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The nanostructural adaptation of bone is crucial for its biocompatibility with orthopedic implants. The bone nanostructure also determines its mechanical properties and performance. However, the bone's temporal and spatial nanoadaptation around degrading implants remains largely unknown. Here, we present insights into this important bone adaptation by applying scanning electron microscopy, elemental analysis, and small-angle X-ray scattering tensor tomography (SASTT). We extend the novel SASTT reconstruction method and provide a 3D scattering reciprocal space map per voxel of the sample's volume. From this reconstruction, parameters such as the thickness of the bone mineral particles are quantified, which provide additional information on nanostructural adaptation of bone during healing. We selected a rat femoral bone and a degrading ZX10 magnesium implant as model system, and investigated it over the course of 18 months, using a sham as control. We observe that the bone's nanostructural adaptation starts with an initially fast interfacial bone growth close to the implant, which spreads by a re-orientation of the nanostructure in the bone volume around the implant, and is consolidated in the later degradation stages. These observations reveal the complex bulk bone-implant interactions and enable future research on the related biomechanical bone responses. Statement of significance Traumatic bone injuries are among the most frequent causes of surgical treatment, and often require the placement of an implant. The ideal implant supports and induces bone formation, while being mechanically and chemically adapted to the bone structure, ensuring a gradual load transfer. While magnesium implants fulfill these requirements, the nanostructural changes during bone healing and implant degradation remain not completely elucidated. Here, we unveil these processes in rat femoral bones with ZX10 magnesium implants and show different stages of bone healing in such a model system., Acta Biomaterialia, 134, ISSN:1742-7061, ISSN:1878-7568

The nanostructural adaptation of bone is crucial for its compatibility with orthopedic implants. The bone’s nanostructure determines its mechanical properties, however little is known about its temporal and spatial adaptation in degrading implants. This study presents insights into this adaptation by applying electron microscopy, elemental analysis, and small-angle X-ray scattering tensor-tomography (SASTT). We extend the SASTT reconstruction to multiple radii of the reciprocal space vector q, providing a 3D reciprocal-space map per voxel. Each scattering curve is spatially linked to one voxel in the volume, and properties such as the thickness of the mineral particles are quantified. This reconstruction provides information on nanostructural adaptation during healing around a degrading ZX10 magnesium implant over the course of 18 months, using a sham as control. The nanostructural adaptation process is observed to start with an initially fast interfacial organization towards the implant direction, followed by a substantial reorganization of the volume around the implant, and an adaptation in the later degradation stages. The study sheds light on the complex bone-implant interaction in 3D, allowing a more guided approach towards the design of future implant materials, which are expected to be of great interest for further clinical studies on the bone-implant interaction.TOC text and figureDegrading Magnesium implants are mechanically and chemically well adapted orthopedic implant materials and ensure a gradual load transfer during bone healing due to their degradation. The impact of the implant degradation on the bone nanostructure is however not fully understood. This study unveils the processes 3D and shows different stages of bone healing.

Mg-based biodegradable materials are considered promising candidates in the paediatric field due to their favourable mechanical and biological properties and their biodegrading potential that makes a second surgery for implant removal unnecessary. In many cases the surgical fixation technique requires a crossing of the growth plate by the implant in order to achieve an adequate fragment replacement or fracture stabilisation. This study investigates the kinetics of slowly and rapidly degrading Mg alloys in a transphyseal rat model, and also reports on their dynamics in the context of the physis and consecutive bone growth. Twenty-six male Sprague–Dawley rats received either a rapidly degrading (ZX50; n = 13) or a slowly degrading (WZ21; n = 13) Mg alloy, implanted transphyseal into the distal femur. The contralateral leg was drilled in the same manner and served as a direct sham specimen. Degradation behaviour, gas formation, and leg length were measured by continuous in vivo micro CT for up to 52 weeks, and additional high-resolution µCT (HRS) scans and histomorphological analyses of the growth plate were performed. The growth plate was locally destroyed and bone growth was significantly diminished by the fast degradation of ZX50 implants and the accompanying release of large amounts of hydrogen gas. In contrast, WZ21 implants showed homogenous and moderate degradation performance, and the effect on bone growth did not differ significantly from a single drill-hole defect. Statement of Significance This study is the first that reports on the effects of degrading magnesium implants on the growth plate in a living animal model. The results show that high evolution of hydrogen gas due to rapid Mg degradation can damage the growth plate substantially. Slow degradation, however, such as seen for WZ21 alloys, does not affect the growth plate more than drilling alone, thus meeting one important prerequisite for deployment in paediatric osteosynthesis.

