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.

In patients with severe heart failure, the surgical reconstruction of the damaged myocardium with regenerative biological grafts is an innovative therapeutic option. However, natural patch materials are often too delicate for a full wall repair of the left ventricle. A degradable magnesium scaffold could provide temporary mechanical stability until the sufficient physiological remodeling of such grafts. An autologous vascularised gastric patch was employed for the reconstruction of the left ventricular myocardium in a porcine model. Magnesium alloy (LA63) scaffolds were fixed over the biological patch. The function of the implant was assessed via magnetic resonance imaging. Angiography was carried out to detect a connection between the gastric and coronary vasculature. The explants were examined via µ-computer tomography and light microscopy. All the test animals survived. The prostheses integrated biologically and functionally into the myocardium. No rupture of the prostheses occurred. An anastomosis of the gastric and coronary vasculature had developed. The magnesium scaffolds degraded, on average, to 30.9% of their original volume. This novel technique responds to the increasing demand for regenerative myocardial grafts. The magnesium scaffolds’ biocompatibility and degradation kinetics, as well as their stabilizing effects, indicate their applicability in the surgical treatment of terminal heart failure.

Abstract 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.

Therapy in cardiovascular medicine often relies on implantation of prosthetic materials or application of stents. The diseases of many cardiovascular structures require their complete and immediate repair by utilising prosthetic materials. The ideal cardiovascular prosthesis involves good functional properties, capability of regeneration and does not activate the host's immune system. Ideally, the graft can be applied for a temporary use and degrades after a predefined period according to controlled degradation kinetics. Only biological grafts would provide this spectrum of properties by today's level of knowledge. However, biological prostheses exhibit some relevant drawbacks as well, such as insufficient mechanical stability or restricted availability. Implants or supporting structures of magnesium alloys would bridge this gap and would either provide a substrate for innovative and temporary grafts or would—as supporting structures—transiently add some missing properties to regenerative biological prostheses. This chapter reviews the different fields of cardiovascular therapeutic applications of magnesium alloys. The required properties of magnesium alloys and their preparation, fabrication and testing will be discussed under the specific cardiovascular perspective.

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.

Lesioned myocardial tissue can be replaced with innovative biological grafts. However, the strength of most biological grafts is initially not sufficient for left ventricular applications. Implants that mechanically support these grafts and gradually lose their function as the graft develops its strength are a possible solution. We are developing magnesium alloy scaffolds for this purpose. The finite element method was used to perform simulations wherein scaffolds are deformed according to the heart movement. This allows us to identify highly stressed regions within the implant that need design changes. Preformed scaffolds were determined to have significantly lower stresses in comparison to flat ones. The method of tensile triangles suggests shape changes for notable stress reduction. Furthermore, new scaffold shapes were developed and simulated. Two of them are recommended for further examinations through in vitro and in vivo tests. A completely new alternative scaffold concept is also proposed.

High-pressure water jet technology is used progressively in industrial applications since 1971. The material behavior of pure water (H 2O without additions) has been studied for a wide temperature and pressure range. Usually, tap water is used as process medium for cutting applications. However, only little data is available for the behavior of tap water at elevated temperature and pressure changes. It is commonly known that the use of ion exchangers leads to a significant softening of the water, which has a negative effect on seal lifetime. Hard water has similar negative effects. It leads to calcification, which causes life reduction of high pressure pump components and also seals due to tribological effects. In order to understand the relationship between water and its constituents at high pressure up to 300 MPa, a chamber for spectroscopic and photometric measurements was constructed and built. After loading the chamber with different water specimens, the pressure was increased in 25 MPa steps and the spectral light intensity was measured. In this study, deionized water was employed as a reference and compared to common tap water and pure water with added NaCl and CaCl 2. The results were evaluated statistically though a selfdevised, “R”-based software. Significant alterations when applying given pressure could be observed both through photometric measurements and spectrometric investigations. By using deionized water as a reference, the pressure-dependent intrinsic behavior of the measurement setup was compensated. With the described method, a variance in spectral intensities was shown when using different fluids and different pressure levels. Particularly, calcium chloride blended water solutions showed a behavior of the spectral intensities similar to tap water. Organized and Sponsored by WJTA®-IMCA®

