Bioactive glass
Encyclopedia
Bioactive glasses are a group of surface reactive glass-ceramic
biomaterial
s 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 bone
.
first developed these materials in the late 1960s and they have been further developed by his research team at the Imperial College London
and other researchers worldwide. hi
(FDA) approved and termed Bioglass. This composition is known as 45S5. Other compositions are in the list below.
. Early attention was paid to changes in the bioactive glass surface. Five inorganic reaction stages are commonly thought to occur when a bioactive glass is immersed in a physiological environment: 1) Ion exchange in which modifier cations (mostly Na+) in the glass exchange with hydronium
ions in the external solution, 2) Hydrolysis
in which Si-O-Si bridges
are broken, forming Si-OH silanol groups, and the glass network is disrupted, 3) Condensation of silanols in which the disrupted glass network changes its morphology to form a gel-like surface layer, depleted in sodium and calcium ions 4) Precipitation in which an amorphous calcium phosphate layer is deposited on the gel, and 5) Mineralization in which the calcium phosphate layer gradually transforms into crystalline hydroxyapatite, that mimics the mineral phase naturally contained with vertebrate bones. Later, it was discovered that the morphology of the gel surface layer was a key component in determining the bioactive response. This was supported by studies on bioactive glasses derived from sol-gel processing. Such glasses could contain significantly higher concentrations of SiO2 than traditional melt-derived bioactive glasses and still maintain bioactivity (i.e., the ability to form a mineralized hydroxyapatite layer on the surface). The inherent porosity of the sol-gel-derived material was cited as a possible explanation for why bioactivity was retained, and often enhanced with respect to the melt-derived glass.
Subsequent advances in DNA microarray
technology enabled an entirely new perspective on the mechanisms of bioactivity in bioactive glasses. Previously, it was known that a complex interplay existed between bioactive glasses and the molecular biology of the implant host, but the available tools did not provide a sufficient quantity of information to develop a holistic picture. Using DNA microarrays, researchers are now able to identify entire classes of genes that are regulated by the dissolution products of bioactive glasses, resulting in the so-called "genetic theory" of bioactive glasses. The first microarray studies on bioactive glasses demonstrated that genes associated with osteoblast
growth and differentiation, maintenance of extracellular matrix
, and promotion of cell-cell and cell-matrix adhesion were up-regulated by conditioned cell culture media containing the dissolution products of bioactive glass.
NMR spectroscopy. The chemical shift from MAS NMR is indicative of the type of chemical species present in the glass. The 29Si MAS NMR spectroscopy showed that Bioglass 45S5 was a Q2 type-structure with a small amount of Q3 ; i.e., silicate
chains with a few crosslinks. The 31P MAS NMR revealed predominately Q0 species; i.e., PO43-; subsequent MAS NMR spectroscopy measurements have shown that Si-O-P bonds are below detectable levels
:
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...
biomaterial
Biomaterial
A biomaterial is any matter, surface, or construct that interacts with biological systems. The development of biomaterials, as a science, is about fifty years old. The study of biomaterials is called biomaterials science. It has experienced steady and strong growth over its history, with many...
s and include the original bioactive glass, Bioglass
Bioglass
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 , high amount of sodium and calcium, and high calcium/phosphorus ratio.High ratio of...
. The biocompatibility
Biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used , or to more empirical clinical success of a whole device in...
of these glasses has led them to be investigated extensively for use as implant
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...
materials in the human body to repair and replace diseased or damaged 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...
.
History
Larry Hench and colleagues 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...
first developed these materials in the late 1960s and they have been further developed by his research team at the Imperial College London
Imperial College London
Imperial College London is a public research university located in London, United Kingdom, specialising in science, engineering, business and medicine...
and other researchers worldwide. hi
Compositions
There have been many variations on the original composition which was Food and Drug AdministrationFood 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 and termed Bioglass. This composition is known as 45S5. Other compositions are in the list below.
- 45S5: 46.1 mol% SiO2Silicon dioxideThe chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
, 26.9 mol% CaOCalcium oxideCalcium 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....
, 24.4 mol% Na2OSodium oxideSodium 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....
and 2.5 mol% P2O5Phosphorus pentoxidePhosphorus 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:...
. BioglassBioglassBioglass 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 , high amount of sodium and calcium, and high calcium/phosphorus ratio.High ratio of... - 58S: 60 mol% SiO2Silicon dioxideThe chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
, 36 mol% CaOCalcium oxideCalcium 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 4 mol% P2O5Phosphorus pentoxidePhosphorus 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:...
. - S70C30: 70 mol% SiO2Silicon dioxideThe chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
, 30 mol% CaOCalcium oxideCalcium 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....
.
Mechanism of bioactivity
The underlying mechanisms that enable bioactive glasses to act as materials for bone repair have been investigated since the first work of Hench et al. 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...