This pilot study highlights the substantial potential of using isotopically enriched (non-radioactive) metals to study the fate of biodegradable metal implants. It was possible to show that magnesium (Mg) release can be observed by combining isotopic mass spectrometry and isotopic pattern deconvolution for data reduction, even at low amounts of Mg released a from slowly degrading 26 Mg enriched (>99%) Mg metal. Following implantation into rats, structural in vivo changes were monitored by μCT. Results showed that the applied Mg had an average degradation rate of 16 ± 5 μm year −1 , which corresponds with the degradation rate of pure Mg. Bone and tissue extraction was performed 4, 24, and 52 weeks after implantation. Bone cross sections were analyzed by laser ablation inductively coupled plasma mass spectrometry (ICP-MS) to determine the lateral 26 Mg distribution. The 26 Mg/ 24 Mg ratios in digested tissue and excretion samples were analyzed by multi collector ICP-MS. Isotope pattern deconvolution in combination with ICP-MS enabled detection of Mg pin material in amounts as low as 200 ppm in bone tissues and 20 ppm in tissues up to two fold increased Mg levels with a contribution of pin-derived Mg of up to 75% (4 weeks) and 30% (24 weeks) were found adjacent to the implant. After complete degradation, no visual bone disturbance or residual pin-Mg could be detected in cortical bone. In organs, increased Δ 26 Mg/ 24 Mg values up to 16‰ were determined compared to control samples. Increased Δ 26 Mg/ 24 Mg values were detected in serum samples at a constant total Mg level. In contrast to urine, feces did not show a shift in the 26 Mg/ 24 Mg ratios. This investigation showed that the organism is capable of handling excess Mg well and that bones fully recover after degradation. Statement of Significance Magnesium alloys as bone implants have faced increasing attention over the past years. In vivo degradation and metabolism studies of these implant materials have shown the promising application in orthopaedic trauma surgery. With advance in Mg research it has become increasingly important to monitor the fate of the implant material in the organism. For the first time, the indispensible potential of isotopically enriched materials is documented by applying 26 Mg enriched Mg implants in an animal model. Therefore, the spatial distribution of pin-Mg in bone and the pin-Mg migration and excretion in the organism could be monitored to better understand metal degradation as well as Mg turn over and excretion.

The purpose of this study was to compare short term in vitro and in vivo biodegradation studies with low purity Mg (> 99.94 %), Mg-10Gd and Mg-2Ag designed for biodegradable implant applications. Three in vitro testing conditions were applied, using (i) phosphate buffered saline (PBS), (ii) Hank's balanced salt solution (HBSS) and (iii) Dulbecco's modified eagle medium (DMEM) in 5 % CO2 under sterile conditions. Gas evolution and mass loss (ML) were assessed, as well as the degradation layer, by elemental mapping and scanning electron microscopy (SEM). In vivo, implantations were performed on male Sprague-Dawley rats evaluating both, gas cavity volume and implant volume reduction by micro-computed tomography (µCT), 7 d after implantation. Samples were produced by casting, solution heat treatment and extrusion in disc and pin shape for the in vitro and in vivo experiments, respectively. Results showed that when the processing of the Mg sample varied, differences were found not only in the alloy impurity content and the grain size, but also in the corrosion behaviour. An increase of Fe and Ni or a large grain size seemed to play a major role in the degradation process, while the influence of alloying elements, such as Gd and Ag, played a secondary role. Results also indicated that cell culture conditions induced degradation rates and degradation layer elemental composition comparable to in vivo conditions. These in vitro and in vivo degradation layers consisted of Mg hydroxide, Mg-Ca carbonate and Ca phosphate. ispartof: EUROPEAN CELLS & MATERIALS vol:33 pages:90-104 ispartof: location:Switzerland status: published

