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

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

Wt% = (Mass Solute)/(Total Solution Mass) × 100%

THIOL-NORBORNENE PRECURSORS

Thiol:•2SH

•3SH

•4SH

PEG-Norbornene:•2kD-PEG

•10kD-PEG

•20kD-PEG

10kD-PEG + 3SH

3SH

10kD-PEG

formation of a cross-linked 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. 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

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 3Investigate 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!!!