B
L
M
P
Monday, January 23 rd & Tuesday, January 24 th
BME 245/445 – Lab 1



(Engler. 2006)

W
P
C
Wt % = (Mass Solute)/(Total Solution Mass) × 100%
1.
Determine total mass solute
2.
Determine mass PEG
3.
Determine mole ratio of PEG MOLECULE to Thiol
MOLECULE , using number of reactive species each & molecular weight
4.
Solve for mass/vol of each

T
-N
P
PEG-Norbornene:
•
2kD-PEG
Thiol:
•
2SH
•
10kD-PEG
• 20kD-PEG
•
3SH
• 4SH

10kD-PEG + 3SH
3SH
10kD-PEG formation of a crosslinked mesh network

T
P
1 Arm
PEG
(n=56)
Norbornene
Fairbanks, B.D. Adv Mater .
2009

S
1
Influence of precursors on end-stage mechanics

Look at different PEG-thiol combinations, constant polymerization time
 Measure young’s modulus of resulting network

Make connections between precursors and mechanics
 Number of “arms”

Mesh size
 Steric hindrance ?

S
Determine network growth mechanism

PEG10,000 3SH

Look at how network develops over time

Step-growth polymerization?

Chain-growth polymerization?
 Network “interaction” is related to observed mechanics
Step-Growth Polymerization. Wikipedia . 2011

H
S
1.
10wt% PEG in DMSO (20wt% for 2kD-PEG)
2.
solution is thoroughly mixed (solublize PEG)
3.
1:1 mole ratio of thiol-linker
4.
10% photo-initiator by volume
5.
40μL placed in 1mL syringe (tip cut off)
 to create cylindrical hydrogel sample geometry
6.
exposed to UV-lamp for 10min
7.
hydrogel removed and placed in DMSO

M
T

MTS system in Materials Testing Lab – 5N load cell
“Benoit Lab Test”
 cyclic compression at 5-10% elongation of gel height
 0.1mm/sec compression rate

Modulus calculated using 1-4% strain range (linear)

S
3
Investigate Tensile Properties & Fracture of Biomaterials

Load sample into PASCO stress/strain apparatus

Begin data collection, steadily turn handle to apply tension

Once bar breaks, stop data collection and remove sample

Export data to Excel for post-lab calculations
 Expected vs. observed behavior for each material

Take image of fracture site using stereo microscope
 Observed differences in fracture mechanics?

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
Lab glasses, gloves, closed toed shoes
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No food, no drinks, no applying makeup
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
DMSO: Eye, skin irritant; ingestion leads to nausea, vomiting, diarrhea, central nervous system damage

Thiols: Eye, skin, respiratory irritant; cause nausea, headache, vomiting; unpleasant smell

Use in HOOD!!!