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.

Abrazivni vodni curek (AVC) je v industriji znan kot hladni rezalni postopek, saj ne opazimo pomembnega toplotnega segrevanja na rezalnih robovih v primeru rezanja kovinskih materialov. Zaradi tega se AVC uporablja predvsem tam, kjer ne dovolimo toplotno prizadete cone v samem rezalnem materialu. Za medicinske uporabe je kritièna temperatura dosti nižja kakor pri industrijski rabi, saj so kosti zelo obèutljive za toploto. Poškodbe na tkivu so odvisne od same temperature v rezalni coni ter èasu rezanja. Tkivo se unièi že pri izpostavljanju za 10 sekund temperaturam, višjim od 57°C. Da bi se izognili temu uèinku, tako imenovani nekrozi, ki povzroèa slabše rasti kosti, je treba upoštevati temperaturo pri samem rezanju z AVC. Prvi koraki so narejeni v tem prispevku. Generacija toplote pri rezanju kosti z AVC je bila izmerjena z uporabo termoelementov, ki so bili vstavljeni v kortièno votlino goveje kosti. Vplivi parametrov kakor so: tlak, rezalna hitrost, pretok abraziva, abrazivni material so prikazani v tem prispevku, prav tako tudi vplivi postavitve termoelementov. © 2006 Strojniški vestnik. Vse pravice pridržane. (Kljuène besede: medicina, rezanje kosti, curek vodni, curek abrazivni, meritve temperature, termoèleni)

In der orthopädischen Chirurgie werden selbstauflösende Implantate aus Polyglykolid oder Polylaktid, z.B. zur ossären Fixierung von Kreuzbandimplantaten, regelhaft verwendet. Primäre Vorteile sind eine artefaktfreie Darstellung in Nativröntgenbild oder in der Schnittbilddiagnostik sowie die Vermeidung von Sekundäreingriffen zur Implantatentfernung. Sekundär kann das so genannte „stress-shielding“ zwischen Implantat und Knochen vermieden werden. Allerdings werden auch Fremdkörperreaktionen beobachtet. Ihre Häufigkeit wird in der Literatur mit bis zu 23% angegeben. Bereits in den fünfziger Jahren des letzten Jahrhunderts wurden biologische Schrauben aus Knochenmaterial zur Osteosynthese mit gutem Erfolg angewandt. Ein wesentliches Problem, an dem die klinische Umsetzung letztendlich scheiterte, war die aufwändige mechanische Herstellung der Schrauben und damit einhergehende herstellungsspezifische Probleme. Mit dem Wasserabrasivinjektorstrahl (WAIS) - Verfahren konnten aus boviner Femurkortikalis Knochenzylinder geschnitten und anschließend mit dem für Interferenzschrauben typischen selbstschneidenden Sägegewinde und einer Durchgangsbohrung versehen werden. Vorteile bei diesem Herstellungsprozess sind neben der geringen mechanischen und thermischen Belastung des Materials auch fertigungstechnische Aspekte und die Einhaltung der Sterilitätskette, da das Verfahren im Non-contact-Modus, also berührungsfrei, arbeitet. Die normierte mechanische Testung der so hergestellten Implantate wurde unter Berücksichtigung der ASTM-NormF 1839 [1] durchgeführt. Geprüft wurden das Drehmoment bis zum Versagen der Schraube sowie die Gewindeflankenfestigkeit durch Aufbringen einer axialen Zugkraft (Pull-out-Testung). Die gefertigten biologischen Schrauben erfüllten die ASTM-Normwerte. In einer vergleichenden Studie, mit dem Zielkriterium des Einwachsverhaltens, wurden daher Interferenzschrauben aus xenogenem Knochenmaterial und kommerziell verfügbare Interferenzschrauben aus Poly(L-Lactid) beim Göttinger Miniaturschwein vergleichend getestet. Als wesentliches Merkmal wurden die Schrauben im Maßstab 1:1 getestet. Die bovinen Knochenschrauben wurden innerhalb des Untersuchungszeitraumes zum Teil vollständig in den Wirtsknochen ossär integriert. Bereits nach 30 Tagen konnten unbestimmt einwachsende Knochenbälkchen in den Schraubenkörper nachgewiesen werden. Aufgrund der positiven Erfahrungen mit bovinen Knochenschrauben ist die Verwendung xenogenen bovinen Knochenmaterials zur Herstellung biomechanisch primär gering belasteter Implantate für Osteosynthesen z.B. im Vorfuß- o. Mittelgesichtsbereich möglich. Interference screws are state of the art of bone-tendon-bone fixation in anterior-cruciate-ligament (ACL) reconstruction. These screws normally consist of materials like different polylactic acids because of their biodegradability. In this paper our first investigation of machining interference screws made of bovine bones by means of an abrasive waterjet is presented. The material bone as an implant has the advantage to be resorbed and replaced by new own bone tissue. In this paper it is shown that an abrasive waterjet is able to machine the whole interference screw's geometry with different process's steps including drilling, turning, manufacturing a screw thread profile and an inside contour as a drive system. The developing of the thread profile by overlapping the abrasive waterjet's trace will be focused in this paper as well as the manufacturing of a hexagonal inside contour as a drive system. In a comparative study, the osseous integration of xenogenic bone and commercially available interference screws of poly (L-lactide) interference screws were comparatively tested in-vivo. As a key feature the screws were tested at a scale of 1: 1. The bovine bone screws have been fully integrated into the host osseous bone within the examination time of 270 days. Already after 30 days ingrowing trabeculae could be detected in the screw body. Based on this positive experiences with bovine bone screws the development of screws for use in the forefoot or midface area seems to be possible.

