BIOMATERIALS LAB
MATERIAL MECHANICAL PROPERTIES
Monday, January 23rd & Tuesday, January 24th
BME 245/445 – Lab 1
PRE-LAB
 Sign-in
 Quiz (Engler. 2006)
WEIGHT PERCENT CALCULATIONS
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
THIOL-NORBORNENE PRECURSORS
PEG-Norbornene:
•2kD-PEG
Thiol:
•2SH
•10kD-PEG
•3SH
•20kD-PEG
•4SH
10kD-PEG + 3SH
3SH
10kD-PEG
formation of a crosslinked mesh network
THIOL-ENE POLYMERIZATION
1 Arm
PEG
(n=56)
Norbornene
Fairbanks, B.D. Adv Mater.
2009
SECTION 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 ?
SECTION 2
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
HYDROGEL SYNTHESIS
1.
2.
3.
4.
5.
10wt% PEG in DMSO (20wt% for 2kD-PEG)
solution is thoroughly mixed (solublize PEG)
1:1 mole ratio of thiol-linker
10% photo-initiator by volume
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
MECHANICAL TESTING
 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)
SECTION 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?
Safety
 General
 Lab glasses, gloves, closed toed shoes
 No food, no drinks, no applying makeup
 Specific
 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!!!