1. Chapter 5 Biomineralization
Introduction 5.1 Nucleation 5.2 Growth and morphology of crystals 5.3 Structures 5.4 Origins and structures Summary

2. Homogeneous and Heterogeneous Nucleations

3. Critical level of saturation for homogeneous and heterogeneous nucleation

4. Biomineralization
Biomineralization is the process by which living organisms produce minerals, often to harden or stiffen existing tissues
Biominerals perform a variety of roles in organisms, the most important are support, defense and protection

5. Principal components of biological materials
Calcium phosphate (hydroxyapatite Ca10(PO4)6(OH)2 + collagen
Calcium carbonate
(CaCO3) + chitin +
protein
Turtle shell, toucan beak, armadillo shell have thin layer of keratin on top.
Glass sponge has outstanding flexural toughness, diatoms. Ability to create sophisticated composites from relatively weak constituent materials.
Amorphous
Silica (SiO2 )(H2 O)n 5
Meyers et al., 2008 5

6. Basic Biomineralization Principles
Starts with an amorphous mineral phase
The main processes are nucleation and crystal growth; they depend on:
- level of supersaturation of the medium
- nature of the molecular interactions between biomineral and organic macromolecules
Organic molecules control nucleation
Proteins (organic matrix) play the most important role in biomineralization
Aragonite tiles
Aragonite crystals
Biomineralization begins when the supersaturation of this amorphous state is occur.
Organized surfaces of organic molecules act as catalysts and molecular template for oriented crystallization. 6 6

7. Minerals in Biological System7

8. Biominerals: types and functions
The most fascinating functions of mineral in the living tissues:
Reinforcement
Gravity sensors
Inertia sensors
Sensors of the Earth’s magnetic field
Optical systems
Single crystals of calcite were also used in the compound eyes of trilobites. But, single crystals of calcite are renown for their ability to doubly refract white light, suggesting that the trilobites suffered a life of continual double vision! 8
Mann, 1991 8

12. Biomineralization: Thermodynamics & Kinetics
Representation of activation energies of nucleation in the presence and absence of an organic matrix for two nonspecific polymorphs
phase transformation is dictated by the solubilities of amorphous precursor into the crystalline intermediates
AFM images; (a) pure calcite growth hillock. (b-d) growth hillocks after the addition of supersaturated solutions of (b) glycine, an achiral amino acid, (c and d) aspartic acid enantiomers. (From Orme CA)
Mann S. Biomineralization. Oxford, 2001.
Orme CA, Noy A, Wierzbickl A, McBride MT, Grantham M, TengHH, et al. Nature 2001;411:

21. Mineral Crystals TEM X-ray Diffraction antler non-stoichiometricnm
antler
bovine femur
X-ray Diffraction
2- 4 nm
(2θ)
non-stoichiometric
hydroxyapatite Ca10(PO4)6(OH)2
Scherrer Formula:
λ = 0.15 nm
B = radian
2θB = 32.2°
Thickness ~ 4 nm

25. Nanocrystalline minerals
= failure strength of the mineral
γs = surface energy
Em = elastic modulus of the mineral
h = critical dimension of the mineral
The critical length scale can be determined using the Griffith fracture criterion
Bone and teeth have nanocrystalline minerals as the reinforcement
Platelets
Abalone ~ 500 nm x 10 µm
Bone ~ 4 nm x 40 nm
H. Gao, et al., PNAS, 100[10], (2003).
Critical crack length in the mineral phase > size of the mineral
Ceramic phase does not fracture 25

26. Aspect ratio of mineral phase
The aspect ratio of the mineral phase is large (20-100)
The elastic modulus is stiffer with higher aspect ratio minerals
Spherical minerals not observed in most biological materials
β = volume fraction of mineral
Gp = shear modulus of the protein
α = aspect ratio of the mineral
Em = elastic modulus of the mineral
H. Gao, et al., PNAS, 100[10], (2003). E
α = 1 α 26

27. Biomineral-related Diseases
Study diseased, aged, and injured tissues using the Materials Science/Mechanical approaches
Kinetic studies on osteoporosis, kidney stone, metabolic arthritis, and other mineral related diseases
The use of nano-mechanic methodologies applied to regenerative medicine
AFM studies on calcium oxalate monohydrate (COM), the major inorganic component of kidney stone
Osteoporosis
Calcium oxalate monohydrate (COM), which plays a functional role in plant physiology, is a source of chronic human disease, forming the major inorganic component of kidney stones.
Qui et al. PNAS 2004;101:1811