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INTRODUCTION TO BIOMECHANICS David Malicky University of San Diego.

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Presentation on theme: "INTRODUCTION TO BIOMECHANICS David Malicky University of San Diego."— Presentation transcript:

1 INTRODUCTION TO BIOMECHANICS David Malicky University of San Diego

2 Biomechanics is (for the most part) not: “We can rebuild him. We have the technology”

3 Biomechanics is: Research: To understand and/or repair nature Industry: Develop prosthetic joint, therapy, or treatment

4 Biomechanics and Engineering Industrial Engr Bioengineering (Occupational Biomechanics) Mechanical Engr. Bioengineering (Biomechanics) Elec/Comp Engr. Bioengineering

5 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

6 Bones: Why are they hollow? B. Kosoff, Bones

7 Bones: Why are they hollow? Bending of a Long, Solid, Bone: Tension Compression Stress Free in the middle

8 Bones: Why are they hollow? Eliminate the inside to save weight but keep strength: Tension Compression

9 Bone: An Old, High Tech Material Human Skull: Porous Center with Solid Sides. Resists Denting Composite Honeycomb Sandwich Panel B. Kosoff, Bones

10 Bone: A Living, Responsive, Material Unloaded Control Loaded for 12 weeks Univ. of Michigan Load Micro-CT scan of 1cm bone cylinder: FEA

11 Joints: How does cartilage work? Bone Cartilage: 80% water in a “tight sponge” of solid matrix. Water does not squeeze out:  takes most of load Water can’t fail; little stress on solid (living) portion Also: self-lubricating (u=0.005), ~self-repairing Cartilage Bone Cartilage

12 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.

13 Spine: Lower Back Pain Lever Model 50 lb Hand Load F spine F muscle 2” 20” F muscle =(20/2)*50lbs = 500lbs. F spine =F m +50lbs = 550lbs. Forces up to 1000lbs Fulcrum

14 Spine: Lower Back Pain Computer models predict muscle and spine forces for any posture and loads. Design safer work environments Univ. of Michigan

15 Knee: Chondromalacia Bottom View Resultant Force Outside Excessive Pressure

16 Knee: Chondromalacia Normal: Chondromalacia Pain

17 Knee: Chondromalacia Solution: Increase Force from inner quadriceps with physical therapy Resultant Force Inner Quad

18 Computer Models: Knee Columbia Univ. MRI scan of knee Reconstruct 3D Geometry Make FEM Model of bones and cartilage Predict Contact Forces

19 Artificial Joints Arthritis = worn cartilage Corrosive, unpredictable environment Titanium Stem/Ball and Polyethelene Socket Wear debris  immune response Ceramic-Ceramic

20 Tissue Engineering: Grow Your Own Carnegie-Mellon U. 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

21 Assistive Technology iBot – Dean Kamen

22 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 ~ Size 2 Mass ~ Volume ~ Size 3

23 Cube-Square Law Acceleration Capacity of Animals: F = m*a a = F/m a ~ (Size 2 ) / (Size 3 ) = Size -1 Smaller animals can accelerate faster: - Hard to catch a fly - Football kick-returners - Soccer players

24 The Cube-Square Law Jumping Height of Animals (1st order model): Mass ~ Size 3 Force ~ Size 2 Work = Increase in Potential Energy F * Distance = M * g * Height change Size 2 * Size ~ Size 3 * Height change Size cancels on both sides: Height change of CG is not a function of Size

25 Cube-Square Law: Jumping Height Mice, cat, dogs, human, horse… CH height change = ~3-4 feet.

26 Cube-Square Law: Scaling Problems ? ? Iguana Godzilla

27 Human Shoulder: Dislocation Most Range of Motion Most dislocated major joint Repetitive dislocations common after first occurrence da Vinci

28 Shoulder Instability: Dislocation Glenoid “socket” Humerus (upper arm bone) Scapula (shoulder blade) Rib Cage Humeral Head

29 Shoulder Anatomy Humerus Scapula Capsule Glenoid Capsule: “Membranous ligament” Thickenings Complex structure

30 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

31 Shoulder Experiment Scapula Calibration Frame Xray Cassette Dislocation Arm Humerus

32 Total Max Principal Strain N O I D H U M E R U S SUPERIOR INFERIOR G L E

33 Biomechanics is:

34 Thank You


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