Biological Materials Flashcards
What three things do bones contain?
- Water (25-30%) 2. Collagen (30% of dry weight) 3. Minerals (70% of dry weight)
Bone is capable of withstanding what?
Loads six times those experienced in normal life.
A specialised form of connective tissue, bone consists of many cells (osteocytes), which are:
Light In a collagen matrix Packed with minerals
Biomechanically what are the two types of bones?
Cortical (Thick layer outside the bone) Trabecular (Layered maze like mass within the bone)
The two main forms of bone damage comes in what forms?
- Fractures, which can be either traumatic (usually a one-off impact) 2. Fatigue-induced (these are often called stress fractures although this term is slightly misleading).
A diaphyseal impaction fracture is caused by what load?
Axial compression
A transverse fracture is caused by what load?
Bending
A spiral fracture is caused by what load?
Torsion
A oblique transverse is caused by what load?
Axial compression Bending
A oblique is caused by what load?
Axial compression Bending Torsion
Transverse fractures
Bending load Cortical bone weaker in tension than compression, so bone under tension fails first. Failure mechanism is break propagation perpendicular to bone’s long axis, from surface layer inwards
Cells are widely separated within a fibrous, organic matrix which may:
Appear (but isn’t) structureless as in rigid hyaline cartilage
Contain more connective tissue fibres in the matrix (e.g. fibrocartilage)
Cells (chondrocytes) account for less than what percentage of the tissue volume?
10%
The organic matrix of cartilage consists of what?
Collagen fibrils (10-30% net weight) within a proteoglycans solution (3-10% net weight).
What is a tissue made up of?
60-87% is made up of water, inorganic salts and small quantities of matrix proteins, glycoproteins and lipids.
What does a cartilage mechanical properties depend on?
The direction of loading (anisotropic)
Cartilage shows what three typical viscoelastic behaviours?
Loading leads torapid initial deformation followed by more gradual increase Returns to initial shape on load removal (hysteresis) Prolonged standing causes creep of intervertebral discs (hence shortening of the body’s overall height0
Articular cartilage (Fact Card)
Capable of deformation; decreases stress on joints by increasing load-bearing area. Avascular with few nerve endings, injured cartilage shows little external symptoms and repairs poorly. Overuse injuries cause cartilage to wear away, leading to osteoarthritis. High impact loads lead to swelling; if severe enough may fracture.
What are Aponeuroses tendons?
Sheet-like tendons that attach muscles to bones and transmit tensile loads so that movement can occur
What are tendons?
Tough cords of closely packed collagen fibres that attach muscles to bones
What are ligaments?
Like tendons but contain some elastic fibre (elastin). Ligamentous joint capsules connect bone to bone, guide joint motion, enhance mechanical stability and prevent excessive motion
What is Intermuscular septa?
Separates muscle groups passing from the deep fascia to the bone.
What is the ultimate failure train of tendons?
8-10%
What hysteresis personage do tendons have?
Limited viscoelastic behaviour with only 2.5% to 20%
What is considered the main site for high energy return during elastic recoil in the muscle-tendon unit?
Tendons due to there Limited viscoelastic behaviour (For example the achilles tendon for jumping athletes)
Ligaments (Fact Card)
Ligaments are designed to cope best with tensile forces. Ligaments have mechanoreceptors which may initiate tension in nearby muscles in order to assist in maintaining joint stability. This can be important, for example, during rapid knee
Ligament injuries (Fact Card)
Sprains caused by excessive joint motion, most not severe. Direct blows can cause stretching and permanent deformation. Failure often due to bending and torsional loads applied to distal limb, as in a tackle, and depends on load rate
What are the four effects of a ligament tear?
- Loss of stability 2. Joint misalignment 3. Abnormal contact pressure 4. Loss of proprioception
Muscles (Fact Card)
Most commonly injured form of connective tissue because of its low stiffness. However, the quickest to recover because of its large blood supply. Muscle stiffness is related to the force produced in relation to its length. Maximal stiffness is encountered during eccentric contraction, up to 200 times that in concentric and is probably under reflex control.
How far can muscles stretch of resting length before rupture?
160%
