Polymers

Question 1

How are plolymers are used in biosensing?

Answer 1

(1) as part of sensing mechanisms
(2) to immobilize bioreceptors
(3) to enhance the sensitivity and selectivity

Question 2

What are the types of polymers? based on orgin, processing, and structure

Answer 2

Based on origin: Natural and synthetic
Based on processing: Thermoplastic and Thermoset
Based on the structure: Homopolymer and copolymer

Question 3

What are the advantages of natural polymers for biosensor fabrication:

Answer 3

(1) natural origin
(2) biodegradability
(3) recyclability
(4) lower antigenicity
(5) suitable interaction with living systems

Question 4

What are the limitation of natural polymers for biosensor fabrication:

Answer 4

(1) Batch-to-batch variation
(2) Slow synthesis/production
(3) Complicated extraction

Question 5

What are the advantages of synthetic al polymers for biosensor fabrication:

Answer 5

(1) Easily tuneable
(2) More controlled properties
(3) Higher reproducibility
(4) Better mechanical and chemical stability
(5) Better conjugation properties

Question 5

What are the limitation of synthetic polymers for biosensor fabrication:

Answer 5

(1) Lack of intrinsic biocompatibility
(2) May cause toxicity and immunogenic response
(3) Difficult/Expensive synthesis

Question 6

What is Thermoplastic polymers?

Answer 6

1) Polymers that can be moulded to shape by
extrusion type processes in the molten state, above
Tg (injection molding) -> Heat & pour into mold
2) Long thin “string like” molecules which can be
entangled
3) Not crosslinked – only weak intermolecular forces (hydrogen bonds, hydroelasticity, non-covalnet bonds)
4) Normally formed by addition polymerization

Question 7

What is Thermoset polymers?

Answer 7

1) Polymer chains that are attached by crosslinks, i.e. strong covalent bonds
2) Toughness and fracture properties depend on
crosslinking-density
3) Normally formed by condensation polymerization

Question 8

How are polymers syhnthsized?

Answer 8

1) chain growth/ addition polymerization/ free radical polymerization
2) Step growth/ Condensation polymerization

Question 9

Compare between addition polymerization and condensation polymerization

Answer 9

addition polymerization:
1) Polymers are formed from unsaturated monomers (= bonds)
2) the polymer chain is formed at the beginning by monomers attachment at a time
3) Monomers are unsaturated
4) there is NO rapid loss of monomers
5) Monomers have active sites
6) requires initiators (energy) to break the = bonds of the monomers

condensation polymerization
1) Polymers are formed from bi/multifunctional monomers
2) Oligomers are formed first, then combine to form the polymer chain
3) Monomers are bi/multifunctiona
4) there is rapid loss of monomers
5) Monomers ARE active themselves
6) No initiators (energy) required

Question 10

What are the steps of addition polymerzation?

Answer 10

1) initiation -> forming a radical (lone electron)
2) propagation -> breaking the double bond
3) Termination -> two radicals react together to form a stable adduct

Question 11

Draw the process of addition polymerization

Answer 11

-

Question 12

What is Condensation pymerzation?

Answer 12

Step growth

1) Condensation polymerization: a form of step-growth formed where two different monomers
react to form larger units, while releasing small molecules (e.g. H2O or methanol).
2) Condensation polymers can be hydrolysed in the body
3) E.g. most natural polymers (polysaccharides, proteins), polyamides, polyesters

Question 13

What are the properties of polymers?

Answer 13

1) Crystallinity: Amorphous (random & see through) vs. semi crystalline
2) Melting Temperature (Tm): directly proportional to Mw, cross linking, and crystallinity. inversely propositional to chain rotation degree
3) Glass transition temperature (TG)

Question 14

What isGlass transition temperature (TG)?

Answer 14

Temperature at which a polymer will undergo a transition from the glassy to the rubbery state.
If temp>Tg, Rubbery
If temp<Tg, Hard

Question 15

How do Bioresorbable/biodegradable polymers degrade?

Answer 15

(1) under action of enzymes or cells
(2) by chain scission, often by hydrolysis of ester bonds

Question 16

What is the pH conditions that accelerates Hydrolysis?

Answer 16

extremely acidic and alkaline conditions. Hydrolysis forms carbolic acid causing pH to fall and accelerate degredation

Question 17

What are the classification of biocompatible (non toxic) polymers?

Answer 17

1) bioresorbable - get absorbed/degrade in the body
2) bioinert - Has ultrahigh MW and does not degrade (has Si, and lakcs polar groups) ( PMMA, Polysiloxanes(PDMS))

Question 18

What is the Acrylate?

Answer 18

A chemical group that consists of vinyl (C=C) and an Ester group (COOR)

Question 19

What are the advantages of Polysiloxanes?

Answer 19

1) Optical transparency
2) High oxygen permeability
3) High flexibility at low temperature
molds and excellent contact

Question 20

Compare between PDMS and PMMA in microfluidics biosensors.

Answer 20

1) PDMS is a soft transparent thermoset thermally curable polymer widely used for rapid prototyping of microfluidics.

2) PMMA isa transparent thermoplastic lightweight polymer that is nonbiodegradable but bioinert.

Question 21

What are the key advantages of using Microfluidics in biosensing

Answer 21

1) enhanced reaction efficiency -> reduced analysis time
2) simplified procedures
3) Useful flow properties -> manipulation
4) Miniaturization and portability -> amenable for POC
5) lower reagent consumption and waste -> cost-effective

Question 22

Explain Casting by Soft Lithogrpahy

Answer 22

1) Casting is the most common technique to fabricate microfluidic chips due to its low capital cost, simple procedure, and high fidelity
2) PDMS has been the primary material used in casting – this is called “Soft Lithography”

Question 23

What are the steps of Soft Lithogrpahy

Answer 23

1) Make Mold: construct a positive mold with a microfluidic design with protruded structures
2) Cast: PDMS base and curing agent are mixed at the weight ratio of 10:1 and degassed, followed by being pouring onto the mold
3) Bake: assembly is then placed at ambient condition for >24 h or in an oven at ~65 C for typically 4h
4) Bond: The PDMS replica is separated from the mold and bonded (after plasma treatment) to a glass substrate to make a microfluidic chip

Question 24

What are the some of the major problems that affect the performance of biosensors?

Answer 24

presence of interferents & biofouling

Question 25

What is biofouling?

Answer 25

Physiological fluids like blood deposit materials such as proteins, usually irreversibly, on to solid surfaces.

Question 26

Give examples to Polymer-based Antibiofouling Approache.

Answer 26

1) PEG
2) hydrogels
3) zwitterionic polymers

Question 27

What are the principals governing antifouling strategies?

Answer 27

1) Surface Chemistry - creating hydration layer via (hydrophilic -> hydrogen bonds, Zwitterionic -> ionic solvation) that prevents adsorption
2) Surface topography
3) Architecture (coating)