BS ISO 23317:2007 Implants for surgery. In vitro evaluation for apatite-forming ability of implant materials
BS ISO 23317 is the international standard that describes the method for detecting apatite formed on a surface of a material in simulated body fluid.
Materials of various kinds bind to living bone through a layer of apatite. This apatite layer can be reproduced on their surfaces in an acellular and protein-free simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. The apatite formed has a similar composition and structure to bone mineral.
This evaluation of apatite-forming ability on implant material in SBF is useful for evaluating its ‘in vivo’ bonebonding ability preliminary to animal experiments. When a bioactive material is implanted in a living body, a thin layer rich in Ca and P forms on its surface. The material then connects to the living tissue through this apatite layer without a distinct boundary. This apatite layer can be reproduced on the surfaces of materials in SBF as well, and forms apatite which is similar to bone mineral in its composition and structure.
As bioactivity increases, apatite forms on the material surface in a shorter time in proportion to this increase. The formation of apatite layers can be detected by thin film X-ray diffraction spectrometry and/or scanning electron microscopy.
The material that forms apatite on its surface ‘in vivo’ can bond to living bone, since this apatite is biologically active. Their ‘in vivo’ apatite deposition can be reproduced on their surfaces even ‘in vitro’ in SBF. For example, ‘in vivo’ calcification on surfaces of Bioglass®, CaO-SiO2 glasses, Na2O-CaO-SiO2 glasses, Cerabone®A-W, Ceravital®-type glass-ceramic, sintered hydroxyapatite and alkali-heat-treated titanium metal, are correlated with in vitro calcification in SBF. However, this does not exclude the possibility that materials, which do not form apatite on their surfaces ‘in vivo’, bond to living bone.
For example, it is reported that such resorbable materials as beta-tricalcium phosphate (Ca3(PO4)2) and calcium carbonate bond to living bone without forming an apatite layer on their surfaces.
It has been reported that glasses with different compositions in the system Na2O-CaO-SiO2 show a correlation between bone-forming ability of materials implanted into a bone defect of a rabbit and apatite-forming ability on its surface in SBF.
Contents of BS ISO 23317 include:
- Foreword
- Introduction
- Scope
- Normative references
- Terms and definitions
- Apparatus
- Test specimen
- Specimen configuration and size
- Specimen preparation
- Simulated body fluid
- Reagents for SBF
- Ion concentrations and pH of SBF
- Preparation of SBF
- Confirmation of ion concentration of SBF
- Preservation of SBF
- Procedure
- Test report
- Apparatus for preparing SBF
- Preparation of standard glasses for evaluating apatite-forming ability
- Bibliography
