Georgia Institute Of Technology BMED/MSE 4751 HW4 Solutions.
BMED/MSE 4751
HW4 Solutions
1. You are working with a progenitor cell line to induce
... [Show More] fibroblastic differentiation on a
copolymer of negatively-charged polymer X and neutral-charge polymer Y. You find that
your progenitor cells attach and spread in the presence of a new integrin-binding peptide
(IBP).
a. (3 points) You can attach the IBP to the end of two different proteins – one which has
a large negative charge, and one which is highly positively charged. Which protein
would you use as a carrier for the IBP and why? (3 sentences or less)
You examine water contact angle and progenitor cell spreading on the copolymer surface and
find the following results:
Polymer Composition (% X) Water Contact Angle (deg) % Spread Cells *
5 115 18
10 100 35
25 85 73
50 65 92
75 40 89
100 20 93
* “% Spread Cells” refers to the number of cells on the surface that are considered “spread”
(e.g. have a surface area larger than a certain threshold value).
b. (3 points) Discuss the relative hydrophilicity of polymer X and polymer Y and
explain how you arrived at your answer based on the chart above. (3 sentences or
less)
c. (7 points) Explain the spreading phenomena observed in terms of surface properties
of the material and cell and protein interactions with this surface. In particular,
provide justification for the amount of cell spreading seen at 5% X, 25% X, and
100% X, as well as why a plateau in cell adhesion is seen at 50-100% X. (5 sentences
or less)
d. (7 points) To make sure the results are consistent, you ask a colleague to repeat the
experiment above. Your coworker accidentally places all the samples in a mixture
containing 75% IBP attached to the negative protein and 25% IBP attached to the
positive protein. How would this affect cell adhesion at 5% X and 100% X (give an
estimate of % spread cells)? Explain based on protein interactions with the surface
and the cells. (6 sentences or less)
(Note: In this case, if all the protein in solution is adsorbed, it will form a single
monolayer on the biomaterial surface.)
e. (5 points) After adhesion, what is one way to check to see if your progenitor cells
have differentiated to possess a fibroblastic phenotype? (4 sentences or less)
2. You are investigating a polymer coating that inhibits leukocyte migration with the intent of
minimizing inflammation in response to a porous coating for the stem of a hip implant. You
choose to do a capillary tube test to observe leukocyte migration over 4 days.
a. (5 points) Explain how a capillary tube test is used to measure cell migration. (4
sentences or less)
b. (3 points) The capillary tube test gave the following results over 4 days for leukocytes
on coated and uncoated surfaces. Would you recommend using the polymeric
coating to inhibit leukocyte migration? Justify your answer. (3 sentences or less)
Time (d)
Inhibitory Coating:
Area of Cells (mm2)
Uncoated Control Surfaces:
Area of Cells (mm2)
0 0 0
1 2 3
2 3 7
3 7 35
4 10 52
c. (4 points) What is the major drawback to this study as a measure of cell migration
over 4 days? Explain your answer. (4 sentences or less)
d. (8 points) To determine to effect of the coating on other cell types, migration of
leukocytes, endothelial cells, and osteoblasts (bone-forming cells) were compared on
polymer-coated surfaces by capillary tube tests. Do these results support the use of
this coating for the stem of a hip implant? Justify your answer using the table below.
(6 sentences or less)
Time (d)
Leukocytes on
Coated Surfaces:
Area of Cells (mm2)
Endothelial Cells on
Coated Surfaces:
Area of Cells (mm2)
Osteoblasts on Coated
Surfaces:
Area of Cells (mm2)
0 0 0 0
1 2 2 1
2 3 2 3
3 7 5 6
4 10 7 9
3. (15 points) Complete the following table to explain the difference between monocytes and
macrophages. Specifically address differences in cell origin/formation, location where these
cells appear in the body, time of occurrence in the inflammatory process (hours/days/weeks?),
and cell function.
Monocytes Macrophages
Cell origin/formation
Location in the body
Time of occurrence
in the inflammatory
process
4. (10 points) List the 4 cardinal signs of inflammation and explain their cellular and molecular
causes. (7 sentences or less)
5. (10 points) List 3 parameters that can be tested as indicators of neutrophil activation and
describe why each of these things are important for the overall function of neutrophils in the
inflammatory response. (7 sentences or less)
6. In experiments to evaluate tissue responses to a biomaterial, a control group is often included
involving the complete surgical procedure but without implanting the biomaterial.
a. (3 points) Why is the surgery-only group an important control for these studies? (2
sentences or less)
b. (7 points) List the differences in the tissue response at the wound site following
implantation of a nondegradable biomaterial as compared to a simple lesion. (6
sentences or less)
7. You have developed a novel non-degradable biomaterial for controlled drug release. In vitro
experiments on a thin slab (20 mm x 10 mm x 2 mm) showed that your material has the
release profile shown below (solid line) with linear release over ~30 days. Following
implantation in vivo, however, the release rate into the surrounding tissue was severely
decreased within the first 4 days (dashed line) and zero release occurred after 12 days.
0
20
40
60
80
120
0 5 10 15 20 25 30
Drug Release Rate (ng/hr)
100
Time (days)
a. (6 points) What is the most likely explanation for the difference between the in vitro
and in vivo release rates? (5 sentences or less)
b. (4 points) Your company is investigating a degradable polymer as an alternative to
the non-degradable material above. In-vitro release studies show the same results as
the non-degradable polymer (solid line on graph above). However, when implanted
in vivo, it was observed that the polymer quickly (<3 days) formed particulates at the
implantation site. Draw the expected drug release from the degradable polymer in
vivo and explain why you drew the graph this way. (3 sentences or less)
Drug Release Rate (ng/hr)
100
Time (days) [Show Less]