Biological ceramics - biomineralization

Question 1

Give some examples of biological ceramics

Answer 1

Mollusc Shell, bone, teeth, egg shell

Question 2

Which elements does ceramics usually contain

Answer 2

calcium or silica

Question 3

What are the mechanical properties of ceramics

Answer 3

components are brittle but overall composite have excellent properties due to orientation, stiff and strong

Question 4

How can brittle behavior be prevented?

Answer 4

Crazing, multilayer (plywood), debonding and yielding/plasticization (dissipate molecules and energy)

Question 5

What needs to be controlled when growing crystals

Answer 5

The size, form , orientation, chemical composition, crystalline structure and the interaction with matrix

Question 6

What important components does nacre consists of?

Answer 6

It is a composite of Chitin (polysaccharide), Aragonite (CaCO3 mineral) and proteins

Question 7

What makes nacre so tough despite its brittle components?

Answer 7

The crystal calcium carbonate plates are bound together with protein matrix. Crazing often happens

Question 8

How does crystal grows

Answer 8

By directed growth by the matrix, epitaxial growth. Cells produce proteins and polysaccharides (chitin) which becomes the matrix/template that can absorb ions like calcium and carbonate to grow the crystal.

Question 9

What is the hierarchical structure of bone?

Answer 9

Hydroxyapatite mineralized collagen - tropocollagen (triple helix) - collagen fibril - llamellae (twisted plywood arrangement) - osteon - compact bone

Question 10

What’s the role of osteocytes

Answer 10

Maintain bone tissue

Question 11

What’s the role of osteoblasts

Answer 11

Forms bone matrix and surrounded collagen fibers. Then becomes osteocyte

Question 12

What’s the role of osteogenic cell

Answer 12

stem cell

Question 13

What’s the role of osteclasts

Answer 13

resorbs/degrade bone which helps with the continous remodeling of replacing old and damaged bone

Question 14

What is bone formation also called?

Answer 14

Ossification

Question 15

What is intra membranous ossification?

Answer 15

Bone is formed by direct mineralization of the matrix secreted by osteoblasts

Question 16

What is Endochondral ossification?

Answer 16

A cartilage model serves as the precursor of the bone

Question 17

How is bone formed?

Answer 17

Osteoblasts secrete bone matrix and collagen fibers that initiates crystallisation process of hydroxyapatite (HA) that creates thin crystal plates

Question 18

What is calcification?

Answer 18

The formation of calcium-based salts and crystals within cells and tissue

Question 19

How is Bone composed as a composite?

Answer 19

65-70% crystalline hydroxyapatite that reinforce the collagen fibers. Also contain pores that works as cell holders. The collagen fibrils are organized in both an oriented way and randomly.

Question 20

What does teeth mainly consists of and describe these

Answer 20

Dentin - collagen in tubular form with calcified zone

Enamel - a coating with dahllite crystals (carbonate apatite)

Question 21

What does enamel consists of?

Answer 21

Mainly two different proteins:

• Acidic enamelin covalently bonded to polysaccharides
• Hydrofobic amelogenin

Question 22

What makes dentin tough?

Answer 22

It’s tubular construction and the orientation of the collagen layers. The cracks must always pass through several layers of collagen.

Question 23

What makes enamel tough?

Answer 23

The week boundary layer between the crystals and thir “fiber” form

Question 24

What are egg shells mainly composed of?

Answer 24

96-98 % calcite (CaCO3)

Question 25

What are the three main components of bone?

Answer 25

Bone is a composite of hydroxyapatite mineral, collagen and water

Question 26

What are the main intrinsic toughening mechanism of bone?

Answer 26

Molecular uncoiling (tropocollagen), diffuse damage between molecules such as collagen and hydroxyapatite (sacrificial bonding), fibrillar sliding (sacrificial bonding)

Question 27

Whats the difference of intrinsic and extrinsic?

Answer 27

Intrinsic toughening: Molecular uncoiling and intermolecular sliding of collagen, micro-cracking of the mineral matrix
Extrinsic toughening: collagen fibril bridging, uncracked ligament bridging, crack deflection and twisting

Question 28

What’s the hierarchical structure of abalon nacre?

Answer 28

1. Aragonite/calcium carbonate + chitin chains 2. Mineral bridges + chitin matrix 3. Hexagonal Tiles + organic matrix layer 4. Mesolayer related to growth cycle 5. The entire abalon structure