Design Alternatives for Polymer Degradation Model Sara Goldgraben Bill Hauser Michael Savarese BME 440 Design December 5, 2005

Background Required parametersRequired parameters –Aneurysm neck: 4mm –Vasculature diameter: 4mm –Aneurysm diameter: 7mm –Flow Velocity: 100cm/min Transparent HousingTransparent Housing –Optical data acquisition –Mechanically strong Closed Loop systemClosed Loop system –Less fluid required Easily DisassembledEasily Disassembled –Maintenance –Weight measurement of polymer –Durable Water-tight sealsWater-tight seals –Seal between different halves and input/output flow Versatility of DesignVersatility of Design –Varied data acquisition techniques –Variable flow Velocity Steady/Pulsatile

Background BifurcationBifurcation More prevalent than lateral wall aneurysms A bifurcated aneurysm is under different stresses than a lateral wall aneurysm Previous Design Idea - Composite Split Shell ModelPrevious Design Idea - Composite Split Shell Model Polycarbonate or Plexiglass Attachable vessel for bifurcation model Plugged for lateral wall model Raymond et al. Radiology. 2001;221: Soga, et al. Neurosurgery

Alternatives Overview Structural Alternatives Flow Generation –Pumps and Accessories Sealing –Materials and Sealing methods Housing Material Data Acquisition –Camera Type

Calculations v=100cm/min=1.67cm/s, D=4mm=0.4cm, u=0.06cm 2 /s, H=head, p=1.05g/cm 3 Flow RateFlow Rate Reynold’s NumberReynold’s Number TubingAneurysm Entry LengthEntry Length (0.06 is derived empirically)

Calculations Head, PressureHead, Pressure –Aneurysm: Assuming 2.67mm on either side of the aneurysm and 4mm opening –Assuming 50cm of 3mm tubing 189 Pa = 1.42 mmHg 189 Pa = 1.42 mmHg Camera acquisition speedCamera acquisition speed Velocity: 100cm/min  1.67cm/s  1sec = 1.67cm 60fields per frame per second (NTSC format) Each field: 1.67/60 = cm/field = cm/frame

Structural Alternatives 3D Model Block Engraving vs. Shell Model Bifurcation Model –Separate from lateral wall model vs. composite Flow Entry –Side vs. Top Soga, et al. Neurosurgery

2D Model

CAD Designs

Diaphragm Pump Pulsatile Max Pressure output 15psi 4.3mm port Brush motor –Lasts 800hours continuous, 1600hours intermittent use –Heavy duty motor lasts ~ 5000 hours continuous, ~10,000 intermittent Max flow rate: 100ml/min APT Instruments

Oscillating Piston Pump Pulsatile Max Pressure: 20psi 4mm Inlet, 4mm Outlet Brush Motor –800/1600hours or 5k/10k hours Max flow rate: 190mL/min APT Instruments

Peristaltic Pump Pulsatile Brushless Variable Flow Peristaltic Pump (SP200VOBL) Max Pressure: 30psi Brushless lasts ~20,000 hours +- 2% accuracy Flow rates from 0.4 to 100 ml/min. APT Instruments

Pump Accessories Control Board Tubing –Norprene Tubing Longevity –0.8mm & 3mm Power Supply Flow Meter APT Instruments

Pulsation Dampener Creates steady flow from pulsatile flow Compressible chamber Varied Sizes and prices ~$30-$ cat=14487&origin=VURL&prof=142428&itemid= &phid= &search_type=ph&searchstring= 4 cu in (65.5ml) capacity 1ml capacity Matronix 50ml/min

Water-tight Seals Sealing For Main Structure –Types of Seals O-ring –Natural Rubber –Silastic Silicon –Nitrile –Neoprene Caulk –Silicone Gasket Sheets –Same materials as o-ring (top) (mid) (bottom)

If O-Rings, Which Material? Silastic Silicone –Variable Durometer –Excellent Compression Set Resistance –Poor Wear Resistance –Poor Short Term Resilience Neoprene –Variable Durometer –Moderate Compression Set Resistance –Good Wear Resistance –Good Short Term Resilience Buna-N (Nitrile) –Variable Durometer –Good Compression Set Resistance –Good Wear Resistance –Good Short Term Resilience –Cheap –Readily Available –Good for use with water Natural Rubber (Polyisoprene) –Variable Durometer –Low Compression Set Resistance –Excellent Short Term Resilience

O-Ring Gland Design Cut Gland Depth and Width Based on the O-rings Cross Sectional Area (or O-ring is selected vice versa) O-Ring width should be ~25% greater than Gland Depth and Gland Width should be ~50% greater than O-rings width (will vary based on durometer)

System Construction Compression Methods –Screws Aluminum Backing for anchoring –Rubber Bands –Clamps C-clamps (model assembly) Bench-top Clamp (holds system during testing; i.e. vice) (top) (bottom)

Flow/Pump Attachment Adaptors –Threaded Machine our threads to match adaptor –Straight Reducer –O-ring sealed Barbed Insert Flow Seals –Hose Clamps –Zip Ties (top 2) (bottom)

Structural Material Glass Expensive Easily destroyed Primitive Plexiglass Cheap Mechanically Strong Machinable (risk of melting) Polycarbonate Very similar to plexiglass. Slightly more expensive, but is better for most mechanical properties

Data Acquisition Outside camera looking inwards Fluorescence Imaging –Fluorescent camera looking inwards –Integrate dye into the polymer Fiber optic camera –Embedded into model –Enable Intra-Aneurysmal pressure to be measured –Stress and Strain measurements with CASI Integrate speckles into the polymer Weight analysis of polymer Adept Electronic Solutions Pty Ltd.

Composite Design The Best of Everything –Housing Material Polycarbonate –Flow Generation Peristaltic Pump Pulsation Dampener –Water Tight Seals O-ring from synthetic rubbers –Compression method Compression Clamps (C-clamps and vice) –Flow Attachment Hose Clamps –Data Acquisition Light Camera

Cost of Project Total Cost for Pump: $334 –Pump = $189 –Control Board = $90 –Case = $24 –Power Supply = $25 –Extra tube set (0.8mm) = $4 –Norprene tubing upgrade = $2 Pulsation Dampener: $150 –High estimate Flow Meter = $29 Flow adaptors = $50 –High estimate Sealing Materials Clamps and rubber seals = $20 (High Estimate) Housing material Possibly free from the machine shop $10 Labor – Machine shop ($28/hour) Unsure if this is charged to us or the school. Total Project cost: $603 + laborTotal Project cost: $603 + labor

Acknowledgements Professor Chen – Customer Professor Strey – Advisor Lester Orlick - Instructional Support Technician CEAS Greg Pollard – APT Instruments

References 1.Soga et al. Neurosurgery, 55(6): , APT Instruments. Flow Pumps and Accessories Dow Corning. Rubber Applications and Markets. WT.srch=1 WT.srch=1 4.Jean Raymond, MD, François Guilbert, MD and Daniel Roy, MD. Neck- Bridge Device for Endovascular Treatment of Wide-Neck Bifurcation Aneurysms: Initial Experience. Radiology. 2001;221: Adept Electronic Solutions Pty Ltd Standard Resolution Monochrome Camera. 6.Matronix. 7.Macrorubber. 8.O-Ring USA.