Bioglass
Encyclopedia
Bioglass is a commercially available family of bioactive glass
es, composed of SiO2, Na2O
, CaO
and P2O5
in specific proportions. The proportions differ from the traditional soda-lime glass
es 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 osteoblast
s through the material. Generally, there are four classes of bioglasses:
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:
in the late 1960s. He was challenged by a MASH
army officer to develop a material to help regenerate bone
, as many Vietnam war
veteran
s suffered badly from bone damage, such that most of them injured in this way lost their limbs.
The composition was originally selected because of being roughly eutectic.
The 45S5 name signifies glass with 45 wt.% of SiO2 and 5:1 ratio of CaO to P2O5. Lower Ca/P ratios do not bond to bone.
The key composition features of Bioglass is that it contains less than 60 mol% SiO2, high Na2O and CaO contents, high CaO/P2O5 ratio, which makes Bioglass highly reactive to aqueous medium and bioactive.
High bioactivity is the main advantage of Bioglass, while its disadvantages includes mechanical weakness, low fracture resistance due to amorphous 2-dimensional glass network. The bending strength of most Bioglass is in the range of 40–60 MPa, which is not enough for load-bearing application. Its Young's modulus
is 30–35 GPa, very close to that of cortical bone
, which can be an advantage. Bioglass implants can be used in non-load-bearing applications, for buried implants loaded slightly or compressively. Bioglass can be also used as a bioactive component in composite material
s or as powder.
The first successful surgical use of Bioglass 45S5 was in replacement of ossicles
in middle ear
, as a treatment of conductive hearing loss
. The advantage of 45S5 is in no tendency to form fibrous tissue. Other uses are in cones for implantation into the jaw following a tooth extraction. Composite materials made of Bioglass 45S5 and patient's own bone can be used for bone reconstruction.
Bioglass is comparatively soft in comparison to other glasses. It can be machined, preferably with diamond tools, or ground to powder. Bioglass has to be stored in a dry environment, as it readily absorbs moisture and reacts with it.
Bioglass 45S5 is manufactured by conventional glass-making technology, using platinum or platinum alloy crucible
s to avoid contamination. Contaminants would interfere with the chemical reactivity in organism. Annealing
is a crucial step in forming bulk parts, due to high thermal expansion
of the material.
Heat treatment of Bioglass reduces the volatile alkali metal oxide content and precipitates apatite crystals in the glass matrix. The resulting glass-ceramic material, named Ceravital, has higher mechanical strength and lower bioactivity.
used for encapsulation of implanted devices
. The most common use of Bioglass 8625 is in the housings of RFID transponders for use in human
and animal
microchip implants. It is patented and manufactured by Schott AG. Bioglass 8625 is also used for some piercings.
Bioglass 8625 does not bond to tissue or bone, it is held in place by fibrous tissue encapsulation. After implantation, a calcium-rich layer forms on the interface between the glass and the tissue. Without additional antimigration coating it is subject to migration in the tissue. The antimigration coating is a material that bonds to both the glass and the tissue. Parylene
, usually parylene type C, is often used as such material.
Bioglass 8625 has a significant content of iron
, which provides infrared light absorption and allows sealing by a light source, e.g. a Nd:YAG laser or a mercury-vapor lamp
. The content of Fe2O3
yields high absorption with maximum at 1100 nm, and gives the glass a green tint. The use of infrared radiation instead of flame or contact heating helps preventing contamination of the device.
After implantation, the glass reacts with the environment in two phases, in the span of about two weeks. In the first phase, alkali metal
ions are leached from the glass and replaced with hydrogen ions
; small amount of calcium ions also diffuses from the material. During the second phase, the Si-O-Si bonds in the silica matrix undergo hydrolysis
, yielding a gel-like surface layer rich on Si-O-H groups. A calcium phosphate-rich passivation layer gradually forms over the surface of the glass, preventing further leaching.
Bioglass 8625 is extensively tested in a series of studies since the 1970s. It is used in microchips for tracking of many kinds of animals, and recently in some human implants. The U.S. Food and Drug Administration
(FDA) approved use of Bioglass 8625 in humans in 1994.
Bioactive glass
Bioactive glasses are a group of surface reactive glass-ceramic biomaterials and include the original bioactive glass, Bioglass. The biocompatibility of these glasses has led them to be investigated extensively for use as implant materials in the human body to repair and replace diseased or damaged...
es, composed of SiO2, Na2O
Sodium oxide
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....
