Unit 3 Material

Hysteresis

*What you do to the muscle 5 minutes ago will affect what happens to it now . ex: if you stretched a muscle 5 minutes then it will more likely stretch more later on as opposed to not stretching at all. • A lag of effect when the forces acting on a body are changed. • Stretching a muscle immediately prior to a football/soccer game will affect how this muscle will react to stress during the game. • Lumbar flexion changes the shape of the lumbar disc, this may take seconds or minutes to return to normal. Disc more likely to get injured after prolonged lumbar flexion (driving, then bending to unload a truck). • When we load and unload a biological tissue, the tissue will recover its shape, but the recovery might take a few seconds, minutes, or even hours to occur • The tissue deforms more quickly when it is loaded than when it is unloaded. Some of the energy that is absorbed during load application is dissipated as heat. • E.g.; every time you take a ROM measurement, the recording may increase; you may load a muscle before an exercise to prevent injury because its tissue will be lengthened before the exercise; patients may have worse symptoms late in the afternoon because of the cumulative tissue deformation that may occur during ADLs, etc.

articular cartilage composition

- 70-85% weight of cartilage is water - 15-30% dry weight ( 30% proteoglycans and 70% type 2 collagen)

Qt: in Physics

- Temperature, mass, and pressure are scalar quantity(magnitude). - Velocity and force are vector quantity (magnitude &direction). - Stress is tensor quantity (magnitude, direction, and plane).

adult hyaline cartilage functions

- provides the bearing surface of synovial joints -increases surface loading area and can transfer enormous forces relatively evenly from one subchonral bone plate to another - under physiological conditions it provides an almost frictionless gliding surface *** mechanical stimuli regulate biosynthetic activity of it cells ( chondrocytes)**

The mechanical behavior of viscoelastic tissues depend on:

-How long the load stays applied on the material (time-dependent: creep, stress-relaxation) -How quickly the material is loaded (rate/speed of load application) -Te m p e r a t u r e o f t h e m a t e r i a l -Previous loads applied on the material (hysteresis). -Flow behavior of the liquid in the tissue (thixotropy).

muscle injury and repair

-Muscle strains or tears. High speed activities, rare in spine except in car accidents. Long muscles (longer fibers) and thin. Bi-articulate muscles. Often in single sudden events. Most common in distal MT junction insertion. Insertion or origin with less surface area. Affects the MT junction, not the muscle belly. Caused by tension stress • Other types: contusion and compartment syndrome (caused by compression), laceration (shear), denervation, lack of blood supply. • Muscle tissue replaced by connective tissue when sarcolemma torn.

mechanical response to compression forces

-Negative sites on proteoglycans are pushed closer together, this increases their mutual repulsive force and increases compressive stiffness of the cartilage itself -Mechanical Response strongly tied to fluid flow in and out of the cartilage - There is fluid flow through the tissues and across the surface when cartilage is deformed. "a highly dense sponge with micropores" Fluid flow and deformation are interdependent

Stress Strain Curve

-Once the straight line changes then it starts the Plastic region

Fatigue and Resilience

-Overtime, the application of loads reduces the resilience of the material and its elastic limit. -note:Decreased stress or larger resting time may allow biologic tissue to recover resilience and prevent injury

Stress

-Stress is the resistance of a material to the external loads. -Stress = the reaction forces / the internal area of the material. -Stress applies to solids; while pressure applies to internal reaction to forces in fluid and air.

Nutrition/Innervation of Ligaments and Tendons

-Te n d o n s o f t h e h a n d a n d fe e t h a v e s y n o v i a l s h e a t h s w i t h synovial fluid and fibroblasts to add in slide and reduce friction. -Nutrition comes mostly of blood supply and it is richer on the bone insertions (especially on ligaments). -Tendon overuse microtears more likely away from insertion, away from blood supply. -Innervations: mechanical receptors and pain receptors are richer on the insertions as well. That is why tendonitis is more painful on the insertion or origin site

Fatigue and Load repetition

-The higher the frequency of load application, the quicker the tissue will fatigue or injury. The closer the stress level to the elastic limit of the material, the quicker the material will fatigue or injury

Resilience

-The property of a tissue to absorb energy when it is elastically deformed and then, upon unloading to have this energy reseased. ex; rubber bands -Tendons have the ability to release the energy from being stretched very vigorously.

Tissue Damping

-The property of a tissue to absorb energy when the tissue is deformed. The energy is not released quickly when the tissue is unloaded. The tissue may not recover its shape quickly or may stay deformed permanently

Viscosity

-The resistance to flow/shear is? -Application of a continuous force to a fluid body........the fluid body will "continually deform".......and we call this flow? Water has least Blood has more Synovial fluid has the most Olive oil has a whole more more

External loads

-can cause compressive pressure and shear pressure, but never any type of tension in liquids.

material properties of cartilage

-collagen: forms a fibrillar meshwork- defines the shape and tensile properties -proteoglycan: resists compressive forces

articular cartilage proteoglycans

-compressive functions due to hydrophillic and polyanionic -Note there are more proteoglycans in the deep zone and more fibers in the superficial zone. Also, note structure orientation to resist stress

Plastic Strain

-deformation a material undergoes with permanent changes in its internal structural integrity. The material does not recover its shape once the external forces are removed from it. -

Elastic Strain

-deformation a material undergoes without permanently changing its internal structural integrity. the material recovers its shape once the external forces are removed from it.

