Wiktionary
n. bioactive glass
Wikipedia
Bioglass is a commercially available family of bioactive glasses, composed of SiO, NaO, CaO and PO in specific proportions. The proportions differ from the traditional soda-lime glasses in low amount of silica (less than 60 mol.%), high amount of sodium and calcium, and high calcium/phosphorus ratio.
High ratio of calcium to phosphorus promotes formation of apatite crystals; calcium and silica ions can act as crystallization nuclei.
Bioglasses have different formulations. Some bind to soft tissues and bone (e.g. 45S5), some only to bone (e.g. 5S4.3 or Ceravital), some do not form a bond at all and after implantation get encapsulated with nonadhering fibrous tissue, and others are completely resorbed within few weeks. Fine powders resorb faster than bulk materials. A thin layer of apatite forms on the glass-tissue interface, facilitating strong bond to the bone. Some formulations can facilitate growth of osteoblasts through the material. Generally, there are four classes of bioglasses:
- 35-60 mol.% SiO, 10-50 mol.% CaO, 5-40 mol.% NaO: bioactive, bonds to bone, some formulations bond to soft tissues
- <35 mol.% SiO: non glass-forming
- >50 mol.% SiO, <10 mol.% CaO, <35 mol.% NaO: bioactive, resorption within 10–30 days
- >65 mol.% SiO: non-bioactive, nearly inert, gets encapsulated with fibrous tissue
Some CaO can be replaced with MgO and some NaO with KO without much effect to bone bonding. Some CaO can be replaced with CaF without altering bone bonding, this however modifies the dissolution rate of the glass. BO or AlO may be added for easier material processing, however these influence the bone bonding; alumina inhibits bonding and its content is therefore restricted to small levels of about 1-1.5%.
Phosphate-free glasses also exhibit bioactivity. The role of the phosphate is only in aiding of nucleation of apatite on the surface; phosphate ions adsorbed from the organism itself can play the same role.
Bioglasses are divided to two categories:
- Class A bioglasses are osteoproductive. They bind with both soft tissues and bone. The HCA layer forms within several hours.
- Class B bioglasses are osteoconductive. Bond to soft tissues is not facilitated. The HCA layer takes one to several days to form.
glass
others
properties
Bioglass 42S5.6
42.1
2.6
29.0
26.3
mol.%
Bioglass 46S5.2
46.1
2.6
26.9
24.4
mol.%; best tissue bonding of Bioglass formulas
Bioglass 49S4.9
49.1
2.6
25.3
23.8
mol.%
Bioglass 52S4.6
52.1
2.6
23.8
21.5
mol.%
Bioglass 55S4.3
55.1
2.6
22.2
20.1
mol.%
Bioglass 60S3.8
60.1
2.6
19.6
17.7
mol.%; no phosphate film formed
Bioglass 45S5
45
6
24.5
24.5
the original Bioglass formulation; binds with bone and soft tissues
Bioglass 45S5F
45
6
12.25
12.25
24.5
Bioglass 45S5.4F
45
6
14.7
9.8
24.5
Bioglass 40S5B5
40
6
24.5
24.5
5 BO
Bioglass 52S4.6
52
6
21
21
Bioglass 55S4.3
55
6
19.5
19.5
Bioglass 8625
?
?
?
?
FeO
highly biocompatible, does not bind with tissues, fibrous encapsulation; absorbs infrared radiation, can be laser-sealed, used for RFID tag encapsulation
Ceravital KGC
46.2
20.2
25.5
4.8
Ceravital KGS
46
33
16
5
Ceravital KGy213
38
31
13.5
4
Ceravital bioactive
40-50
10-15
30-35
5-10
Ceravital nonbioactive
30-35
7.5-12
25-30
3.5-7.5
1-2.5 MgO, 0.5-2 KO, 5.0-15.0 AlO, 5-15 TaO, 1.0-5.0 TiO
A-W GC (Cerabone)
34.2
16.3
44.9
0.5
4.6 MgO
Oxyfluoro apatite/ Wollastonite glass-ceramic; high strength, used to replace parts of bones; interfacial apatite forms quickly and the bond is stronger than the bone itself.
Bioverit
bioactive, machinable glass-ceramics containing apatite and phlogophite, used as artificial vertebra