Date of Award

Summer 8-11-2017

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Engineering

Advisor

Michael Mason

Second Committee Member

Douglas Bousfield

Third Committee Member

Paul Millard

Additional Committee Members

Dr. Ian Dickey

Abstract

The field of biomaterials is of immense importance and will continue to grow and develop in the coming years. Novel materials, as well as new approaches for use of existing materials, are sought after now more than ever. Current metal orthopedic implants have an over engineered stiffness and Young’s modulus, causing a phenomenon called stress shielding. Metal implants absorb the majority of force typically exerted on bone and the osteocytes within. When osteocytes fail to sense mechanical forces bones become less dense and weaken, causing possible fracture and other complications. A new orthopedic material is needed matching Young’s modulus of bone (0.1-40GPa) and is tunable. This thesis investigates the use of dewatered cellulose nanofiber (CNF) based solid-forms for use in biomedical applications; specifically as synthetic bone and bone scaffolds. In this application, it is paramount that all materials be biocompatible, and if not biodegradable, resistant to long-term biological attacks in vivo.

The engineering task of dewatering the cellulose nanofiber slurry was solved via a combination of capillary action, convection, and lyophilization. This process produced CNF solids in a wide range of controlled and selected porosities. Three point bend testing suggested a correlation between CNF porosity and Young’s modulus. Further suggesting tunability of Young’s modulus of CNF is possible. Results suggest porosity of CNF solids is an important feature that predetermines strength of the material and surface area for possible osteocyte growth. Low porosity CNF solids were found to have a maximum Young’s modulus of 6GPa, Maximum stress yield of 80GPa, and maximum compressive and tensile stresses of 30MPa and 25MPa respectively. This is comparable or better to poly lactic acid, a state of the art orthopedic polymer, and collagen, the fibrous protein found in bone and other connective tissue. Viscoelastic properties of CNF with confirmed and found similar to bone. High porous CNF was found to be press moldable and low porous CNF highly machinable. Orthopedic fixation plates and screws were fabricated via a lathe and CNC device, yielding positive qualitative results while mimicking the shape of the existing art

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