Zinc- and calcium-containing magnesium alloys, denominated ZX alloys, excel as temporary implant materials because of their composition made of physiologically essential minerals and lack of commonly used rare-earth alloying elements. This study documents the specific role of nanometric intermetallic particles (IMPs) on the in vitro and in vivo biocorrosion behavior of two ZX-lean alloys, Mg‒Zn1.0‒Ca0.3 (ZX10) and Mg‒Zn1.5‒Ca0.25 (ZX20) (in wt.%). These alloys were designed according to thermodynamic considerations by finely adjusting the nominal Zn content towards microstructures that differ solely in the type of phase composing the IMPs: ZX10, with 1.0 wt.% Zn, hosts binary Mg2Ca-phase IMPs, while ZX20, with 1.5 wt.% Zn, hosts ternary IM1-phase IMPs. Electrochemical methods and the hydrogen-gas evolution method were deployed and complemented by transmission electron microscopy analyses. These techniques used in concert reveal that the Mg2Ca-type IMPs anodically dissolve preferentially and completely, while the IM1-type IMPs act as nano-cathodes, facilitating a faster dissolution of ZX20 compared to ZX10. Additionally, a dynamically increasing cathodic reactivity with progressing dissolution was observed for both alloys. This effect is explained by redeposits of Zn on the corroding surface, which act as additional nano-cathodes and facilitate enhanced cathodic reaction kinetics. The higher degradation rate of ZX20 was verified in vivo via micro-computed tomography upon implantation of both materials into femurs of Sprague DawleyⓇ rats. Both alloys were well integrated with direct bone‒implant contact observable 4 weeks post operationem, and an appropriately slow and homogeneous degradation could be observed with no adverse effects on the surrounding tissue. The results suggest that both alloys qualify as new temporary implant materials, and that a minor adjustment of the Zn content may function as a lever for tuning the degradation rate towards desired applications. Statement of Significance In Mg‒Zn‒Ca (ZX)-lean alloys Zn is the most electropositive element, and thus requires special attention in the investigation of biocorrosion mechanisms acting on these alloys. Even a small increase of only 0.5 wt.% Zn is shown to accelerate the biodegradation rate in both simulated body conditions and in vivo. This is possible due to Zn's role in influencing the type of intermetallic particles (IMPs) in these alloys. These IMPs in turn, even though minute in size, are shown to govern the biocorrosion behavior on the macroscopic scale. The deep understanding gained in this study on the role of Zn and of the IMP type it governs is crucial to ensuring a safe and controllable implant degradation.

Biodegradable magnesium implants are under investigation because of their promising properties as medical devices. For enhancing the mechanical properties and the degradation resistance, rare earth elements are often used as alloying elements. In this study Mg10Gd pins were implanted into Sprague–Dawley® rats. The pin volume loss and a possible accumulation of magnesium and gadolinium in the rats’ organs and blood were investigated in a long-term study over 36 weeks. The results showed that Mg10Gd is a fast disintegrating material. Already 12 weeks after implantation the alloy is fragmented to smaller particles, which can be found within the intramedullary cavity and the cortical bones. They disturbed the bone remodeling until the end of the study. The results concerning the elements’ distribution in the animals’ bodies were even more striking, since an accumulation of gadolinium could be observed in the investigated organs over the whole time span. The most affected tissue was the spleen, with up to 3240 μg Gd/kg wet mass, followed by the lung, liver and kidney (up to 1040, 685 and 207 μg Gd/kg). In the brain, muscle and heart, the gadolinium concentrations were much smaller (less than 20 μg/kg), but an accumulation could still be detected. Interestingly, blood serum samples showed no accumulation of magnesium and gadolinium. This is the first time that an accumulation of gadolinium in animal organs was observed after the application of a gadolinium-containing degradable magnesium implant. These findings demonstrate the importance of future investigations concerning the distribution of the constituents of new biodegradable materials in the body, to ensure the patients’ safety. Statement of Significance In the last years, biodegradable Mg alloys are under investigation due to their promising properties as orthopaedic devices used for bone fracture stabilization. Gadolinium as Rare Earth Element enhances the mechanical properties of Mg-Gd alloys but its toxicity in humans is still questionable. Up to now, there is no study investigating the elements’ metabolism of a REE-containing Magnesium alloy in an animal model. In this study, we examined the gadolinium distribution and accumulation in rat organs during the degradation of Mg10Gd. Our findings showed that Gd is accumulating in the animal organs, especially in spleen, liver and kidney. This study is of crucial benefit regarding a safe application of REE-containing Magnesium alloys in humans.

