Injectable calcium phosphate foams for the delivery of Pitavastatin as osteogenic and angiogenic agent

Apatitic bone cements have been used as a clinical bone substitutes and drug delivery vehicles for therapeutic agents in orthopedic applications. This has led to their combination with different drugs with known ability to foster bone formation. Recent studies have evaluated Simvastatin for its role in enhanced bone regeneration, but its lipophilicity hampers incorporation and release to and from the bone graft. In this study, injectable calcium phosphate foams (i-CPF) based on a-tricalcium phosphate were loaded for the first time with Pitavastatin. The stability of the drug in different conditions relevant to this study, the effect of the drug on the i-CPFs properties, the release profile, and the in vitro biological performance with regard to mineralization and vascularization were investigated. Pitavastatin did not cause any changes in neither the micro nor the macro structure of the i-CPFs, which retained their biomimetic features. PITA-loaded i-CPFs showed a dose-dependent drug release, with early stage release kinetics clearly affected by the evolving microstructure due to the setting of cement. in vitro studies showed dose-dependent enhancement of mineralization and vascularization. Our findings contribute towards the design of controlled release with low drug dosing bone grafts: i-CPFs loaded with PITA as osteogenic and angiogenic agentPeer ReviewedPostprint (author's final draft

Critical assessment of two-dimensional methods for the microstructural characterization of cemented carbides

Cemented carbides, or hard metals, are ceramic–metal composites usually consisting of tungsten carbide particles bound by a cobalt-based alloy. They are the backbone materials for the tooling industry, as a direct consequence of the outstanding range of property combinations, depending on their effective microstructural assemblage, i.e., the physical dimensions and relative content of their constitutive phases. Hence, reliable microstructural characterization becomes key for hard metal grade selection and quality control. This work aimed to assess the practical twodimensional characterization methods for the most important one- and two-phase properties of cemented carbides, i.e., the carbide grain size, phase fraction, carbide contiguity, and binder mean free path. Three different methods—point, line, and area analysis—were implemented to characterize four microstructurally distinct grades. The images were acquired by optical and scanning electron microscopy, with the latter through both secondary and backscattered electrons. Results were critically discussed by comparing the obtained values of properties and the different characterization methodology. Inspection technique combinations were finally ranked based on accuracy, accessibility, and operability considerations. The line method was used to analyze all the properties, the area method, for the one-phase properties, and the point method, for only the phase fraction. It was found that the combination of optical microscopy and the line analysis method was suitable for a direct inspection and rapid estimation for carbides above fine grain size. The most precise results were achieved using line analysis of the images obtained by the backscattered electrons of the scanning electron microscopeThe work leading to this publication was supported by the Feodor Lynen Research Fellowship of the Alexander von Humboldt Foundation, by the individual research grant from the Deutsche Forschungsgemeinschaft (DFG-425923019), by the Spanish Ministerio de Ciencia e Innovación MICINN-FEDER (Spain) through grant PID2019-106631GB-C41 (AEI/10.13039/501100011033), and by the “Open Access Publication Funding” program of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) and Saarland University. The work also obtained funding for the FIB/SEM instrument used for SEM imaging and EBSD by the Deutsche Forschungsgemeinschaft (INST 256/510-1 FUGG)Postprint (published version

One- and two-dimensional photonic crystal micro-cavities in single crystal diamond

The development of solid-state photonic quantum technologies is of great interest for fundamental studies of light-matter interactions and quantum information science. Diamond has turned out to be an attractive material for integrated quantum information processing due to the extraordinary properties of its colour centres enabling e.g. bright single photon emission and spin quantum bits. To control emitted photons and to interconnect distant quantum bits, micro-cavities directly fabricated in the diamond material are desired. However, the production of photonic devices in high-quality diamond has been a challenge so far. Here we present a method to fabricate one- and two-dimensional photonic crystal micro-cavities in single-crystal diamond, yielding quality factors up to 700. Using a post-processing etching technique, we tune the cavity modes into resonance with the zero phonon line of an ensemble of silicon-vacancy centres and measure an intensity enhancement by a factor of 2.8. The controlled coupling to small mode volume photonic crystal cavities paves the way to larger scale photonic quantum devices based on single-crystal diamond

Microstructural and metallurgical assessment of the laser-patterned cemented tungsten carbide (WC-CoNi)

