Lebenswissenschaften und Ethik
Refine
Year of publication
Document Type
- Article (108)
- conference proceeding (article) (86)
- conference talk (37)
- conference proceeding (presentation, abstract) (30)
- Part of a Book (4)
- Doctoral Thesis (3)
- Moving Images (2)
- Other (2)
- conference proceeding (volume) (1)
- Edited collection (1)
- Preprint (1)
- Report (1)
- Working Paper (1)
Is part of the Bibliography
- no (277)
Keywords
- Biomechanik (13)
- Biomechanics (10)
- Simulation (10)
- Hüftgelenkprothese (9)
- Biomechanische Analyse (7)
- Stent (6)
- Bewegungsapparat (4)
- Finite element analysis (4)
- Spongiosa (4)
- biomechanics (4)
Institute
- Fakultät Maschinenbau (277) (remove)
Begutachtungsstatus
- peer-reviewed (100)
- begutachtet (10)
A new bone substitute, consisting of hydroxylapatite and calcium sulphate, was prepared in two formulations and analysed for its mechanical strength and antibiotic elution.The bone substitute PerOssal has osteoconductive and degradable properties. The material has a built-in capillary structure, which results in an immediate fluid uptake. Antibiotics absorbed to the bone substitute resulted in a prolonged release rate. Mechanical strength was investigated by an unconfined compression test up to failure under both wet and dry conditions for both formulations of the bone substitute. Antibiotic release was analysed microbiologically for two antibiotics, vancomycin and gentamicin, over an elution period of 10 days using the agar diffusion method.The drug release analysis resulted in a prolonged release rate of both antibiotics over 10 days. In vitro the amount of gentamicin and vancomycin eluted at day 10. From one pellet still exceeded the minimal inhibitory concentration of most aetiologically important pathogens. Formulation two of the present bone substitute is significantly harder in both wet and dry conditions when compared to formulation one. Both formulations lose strength in the wet condition relative to their performance in the dry condition. However, formulation two is as hard under wet conditions as formulation one is when dry.PerOssal is a suitable new degradable osteoconductive bone substitute that can be loaded with antibiotic solutions, which are released in effective doses over 10 days. The mechanical strength of PerOssal is sufficient to support cancellous bone defects in non-weight-bearing areas or in combination with osteosynthesis.
The mechanical complications of osteosyntheses after hip fractures are previously investigated by mostly static or dynamic uniaxial loading test systems. However, the physiologic loading of the hip joint during a normal gait is a multiplanar, dynamic movement. Therefore, we constructed a system to test osteosyntheses for hip fractures under physiologic multiplanar loading representative of normal gait. To evaluate the testing system, 12 femora pairs were tested under 25,000 cycles with two standard osteosyntheses (Proximal Femoral Nail Antirotation/Gamma3 Nail). For angular movement, the varus collapse to cut out (∝CO) (∝CO=4.8°±2.1° for blade and ∝CO=7.8°±3.8° for screw) was the dominant failure mode, and only slight rotational angle shifts (∝Rot) (∝Rot=1.7°±0.4° for blade and ∝Rot=2.4°±0.3° for screw) of the femoral head around the implant axis were observed. Angular displacements in varus direction and rotation were higher in specimens reinforced with screws. Hence, the cut out model and the migration directions showed a distinction between helical blade and hip screw. However, there were no significant differences between the different implants. The new setup is able to create clinical failures and allows to give evidence about the anchorage stability of different implant types under dynamic gait motion pattern.
Repeated loadings may cause fatigue fractures in bony structures. Even if these failure types are known, data for trabecular bone exposed to cyclic loading are still insufficient as the majority of fatigue analyses on bone concentrate on cortical structures. Despite its highly anisotropic and inhomogeneous structure, trabecular bone is treated with continuum approaches in fatigue analyses. The underlying deformation and damage mechanism within trabecular specimens are not yet sufficiently investigated. In the present study different types of trabecular bone were loaded in monotonic and cyclic compression. In addition to the measurement of integral specimen deformations, optical deformation analysis was employed in order to obtain strain distributions at different scale levels, from the specimens' surface to the trabeculae level. These measurements allowed for the possibility of linking the macroscopic and microscopic mechanical behaviour of cancellous bone. Deformations were found to be highly inhomogeneous across the specimen. Furthermore strains were found to already localise at very low load levels and after few load cycles. Microcracks in individual trabeculae were induced in the very early stage of cyclic testing. The results provide evidence of the capability of the method to supply essential data on the failure behaviour of individual trabeculae in future studies.
