Date of Award

January 2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Engineering

First Advisor

Surojit Gupta

Abstract

This dissertation investigates the synthesis and characterization of 3D printed polymer composites, with engineered porosity and both natural and synthetic additives, using fused deposition modeling (FDM) and selective laser sintering (SLS) for potential biomedical applications. The structural, mechanical, tribological, and surface behavior of these composites were evaluated with respect to their suitability for orthopedic load-bearing implants and scaffolds. In the first phase, PEEK-based composites reinforced with 10 or 20 wt% carbon fibers or 20 wt% E-glass fibers were fabricated using FDM with varying infill densities of 30-100% to introduce porosity. Results revealed that loading additives, infill densities, and porosity play a critical role on the mechanical properties, often leading to reduced strength. Increasing additive loading and porosity was observed to increase the hydrophobicity of PEEK with 20% carbon fiber composites at 30% infill exhibiting the highest contact angle of ~111.1°. In the second phase, SLS printed nylon 12 (polyamide 12 (PA 12)) composites reinforced with 5 and 10 vol% laver seaweed, dried distillers grains with solubles (DDGS), and hydroxyapatite (HA) were fabricated and characterized. Composites with engineered microchannels of ~500-550 µm and porosity of ~50-60% were analyzed for their sintering quality, microstructural, mechanical, hydrophilic, tribological, and bioactive properties. Additive loadings of 5% DDGS, 1% HA, and 5 and 10% laver enhanced mechanical strength while preserving dimensional stability and sintering quality. Higher loading of DDGS and HA led to warping and reduced sintering quality and mechanical strength. All additives enhanced moisture affinity, with 5% laver and 10% HA composites completely absorbing water droplets, indicating wettability favorable for cell attachment and fluid exchange. Under DDI water and SBF lubricated sliding, all additive systems showed a reduction in friction and wear with low coefficients of friction and wear rates. Surface analysis indicated lower abrasive wear in laver and DDGS reinforced composites compared to HA reinforced composites. Additionally, the addition of HA and laver were found to promote apatite formation in SBF. Overall, these studies offer strategies for designing additive-reinforced polymer composites using additive manufacturing for enhanced mechanical, tribological, and biological performance suitable for biomedical applications such as orthopedic implants and scaffolds.

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