Biomechanics, Electroactive Polymers

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Biomechanics, Electroactive Polymers
Artificial Muscles
MECH 500 Lecture 4

• Biomechanics of the Musculoskeletal System
• Rheological and Molecular Models
• Electroactive Polymers
• Artificial Muscles Robotics
• Biomimetic Artificial Muscles
• Artificial Muscles in Bioactive Implants
• Towards Integrated Neuromuscular Devices

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Recap The story so far .

• Bionic Implants is a vast, multidisciplinary
  effort involving biology, chemistry, mechanics
  and electrophysiology
• Bionics refers to both (a) a biomimetic approach
  and (b) devices that interface bidirectionally
  with the human body
• Bionic Implants are based on biomimetic
  multifunctional materials
• Functional Tissue Engineering refers to the
  re-engineering of living tissues using synthetic
  scaffolds.
• So far, we have used passive organs as examples
  Bone, cartilage, ligaments ..
• Now What about implants that move?

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Biomechanics

• Study of locomotion and motility in living
  systems using classical mechanical models and
  paradigms
• Critical to understanding the skeletal system,
  fluid flow and movement in the human body, the
  animal and plant world
• Models derives are crucial to designing bionic
  implants

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Muscles

• At the nexus of chemistry, biology, mechanics and
  electricity and thermodynamics

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Muscle Bio-chemo-electro-mechanical system!

• Hierarchical Structure
• More than jsut a motor
• Responsible for motility throughout the human
  body
• Muscles are of three kinds

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Types of Muscles in Humans
Cardiac Muscle
Skeletal Muscle
Smooth Muscle
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Muscle More than a Motor!

• Motors Generate Force
• Brakes They absorb energy and damp vibrations
• Springs Store and Release Energy
• StrutsResists longitudanal compression

How Animals Move An Integrative View, Michael H.
Dickinson, VOL 288 7 APRIL 2000
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Hills Model

• Seminal Work published in 1938
• Black Box model
• Force-velocity relationship arises only as a
  result of the contractile element
• Limitations
• Does not predict force enhancement/depression
• Does not account for non-linearities in the
  muscle

Hills Equation (P a)(Vb) c
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Huxleys Model Sliding Filament Theory

• Muscle Contraction activated by calcium Ions
• Force produced through overlap of actin and
  myosin filaments

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Co-operativity All or nothing

• Threshold calcium Ion concentration for
  activation
• Individual sarcomeres follow the  all or
  nothing  rule
• Why is this architecture favourable?

Hills equation Force Forcemax . Ca2N/
Ca50N Ca2N
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Closed-Loop Control Feedback in Muscles
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MUSCLES REMEMBER!

• Muscles are heirarchical structures
• Muscle fibers contract in an ALL or NOTHING
  FASHION Critical Phenomenon
• Individual Fibers are recruited DISCRETELY and
  SEQUENTIALLY
• Relaxation is coupled to contraction
• Force is transmitted to joints through TENDONS.
  Why?
• Closed-Loop Control

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Artificial Muscle The Grand Challenge

• Challenge issued in 1999 by JPL, NASA
• Robot beaten by teenage girl in 2005

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Artificial Muscles in Medicine Why are they
important?

• Assist weak muscles
• Drug Delivery
• Valves
• Pumps
• Bioactive Implants
• BIOMIMETIC (BIONIC) SOLUTION!