In the Abrasive Water Injection Jet (AWIJ) process, abrasive injection is p eumatically enabled through the generation of technical vacuum by a water jet. Fed particles are collected by the jet in a mixing chamber and are subsequently accelerated. Before impact on the work piece surface, the turbulent multiphase flow containing air, water and abrasive particles is focused at a certain distance, enabling cutting applications. During acceleration and focusing, the current flow conditions provoke numerous collisions of the abrasive particles with the focusing tube. Thus, highly wear resistant materials like tungsten carbide are necessary for this component. The abrasive particles themselves are also subject to wear during collision with each other or the harder focusing tube. As a result, the actual size of the readyto-cut particles is smaller than the original particle size. Manufacturers of currently available machines and cutting systems tend to increase the hydraulic power through higher-pressure levels (> 500 MPa), and to minimize jet diameters for micromachining. However, the size of the particles, which carry out the actual micro chipping process, is unknown. In this study particle disintegration in the abrasive water injection jet process was investigated. The objective was to better understand the material removal procedure during AWIJ machining. Microand macro cutting systems corresponding to the actual state of the art were utilized in a pressure range between 250 MPa and 550 MPa. The particle disintegration was investigated for several abrasive load ratios. Organized and Sponsored by WJTA®-IMCA ® 1. INTRODUC TION In the Abrasive Water Injection Jet (AWIJ) process, the initially formed jet includes air at its surface and at the surface of its droplets, which results in a technical vacuum formed in the mixing chamber . This allows for a pneumatic transport of abrasive particles into the jet. The high-speed waterjet collects the fed particles along with a substantial amount of air in a mixing chamber and subsequently accelerates them (Figure 1). During acceleration and focusing, the flow conditions provoke collisions of the abrasive particles among themselves or with the focusing tube. Manufacturers of currently available machines and cutting systems tend to increase the hydraulic power through higher-pressure levels (p > 500 MPa), and to minimize jet diameters for micromachining. These parameters have major influence on the transport process in the focusing tube. However, due to particle wear, the size of the particles, which carry out the actual micro chipping process, is unknown. Thus, the objective of the present study was to investigate particle disintegration and contribute to understanding of the material removal procedure. 2. STATE-OF-THE-ART The utilization of the water jet’s kinetic energy as an acceleration medium for abrasive particles has a major effect on the jet’s material removal behavior. The accelerated, sharp-edged abrasive particles cause the micro-chipping process. Prior to impact on the work piece surface, the turbulent multiphase flow containing air, water and abrasive particles is focused at a istance l f (30 mm ≤ lf ≤ 100 mm, dependent on orifice diameter d o and focusing tube diameter d f). During acceleration and focusing, the current flow conditions provoke numerous collisions. The particle acceleration direction finally results from the sum of the particles’ eccentric and centric impacts among themselves, as well as with the focusing tube’s cladding (1,2). Thus, highly wear resistant materials like tungsten carbide are necessary for this component. In addition to the tool wear, the abrasive particles are also subject to wear during collision between each other or with the harder focusing tube. The accelerated particles either cause micro-chipping, micro-crenation or micro-cracking processes at the work piece. Velocity, shape and mass of the abrasive particles are important parameters that affect material removal. Criteria typically used to evaluate the material removal potential of abrasives are cutting ability, cutting quality and degree of fragmentation and particle size is a key parameter in this respect. A decrease of the particle size directly involves a decrease of cutting power because of the lower maximum momentum transfer. However, microscopic comparison of particles prior to and after the jetting process indicated a significant particle disintegration. Secondary disintegrations occur on work piece impact, as well as collisions with slowed-down particles after work-piece impact. On particle disintegration, the kinetic energy is split between the fragments. The direction of movement alters and disturbs the abrasive waterjet (2). Since the beginning of its industrial applications, several authors have studied the Abrasive Water Injection Jet (AWIJ) process. Given the complexity of the process, most of the models developed are empirical in nature and assume given values