Biology & Life Sciences Chapter 1 Homework Close packing means that the molecules touch each other at their boundaries

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PROBLEMS

1. What are the three main driving forces that affect the

competitive adsorption of proteins to biomaterials

from complex mixtures such as blood plasma?

2. Calculate the amount of adsorbed protein in a close

packed monolayer for an average protein of molecu-

lar weight 100,000. Assume the protein is spherical

explained?

4. What are three methods that show the specific effect

of adsorbed proteins on cellular interactions with

biomaterials?

5. As illustrated in Figure II.1.2.5, polystyrene and other

hydrophobic surfaces become more wettable after

SOLUTIONS TO PROBLEMS

1. The three main factors that are believed to control

the outcome of competitive adsorption processes are:

(1) the intrinsic affinity of each protein for surfaces,

will not be present in high amounts on the surface

if it is present in low bulk concentration compared

to the other proteins, since the excess concentration

of the competing proteins will overcome the affinity

differences.

2. Close packing means that the molecules touch each

other at their boundaries, so the problem can be

Protein Monolayer Calculation

The specific volume (volume per gram) of a protein

can be used to calculate the volume of an individual

protein molecule by using the molecular weight and

Avogadro’s number:

sions of proteins measured by X-ray crystallogra-

phy. For proteins in the range of 100,000 molecular

weight, average long dimensions are around 70 Å,

giving a radius of around 35 Å, fairly close to what we

just calculated using the specific volume of proteins.)

The radius of the protein molecule can then be

CHAPTER II.1.2

Adsorbed Proteins on Biomaterials

square centimeter nprotein, assuming close packing of

circles representing the footprint area occupied by

each spherical protein molecule. (This is a small over-

protein

*M/N

Avogadro

=5.6×10 −7g

0.56 microgram

3. Due to differences in relative competitive affinity of

proteins for various surfaces, the amount of adsorp-

tion of each protein varies with surface chemistry. For

example, some surfaces have more adsorbed fibrin-

ogen and others more adsorbed albumin, and since

platelets bind only to fibrinogen, surfaces enriched in

4. Three methods to show the role of adsorbed proteins

are as follows.

a. If surfaces are preadsorbed with various purified

proteins, it is found that most inhibit cell adhe-

sion to the surface, but a few such as fibronectin,

b. Preadsorption with complex protein mixtures,

such as blood plasma selectively deficient in only

one protein, is a more physiologically relevant way

to show if a protein is contributing an important

c. Addition of antibodies specific to a given adhe-

sion protein or to its receptor to a cell suspen-

sion incubating with a biomaterial will result in

5. An increase in contact angle after exposure to pro-

tein-containing media can be explained by adsorp-

tion of protein if the adsorbed protein layer is less

wettable than the starting surface. For certain solid

proteins interact with water less strongly than the

starting Germanium oxide surface. Thus, while pro-

teins are much more wettable than polystyrene, they

evidently are not as wettable as some solid surfaces.

6. The irreversible, tight binding of proteins to surfaces

is due to the large size of protein molecules, so that

broken simultaneously is low, so multivalent bonding

results in strong bonding.

Note: Latour (2008) adds another way to look at this

issue. He notes that because of the large number of

contacts between functional groups of a protein and a

water molecule to be 0.5, the probability for all of the

functional groups of an adsorbed protein to dissociate

from the protein at the same time would be P = (0.5)n,

with n being the number of functional group contacts