Extra cellular component of CT

-fibrillar component : collagen, reticulin (mesh or net designed to hold muscles and organs), and elastin -collagen and elastin are designed to resist TENSION NOT COMPRESSION

collagen producing cells

-fibroblasts: connective tissue matrix -chrondroblasts/chondrocytes: in cartilage -osteoblasts: in the bone -skeletal muscle cells: in skeletal muscle - smooth muscle cells: in blood vessels and some organs

elastin

-gives tissues some of their elastic resillience -ligaments generally contain more elastin than tendons making them less stiff and just slightly weaker than tendons.

collagen links

-immature collagen fibers are initially bound with reducible cross-links. as these fibers mature, their cross-links became non-reducible. collagen with nonreducible cross-links is more difficult to break than collagen with reducible cross-links. there is also an increase in cross links with maturation.

Pressure

-is always the result of compressive forcers applied perpendicular to the surface of the material, whereas stress can also be parallel to a surface or perpendicular to it.

strain

-the deformation a material undergoes in response to the application of loads. Always expressed in percentage of deformation, (shape, length, or width), of a tissue. •Strain = Area before load - area after load / area before load

Stiffness

-the slope of the stress/strain curve. It represents the resistance of the structure to -Collagen: the greater the density of bonds, the greater the stiffness -The greater the covalent cross-links between fibers, the greater the stiffness.

types of collagen fibers

-type 1: 90% of body collagen, tendon, ligament, skin, annulus, menisci, fibrocartilage, capsule, and scar tissue --> osteogenisis imperfecta -type 2:makes up 50% of all cartilage protein. present in nucleous pulposus and annulus fibrosus. hyaline cartilage (90-95%)--> collagenopathy, types 2/6 -type 3: skin, tendons, and ligaments. this is the collagen of granulation tissue, and is produced quickly by young fibroblast before the tougher type I collagen in synthesized --> ehlers-danlos syndrome -type 4: ubiquitous in connective tissue. bridges and anchor cells to other component.---> downs syndrome

Viscous Effects and Time Dependent Behaviors of CTs

1: Deformation Creep Response The tendency of a solid material to slowly deform (strain occurs) under the influence of a constant load. Creep is the continued deformation of a material under constant load over time. The material initially deforms rapidly and then continues to deform over a finite time even if the load remains constant. 2. Deformation Stress-Relaxation Response The tendency for a material held at constant length to experience a decreased in magnitude of stress. Time dependent decrease in stress with constant length 3. Temperature vs creep and stress-relaxation Viscoelastic tissues will deform more quickly and relax more easily at higher temperatures than cooler temperatures. Viscoelastic tissues loose elastic ability to recover and undergo plastic deformation sooner under cooler temperatures.

types of CT

1: Ordinary -loose ( membrane, protects structures -dense: regular =( ligament, tendon) irregular=scar tissue, immature tissue -components of ordinary tissue: water, fibers, cells, and ground substance (GAGs and proteoglycans 2: Specialized -bone = mineral, water, collagen I, ground substance -cartilage (water, fibers, ground substance, collagen)

composition of ligaments and tendons

1: ligaments/tendon - 20% cellular and 80% extracellular -60%-80% liquid and 20-40% solids 1a: only ligament -70-80% solid collagen total ( 90% type 1 and 10% type 2) -20-30% solid proteoglycans dermatan sulfate 1b: only tendons -slightly higher % in solid collagen total ( 95%-99% type 1, 1-5% type 2) - a bit less of solid proteoglycans dermatan sulfate

collagen arrangements

1: tendons: parallel, crossing, complex crossing, braiding, and spiraling 2:ligament: criss-crossed layers

basic mechanical functions

1: tendons: serve as the muscle to bone connection, transfer tensile forces between muscle and bone, provide energy storage and return, provide damping effects 2: ligaments: augment the mechanical stability of joints beyond that provide by muscle forces and joint geometry, prevent excessive or unwanted joint motions, provides proprioception and kinesthesia.

collagen

3 repeating amino acid sequences that fold into a characteristic triple-helical structure

types of Loading

:tension (stress) :compression (stress and pressure) :Bending :Shear (stress) :Torsion :Combined loading

Speed Rate Sensitivity in Viscoelastic Tissues (GRAPH)

Clinical implications: faster movements may increase tissue stress more quickly and be more dangerous for musculoskeletal structures (with higher stress, more strain is possible without deformation. Ballistic stretch riskier than slower stretch.

