Bioengineering applications based on 3D reconstruction

of bone model developed from CT images and CAD

CAE tools for engineering analysis using the finite

element method

Clara Isabel López

John Faber Archila

GIROD Research Group

Universidad Industrial de Santander

Bucaramanga-Colombia

UNIVERSIDAD INDUSTRIAL DE SANTANDER

• The university is located in Bucaramanga-Colombia.

• This study was developed through the research in

biomaterials, from the engineering materials master’s

degree course.

Campus Universidad Industrial Santander

• Currently the study about evaluation of

implants or biomedical devices are carried

on virtual 3D tools, followed by CAE

analyses, since this kind of studies are very

complex for experimental testing.

• It is necessary to consider the architecture

of bone tissue as well as the density and

mechanical properties, because these

factors influence over the behavior of the

implant at the bone-implant interface .

• For those reasons, good results from CAE

mechanical simulation depends on a well

developed bone model.Initial model built by CAD software

Problem Description

The Cortical bone has more

density and is more compact

than the cancellous bone and

it supports compressive and

torsion loads.

The Cancellous bone has

less density. It has good

properties for fatiguePhotography of a section of jaw bone,

built in Mimics Software® from

computer axial tomography CT. By

Materialise Enterprise

Introduction

D4 Low density

cancellous bone

D3 High density

cancellous bone

(Lemonth y Zarb, 2009)

D1 High density

cortical bone

D2 Low density

cortical bone

Bone Tissue Density

Misch

Implant loadCompression (implant)Shear (bone)

The first load produced is the insertion

torque

The preload produces a stress in the

material. Less deformation occurs with

larger implant's diameter

Finally, deformation in the tissue occurs

Bone-Implant Interface

A method for obtaining

better resolution in this case

is required to develop a

precise model of the bone for

a CAE analysis. For this

reason it was necessary to

generate the model of the

bone using imaging

techniques obtained by CT

scanning. Toshiba Aquilion 64 CT scanning

Justification

CAD – CAE Methodology

Methodology

The bone model was developed using imaging

techniques obtained by a CT scanner

CT obtained by Aquilion THM . Courtesy universitario hospital

Aquilion 32 Toshiba multislide helical CT scannerTechnique: 3D face protocol

Saggital and coronal slide1200KV/75 mAs

0,5s/2.0mm/0,5x32HP21.0

Cortes a 2 mm

CT SCANNER equipment

Hounsfield Scale Classification

According to Electron Density

• Knowledge of electron density is

necessary for radiotherapy

treatment planning.

• The calibration is based on

parameterizing HU as a function

of relative electron density and

effective atomic number, by

using materials of known

composition.

Hounsfield unviersal scale by gray scale

element Hounsfield scale Gray scale

Air -1000

Water 0

Bone or tissue +100 ,+3000

Building of 3D Jaw Bone by Mimics software

HU calculated from Mimics

Top view by mimics software

3D jaw bone by Mimics software

Remesh of jaw bone

view of jaw bone

• We could choose the

number of materials for the

definition of properties, like

density and Young’s

Modulus.

load properties of materials on window

Material Definition

Mesh Import to Ansys®

The mesh from Mimics was

loaded to Ansys®.

Figure. The model has three differents materials for

cancellous bone cortical bone and implantImage of 3D model obtained by mimics software.

Import the mesh to Ansys® 11.0 Release

Mesh of the 3D model imported from Mimics to Ansys. The

volumes are recognized by differents densities based on

HU scale.

Figure. Mesh of bone-implant model

Simulation Environment

Material properties

Structural

Young's Modulus 1,138e+011 Pa

Poisson's Ratio 0,34

Density 4430, kg/m³

Thermal Expansion 0, 1/°C

Tensile Yield

Strength7,9e+008 Pa

Compressive Yield

Strength8,6e+008 Pa

Tensile Ultimate

Strength8,6e+008 Pa

Specific Heat 0, J/kg·°C

Ti6Al4V

Structural

Young's Modulus 1,8e+010 Pa

Poisson's Ratio 0,3

Density 630, kg/m³

Thermal Expansion 0, 1/°C

Compressive Yield

Strength1,3e+008 Pa

Thermal

Thermal Conductivity 0, W/m·°C

Specific Heat 0, J/kg·°C

Electromagnetics

Relative Permeability 0,

Cortical bone

Structural

Young's Modulus 1,e+010 Pa

Poisson's Ratio 0,32

Density 350, kg/m³

Thermal Expansion 0, 1/°C

Compressive Yield

Strength2,9e+007 Pa

Thermal

Thermal

Conductivity0, W/m·°C

Specific Heat 0, J/kg·°C

Electromagnetics

Cancellous bone

Stress Ti6Al4V

Von mises 44,05 MPa

Maximun shear 27,25 MPa

Strain

Von mises 0,00040

Maximum shear

elastic strain

0,000599

Microdeformation

of bone

Cortical bone 400

Cancellous bone 133

Maximun shear stress

Equivalent Elastic Strain Ti6Al4V

Results on bone-implant interface

model by Mimics®

Object Name Equivalent

Stress

Maximum

Shear Stress

Total

Deformation

Equivalent

Elastic Strain

Maximum

Shear Elastic

Strain

State Solved

Scope

Geometry All Bodies

Definition

Type

Equivalent

(von-Mises)

Stress

Maximum

Shear Stress

Total

Deformation

Equivalent

(von-Mises)

Elastic Strain

Maximum

Shear Elastic

Strain

Results

Minimum 2200,4 Pa 1263,6 Pa 0, m1,2225e-007

m/m

1,8252e-007

m/m

Maximum 180,49 MPa 100,66 MPa2,6249e-005

m

1,8931e-003

m/m

2,7065e-003

m/m

Cancellous BoneCortical Bone

Conclusion

The results of the two models created by different methods were

compared, showing stress and strain values higher for processed

and Mimics models. Therefore the model with a geometry closest to

the real one shows that model’s geometry has influence over the

results.

The developed procedure shows that the last results obtained by

CAE software are most reliable when 3D virtual models are

developed using imaging methods or techniques based on

tomographic images. This methodology can bring a major

contribution to the advance of simulation-based studies.

ACKNOWLEDGEMENTS

Robotics and Design Research

Group GIROD

USM Colombia S.A.