Prototypenanlage und Prozessuntersuchung zum elektrolytischen Plasmapolieren von Rohrinnenoberflächen

Ziel dieser Arbeit ist, durch eine Weiterentwicklung des Plasmapolierprozesses mit Hilfe einer innovativen Prototypenanlage samt Polierkopf den Nachweis zu erbringen, dass ein elektrolytisches Plasma auch an der Innenoberfläche von Rohren erzeugt und somit die Rauheit im Inneren des Rohres reduziert werden kann. Die Entwicklung eines Prozesses zum elektrolytischen Plasmapolieren von Rohrinnenoberflächen mit entsprechender Anlagentechnik und notwendigen Werkzeugen erfordert einen komplett neuen technischen Ansatz

Bone regeneration of minipig mandibular defect by adipose derived mesenchymal stem cells seeded tri-calcium phosphate- poly(D,L-lactide-co-glycolide) scaffolds

Reconstruction of bone defects represents a serious issue for orthopaedic and maxillofacial surgeons, especially in extensive bone loss. Adipose-derived mesenchymal stem cells (ADSCs) with tri-calcium phosphates (TCP) are widely used for bone regeneration facilitating the formation of bone extracellular matrix to promote reparative osteogenesis. The present study assessed the potential of cell-scaffold constructs for the regeneration of extensive mandibular bone defects in a minipig model. Sixteen skeletally mature miniature pigs were divided into two groups: Control group and scaffolds seeded with osteogenic differentiated pADSCs (n=8/group). TCP-PLGA scaffolds with or without cells were integrated in the mandibular critical size defects and fixed by titanium osteosynthesis plates. After 12 weeks, ADSCs seeded scaffolds (n=7) demonstrated significantly higher bone volume (34.8%+/- 4.80%) than scaffolds implanted without cells (n=6, 22.4%+/- 9.85%) in the micro-CT (p < 0.05). Moreover, an increased amount of osteocalcin deposition was found in the test group in comparison to the control group (27.98 +/- 2.81% vs 17.10 +/- 3.57%, p < 0.001). In conclusion, ADSCs seeding on ceramic/polymer scaffolds improves bone regeneration in large mandibular defects. However, further improvement with regard to the osteogenic capacity is necessary to transfer this concept into clinical use

Influence of the Velocity and the Number of Polishing Passages on the Roughness of Electrolytic Plasma Polished Pipe Inner Surfaces

Electrolytic plasma polishing (EPP) is an emerging technology for polishing, cleaning, deburring and smoothing of free-formed metal surfaces. The electrolytic plasma polishing of outer metal surfaces is state-of-the-art, whereas the polishing of pipe inner surfaces has only recently been reported by the authors. A prototype system and first experimental results were presented. It was found in the previous study that the average surface roughness Sa reaches a range from 0.065 µm to 0.090 µm. The current study systematically investigates the influence of the velocity v as well as the number n of polishing passages on the average surface roughness Sa . The polishing of the pipe inner surface and weld seam are considered separately. The results show that the average roughness Sa is mainly dependent on the effective polishing time t e p t of the polishing process. The average surface roughness Sa of the pipe inner surface can reach a range from 0.030 µm to 0.034 µm starting from an initial surface roughness S a 0 of 0.719 µm, whereas the average surface roughness Sa of the weld seam can reach a range from 0.088 µm to 0.096 µm starting from an initial surface roughness Sa 0 of 0.282 µm. These ranges are achieved after an effective polishing time of approximately 25 s for both the inner pipe surface and the weld seam

Electrolytic Plasma Polishing of Pipe Inner Surfaces

Smooth surfaces are becoming increasingly important in many industries, such as medical, chemical or food. In some industrial areas, the mechanical treatment of surfaces (grinding and polishing) does not fulfil desired specifications. Non-abrasive methods (chemical and electrochemical) have the advantage that even complex geometries and free-form shapes can be polished. In the context of this paper, electrochemical surface treatment is considered in more detail. Both electro polishing, which is state of the art, and the novel electrolytic plasma polishing (EPP) process are presented. This paper focusses on the electrolytic plasma polishing because it has many advantages compared to the process of electro polishing. The theoretical operation of the electrolytic plasma polishing is shown. A prototype system for plasma polishing of internal surfaces of pipes was installed and a polishing head was developed. Several parameters are investigated, such as the width of the adjustable polishing head gap and different velocities v or different applied potential differences U, and first results of the average surface roughness Sa as function of the various parameters were evaluated. It can be seen that a stable polishing process can be achieved at the highest potential difference of 320 V and that the average surface roughness Sa reaches a range from 0.065 to 0.090 µm. At the same time, it has been shown that with increasing potential difference, the average surface roughness becomes independent of the width of the adjustable polishing head gap

Migration Capacity and Viability of Human Primary Osteoblasts in Synthetic Three-dimensional Bone Scaffolds Made of Tricalciumphosphate

In current therapeutic strategies, bone defects are filled up by bone auto- or allografts. Since they are limited by insufficient availability and donor site morbidity, it is necessary to find an appropriate alternative of synthetic porous bone materials. Because of their osteoconductive characteristics, ceramic materials like tricalciumphosphate (TCP) are suitable to fill up bone defects. Another advantage of TCP implants is the ability of patient-specific engineering. Objective of the present in-vitro study was to analyze the migration capacity and viability of human primary osteoblasts in porous three-dimensional TCP scaffolds in a static cell culture. To obtain data of the cellular supply with nutrients and oxygen, we determined the oxygen concentration and the pH value within the 3D scaffold compared to the surrounding medium using microsensors. After eight days of cultivation we found cells on all four planes. During incubation, the oxygen concentration within the scaffold decreased by approximately 8%. Furthermore, we could not demonstrate an increasing acidification in the core of the TCP scaffold. Our results suggest that osteoblasts could migrate and survive within the macroporous TCP scaffolds. The selected size of the macropores prevents overgrowth of cells, whereby the oxygen and nutrients supply is sufficiently guaranteed

Railway track allocation: models and methods

Efficiently coordinating the movement of trains on a railway network is a central part of the planning process for a railway company. This paper reviews models and methods that have been proposed in the literature to assist planners in finding train routes. Since the problem of routing trains on a railway network entails allocating the track capacity of the network (or part thereof) over time in a conflict-free manner, all studies that model railway track allocation in some capacity are considered relevant. We hence survey work on the train timetabling, train dispatching, train platforming, and train routing problems, group them by railway network type, and discuss track allocation from a strategic, tactical, and operational level