for the particle mass or particle energy (1,3 –8). In a related study, particle disintegration has been investigated with the aim of estimating the recycling potential (2). The grade of disintegration was analyzed for three different stages (jet formation, cutting process and residual energy conversion). It was shown that the predominant disintegration takes place within the jet formation process, whereas the actual cutting process has only a minor influence in this respect. The grade of fragmentation decreases when smaller particles are used in the same cutting head (d o = 0.25 mm, df = 0.9 mm, lf = 40 mm). The grade of fragmentation ranged from 20% (d p = 40 μm) to 60% (dp = 600 μm) (2). However, these data were acquired with nozzle combinations that are unusual in today’s industrial applications and did not consider modern ultra-high pressure and micro-cutting applications. Thus, the present study was conducted to determine the resulting particle size under such conditions and help to better understand the material removal process. 3. MATERIALS AND METHODS 3.1 Materials Abrasives used were GMA Garnet #120 (GMA Garnet Pty Ltd, Perth, Australia) for macro applications and Barton HPX #220 (Barton Mines Co LLC, Glen Falls, NY, USA) for micro applications, technical specifications are summarized in Table 1. Initially , both abrasives were subject to a sieve analysis. According to specifications from GMA and Barton (9,10), the analysis was carried out according to DIN ISO 565 (11), series R40/3. The results were used as reference values for the following investigations, but also for verification of the particle size distribution specified by the manufacturers. For the sieve analysis, an analytical sieve shaker (manufacturer Retsch, type VS 100) was used. According to DIN ISO 565 series R40/3, the installed sieves were: 250 μm, 212 μm, 180 μm, 150 μm, 106 μm, 90 μm, 75 μm, 63 μm, 53 μm, 45 and 38 μm. For the gravimetric analysis, a precision balance (manufacturer Shinko, type DJ-1506, accuracy of measurements 0.001 g) was used. All jetting experiments were carried out on a lab machine with an Engelhardt C-55 control unit. The high pressure pump was a ThyssenKrupp Uhde HPS 6045 (max. operating pressure pw = 600 MPa, max. volume flow rate Q w = 2.8 l/min). A total of three cutting heads were used. To represent normal job shop operation, a standard cutting head commonly used in industry was employed. This was equipped with a common nozzle combination (manufacturer BFT, type TJ006070/591, d o = 0.28 mm, df = 0.76 mm, l f = 70 mm), in the following referred to as “Macro”. To represent common micro-cutting applications, the nozzle combination used was: do = 0.125 mm, df = 0.3 mm, l f = 32 mm. The use of two different cutting heads was necessary in order to provide the best possible nozzle centering on the one hand, but also providing the necessary sealing for pressures p ≥ 450 MPa on the other. The cutting heads used were a self-centering one for operating pressures of p ≤ 350 MPa (IW Hannover / Dick & Dick GmbH, referred to as “Micro A”) and a statically centering one for operating pressures p ≥ 450 MPa (manufacturer Allfi, type Centerline II, referred to as “Micro B”). All water orifices were sapphires (manufacturer Comadur); all focusing tubes were made of tungsten carbide (manufacturer Ceratizit, type WJNS/Standard). 3.2 Cutting performance benchmark Prior to the jetting experiments, the cutting performance of the Micro and Macro cutting systems was benchmarked by kerf tests with wedge-shaped specimen . Th feed rate was oriented from the summit into the specimen. The tests were carried out with five different abrasive mass flow load ratios (5 %, 10 %, 15 %, 20 % and 25 % by weight), which allowed for the determination of cutting power at different loading situations. In most industrial applications, an abrasive/water load ratio between 0.18 and 0.20 by weight has been evaluated as very economical. Dependent on the particle size mixture, a certain saturation level can already exist on lower abrasive/water proportions. The applied investigation method not only provides for a benchmark of the abrasives but only allows for an estimation of the optimum abrasive/water load ratio. The tests were carried out with stainless steel specimen ( DE 1.4301, similar to AISI 304) and a wedge angle of g = 15°. The feed rate was kept constant at f = 100 mm/min, and two pressure levels were employed (p 2 = 350 MPa and p 4 = 550 MPa). 3.3 Jetting experiments This test series was carried out in order to investigate the abrasive particle disintegration in the jet forming process; all experiments were carried out without a work piece. For the experiments, abrasive collecting vessels according to Figure 2 were constructed. Prior to the experiments, the vessels were completely filled up with water. The focusing tube of the cutting head was positioned slightly underneath water level before the experiment was started for a determined te

