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Biomechanics

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Published on Wednesday, 03 March 2010 12:03

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1. Modelling of bone adaptation, healing process and elastic properties.

• The new approach based on application of hypothesis of optimal response of bone was proposed to enable formal derivation of a wide class of mathematical models of functional bone adaptation. Among the other cases the bone adaptation after hip joint implantation, osteoporosis development and intramedullar nail durability were analyzed and compared with the clinical cases (Fig. 6).
• Interaction of bone tissue and metallic implant was considered and the relation between the microstructure of implant surface and tissue differentiation at the interface and its microstructure development was analyzed using computer simulations based on derived bone remodeling models.
• A new model of bone tissue remodeling in case of osteoporosis including biological effects and interactions between specialized cells was proposed and preliminary computational tests were performed (Fig. 5).
• The model of bone tissue healing process was elaborated and computational tests of simplified cases were performed and compared with the clinical observations. The works concerning external stabilizer enabling stimulation of bone healing process are being performed.
• The models of composite material with hierarchical structure were adopted to calculate the anisotropic elastic properties of compact and trabecular bone. The results are in acceptable agreement with experiments.

All of these works were performed and are being performed in a close cooperation with several clinics from Medical Academy and orthopedic departments in hospitals.

2. Wear particles produced during normal functioning of artificial joints.

• The problem was examined on two planes, the in vivo and in vitro experiments. The in vivo experiments were concentrated on the influence of wear particles of polyethylene material on the cell cultures (Fig.1). The biological activity of these cells was determined by measuring levels of different cytokines or enzymes in the supernatants.
• The in vivo studies were conducted on the implants and fibrous tissue samples (tissues surrounded loosened implants) obtained from patients who suffered from aseptic loosening.
• The tissues samples were digested according to specialized procedure and obtained particles were observed under scanning electron microscopy (Fig. 2). From the tissue samples also histological slides were prepared. Those slides demonstrated wear particles inside the tissues, inside the cells (Fig. 3).
• The roughness of the surfaces of the implant heads was examined using the 2D profilmeter. The roughness measurements gave undirected information of the intensity of the wear process in the artificial joint.

3. Heat transfer in soft tissues.

• Mathematical model of arterial tree was constructed.
• Temperature distribution in soft tissues was calculated ( Fig. 4).

VARIATIONAL METHODS IN MECHANICS

1. Effective properties of piezoelectric composite.

• The concept of strength surface of piezoelectric material was introduced
• Design problem of FGM piezoelectric composite with constrains on the level of stresses and electric induction was analyzed.

During the last two years 1 Ph. D. and 2 habilitations works in the form of monographs were finished.

Fig.1. Wear particle of polyethylene produced in vivo on the pin-on-disc tester (SEM image)

Fig.2.Polyethylene particles isolated from tissue samples (SEM image magnification x 3000).

Fig.3.Polyethylene particle inside giant cell in periprosthetic tissue under polarized light (magnification x 200).

Fig. 4 Heat transfer in arterial tree.

• Modelling of functional bone adaptation in application to bone remodelling after hip joint implantation, tissue differentiation at the interface bone - metalic implant and osteoporosis development.

• Mathematical models of coupled fields phenomena inbiomaterials.