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Mixing and Injection System for Polyurethane Foam Scaffolds

Mixing and Injection System for Polyurethane Foam Scaffolds. Michael Scherer Dustin Dowell Andrew Solomon. March 13 th , 2008. Design Objectives. Novel device which effectively mixes two-component polyurethane foam scaffolds for bone injection in situ

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Mixing and Injection System for Polyurethane Foam Scaffolds

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  1. Mixing and Injection System for Polyurethane Foam Scaffolds Michael Scherer Dustin Dowell Andrew Solomon March 13th, 2008

  2. Design Objectives • Novel device which effectively mixes two-component polyurethane foam scaffolds for bone injection in situ • Transfer of composite from mixing device to injection device • Design must have practical use in the OR

  3. Background • Indications:  Minimally invasive techniques • Small bone fractures (i.e. distal radius fracture) • Osteoporotic fractures • Vertebral compression fractures • Bone cancer repairs (void filler) • Antibiotic delivery • Growth hormone delivery

  4. Current State-of-The-Art • ~1 million hospitalizations due to bone fractures per year in the United States • 700,000 of these per year are treated via autogenous bone graft (within same patient) • Limited donor bone tissue • Increased risk of pain and morbidity at donor site  Demand for synthetic material that is safe and effective

  5. Market Forecast • Capture 10% market share ~70,000 procedures per year • Cost of system (including mixer): $300 • Retail price: $1500 (approx.) • Total Revenue: $105,000,000 • Total Profit = $84,000,000

  6. Polyurethane Constituents • Isocyanate • Hardener • Polyol • Water • Catalyst • Stabilizer • Pore opener Polyol + isocyanate  polyurethane Water + isocyanate  CO2 (helps pores form)

  7. Polyurethane Variables • Polyol – 1.5315 g (depends on formulation) • Water - .023 g  23 uL • Catalyst – Tegoamine - .0682 g • Stabilizer – Turkey red oil - .023 g • Pore opener – Calcium stearine - .0625 g • Isocyanate – 1.323 g • Total mass = 3.0303 g • Hardener = 1.7073 g • Isocyanate = 1.323 g

  8. Desired Foam Properties • Porosity characteristics • Macroscopic observation • SEM imaging • Analyze PDI (uniformity) • Analyze pore size (200-600 um) • Mechanical characteristics (DMA) • Compressive stress • Compressive modulus • Young’s Modulus

  9. Procedure • In the OR, the polymer is stored as two separate components (hardener + isocyanate) • When needed, both elements will be added to the canister • The canister will then be inserted into the mixing fixture.

  10. Procedure • After mixing is complete, the canister is removed from the fixture. (Mixing time estimated 45 sec) • An attachment is then employed to move the mixture into an injection device. • Polymer is injected into the body • 5-10 minute working time depending on composition

  11. Current Budget Estimate • Agitator requires special manufacturing • All estimates are conservative

  12. Outside Advisor – Dr. Frank Papay • Personal practice – craniofacial plastic surgery using PMMA • Volume of injection between 5 and 35cc • Referenced Synthes Norian SRS as comparison

  13. FDA / IP Considerations • Class II device • 510(k) submission • Substantial equivalence to predicate device: • Has same technological characteristics OR • Has different technological characteristics but does not raise new questions of safety/efficacy

  14. Future Work for 510(k) Submission • Identify predicate device • Define equivalent characteristics/functions • Data to demonstrate why the differing characteristics/functions do not affect • Safety • Effectiveness

  15. Optimization of Impeller Design • Rushton turbine – radial flow impeller • Important parameters: • D/T ratio = 0.75 (D = impeller diameter; T = tank diameter) • 0.75” impeller OD : 1.00” tank diameter ID • Off-bottom clearance C = variable according to design

  16. Experimental Testing • Foams produced 3.12.08 / 3.13.08 • Testing parameters • 40-50 second mixing time • RPM between 5000 – 11000 • ~10 cc produced • Porosity and mechanical testing to be conducted within the coming week • Significant observations • Foam possessed equivalent macroscopic characteristics to previous foams

  17. Current Work • Evaluate results of first two mixes • Immediate obstacles: • Finalize canister • Create fixture (minimize size) http://www.postmixing.com/mixing%20forum/images/rt6.jpg

  18. Future Work • Experimental testing • Pinpoint mixing speed (5,000 – 15,000 RPM) • Pinpoint mixing time upon further testing (15 - 45 sec) • Develop a system for transferring mixture from canister to syringe • Mimic operating room conditions • Maintaining sterility throughout process

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