We report on the long-term effects of degrading magnesium implants on bone tissue in a growing rat skeleton using continuous in vivo micro-Computed Tomography, histological staining and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Two different magnesium alloys—one rapidly degrading (ZX50) and one slowly degrading (WZ21)—were used to evaluate the bone response and distribution of released Mg and Y ions in the femur of male Sprague-Dawley rats. Regardless of whether the alloy degrades rapidly or slowly, we found that bone recovers restitutio ad integrum after complete degradation of the magnesium implant. The degradation of the Mg alloys generates a significant increase in Mg concentration in the cortical bone near the remaining implant parts, but the Mg accumulation disappears after the implant degrades completely. The degradation of the Y-containing alloy WZ21 leads to Y enrichment in adjacent bone tissues and in newly formed bone inside the medullary space. Locally high Y concentrations suggest migration not only of Y ions but also of Y-containing intermetallic particles. However, after the full degradation of the implant the Y-enrichment disappears almost completely. Hydrogen gas formation and ion release during implant degradation did not harm bone regeneration in our samples., Acta Biomaterialia, 42, ISSN:1742-7061, ISSN:1878-7568

Biodegradable materials are under investigation due to their promising properties for biomedical applications as implant material. In the present study, two binary magnesium (Mg) alloys (Mg2Ag and Mg10Gd) and pure Mg (99.99%) were used in order to compare the degradation performance of the materials in in vitro to in vivo conditions. In vitro analysis of cell distribution and viability was performed on discs of pure Mg, Mg2Ag and Mg10Gd. The results verified viable pre-osteoblast cells on all three alloys and no obvious toxic effect within the first two weeks. The degradation rates in in vitro and in vivo conditions (Sprague–Dawley® rats) showed that the degradation rates differ especially in the 1st week of the experiments. While in vitro Mg2Ag displayed the fastest degradation rate, in vivo, Mg10Gd revealed the highest degradation rate. After four weeks of in vitro immersion tests, the degradation rate of Mg2Ag was significantly reduced and approached the values of pure Mg and Mg10Gd. Interestingly, after 4 weeks the estimated in vitro degradation rates approximate in vivo values. Our systematic experiment indicates that a correlation between in vitro and in vivo observations still has some limitations that have to be considered in order to perform representative in vitro experiments that display the in vivo situation.

Aim of this study was to evaluate the response of bone to novel biodegradable polymeric composite implants in the femora of growing rats. Longitudinal observation of bone reaction at the implant site (BV/TV) as well as resorption of the implanted pins were monitored using in vivo micro-focus computed tomography (µCT). After 12, 24 and 36 weeks femora containing the implants were explanted, scanned with high resolution ex vivo µCT, and the surface roughness of the implants was measured to conclude on the ingrowth capability for bone tissue. Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to observe changes on the surface of Polyhydroxybutyrate (PHB) during degradation and cell ingrowth. Four different composites with zirconium dioxide (ZrO2) and Herafill(®) were compared. After 36 weeks in vivo, none of the implants did show significant degradation. The PHB composite with ZrO2 and a high percentage (30%) of Herafill® as well as the Mg-alloy WZ21 showed the highest values of bone accumulation (increased BV/TV) around the implant. The lowest value was measured in PHB with 3% ZrO2 containing no Herafill®. Roughness measurements as well as EDX and SEM imaging could not reveal any changes on the PHB composites׳ surfaces. Biomechanical parameters, such as the adhesion strength between bone and implant were determined by measuring the shear strength as well as push-out energy of the bone-implant interface. The results showed that improvement of these mechanical properties of the studied PHBs P3Z, P3Z10H and P3Z30H is necessary in order to obtain appropriate load-bearing material. The moduli of elasticity, tensile strength and strain properties of the PHB composites are close to that of bone and thus promising. Compared to clinically used PLGA, PGA and PLA materials, their additional benefit is an unchanged local pH value during degradation, which makes them well tolerated by cells and immune system. They might be used successfully for personalized 3D printed implants or as coatings of rapidly dissolving implants.

