Mixing and Injection System for Polyurethane Scaffolds Michael

Mixing and Injection System for Polyurethane Scaffolds Michael Scherer Dustin Dowell Andrew Solomon February 21 th, 2007

Background l 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

Current State-of-The-Art l l ~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 –

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

Polyurethane Constituents l l Isocyanate Hardener – – – Polyol Water Catalyst Stabilizer Pore opener Polyol + isocyanate polyurethane Water + isocyanate CO 2 (helps pores form)

Desired Foam Properties l 200 -600 um pore size l Low PDI – maintain uniform pore sizes l To be validated experimentally Foam strength l

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

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

Current Budget Estimate Item Dremel Agitator Canister Cost $75 (known) $150 (estimate) $50 (est. ) Device Housing $50 (est. ) Miscellaneous Fixtures $50 (est. ) Polymer components $25 TOTAL: $400 – – Agitator requires special manufacturing All estimates are conservative

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

Current Work l l Fabrication in process – Rapid Prototype Machine Immediate obstacles: – Rotary shaft to impeller coupling http: //www. postmixing. com/m ixing%20 forum/images/rt 6. jpg

Optimization of Impeller Design l l Rushton turbine – radial flow impeller Important parameters: – – D/T ratio = 0. 6 (D = impeller diameter; T = tank diameter) Off-bottom clearance C = variable according to design

Future Work l Experimental testing – – – l l l What speed to mix (5, 000 – 15, 000 RPMs) How much mixing time is needed (30 - 90 s) Achieve necessary physical properties Canister fabrication Develop a system for transferring mixture from canister to syringe Maintaining sterility throughout process