Elastic and Plastic Strain Example

elastic elongation of a rubber band, elastic elongation of a muscle or vertebral disc. Pure glass does not have elastic strain. Clay or ball of bread may be analastic. Every human tissue has elastic and plastic properties.

mechanical response to compression forces

negative sites on aggregans are pushed closer together: this increases their mutual repulsive force and increases compressive stiffness of the cartilage

Load

the external application of one or a group of forces in an body part (object). Load may be one unidirectional force or several forces with different directions, magnitudes, and directions.

Thixotropy

• A phenomenon exhibited by various gels, in which the system displays the mechanical properties of a gel when undisturbed, but becomes a liquid when mechanically agitated and again becomes a gel when allowed to stand. This "reduction in viscosity" is due to a temporary breaking down of an internal structure of a system under shear. • A property of adhesive systems which causes them to thin upon isothermal agitation and thicken when allowed to stand • Viscoelastic tissues has thixotropic behavior.

Key points part 2: 34

• Ligaments and tendons have similar composition, but their composition are not equal. • Tendons have better ability to absorb and release energy than ligaments (resilience). • Tendons have more collagen type I and less proteoglycans than ligaments, these may help explain why tendons are stiffer than tendons. • Tendons and ligaments are better innervated where they attach to bone. • Immobilization and rest reduces the ability of ligaments to resist stress. Same likely to occur with tendons. • The myotendon junction is a specialized area to transmit stress between muscle cells and tendons. • Muscles strains occur most commonly near the MT junction. Muscle strains are more common near the muscle insertion because of the reduced area to transfer stress compared to the proximal muscle origin.

Key points # 2

• Material fatigue can result from repetitive low magnitude loading, loss of material resilience over time, and mechanical wearing. • Viscosity refers to the ability of fluids to resist flow. • Viscoelastic materials have mechanical properties of fluids and solids. • Mechanical behavior of viscoelastic materials depend on: tissue temperature, duration of load application (creep & stress relaxation), speed/rate of load application, and previous load/deformation of the tissue (hysteresis). • All musculoskeletal tissues have viscoelastic properties, including bones.

Mechanical Wear

• Mechanical wear speeds up fatigue. • Mechanical wearing refers to the removal of superficial layers of a material. In the human body, mechanical wearing occurs because of friction and/or corrosion of the tissues: - Inflammatory process (phagocytosis). - Injections with corrosive medication (steroids). - Friction between tissues during motion

key points to remember pt. 2

• Ordinary connective tissue is composed of fibers (collagen, reticulum, elastin), cells, and ground substance (GAGs & proteoglycan). • The fibers of connective tissue are designed to resist tension stress. • Collagen (particularly type I) designed to provide stiffness, elastin designed to enhance tissue elasticity. • Different collagen: type I (most abundant in musculoskeletal ligaments, strongest), type II abundant in cartilage), high % of type III may indicate newly synthetized connective tissue (scar) or young tissue (babies). • Collagen fiber orientation in ordinary connective tissue designed to resist shear and tension stresses • GAGs and proteoglycan are designed to resist compression stress. • The intermolecular repulsive charges of chondroitin and keratin absorbs and retain tissue fluid to provide resistance to compressive loads. • Fluid exudation in connective tissue during loading helps to explain how creep and stress-relaxation occurs.

Mechanical Fatigue

• Plastic deformation of material under the repetitive application of low magnitude loads. • Repetition with time reduces resilience of material (worn tennis ball). • Eventually, this reduction in the resilience of the material allows low magnitude loads to plastically strain the tissues under stress.

Key points

• There are 5 types of loads and 3 types of stress. • Tension stress is unique to solid materials. Ligaments,muscles, tendons, and even bone can undergo tension stress. • Strain is different from tissue deformation. • Elastic tissue deformation occurs without permanent tissue structural change, unlike plastic tissue deformation. • Stiffness refers to the ability of a material to resist deformation and toughness the ability of the material to absorb energy before failure. • Resilience refers to the ability of a tissue to absorb energy when elastically deformed and release it when unloaded. • Damping refers to the ability of a material to absorb energy when deformed without quickly releasing the energy.

Mechanical Properties of MT Junction

• To p o g ra p h i c f u n c t i o n : fo l d i n g i n c r e a s e s s u r fa c e a r e a to disperse stress. It places the Basement Membrane at low angles to vector forces. This increases adhesiveness of cell/membrane junction compared to same without folding. • Elastic connective tissue parallel to contractile mechanism allows: (a) muscle ready for contraction, (b) return to resting and ready position faster, (c) protect against overstretch of contractile unit, and (d) better viscoelastic properties than contractile unit alone.

Viscoelastic material

•A material that seems to have both fluid and solid properties • It displays both viscous and elastic characteristics when undergoing deformation (examples: tendons and ligaments)