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 Transfer of composite from mixing device to injection device Design must have practical use in the OR

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

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

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

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

Polyurethane Variables Polyol – g (depends on formulation) Water g  23 uL Catalyst – Tegoamine g Stabilizer – Turkey red oil g Pore opener – Calcium stearine g Isocyanate – g Total mass = g – Hardener = g – Isocyanate = g

Desired Foam Properties Porosity characteristics – Macroscopic observation – SEM imaging Analyze PDI (uniformity) Analyze pore size ( um) Mechanical characteristics (DMA) – Compressive stress – Compressive modulus – Young’s Modulus

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.

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

Current Budget Estimate ItemCost Dremel$75 (known) Agitator$25 (estimate) Canister$25 (est.) Device Housing$25 (est.) Miscellaneous Fixtures$25 (est.) Polymer components$25 TOTAL:$200 – Agitator requires special manufacturing – All estimates are conservative

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

FDA / IP Considerations Class II device 510(k) submission Substantial equivalence to predicate device: 1. Has same technological characteristics OR 2. Has different technological characteristics but does not raise new questions of safety/efficacy

Future Work for 510(k) Submission Identify predicate device Define equivalent characteristics/functions Data to demonstrate why the differing characteristics/functions do not affect 1. Safety 2. Effectiveness

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

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

Current Work Evaluate results of first two mixes Immediate obstacles: – Finalize canister – Create fixture (minimize size) ixing%20forum/images/rt6.jpg

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