The aim of this experimental in-vitro study was to investigate the machining of human dentin using an abrasive water jet and to evaluate the influence of different abrasives and water pressures on the removal rate. Seventy-two human teeth had been collected after extraction and randomly divided into six homogeneous groups (n=12). The teeth were processed in the area of root dentin with an industrial water jet device. Different abrasives (saccharose, sorbitol, xylitol) and water pressures (15 or 25 MPa) were used in each group. Dimensions of dentin removal were analysed using a stripe projection microscope and both drilling depth as well as volume of abrasion were recorded. Morphological analyses of the dentin cavities were performed using scanning electron microscopy (SEM). Both drilling depth and volume of abrasion were significantly influenced by the abrasive and the water pressure. Depending on these parameters, the drilling depth averaged between 142 and 378 μm; the volume of abrasion averaged between 0.07 and 0.15 mm3. Microscopic images revealed that all cavities are spherical and with clearly defined margins. Slight differences between the abrasives were found with respect to the microroughness of the surface of the cavities. The results indicate that abrasive water jet machining is a promising technique for processing human dentin.

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.

The clinical application of waterjet technology for machining tough human tissues, such as articular bone, has advantages, as it produces clean sharp cuts without tissue heating. Additionally, water supply is possible via flexible tubing, which enables minimally invasive surgical access. This pilot study investigates whether drilling bony tissue with pure waterjets is feasible.Water pressures between 20 and 120 MPa with an orifice of 0.6 mm were used to create waterjets to drill blind borings in the talar articular surface of cadaveric calcaneus bones of human, sheep, goats and pigs. A stand-off distance between 2.5 and 5.5 mm and a jet-time of 5 seconds were chosen. The depth of the holes was measured using a custom-adapted dial gauge.At least 30 MPa of water pressure is required to penetrate the human and goat specimens, and 50 MPa for the pig and sheep specimens. Overall, the machined holes were conically shaped and increased in depth with an increase of pressure. Above certain pressure levels, pure waterjets can be used for machining holes in articular bone, thereby opening a window for further research on pure waterjet drilling in orthopedics.

Today’s standard procedures for the repair of fiber reinforced plastics are not optimized for the structural rearrangement of the original material properties. Alongside lap repair and scarf repair, a newly introduced method for the machining of a stepped peripheral zone is discussed. For this purpose, the methods of dry ice blasting and snow blasting as well as the water jet are being investigated. Reference material is carbon fiber reinforced plastic (CFRP) compliant to laminates used in the aviation industry. It was found that snow blasting and dry ice blasting were not suitable for this purpose in the experimental set-up. In contrast, the water jet allowed a precise control of the material removal. Subsequently to the feasibility study, a parameter study was carried out to determine applicable parameters for the surface preparation of CFRP. After successful machining of a stepped peripheral zone, a repair experiment was carried out with promising results.

Ziele: Prothetische Materialien zum Ersatz von erkrankten Aortenabschnitten sind limitiert durch Fehlen einer Windkesselfunktion, eingeschränkte Handhabbarkeit von Infektionen und fehlendes physiologisches Remodelling/Wachstum. Dezellularisierte, allogene Grafts, die in vivo mit den Zellen des Empfängers besiedelt werden, könnten eine Alternative darstellen. Allerdings ist die initial eingeschränkte mechanische Stabilität der dezellularisierten Grafts eine Gefahr für Aneurysmabildung, Dissektion oder Ruptur. In der vorliegenden Studie wurde die in vivo-Funktion verschiedener dezellularisierter Aortenprothesen mit MRT untersucht. Methode: In 12 Schafen wurden 5cm der absteigenden Aorta thoracica durch allogene, dezellularisierte, zur Prothese vernähten Aorten- und Pulmonalarteriensegmente ersetzt. Bei 6 Tieren wurden die Grafts zusätzlich mit einer Fluor beschichteten, starren Magnesiumspange stabilisiert (Mg-Gruppe). Einen Monat postoperativ erfolgte die Beurteilung der Prothesendurchmesser mittels MRT. Ergebnis: In der Vergleichsgruppe (ohne Magnesiumspange) verstarb ein Tier 5 Tage postoperativ durch Ruptur des pulmonalarteriellen Segmentes. Im Gegensatz zur Mg-Gruppe wurde in der Vergleichsgruppe bereits intraoperativ eine Aufweitung des pulmonalarteriellen Segmentes beobachtet. Die MRT zeigte 1 Monat postoperativ zwischen den beiden Gruppen keinen Unterschied der Durchmesser im dezellularisierten Aortensegment (14,95±2,20mm vs. 14,44±0,42mm, p=0,628), jedoch einen signifikanten Unterschied im dezellularisierten Pulmonalissegment (20,53±3,34mm vs. 15,55±2,05mm, p=0,017). Entsprechend waren nur in der Vergleichsgruppe die Durchmesser der dezellularisierten Pulmonalissegmente signifikant größer als die der nativen Aorta (20,53±3,34mm vs. 13,67±1,42mm, p=0,003). Schlussfolgerung: Die Entwicklung regenerativer, biologischer Aortenprothesen mittels Tissue Engineering erscheint möglich. Nur die Mg-Gruppe zeigt 1 Monat postoperativ eine ausreichende Stabilität der dezellularisierten Pulmonalissegmente.

