Scientific report

 

GESTO

 

GESTO

Association pour l'étude des Greffes Et Substituts Tissulaires de l'Appareil Locomoteur.

Secretary office :

Bureaux de la SOFCOT
56,rue Boissonade
75014 PARIS CEDEX
Tél : + 33 (0)1.43.22.47.54
Fax :+ 33 (0)1.43.22.46.70

Chairman : D. MAINARD (Nancy - France)

Definitions

Mechanical bone properties : (Mpa = 106 N/m2) (1Kg @ 10 N) :

Compression breaking stress
Cortical bone : 150 Mpa
Spongy bone : 1 to 7 Mpa

Elastic modulus (Young) :
Cortical bone : 18000 to 20000 Mpa
Spongy bone : 70 to 80 Mpa

 

Chemical bone characterization :

The mineral fraction accounts for 70 % of the bone tissue. It is made up of calcium phosphate with an apatite structure. The crystalinity and Calcium/Phosphorus ratio are dependent on the cortical or spongious type of the bone and on the age. Numerous ions are found as trace in apatite crystals.

Average values :
Calcium : 35.5 %
Phosphorus : 18.5 %
Ca/p ratio : 1.61

The organic fraction is made up of 95 % type I collagen..

Porosity :

Expressed as a percentage, it corresponds to the ratio of the empty matter space volume to the overall material volume. The porosity is referred to as continuous if the pores are interconnected between one another, and closed if the pores open onto the outside. There is macroporosity when the pores are over 100 µm in diameter, and microporosity when the diameter is under 5 µm. The respective microporosity and macroporosity ratio and the size of the pores affect the mechanical properties and bone growth in the material. Therefore, these materials should be indicated separately when characterizing a ceramic. Imagery is the most appropriate tool (especially electronic scanning microscopy) to specify the micro and macroporosity ; mercury porometry and compactness rate only express the overall porosity.

Osteoconduction, osteoinduction, osteoformation :

Osteoconduction : a material's passive capacity to receive the bone regrowth, by means of vascular and cellular invasion from the receiving bone tissue in contact with the material.

Osteoinduction : ability to generate cellular differentiation to synthesize a mineralisable bone matrix.

Osteoformation or osteogenesis : bone matrix construction by osteoforming cells.

Bio-activity :

Bio-activity is defined as the ability to allow specific chemical reactions at the graft-receiving tissue interface. It is directly dependent on the material's chemical and physical-chemical properties, and is the opposite of bio-inertia (bio-compatible but inert materials). In terms of bone tissue, it represents the setting up of chemical links between the graft and the surrounding bone, but does not imply the existence of osteoconduction, osteoinduction or osteogenesis.

Biodegradation, biodissolution, bioresorption :

Material alteration in a biologic environment, resulting from cell, enzyme, bacteria or viral activity. Biodegradation constitutes the loss of physical properties, biodissolution is the loss of chemical properties. Bioresorption means biodegradation leading to material disappearance, the degradation products being eliminated through the kidneys or metabolized.

Ceramics :

Non metal non organic material whose formation required a pressure and temperature treatment (sintering). Ceramics have a two-phase structure. : vitreous phase (matrix), and crystalline phase (crystallized needles).

New ceramics, as opposed to conventional ceramics (terra cotta products, china, porcelain, glass), feature interesting common properties :

- high corrosion resistance
- mechanical properties in dense ceramics
- electric properties, ionic in their industrial use.

There are several ceramic families, depending on composition :

- calcium phosphates (bioactive)
- aluminum, zircon oxides (bio-inert)
- silica and tungsten carbides (bio-inert)

The science of ceramics helped develop new products :

- metal ceramics
- reinforced ceramics (reinforcement fibers)
- glass-ceramics

Abbreviation :

HAP : hydroxyapatite
TCP : tricalcium phosphate
BPC : biphasic phosphorus-calcium material