. Early attention was paid to changes in the bioactive glass surface. Five inorganic reaction stages are commonly thought to occur when a bioactive glass is immersed in a physiological environment: 1) Ion exchange in which modifier cations (mostly Na+) in the glass exchange with hydronium
Hydronium
In chemistry, a hydronium ion is the cation , a type of oxonium ion produced by protonation of water. This cation is often used to represent the nature of the proton in aqueous solution, where the proton is highly solvated...
ions in the external solution, 2) 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...
in which Si-O-Si bridges
are broken, forming Si-OH silanol groups, and the glass network is disrupted, 3) Condensation of silanols in which the disrupted glass network changes its morphology to form a gel-like surface layer, depleted in sodium and calcium ions 4) Precipitation in which an amorphous calcium phosphate layer is deposited on the gel, and 5) Mineralization in which the calcium phosphate layer gradually transforms into crystalline hydroxyapatite, that mimics the mineral phase naturally contained with vertebrate bones. Later, it was discovered that the morphology of the gel surface layer was a key component in determining the bioactive response. This was supported by studies on bioactive glasses derived from sol-gel processing. Such glasses could contain significantly higher concentrations of SiO2 than traditional melt-derived bioactive glasses and still maintain bioactivity (i.e., the ability to form a mineralized hydroxyapatite layer on the surface). The inherent porosity of the sol-gel-derived material was cited as a possible explanation for why bioactivity was retained, and often enhanced with respect to the melt-derived glass.
Subsequent advances in DNA microarray
DNA microarray
A DNA microarray is a collection of microscopic DNA spots attached to a solid surface. Scientists use DNA microarrays to measure the expression levels of large numbers of genes simultaneously or to genotype multiple regions of a genome...
technology enabled an entirely new perspective on the mechanisms of bioactivity in bioactive glasses. Previously, it was known that a complex interplay existed between bioactive glasses and the molecular biology of the implant host, but the available tools did not provide a sufficient quantity of information to develop a holistic picture. Using DNA microarrays, researchers are now able to identify entire classes of genes that are regulated by the dissolution products of bioactive glasses, resulting in the so-called "genetic theory" of bioactive glasses. The first microarray studies on bioactive glasses demonstrated that genes associated with 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...
growth and differentiation, maintenance of extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
, and promotion of cell-cell and cell-matrix adhesion were up-regulated by conditioned cell culture media containing the dissolution products of bioactive glass.
Structure
Solid state NMR spectroscopy has been very useful in elucidating the structure of amorphous solids. Bioactive glasses have been studied by 29Si and 31P solid state MASMas
Mas or Más may refer to:* Mas , a surnameIn arts:* Más , an album by Spanish singer Alejandro Sanz* "Más", a song by Kinky from their 2002 album Kinky...
NMR spectroscopy. The chemical shift from MAS NMR is indicative of the type of chemical species present in the glass. The 29Si MAS NMR spectroscopy showed that Bioglass 45S5 was a Q2 type-structure with a small amount of Q3 ; i.e., silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
chains with a few crosslinks. The 31P MAS NMR revealed predominately Q0 species; i.e., PO43-; subsequent MAS NMR spectroscopy measurements have shown that Si-O-P bonds are below detectable levels
Medical applications
Bioactive glasses have many applications but these are primarily in the areas of bone repair and bone regeneration via tissue engineeringTissue engineering
Tissue engineering is the use of a combination of cells, engineering and materials methods, and suitable biochemical and physio-chemical factors to improve or replace biological functions...
:
- Synthetic bone graftMedical graftingGrafting refers to a surgical procedure to move tissue from one site to another on the body, or from another person, without bringing its own blood supply with it. Instead, a new blood supply grows in after it is placed. A similar technique where tissue is transferred with the blood supply intact...
materials for general orthopaedic, craniofacial (bones of the skull and face), maxillofacial and periodontalPeriodontologyPeriodontology or Periodontics is the specialty of dentistry that studies supporting structures of teeth, diseases, and conditions that affect them...
(the bone structure that supports teeth) repair. These are available to surgeons in a particulate form - Cochlear implants
- Bone tissue engineering scaffolds. These are being investigated in many forms, in particular as porous (contains pores into which cells can grow and fluids can travel) 3-dimensional scaffolds
- Treating dentine hypersensitivityDentine hypersensitivityDentine hypersensitivity is sensation felt when the nerves inside the dentin of the teeth are exposed to the environment. The sensation can range from irritation all the way to intense, shooting pain...
and promoting enamel remineralization
See also
- Porous mediumPorous mediumA porous medium is a material containing pores . The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a fluid...
- Ceramic foamCeramic foamCeramic foam is a tough foam made from ceramics. Manufacturing techniques include impregnating open-cell polymer foams internally with ceramic slurry and then firing in a kiln, leaving only ceramic material...
- NanofoamNanofoamNanofoams are a class of nanostructured, porous materials, foams, containing a significant population of pores with diameters less than 100 nm. Aerogels are one example of nanofoam.- Metal Nanofoams :...
- Metal foamMetal foamA metal foam is a cellular structure consisting of a solid metal, frequently aluminium, containing a large volume fraction of gas-filled pores. The pores can be sealed , or they can form an interconnected network . The defining characteristic of metal foams is a very high porosity: typically...
- OsseointegrationOsseointegrationOsseointegration derives from the Greek osteon, bone, and the Latin integrare, to make whole. The term refers to the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant...