Institute of Fundamental Technological Research

An increasing prevalence of bone-related injuries and aging geriatric populations continue to drive the orthopaedic implant market. A hierarchical analysis of bone remodelling after material implantation is necessary to better understand the relationship between implant and bone. Osteocytes, which are housed and communicate through the lacuno-canalicular network (LCN), are integral to bone health and remodelling processes. Therefore, it is essential to examine the framework of the LCN in response to implant materials or surface treatments.Biodegradable materials offer an alternative solution to permanent implants, which may require revision or removal surgeries. Magnesium alloys have resurfaced as promising materials due to their bone-like properties and safe degradation in vivo. To further tailor their degradation capabilities, surface treatments such as plasma electrolytic oxidation (PEO) have demonstrated to slow degradation.For the first time, the influence of a biodegradable material on the LCN is investigated by means of non-destructive 3D imaging. In this pilot study, we hypothesise noticeable variations in the LCN caused by altered chemical stimuli introduced by the PEO-coating.Utilising synchrotron-based transmission X-ray microscopy, we have characterised morphological LCN differences around uncoated and PEO-coated WE43 screws implanted into sheep bone. Bone specimens were explanted after 4, 8, and 12 weeks and regions near the implant surface were prepared for imaging. Findings from this investigation indicate that the slower degradation of PEO-coated WE43 induces healthier lacunar shapes within the LCN. However, the stimuli perceived by the uncoated material with higher degradation rates induces a greater connected LCN better prepared for bone disturbance.

nanotomography, lacuno-canalicular network, Bone, magnesium, biodegradable implants

Implant removal is unnecessary for biodegradable magnesium (Mg)-based implants and, therefore, the related risk for implant-induced fractures is limited. Aging, on the other hand, is associated with low bone-turnover and decreased bone mass and density, and thus increased fracture risk. Osteoporosis is accompanied by Mg deficiency, therefore, we hypothesized that Mg-based implants may support bone formation by Mg2+ ion release in an ovariectomy-induced osteoporotic rat model. Hence, we investigated osseointegration and implant degradation of a low-alloyed, degrading Mg–Zn–Ca implant (ZX00) in ovariectomy-induced osteoporotic (Osteo), old healthy (OH), and juvenile healthy (JH) groups of female Sprague Dawley rats via in vivo micro-computed tomography (µCT). For the Osteo rats, we demonstrate diminished trabecular bone already after 8 weeks upon ovariectomy and significantly enhanced implant volume loss, with correspondingly pronounced gas formation, compared to the OH and JH groups. Sclerotic rim development was observed in about half of the osteoporotic rats, suggesting a prevention from foreign-body and osteonecrosis development. Synchrotron radiation-based µCT confirmed lower bone volume fractions in the Osteo group compared to the OH and JH groups. Qualitative histological analysis additionally visualized the enhanced implant degradation in the Osteo group. To date, ZX00 provides an interesting implant material for young and older healthy patients, but it may not be of advantage in pharmacologically untreated osteoporotic conditions.

Magnesium-based implants, Osteoporosis, Degradation, Histology, Micro-computed tomography, Synchrotron radiation

Magnesium (Mg)-based implants are highly attractive for the orthopedic field and may replace titanium (Ti) as support for fracture healing. To determine the implant-bone-interaction in different bony regions, we implanted Mg-based alloy ZX00 (Mg < 0.5 Zn < 0.5 Ca, in wt%) and Ti-screws into the distal epiphysis and distal metaphysis of sheep tibiae. The implant degradation and osseointegration were assessed in vivo and ex vivo after 4, 6 and 12 weeks, using a combination of clinical computed tomography (cCT), medium-resolution micro CT (µCT) and high-resolution synchrotron radiation µCT (SRµCT). Implant volume loss, gas formation, and bone growth were evaluated for both implantation sites and each bone region independently. Additionally, histological analysis of bone growth was performed on embedded hard-tissue samples. We demonstrate that in all cases, the degradation rate of ZX00-implants ranges between 0.23-0.75 mm/year. The highest degradation rates were found in the epiphysis. Bone-to-implant-contact varied between the time points and bone types for both materials. Mostly, bone-volume-to-total-volume was higher around Ti-implants. However, we found an increased cortical thickness around the ZX00-screws when compared to the Ti-screws. Our results showed the suitability of ZX00-screws for implantation into the distal meta- and epiphysis