, CaO
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
and P2O5
Phosphorus pentoxide
Phosphorus pentoxide is a chemical compound with molecular formula P4O10 . This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant.-Structure:...
in specific proportions. The proportions differ from the traditional soda-lime glass
Soda-lime glass
Soda-lime glass, also called soda-lime-silica glass, is the most prevalent type of glass, used for windowpanes, and glass containers for beverages, food, and some commodity items...
es 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
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
forms on the glass-tissue interface, facilitating strong bond to the bone. Some formulations can facilitate growth of osteoblast
Osteoblast
Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin.Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen...
s 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.
| glass | SiO2 | P2O5 Phosphorus pentoxide Phosphorus pentoxide is a chemical compound with molecular formula P4O10 . This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant.-Structure:... |
CaO Calcium oxide Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature.... |
Ca(PO3)2 Calcium phosphate Calcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions .... |
CaF2 Calcium fluoride Calcium fluoride is the inorganic compound with the formula CaF2. This ionic compound of calcium and fluorine occurs naturally as the mineral fluorite . It is the source of most of the world's fluorine. This insoluble solid adopts a cubic structure wherein calcium is coordinated to eight fluoride... |
Na2O Sodium oxide Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide.... |
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 B2O3 | |||
| Bioglass 52S4.6 | 52 | 6 | 21 | 21 | ||||
| Bioglass 55S4.3 | 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 | 46.2 | 20.2 | 25.5 | 4.8 | 2.9 MgO Magnesium oxide Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds... , 0.4 K2O Potassium oxide Potassium oxide is an ionic compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive compound... |
|||
| Ceravital KGS | 46 | 33 | 16 | 5 | ||||
| Ceravital KGy213 | 38 | 31 | 13.5 | 4 | 7 Al2O3, 6.5 Ta2O5/TiO2 Titanium dioxide Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of... |
|||
| Ceravital bioactive | 40-50 | 10-15 | 30-35 | 5-10 | 2.5-5 MgO Magnesium oxide Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds... , 0.5-3 K2O Potassium oxide Potassium oxide is an ionic compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive compound... |
|||
| Ceravital nonbioactive | 30-35 | 7.5-12 | 25-30 | 3.5-7.5 | 1-2.5 MgO Magnesium oxide Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds... , 0.5-2 K2O Potassium oxide Potassium oxide is an ionic compound of potassium and oxygen. This pale yellow solid, the simplest oxide of potassium, is a rarely encountered, highly reactive compound... , 5.0-15.0 Al2O3, 5-15 Ta2O5, 1.0-5.0 TiO2 Titanium dioxide Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula . When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. Generally it comes in two different forms, rutile and anatase. It has a wide range of... |
|||
| A-W GC (Cerabone) | 34.2 | 16.3 | 44.9 | 0.5 | 4.6 MgO Magnesium oxide Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds... |
Oxyfluoroapatite Apatite Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal... /Wollastonite Wollastonite Wollastonite is a calcium inosilicate mineral that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or dolostone is subjected to high temperature and pressure sometimes in the presence of silica-bearing fluids... glass-ceramic Glass-ceramic Glass-ceramics are polycrystalline material produced through controlled crystallization of base glass. Glass-ceramic materials share many properties with both glasses and ceramics... ; 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 |
Bioglass 45S5
Bioglass 45S5, one of the most important formulations, is composed of SiO2, Na2O, CaO and P2O5. Professor Larry Hench developed Bioglass at the University of FloridaUniversity of Florida
The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
in the late 1960s. He was challenged by a MASH
Mobile Army Surgical Hospital
The Mobile Army Surgical Hospital refers to a United States Army medical unit serving as a fully functional hospital in a combat area of operations. The units were first established in August 1945, and were deployed during the Korean War and later conflicts. The U.S...
army officer to develop a material to help regenerate bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
, as many Vietnam war
Vietnam War
The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...
veteran
Veteran
A veteran is a person who has had long service or experience in a particular occupation or field; " A veteran of ..."...
s suffered badly from bone damage, such that most of them injured in this way lost their limbs.
The composition was originally selected because of being roughly eutectic.
The 45S5 name signifies glass with 45 wt.% of SiO2 and 5:1 ratio of CaO to P2O5. Lower Ca/P ratios do not bond to bone.
The key composition features of Bioglass is that it contains less than 60 mol% SiO2, high Na2O and CaO contents, high CaO/P2O5 ratio, which makes Bioglass highly reactive to aqueous medium and bioactive.
High bioactivity is the main advantage of Bioglass, while its disadvantages includes mechanical weakness, low fracture resistance due to amorphous 2-dimensional glass network. The bending strength of most Bioglass is in the range of 40–60 MPa, which is not enough for load-bearing application. Its Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...
is 30–35 GPa, very close to that of cortical bone
Cortical bone
Cortical bone, synonymous with compact bone, is one of the two types of osseous tissue that form bones. Cortical bone facilitates bone's main functions: to support the whole body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium. As its name...
