Porous structures, bionics, fiber spinning, 3D printing

Question 1

What is often needed to be done before working with cellulose nanofibrils (CNS)?

Answer 1

They doesn’t melt so to be able to work with them (like 3D printing) they need to be a gel/foam/hydrogel/emulsion. The gels are often 97% water.

Question 2

What is the layer by layer (LBE) method?

Answer 2

Important for packaging and to create multilayer films. The method is based on electrostatic interaction with positive and negative charged nanocelluloses. Give different layers, and do not become neutral since only the surface interact.

Question 3

What is QCM D?

Answer 3

A technique based on the quartz crystal oscillating due to the piezoelectric effect. The mass can be found of a substance. When it is absorbed on the surface the frequency change and correlates to the mass.

Question 4

How can CNF be used as an adhesive?

Answer 4

It mimics a mussel that can attach to most surfaces under water. The CNF can be chemically modified to become an multilayer adhesive film. Works with metal-induced cross-linking where Dopamine form a metal-organic complex with a metal ion. this complex is very sticky.
This film can be used as an anti-corrosive film for metals /cars.

Question 5

Is CNFC visible?

Answer 5

No, it cannot be seen alone, but in complex with DOPA it can be seen in the UV-visible spectra.

Question 6

Whats the definition of a gel?

Answer 6

A gel is a diluted cross-linked system which exhibits no flow when in steady-state. Low amount of material. The cross-linking is either chemical or physical.

Question 7

What’s the def. of foam?

Answer 7

A substance formed by trapped pockets of gas in a liquid or solid.

Question 8

What’s an aerogel?

Answer 8

If you replace your solvent with air it is called aerogel. The surface area for one gram can be several hundred square METERS. Can be used to carry water, wound healing, packaging materials, energy storage (many thing can be stored).

Question 9

How is an aerogel created?

Answer 9

Water will evaporate and the gel will collapse so to prevent this you freeze-dry it (freeze in vacuum). This will create a aerogel! The freezing step form ice-crystals. The crystals expand and compress the nanofibrils - form sheet-like structures. If the dry material/aerogel is wetted again - it will keep structure if the stirring is not to much. If the material is modified with carboxylic acid the material becomes like a sponge, it is elastic and can absorb water like a regular sponge.

Question 10

What can the CNF aerogel be used as?

Answer 10

It’s flexible, compressible, quick to fabric and can store charges. The film can be used to store polymers in the pores (channels). Can be used as a supercapacitor and a battery. The CNT is electrode 1, then a polymer is used as a separator (in the pores), then electrode 2 is CNT. It is bendable, compressible and rechargeable.

Question 11

Whats the difference of technical biology vs. bionics

Answer 11

Technical biology - the aim is to understand nature with input from technology.
Bionics - combine biology and technology. The aim is to find a solution of technical problems with input from nature.

Question 12

What is structural bionics?

Answer 12

Exploration of processes how structures are formed (e.g. in complex, hierarchically organized materials). Example is Honey comb vs corrugated cardboard

Question 13

What is construction bionics?

Answer 13

Efficient use of space (area/use), Orientation (sun/wind), Lightweight construction (increase of mechanics), Recyclability, Membranes and shells

Question 14

What is movement bionics?

Answer 14

Flow adjustment of animals (e.g. sharkskin - wet suit), analysis of motion (drive mechanisms for cars etc.)

Question 15

What are device bionics?

Answer 15

Development of machines and devices like pumps, hydraulic/pneumatic devices, systems for collecting water, oils and other resources.

Question 16

What are engineering of technologies?

Answer 16

Engineering elements and functional mechanisms of nature. Comparison to analogous technologies in engineering e.g. Velcro fastener mimics “thistles” with their small hooks

Question 17

What is anthrobionics?

Answer 17

Optimization of human-machine-interactions: Performance increase in robotics, Ergonomic design of user surfaces and displays, Efficiency increase in muscle-driven locomotion. Ex. Robotic arm

Question 18

How can bionics be used in neurology?