Synthetic patch materials currently in use have major limitations, such as high susceptibility to infections and lack of contractility. Biological grafts are a novel approach to overcome these limitations, but do not always offer sufficient mechanical durability in early stages after implantation. Therefore, a stabilising structure based on resorbable magnesium alloys could support the biological graft until its physiologic remodelling. To prevent early breakage in vivo due to stress of non-determined forming, these scaffolds should be preformed according to the geometry of the targeted myocardial region. Thus, the left ventricular geometry of 28 patients was assessed via standard cardiac magnetic resonance imaging (MRI). The resulting data served as a basis for a finite element simulation (FEM). Calculated stresses and strains of flat and preformed scaffolds were evaluated. Afterwards, the structures were manufactured by abrasive waterjet cutting and preformed according to the MRI data. Finally, the mechanical durability of the preformed and flat structures was compared in an in vitro test rig. The FEM predicted higher durability of the preformed scaffolds, which was proven in the in vitro test. In conclusion, preformed scaffolds provide extended durability and will facilitate more widespread use of regenerative biological grafts for surgical left ventricular reconstruction.

Introduction: Several pathologies of the thoracic aorta such as blunt chest traumas, aortic aneurysms/ dissections require surgical treatment and are associated with a high risk of rupture and organ ischemia. Aside from endovascular aortic repair, often invasive treatment is unavoidable. Widely used dacron prostheses have many limitations such as the inability to grow, repair and remodel as well as the predisposition for infections, risk of thrombosis and lack of windpipe function. Here, we report the successful stabilization of decellularized aortic allografts with an absorbable magnesium scaffold (AMS) in descending aorta position.

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.

Damaged myocardial tissue can be replaced by biological grafts. These grafts often cannot withstand the high blood pressure in the left ventricle. Therefore stabilising structures were developed to support the grafts. They are manufactured from biodegradable magnesium alloys. However, early breaks following implantation of these structures occur. On that account a finite element model was developed to numerically determine stresses within the structures, identify weak points and develop new designs. A few improved structures to be tested in vitro and in vivo are presented.

Surgical reconstruction of lesioned myocardium with vascularized bowel segments could provide a regenerative therapeutic approach. Because of the tissue's low load capacity shortly after surgery, a mechanical support of the biological graft with a stabilizing structure of magnesium alloy is necessary. In this study modification of surface roughness as a corrosion rate determining parameter by shot peening of stabilizing magnesium structures in vitro is assessed.

Damage of the heart muscle's tissue is irreversible due to the inability of adult cardiomyocytes to proliferate.Biological grafts like vascularized bowel segments are a novel approach to overcome these limitations.We found cardiac muscle cells within the heterotopically used gastric tissue in previous studies [1].This may indicate an in vivo remodeling process.Unfortunately, early after transplantation the biological tissue does not exhibit sufficient mechanical strength to withstand high systolic pressures in the left ventricle (up to 240 mm Hg).Therefore, a stabilizing structure based on the bioresorbable magnesium alloys is needed for the support of the tissue until its physiologic remodeling.It is hypothesized that preformed structures adapted to the specific geometry of the targeted myocardial area are less likely to fracture during implantation or shortly after.In order to preform the structure, common areas of lesioned myocardium after infarction have been characterized by magnetic resonance imaging (MRI).Hereafter, the plane structures could be virtually preformed and the expected stresses were simulated with the finite elements method (FEM).This allows reduction of costs and time for developing new structures.Subsequently, structures of the magnesium alloys LA63 and ZEK100 were manufactured by abrasive water injection jet cutting (AWIJ), and preformed on the basis of the MRI data.Finally, the performance of preformed and non-preformed structures of different alloys was tested in an in-vitro testing rig.