Stabilizing A Vascularized Autologous Matrix with Flexible Magnesium Scaffolds to Reconstruct Dysfunctional Left Ventricular Myocardium in a Large-Animal Feasibility Study.

The surgical reconstruction of dysfunctional myocardium is necessary for patients with severe heart failure. Autologous biomaterials, such as vascularized patch materials, have a regenerative potential due to in vivo remodeling. However, additional temporary mechanical stabilization of the biomaterials is required to prevent aneurysms or rupture. Degradable magnesium scaffolds could prevent these life-threatening risks. A left ventricular transmural defect was reconstructed in minipigs with a piece of the autologous stomach. Geometrically adaptable and degradable scaffolds made of magnesium alloy LA63 were affixed on the epicardium to stabilize the stomach tissue. The degradation of the magnesium structures, their biocompatibility, physiological remodeling of the stomach, and the heart's function were examined six months after the procedure via MRI (Magnetic Resonance Imaging), angiography, µ-CT, and light microscopy. All animals survived the surgery. Stable physiological integration of the stomach patch could be detected. No ruptures of the grafts occurred. The magnesium scaffolds showed good biocompatibility. Regenerative surgical approaches for treating severe heart failure are a promising therapeutic alternative to the currently available, far from optimal options. The temporary mechanical stabilization of viable, vascularized grafts facilitates their applicability in clinical scenarios.

Investigations into Flux-Free Plasma Brazing of Aluminum in a Local XHV-Atmosphere.

As a lightweight construction material, aluminum plays a key role in weight reduction and, thus, sustainability in the transport industry. The brazing of aluminum and its alloys is impeded by the natural passivating oxide layer, which interferes with the brazing process. The presented study investigates the possibility of using a thermal silane-doped argon plasma to reduce this oxide layer in situ and thus eliminating the need to use hazardous chemical fluxes to enable high-quality brazing. Using plasma spectroscopy and an oxygen partial pressure probe, it was shown that a silane-doped argon plasma could significantly reduce the oxygen concentration around the plasma in a thermal plasma brazing process. Oxygen concentrations below 10-16 vol.-% were achieved. Additionally, metallographic analyses showed that the thickness of an artificially produced Al2O3-Layer on top of AlMg1 samples could be substantially reduced by more than 50%. With the oxide layer removed and inhibition of re-oxidation, silane-doped plasma brazing has the potential to become an economically efficient new joining method.

Induction Heating in Underwater Wet Welding-Thermal Input, Microstructure and Diffusible Hydrogen Content.

Hydrogen-assisted cracking is a major challenge in underwater wet welding of high-strength steels with a carbon equivalent larger than 0.4 wt%. In dry welding processes, post-weld heat treatment can reduce the hardness in the heat-affected zone while simultaneously lowering the diffusible hydrogen concentration in the weldment. However, common heat treatments known from atmospheric welding under dry conditions are non-applicable in the wet environment. Induction heating could make a difference since the heat is generated directly in the workpiece. In the present study, the thermal input by using a commercial induction heating system under water was characterized first. Then, the effect of an additional induction heating was examined with respect to the resulting microstructure of weldments on structural steels with different strength and composition. Moreover, the diffusible hydrogen content in weld metal was analyzed by the carrier gas hot extraction method. Post-weld induction heating could reduce the diffusible hydrogen content by -34% in 30 m simulated water depth.

Pressure-compacted and spider silk-reinforced fibrin demonstrates sufficient biomechanical stability as cardiac patch in vitro.

OBJECTIVE: The generation of bio-/hemocompatible cardiovascular patches with sufficient stability and regenerative potential remains an unmet goal. Thus, the aim of this study was the generation and in vitro biomechanical evaluation of a novel cardiovascular patch composed of pressure-compacted fibrin with embedded spider silk cocoons. METHODS: Fibrin-based patches were cast in a customized circular mold. One cocoon of Nephila odulis spider silk was embedded per patch during the casting process. After polymerization, the fibrin clot was compacted by 2 kg weight for 30 min resulting in thickness reduction from up to 2 cm to <1 mm. Tensile strength and burst pressure was determined after 0 weeks and 14 weeks of storage. A sewing strength test and a long-term load test were performed using a customized device to exert physiological pulsatile stretching of a silicon surface on which the patch had been sutured. RESULTS: Fibrin patches resisted supraphysiological pressures of well over 2000 mmHg. Embedding of spider silk increased tensile force 1.8-fold and tensile strength 1.45-fold (p < .001), resulting in a final strength of 1.07 MPa and increased sewing strength. Storage for 14 weeks decreased tensile strength, but not significantly and suturing properties of the spider silk patches were satisfactory. The long-term load test indicated that the patches were stable for 4 weeks although slight reduction in patch material was observed. CONCLUSION: The combination of compacted fibrin matrices and spider silk cocoons may represent a feasible concept to generate stable and biocompatible cardiovascular patches with regenerative potential.

