BM_N4

• 1) Pro-colloagen molecules are constructed and the ends are cleaved by enzymes.
• 2) These form alpha-chains (Gly-X-Y)
• In Glycine the R-group is a Hydrogen
• X and Y are determined by the R-group
• 3) Three alpha-chains combine in a helix.
• Glycine holds chain together. We get brittle structures without it.
• 4) X and Y determine collagen type (29 different)
• 5) Micro fibrils are constricted by cross-linking alpha-helices.
• 6) Fibrils are then made from micro fibrils

• Type 1 - Ligament, tendon, bone, skin
• Type 2 - Articular cartilage
• Type 11,5,3,9 are all connective tissue.

• 1) Composition (Collagen and Elastin)
• 2) Cross linking
• 3) Architecture

• 1) Entropic Spring - Fibrils try to be in chaos but stretch out doe to load.
• 2) Hydrophobic folding - Polar side charges repel one another causing tangling.

• 1) Stress Relaxation
• input: Strain
• -Initial stress is high and relaxes over time
• E(t) = sigma(t)/Eo

• 2) Creep
• input: Stress
• -Initial strain is low and increases asymptotically
• D(t) = strain(t)/sigmao

• **Note Eto = 1/Dto and Etinf = 1/Dtinf but E(t) does not equal 1/D(t).
• **Note Constant part is elastic and dissipating or increasing part is viscous.

As tissue is stretch multiple times Aloop goes down, sigma|max goes down.

**Steady state is reached after approximately 20 loads (Pre-conditioning).

• 1) The stress response is delayed from the strain input by delta.
• 2) The stress response can be manipulated to have an in phase (elastic) and out of phase(viscous) part.
• -Storage Modulus = (s/e)*cos(delta)
• -Loss Modulus = (s/e)*sin(delta)
• 3) Complex modulus = (s/e)

**Delta = 0 - Perfectly elastic, Delta = pi/2 - Perfectly viscous.

• 1) Maxwell Model - Spring and Damper in Series.
• - Bad creep, Mediocre SR
• 2) Kelvin Boide - Spring and Damper in Parallel
• - Good creep, bad SR
• 3) Standard Linear Solid - (Spring and Damper in series) in parallel with another spring.
• -Good agreement with both.