Objectives: Surgical replacement of aortic segments with synthetic prosthesises often is the therapy of choice. Drawbacks of these prosthesises include absence of function of windkessel with subsequent refractory hypertonia, limited options for therapy of prosthesis infection and the inability of the graft to remodel or to grow. Decellularized allogeneic grafts, reseeded with the recipient's cells according to the principles of tissue engineering could overcome these limitations. However, the initial mechanical capacity of decellularized grafts is insufficient to withstand pressures up to 240 mmHG. There is a strong need to support the decellularized graft until mechanical durability is achieved by physiologic remodelling processes.

Objectives: We introduced feasibility of using autologous small bowel without mucosa but with adjacent jejunal artery and vein for the replacement of right ventricular transmural defects in pigs. Stability and thickness of the patch increased significantly after 3 month because of remodelling processes. However, the initial mechanical capacity of these myocardial grafts is insufficient to withstand pressures up to 240mmHg of the left ventricle in the early stage after surgery. Hence, there is a strong need to support the patch material until mechanical durability is achieved by physiologic remodelling processes.

Water-jet technology is known in industry as a cold-cutting process because no significant thermal effects are observed at the cutting edges of e.g., metallic workpieces. Thus, water jets are mostly used for applications where no structural changes are allowed. For medical applications the critical temperature is much lower than for industrial use, because bones react very sensitively to heat. The damage to the tissue depends on the temperature and the time of exposure. The tissue is irreversibly destroyed after a period of approximately 10 seconds at 57°C. To avoid this effect, which causes the so-called necrosis formation, and which results in poor bone healing, heat management is required for water-jet osteotomies. The first step is made in this paper. The heat generation during abrasive water-jet osteotomies was measured by thermocouples that were inserted into the cortical hollow bone segments of cattle. The influence of parameters like pressure, traverse rate, abrasive flow rate and abrasive material are shown in this paper together with the influence of the location of thermocouples, which represents an increment of the bone tissue.

Water-jet technology is known in industry as a cold-cutting process because no significant thermal effects are observed at the cutting edges of e.g., metallic workpieces. Thus, water jets are mostly used for applications where no structural changes are allowed. For medical applications the critical temperature is much lower than for industrial use, because bones react very sensitively to heat. The damage to the tissue depends on the temperature and the time of exposure. The tissue is irreversibly destroyed after a period of approximately 10 seconds at 57 degrees C To avoid this effect, which causes the so-called necrosis formation, and which results in poor bone healing, heat management is required for water-jet osteotomies. The first step is made in this paper The heat generation during abrasive water-jet osteotomies was measured by thermocouples that were inserted into the cortical hollow bone segments of cattle. The influence of parameters like pressure, traverse rate, abrasive flow rate and abrasive material are shown in this paper together with the influence of the location of thermocouples, which represents an increment of the bone tissue. (c) 2006 Journal of Mechanical Engineering. All rights reserved.

Cardiovascular diseases are the most frequent cause for morbidity and mortality worldwide. The damage of the heart muscle’s tissue is irreversible since cardiomyocytes do not have the capability to divide, and therefore myocardial regeneration does not take place. A surgical approach for therapy is the substitution of damaged heart tissue by a decellularized and revascularized small intestine mucosa. For the right ventricle and the atria (pressures ≤ 40-60 mmHg) the substitution of the damaged area could already be realized in animal studies. However, for the left ventricle (pressures up to 240 mmHg) the mechanical strength of these myocardial grafts is not sufficient in the early stage after the surgery. In this work first results in the processing of stabilising structures made of magnesium alloys for the cardiovascular surgery by high precision AWIJ are presented. In detail the aspects of cutting strategy, geometrical design, cutting edge roughness and burr generation are discussed.