Magnetic Supports

Question 1

What are the three characteristic categories that must be considered in the design of an ideal magnetic support for High gradient Magnetic Fishing (HGMF)?

Answer 1

• magnetic characteristics
• size, shape, etc
• surface architecture and chemistry

Question 2

What are the key magnetic characteristics that must be considered in the design for an ideal support for HGMF?

Answer 2

1) no magnetic memory, i.e. superparamagnetic = easy redispersion, product elution and reuse
2) high magnetisation = fast, efficient separation (80-90 wt% MPs)

Question 3

What are the key characteristics regarding size and shape that must be considered in designing the ideal support for HGMF ?

Answer 3

1) mono sized = move with same velocity, predictability and reliability of separation
2) approximately spherical = high packing density (greater weight percent MP in small size)
3) particle density in range 2.5-4 g/cm^3 = slow settling velocity, stay in suspension

Question 4

What are the key characteristics that must be considered regarding surface chemistry and architecture in the design of ideals supports for HGMF?

Answer 4

1) physio chemically robust = tolerate harsh chemicals, corrosion resistant and long lifespan
2) non-porous = foiling and mechanically attrition resistance, ease of cleaning, improved ligand bonding, fast kinetics
3) textured, accessible surface (greater than 50 m^2/g) = high surface area, enhance product sorption capacity and increased target binding capacity
4) hydrophilic, easy to derivatise surface = reduces non specific binding, increases ligand coupling density
5) small, cheap ligands = increased capacity and low cost, accessibility

Question 5

What’s are the pros of the lab scale HGMF support PG-coated magnetic particles?

Answer 5

1) high surface area
2) high binding capacity
3) easy derivatised surface

Question 6

What are the cons of the lab scale PG-coated magnetic particles for use in HGMF?

Answer 6

1) difficult manufacturing process
2) not spherical therefore packing density not high
3) robustness over many uses in unknown
4) difficult to release from magnetic filters

Question 7

What type of magnetic particle is the PG-coated ?

Answer 7

Type VIII
Single magnetic particle, silane coated and the graft polymerised to afford greater stability. Coated with tightly bound synthetic polymer which is then derivatised with lights to its surface.

Question 8

What type of magnetic particle is Chemagen’s M-PVA ?

Answer 8

Type IV
Encapsulated, non-porous support. Multiple magnetic sub particles contained within impervious material, with ligands derivatised to the surface.

Question 9

What are the pros of the Chemagen M-PVA magnetic support particles?

Answer 9

1) facile manufacture
2) good magnetic separation velocity
3) good packing density
4) high protein binding surface
5) better release from magnetic filters

Question 10

What are the cons of the Chemagen M-PVA magnetic support particles?

Answer 10

1) low surface area
2) difficult to derivatise with ligands therefore low product binding capacity
4) robustness with many uses unknown

Question 11

What are key main important characteristics of the two HGMF magnetic support particles?

Answer 11

• HIGH capacity of the PG-coated

- EASE of manufacture of the M-PVA

Question 12

What are the different routes for manufacture of magnetic support particles and the types of support they produce?

Answer 12

• encapsulation (Type II-V)
• infiltration (Type I)
• coating (Type VI-X)

Combinations include:
• infiltration and coating (Type XI)
• encapsulation and coating (Type XII &XIII)

Question 13

Describe the process of encapsulation in producing magnetic support particles ?

Answer 13

Trapping of solid magnetic elements within natural gels (porous), synthetic resins (non porous), glass or liquid filled micro capsules

Question 14

Describe the production of type II and III magnetic support particles ?

Answer 14

Magnetic particles incorporated into molten agarose, forms highly macro porous gel on cooling in water (control of the mixing produces desired particle size distribution)

Question 15

What common non magnetic compounds are used in the manufacture of magnetic support particles, why are they used?

Answer 15

Natural Polymer:
• agarose = bioinert, mechanically rigid, forms gels on cooling with water

Synthetic Polymers:
• either hydrophobic or hydrophilic
• most common = poly(styrene-co-divynlbenzene), cheap, easy to make, small uniform size but very hydrophobic

Question 16

Describe the process of infiltration, what is it’s major drawback?

Answer 16

Porous bead is put into suspension of magnetic nano particles, which disperse into the bead’s pores. The bead must then be coated to to protect the magnetic particles within it.

Looks like magnetic particles, ligands and other components all mixed up in bead.

Question 17

Describe the process of coating to produce a magnetic support particle?

Answer 17

Magnetic core particles coated with natural or synthetic polymers or inorganic materials such as silica. Allowing for ligand attachment and/or stabilisation (Type VI-X)

Question 18

What are the four different approaches that can be taken when coating a magnetic particle?

Answer 18

1) polymer adsorption
2) silanisation
3) graft polymerisation
4) co-precipitation

Question 19

Describe the process of polymer adsorption ? What type of magnetic particle does it produce?

Answer 19

Usually polyamines, electrostatic adsorption onto charged surface of MP. Allowing for easy ligand attachment/functionalistsion (Type VII)

Question 20

Describe the process of silane coupling onto the surface of a MP?

Answer 20

Adding reactive organic group to the inorganic surface, allows for ligand attachment. Group is of formula X3-SiR-Y ( Y chosen for reactivity with organic species and X for formation of silane bond)

Question 21

Describe the process of graft polymerisation to a MP?

Answer 21

Multilayer coating affords greater stability of MP. second coat or cross linking polymer added to silane surface

Question 22

For an encapsulation route, what magnetic compound would you suggest using and why?

Answer 22

Pure magnetite, due to its super paramagnetism (small subparticles contained within impervious material, therefore require highest density magnetisation per unit size)

Question 23

For magnetic supports produced by coating what type of magnetic compound would you suggest utilising?

Answer 23

A mixture of super paramagnetic and just paramagnetic compounds (ie magnetite and ferrihydrite) to guarantee high surface area for target binding whilst also exhibiting high magnetisation