Conference info

8th INTERNATIONAL SYMPOSIUM ON COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING

27 February - 1 March 2008 

Porto, Portugal

The key objectives of the meeting are to communicate advances in 'Computer Simulation’ being applied across the multidisciplinary areas on medical technical and to highlight areas of future potential such as mechanotransduction, mechanobiology, cytoskeletal systems, scaffold architecture, micro/macro/nanobiomechanics, injury/forensic and impact biomechanics, modelling cellular and molecular mechanics, bioreactor simulation, movement science and human body performance which reflect the many advances that are presently taking place in computer based simulation.

Upcoming conference (22nd European Conference on Biomaterials)

ESB2009, organised by the Swiss Society for Biomaterials, will be held in Lausanne, Switzerland from Sept 7th until 11th 2009.
ESB2009 intends to draw on the extensive MedTech industry within Switzerland to bring closer relationships between academia and industry which link the basic research world to final applications.

Dead lines:

ESB2009 07.09.2009 - 11.09.2009
Congress Workshops 07.09.2009
ESB Congress Registration and Welcome reception 07.09.2009

Oral Abstract Submission Deadline (18.00, Central EuropeanTime) 26.01.2009

Interesting book

Green composites : polymer composites and the environment

Edited by C Baillie, Queen's university, Canada

With an internationally recognized team of contributors, Green Composites examines fibre reinforced polymer composite production and explains how environmental footprints can be diminished at every stage of the life cycle. The introductory chapters examine why green composites should be considered. The book then discusses properties of cellulose and wood. It examines recyclable synthetic fibre-thermoplastic composites as alternatives, then covers polymers derived from natural sources. The text details the factors that influence properties, and considers clean processing, applications, recycling, degradation, and reprocessing. The book is essential for government agricultural departments, automotive companies, and others devoted to eco-friendly materials and production.

ISBN 1 85573 739 6

[ISBN-13: 978 1 85573 739 6]
September 2004

quote

Today, one of my friends who is writing the final version of his thesis called me to ask about a quote from Prof. Ashby that I used it in my public defence. I wish to share it with you:

When modern man builds large load-bearing structures, he uses dense solids: steel, concrete. When nature builds large load-bearing structures, she generally uses cellular materials: wood, bone. There must be a good reason for it.

Michael F. Ashby

Osteoporosis and orthopedic surgery

How does osteoporosis change the the mechanical properties of tibia bone? where are the major changes, in cortical layer or in cancellous bone? and is this about change in the density or the cortical layer thickness?

Voila, my short conclusion:

Osteoporosis is a condition in which the bone mineral density and consequently its strengths are decreased. Because osteoblasts and osteoclasts inhabit the surface of bones, cancellous bone is more active, more subject to bone turnover and remodeling[wiki]. It makes us to understimate the important role of the cortical bone in osteoporosis phenomenon. Lower overall bone mass, lower thickness of cortical bone and lower bone mineral density increase the failure risks of revision knee surgery. But age does not change these parameters (no statistically significant correlation) and smoking does.

Mechanobiology

Mchanical stimulation influences the growth, adaptation, regeneration and engineering of cells and tissues. For example, in mechanobiology of skeletal tissues around orthopedic implants, regeneration of bone tissue is a function of shear stress transfer at the bone-implant interface. Osteoblasts are sensitive to mechanical stimulation and so it is important to study their reaction in a situation which is similar to the mechanical boundary conditions at the bone-implant interface.

In mechanobiology , this interaction between mechanical stimulations and biological process in living tissues is studied. In vivo and in vitro experiments plus computational modeling tools are used to explain the link between mechanics and biology.

lattice modelling approach

Comparing to the continuum-based models, lattice model is well adapted to map the ordered or random anisotropic microstructure of composite materials. The other advantage of lattice model is the simplicity of the physical interpretation of a phenomenon like fracture in each step of the analysis.

The main idea of lattice model is simulation of the material structure and mechanical properties by construction of a network of interconnected discreet line elements. The defined network can be two-dimensional or three-dimensional and has random or regular structure.

