Yinyin Bao Gyoza

Question 1

Why and when is additive manufacturing efficient? Example?

Answer 1

3D printing is an additive technique, you don’t have waste of material

3D printing is not fast as subtractive (machining) or formative (molding) manufacturing BUT for fewer units like in biomedicine, you have a way lower cost per unit.

Question 2

2 main 3D printing approaches

Answer 2

1. Light based: photopolymerization, also called stereolithography SLA, chemical process
2. Extrusion based: deposition of a filament, physical process

Question 3

SLA 3D printer: working principle & components

Answer 3

Light on the bottom and platform on the top –> solid is formed out of the liquid

• Photoinitiator: forms radical that start the polymerization, example: BAPO
• Photoactive monomer: example butyl acrylate
• Crosslinkable monomer: to crosslink the chains, example: PEGDA
• Light absorber: used to minimise the light penetration in the resin and be sure only one layer polymerises at one time, example: Sudan I
• Radical inhibitor: prevents the premature polymerization of the resin in the printing process –> helps maintaining the desired shape, example: vitamin E
• Solvent: example benzyl alcohol

Question 4

Digital light processing DLP (or projection SLA)

Answer 4

Uses a projector to flash an entire layer of the object onto liquid resin, solidifying it all at once. Like taking a picture of each layer and printing it instantly.
+ Faster than SLA
+ Smother surface finishes
- May have less resolution

Question 5

Continuous liquid interface production CLIP

Answer 5

Continuous pulling (elevation) of an objects from a pool of liquid resin using light and oxygen.
+ Fast
+ Smooth print without distinct layers
+ Can work with various materials beyond just resin
+ Commercialised

Question 6

What is the “dead zone” in CLIP?

Answer 6

A thin, oxygen-rich layer of uncured resin that forms between the build platform and the UV image projection window.

It prevents the resin from adhering directly to the window because there the resin does not cure, despite exposure to UV light.

Question 7

Volumetric printing: dual color photopolymerization)

Answer 7

Allow for simultaneous solidification of two different photopolymer material within a single volume
+ Complex objects with distinct colours and properties can be made in a single process
+ Layerless fabrication = smooth transition between different printed polymers

Question 8

Volumetric printing: computed axial lithography CAL

Answer 8

It operates by projecting 2D cross-sectional images of the object onto a rotating cylinder of light-sensitive resin. As the cylinder rotates, the projected images solidify the resin, gradually building up the desired 3D shape within the volume of the resin.
+ Rapid fabrication
+ Complex shaped objects
+ High resolution
+ Fast

Question 9

Volumetric printing: hydrogels

Answer 9

Hydrogels are water absorbing polymers that can hold large amount of water while maintaining their structure. The 3D printing deposit layers of hydrogel solution, then must be chemically or physically cross linked to stabilise the structure.

Applications: tissue engineering, drug delivery, soft robotics.

Requirements: precise concentration, viscosity and cross linking density

Question 10

Volumetric printing: xolography

Answer 10

Employs holographic light patterns to solidify a light-sensitive resin throughout a volume, resulting in the simultaneous formation of complex shapes.
Xolography involves a digital light projector that precisely controls the interference patterns of light within the resin, which are tailored to define the desired shape and structure of the object.
+ No need of layering
+ Rapid fabrication
+ High speed printing
+ Multi-layer printing in a single volume is possible

Applications: biomedical eng. and advanced prototyping.

Question 11

Two-photon 3D printing (Micro-SLA)

Answer 11

Two photon absorption is a non linear phenomena that occurs in all materials when the irradiance is sufficiently high when the combined energy of two photons matches the transition energy between ground state and excited state.

Quadratic dependence of two-photon absorption rate on the light intensity confines this phenomena to the focal point area –>. confined photopolymerization in sub micron volumes.

+ Extremely high resolution
+ Focudes laser beam to induce polymerization = no layering
+ Minimal feature size
+ Complex geometry
+ Submicron precision

Applications: microfluidics, biomedical devices, optical components.

Question 12

Upconversion 3D printing

Answer 12

Use up conversion nanoparticles (UCNPs) to enable fabrication of 3D structures with precise control over their properties and functionalities.

UCNPs containing resin is irradiated with NIR light, which is then converted into VIS or UV by UCNPs –> up conversion process
Converted light then triggers the photopolymerization of the resin, allowing precise solidification of the desired structure

+ Enhanced resolution
+ Compatible with wide range of materials
+ Incorporate functional nanoparticles for application such as sensing, imaging, drug deliver.
+ Deeper tissue penetration for biomed and bioeng applications

Question 13

3D Biodegradable photopolymers

Answer 13

Made with ring-opening polymerisation, They consist of 3 parts:
1. biodegradable polymers, e.g. PLA-MA
2. photocrosslinking groups
3. Bi/multidirecitonal arms
Biodegradable polymers in the middle and the other on their sides.