, which can be an advantage. Bioglass implants can be used in non-load-bearing applications, for buried implants loaded slightly or compressively. Bioglass can be also used as a bioactive component in composite material
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
s or as powder.
The first successful surgical use of Bioglass 45S5 was in replacement of ossicles
Ossicles
The ossicles are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth . The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss...
in middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
, as a treatment of conductive hearing loss
Conductive hearing loss
Conductive hearing loss occurs when there is a problem conducting sound waves anywhere along the route through the outer ear, tympanic membrane , or middle ear ....
. The advantage of 45S5 is in no tendency to form fibrous tissue. Other uses are in cones for implantation into the jaw following a tooth extraction. Composite materials made of Bioglass 45S5 and patient's own bone can be used for bone reconstruction.
Bioglass is comparatively soft in comparison to other glasses. It can be machined, preferably with diamond tools, or ground to powder. Bioglass has to be stored in a dry environment, as it readily absorbs moisture and reacts with it.
Bioglass 45S5 is manufactured by conventional glass-making technology, using platinum or platinum alloy crucible
Crucible
A crucible is a container used for metal, glass, and pigment production as well as a number of modern laboratory processes, which can withstand temperatures high enough to melt or otherwise alter its contents...
s to avoid contamination. Contaminants would interfere with the chemical reactivity in organism. Annealing
Annealing (glass)
Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The process may be carried out in a temperature-controlled kiln known as a Lehr. Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change...
is a crucial step in forming bulk parts, due to high thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
of the material.
Heat treatment of Bioglass reduces the volatile alkali metal oxide content and precipitates apatite crystals in the glass matrix. The resulting glass-ceramic material, named Ceravital, has higher mechanical strength and lower bioactivity.
Bioglass 8625
Bioglass 8625, also called Schott 8625, is a soda-lime glassSoda-lime glass
Soda-lime glass, also called soda-lime-silica glass, is the most prevalent type of glass, used for windowpanes, and glass containers for beverages, food, and some commodity items...
used for encapsulation of implanted devices
Implant (medicine)
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. Medical implants are man-made devices, in contrast to a transplant, which is a transplanted biomedical tissue...
. The most common use of Bioglass 8625 is in the housings of RFID transponders for use in human
Microchip implant (human)
A human microchip implant is an integrated circuit device or RFID transponder encased in silicate glass and implanted in the body of a human being...
and animal
Microchip implant (animal)
A microchip implant is an identifying integrated circuit placed under the skin of a dog, cat, horse, parrot or other animal. The chips are about the size of a large grain of rice and are based on a passive RFID technology....
microchip implants. It is patented and manufactured by Schott AG. Bioglass 8625 is also used for some piercings.
Bioglass 8625 does not bond to tissue or bone, it is held in place by fibrous tissue encapsulation. After implantation, a calcium-rich layer forms on the interface between the glass and the tissue. Without additional antimigration coating it is subject to migration in the tissue. The antimigration coating is a material that bonds to both the glass and the tissue. Parylene
Parylene
Parylene is the tradename for a variety of chemical vapor deposited poly polymers used as moisture and dielectric barriers. Among them, Parylene C is the most popular due to its combination of barrier properties, cost, and other processing advantages.Parylene is green polymer chemistry...
, usually parylene type C, is often used as such material.
Bioglass 8625 has a significant content of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, which provides infrared light absorption and allows sealing by a light source, e.g. a Nd:YAG laser or a mercury-vapor lamp
Mercury-vapor lamp
A mercury-vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb...
. The content of Fe2O3
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...
yields high absorption with maximum at 1100 nm, and gives the glass a green tint. The use of infrared radiation instead of flame or contact heating helps preventing contamination of the device.
After implantation, the glass reacts with the environment in two phases, in the span of about two weeks. In the first phase, alkali metal
Alkali metal
The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
ions are leached from the glass and replaced with hydrogen ions
Hydron (chemistry)
In chemistry, a hydron is the general name for a cationic form of atomic hydrogen : most commonly a "proton". However, hydron includes cations of hydrogen regardless of their isotopic composition: thus it refers collectively to protons , deuterons , and tritons...
; small amount of calcium ions also diffuses from the material. During the second phase, the Si-O-Si bonds in the silica matrix undergo hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
, yielding a gel-like surface layer rich on Si-O-H groups. A calcium phosphate-rich passivation layer gradually forms over the surface of the glass, preventing further leaching.
Bioglass 8625 is extensively tested in a series of studies since the 1970s. It is used in microchips for tracking of many kinds of animals, and recently in some human implants. The U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
(FDA) approved use of Bioglass 8625 in humans in 1994.