ʺIt is very clearly apparent from the admonitions of Galen how great is the usefulness of a knowledge of the bones, since the bones are the foundation of the rest of the parts of the body and all the members rest upon them and are supported, as proceeding from a primary base. Thus if any one is ignorant of the structure of the bones it follows necessarily that he will be ignorant of very many other things along with them.ʺ Niccolo Massa, 1559 Biomechanics { Experimental methods in Bone Mechanics Karun Vij & Yaser Al Saad
Presentation: Introduction Structure of the Bone (General) Experiment Methods 2011
Why study Bone?
Osteomyletis Bone infection caused by bacteria Biomechanical Engineers need to mimic true bone if we want to solve long term problems
Introduction What is Biomechanics? The study of mechanical laws in living organisms using the science of motion The application of Biomechanics to human movement can be classified into two main areas Improvement of Performance Reduction / Treatment of injury
Introduction To Bones Advancement in Bone study parallels with history of light microscopes (18 th century) 1800 s consisted of mechanical testing ( destructive ) but values obtained were not correct due to microcracks
Introduction to Bones 1920 s Griffith analysis of crack and effects on brittle material documented 1970 s Lang experiment using Ultrasonic Method (Youngs modulus) Dr Karl Dussik Professor Ian Donald of Scotland (Pioneer of Ultrasound Application)
Bones At levels Bone structure is HIGHLY complex Ranges from Angstroms to microns Hierarchical structure relates to mechanical properties 1. Subnano Structure (matrix) 2. Nanostructure (collagen, minerals) 3. SubMicro structure (lamallae) 4. Microstructure (Harvesian and Osteon systems) 5. Macrostructure (Cancellous and Cortical)
Bones At levels Bone structure is HIGHLY complex Ranges from Angstroms to microns Hierarchical structure relates to mechanical properties 1. Subnano Structure (matrix) 2. Nanostructure (collagen, minerals) 3. SubMicro structure (lamallae) 4. Microstructure (Harvesian and Osteon systems) 5. Macrostructure (Cancellous and Cortical)
MacroStructure Bones are distinguished into the cortical (compact) and cancellous (spongy/trabecular) types
Macrostructure: They are distinguished by their degree of porosity or density (Macrostructure), and the shape of lamellae (Microstructure) Cancellous bone Cortical bone
MacroStructure Cancellous bone is more active, therefore younger on average than cortical bone Cancellous bones made of bony trabecular struts and marrow filled cavities (structural and material properties)
MacroStructure In cortical bones, mechanical properties influenced by porosity and the organization of the solid matrix Different bones have different mechanical properties, as well these properties varies within a bone
MicroStructure Harvesian systems Osteons: Collagen in lamellae lie parallel With a change in orientation of fibrils from one lamella to the next
SubMicro Structure Lamellae (building blocks, if you will) Connection of collagen fibers We need power and resolution! Neighboring lamellae have varied fibril structure and depending on structure, they will form different systems. This leads to anisotropic properties!
Anisotropic behavior:
Anistropic Behaviour
Nanostructure We see collagen crystal composite **Very much in question **Why/How are crystals are organized respective to fibrils? Crystals infiltrate fibrils, and now are called mineralized collagen.
SubNano Structure Composed of crystals, collagen and non collagenous proteins Crystals are called dahllite (apatite minerals) Crystals occur in discrete spaces within collagen fibrils Non collagenous proteins functions may function as a regulator of size and orientation.
SubNano Structure Cont
Fig. 1. Stiffness of bone increases with increasing mineralization, but bone tissue also becomes more brittle (decreased ultimate displace ment).
Remodelling Osteoblasts Derived from bone lining cells (osteoprogenitor cells) Responsible for formation of bone Osteocytes Cells IN the body of bone Connect with neighboring Osteocytes and form junctions Osteoclasts Bone destroying cells Release minerals to blood
Feedback?
All the pieces in the puzzle...
Microscopy, CT Microscopy, xsas Optical Microscopy Electron Microscopy X Ray Diffraction Figure 3: Imaging techniques at levels
Testing / Techniques 1) Destructive 2) Non destructive Mechanical Testing
Testing / Techniques Strain gauges Extensometer Four point bending Torsion of long bones
X ray imaging: X ray (Radiographic): First x ray created in 1895 Electromagnetic waves Color depends on density X ray Computed Tomography (CT): Created nearly 30 years ago Visualize interior features within solid objects, and for obtaining digital information on their 3 D geometries and properties.
Ultrasonic imaging: A very short pulse waves that are lunched into materials to detect internal flaws or to characterize materials Their velocity and degree of penetration depends on the matter they traveling through
Testing/Techniques
Nano indentation: Variety of indentation hardness tests applied to small volumes What are the differences between traditional indentation (micro and macro) and Nano indentation?
Nano Indentation Measure the stiffness which is equal to the slope Measure youngs modolus by using:
Complications We are testing smooth surfaced specimens which is not the same as real bone We cannot mimic TRUE shape Devoted science (Fracture Mechanics) Hierarchical structure of bone Anisotropic Viscoelasticity Size Mechanical properties in cancellous bone depend on length Friction Effects contact of specimen and device
Complications
Mcmaster Biomechanical Research
Conclusion Questions like effects of size, interactions of collagen mineral matrix, and levels resolution are key in understanding true mechanical properties We need high precision, accuracy and control We must learn from history, develop and always stay curious!
http://www.engr.iupui.edu/~turnerch/oi bone%20quality.pdf http://www.abcbodybuilding.com/magazine03/bonemechanics2.htm http://www.spineuniverse.com/exams tests/devices/new anterior cervical plate makes headlines http://www.sciencedirect.com.libaccess.lib.mcmaster.ca/science/article/pii/s1350453301000625 http://www.sciencedirect.com.libaccess.lib.mcmaster.ca/science/article/pii/s875632829900109x Bones Structure and Mechanics by John D.Currey Biomechanics of Human Motion by Williams and Lissner http://www.sciencedirect.com.libaccess.lib.mcmaster.ca/science?_ob=miamiimageurl&_cid=273103&_user=1067350&_pii=s0 16960090880205X&_check=y&_coverDate=1994 04 01&view=c&wchp=dGLzVlBzSkWb&md5=9b4289e8fa11a2bd3ac25b902ddfbcb7/1 s2.0 S016960090880205X main.pdf