The biodegradation of ultrahigh-purity Mg (XHP Mg, Fe approximate to 2 ppm) was tested in vitro in NaHCO3/CO2-buffered simulated body fluid and in vivo in the femur of rats. The in vitro degradation rate, which was evaluated using an also here described newly designed hydrogen evolution testing setup, is with approximate to 10 +/- 3 mu m/y very low and shows very good agreement with in vivo data. The results for XHP Mg are also compared with in vitro tests on high-purity Mg (Few approximate to 37 ppm) in the as-cast and annealed states. The less pure specimens exhibit significantly higher degradation rates due to the formation of Fe-containing precipitates during casting and annealing.

The spatially and timely resolved degradation of Mg alloys used as implants in bone material was monitored by LA-ICP-MS. Data evaluation and interpretation was accomplished by means of a geospatial information software (ArcGIS) tool to match spatially referenced LA-ICP-MS data to the microscopic images and to create regionalized images of quantitative data in order to describe the biodegradation process. Quantification was accomplished by matrix matched hydroxyapatite standards. Total combined uncertainty budgets were assessed for the entire quantification process. In the study, rat bones were extracted after 2 and 6 months implantation time and were analyzed for the lateral distribution of the alloying elements (Mg, Mn, Zn, Zr and Yb) in bone cross sections. The use of ArcGIS enabled the spatial referencing of data points and the identification of regions of interest by means of chemical and structural parameters. Moreover, ArcGIS allowed for the direct statistical analysis of defined areas (zones of interest) within these regions. Selected zones visualizing the Mg mass fractions at different distances from the pin after 2 and 6 months and within the blank sample were determined by chemometric means using cluster analysis and showed a clear decrease of the Mg content in the bone material surrounding the pin over time. Four meaningful different zones with significantly different Mg mass fractions in hydroxyapatite could be identified ranging from 8 μg g−1 in undisturbed cortical bone to 16 μg g−1 adjacent to the pin.

This study investigates the degradation performance of three Fe-based materials in a growing rat skeleton over a period of 1 year. Pins of pure Fe and two Fe-based alloys (Fe-10 Mn-1Pd and Fe-21 Mn-0.7C-1Pd, in wt.%) were implanted transcortically into the femur of 38 Sprague-Dawley rats and inspected after 4, 12, 24 and 52 weeks. The assessment was performed by ex vivo microfocus computed tomography, weight-loss determination, surface analysis of the explanted pins and histological examination. The materials investigated showed signs of degradation; however, the degradation proceeded rather slowly and no significant differences between the materials were detected. We discuss these unexpected findings on the basis of fundamental considerations regarding iron corrosion. Dense layers of degradation products were formed on the implants' surfaces, and act as barriers against oxygen transport. For the degradation of iron, however, the presence of oxygen is an indispensable prerequisite. Its availability is generally a critical factor in bony tissue and rather limited there, i.e. in the vicinity of our implants. Because of the relatively slow degradation of both pure Fe and the Fe-based alloys, their suitability for bulk temporary implants such as those in osteosynthesis applications appears questionable.

This article deals with the development of fine-grained high-strength low-alloy (HSLA) magnesium alloys intended for use as biodegradable implant material. The alloys contain solely low amounts of Zn and Ca as alloying elements. We illustrate the development path starting from the high-Zn-containing ZX50 (MgZn5Ca0.25) alloy with conventional purity, to an ultrahigh-purity ZX50 modification, and further to the ultrahigh-purity Zn-lean alloy ZX10 (MgZn1Ca0.3). It is shown that alloys with high Zn-content are prone to biocorrosion in various environments, most probably because of the presence of the intermetallic phase Mg6Zn3Ca2. A reduction of the Zn content results in (Mg,Zn)2Ca phase formation. This phase is less noble than the Mg-matrix and therefore, in contrast to Mg6Zn3Ca2, does not act as cathodic site. A fine-grained microstructure is achieved by the controlled formation of fine and homogeneously distributed (Mg,Zn)2Ca precipitates, which influence dynamic recrystallization and grain growth during hot forming. Such design scheme is comparable to that of HSLA steels, where low amounts of alloying elements are intended to produce a very fine dispersion of particles to increase the material’s strength by refining the grain size. Consequently our new, ultrapure ZX10 alloy exhibits high strength (yield strength R p = 240 MPa, ultimate tensile strength R m = 255 MPa) and simultaneously high ductility (elongation to fracture A = 27%), as well as low mechanical anisotropy. Because of the anodic nature of the (Mg,Zn)2Ca particles used in the HSLA concept, the in vivo degradation in a rat femur implantation study is very slow and homogeneous without clinically observable hydrogen evolution, making the ZX10 alloy a promising material for biodegradable implants.