This approach was first developed to study the theory of elasticity (Hrennikoff 1941). Later lattice model was used in modeling the fracture process by removing the elements reaching a strength criterion at different loading steps. VanMier were one among of the first who used the lattice fracture model in concrete, aiming to simulate the quasi-brittle material behavior (Schlangen and VanMier 1992). In this model, beam elements were chosen in such a way that they represented the different phases of concrete (aggregates, matrix and interfaces). After that, the lattice fracture model was applied for several years in analyzing the concrete and sandstone fracture. All these studies confirmed that lattice fracture model is successful in predicting the influence of material microstructure on the pre-peak and softening behavior of force-displacement curve and crack propagation paths.

Now, lattice model is a well known approach in analysing the mechanical behavior and mechanism of fracture in cellular and fibrous structure such as wood, bone and soft tissues.

Different microstructure of softwood and hardwood

Trees are classified into two main groups, softwoods (narrow leaf trees) and hardwoods (broad leaf trees). The major difference between the anatomy of hardwoods and softwoods is the lack of vessels in softwood. Vessels are created to conduct the fluid in the tree trunk. In softwood, the longitudinal tracheids perform the role of conducting the fluid (Wangaard 1979). These microstructural differences are the origin of different mechanical properties in softwood and hardwood.

Cross sectional views of two hardwood and softwood specimens, photo by Marjan 2006

Bone

The primary tissue of bone is osseous tissues which is a hard and lightweight composite of ‘calsium phosphate’ in the chemical arrangement termed calcium hydrocylapatite. Bone has a relatively high compressive strength and poor tensile strength. It is essentially brittle with anisotropic mechanical properties. All bones consist of living cells embedded in the mineralised organic matrix that makes up the osseous tissue.


Cortical bone:

It is one of two main types of osseous tissues. It has a dense structure and forms the surface of bones, contributing 80% of the weight of a human skeleton.

Cortical bone has anisotropic mechanical properties which are due to different mechanical properties of the constituents (ostenic and interstitial lamellae) and the hierarchical structural organization of material.

microscopic image of ostenic and interstitial lamellae

Trabecular (cancellous ) bone:

It has a spongy structure and makes up the bulk of the interior of most bones, including the vertebra, tibia and femur.

Young's moduli and the strength of cancellous bone are proportional to the square of apparent density of the tissue and are therefore proportional to one another (Rice et al 1988).

	Strength Mpa	Modulus MPa
Cancellous bone in tension and compression	5-10	50-100
Cortical bone in compression	130-220	17000-20000
Cortical bone in tension	80-150	17000-20000

Bone Eng. By Davies

Poromechanics

Poromechanics is a branch of physics and specifically continuum mechanics and acoustics that studies the behavior of fluid-saturated porous media. A porous media consists of a solid matrix containing interconnected fluid-saturated pores and is called poroelastic when the matrix is elastic and the fluid is viscous. A poroelastic medium is characterized by its porosity, permeability as well as the properties of its constituents (solid matrix and fluid).

In physical terms the theory postulates that when a porous material is subjected to stress, the resulting matrix deformation leads to volumetric changes in the pores. Since the pores are fluid-filled, the presence of the fluid not only acts as a stiffener of the material, but also results in the flow of the pore fluid (diffusion) between regions of higher and lower pore pressure.

The concept of a porous medium originally emerged in soil mechanics while now has a wide application in biological cellular tissues and man made materials such as foam and ceramics.

Wood

Wood is a bio-polymeric composite with complex physical and mechanical properties. It has a heterogeneous structure from micro to macro scales (Fig *). These heterogeneities and variation of humidity and temperature change the mechanical properties of different wood specimens from sample to sample. In wood material science, a special attention is paid to multi-scale modeling and taking the role of structural elements at smaller scales; fibers, ray cells and cellulose microfibrils in to account.

* Wood heterogeneities in different scales, photo by Marjan 2006