anton; Hokkanen, Ari; Haeggstrom, Edward; Kassamakov, Ivan; Franssila, Sami; Department of Chemistry and Materials Science; Aalto Nanofab; Microfabrication; University of HelsinkiWe have investigated elastic and fracture properties of amorphous Al2O3 thin films deposited by atomic layer deposition (ALD) with bulge test technique using a free-standing thin film membrane and extended applicability of bulge test technique. Elastic modulus was determined to be 115 GPa for a 50 nm thick film and 170 GPa for a 15 nm thick film. Residual stress was 142 MPa in the 50 nm Al2O3 film while it was 116 MPa in the 15 nm Al2O3 film. Density was 3.11 g cm(-3) for the 50 nm film and 3.28 g cm(-3) for the 15 nm film. Fracture strength at 100 hPa s(-1) pressure ramp rate was 1.72 GPa for the 50 nm film while for the 15 nm film it was 4.21 GPa, almost 2.5-fold. Fracture strength was observed to be positively strain-rate dependent. Weibull moduli of these films were very high being around 50. The effective volume of a circular film in bulge test was determined from a FEM model enabling future comparison of fracture strength data between different techniques.Item Evaluation of bone growth around bioactive glass S53P4 by scanning acoustic microscopy co-registered with optical interferometry and elemental analysis(Nature Publishing Group, 2023-12) Holmström, Axi; Meriläinen, Antti; Hyvönen, Jere; Nolvi, Anton; Ylitalo, Tuomo; Steffen, Kari; Björkenheim, Robert; Strömberg, Gustav; Nieminen, Heikki J.; Kassamakov, Ivan; Pajarinen, Jukka; Hupa, Leena; Salmi, Ari; Hæggström, Edward; Lindfors, Nina C.; Department of Neuroscience and Biomedical Engineering; University of Helsinki; Åbo Akademi UniversityBioactive glass (BAG) is a bone substitute that can be used in orthopaedic surgery. Following implantation, the BAG is expected to be replaced by bone via bone growth and gradual degradation of the BAG. However, the hydroxyapatite mineral forming on BAG resembles bone mineral, not providing sufficient contrast to distinguish the two in X-ray images. In this study, we co-registered coded-excitation scanning acoustic microscopy (CESAM), scanning white light interferometry (SWLI), and scanning electron microscopy with elemental analysis (Energy Dispersive X-ray Spectroscopy) (SEM–EDX) to investigate the bone growth and BAG reactions on a micron scale in a rabbit bone ex vivo. The acoustic impedance map recorded by the CESAM provides high elasticity-associated contrast to study materials and their combinations, while simultaneously producing a topography map of the sample. The acoustic impedance map correlated with the elemental analysis from SEM–EDX. SWLI also produces a topography map, but with higher resolution than CESAM. The two topography maps (CESAM and SWLI) were in good agreement. Furthermore, using information from both maps simultaneously produced by the CESAM (acoustic impedance and topography) allowed determining regions-of-interest related to bone formation around the BAG with greater ease than from either map alone. CESAM is therefore a promising tool for evaluating the degradation of bone substitutes and the bone healing process ex vivo.