The Applicability of the Standard DIN EN ISO 3690 for the Analysis of Diffusible Hydrogen Content in Underwater Wet Welding.

The European standard ISO 3690 regulates the measurement of diffusible hydrogen in arc-welded metal. It was designed for different welding methods performed in dry atmosphere (20% humidity). Some details of the standard are not applicable for wet underwater welding. The objective of this study was to extend the applicability of DIN EN ISO 3690:2018-12 to underwater wet-shielded metal arc welding (SMAW). Four different aspects regulated within the standard were accounted for: (1) sample dimensions and number of samples taken simultaneously; (2) time limitations defined by the standard regarding the welding and the cleaning process; (3) time, temperature, and method defined for analysis of the diffusible hydrogen content; (4) normalization of the hydrogen concentration measured. Underwater wet welding was performed using an automated, arc voltage-controlled welding machine. The results are discussed in light of standard DIN EN ISO 3690, and recommendations are provided for the analysis of diffusible hydrogen content upon underwater wet welding.

Investigation of the Prediction Accuracy of a Finite Element Analysis Model for the Coating Thickness in Cross-Wedge Rolled Coaxial Hybrid Parts.

The Collaborative Research Centre 1153 (CRC 1153) "Process chain for the production of hybrid high-performance components through tailored forming" aims to develop new process chains for the production of hybrid bulk components using joined semi-finished workpieces. The subproject B1 investigates the formability of hybrid parts using cross-wedge rolling. This study investigates the reduction of the coating thickness of coaxially arranged semi-finished hybrid parts through cross-wedge rolling. The investigated parts are made of two steels (1.0460 and 1.4718) via laser cladding with hot-wire. The rolling process is designed by finite element (FE)-simulations and later experimentally investigated. Research priorities include investigations of the difference in the coating thickness of the laser cladded 1.4718 before and after cross-wedge rolling depending on the wedge angle ß , cross-section reduction Δ A , and the forming speed ν . Also, the simulations and the experimental trials are compared to verify the possibility of predicting the thickness via finite element analysis (FEA). The main finding was the ability to describe the forming behavior of coaxially arranged hybrid parts at a cross-section reduction of 20% using FEA. For a cross-section reduction of 70% the results showed a larger deviation between simulation and experimental trials. The deviations were between 0.8% and 26.2%.

Engineering of biodegradable magnesium alloy scaffolds to stabilize biological myocardial grafts.

OBJECTIVE: Regenerative bioprostheses are being investigated for replacement of dysfunctional myocardium worldwide. The aim of this study was to develop a degradable magnesium structure to mechanically support the delicate biological grafts during the early remodeling phase. METHODS: Sheets of magnesium alloys (LA33, LA63 and AX30) were manufactured into scaffolds by abrasive water jet cutting. Thereafter, their surface properties, corrosion kinetics, and breakage behaviors were investigated. RESULTS: The magnesium alloy LA63 sheets proved superior to the other alloys in terms of load cycles (lc) until break of the specimens (LA63: >10 Mio lc; AX30: 676,044±220,016 lc; LA33: 423,558±210,063 lc; p<0.01). Coating with MgF led to better protection than coating with MagPass. Less complex, yet sufficiently flexible scaffolds were less prone to early breakage. A slow traverse rate during water jet cutting resulted in the lowest burr, but in a widening of the kerf width from 615±11 µm at 500 mm/min to 708±33 µm at 10 mm/min (p<0.01). CONCLUSION: The findings on alloy composition, coating, structural geometry and manufacturing parameters constitute a basis for clinically applicable magnesium scaffolds. The use of stabilized, regenerative myocardium prostheses could save the patients from severe morbidity and eventually death.

Impact of intraprosthetic drilling on the strength of the femoral stem in periprosthetic fractures: A finite element investigation.