The fatigue behaviour of materials is of particular interest for the failure prediction of materials and structures exposed to cyclic loading. For trabecular bone structures only a few sets of lifetime data have been reported in the literature and structural measures are commonly not considered. The influence of load contributions not aligned with the main physiological axis remains unclear. Furthermore age effects on the fatigue behaviour are not well described. In the present study, different groups of human vertebral cancellous bone were exposed to cyclic compression. The inital modulus and therefore lifetimes were found to be highly dependent on age. The decrease in both with increasing age was much more pronounced in specimens which were not aligned with the main physiological axis. This implies that old bone is much more sensitive to (cyclic) failure loads in general but particularly to loads which are not coincident with the physiological main axis.
Objectives: The mechanical properties and seeding with endothelial cells were investigated in fresh and cryopreserved human umbilical vein.
Methods: Human umbilical veins (HUV) were frozen in Euro-Collins/1M DMSO at –1°C/min and stored in liquid nitrogen. Stress-strain relationships of fresh and thawed veins were determined in an uniaxial tension-testing rig. HUV endothelial cells (HUVEC) were seeded onto denuded HUV under static conditions and grown for 3d. Luminal surfaces were analyzed by scanning electron microscopy. Calcein-stained cells were seeded hyperconfluently to determine the cell retention capacity of fresh and cryopreserved veins.
Results: The stress-strain relationships of HUV followed a biphasic pattern typical for natural vessels. Neither the failure stress (2.71±0.36 vs. 3.25±0.97 N, n=3) nor the displacement required to achieve failure (9.73±0.9 vs. 7.43±2.07mm, n=3) were altered by cryopreservation. The burst pressure was estimated as approx. 1000mm Hg within the limitations of the uniaxial model. HUVEC seeded onto denuded HUV formed patches (at 9E3 cells per cm2) or an almost confluent endothelium (at 3E4 cells per cm2) within three days. The capacity to retain seeded HUVEC of denuded HUV was not altered by cryopreservation (1.15±0.08E5 vs. 1.26±0.14E5 cells per cm2, n=6).
Conclusions: The burst pressure of HUV seems to be sufficiently high for the human arterial circulation and is not altered by cryopreservation. HUVEC can establish a confluent endothelium on denuded HUV. Therefore HUV appears to be a suitable storable scaffold for vascular tissue engineering.
A 3-point skeletal anchorage with taping screws for distraction osteogenesis after a Le Fort III osteotomy was applied for the first time in a severely mentally impaired patient where intraoral devices had to be avoided. All 3-force application points included the center of resistance, which allowed an optimal control on the resulting moment. A novel device for skeletal long-term retention into the nasal dorsum prevented a relapse, whereas adjustment of the midface position was observed. Fusioned three-dimensional computed tomography analysis revealed real movements not accessible by a conventional cephalometry.
Medicine Meets Engineering: Proceedings of the 2nd Conference on Applied Biomechanics Regensburg
(2008)
Biomedical Engineering is defined as the science that integrates medical and engineering sciences to improve diagnosis and treatment of patients. Only by this integration progress can be achieved. Both medical and engineering sciences comprise a huge diversity in topics, so it is imaginable that Biomedical Engineering, combining these two science areas, is even more huge. Thanks to this megadisciplinary approach many breakthroughs can be achieved. More and more research groups realize this and start new research projects, which results in a rapid increase in knowledge in Biomedical Engineering. This will only benefit the main goal of Biomedical Engineering; improving diagnosis and treatment of patients when it is spread and applied. The 2nd Regensburg Applied Biomechanics conference is special in that it realized both the distribution of new knowledge and the essential integration of medical and engineering specialists. The conference dealt with the latest results in applied biomechanics, ranging from fundamental bone strength properties via bone remodeling phenomena to new implants that replace lost human functions. Also new research areas like robot surgery and tissue engineering were discussed.
Finite element (FE)–based studies of preoperative processes such as folding,pleating, and stent crimping with a comparison with experimental inflation tests are not yet available. Therefore, a novel workflow is presented in which residual stresses of balloon folding and pleating, as well as stent crimping, and the geometries of all contact partners were ultimately implemented in an FE code to simulate stent expansion by using an implicit solver. The numerical results demonstrate that the incorporation of residual stresses and strains experienced during the production step significantly increased the accuracy of the subsequent simulations, especially of the stent expansion model. During the preoperative processes, stresses inside the membrane and the stent material also reached a rather high level. Hence, there can be no presumption that balloon catheters or stents are undamaged before the actual surgery. The implementation of the realistic geometry, in particular the balloon tapers, and the blades of the process devices improved the simulation of the expansion mech-anisms, such as dogboning, concave bending, or overexpansion of stent cells. This study shows that implicit solvers are able to precisely simulate the mentioned preoperative processes and the stent expansion procedure without a preceding manipulation of the simulation time or physical mass.