Answer 18

Neuronal circuits, biochips, neurobiology and biologic cybernetics (biocybernetics)

Question 19

What is sensor technology bionics?

Answer 19

Translation of engineering constructs of biologic sensing (e.g. bat echo sound/sonar), Ultrasonics, Electrolocalization, IR radiation, odor. Can be used for sensors for parking and explosives detection.

Question 20

What is process bionics?

Answer 20

Control of complex biologic processes (like electron transport chain). Translation of (nearly) complete recycling to industrial production. Cybernetic process control at complex industrial facilities.

Question 21

What is energy balance bionics?

Answer 21

Reduction of energy consumption, higher comfort/quality of living passive ventilation, cooling/heating according to housing of animals (termites)

Question 22

How is the top down approach used when designing bionic materials?

Answer 22

Analysis of the problem - search for analogies in nature - analysis of the analogies - explore solutions

Question 23

How are car tires optimized by bionics?

Answer 23

When the cheetah’s running straight the paws are narrow but when turning or braking they widen. This knowledge is used for tires which have contours that can widen and narrow.

Question 24

How are winglets optimized by bionics?

Answer 24

To minimize the problem with turbulence they try mimicking bird feather => many small vortexes instead of one vortex.

Question 25

How is the bottom up approach used when designing bionic materials?

Answer 25

Fundamental research is made - understanding of the principle of action - Abstraction - explore applications and translation.

Question 26

How are the bottom up approach used with lotus leaves?

Answer 26

Lotus leaves have a self cleaning mechanism that help the surface stay dry and clean. Water just rolls of and bring with dirt particles. The mechanism is due to the structure which have small tips. Material prep. made by extrusion, 2D/3D printing, dip-coating, spraying, spincoating and patterning by lithography and phase separation

Question 27

How does spin coating work and what is it used for?

Answer 27

It is used to manufacture thin films and modify flat substrates.
The substrate is fixed on a sample disk via vacuum. Then the solution (ex. polymer) is added to the plate from above while disk is rotated. The rotation make the solution spread out => film/coat. Important Parameter is speed, acceleration, time.

Question 28

What is photolithography?

Answer 28

The basic idea is to change solubility of a film by exposing it to UV-light to be able to make patterns. UV induces crosslinking, polymerization, cleavage/addition of functional groups and development of the films. Photolabile functionalities required, either directly at polymers or via addition of initiators or photoacid/base generators. Photomasks: opaque plate with pattern in the micrometer area

Question 29

What is DNA origami

Answer 29

Uses folding of DNA to create 2/-3 dimensional shapes at the nanoscale. The specificity of the BPs make DNA useful as construction material. It hold other molecules in place or just create a structure on its own. Can be used in drug delivery.

Question 30

What’s the properties of a textile fiber?

Answer 30

A semi-crystalline polymer length 15-150 mm with diameter 10-50 μm. high tenacity (strength per linear density), recoverable extensibility, take colour, heat resistant to chemicals and heat up to 200.
Linear density - g/m

Question 31

How are fibers manufactured?

Answer 31

1. Preparation of a spinnable liquid. The polymer is dissolved or melted. Control of the viscosity is an important factor.
2. Extrusion of the liquid through a spinneret (die) to form a jet
3. Jet hardening. The polymer is solidified by cooling or solvent removal.
4. Cool or warm drawing
5. (Surface treatment, texturing, cutting)
   This creates a manufactured fiber which is always continous with cuttable filaments (cut to staple fibers).

Question 32

How does melt spinning work?

Answer 32

Most common, used to make fibers from nylon, polyester. The polymer is melted in the extruder and fed to the spinneret which has many small holes. the melt is pressed through the spinneret and when out it is cooled down with an air stream and drawn until it is solidified. The resulting fiber depends on polymer density and the melt draw ratio (spinneret to solidification). Cold drawing before winding increase the fibers tenacity.

Question 33

Why is cold drawing good?