Biodegradable implants,Magnesium-based alloys,Computed tomography,Mg-Zn-Ca,Sheep,Histology

Magnesium is attractive for the application as a temporary bone implant due to its inherent biodegradability, non-toxicity and suitable mechanical properties. The degradation process of magnesium in physiological environments is complex and is thought to be a diffusion-limited transport problem. We use a multi-scale imaging approach using micro computed tomography and transmission X-ray microscopy (TXM) at resolutions below 40 nm. Thus, we are able to evaluate the nanoporosity of the degradation layer and infer its impact on the degradation process of pure magnesium in two physiological solutions. Magnesium samples were degraded in simulated body fluid (SBF) or Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum (FBS) for one to four weeks. TXM reveals the three-dimensional interconnected pore network within the degradation layer for both solutions. The pore network morphology and degradation layer composition are similar for all samples. By contrast, the degradation layer thickness in samples degraded in SBF was significantly higher and more inhomogeneous than in DMEM+10%FBS. Distinct features could be observed within the degradation layer of samples degraded in SBF, suggesting the formation of microgalvanic cells, which are not present in samples degraded in DMEM+10%FBS. The results suggest that the nanoporosity of the degradation layer and the resulting ion diffusion processes therein have a limited influence on the overall degradation process. This indicates that the influence of organic components on the dampening of the degradation rate by the suppression of microgalvanic degradation is much greater in the present study.

magnesium degradation, porosity, transmission X-ray microscopy, 3D imaging

Highly accurate segmentation of large 3D volumes is a demanding task. Challenging applications like the segmentation of synchrotron radiation microtomograms (SRμCT) at high-resolution, which suffer from low contrast, high spatial variability and measurement artifacts, readily exceed the capacities of conventional segmentation methods, including the manual segmentation by human experts. The quantitative characterization of the osseointegration and spatio-temporal biodegradation process of bone implants requires reliable, and very precise segmentation. We investigated the scaling of 2D U-net for high resolution grayscale volumes by three crucial model hyper-parameters (i.e., the model width, depth, and input size). To leverage the 3D information of high-resolution SRμCT, common three axes prediction fusing is extended, investigating the effect of adding more than three axes prediction. In a systematic evaluation we compare the performance of scaling the U-net by intersection over union (IoU) and quantitative measurements of osseointegration and degradation parameters. Overall, we observe that a compound scaling of the U-net and multi-axes prediction fusing with soft voting yields the highest IoU for the class “degradation layer”. Finally, the quantitative analysis showed that the parameters calculated with model segmentation deviated less from the high quality results than those obtained by a semi-automatic segmentation method.

We have studied the degradation of pure magnesium wire in simulated body fluid and its subsets under physiological conditions to enable the prediction of the degradation rate based on the medium's ionic composition. To this end, micro-computed tomography and scanning electron microscopy with energy-dispersive X-ray spectroscopy were used, followed by a tree regression analysis. A non-linear relationship was found between degradation rate and the precipitation of calcium salts. The mean absolute error for predicting the degradation rate was 1.35 mm/yr. This comparatively high value indicates that ionic interactions were exceedingly complex or that an unknown parameter determining the degradation may exist.

magnesium degradation, simulated body fluid, MicroCT, tree regression

Magnesium–silver alloys are of high interest for the use as temporary bone implants due to their antibacterial properties in addition to biocompatibility and biodegradability. Thin wires in particular can be used for scaffolding, but the determination of their degradation rate and homogeneity using traditional methods is difficult. Therefore, we have employed 3D imaging using X-ray near-field holotomography with sub-micrometer resolution to study the degradation of thin (250 μm diameter) Mg-2Ag and Mg-6Ag wires. The wires were studied in two states, recrystallized and solution annealed to assess the influence of Ag content and precipitates on the degradation. Imaging was employed after degradation in Dulbecco’s modified Eagle’s medium and 10% fetal bovine serum after 1 to 7 days. At 3 days of immersion the degradation rates of both alloys in both states were similar, but at 7 days higher silver content and solution annealing lead to decreased degradation rates. The opposite was observed for the pitting factor. Overall, the standard deviation of the determined parameters was high, owing to the relatively small field of view during imaging and high degradation inhomogeneity of the samples. Nevertheless, Mg-6Ag in the solution annealed state emerges as a potential material for thin wire manufacturing for implants.

