Nikola Korunović

DESIGN STUDY OF ANATOMICALLY SHAPED LATTICED SCAFFOLDS FOR THE BONE TISSUE RECOVERY

The current major scaffold design concepts for bone tissue recovery are characterized by labyrinthine design. Their main shortcomings are low level of permeability for new growing tissue, poor design adaptability in regard to particular anatomy and required biomechanical conditions during recovery, as well as very demanding post processing after free form fabrication. In contrast to the most of the existing solutions, latticed scaffold design does not try to imitate the trabecular structure and rejects the labyrinthine concept. It is characterized by simple 3D latticed support structure, which provides a high level of permeability for the new growing tissue cells, and in the same time a proper level of bio-adhesiveness. In addition, its design is easy to manage in order to make it follow the particular anatomical shape and at the same time provide the required elastic properties and structural strength. The paper presents a part of design concept proving process, which is related to stress analysis of the anatomically shaped lattice scaffold design. The aim of the analysis was to identify functional relation between design parameters and elastic properties of the scaffold. The established relations are crucial for getting optimal values of elastic properties of scaffold that are required in a specific trauma-fixation case. The design study shown in the paper was done for the case of lattice scaffold anatomically shaped to the upper part of proximal diaphyseal trauma of rabbit tibia. Design parameters which were altered within the design study were lattice’s struts cross-sectional area, density of the struts and angle of the struts intersection. The analysis showed that structural flexibility of latticelike scaffold may easily be changed through modification of three selected design parameters. In this way, it is confirmed that the proposed type of scaffold has an important capability to adapt its elastic properties to the required values, while being able to keep its great permeability and geometrical consistency to the particular anatomy of trauma region.

MATERIAL CHARACTERIZATION ISSUES IN FEA OF LONG BONES

One of the main issues that arise during preparation of models for subject specific finite element analysis (FEA) of long bones is the accuracy of material characterization. This paper tends to identify the most common sources of material characterization errors, which are sometimes also interconnected with bone geometry reconstruction errors, in order to help in creation of more accurate finite element models of long bones. Reconstruction of patients bone geometry is usually based on medical images obtained by means of computational tomography (CT). Material characterization is performed either by segmentation of the model to characteristic zones that are assigned typical averaged material properties, or by local material mapping, based on bone density values estimated from CT numbers. Some of the main factors that influence material characterization accuracy are the choice of material model, the approach to material properties averaging, x-ray tube parameters, scanner calibration, relations between CT image gray values and bone density and relations between bone density and elastic properties of the bone. The paper brings a comparison of numerical results obtained from a number of subject-specific analyses of human femur, in which the approaches to material modeling were varied. Material modeling was performed using either geometry segmentation with material properties averaging or local material mapping. The results of the analyses were examined and mutually compared, and the influence of material characterization errors to analyses results was identified and explained.

Imaging in Clinical and Preclinical Practice

Over the years, medical imaging has become an inherent part of modern medicine and biomedical engineering. Various imaging methods, which provide the detailed insight into human body interior, are widely used in clinical and preclinical practice. They enable the accurate diagnosis of complex pathological states, planning and performing of challenging surgical operations, tissue engineering, design of medical devices and much more. The area of medical imaging is very complex, as it is comprised of different imaging modalities and it keeps expanding due to rapid development of modern technologies. An overview of most important imaging techniques, containing references that describe various applications of each of the methods, is given first. More detail is given on the following methods: radiography, computed tomography (CT), ultrasound imaging, magnetic resonance imaging (MRI), mammography and positron emission tomography (PET). Two detailed examples accompany the overview, which are related to monitoring of osteogenesis in large animals using CT and application of imaging techniques in diagnosis and management of osteoporosis.