Biomechanics

Biomaterials

Chapter7Part_2.pdf-Callus Calculation 7. Bone-Implant Systems &

Biocompatibility: ability of a material to perform with an appropriate host response in a specific application . Williams D. F. (Ed.) (1991) Definitions in Biomaterials. Proc. 2nd Concensus Conf. On Biomaterials, Chester, UK. Biocompatibility The inflammatory Response Immune response triggered when substances foreign to the body (antigens) are re

BME423biocompa2017.pdf-Biocompatibility: ability of a material to

36 Calcium Intake (1) • 99% of total calcium is stored in skeletal matrix • Circulating (serum) calcium must be maintained within  2% • If circulating levels fall, Ca is resorbed from bone for equilibrium – link to osteoporosis • Threshold nutrient – body cannot store dietary surplus of calcium (800mg/day ≤ 50 years, 1200 mg/day > 50 years) 37 Calcium Intake (2) • Dietary sources - Content - Bioavailability • Supplementation - Increase BMD - Decrease bone loss - Decrease FR 38 Vitamin D • At low to moderate calcium intakes, calcium absorption is dependent on the action of vitamin D3 • Sources of vitamin D include sunlight, fatty fish and eggs • Recommended dietary intake 0-400IU/d up to age 65y and 400+ thereafter • Additional benefits of Vitamin D supplementation in combination with Calcium 39 • Inhibits osteoblasts supressing bone formation and increases bone resorption • Smoking leads to inefficient calcium absorption • Decreased BMD & increased FR Smoking Status 40 • FR ratio for intake of >2 units/day is 1.68 • With high alcohol intakes BMD decreases in parallel with duration of drinking history Alcohol Consumption Moderate intake of alcohol (1-6 units/wk) slightly decreased risk of osteoporosis 41 Weight & BMI • Body weight impacts on both bone turnover & density • Low BMI is risk factor for fracture • In comparison to BMI of 25kg/m² a BMI of 20kg/m² is associated with a nearly 2-fold increase in FR. • BMI >30kg/m² does not induce further protective effects 42 Weight & BMI risk of a hip fracture is twice as high in somebody with a BMI of 20 compared to somebody with a BMI of 25. Some of this is caused by decreased bone density, but even when adjusted for bone density (as shown in the dark blue line) there is an increased fracture risk with low weight. 43 Physical Activity (PA) PA has the unique ability to activate the bone formation via both mechanical and metabolic stimuli 44 Strength vs. Endurance • Strength trained - Up to 26% higher BMD than endurance trained athletes at weight-bearing anatomical sites - Site specific Female Athletic Triad 3 issues affecting female athletes: amenorrhea eating disorders osteoporosis . Increasing pressure on adolescent girls to maintain "ideal" body weight. Sports lend themselves to increasing the pressure that girls feel to be thin. Amenorrhea lack of menstrual periods. larger number of athletes have amenorrhea than the 5% of women in the general population. The decreased estrogen levels associated with amenorrhea may be the cause of premature osteoporosis found among female athletes.