X-ray computed tomography, magnesium-silver alloy, wire, degradation, near-field holotomography

Magnesium and its alloys attract increasingly wide attention in various fields, ranging from transport to medical solutions, due to their outstanding structural and degradation properties. These properties can be tailored through alloying and thermo-mechanical processing, which is often complex and multi-step, thus requiring in-depth analysis. In this work, we demonstrate the capability of synchrotron-based nanotomographic X-ray imaging methods, namely holotomography and transmission X-ray microscopy, for the quantitative 3D analysis of the evolution of intermetallic precipitate (particle) morphology and distribution in magnesium alloy Mg–5.78Zn-0.44Zr subjected to a complex multi-step processing. A rich history of variation of the intermetallic particle structure in the processed alloy provided a testbed for challenging the analytical capabilities of the imaging modalities studied. The main features of the evolving precipitate structure revealed earlier by traditional light and electron microscopy methods were confirmed by the 3D techniques of synchrotron-based X-ray imaging. We further demonstrated that synchrotron-based X-ray imaging enabled uncovering finer details of the variation of particle morphology and number density at various stages of processing—above and beyond the information provided by visible light and electron microscopy.

In this work, (W,Ti)B2 films with different stoichiometric ratio Ti/W deposited on silicon and 304 stainless steel by radio frequency magnetron sputtering are presented. The coatings were deposited from plasma spark sintered targets obtained from the mixture of pure boron, tungsten and titanium powders. It is shown that during plasma spark sintering process using overstoichiometric boron and a low content of titanium change the WB2 to WB4 phase with almost no secondary phases. Subsequently, the impact of titanium content on the films properties is investigated systematically, including the chemical and phase composition, crystalline structure, surface and cross-section morphology. Simultaneously, nano-indentation test and ball-on-disk tribometery are performed to analyse the hardness and tribological properties of the films. It is shown that deposited films with titanium content of 3.6 and 5.5 at.% are formed in the zone T of the Thornton's Structural Zone Model. In opposite to α-WB2 magnetron sputtered coatings they are more flexible and hard nanocomposite coatings. The results show that the addition of titanium is apparently changing the film structure from nanocrystalline columnar to amorphous, very dense and compact structure with the addition of TiB2 phase. That films are simultaneously hard (H > 37.5 GPa), have high hardness to effective Young's modulus ratio values (H/E* > 0.1) and elastic recovery (We > 60%) appropriate for tough and resistant to cracking materials. The presented (W,Ti)B2 films exhibit also tribological and corrosion properties better than unalloyed coatings.

superhard films, ternary tungsten borides, RF magnetron sputtering, wear resistance, corrosion

Manufacturing process of wire-like binary or ternary metal nanoalloys applying the magnetic-field-induced (MFI) synthesis is still a challenging task. Hence, this work demonstrates for the first time how to produce the iron-nickel wire-like nanostruc-tures with Fe0.75Ni0.25, Fe0.5Ni0.5 and Fe0.25Ni0.75 compositions. In a contrary to the previously reported synthesis of the Fe-Ni wire-like nanomaterials, this process has been carried out at room temperature without employment of templates, surfactants, organic solvents, and other chemical additives. The as-prepared samples exhibit specific structures with the amorphous bimetallic alloy cores covered by thin amorphous oxide shells. Moreover, they are composed of nanoparticles which are aligned in nearly linear chains. The Fe-Ni samples are ferromagnetic materials. Their coercivity values and saturation magnetizations depend on chemical compositions and dimensions of the investigated chains. The highest saturation magnetization and the lowest coercivity is found for the material with the lowest content of nickel and vice versa.

amorphous materials, Fe–Ni chains, magnetic-field-induced synthesis, magnetic materials, wire-like nanostructure

