34. biodegradable spongy bone implants: strength through bioinspiration

Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Agile - CaliBaja Center for Resilient Materials & Systems
Faculty Advisor(s): Joanna M. McKittrick

Primary Student
Name: Michael Brian Frank
Email: mbfrank@ucsd.edu
Phone: 858-229-6146
Grad Year: 2017

Abstract
Degradation of the interior spongy bone layer due to erosion of the hard mineral phase can lead to bone brittleness over time. Preventative surgery to reinforce bone with a titanium implant leads to stress shielding which requires follow-up surgeries due to bone remodeling and insufficient osteoblast integration. Spongy bone implants must more closely resemble bone as a biodegradable and biocompatible composite with mineral and biopolymer phases. One option is to infiltrate a porous hydroxyapatite scaffold with a mechanically robust dual network hydrogel that can provide a suitable 3D matrix environment for osteoblast growth. Hydroxyapatite particles were surface magnetized by cationic charged ferrofluid through electrostatic adsorption of superparamagnetic magnetite particles and magnetized hydroxyapatite was made into a slurry for magnetic freeze casting. A low magnetic field aggregated particles into chains aligned along the transverse magnetic field axis before directional ice crystal growth segregated them into aligned lamellar structures that resulted in multi-axis strengthened porous scaffolds. Shrink wrapping scaffolds with polylactic acid film (≈ 50 Ám) to enhance radial strengthening was bioinspired by keratinous porcupine quills made up of a cortex sheath wrapped around a closed-cell foam. Infiltrating scaffolds with a dual network hydrogel effectively integrated mineral and polymer phases through joint use of calcium acetate to bind phosphate in hydroxyapatite lamellar walls and ionically crosslink alginate in the hydrogel. Future applications for these composite materials include serving as load bearing bone implants to replace osteoporotic bone. This work is supported by a Multi-University Research Initiative through the Air Force Office of Scientific Research (AFOSR-FA9550-15-1-0009) and by a National Science Foundation, Biomaterials Grant 1507978.

Industry Application Area(s)
Energy/Clean technology | Life Sciences/Medical Devices & Instruments | Materials

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