May 17, 2007Final Project Presentation

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PemPlant Co.

Maricela DelgadilloKay FurmanYushan Kim

PemPlant Co.2

Industrial Application: Medical Devices

• Pacemakers and Defibrillators▪ Correct abnormal heart rhythm▪ Size: 1.7x1.9x.3 in; 2.4x2x0.6 in

• Potential for Bacteria Exposure▪ 6% of all vascular surgeries result in surgery site infection (HPA)▪ Skin contact, handling, open wound▪ 1-2 hr surgical procedure▪ Current standard of care: antibiotics

• Our Solution: ▪ Antibacterial poly-electrolyte multilayer

coatings on titanium Images from http://www.medtronic.com/

Polyelectrolyte Multilayers (PEMs)

• Systems Analyzed▪ 3.0/3.0 polyacrylic

acid/polyacrylamide (PAA/PAAm)

◦ 5.5 Bilayers◦ Crosslink 130ºC for 2 hrs

▪ 2.0/2.0 polyacrylic acid/polyallylamine hydrochloride (PAA/PAH)

◦ 9.5 Bilayers ◦ Crosslink 80ºC for 30 min

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Michael C. Berg March 2005

PAA PAAm PAH

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Validation: Methylene Blue

bare Ti

3.0/3.0

PAAm/PAA

• Solution of 1 M pH 7.0• Binds carboxylates

• Indicates adhesion of polymer on Ti substrates

2.0/2.0

PAH/PAA

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Modulus by AFM

• Si3N4 nitride probe on cantilever to measure F vs s upon approach

• E obtained by linear regression of Hertzian contact model

• Ti substrate: E = 123 KPa• Glass: E = 500 Kpa1

• Surface roughness challenges

PAA/PAH 2.0/2.0 on Ti

1 Thompson et al., Biomaterials 26 (2005) 6836–6845

5.1sCFp

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Bacteria Experiment: Methods

Samples in Staph. epidermidis bacteria solution [106 cells/mL]

2 h, 4 h, or 8 h 37°C incubation for cell adhesion

Remove sample, lay agar gel on top

Approx. 24 h incubation for growth of attached cells

Visible colonies:1 per adhered cell

TiGlass

Whole-slide photographyMicroscopy

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Whole-slide image analysis (WCIF ImageJ)

Bacteria Experiment: Methods

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Bacteria Results

Bacterial attachment on Ti PEM

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bare 2.0/2.0 3.0/3.0

Surface on Ti Substrate

Col

onie

s /

sq c

m

2 h 4 h

*

• Ti performs well as a PEM substrate

• Effects withstand time-course test of 4 hours

• Decreased bacteria viability over time: 8 hour adhesion incubation yielded no viable bacteria

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Bacterial Adhesion

Bare substrate 2.0/2.0 3.0/3.0Glass

Ti

• Surface features▪ Bacteria settle in imperfections on bare Ti▪ PEMs even prevent colony formation on features

40 μm

5 mm

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Wear Testing Apparatus/Procedure

• Finger Pressure ~ 50g-100 g

• Probe mass: 61.3 g▪ 50 g weight▪ Rubber ball▪ Casting wax

• Wore samples for 10 min at 2 rpm 20 swipes

Wear Assessment: Contact Angle

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• Increased contact angle values after wearing

Contact angle wear assesment

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90

worn

Bare Ti 2.0/2.0 3.0/3.0 nitrile glove

Wear Assessment: Bacteria

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• Worn Ti samples remained bacterial resistantWear testing

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bare 2.0/2.0 3.0/3.0

Col

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Worn Control

Stability in Buffer Solution

• 1 week in Phosphate-Buffered Saline (PBS)

• Demonstrated bacteria resistant after 1 wk in model biological fluid (n=3)

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Conclusion

• Primary deliverables:▪ PEM deposited on titanium▪ Demonstrated bacteria resistant properties▪ Sustained properties at 4 h bacteria exposure▪ Properties retained after handling simulation,

after 1 week in model fluid environment• Recommend 2.0/2.0 system• Ready for animal studies, industrial

implementation

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Acknowledgements

• Prof. Chiang, Todd Thompson• Joe Parse, Yin-Lin Xie, Mike Tarkanian• Prof. Van Vliet, Prof. Rubner• Jenny Lichter, Alan Scwartzman, David Bono• 3.042 Classmates

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Questions?

• Visit our website for more information: http://web.mit.edu/3.042/team1_07/

• Thank you!PemPlant Co.

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Backup

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Wear Assessment: Profilometry• Profilometry conducted on Tencor P-10 surface profiler• 2 μm radius diamond stylus scans at 6.0 mg• 590 μm scan on a scratched film: