Magnetic Freeze Casting with Surface Magnetized Hydroxyapatite for Bioinspired Bone Implants

CINDY AYALABIOENGINEERING REUDEPARTMENT OF MECHANICAL AND AEROSPACE ENGINEERINGADVISOR: PROF. JOANNA MCKITTRICKGRAD STUDENT MENTOR: M ICHAEL FRANK

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Motivation Osteoporosis

- causes erosion of trabecular (spongy) bone

- leads to decreased bone mass, especially in the elderly

- results in brittle bones that lead to unexpected failure

- titanium implants can lead to stress shielding (reduction in bone density due to removal of stress from bone by the implant)

- titanium implants often require adjustment surgeries

[1] http://www.medguidance.com/thread/What-Causes-Osteoporosis.html

Goal Create a porous scaffold made of bone

mineral which mimics the structure of bone

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Freeze Casting

Y

X

Z

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Magnetic Freeze Casting

X-AxisY

X

Z

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Procedures• For this experiment, hydroxyapatite is used because it is the essential mineral

component of bone and teeth.

• Hydroxyapatite particles are magnetized by mixing cationic charged ferrofluid, hydroxyapatite and water

Magnet

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Data Collection

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Results (10 Vol% Slurry, ≈ 85% Porosity)

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SEM Imaging of Scaffolds (10 Vol% Slurry, ≈ 85% Porosity, 50 mT Magnetic Field)

Magnetic Field (x-axis)

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SEM Imaging of Scaffolds (10 Vol% Slurry, ≈ 85% Porosity, 25 mT Magnetic Field)

Magnetic Field (x-axis)

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SEM Imaging of Scaffolds (10 Vol% Slurry, ≈ 85% Porosity, 25 mT Magnetic Field)

Magnetic Field (x-axis)

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Results (20 Vol% Slurry, ≈75% Porosity)

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Conclusion• Hydroxyapatite particles (HA, 2 μm) are compared to

past work with alumina (195, 225, 350 nm).

• Bigger particle size (HA) needs lower magnetic field to align more particle chains in scaffold center.

• Stiffness (Young’s Modulus) is enhanced when more particle chains are aligned in scaffold center.

• 20 vol% HA (≈75% porosity) at 25 mT was best condition.

Scaffold X-section

Scaffold Center Cube

Particle Chains

No Alignment Goal

More particle chain alignment in scaffold center rather than at poles

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Future Work• Take best condition (20 vol% HA, ≈75% porosity, 25 mT) and do further work to strengthen scaffold.

• Wrap scaffold cylinder with a biodegradable thermopolymer (polylactic acid, PLA) to resemble impact resistant porcupine quill that is a keratin foam wrapped with a keratin cortex sheath.

• Infiltrate scaffold pores with a biodegradable polymer (polyethylene glycol diacrylated, PEGDA), photoinitiator and phosphate binding element (calcium acetate) and then UV cure to crosslink PEGDA within HA scaffold.

• Compare overall mechanical properties of reinforced HA scaffold implant in axial and radial (Brazilian Test) compression to assess viability of structural design for spongy bone biomedical implants.

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Acknowledgements•Professor McKittrick for welcoming me into her team

•PhD student Michael Frank for mentoring me through this project

•Fellow undergrads Sze Hei Siu, Louis Guibert, and Joyce Mok for assisting me in my research