Bioactive glasses

Question 1

stages of bone bonding, glass surface

Answer 1

1) formation of Si-OH(silanol) bonds via cation(Na+ or Ca2+) exchange with H+ or H3O+ in solution
2) Breakdown of the silica network(Si-O-Si) to form more Si-OH bonds
3) Condensation and repolymerisation of Si-O2 rich layer on the surface
4) Migration of Ca2+ and (PO4)3- from solution on surface to form CaO-P2O5 later
5) Crystallisation of the amorphous layer via incorporation of anions((CO3)2- and OH-) to form HCA

Question 2

2 mechanisms of bioactivity

Answer 2

osteoconductive - bone growth along the surface of the material
osteoinductive - when implanted into areas that bone does not normally grow, bone grows on this material away from bone/biomaterial interface

Question 3

Composition of HA

Answer 3

Ca10(PO4)6(OH)2

Question 4

What is the effect of Si content on bioactivity?

Answer 4

Increasing SiO2 content of the glass towards 60mol% reduces the rates of ion exchange, network dissolution and HCA crystallisation
Bioactivity decreases proportionally

Question 5

Why can’t Bioglass be used to coat hip prostheses?

Answer 5

1) It crystallises during sintering

2) Thermal expansion coefficient mismatch [no processing window] Refer to graph on lecture notes

Question 6

Stages of bone bonding, suggested biological

Answer 6

1) Adsorption and desorption of biological growth factors, in the HCA layer to activate differentiation of stem cells
2) Action of macrophages to remove debris from the site allowing cells to occupy the space
3) Attachment of stem cells on the bioactive surface
4) Differentiation of stem cells to form bone growing cells, such as osteoblasts
5) Generation of extra cellular matrix by the osteoblasts to form bone
6) Crystallisation of inorganic calcium phosphate matrix to enclose bone cells in a living composite structure

Question 7

Is Bioglass osteo conductive or inductive?

Answer 7

osteoconductive and resobable