This document discusses research into using magnetic freeze casting to create porous hydroxyapatite scaffolds for bone implants. Hydroxyapatite particles are magnetized and freeze cast into aligned structures that mimic bone's trabecular structure. Testing shows 20% hydroxyapatite slurries frozen with a 25mT magnetic field produce scaffolds with the highest porosity and particle chain alignment in the center. Future work will reinforce the scaffolds and test them as potential implants for treating osteoporosis.

1. Magnetic Freeze Casting with Surface
Magnetized Hydroxyapatite for
Bioinspired Bone Implants
CINDY AYALA
BIOENGINEERING REU
DEPARTMENT OF MECHANICAL AND AEROSPACE ENGINEERING
ADVISOR: PROF. JOANNA MCKIT TRICK
GRAD STUDENT MENTOR: MICHAEL FRANK

2. 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
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[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

3. Freeze Casting
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Y
X
Z

4. Magnetic Freeze Casting
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X-Axis
Y
X
Z

5. 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
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Magnet

6. Data Collection
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7. Results (10 Vol% Slurry, ≈ 85% Porosity)
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8. SEM Imaging of Scaffolds
(10 Vol% Slurry, ≈ 85% Porosity, 50 mT Magnetic Field)
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Magnetic Field (x-axis)

9. SEM Imaging of Scaffolds
(10 Vol% Slurry, ≈ 85% Porosity, 25 mT Magnetic Field)
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Magnetic Field (x-axis)

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

11. Results (20 Vol% Slurry, ≈75% Porosity)
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12. 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.
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Scaffold
X-section
Scaffold
Center Cube
Particle
Chains
Goal
More particle chain alignment in
scaffold center rather than at poles

13. Future Work
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• 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.

14. 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
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