The use of biodegradable magnesium implants in pediatric trauma surgery would render surgical interventions for implant removal after tissue healing unnecessary, thereby preventing stress to the children and reducing therapy costs. In this study, we report on the immunological response to biodegradable magnesium implants—as an important aspect in evaluating biocompatibility—tested in a growing rat model. The focus of this study was to investigate the response of the innate immune system to either fast or slow degrading magnesium pins, which were implanted into the femoral bones of 5-week-old rats. The main alloying element of the fast-degrading alloy (ZX50) was Zn, while it was Y in the slow-degrading implant (WZ21). Our results demonstrate that degrading magnesium implants beneficially influence the immune system, especially in the first postoperative weeks but also during tissue healing and early bone remodeling. However, rodents with WZ21 pins showed a slightly decreased phagocytic ability during bone remodeling when the degradation rate reached its maximum. This may be due to the high release rate of the rare earth-element yttrium, which is potentially toxic. From our results we conclude that magnesium implants have a beneficial effect on the innate immune system but that there are some concerns regarding the use of yttrium-alloyed magnesium implants, especially in pediatric patients.

Bioresorbable magnesium materials are widely investigated because of their promising properties as orthopedic devices. Pure magnesium (99.99%) and two binary magnesium alloys (Mg2Ag and Mg10Gd) were used to investigate the degradation behavior, the bone adherence and bone-implant interface mechanics of these materials in growing Sprague-Dawley® rats in a long-term study of 36 weeks. In vivo micro-computed tomography (μCT) scans were performed at specific time points to observe the longitudinal degradation of each alloy within the same animal. Pin volume and surface, gas volume and degradation rates were calculated. The results showed a slower degradation of pure magnesium and Mg2Ag in comparison to the fast disintegrating Mg10Gd. Changes in bone morphology were determined by high resolution ex vivo μCT scans and bone sections stained with Toluidine blue. Pure magnesium and Mg2Ag were well integrated and surrounded by bony tissue 24 weeks after implantation. On the contrary, Mg10Gd remnants were surrounded by fibrous and bone tissue. Push-out tests revealed higher bone-implant-interface strengths of pure magnesium pins compared to Mg2Ag and Mg10Gd. Mg10Gd induces less beneficial tissue reactions, while Mg2Ag showed adequate biodegradation and no adverse reactions in bone healing process which might be promising as an orthopedic device.

The hydrogen evolution method and animal experiments were deployed to investigate the effect of trace impurity elements on the degradation behavior of high-strength Mg alloys of type ZX50 (Mg–5Zn–0.3Ca). It is shown that trace impurity elements increase the degradation rate, predominantly in the initial period of the tests, and also increase the material’s susceptibility to localized corrosion attack. These effects are explained on the basis of the corrosion potential of the intermetallic phases present in the alloys. The Zn-rich phases present in ZX50 are nobler than the Mg matrix, and thus act as cathodic sites. The impurity elements Fe and Mn in the alloy of conventional purity are incorporated in these Zn-rich intermetallic phases and therefore increase their cathodic efficiency. A design rule for circumventing the formation of noble intermetallic particles and thus avoiding galvanically accelerated dissolution of the Mg matrix is proposed.

Axillary arterio-arterial graft interposition has been described as a reasonable haemodialysis access in selected patients. In a patient with this unusual access, we measured and calculated effective clearance at different extracorporeal blood flows (Q(b)). Effective clearance increased with increasing blood flow and reached a maximum at a Q(b) of ~200 mL/min but then decreased when Q(b) was increased further. As this type of access typically provides low access flow, one has to be aware that local recirculation will easily occur. Therefore, a Q(b) above access flow has to be avoided since any increase beyond that threshold reduces effective clearance.

