Date of Award

December 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

James H. Henderson

Keywords

3D Printing, Biomaterials, Shape memory polymers

Subject Categories

Engineering

Abstract

The development of 3D printing techniques using shape-memory polymers (SMPs) hascreated potentials for creating dynamic, three-dimensional structures that can be produced rapidly and be customized for specific and complex architectures. These qualities have made 3D printing a popular fabrication method for future SMP parts and devices. While important information about is known about the effects of printing parameters on 3D printed SMPs, there remains a gap in the understanding of these parameters on fundamental shape memory properties. Understanding the shape memory behavior of the SMPs post-printing can implicate potential advantages or weaknesses in using these materials in biomedical applications. Furthermore, understanding how these materials perform can lead to new advancements in platforms for cell culture, personalized medicine, and medical devices.

The primary goal of this dissertation was to evaluate a cytocompatible SMP to develop techniques to 3D print predictable substrates for biomedical applications. This was accomplished through two major aims: 1) by printing and performing material characterization of cytocompatible SMP dogbones, and 2) studying and applying programming via printing in different geometric constructs. The first part of this thesis covered the preparation of cytocompatible SMP filament and the fundamental materials characterization. The second portion addressed the development and implementation of PvP.

Chapter 2 described the process for selecting the appropriate material and developing a protocol for a printer-compatible filament for printing during the fundamental and PvP studies later in the thesis. It was determined that a commercially available SMP (SMP MM4520) would best fit the needs of the remaining experiments. A custom-made melt-spinner was chosen to produce filament from the SMP pellets.

Next, a study was carried out to evaluate the shape memory behavior of the SMP (chapter 3). While several studies have reported the effects certain parameters of the printing process has on mechanical properties or part quality, the effects of printing parameters on the shape memory abilities of the printed SMP structures is not well understood. To determine the extent to which the 3D printing process affects the fundamental shape-memory properties of a printed SMP structure, we systematically varied temperature, multiplier, and fiber orientation, that is, the direction of the individual fibers that make up the sample, and studied the effect on fixing and recovery ratios of shape-memory dogbone samples. It was found that fiber orientation significantly impacted the fixing ratio, while temperature and multiplier had little effect. No significant effects on recovery ratio were seen from any of the parameters. However, as fiber orientation went from 0° to 90°, the variability of the recovery ratios increased. These results indicate that fiber orientation is a dominant factor in the resulting shape memory capacities, specifically the fixity, of a 3D printed SMP. Further, these results suggest that the parameters have an impact on the reliability of the shape memory polymer to recover back to its original shape.

A technique for trapping strains in the SMP during printing was developed (chapter 4) for fabricating ready-to-trigger objects immediately after printing. Trapped strains were measured in 1D, 2D, and 3D samples with varied temperature, multiplier, and fiber orientation. Different geometries were observed post-triggering and simulated, and an application in vitro was presented in chapter 5.

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