Transcript My Intro to Biomechanics talk

INTRODUCTION TO BIOMECHANICS
David Malicky
University of San Diego
Biomechanics is (for the most part) not:
“We can rebuild him.
We have the technology”
Biomechanics is:
Research: To understand
and/or repair nature
Industry: Develop prosthetic
joint, therapy, or treatment
Biomechanics and Engineering
Industrial Engr
Mechanical Engr.
Elec/Comp Engr.
Bioengineering
(Occupational
Biomechanics)
Bioengineering
(Biomechanics)
Bioengineering
Types of Biomechanics
Orthopaedic:
• Growth, Damage, and Healing of
Bones, Joints, Spine, Cartilage, Tendons, Ligaments...
• Artificial Joints
• Gait and Falls
Cardiovascular: Cardiac Assist Devices, Blood Flow
Occupational: Lower Back Pain
Rehabilitation: Assistive Technology
Nature: Plants, Animals
Bones: Why are they hollow?
B. Kosoff, Bones
Bones: Why are they hollow?
• Bending of a Long, Solid, Bone:
Tension
Stress Free
in the middle
Compression
Bones: Why are they hollow?
• Eliminate the inside to save weight but keep strength:
Tension
Compression
Bone: An Old, High Tech Material
Human Skull:
Porous Center with Solid Sides.
Resists Denting
B. Kosoff , Bones
Composite Honeycomb
Sandwich Panel
Bone: A Living, Responsive, Material
Micro-CT scan of 1cm bone cylinder: Load
FEA
Unloaded Control
Loaded for 12 weeks
Univ. of Michigan
Joints: How does cartilage work?
Cartilage: 80% water in a
“tight sponge” of solid
matrix.
Bone
Cartilage
Water does not squeeze out:
 takes most of load
Cartilage
Water can’t fail; little stress
on solid (living) portion
Cartilage
Also: self-lubricating
(u=0.005), ~self-repairing
Bone
Spine: Lower
Back Pain
• LBP costs $20-$50B/yr
• Affects 80% of population
• Hand load creates
reactions in spine and
back muscles
Back Muscle Force
Spinal Column Force
50lbs.
Spine: Lower Back Pain
Lever Model
Fmuscle
Fulcrum
Fmuscle=(20/2)*50lbs
= 500lbs.
Fspine=Fm+50lbs
2”
20”
= 550lbs.
Forces up to 1000lbs
Fspine
50 lb
Hand Load
Spine: Lower Back Pain
• Computer models
predict muscle and
spine forces for any
posture and loads.
• Design safer work
environments
Univ. of Michigan
Knee: Chondromalacia
Resultant
Force
Bottom View
Outside
Excessive Pressure
Knee: Chondromalacia
• Normal:
• Chondromalacia
Pain
Knee: Chondromalacia
Solution: Increase
Force from inner
quadriceps with
physical therapy
Resultant
Force
Inner
Quad
Computer Models: Knee
•MRI scan of knee
•Reconstruct 3D Geometry
•Make FEM Model of bones
and cartilage
•Predict Contact Forces
Columbia Univ.
Artificial Joints
• Arthritis = worn cartilage
• Corrosive, unpredictable environment
• Titanium Stem/Ball and
Polyethelene Socket
• Wear debris  immune response
• Ceramic-Ceramic
Tissue Engineering: Grow Your Own
• Stem cells seeded onto a biodegradable scaffold/matrix
• Local gene therapy instructs cells to regenerate bone,
ligament, cartilage, skin, nerves, organs…
• Body’s cells join in
• Bone cartilage forms, scaffold is absorbed
Carnegie-Mellon U.
Assistive Technology
iBot – Dean Kamen
Nature: The Cube-Square Law
• Why can fleas jump 100x their own height?
• Why can’t elephants even jump ¼ x their own height?
• Cube-Square Law:
“Size”: “average dimension” of the animal
Muscle Force ~ Cross-Sectional-Area ~ Size2
Mass ~ Volume ~ Size3
Cube-Square Law
Acceleration Capacity of Animals:
• F = m*a
a = F/m
a ~ (Size2 ) / (Size3) = Size-1
• Smaller animals can accelerate faster:
- Hard to catch a fly
- Football kick-returners
- Soccer players
The Cube-Square Law
Jumping Height of Animals (1st order model):
• Mass ~ Size3
• Force ~ Size2
• Work = Increase in Potential Energy
F * Distance = M * g * Height change
Size2 * Size ~ Size3 * Height change
Size cancels on both sides:
Height change of CG is not
a function of Size
Cube-Square Law: Jumping Height
Mice, cat, dogs, human, horse… CH height change = ~3-4 feet.
Cube-Square Law: Scaling Problems
Iguana
?
Godzilla
?
Human Shoulder: Dislocation
• Most Range of Motion
• Most dislocated major joint
• Repetitive dislocations common
after first occurrence
da Vinci
Shoulder
Instability:
Dislocation
Scapula
(shoulder blade)
Rib Cage
Glenoid “socket”
Humeral
Head
Humerus
(upper arm bone)
Shoulder Anatomy
Humerus
Glenoid
Capsule
Capsule:
• “Membranous ligament”
• Thickenings
• Complex structure
Scapula
Shoulder Experiment
• Doctors believe the capsule is stretched after the
first dislocation, allowing further dislocations, but it
has not been shown.
• Surgical shortening of the capsule improves stability.
• Shortening can restricts range of motion.
Aim of my experiment: Measure the strain
field in the capsule due to a dislocation
Shoulder
Experiment
Scapula
Calibration Frame
Xray Cassette
Dislocation Arm
Humerus
Total Max Principal Strain
SUPERIOR
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INFERIOR
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Biomechanics is:
Thank You