Biomechanics Connective Tissue Flashcards
What are the four types of tissue?
connective tissue
muscle
nerve
epithelium
types of connective tissue
periarticular connective tissues
-ligament, tendon, perimuscular fascia, capsule, articular cartilage
bone
-specialized CT
composition of periarticular connective tissue (3 general)
-structure drives…
fibrous proteins ground substance cells structure drives function -different composition, proportions, arrangements
fibrous proteins
-types
type I, II collagen
elastin
ground substance
-composition
proteoglycans (glycosaminoglycans - GAGs)
water
solutes
cells
-types
fibroblasts
chondrocytes
type I collagen
- characteristics
- higher proportions in
characteristics -thick, little elongation -stiff, strong -binds, supports body articulations higher proportions in -ligaments -fibrous joint capsules -tendons -perimuscular fascia
type II collagen
- characteristics
- higher proportions in
characteristics -thinner than type I -lower tensile strength -provide framework, structure for other tissues -provide internal strength higher proportions in -hyaline cartilage
elastin
- characteristics
- higher proportions in
characteristics -small fibrils (but larger than type II collagen) -resist tension but have 'give' -elastic properties (return to original shape) higher proportions in -hyaline cartilage -perimuscular fascia -ligamentum flavum
ground substance
- saturated with
- GAG molecule
- -charge
- –purpose
- -hydrophilic or hydrophobic?
- water
- -purpose
saturated with water GAG molecules -repel each other --> increases volume -hydrophilic --> high water content water -allows for diffusion of nutrients -provides mechanical properties
cells
- functions
- two specific types
functions -synthesize ground substance -tissue maintenance and repair -constant turnover -do not influence mechanical properties (sparse) types -fibroblasts -chondrocytes
fibroblasts
-found in…
ligaments
tendons
supportive CTs
chondrocytes
-found in…
hyaline articular cartilage
fibrocartilage
non-muscular soft tissues
- types (examples)
- composition
- characteristics
types
-irregular (joint capsules, perimuscular fascia)
-regular (ligaments, tendons, perimuscular fascia)
composition
-HIGH type I collagen
-LOW elastin
-LOW fibroblasts
characteristics
-poor healing (low vascularity)
-adapts to stress/strain with increased stiffness (increased collagen, fibroblast, and GAG synthesis)
irregular dense connective tissue
- locations
- how does it get its name?
- purpose
locations
-joint capsule
-perimuscular fascia
how
-collagen is arranged irregularly in ground substance
purpose
-resists tensile forces from multiple directions
regular dense connective tissue
- locations
- how does it get its name?
- purpose
locations -ligaments -tendons -fascia how -orderly, parallel (or nearly) arrangement of collagen purpose -resists tension along the longitudinal axis
ligaments
-purpose
constrain excess movement at bony articulations
tendons
- purpose
- elastin content vs. ligament
transmit large forces from muscle to bone
more elastin in tendon
fascia
-purpose
transmits forces between muscles
scar tissue
- how are collagen fibers laid down?
- what type of collagen fibers
- what happens to these fibers?
disorganized deposition of collagen fibers
Type II collagen fibers
-remodeled into Type I during maturation phase of healing
stress-strain curves
- stress =
- strain =
stress = force/area (omega)
-newtons/meter squared (Pascal)
strain = change in length/initial length (epsilon)
-measures as percentage
stress-strain curves
- how is stiffness measured
- how is energy measured?
- how is elasticity measured
stiffness -slope of linear (elastic) region energy -area under curve elasticity -Young's Modulus of Elasticity -stress/strain
viscoelastic
-what does it mean and what is an implication?
has fluid properties
elastic properties are largely determined by fluid content
biological materials toe region
- what is it?
- why does it occur?
what
- non-linear beginning to curve
- due to collagen fibers - begin to straighten and take up slack
rate dependent response of biological materials
- explain
- faster loading rate results in
if you load a tissue rapidly, it behaves differently than if you load it slowly
if loaded rapidly
-increase tissue stiffness (steeper slope in the stress-strain diagram)
-higher modulus
viscoelastic creep
- what is it?
- when does it happen
- what characterizes this phenomenon?
what
-deformation (strain) response
occurs when exposed to a constant load (stress) for a period of time
characterized by rapid initial deformation, followed by a slow deformation (creep) until equilibrium reached
clinical application of creep
plastic changes to connective tissue are thought to be brought about by slow, low-intensity, and long-duration stretches
what happens if we apply a fast stretch
minimal changes due to
1. rate-dependent response to stretch
AND
2. lack of stretch time
stress-relaxation
- what is it
- when does it occur?