Treatment of periprosthetic femur fractures after total hip arthroplasty remains a major challenge in orthopedic surgery. Recently, a novel surgical technique using intraprosthetic screw fixation has been suggested. The purpose of this study was to evaluate the influence of drilling the femoral hip stem on integrity and strength of the implant. The hypothesis was that intraprosthetic drilling and screw fixation would not cause the load limit of the prosthesis to be exceeded and that deformation would remain within the elastic limit. A sawbone model with a conventional straight hip stem was used and a Vancouver C periprosthetic fracture was created. The fracture was fixed with a nine-hole less invasive stabilization system plate with two screws drilled and inserted through the femoral hip stem. Three different finite element models were created using ANSYS software. The models increased in complexity including joint forces and stress risers from three different dimensions. A variation of drilling positions was analyzed. Due to the complexity of the physiological conditions in the human femur, the most complex finite element model provided the most realistic results. Overall, significant changes in the stresses to the prosthesis caused by the drilling procedure were observed. While the stresses at the site of the bore hole decreased, the load increased in the surrounding stem material. This effect is more pronounced and further the holes were apart, and it was found that increasing the number of holes could counteract this. The maximum load was still found to be in the area of the prosthesis neck. No stresses above the load limit of titanium alloy were detected. All deformations of the prosthesis stem remained in the elastic range. These results may indicate a potential role for intraprosthetic screw fixation in the future treatment of periprosthetic femur fractures.

In vitro and in vivo corrosion properties of new iron-manganese alloys designed for cardiovascular applications.

The principle of biodegradation for the production of temporary implant materials (e.g. stents) plays an important role in the treatment of congenital heart defects. In the last decade several attempts have been made with different alloy materials-mainly based on iron and magnesium. None of the currently available materials in this field have demonstrated satisfying results and have therefore not found entry into broad clinical practice. While magnesium or magnesium alloy systems corrode too fast, the corrosion rate of pure iron-stents is too slow for cardiovascular applications. In the last years FeMn alloy systems were developed with the idea that galvanic effects, caused by different electrochemical properties of Fe and Mn, would increase the corrosion rate. In vitro tests with alloys containing up to 30% Mn showed promising results in terms of biocompatibility. This study deals with the development of new FeMn alloy systems with lower Mn concentrations (FeMn 0.5 wt %, FeMn 2.7 wt %, FeMn 6.9 wt %) to avoid Mn toxicity. Our results show, that these alloys exhibit good mechanical features as well as suitable in vitro biocompatibility and corrosion properties. In contrast, the evaluation of these alloys in a mouse model led to unexpected results-even after 9 months no significant corrosion was detectable. Preliminary SEM investigations showed that passivation layers (FeMn phosphates) might be the reason for corrosion resistance. If this can be proved in further experiments, strategies to prevent or dissolve those layers need to be developed to expedite the in vivo corrosion of FeMn alloys.

Intraprosthetic screw fixation increases primary fixation stability in periprosthetic fractures of the femur - a biomechanical study.

BACKGROUND: The purpose of this study was to develop a new fixation technique for the treatment of periprosthetic fractures using intraprosthetic screw fixation. The goal was to biomechanically evaluate the increase in primary fixation stability compared to unicortical locked-screw plating. METHODS: A Vancouver C periprosthetic fracture was simulated in femur prosthesis constructs. Fixation was then performed with either unicortical locked-screw plating using the LISS-plate or with intraprosthetic screw fixation. Fixation stability was compared in an axial load-to-failure model. RESULTS: The intraprosthetic fixation model was superior to the unicortical locked-screw fixation in all tested devices. The intraprosthetic fixation model required 11,807N±1596N for failure and the unicortical locked-screw plating required 7649N±653N (p=0.002). CONCLUSION: Intraprosthetic screw anchorage with a special prosthesis drill enhances the primary stability in treating periprosthetic fractures by internal fixation.

In vivo degradation of magnesium alloy LA63 scaffolds for temporary stabilization of biological myocardial grafts in a swine model.

Synthetic or biological patch materials used for surgical myocardial reconstruction are often fragile. Therefore, a transient support by degradable magnesium scaffolds can reduce the risk of dilation or rupture of the patch until physiological remodeling has led to a sufficient mechanical durability. However, there is evidence that magnesium implants can influence the growth and physiological behavior of the host's cells and tissue. Hence, we epicardially implanted scaffolds of the magnesium fluoride-coated magnesium alloy LA63 in a swine model to assess biocompatibility and degradation kinetics. Chemical analysis of the pigs' organs revealed no toxic accumulation of magnesium ions in the skeletal muscle, myocardium, liver, kidney, and bone of the pigs 1, 3, and 6 months postimplantation. The implants were surrounded by a fibrous granulation tissue, but no signs of necrosis were histologically evaluable. A sufficiently slow degradation rate of the magnesium alloy scaffold can be demonstrated via micro-computed tomography investigation. We conclude that stabilizing scaffolds of the magnesium fluoride-coated magnesium alloy LA63 can be used for epicardial application because no significant adverse effects to myocardial tissue were noted. Thus, degradable stabilizing scaffolds of this magnesium alloy with a slow degradation rate can extend the indication of innovative biological and synthetic patch materials.

