Microindentation of Polymethyl Methacrylate (PMMA) Based Bone Cement

Characterization of polymethyl methacrylate (PMMA) based bone cement subjected to cyclical loading using microindentation technique is presented in this paper. Indentation technique represents flexible mechanical testing due to its simplicity, minimal specimen preparation and short time needed for tests. The mechanical response of bone cement samples was studied. Realised microindentation enabled determination of the indentation testing hardness HIT and indentation modulus EIT of the observed bone cement. Analysis of optical photographs of the imprints showed that this technique can be effectively used for characterization of bone cements

Mechanical behaviour of small load bearing structures fabricated by 3d printing

© 2019 Published by the Serbian Academic Center. 3D printing is state‐of‐the‐art manufacturing technology. In addition to prototyping, the development of this technology allows the parts produced by this technology to be used as fully functional assemblies. There are different 3D printing technologies (Fused Deposition Modeling, FDM, Selective Laser Sintering, SLS, Stereolithography, SLA and others), and different materials can be used (polymer filaments, polymer and composite powders for sintering, photopolymers). This paper presents the process of design and fabrication of small load bearing structures by FDM and verification of its mechanical properties, by using three‐point bending test. The printing parameters and setup of the three‐point bending test were analysed from aspects of flexural strength and final bending angle that was determined experimentally and by calculation

Numerical modeling and experimental behavior of closed-cell aluminum foam fabricated by the gas blowing method under compressive loading

© 2019 by the authors. This paper deals with the experimental and numerical study of closed-cell aluminum-based foam under compressive loading. Experimental samples were produced by the gas blowing method. Foam samples had an average cell size of around 1 mm, with sizes in the range 0.5-5 mm, and foam density of 0.6 g/cm3. Foam samples were subjected to a uniaxial compression test, at a displacement rate of 0.001 mm/s. Load and stress were monitored as the functions of extension and strain, respectively. For numerical modeling, CT scan images of experimental samples were used to create a volume model. Solid 3D quadratic tetrahedron mesh with TETRA 10-node elements was applied, with isotropic material behavior. A nonlinear static test with an elasto-plastic model was used in the numerical simulation, with von Mises criteria, and strain was kept below 10% by the software. Uniform compressive loading was set up over the top sample surface, in the y-axis direction only. Experimental tests showed that a 90 kN load produced complete failure of the sample, and three zones were exhibited: an elastic region, a rather uniform plateau region (around 23 MPa) and a densification region that started around 35 MPa. Yielding, or collapse stress, was achieved around 20 MPa. The densification region and a rapid rise in stress began at around 52% of sample deformation. The numerical model showed both compressive and tensile stresses within the complex stress field, indicating that shear also had a prominent role. Mainly compressive stresses were exhibited in the zones of the larger cells, whereas tensile stresses occurred in zones with an increased number of small cells and thin cell walls

Cost optimization of additive manufacturing in wood industry

© Faculty of Mechanical Engineering, Belgrade. Software packages for 3D design and additive manufacturing (AM) technologies, initially known as rapid prototyping (RP) have emerged during the last years, as a cutting edge solutions for custom prototyping. These new tools and technologies lower the design costs, but also allow rapid creation of fully functional components. This paper describes the FDM and 3DP rapid prototyping technologies that were used to create elements and tools in the wood industry field. Total costs of manufacturing related to the fabrication of sample elements and tools are analysed. One of the main recognised issues of wider application of rapid prototyping technologies is their still very high costs related to all production aspects, starting with a lack of available materials, material cost, up to high cost of available commercial equipment, usually focused only on specific solutions and limited range of materials. Generally, AM costs can be divided into the group of fixed costs and variable ones. This paper deals with the optimization of the production costs of fabricated elements in case of small-scale production, and optimization of variable costs (processing and post-processing, costs of enforcement, and material costs)

Tribometry of Materials for Bioengineering Applications

Development of materials for biomedical implants (metals, polymers, ceramics and composites) is directly determined by characteristics and nature of the tissue, organs and systems that are being replaced or supplemented. Modern material investigations at micro- and nano- level enable introspection into new aspects of material behaviour and offer possibilities to significantly improve systems in use, from different aspects, such as improvement of manufacturing technologies or surface technologies modifications. Biomaterial investigations from a tribology point of view offer contribution to testing realised in this area, especially with use of novel devices for research in area of nanotribology