- purpose
stress response
-rapid high initial stress
-followed by a slow decreasing stress required to maintain the deformation
occurs when exposed to a constant deformation
purpose
-distributes the stress across the tissue - protective
articular cartilage functions (3)
increase area of load distribution for joints
-attenuate joint contact stresses
provide a smooth, wear resistant bearing surface
-near frictionless behavior between joint survaces (due to synovial fluid)
limited capacity for repair
-injuries near sub-chandral bone may heal better
–if it does heal, it repairs with fibrocartilage rather than hyaline cartilage
biomechanical behavior
- contact forces between joint surfaces
- contact areas between joint surfaces
- stress =
contact forces -varies greatly depending on the joint and the activity contact areas -varies depending on the joint stress = force/unit area contact stress can be very high
anisotropic material
- what does it mean
- what gives it this characteristic
mechanical properties very between directions/modes of loading
collagen fiber arrangements and densities vary throughout the tissue
bi-phasic material
-composed of…
solid components (porous, permeable) fluid components (incompressible)
solid components of articular cartilage
- what makes up these?
- organic matrix characteristics
organic matrix
-fibrous proteins (type II collagen)
-proteoglycans (PGs): organic part of ground substance
-organic part is strong in tension but not compression (like pulling vs. pushing a string
cells
-chondrocytes: manufacture and maintain organic component
PGs
-purposes
provides structural framework (along with collagen)
provides stiffness and strength (collagen)
fluid components of articular cartilage
- purpose
- location
- permits exchange of _____ between _____ and _____
dictates the biomechanical behavior
-viscoelastic responses, resists compression
concentrated near articular surface (80%)
-decreases linearly with depth (65%)
permits exchange between chondrocytes and synovial fluid of
-gases
-nutrients
-waste products
water
- primarily located where?
- fluid shifts with…
most fluid in extracellular matrix
-water, solutes (60-85% of volume)
fluid shifts with
-electrochemical stimuli
–solutes have charges: Na+, K+, Ca2+
-mechanical loads (compression) create pressure gradients
–compression –> deformation –> internal pressure > external pressure –> fluid flows out
–like a saturated spongs
-up to 70% of fluid may shift with compression
creep in articular cartilage
-____ is balanced by ____
-creep caused by
-
applied load balanced by resistive stress within the tissue
creep caused by fluid ‘leaking’ out (exudation)
when resistive stress in the solid matrix = applied stress
-fluid flow ceases
-creep equilibrium (no further deformation)
creep equilibrium
- how long does it take to reach?
- how much fluid can be lost
- condition necessary for recovery
takes 4-16 hours to reach creep equilibrium for thick (2-4 mm) articular tissues
50% of the fluid may be lost
recovery if experiment done in physiological conditions
stress-relaxation in articular cartilage
- how is this applied in tissues?
- what do we find?
apply load until equilibrium displacement reached
maintain this displacement, and monitor the stress required
stress-relaxation
-the magnitude of stress required to maintain the equilibrium displacement decreases over time
stress-relaxation in articular cartilage
- initial increase in stress is due to…
- stress-relaxation is due to
- purpose during physiological loading
initial increase in stress (during displacement phase) due to fluid exudation
stress-relaxation during the displacement maintenance phase due to fluid redistribution
under physiological loading, stress-relaxation attenuates stress developed within the tissue
tensile properties of articular cartilage
- stiffens with…
- toe region caused by…
- final elastic region caused by…
- failure occurs when…
stiffens with increasing strain when strain becomes large (ie elastic region)
toe region
-caused by collagen fiber pull-out
final elastic region
-stretching of the straightened collagen fibers
failure
-all fibers rupture
cyclic loading (fatigue)
- occurs in what structures?
- due to…
occurs in cartilage
due to…
-repeated application of high loads over a short time
-repeated application of low loads over a long time
proposed mechanisms wearing out (3)
tensile failure of collagen fiber network
-accumulate tissue damage leads to lower strength
‘washout’ of PGs from extracellular matrix from repeated fluid exudation/imbibition
-results in decreased stiffness and increased permeability
rapid applications of high loads
-if loads applied too quickly, no time for stress-relaxation (fluid redistribution) resulting in high stresses that may cause damage
cartilage defects
fibrillation -splitting of the cartilage surface -can extend through the full depth to sub-chondral bone erosion of the cartilage surface -smooth-surfaced destructive thinning
markers of articular cartilage degeneration and how does it occur?
progressive deterioration of the tensile properties of solid matrix
loosening of structural collagen matrix responsible for swelling
how
-increase water content: decreased compressive stiffness and increased permeability
-may be influenced by contact stress
osteoarthritis
-factors
tissue level
-changes in collagen and PG content and structure
loosening of structure
-increased permeability and fluid content
increased fluid flow
-increased deformation –> decreased ability to resist loading
biomechanical changes at muscle/skeletal level may change loading profiles
effects of aging (4)
-what can be done?
cell turnover (fibroblast and chondrocyte) is decreased
accumulation of microtrauma can lead to tissue failure
smaller and fewer GAG molecules –> lower water content, less force attenuation
decreased tendon stiffness
-collagen fibers become stiffer, but there are fewer of them
mitigated through physical activity