Different thermal conductivity in drilling of cemented compared with cementless hip prostheses in the treatment of periprosthetic fractures of the proximal femur: an experimental biomechanical analysis.

PURPOSE: The purpose of this study was to evaluate the different temperature levels whilst drilling cemented and cementless hip prostheses implanted in bovine femora, and to evaluate the insulating function of the cement layer. METHODS: Standard hip prostheses were implanted in bovine donor diaphyses, with or without a cement layer. Drilling was then performed using high-performance-cutting drills with a reinforced core, a drilling diameter of 5.5 mm and cooling channels through the tip of the drill for constantly applied internal cooling solution. An open type cooling model was used in this setup. Temperature was continuously measured by seven thermocouples placed around the borehole. Thermographic scans were also performed during drilling. RESULTS: At the cemented implant surface, the temperature never surpassed 24.7 °C when constantly applied internal cooling was used. Without the insulating cement layer (i.e. during drilling of the cementless bone-prosthesis construct), the temperature increased to 47 °C. CONCLUSION: Constantly applied internal cooling can avoid structural bone and soft tissue damage during drilling procedures. With a cement layer, the temperatures only increased to non-damaging levels. The results could be useful in the treatment of periprosthetic fractures with intraprosthetic implant fixation.

Temperature control with internally applied cooling in solid material drilling: an experimental, biomechanical study.

PURPOSE: The purpose of this study was to evaluate the different temperature levels while drilling solid materials and to compare different cooling solutions for possible temperature control. An additional purpose was to develop an internal cooling device which can be connected to routinely used manual drilling devices in trauma surgery. METHODS: Drilling was performed on a straight hip stem implanted in bovine femora without cooling, with externally applied cooling and with a newly developed internal cooling device. Temperature changes were measured by seven thermocouples arranged near the borehole. Additionally, thermographic scans were performed during drilling. RESULTS: Drilling without cooling leads to an immediate increase in temperature to levels of thermal osteonecrosis (over 200 °C). With externally applied cooling temperatures were decreased, but were still up to a tissue damaging 85 °C. Internally applied cooling led to a temperature decrease to tissue-preserving levels during the drilling procedure (24.7 °C). CONCLUSION: Internal cooling with HPC-drillers lowered the measured temperatures to non-tissue damaging temperatures and should avoid structural tissue damage.

Biocompatibility of fluoride-coated magnesium-calcium alloys with optimized degradation kinetics in a subcutaneous mouse model.

The principle of biodegradation has been considered for many years in the development of cardiovascular stents, especially for patients with congenital heart defects. A variety of materials have been examined with regard to their suitability for cardiovascular devices. Iron- and magnesium-based stents were investigated intensively during the last years. It has been shown, that iron, or iron based alloys have slow degradation kinetics whereas magnesium-based systems exhibit rapid degradation rates. Recently we have developed fluoride coated binary magnesium-calcium alloys with reduced degradation kinetics. These alloys exhibit good biocompatibility and no major adverse effects toward smooth muscle and endothelial cells in in vitro experiments. In this study, these alloys were investigated in a subcutaneous mouse model. Fluoride coated (fc) magnesium, as well as MgCa0.4%, MgCa0.6%, MgCa0.8%, MgCa1.0%, and a commercially available WE43 alloy were implanted in form of (fc) cylindrical plates into the subcutaneous tissue of NMRI mice. After a 3 and 6 months follow-up, the (fc) alloy plates were examined by histomorphometric techniques to assess their degradation rate in vivo. Our data indicate that all (fc) alloys showed a significant corrosion. For both time points the (fc) MgCa alloys showed a higher corrosion rate in comparison to the (fc) WE43 reference alloy. Significant adverse effects were not observed. Fluoride coating of magnesium-based alloys can be a suitable way to reduce degradation rates. However, the (fc) MgCa alloys did not exhibit decreased degradation kinetics in comparison to the (fc) WE43 alloy in a subcutaneous mouse model.

