abstract
| - 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. 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.% 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%. 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.
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