Bioglass is a commercially available family of bioactive glasses, composed of SiO₂, Na₂O, CaO and P₂O₅ 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.^[1]

High ratio of calcium to phosphorus promotes formation of apatite crystals; calcium and silica ions can act as crystallization nuclei.^[2]

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.^[1] Generally, there are four classes of bioglasses:^[2]

• 35-60 mol.% SiO₂, 10-50 mol.% CaO, 5-40 mol.% Na₂O: bioactive, bonds to bone, some formulations bond to soft tissues
• <35 mol.% SiO₂: non glass-forming
• >50 mol.% SiO₂, <10 mol.% CaO, <35 mol.% Na₂O: bioactive, resorption within 10–30 days
• >65 mol.% SiO₂: non-bioactive, nearly inert, gets encapsulated with fibrous tissue

Some CaO can be replaced with MgO and some Na₂O with K₂O without much effect to bone bonding. Some CaO can be replaced with CaF₂ without altering bone bonding, this however modifies the dissolution rate of the glass. B₂O₃ or Al₂O₃ 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%.^[2]

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.^[2]

Bioglasses are divided to two categories:^[3]

• 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.

Composition of bioglasses and glass-ceramics (wt.%)

glass	SiO2	P2O5	CaO	Ca(PO3)2	CaF2	Na2O	others	properties
Bioglass 42S5.6[4]	42.1	2.6	29.0			26.3		mol.%
Bioglass 46S5.2[4]	46.1	2.6	26.9			24.4		mol.%; best tissue bonding of Bioglass formulas
Bioglass 49S4.9[4]	49.1	2.6	25.3			23.8		mol.%
Bioglass 52S4.6[4]	52.1	2.6	23.8			21.5		mol.%
Bioglass 55S4.3[4]	55.1	2.6	22.2			20.1		mol.%
Bioglass 60S3.8[4]	60.1	2.6	19.6			17.7		mol.%; no phosphate film formed
Bioglass 45S5[1]	45	6	24.5			24.5		the original Bioglass formulation; binds with bone and soft tissues
Bioglass 45S5F[1]	45	6	12.25		12.25	24.5
Bioglass 45S5.4F[1]	45	6	14.7		9.8	24.5
Bioglass 40S5B5[1]	40	6	24.5			24.5	5 B2O3
Bioglass 52S4.6[1]	52	6	21			21
Bioglass 55S4.3[1]	55	6	19.5			19.5
Bioglass 8625	?	?	?			?	Fe2O3	highly biocompatible, does not bind with tissues, fibrous encapsulation; absorbs infrared radiation, can be laser-sealed, used for RFID tag encapsulation
Ceravital KGC[1]	46.2		20.2	25.5		4.8	2.9 MgO, 0.4 K2O
Ceravital KGS[1]	46		33	16		5
Ceravital KGy213[1]	38		31	13.5		4	7 Al2O3, 6.5 Ta2O5/TiO2
Ceravital bioactive[4]	40-50	10-15	30-35			5-10	2.5-5 MgO, 0.5-3 K2O
Ceravital nonbioactive[4]	30-35	7.5-12	25-30			3.5-7.5	1-2.5 MgO, 0.5-2 K2O, 5.0-15.0 Al2O3, 5-15 Ta2O5, 1.0-5.0 TiO2
A-W GC (Cerabone)[1]	34.2	16.3	44.9		0.5		4.6 MgO	Oxyfluoroapatite/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[5]

Contents  [hide]  1 Bioglass 45S5 2 History of Bioglass45S5 3 Bioglass 8625 4 References