Answer 33

After the spinneret the chains are in semi-crystalline state but not oriented. Cold drawing breaks up the semi-crystalline structure and induces orientation in the fiber direction. The goal is to have fullt oriented and extended chains.

Question 34

What is solution spinning?

Answer 34

The polymer cannot be maintained as a melt, instead it is dissolved in a solvent before spinning. Wet or dry, depending on how they are solidified. Examples of wet spun polymers are rayon, acrylic, aramid, and spandex.

Question 35

How does dry spinning work? One type of solution spinning

Answer 35

The spinning solution is pumped through the spinneret with thousands of holes. When the solution is extruded into the drawing step hot air is blown over it to make the solvent evaporate. The solvent can be reused.

Question 36

How does wet spinning work? One type of solution spinning

Answer 36

For polymers that need to be dissolved in a solvent to be spun. The spinneret is submerged into chemical bath (nonsolvent) causing the fiber to precipitate and then solidify as it emerges. Then the fiber is going through a stretch bath before winding.

Question 37

How does dry-jet (air-gap) spinning work?

Answer 37

Useful to make strong fibers! Aramids polymer chains are
extremely rigid. For solution
spinning, the polymer is
dissolved in H2SO4 and
extruded into cold water
through an air gap.
The air gap aids orientation of liquid-crystalline polymers.

Question 38

Which two spinning methods creates the strongest and stiffest fibers?

Answer 38

Require fully oriented and extended chains of the fiber. Entanglement is removed. Done with spinning in the liquid-crystalline state or by gel spinning

Question 39

How does spinning in the liquid-crystalline state work?

Answer 39

Polymers with a stiff main chain may form liquid crystals. In that state the polymer chains are fully extended and with an orientation that lead to low viscosity. A rapid quench preserve the extended state. Kevlar - benzene ring make polymer extremely rigid.

Question 40

How does gel spinning work?

Answer 40

To obtain high strength fibers. The polymer, often of high molecular weight, is dissolved at a high temperature, and substantially drawn while in a gel state. high molecular weight polymers have the ability to entangle even at small conc. and create a gel. A rapid precipitation leads to crystallization with a low entanglement density. The fiber can then be drawn much more than after e.g. melt spinning.

Question 41

What’s the main difference of a fabric produced through weaving vs. knitting?

Answer 41

Knitted fabrics are stretchable and flexible while weaved are not so much.

Question 42

What’s a nonwoven?

Answer 42

In nonwovens the fibers are laid down with or without orientation and bonded by friction and/or cohesion and/or adhesion.

Question 43

What is good about 3D printing?

Answer 43

Cost effective, material use, on demand, storage, transport, specialized products, health care (wound healing bandage, printed tissue)

Question 44

What’s the main challenge when 3D printing wood polysaccharides? How can it be solved?

Answer 44

They do not melt and cellulose does not dissolve in common in-/organic solvents. So the common extrusion step is hard. Can be solved by using water in which the cellulose creates a gel.

Question 45

Which 3 methods are there for 3D printing?

Answer 45

1. Inkjet bioprinter
2. Microextrusion bioprinter - air or piston pressure is applied from the top. most common and most cell friendly.
3. Laser-assisted - print then solidify then print another layer. repeat

Question 46

What is shear thinning?

Answer 46

When shear strain is applied the liquid get lower viscosity but as soon as the shear stops it regains its initial viscosity.

Question 47

What’s the difference between biomimetics and bionics?

Answer 47

Bionics are more of the technical side, the technical advances that take inspiration from nature. The design of engineering systems especially electronic ones based on that of biological systems.
Biomimetics is the study of the structure and function of living things as models for the creation of materials or products by reverse engineering.

Question 48

List 5 bioinspired designs

Answer 48

1. Cheetah paws - Car tires
2. Lotus leaf - self cleaning surfaces
3. Honey comb - card board
4. Shark skin - wet suit
5. Thistle - Velcro fastener
6. Bat ultrasonics - sensor for parking
7. Bird wings - aircraft winglets