Protein Adsorption on Biomaterials

Question 1

What is the isoelectric point?

Answer 1

PI or pH(I)

pH at which a molecule carries no net electrical charge

Question 2

What are the isoelectric point conditions?

Answer 2

pH < Ph of PI = cation
at PI = neutral
pH > pH of PI = anion

Question 3

What occurs when a biomaterial is placed in the body?

Answer 3

1. Interaction with water - water is small and makes up bulk of biological environments
2. Proteins dissolved in serum or media arrive - can ad/absorb, desorb, exchange, denature, the function of the protein is usually changed

Question 4

What protein properties affect adsorption?

Answer 4

1. Hydrophilicity/Hydrophobicity: in an aqueous media, hydrophilic side chains are present on the outside of a protein molecule, hydrophobic domains are hidden
2. Size: diffuse through media more quickly, forms fewer contact points with surface
3. Charge: proteins preferentially adsorb to surfaces with the opposite charge, proteins will adsorb the most when at their PI
4. Stability: decreased stability means the protein more easily unfolds upon adsorption, can form more bonds due to increased protein surface area

Question 5

What is the Vroman Effect?

Answer 5

Smaller proteins appear at the surface first (higher diffusion/mobility in the bulk solution
Overtime, larger proteins will replace the small proteins as long as the small protein has a small affinity to the surface

Question 6

Why do proteins make a monolayer?

Answer 6

proteins do not like to interact with one another

Question 7

What surface properties affect protein adsorption?

Answer 7

1. Hydrophobicity/philicity: hydrophobic surfaces adsorb more proteins while hydrophilic surfaces ten to resist protein adsorption
2. Charge: opposite charges attract
3. Topography: increased surface roughness and topography provide more surface area for protein adsorption
4. Chemistry: dictates the type of bonds between protein and material surface

Question 8

Methyl Group surfaces and adsorption?

Answer 8

non polar hydrophobic groups
bind tightly to fibrinogen and IgG
leads to recruitment of inflammatory cells

Question 9

Hydroxyl Group surfaces and adsorption?

Answer 9

reduces affinity for serum proteins

neutral, hydrophilic groups

Question 10

Amine Group surfaces and adsorption?

Answer 10

positive and hydrophilic

Question 11

Carboxylic Group surfaces and adsorption?

Answer 11

negative, hydrophilic

Question 12

What is PEG and its modification ?

Answer 12

polyethylene glycol
most widely used for surface modification
very hydrophilic
forms coils which absorb water
In order for proteins to adsorb, it must compress the coils

Question 13

What environmental factors affect protein adsorption?

Answer 13

Temperature: increase T increases adsorption
induces protein conformational changes and denaturation
pH: PI