Intraprosthetic fixation techniques in the treatment of periprosthetic fractures-A biomechanical study.

AIM: To develop new fixation techniques for the treatment of periprosthetic fractures using intraprosthetic screw fixation with inserted threaded liners. METHODS: A Vancouver B1 periprosthetic fracture was simulated in femur prosthesis constructs using sawbones and cemented regular straight hip stems. Fixation was then performed with either unicortical locked-screw plating using the less invasive stabilization system-plate or with intraprosthetic screw fixation using inserted liners. Two experimental groups were formed using either prostheses made of titanium alloy or prostheses made of cobalt chrome alloy. Fixation stability was compared in an axial load-to-failure model. Drilling was performed using a specially invented prosthesis drill with constantly applied internal cooling. RESULTS: The intraprosthetic fixation model with titanium prostheses was superior to the unicortical locked-screw fixation in all tested devices. The intraprosthetic fixation model required 10 456 N ± 1892 N for failure and the unicortical locked-screw plating required 7649 N ± 653 N (P < 0.05). There was no significant difference between the second experimental group and the control group. CONCLUSION: Intraprosthetic screw anchorage with special threaded liners enhances the primary stability in treating periprosthetic fractures by internal fixation.

Low-temperature degradation of different zirconia ceramics for dental applications.

The aim of this investigation was to determine the influence of simulated ageing on the tetragonal-to-monoclinic phase transformation and on the flexural strength of a 3Y-TZP ceramic, compared to alumina toughened zirconia (ATZ) and ceria-stabilized zirconia (12Ce-TZP). Standardized disc specimens of each material were hydrothermally aged in steam at 134°C and 3bar for 0, 16, 32, 64 or 128h. The phase transformation was determined by X-ray diffraction (XRD) and atomic force microscopy. Scanning electron microscopy was performed to estimate the depth of the transformation zone. The flexural strength was investigated in a biaxial flexural test. XRD revealed a significant increase in the monoclinic phase content for 3Y-TZP and ATZ due to ageing, although this increase was less pronounced for ATZ. In contrast, the monoclinic phase content of 12Ce-TZP was not influenced. For 3Y-TZP and ATZ, a transformation zone was found of which the depth linearly correlated with ageing time, while for 12Ce-TZP no transformation zone could be observed. Changes in flexural strength after ageing were heterogeneous: while 3Y-TZP showed a significant decrease in strength - from 1740 to 1169 MPa - with ATZ there was a considerable increase - from 1093 to 1378 MPa. The flexural strength of 12Ce-TZP remained unaffected at the low level of about 500 MPa. These results indicate that both alumina and ceria, as stabilizing oxides, reduce the susceptibility of zirconia to hydrothermal degradation; the alternative use of these oxides may enhance the clinical long-term stability of dental zirconia restorations.

Novel Repair Concept for Composite Materials by Repetitive Geometrical Interlock Elements.

Material adapted repair technologies for fiber-reinforced polymers with thermosetting matrix systems are currently characterized by requiring major efforts for repair preparation and accomplishment in all industrial areas of application. In order to allow for a uniform distribution of material and geometrical parameters over the repair zone, a novel composite interlock repair concept is introduced, which is based on a repair zone with undercuts prepared by water-jet technology. The presented numerical and experimental sensitivity analyses make a contribution to the systematic development of the interlock repair technology with respect to material and geometrical factors of influence. The results show the ability of the novel concept for a reproducible and automatable composite repair.

Influence of a magnesium-fluoride coating of magnesium-based implants (MgCa0.8) on degradation in a rabbit model.

MgCa0.8 cylinders (2.5 x 25 mm(2)) were coated with a magnesium-fluoride layer and implanted in the marrow cavities of both tibiae of 10 New Zealand White rabbits. The implantation duration was 3 and 6 months. The implants were clinically well tolerated. Micro-computed tomography revealed a new bone formation at the edges of the implants as well as an endosteal and periosteal remodeling. Using EDX-analysis, a calcium and phosphorus rich degradation layer could be found on the implant surface. It was covered by an incomplete layer containing fluoride. The analysis by weight before implantation and after 3 and 6 months, respectively, showed a slight decrease in volume in comparison to uncoated implants. When compared with uncoated implants, the mechanical properties of the coated implants exhibited a reduction in strength after 3 months. After 6 months, the strength of the coated implants was higher than that of uncoated cylinders.