Date of Award

Summer 8-23-2019

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Master of Science in Biomedical Engineering

Department

Biological Engineering

Advisor

Michael Mason

Second Committee Member

Paul Millard

Third Committee Member

Mehdi Tajvidi

Additional Committee Members

Ian Dickey

Abstract

The number of orthopedic surgeries performed globally has steadily increased over the past decade due to the standardization of procedures as well as technological advancements. During this time orthopedic devices have been composed predominantly of metals, such as Titanium, Vanadium, Molybdenum, and Stainless steel, as well as their alloys, due to the high strength and durability of these materials. However, metals may, in fact, be suboptimal for orthopedic devices. For example, metals exhibit Young’s modulus much greater than the surrounding bone, inducing localized stress-shielding promoting cortical atrophy, which can lead to osteoporosis. In recent years polymers have been successfully explored as a potential substitute for metals in non-load bearing locations. Some of these polymers were designed to be bio-absorbable overtime. Unfortunately, this chemical breakdown results in local acidification, which can leach into proximal bone, causing demineralization and weakening of the surrounding bone, along with increased degradation of the implant itself. In other cases, the resorbed device leaves a “mushy” non-calcified mass that is never fully regrown as a structural bone.

Our proposed solution is a cellulose nanofibril (CNF) composite-based platform material for non-load bearing surgical devices (plates, pins, screws). This composite has the potential to be safely bio-resorbable while providing sufficient stiffness during initial implantation, eventually softening overtime promoting the natural formation of strong bone. The method of making composites is adaptive allowing a host of material additives to be introduced during the CNF formation process.

Physical properties of the produced composites were analyzed and compared, in particular, flexural modulus, porosity, and Shore D hardness. Which are the primary physical assessments for many orthopedic devices and materials. Additionally, the use of ceramic synthesized biomimetic hydroxyapatite was used in making composites of CNF, this potentially adding a degree of osteoinduction to the CNF. Lastly, aqueous degradation of CNF was monitored and recorded in two separate tests, long period and short hour periods. Flexural modulus, water content increase, volume increase, and Shore D hardness was measured for all samples, with the material loss being monitored solely with long period testing. For use in material degradation, an apparatus was established and utilized for long term testing. Short term testing demonstrated initially drier specimens resistances to water gain, volume gain, and flexural decay over hydrated specimens which showed less resistance to all three parameters. Long term trials displayed the materials longevity in an aqueous solution with minimal material loss, however, specimens had high flexural decay, water gain, and volume gain after 24 hours. Recent results and recommendations are presented.

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