No Bones About It

Location:

Concepts Shown:

biocompatibility, microstructure, hydroxyapatite

Equipment:

1. Transparencies of the last three pages of this format sheet.

2. Slides of hydroxyapatite orbital implants.

Procedure:

Use overheads and slides to present material. Form a table on the chalkboard which has three headings (temporary, semi-permanent, and permanent) and have students help fill in chart.

Science:

Biocompatibility: A biocompatible material is one such that the body does not suffer any adverse effects when placed in or used upon the body. Biocompatibility is determined by physical properties. Physical properties are determined by microstructure. Hydroxyapatite (HA) Chemical formula: Ca10(PO4)6(OH)2. Reaction used to form HA: 2CaHPO4 + 2 Ca4(PO4)O = Ca10(PO4)6(OH)2. Applications: Implants: Temporary Semi-permanent Permanent Uses: Teeth Leg bone Eye Jaw Skull Socket Picture of jaw is included. Purpose: Temporary: To build in non-critical medical situations. Semi: To provide immediate support and eventual regeneration of bone. Permanent: To fill space and provide support when soft tissue (eye) is lost. Properties: Strength of material: Porosity effects strength. As porosity increases, strength decreases. Biodegradability: The body�s ability to reabsorb a material. The following properties increase biodegradation. 1. Increase in surface area (powder/porous/dense) 2. Crystallinity decrease (amount of tetragonal calcium phosphate increase fig. 13) 3. Crystal perfection decrease 4. Crystal and grain size decrease 5. Ionic Substitutions. Microstructures: Implants Temporary Semi-permanent Permanent Porosity high (powder)* medium low Strength low moderate(100um) high Reabsorption high steady *** never Surface Area high medium low Crystallinity low medium high Perfection low medium high Size low medium high Ions high medium low Example: fig. 7 (fine) fig. 8 (finer) fig. 9-13** Microstructures are only dependent on temperature of processing. It is all the same material. * Powder and blood are mixed and injected into bone deficient areas. ** Microstructure is such that dense hydroxyapatite is surrounded by large pores which provide areas for tissue and vessel growth. *** Bone will only grow into material with approximately 100um porosity. Conclusion: Microstructure Properties Function & biocompatibility. Comments: Overheads are very helpful and easy to use. Slides can be used but are not necessary. Hydroxyapatite (HA) Chemical formula: Ca10(PO4)6(OH)2 Reaction used to form HA: 2CaHPO4 + 2Ca4(PO4)2O = Ca10(PO4)6(OH)2. Properties: Strength of material: Porosity effects strength. As porosity increases strength decreases. Biodegradability: The bodies ability to reabsorb a material. The following properties increase biodegradation. 1. Increase in surface area (powder/porous/dense). 2. Crystallinity decrease. 3. Crystal perfection decrease. 4. Crystal and grain size decrease. 5. Ionic substitutions. [eq].

References:

Author:
Marcia Muller
Credits:


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