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% Determine total mass solute Determine mass PEG Determine mole ratio of PEG MOLECULE to Thiol MOLECULE, using number of reactive species each & molecular weight Solve for mass/vol of each

THIOL-NORBORNENE PRECURSORS PEG-Norbornene: 2kD-PEG 10kD-PEG 20kD-PEG Thiol: 2SH 3SH 4SH

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

THIOL-ENE POLYMERIZATION PEG (n=56) Norbornene 1 Arm 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 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 exposed to UV-lamp for 10min hydrogel removed and placed in DMSO

MECHANICAL TESTING “Benoit Lab Test” 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 Specific 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!!!