FINITE ELEMENT ANALYSIS OF AORTAL BIFURCATION

Arterial bifurcations loaded by internal pressure represent significant stress concentrators. Increased mechanical stress inside arterial wall probably accelerates pathogenic processes at these places. Stress concentration factor (SCF) depends mainly on geometry, loading and material. This work presents a map of SCFs calculated by FEM at aortic bifurcation (AB) loaded by static internal pressure. Influence of geometry (aortic diameter, wall thickness, bifurcation angle, "non-planarity" angle and radius of apex), material properties and internal pressure were evaluated statistically by regression of FEM results. Two variants of materials were used (linear Hook and hyper elastic Ogden). Viscoelastic behaviour, anisotropy and prestrain were neglected. Results indicate that the highest Mises stress appears in the inner side of AB apex and that the SCF is negatively correlated with bifurcation angle and with internal pressure. The SCF varies from 4,5 to 7,5 (Hook) and from 7 to 21 (Ogden)

DEVELOPMENT OF NEW TECHNIQUE FOR ACCURATE WEAR ANALYSIS OF EXPLANTED TOTAL HIP REPLACEMENTS

Wear is a fundamental problem in relation to the life-time of the hip joint implants, especially for the components of the ultra-high molecular weight polyethylene (UHMWPE). Therefore, the better understanding of the properties and capabilities of UHMWPE related to wear is crucial for the improvement of the implants' behavior. The purpose of this study is to present a new methodology for calculating volumetric wear of retrieved hip prostheses using a combination of novel co-ordinate measuring machine data and Matlab GUI program (Mathworks, Inc.). Method utilizes the unworn portion of the explanted acetabular cup to create or reconstruct the original unworn surface. From these unworn surfaces, it is possible to directly calculate volumetric wear and to graphically map the wear scar, i.e. the penetration of the femoral head into the acetabular cup

Designing of PLA scaffolds for bone tissue replacement fabricated by ordinary commercial 3D printer

Abstract Background The primary objective of Tissue engineering is a regeneration or replacement of tissues or organs damaged by disease, injury, or congenital anomalies. At present, Tissue engineering repairs damaged tissues and organs with artificial supporting structures called scaffolds. These are used for attachment and subsequent growth of appropriate cells. During the cell growth gradual biodegradation of the scaffold occurs and the final product is a new tissue with the desired shape and properties. In recent years, research workplaces are focused on developing scaffold by bio-fabrication techniques to achieve fast, precise and cheap automatic manufacturing of these structures. Most promising techniques seem to be Rapid prototyping due to its high level of precision and controlling. However, this technique is still to solve various issues before it is easily used for scaffold fabrication. In this article we tested printing of clinically applicable scaffolds with use of commercially available devices and materials. Research presented in this article is in general focused on “scaffolding” on a field of bone tissue replacement. Results Commercially available 3D printer and Polylactic acid were used to create originally designed and possibly suitable scaffold structures for bone tissue engineering. We tested printing of scaffolds with different geometrical structures. Based on the osteosarcoma cells proliferation experiment and mechanical testing of designed scaffold samples, it will be stated that it is likely not necessary to keep the recommended porosity of the scaffold for bone tissue replacement at about 90%, and it will also be clarified why this fact eliminates mechanical properties issue. Moreover, it is demonstrated that the size of an individual pore could be double the size of the recommended range between 0.2–0.35 mm without affecting the cell proliferation. Conclusion Rapid prototyping technique based on Fused deposition modelling was used for the fabrication of designed scaffold structures. All the experiments were performed in order to show how to possibly solve certain limitations and issues that are currently reported by research workplaces on the field of scaffold bio-fabrication. These results should provide new valuable knowledge for further research