Cost optimization of additive manufacturing in wood industry

Software packages for 3D design and additive manufacturing (AM) technologies, initially known as rapid prototyping (RP) have emerged during the last years, as a cutting edge solutions for custom prototyping. These new tools and technologies lower the design costs, but also allow rapid creation of fully functional components. This paper describes the FDM and 3DP rapid prototyping technologies that were used to create elements and tools in the wood industry field. Total costs of manufacturing related to the fabrication of sample elements and tools are analysed. One of the main recognised issues of wider application of rapid prototyping technologies is their still very high costs related to all production aspects, starting with a lack of available materials, material cost, up to high cost of available commercial equipment, usually focused only on specific solutions and limited range of materials. Generally, AM costs can be divided into the group of fixed costs and variable ones. This paper deals with the optimization of the production costs of fabricated elements in case of small-scale production, and optimization of variable costs (processing and post-processing, costs of enforcement, and material costs)

Experimental study and analytical model of shear thinning in 3d bioprinting of gelatin

© 2020 Published by Faculty of Engineering. This paper presented extrusion-based 3D bioprinting of gelatin hydrogel and optimisation of material properties and process parameters, in order to improve printability of hydrogel. Gelatin hydrogel was prepared by mixing it with water in concentration of 13.04 wt%. Dimensional accuracy of the bioprinting was studied and significant changes in comparison with designed geometry were noted. Gelatin hydrogel made only with water showed inadequate thixotropy for extrusion based bioprinting and poor mechanical properties of the printed sample, and needs additional constituents to enable good printability with satisfying dimensional accuracy. We presented parameter optimisation index (POI), shear thinning model and friction factor of gelatin hydrogel by using analytical approach. Friction factor of the gelatin hydrogel during bioprinting was 0.268 10-5. Analytical models of shear thinning and friction factor were in consistence with experimental data, and indicated that such approach can be used in optimisation of bioprinting parameters and material properties

Influence of the ringer's solution on wear of vacuum mixed poly(Methyl methacrylate) bone cement in reciprocating sliding contact with aisi 316l stainless steel

This paper presents microstructural properties and damage behaviour of a vacuum mixed poly(methyl metacrylate) (PMMA) bone cement, during the sliding contact with AISI 316L stainless steel, under micro-loads. Influence of the Ringer's solution on the wear was analysed in comparison to dry contact. The variation of load did not produce any significant change of the wear factor while the increase in the sliding speed induced significant increases in the wear factor, more pronounced in the case of dry sliding. The obtained wear factors were in average higher for the sliding in Ringer's solution than those obtained under dry conditions. Significant fragmentation of the worn tracks, of irregular shapes with broken edges, was observed, slightly more pronounced for the dry contact. Many cavities and voids were formed on the wear track surface, but they did not extend into the bulk material. Higher loads produced more uniform and less fragmented wear tracks. Abrasive, adhesive wear and plastic deformation grooves were observed, as well as fatigue and erosive wear. Fatigue cracks developed in the direction normal to sliding. Network of fine craze cracks was exhibited on the surface of wear tracks, especially pronounced in the case of dry sliding. These results are important since they contribute to understanding the sites of crack initiation, and development mechanisms on the surface of PMMA bone cements, also including synergistic effects of physiological environments pertaining to the non-steady crack and craze behaviour and crack pattern development in PMMA

Customization of electrospinning for tissue engineering

© 2018 by University of Niš, Serbia. This paper deals with two electrospinning technologies: the melt electrospinning with a customized jet head, adapted from the fused deposition modeling (FDM) 3D printer, in comparison with the standard solution electrospinning, aiming at fabrication of tissue engineering scaffolds. The resulting fibers are compared. The influence of the collector properties on those of the fabricated scaffold is investigated. The resulting electrospun fibers exhibit different characteristics such as morphology and thickness, depending on the technology. The micro-fibers are produced by the melt electrospinning with an inbuilt 3D printer jet head, whereas the solution electrospinning has produced nano-and micro-fibers. The scaffolds fabricated on the rotating drum collector exhibit a more ordered structure as well as thinner fibers than those produced on the stationary plate collector. Further investigations should aim at fabrication of porous hollow fibers and tissue engineering scaffolds with controlled porosity and properties