Unlock document.
This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
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
e2
square centimeter nprotein, assuming close packing of
circles representing the footprint area occupied by
each spherical protein molecule. (This is a small over-
m
protein
=n
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
