Mechanical Properties of Biomaterials Flashcards
what is collagen?
basic structure protein
has fibrous protein with triple helical structure
What is elastin?
fibrous protein with high elastic nature
What are the mechanical properties of collagen?
- moderate hysteresis + stress relaxation
- high modulus at small elongations
- characterised by tendon measurements
What are the mechanical properties of elastin?
- very small hysteresis + stress relaxation
- low modulus
- ## almost linear behaviour
What do collagen and elastin both produce?
A non-linear stress strain curve
What is hardness?
Resistance of a material to localized deformation
What materials are isotropic?
Polycrystalline materials = most metallic and ceramic
as grains are aggregated with uniform distributions
What materials are anisotropic?
Single crystals = polymeric materials + biological tissues
- ORIENTATION DEPENDENT
Bone, ligaments and sutures are all stronger and stiffer in the…..
longitudinal direction than they are in the transverse
What testing machine can you use on a isotropic material?
Universal testing machine - uniaxial stretch
What materials can a biaxial stretcher be used on? Describe key components
Anisotropic
load cells measuring force
stepper motor controls arm movement
Strongly bonded materials =
High MODULUS + STRENGTH
therefore a higher force is required to produce strain
What are the two different types of polymers?
Amorphous and semi-crystalline
what are the stages when you heat an amorphous material
glass > rubbery > GUMMMMY > liquid
What are the stages when you heat a semi-crystalline material
glass > thermoplastic > liquid
What is fatigue
manifestation of progressive fracture in a solid under cyclic loading
What does the stiffness of viscoelastic materials depend on
Loading rate
polymeric + biopolymeric materials exhibit
significant stress relaxation
What are the requirements of a viable biomaterial
- satisfy biomechanical criteria
- avoid material failure
- mitigate undesirable effects of the body environment
