BME213 Sem 5 Flashcards
What are some of the common methods used in processing ceramics and/or glass?
Vitrification & Sintering.
Vitrification :
- A process of converting a glass-forming liquid into a glass-like amorphous solid which is free of any crystalline structure
- Done by quick removal of heat or by mixing with an additive to block crystalization
- End product: hard, brittle, non-crystalline ceramic/glass
Sintering:
-Process of bonding adjacent surfaces of powder particles by heating
- It strengthens a powder mass and increases density
Explain bioactive and host response towards bioactive ceramics. Give examples of bioactive ceramics
Bioactive ceramics are materials that interact with body tissues and form a direct chemical bond with bone. They promote bone growth and healing.
They exchange ions with body fluids, forming a hydroxycarbonate apatite (HCA) layer that is similar to bone mineral, encouraging bone cell attachment and integration.
The body recognizes the HCA layer, promotes osteoblast activity, and allows the material to bond directly with bone (osseointegration), not forming a fibrous capsule.
Examples:
1. Hydroxyapatite (HA) – bone grafts and implant coatings
2. Bioglass (45S5) – bone and dental repairs
3. Tricalcium phosphate – bone fillers and scaffolds
What are some behaviors of ceramics? Provide 5 examples of ceramics.
Behaviours of ceramic: Hard, brittle, thermal and electrical insulators, high melting point
5 examples of ceramics:
1. Bioglass
2. Zirconia
3. Alumina
4. Metal oxides
5. Metal carbides
Describe the mechanisms involved in solid-state and liquid-phase sintering
Solid-State Sintering:
• Occurs below the melting point of the material
• Particles bond through atomic diffusion, without any liquid phase
• Mechanisms include:
1. Surface diffusion – atoms move along surfaces (no densification)
2. Lattice/volume diffusion – atoms move through the solid
3. Grain boundary diffusion – atoms move along grain edges
4. Neck formation and pore shrinkage
Liquid-Phase Sintering:
• A liquid phase forms during heating, while solid remains
• Enables faster densification and rearrangement
• Mechanisms include:
1. Particle rearrangement – due to liquid capillary forces
2. Solution–reprecipitation – solid dissolves and re-forms
3. Solid-state diffusion continues in the solid phase
4. Wetting helps liquid bind and fill between particles
What are the 3 main classifications of bioceramics based on body interaction?
- Bioinert
- Bioactive
- Bioresorbable
Distinguish the host response towards bioinert ceramics compared to bioactive ceramics
Bioinert: The body forms a fibrous capsule around the implant to isolate it.
There is no chemical bonding with tissue. Stability relies on mechanical fixation.
Example: Alumina (Al₂O₃)
Bioactive: They stimulate a biological response, forming a hydroxycarbonate apatite (HCA) layer that bonds with bone or tissue.
They promote osseointegration and bone regeneration.
Example: Bioglass (45S5)
Difference: Bioinert: Forms a fibrous capsule, no bonding.
Bioactive: Bonds directly with bone or tissue through a biologically active surface
What is the typical composition of Bioglass (45S5)?
• 45% SiO₂
• 24.5% CaO
• 24.5% Na₂O
• 6% P₂O₅
This specific ratio makes Bioglass bioactive and able to bond with bone.
What is a bioinert bioceramic? Give one example.
A ceramic that does not bond with tissue and forms a fibrous capsule.
Example: Alumina (Al₂O₃)
What is a bioactive bioceramic? Give one example.
A ceramic that bonds with bone or tissue and promotes regeneration.
Example: Bioglass (45S5)
What is a bioresorbable bioceramic? Give one example.
A ceramic that gradually dissolves and is replaced by natural tissue.
Example: Tricalcium phosphate (TCP)
How does Bioglass interact with host bone tissue?
• Releases ions (Na⁺, Ca²⁺) into body fluids
• Forms a silica gel layer, then a hydroxycarbonate apatite (HCA) layer
• HCA mimics bone mineral → promotes bone bonding and regen
Q: What are typical applications of Bioglass?
• Bone grafts and defect repair
• Coatings on orthopedic and dental implants
• Middle ear bone reconstruction
• Periodontal bone regeneration
