Polymers Flashcards
How are plolymers are used in biosensing?
(1) as part of sensing mechanisms
(2) to immobilize bioreceptors
(3) to enhance the sensitivity and selectivity
What are the types of polymers? based on orgin, processing, and structure
Based on origin: Natural and synthetic
Based on processing: Thermoplastic and Thermoset
Based on the structure: Homopolymer and copolymer
What are the advantages of natural polymers for biosensor fabrication:
(1) natural origin
(2) biodegradability
(3) recyclability
(4) lower antigenicity
(5) suitable interaction with living systems
What are the limitation of natural polymers for biosensor fabrication:
(1) Batch-to-batch variation
(2) Slow synthesis/production
(3) Complicated extraction
What are the advantages of synthetic al polymers for biosensor fabrication:
(1) Easily tuneable
(2) More controlled properties
(3) Higher reproducibility
(4) Better mechanical and chemical stability
(5) Better conjugation properties
What are the limitation of synthetic polymers for biosensor fabrication:
(1) Lack of intrinsic biocompatibility
(2) May cause toxicity and immunogenic response
(3) Difficult/Expensive synthesis
What is Thermoplastic polymers?
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
What is Thermoset polymers?
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
How are polymers syhnthsized?
1) chain growth/ addition polymerization/ free radical polymerization
2) Step growth/ Condensation polymerization
Compare between addition polymerization and condensation polymerization
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
What are the steps of addition polymerzation?
1) initiation -> forming a radical (lone electron)
2) propagation -> breaking the double bond
3) Termination -> two radicals react together to form a stable adduct
Draw the process of addition polymerization
-
What is Condensation pymerzation?
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
What are the properties of polymers?
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)
What isGlass transition temperature (TG)?
Temperature at which a polymer will undergo a transition from the glassy to the rubbery state.
If temp>Tg, Rubbery
If temp<Tg, Hard
How do Bioresorbable/biodegradable polymers degrade?
(1) under action of enzymes or cells
(2) by chain scission, often by hydrolysis of ester bonds
What is the pH conditions that accelerates Hydrolysis?
extremely acidic and alkaline conditions. Hydrolysis forms carbolic acid causing pH to fall and accelerate degredation
What are the classification of biocompatible (non toxic) polymers?
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))
What is the Acrylate?
A chemical group that consists of vinyl (C=C) and an Ester group (COOR)
What are the advantages of Polysiloxanes?
1) Optical transparency
2) High oxygen permeability
3) High flexibility at low temperature
molds and excellent contact
Compare between PDMS and PMMA in microfluidics biosensors.
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.
What are the key advantages of using Microfluidics in biosensing
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
Explain Casting by Soft Lithogrpahy
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”
What are the steps of Soft Lithogrpahy
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
What are the some of the major problems that affect the performance of biosensors?
presence of interferents & biofouling
What is biofouling?
Physiological fluids like blood deposit materials such as proteins, usually irreversibly, on to solid surfaces.
Give examples to Polymer-based Antibiofouling Approache.
1) PEG
2) hydrogels
3) zwitterionic polymers
What are the principals governing antifouling strategies?
1) Surface Chemistry - creating hydration layer via (hydrophilic -> hydrogen bonds, Zwitterionic -> ionic solvation) that prevents adsorption
2) Surface topography
3) Architecture (coating)
