Tissue Loading Mechanics PDF

Connective tissue October 21, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Learning Objectives By the completion of this topic, student will be able 1.Identify the properties of the connective tissues 2.Understand load defor...

Connective tissue October 21, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Learning Objectives By the completion of this topic, student will be able 1.Identify the properties of the connective tissues 2.Understand load deformation curve of connective tissue 3. Know the stress-strain curve of bone/ligament/tendon  Connective tissue It is a term given to several different tissues of the body that serve to connect, support and help bind other tissues in the body.  Connective tissue Classification Loose connective tissue works to hold organs in place and is made up of extracellular matrix and collagenous, elastic and reticular fibers. Dense connective tissue is what makes up tendons and ligaments and consist of a higher density of collagen fibers. Specialized connective tissues are adipose tissue, cartilage, bone, blood, and lymph. Although connective tissue is diverse, all connective tissue consists of three main components: Ground substance Fibers Cells  Ground substance Ground substance is an amorphous sticky material that has a high water content and fills the spaces between cells and fibers, basically forming a gel. It consists of large molecules termed glycosoaminoglycans (GAGs) which link together to forming yet larger molecules called proteoglycans.(Adipose tissue/Bone) This leads to the extracellular matrix being very effective in being resistant compressive forces  Fibres The fibroblasts secrete the connective tissue fibers. The three types of connective tissue fibers are: Collagen fibers - most are type I collagen (most abundant protein in the body). Tensile strength - resistance to stretching Elastic fibers - contain elastin and fibrillin. Elasticity - can be stretched, yet still, return to its original length Reticular fibers - contain type III collagen. Their function is supportive, form a supporting network in the reticular lamina of the basement membrane found in soft tissues such as the liver, bone marrow, spleen, and lymph nodes  Cells Bone contains Osteocytes, and osteoblasts which secrete the type of ECM that makes up bone. Cartilage contains chondrocytes and chondroblasts which secrete the type of ECM found in cartilage, respectively. Blood vessels contain Endothelial cells and present underneath the epithelium of blood capillaries, are cells called Pericytes, which can divide and provide a source of new fibroblasts, especially following tissue injury  Connective tissue & functions Resistance to stretch and tear Structural support Insulation Storage of body fuels A medium for intercellular exchange  Young's modulus Resistance force by an object to the external force is known as modulus of elasticity or young modulus. tension or compression.. Modulus of elasticity vary for different materials. If the slope of curve is steep, modulus of elasticity will be high, compliance low. Ex. Bone If the slope of curve is gradual, modulus of elasticity will be low, High compliance. Ex. Subcutaneous fat.  Stress strain and loading Stress Is acting upon a cross sectional area of a material Stress=Force applied/Area [Mega pascals] Strain: % of change in length on material in response to load application Type of stress a tissue undergoes  Stress on bone The stress-strain curve obtained by loading a sample of compact bone in tension. E is the stiffness of the material (Young's modulus for modelled isotropic materials)  Stress strain on tendon/ligament Typical stress-strain curve for mammalian tendon. Three regions are shown: (1) toe region (2) linear region, and (3) failure region https://youtu.be/11qu6BX_jNg https://youtu.be/glcO_0gPad4 https://youtu.be/WkVpOHBO90E  TISSUE HOMEOSTASIS Many clinical issues can be related to a disruption of the local tissue’s homeostasis due to exposure to stress beyond its adaptive ability.  TISSUE HOMEOSTASIS Loads above this threshold will cause tissue damage at a higher rate than to which it can adapt; loads below will result in a detraining effect. Healthy individuals have a fairly wide gap between the minimal effective dose and the maximum tolerated dose. With injury, this zone narrows and it requires more precise dosage to stay within the continuum of function. The rehabilitation goal is to increase these envelope borders by driving its upper limits to the right. Manual loading Tissue repair , flow dynamics and adaptability are highly dependent on the type of mechanical forces applied during treatment. These forces are called manual loading Two types Tension loading Compression loading Tension loading In tension loading forces are applied in opposite direction causing tissue to elongate Used in lengthening shortened tissue and break excessive cross links. Traction longitudinal and cross fiber stretching and are examples of tendon loading Compression loading Forces are applied into tissue often to the center Under compression loading the tissue will shorten and widen increase the pressure within the tissue and affecting fluid flow Compression is therefore a very useful pump like technique to facilitate the flow of fluid  Reference DeryaÖzer Kaya , Architecture of tendon and ligament and their adaptation to pathological conditions; Comparative Kinesiology of the Human Body, 2020, Pages 115-147