Oriented polycrystal samples of nacre-like aragonite: biomimetic and - - PowerPoint PPT Presentation

Oriented polycrystal samples of nacre-like aragonite: biomimetic and biomedical applications

CRISMAT – ENSICAEN

Team : Crystallography et

E.R.P.C.B.

PhD directors : Daniel CHATEIGNER, Otavio GIL

Christopher KRAUSS

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Ø Aims of this study Ø CaCO3: why aragonite ? Ø Techniques Ø Results Ø Outlooks

Map

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Aims of study

• synthetic nacre for osteopathy

natural nacre is highly osteoinductive prostheses mainly in titanium medical european law: forbids animal proteins in human body

• Electrodeposition of CaCO3 in aragonitic form on

titanium

• Caracterization of obtained microstructures and

textures :

SEM backscattering X-Ray diffraction

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CaCO3: 3 allotropic forms

• Calcite (R3c - trigonal) :

too much stable form non-osteoinductive

• Vaterite (P63/mmc - hexagonal) :

non-stable form too much for applications

• Aragonite (Pmcn - orthorhombic) :

metastable form ΔG0(C->A) = -1kJ/mol

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Nacre: natural Aragonite microstructure

Pinctada maxima Nacre composition: aragonite and organic phases (2% – 5%)

Aragonite Acidic Macromolecules Silk-fibroin-like proteins β-chitin

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Techniques: Electrochemical deposition

Saturated calomel reference electrode Titanium working electrode (foil) Platinium counter electrode (grate) Potentiostat Artificial see-water electrolyte (ASTM-D1141 strd): NaCl ; Na2SO4 ; MgCl2 ; CaCl2 ; KCl ; NaHCO3

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Electrochemical deposition

Chemical reaction:

• O2 + 2H2O + 4e- 4OH-

Highly negatif potentials water reduction:

• 2H2O + 2e- 4OH- + H2
• NaHCO3 Na+ + HCO3
• CaCl2 Ca2+ + 2Cl
• HCO3
• + OH- CO3

2- + H2O

• Ca2+ + CO3

2- CaCO3

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Employed techniques: Texture analysis

• 4-Circles diffractometer for combined

analysis

• Texture program : MAUD
• Rietveld refinement: Texture index F², film

thickness… yi

calc = yi background + ∑Sφ ∑ jφh Lph Pφh(y) [Fφh]² Ωφh with

h=[hkl]*

Pφh(y) = preferred orientation correction factor

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Results: Magnesium induction

• Excluding vaterite and calcite
• Magnesic calcite less stable that aragonite

Without MgCl2 : vaterite +calcite+aragonite [MgCl2, 6H2O] = 2,73.10-2M pure aragonite

002 v 012 c 110+020 v 111a 021 a 104 c 006 c 112+022 v 110 c / 200+102 a 130+022 a 113 c 122+220 a / 202 c 221 a 018 c 116 c 132 a 111 021 012 200+102 112 211 122+220 221 041+202 132 113 231 130+022 031

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Results: Potential induction

• 0.01
• 0.009
• 0.008
• 0.007
• 0.006
• 0.005
• 0.004
• 0.003
• 0.002
• 0.001
• 1.7
• 1.6
• 1.5
• 1.4
• 1.3
• 1.2
• 1.1
• 1
• 0.9
• 0.8
• 0.7
• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

V (V) I (A)

H2O reduction area Optimum area for deposition: O2 reduction Titanium slow reduction rate Transition area: titanium reduction –

• xydation

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Results: Potential At not enough reducting potential, shape and texture differ from natural nacre: c ⊥

10 µm

F² = 1.2 m.r.d.² e = 4.7 µm

• 1.1V

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Results: Potential

• 1.4V

F² = 1.7 m.r.d.² e = 1.9 µm

5 µm

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Results: Potential At too much negative potential; gaseous H2 induces porous deposit and size, orientation inhomogeneity

• 1.5V

10 µm 2 µm

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Results: Temperature, at -1.4V Too much high temperature induces inhomogeneous growth of crystallites

40°C 60°C 50°C

5 µm 5 µm 5 µm

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I(V)

• 0,01

0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08

• 1,9
• 1,8
• 1,8
• 1,7
• 1,7
• 1,6
• 1,6
• 1,5
• 1,5
• 1,4
• 1,4
• 1,3
• 1,3
• 1,2
• 1,1
• 1,1
• 1
• 1
• 0,9
• 0,9
• 0,8
• 0,8
• 0,7
• 0,7
• 0,6
• 0,6
• 0,5
• 0,4
• 0,4
• 0,3
• 0,3
• 0,2
• 0,2

Potentiel (V) Intensité (A) WHM ES

Results: Organic phase induction

Intensity (A) Potential (V)

O2 reduction area

Working area at less negative Potentials

Used organic phases: Nacre powder of Pinctada maxima Extracted by 2 different ways: Ø WSM: water soluble, polar phase Ø ES: ethanol soluble, non-polar phase

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Results: Organic phase induction Cauliflower features, calcite and vaterite reapearance: New parameters to adjust.

WSM phase ES phase

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Perspectives

Crystallites and texture force to be improved:

• Layer optimization (Pot., T°, [C], polyacrylic acid …)
• Layer adhesion (chitosan,…)

Titanium surface (surface treatments) … Titanium foam