Biomechanics Connective Tissue Flashcards

Question

rate dependent response of biological materials - explain - faster loading rate results in

Answer 1

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

Answer 2

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

Answer 3

plastic changes to connective tissue are thought to be brought about by slow, low-intensity, and long-duration stretches

Answer 4

minimal changes due to 1. rate-dependent response to stretch AND 2. lack of stretch time

Answer 5

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

Answer 6

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

Answer 7

``` 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 ```

Answer 8

mechanical properties very between directions/modes of loading collagen fiber arrangements and densities vary throughout the tissue

Answer 9

``` solid components (porous, permeable) fluid components (incompressible) ```

Answer 10

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

Answer 11

provides structural framework (along with collagen) | provides stiffness and strength (collagen)

Answer 12

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

Answer 13

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

Answer 14

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)

Answer 15

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

Answer 16

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

Answer 17

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

Answer 18

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

Answer 19

occurs in cartilage due to... -repeated application of high loads over a short time -repeated application of low loads over a long time

Answer 20

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

Answer 21

``` 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 ```

Answer 22

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

Answer 23

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

Answer 24

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