Biological materials introduction

Question 1

Def. Biological material

Answer 1

Material produced by biological systems, natural materials

Question 2

Def. Biomaterial

Answer 2

A material for implantation or incorporation in a living organism, can both be synthetic and biological for biomedical application

Question 3

Def. Biocomposite

Answer 3

A composite structure tat is constructed of partly/completely of natural materials

Question 4

Def. Biomimetics

Answer 4

Imitation of a system from nature, bio-inspired (for solving an engineering problem), does not have to be a biological material

Question 5

How is biological materials often formed and under which conditions?

Answer 5

Formed by self-assembly, most often bottom up, in mild conditions, in ambient temperature and pressure and aqueous conditions.

Question 6

Some typical properties of biological materials

Answer 6

1. Multi-functional: serve many purposes (e.g. bone)
2. Hierarchy: Different organized scale levels.
3. Hydration: Properties often dependent on hydration i.e level of water in the structure. Usually hydration decease strength and increase toughness.
4. Self-healing capacity

Question 7

Name some pros for why using biological materials

Answer 7

1. Sustainability: renewable, biodegradable
2. Structure: multi-phase materials, hierarchically organized
3. Performance: Often better than man-made, interact with water
4. Manufacturing: In room temp. without solvents, minimum energy consumption

Question 8

Name some non-mineralized “soft” structures

Answer 8

Typically fibrous constituents

1. Collagen (bone, dentine, blood vessels)
2. Keratin (hair, horn)
3. Chitin
4. Cellulose, heicellulose
5. Elastin (skin, lungs, artery walls)

Question 9

Name some mineralized “hard” structures

Answer 9

Typically consisting of hierarchically assembled composites of minerals and organic fibrous components
Minerals: Hydroxyapatite, Calcium carbonate, amorphous silica
Fibrous components: collagen and chitin

Question 10

What mechanical pros does spider silk have

Answer 10

extremely strong and tough

Question 11

What mechanical pros does shells and bone have

Answer 11

Extremely tough

Question 12

Whats the weakness of minerals vs. biopolymers

Answer 12

Tension vs. compression

Question 13

What defines Young’s modulus

Answer 13

Longitudinal stress divided by the strain

Question 14

Mechanical performance of biominerals

Answer 14

high stiffness, low toughness, linear stress-strain plot

Question 15

Mechanical performance of biopolymers

Answer 15

J shaped stress-strain plot, strong and extensible (high tensile strength), high toughness, low young’s modulus

Question 16

Mechanical performance of composites

Answer 16

high toughness

Question 17

Mechanical performance of foams

Answer 17

compressible

Question 18

Name a common bioplymer

Answer 18

Collagen (tendon, ligaments, skin and bone)

Question 19

Whats the hierarchical level of collagen 1

Answer 19

poly-peptides - tropocollagen - fibrils - fibers - fascicles (bundle)

Question 20

Describe the stretching of spider silk

Answer 20

low level: amorphous strands are straightened

higher level: the crystalline beta-sheets sustain the load

Question 21

What makes the bioelastomer whelk egg case strong/tough

Answer 21

Native state is alpha-helices but when stressed by strain they are extended and eventually oriented into strong beta-sheets

Question 22

What defines thoughness

Answer 22

The amount of energy a material can absorb before it fails

Question 23

What makes nacre so though

Answer 23

It has growth layers/tiles with mineral bridges between. If a crack occur it has to travel around the tiles instead of through. The tiles also have a rough surface which creates frictional resistance.

Question 24

What makes the lobsters exoskeleton so though?

Answer 24

Have a twisted plywood structure of chitin. The layers of chitin are mineralized and cracks cannot follow a straight line, thereby increasing the toughness. The minerals fracture and the chitin fibers absorbs the strain. There is no physical separation which means self-healing can take place.

Question 25

What is bone a composite of:

Answer 25

hydroxyapathite mineral, collagen and water

Question 26

How can you increase bending resistance with light-weight materials

Answer 26

with a dense,stiff outer layer that is resistance to flexural tractions and with a low density core for light weight. ex. plants, “stickor på djuret”

Question 27

How many hierarchical levels does biological materials have compared to synthetic

Answer 27

biological have 4-8 while synthetic only have 2-3

Question 28

Give example of 2 hierarchical biological materials

Answer 28

Wood and nacre

Question 29

What is the pros and cons of many hierarchical levels

Answer 29

The strength decreases due to existence of flaws but toughness increases to counteract this. ex. A growing crack will encounter extrinsic and intrinsic barriers as it propagates

Question 30

How does surface hierarchy help lotus leaves?

Answer 30

Pilars on pilars with wax on the smallest ones creates a self-cleaning mechanism

Question 31

How can a material be antimicrobial

Answer 31

It has to distract the bacterial cytoplasmic membrane. It can do this by having cationic peptides/polymers that can absorb and thereby distract negative charged membranes

Question 32

What imaging techniques can be used

Answer 32

Scanning/transmission electron microscopy and atomic force microscopy and x-ray cattering techniques

Question 33

Whats are the 7 items that define biological materials?

Answer 33

1. Formed by self-assembly
2. Multi-functionality
3. Hierarchy
4. Hydration (dependent on water content)
5. Ambient synthesis conditions
6. Environmental constrains (Availability of building blocks)
7. Self-healing capacity