Cemented carbide is difficult to machine using traditional chip-removal methods due to its hardness. Electrical discharge machining (EDM) is the common method applied to shape cemented carbides because high geometric precision can be achieved. However, some important defects (pores, residual stresses or oxidation products) can be induced due to thermal reactions. Ultra-short pulse laser processing can also provide high precision and meanwhile effectively avoid these defects due to its short laser-matter reaction time. In this paper, three different patterns on WC-CoNi cemented carbides for tribological purposes, namely line-like patterns, dimples and grooves, have been created using different laser set-ups with pulse duration in the range of nanoseconds (10-9s), picoseconds (10-12s) and femtoseconds (10-15s). Microstructural and metallurgical changes of modified surfaces have been studied. Laser scanning microscopy (LSM) is conducted to measure the pattern dimensions. Focused ion beam (FIB) in combination with scanning electron microscope (SEM) is used to investigate the microstructural changes of the patterned materials. © 2018 Elsevier B.V. All rights reserved.Postprint (published version

Microstructural and metallurgical assessment of the laser-patterned cemented tungsten carbide (WC-CoNi)

Cemented carbide is difficult to machine using traditional chip-removal methods due to its hardness. Electrical discharge machining (EDM) is the common method applied to shape cemented carbides because high geometric precision can be achieved. However, some important defects (pores, residual stresses or oxidation products) can be induced due to thermal reactions. Ultra-short pulse laser processing can also provide high precision and meanwhile effectively avoid these defects due to its short laser-matter reaction time. In this paper, three different patterns on WC-CoNi cemented carbides for tribological purposes, namely line-like patterns, dimples and grooves, have been created using different laser set-ups with pulse duration in the range of nanoseconds (10-9s), picoseconds (10-12s) and femtoseconds (10-15s). Microstructural and metallurgical changes of modified surfaces have been studied. Laser scanning microscopy (LSM) is conducted to measure the pattern dimensions. Focused ion beam (FIB) in combination with scanning electron microscope (SEM) is used to investigate the microstructural changes of the patterned materials. © 2018 Elsevier B.V. All rights reserved

Tribological performance of laser patterned cemented tungsten carbide parts

Some tools for machining processes used to be guided by supporting parts while using them for cutting or abrasive machining. For instance, the guide stone is used as supporting part in the honing process, which maintains the concentricity of the rotating axis. The contact surfaces of the supporting parts should exhibit the following properties: adequate combination of hardness, toughness and wear resistance. The damage of contact surfaces can be caused by a combination of friction and adhesion, related to the weakness of surface conditions in the tribological system, e.g. asperities, debris and pores. In order to investigate the impact of the surface topography, contact surfaces of the supporting parts made of cemented tungsten carbide (WC-Co) have been treated by means of laser surface patterning (LSP). Two different surface patterns with deterministic geometries on the micro and nano scale are achieved by two distinct LSP methods: line-like patterns by Laser-Interference Metallurgy (LIMET) with ns-laser and dimples by ps-laser. Tangential force coefficients, similar to the coefficient of friction (COF) in the non-abrasive case, are measured to evaluate the impact of the surface patterns. In this paper, the LSP methods as well as the analysis of the resulting surface topography are introduced. It is found that higher friction is obtained by line-like patterns whereas dimples can efficiently reduce the friction. At low load, hydrodynamic effects are reinforced as the dimples work as lubricant reservoirs and trap wear particles, and the observation becomes less obvious at high load. Meanwhile, only slight friction augmentation is observed by line-like patterns when the load increases.Peer Reviewe

Micromechanical investigations of CVD coated WC-Co cemented carbide by micropillar compression

Deformation behavior of an industrial coated cemented carbide (WC-Co substrate coated with CVD multilayer of TiN/Zr(C,N)/Ti(C,N,O)/Al2O3) was investigated by means of micropillar compression method. In addition to the WC-Co substrate pillars, new composite pillar combination consisting of substrate, TiN interlayer and carbonitride hard coating were tested. The study targeted to document and analyze interactions between different phases and components (substrate, interlayer and coating) while subjected to compressive stress. It is found that deformation of the substrate depends mainly on the assemblage and the distribution of WC and Co phases within the pillar. The phase assemblage is subjected to changes after deformation which has an impact on the stiffness. Detailed analysis of plastic deformation within WC coarse grains pointed out that strain energy can be extensively dissipated in this phase by means of single and multiple slip. The composite/hybrid pillar formed by association of the substrate and the coating enhanced the ultimate strength in comparison to their respective individual components, highlighting the effective load-bearing response of coating and substrate acting as a coated system. This assessment was further supported by the excellent interfacial strength attested by the established TiN interlayer between the substrate and the coating.Peer Reviewe

