Week 6 Part 2 Bioceramics Flashcards
What is a bioceramic?
ceramics used for the repair and reconstruction of diseased or damaged tissue.
What are the 3 groups of ceramics?
- bioinert
- bioactive
- bioabsorbable
Bioinert ceramics
stable in vivo, doesn’t react with the body
ex. Aluminum oxide and zirconia
Bioactive ceramics
can bond to bone and promote growth
ex. hydroxyapatite and tricalcium phosphate
Bioabsorbable ceramics
dissolve in the body and promote tissue regeneration.
ex. calcium sulfate and calcium phosphate-based ceramics
What does the porosity of ceramics allow for? (3)
- movement of nutrients and removal of wastes
- promotes tissue growth
- large surface to volume ratio
What are the 4 general properties of bioceramics?
- hard and brittle
- high melting temperature
- biocompatible
- excellent wear resistance
What causes the breakdown of ceramics?
degradation
Because ceramics have strong ionic bonds you need ___________________ to break them.
a lot of energy
What are the four reasons of failure in ceramics?
- degradation
- energy to break ionic bonds
- environment and design
- porosity
How does porosity cause failure?
more surface area to contact environment which increases formation of cracks or crack propagation
How does environment and design cause failure?
the tension causes stress induced degradation
Erosion mechanism
erode under physiological conditions due to pH
Rate of erosion depends on: (4)
- chemical susceptibility of the material
- amount of crystallinity
- amount of media (water) available
- material surface area to volume ratio
Bioactive glasses
undergo a reaction at their surface
How do bioactive glasses degrade?
they undergo a reaction at their surface
- exchange of ions with the physiological fluid
- creates a silica
what is a silica?
rich layer that affects protein and cell interactions with the material over weeks-months
In glass forming, what is the softening point?
maximum temperature the piece can be handled without significant change in shape
- viscosity = 4E7 p
In glass forming, what is the working point?
glass can be easily deformed
viscosity is 10^4 p
Drawing (manufacturing process)
similar to metal
- molten glass is pulled over rollers to form long sheets or tubing
- may also be drawn to small orifices to form glass fibers
Casting is preferred for what structure?
crystalline over amorphous
amorphous
has no definite shape or form
How is casting performed?
- ceramic particles are mixed with water and an organic binder
- poured and pressed into mold
- piece is left to dry a water evaporates
- ceramic shrinks away from walls = easy removal
- further drying removes excess water, but must be monitored or else it cracks
Firing (manufacturing process)
- once the part is shaped and dried the piece is exposed to temperatures between 900-1400 C