With increasing demand for high-performance and long-lasting cutting and forming tools, the members of this expanding class of superhard metals hold promise to address the shortcomings of traditional tool materials. Those shortcoming include their high cost (silicon nitride, cubic boron nitride, and diamond), their inability to cut ferrous metals due to chemical reactions (diamond), instability in the presence of humidity (cubic boron nitride) and relatively low hardness (tungsten carbide). Also the increasing industrial demand for protective coatings with high hardness, good elastic properties and thermal stability calls for the investigation of new material systems. Although transition metal (TM) nitrides are successfully applied for different tasks in automotive or aero-space industries, the search for improved materials is an ongoing topic, being far from its end. In this work the study on deposition of thin films made of new super-hard materials (SHM) such as tungsten boride are presented. Additionally, the influence of doping by titanium of those materials is investigated. Investigated films were deposited by the pulsed laser deposition method. The used targets were synthetized by SPS method. The powders of boron and tungsten in 4.5 to 1 molar faction were used. The films deposited by PLD method have stoichiometric composition such as used targets. The WB2 and WB3 phase are dominant. Research carried out using SEM, XRD and nanoindentation test showed that the phase composition of the targets is more important in the case of laser deposition than magnetron. All obtained layers are very hard and thermally stable. In the case of magnetron sputtering, smooth layers were obtained while the layers deposited by the laser have a very high roughness. Titanium doping increases the amount of WB3 phase in the sintered discs, while it has no significant effect on the properties of the deposited layers.
Z rosnącym zapotrzebowaniem na niezawodne, a jednocześnie zapewniające dużą wydajność, narzędzia do skrawania i obróbki plastycznej, coraz większego znaczenia nabiera rozszerzająca się grupa supertwardych ceramik przewodzących prąd. Materiały te dobrze rokują w związku z rozwiązaniem problemów tradycyjnych materiałów narzędziowych, których niedoskonałości obejmują wysoką cenę (azotek krzemu, azotek boru), niezdolność do cięcia stopów żelaza w wyniku reakcji chemicznych (diament), niestabilność w obecności wilgoci (azotek boru) i względnie małą twardość (węglik wolframu). Również rosnący popyt na powłoki ochronne o wysokiej twardości, o dobrych właściwościach sprężystych i stabilności termicznej powoduje, że badania nad nowymi systemami materiałowymi prowadzone są coraz intensywniej. Pomimo że azotki metali przejściowych są już z powodzeniem stosowane do różnych zadań w przemyśle samochodowym i lotniczym, poszukiwanie ulepszonych materiałów jest tematem wciąż aktualnym. W pracy przedstawiono badania nad osadzaniem cienkich powłok z nowych supertwardych materiałów (SHM), którymi są borki wolframu. Dodatkowo zbadano wpływ domieszkowania tych materiałów tytanem. Warstwy osadzane były metodą ablacji laserowej PLD. Tarcze do osadzania zsyntetyzowane zostały metodą spiekania plazmowego SPS proszków boru i wolframu o stosunku atomów 4,5 do 1. Osadzane z użyciem lasera warstwy mają skład stechiometryczny podobny do użytych tarcz. W warstwach tych dominuje faza WB3. Badania przeprowadzone z użyciem SEM, XRD i nanoindentacji wykazały, że skład fazowy tarcz jest odwzorowany w warstwach osadzonych laserem. Wszystkie uzyskane warstwy są bardzo twarde i stabilne termicznie. Warstwy osadzane laserem odznaczają się dużą chropowatością. Domieszkowanie tytanem zwiększa ilość fazy WB3 w spiekanych tarczach i osadzanych warstwach oraz zmniejsza ilość i wielkość naniesionych na powierzchnię cząstek.

laser ablation, tungsten borides doped titanium, plasma sintering / ablacja laserowa, borki wolframu domieszkowane tytanem, spiekanie plazmowe

The aim of this work was to investigate whether the explosively welded metals are susceptible to hydrogen degradation. The materials described in this article are widely used nickel alloy Inconel C-276 and super duplex steel SAF 2507 as clad materials for their superior resistance to corrosive environment and low alloy steel P355NH as a base material. It was observed that at the explosive bonded interface between the base steel and the stainless steel some local melting zones are formed. It was found that the cathodic hydrogen charging causes changes in the microstructure of bonded materials and decreases the shear strength of bonds as well as the corrosion resistance of clads.

novel materials, explosive welding, hydrogen degradation