In recent decades operative fracture treatment using elastic stable intramedullary nails (ESINs) has mainly taken precedence over conservative alternatives in children. The development of biodegradable materials that could be used for ESINs would be a further step towards treatment improvement. Due to its mechanical and elastic properties, magnesium seems to be an ideal material for biodegradable implant application. The aim of this study was therefore to investigate the cellular reaction to biodegradable magnesium implants in vitro.Primary human growth plate chondrocytes and MG63 osteoblasts were used for this study. Viability and metabolic activity in response to the eluate of a rapidly and a slower degrading magnesium alloy were investigated. Furthermore, changes in gene expression were assessed and live cell imaging was performed.A superior performance of the slower degrading WZ21 alloy's eluate was detected regarding cell viability and metabolic activity, cell proliferation and morphology. However, the ZX50 alloy's eluate induced a favourable up-regulation of osteogenic markers in MG63 osteoblasts.This study showed that magnesium alloys for use in biodegradable implant application are well tolerated in both osteoblasts and growth plate chondrocytes respectively.

The growth plate at the end of long bones is the cartilaginous organ responsible for longitudinal bone growth in children. Trauma to the growth plate, i.e. fractures, can severely impair longitudinal bone growth, leading to growth disorders due to destruction of the epiphyseal circulation and formation of a bone bridge. From the clinical experience it is known that in some patients this bone bridge eventually disappears during the growth process. However, the molecular mechanisms involved in bone bridge formation and dissolution have not been clarified yet. The aim of this study was to investigate the spatial and temporal protein level of molecules potentially involved in these processes, i.e. RANKL, OPG, DKK-1, Coll 10, BMP-2 and IL-6, in an experimental rat model using an immunohistochemical approach. The results from our study suggest that bone bridge formation might be an early event starting immediately after growth plate injury and involving several pro-osteoblastic molecules, i.e. IL-6, BMP-2 as well as OPG and Coll X. In the late studied time points 3- and 9-month post-injury expression of anti-osteoblastic proteins, i.e. DKK1 and RANKL, was increased. This indicates that bone bridge dissolution might be a late event and potentially linked to Wnt signaling inhibition and RANK/RANKL signaling activation.

The extracorporeal transport of glucose was studied to determine the dialyzer mass transfer coefficient K(0)A for glucose in whole blood under conditions of glucose delivery and glucose removal. Glucose was removed from blood or delivered to blood using glucose-free dialysate or dialysate with a glucose concentration of 200 mg/dl (11.1 mmol/L). FX8 dialyzers (Fresenius Medical Care, Bad Homburg, Germany) were studied at constant dialysate flow Q(d) (500 ml/min) and variable blood flows Q(b) (200, 300, and 400 ml/min) under countercurrent flow conditions in a series of laboratory bench studies. Glucose clearance K(d) and glucose distribution volume flow rate Q(e) were determined from glucose mass balance. In 32 studies done with bovine blood at different hematocrit levels glucose was calculated to distribute in plasma water and to be excluded from red cell water when passing the FX8 dialyzer. The dialyzer mass transfer area coefficient K(0)A for glucose computed from Q(e), Q(d), and K(d) was 301.6 ± 45.2 ml/min and not different between modes of glucose delivery or glucose removal but lower than expected from the diffusivity of glucose estimated for aqueous solutions.

Owing to the complex influences of several experimental conditions on the in vitro alteration of blood, there is still a lack of viable in vitro tests and methods for blood compatibility evaluation of biomaterials. The aim of this research was to study a new approach for the haemocompatibility assessment of differently modified PET surfaces using the quartz crystal microbalance with dissipation unit (QCM-D) technique and measure the mass increase caused by clot formation under physiological conditions. For this purpose some of the most frequently applied in vitro methods for haemocompatibility determination, i.e., clotting time measurement and observation of red blood cells' mobility, were applied and their accuracy and sensitivity compared to the new QCM-D approach. Haemocompatibility was evaluated for non-modified poly(ethylene terephthalate) (PET) surfaces and PET surfaces coated with dextran sulphate and heparin. The basic anti-coagulant properties of heparin and dextran sulphate were analysed by means of their activated partial thromboplastine time (APTT). PET, as well as different polysaccharides coatings were chosen for this study due to their promising biocompatible properties and numerous possibilities for biomedical applications. The results showed that the new QCM-D technique to study clot formation in contact with PET surfaces under physiological environment was the most informative and accurate for in vitro haemocompatibility assessment. Although the results achieved with the other two methods were in good correlation, they did not provide such a high level of sensitivity.