BME | 423 | Biomaterials | lecture notes | 36 Calcium Intake (1) • 99% of

Bone Composition and Structure 3. Mechanics of Bone Bone Structure - Bone tissue (osseous tissue). -Fibrous connective tissue. -Cartilage. -Vascular tissue. -Lymphatic tissue. -Adipose tissue. -Nervous tissue. Bones are organs. Thus, they’re composed of multiple tissue types. Bones are composed of: 3. Mechanics of Bone All bones consist of a dense, solid outer layer known as compact bone ( cortical bone ) and an inner layer of spongy bone – a honeycomb of flat, needle-like projections called trabeculae . Bone is an extremely dynamic tissue!!!! Spongy bone 3. Mechanics of Bone Bone Structure Comparison of cortical and spongy bone as viewed with the light microscope 3. Mechanics of Bone Bone Structure Bone Structure The blue arrows indicate the osteoblasts . The yellow arrows indicate the bone matrix they’ve just secreted. Bone tissue is a type of connective tissue, so it must consist of cells plus a significant amount of extracellular matrix. Bone cells: 1. Osteoblasts -Bone-building cells. -Synthesize and secrete collagen fibers and other organic components of bone matrix. -Initiate the process of calcification. -Found in both the periosteum and the endosteum 3. Mechanics of Bone Bone Structure Blue arrow shows an osteoblast in the process of becoming an osteocyte. Yellow arrows indicate osteocytes – notice how they are surrounded by the pinkish bone matrix. On the right, notice how the osteocyte is “trapped” within the pink matrix 2. Osteocytes -Mature bone cells. -Osteoblasts that have become trapped by the secretion of matrix. -No longer secrete matrix. -Responsible for maintaining the bone tissue . 3. Mechanics of Bone 3. Osteoclasts -Huge cells derived from the fusion of as many as 50 monocytes (a type of white blood cell). -Cells that digest bone matrix – this process is called bone resorption and is part of normal bone growth, development, maintenance, and repair. -Concentrated in the endosteum. -The osteoclast secretes digestive enzymes to digest the bone matrix. It also pumps out hydrogen ions to create an acid environment that eats away at the matrix. 3. Mechanics of Bone Bone Structure Bone Matrix: Consists of organic and inorganic components. 1/3 organic and 2/3 inorganic by weight. Organic component consists of several materials that are secreted by the osteoblasts. They are: -Collagen fibers and -Other organic materials They provide the bone with resilience and the ability to resist stretching and twisting. 3. Mechanics of Bone

BME | 406 | Biomechanics | lecture notes | Bone Composition and Structure

1 Tendons and Ligaments • The three principal passive structures that closely surround, connect and stabilize the joints of the skeletal system are the tendons, the ligaments, and the joint capsules. • Tendons and ligaments are dense connective tissues known as parallel fibered collagenous tissues. • The great mechanical stability of collagen gives the tendons and ligaments their characteristic strength and stability. • Both tendon and Ligament contain 60% water. 4. Mechanics of Soft Tissues Composition and Structure of Tendons and Ligaments 4. Mechanics of Soft Tissues Collagen content in tendons and ligaments is generally over 75% and is somewhat greater in tendons than in ligaments. Arrangement of collagen molecules into Tendon 2 Composition and Structure of Tendons and Ligaments 4. Mechanics of Soft Tissues Composition and Structure of Tendons and Ligaments 4. Mechanics of Soft Tissues 3 Characteristic Stress-Strain Relation for Tendons 4. Mechanics of Soft Tissues Characteristic Load-Elongation Relation for Ligaments 4. Mechanics of Soft Tissues 4 4. Mechanics of Soft Tissues Characteristic Load-Elongation Relation for Ligaments stiffness 4. Mechanics of Soft Tissues Mechanical Properties of Human Tissues 5 Ligament and Tendon Injury Mechanisms 4. Mechanics of Soft Tissues Ligament Cadaver Knee Ligament and Tendon Injury Mechanisms 4. Mechanics of Soft Tissues 6 Viscoelastic Behavior in Tendons and Ligaments 4. Mechanics of Soft Tissues Stress relaxation @ a constant strain 4. Mechanics of Soft Tissues PCL ACL Force-deformation of different fiber bundles within the human Anterior Cruciate Ligament (ACL). 7 4. Mechanics of Soft Tissues Typical stress-strain curves for Tendon and Ligament tissues 4. Mechanics of Soft Tissues Stress-Strain Response in Tendon and Ligament In experimental testing on tendon and ligament tissue, Lagrangian strain or “stretch” is usually used as the measure of strain because of the large values strain encountered. This is defined as the ratio of the total deformed length to the initial length: Tensile stress: The relation between stress and strain up to the start of yielding: By differentiating of stress with respect to strain, the stress-strain relation can be converted to a tangent modulus-stress equation: initial L L = λ initial A F = σ ( ) 1 - = λ σ b e a c b d d + = σ λ σ Where c is a constant of integration (c=ab) and presents the tangent modulus as σ  0.

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