Mixing and Injection System for Polyurethane Foam Scaffolds

Mixing and Injection System for Polyurethane Foam Scaffolds

Michael Scherer

Dustin Dowell

Andrew Solomon

March 13th, 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 CO2 (helps pores form)

Polyol + isocyanate polyurethane

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

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

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

Item Cost

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 affect1. 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 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

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

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