Bioactive glasses and glass ceramics 1 Flashcards
What type of response do bioactive materials elicit at the tissue-implant interface?
Elicit a specific biological response at the tissue-implant interface that results in the formation of a chemical bond
include glasses, glass-ceramics, and ceramics
What do bioactive materials differ in terms of?
Mechanism
Rate
Thickness of interfacial layer
Strength of bonding
What type of layer do bioactive glasses, glass ceramics, and ceramics form at the implant-tissue interface
Undergo time dependent modification of the implant surface
From a carbonated hydroxyapatite layer with tissue Very VERY strong interfacial adhesion
Some glasses, like 45S5 bio glass, also bond to soft tissue
What is the carbonated hydroxyapatite layer structurally and chemically close to
The inorganic phase of bone
Bone composition
70% Mineral phase
30% Organic phase
2 % Cells
Mineral phase of bone components
95% Hydroxyapatite Magnesium Sodium Potassium Fluoride Chloride
Organic phase of bone components
98% matrix made of:
- 95% collagen
- 5% non collagenous proteins (BMO, TGFß: 2% NCP
Cells phase of bone components
osteoblasts
osteocytes
osteoclasts
Region A composition of bioactive glass and glass ceramics
Bone bonding glasses
All glasses contain 6wt% P2O5
Region B composition of bioactive glass and glass ceramics
Inert materials
Elicit a fibrous capsule at the implant-tissue interface
Greater than 60% SiO2
Used for window, bottles, and microscope slides
Region C composition of bioactive glass and glass ceramics
Resorbable glasses
Degrade after 10-30 days implantation
Region D composition of bioactive glass and glass ceramics
Not technically practical
Has not been tested as implants
Region E composition of bioactive glass and glass ceramics
Inside dashed line of diagram
Soft tissue bonding glasses
ex: collagenous tissues
Ib > 8
Five principal components of bioactive glasses and glass ceramics
In order of prevalence: SiO2 Na2O CaO CaF2 (only in 45S5F) P2O5
Compositional features of bioactive glass (distinguish them from normal glass)
Contain 6 wt% P2O5
Have less than 60 mol% SiO2
High Na2O and CaO content
High CaO/P2O5 ratio
Does lowering or increasing CaO/P2O5 ratio reduce bioactivity?
lowering the ratio reduces bioactivity
Does the addition of 12.5% CaF2 affect bioactivity?
No, it does not affect bioactivity
What does in addition of 3% Al2O3 in a bioglass do?
It stops the bone bonding ability
Bonding mechanism of bioactive glasses
As bioglasses react with aqueous environment of body, chemical and structural changes occur over time
Chemical composition and pH of solution change as accumulation and dissolution of products changes
What happens when a bio implant is bonded to a bone?
Carbonated hydroxyapatite is formed
What happens when a bio implant is bonded to soft tissue?
Collagen fibrils are chemisorbed through electrostatic, ionic, and hydrogen bonding
Chemical reaction stages of bioactive (glass) implants with bone
- Rapid ion exchange
- Si-OH group formation
- Silica-rich layer formation
- Amorphous calcium phosphate
- Crystalline hydroxyapatite
Step 1 of bioactive implants chemical reaction: ion exchange
Initiation of rapid cation exchange of Na+ and Ca2+ ions from the glass with H+ from solution
Usually controlled by diffusion
Hydrolysis of sola groups creates silanols (Si-OH)
pH increases
Step 2 of bioactive implants chemical reaction: Si-OH group formation
Cation exchange increases [OH- ], leading to attack of silica glass network
Soluble silica lost in the form of Si(OH)4, resulting in breakdown of Is-OSi bonds and continued formation of Si-OH at the glass solution interface
Interface controlled action with t^1 dependence