Tribological performance of laser patterned cemented tungsten carbide parts

Some tools for machining processes used to be guided by supporting parts while using them for cutting or abrasive machining. For instance, the guide stone is used as supporting part in the honing process, which maintains the concentricity of the rotating axis. The contact surfaces of the supporting parts should exhibit the following properties: adequate combination of hardness, toughness and wear resistance. The damage of contact surfaces can be caused by a combination of friction and adhesion, related to the weakness of surface conditions in the tribological system, e.g. asperities, debris and pores. In order to investigate the impact of the surface topography, contact surfaces of the supporting parts made of cemented tungsten carbide (WC-Co) have been treated by means of laser surface patterning (LSP). Two different surface patterns with deterministic geometries on the micro and nano scale are achieved by two distinct LSP methods: line-like patterns by Laser-Interference Metallurgy (LIMET) with ns-laser and dimples by ps-laser. Tangential force coefficients, similar to the coefficient of friction (COF) in the non-abrasive case, are measured to evaluate the impact of the surface patterns. In this paper, the LSP methods as well as the analysis of the resulting surface topography are introduced. It is found that higher friction is obtained by line-like patterns whereas dimples can efficiently reduce the friction. At low load, hydrodynamic effects are reinforced as the dimples work as lubricant reservoirs and trap wear particles, and the observation becomes less obvious at high load. Meanwhile, only slight friction augmentation is observed by line-like patterns when the load increases.Peer Reviewe

Evolution of microstructure and residual stresses in gradually ground/polished 3Y-TZP

A comprehensive study of progressively ground/polished 3Y-TZP was performed with the aim of better understanding the mechanisms driving the microstructural modifications observed after such procedures, and identifying the processing parameters leading to optimal microstructures (i.e. ageing-protective and damage-free). Gradually ground/polished surfaces were produced, yielding four different topographies of increasing roughness (grades 1–4) and two different textures (unidirectionally, U, and multidirectionally, M). Phase transformation, microstructure and residual stresses were investigated by means of advanced characterization techniques. It was found that low-roughness mildly ground/polished specimens (i.e. 2-M/U) presented a nanometric layer with the ageing-related protective features generally associated with coarsely ground specimens. A lower limit for grain refinement in terms of surface abrasion was also found, in which partial recrystallization took place (i.e. 1-M/U). A mathematical relation was established between average surface roughness (Sa), monoclinic volume fraction (Vm) and surface compressive residual stresses, demonstrating that if the processing parameters are controlled, both Vm and residual stresses can be predicted by the measurement of Sa.Peer Reviewe

Peptidic biofunctionalization of laser patterned dental zirconia: A biochemical-topographical approach

A dual approach employing peptidic biofunctionalization and laser micro-patterns on dental zirconia was explored, with the aim of providing a flexible tool to improve tissue integration of restorations. Direct laser interference patterning with a femtosecond Ti:Sapphire laser was employed, and two periodic grooved patterns were produced with a periodicity of 3 and 10 µm. A platform containing the cell-adhesive RGD and the osteo- genic DWIVA peptides was used to functionalize the grooved surfaces. Topography and surface damage were characterized by confocal laser scanning (CLSM), scanning electron and scanning transmission electron micro- scopy techniques. The surface patterns exhibited a high homogeneity and subsurface damage was found in the form of nano-cracks and nano-pores, at the bottom of the valleys. Accelerated tests in water steam were carried out to assess hydrothermal degradation resistance, which slightly decreased after the laser treatment. Interest- ingly, the detrimental effects of the laser modification were reverted by a post-laser thermal treatment. The attachment of the molecule was verified trough fluorescence CLSM and X-ray photoelectron spectroscopy. Finally, the biological properties of the surfaces were studied in human mesenchymal stem cells. Cell adhesion, morphology, migration and differentiation were investigated. Cells on grooved surfaces displayed an elongated morphology and aligned along the patterns. On these surfaces, migration was greatly enhanced along the grooves, but also highly restricted in the perpendicular direction as compared to flat specimens. After bio- functionalization, cell number and cell area increased and well-developed cell cytoskeletons were observed. However, no effects on cell migration were found for the peptidic platform. Although some osteogenic potential was found in specimens grooved with a periodicity of 10 µm, the largest effects were observed from the biomolecule, which favored upregulation of several genes related to osteoblastic differentiation in all the surfaces.Peer ReviewedPostprint (author's final draft