Surface Patterning

Question 1

What is surface patterning?

Answer 1

• The use of surface modification methods to create chemically or physically demarcated regions on a surface

Question 2

Resolution

Answer 2

• the smallest feature size that can be reasonably created by a patterning technique
• high resolution might not be applicable to all situations

Question 3

Throughput

Answer 3

• measure of surface area that can be patterned in a given period of time
• especially important for manufacturing

Question 4

Contrast

Answer 4

• the degree to which components in a pattern are distinguishable from the background substrate
• “surface density of immobilized biomolecule”
• involves intermediate step to prevent non-specific adsorption (like non-fouling surface)

Question 5

Bioactivity

Answer 5

• big concern for biologics that denature in harsh processing conditions
• must work in aqueous conditions and at ambient temperatures

Question 6

Shelf-Life and Durability

Answer 6

• ideal storage conditions would require only ambient conditions for unlimited storage time
• hard to achieve when patterning ‘soft-wet’
• important in point of care

Question 7

Direct-Writing

Answer 7

• scanning a patterning element across a substrate to generate patterns of arbitrary feature shape and size
• high resolution (<100nm), but low throughput (100’s of micrometers)
• types include dip-pen, nano-imprinting/engraving, inkjet, focused fields, beams

Question 8

Dip-pen nanolithography (DPN)

Answer 8

• related to nano-imprinting and nano-engraving
• direct writing with a rigid stylus under control of an atomic force microscope
• more details (look at slides)

Question 9

Inkjet

Answer 9

• pumps bio-ink through a nozzle onto a substrate as 10-20 pL droplets
• resolution of 10-100 micrometers, can use multiple nozzles
• contact free, under ambient conditions, accurate, high throughput
• microarray printers use several fine-point pins

Question 10

Focused Fields

Answer 10

• uses scanning electric and magnetic fields, with lower spatial resolution but generation of electrochemical reactions (redox)
• electron/focused ion beam lithography can be used at resolution of 10-100 nanometers, requires high vacuum and dry samples

Question 11

Electron beam and focused ion beam lithography

Answer 11

• e-beam lithography uses focused beam of electrons as a stylus
• induces cross-linking with accurate resolution, but requires expensive equipment/has low throughput (not used to directly pattern biologics)
• focused beam uses high mass ions to bombard

Question 12

Lithography

Answer 12

• using etched stones coated with ink to create imprints

Question 13

Mask

Answer 13

• any template that modulates a field/radiation that passes through it
• including physically blocking defined regions of substrate from exposure to the media
• can be rigid or elastomeric (potential to confer patterns onto contoured surfaces)

Question 14

Photolithography

Answer 14

• 200 nm resolution, can layer patterns
• photoresist at UV-responsive materials: positive photoresist depolymerize and become soluble, while negative photoresist polymerize and become insoluble
• with mask, can be used to distribute cells or generate electrode arrays

Question 15

Soft lithography

Answer 15

• use elastomeric polymer molds to create patterns (often PDMS)
• cured as a relief pattern from a silicone master
• uses bioink for microcontact printing or adhered stamps for microfluidic patterning
• very cost effective, with medium-high resolution, throughput, contrast, and bioactivity

Question 16

Self-Assembly of Polymers/Colloids

Answer 16

• minimal effort as it’s driven by minimization of free energy (intermolecular or interparticle forces)
• block co-polymer, nanosphere lithography, magnetic self-assembly