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Title:Patterning temporally dynamic 4D hydrogel and nanocomposite material gradients: predictive cellular and actuator responses
Author(s):McCracken, Joselle Marie
Director of Research:Nuzzo, Ralph G.
Doctoral Committee Chair(s):Nuzzo, Ralph G.
Doctoral Committee Member(s):Sweedler, Jonathan V.; Murphy, Catherine J.; Popescu, Gabriel
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):4D print
3D print
Cellular response
Actuator response
Direct Ink Write
Abstract:Direct-Ink Writing (DIW) is a facile form of additive manufacturing that elevates three-dimensional (3D) printed structures into materials regimes whose chemistries enable them to be temporally dynamic (4D). A series of dynamic material systems is prepared that applies DIW methodologies and design principles for the fabrication of bio-compliant 4D printed structures that can adopt two distinct form factors. The first is that of the soft aquatic actuator (SAA) scaffold. In these, the natural hydrogel alginate (Alg) is integrated with starch-based viscosifying agents as well as the inorganic nanoclay, Laponite XLG (LAP) to prepare a family of hydrogel nanocomposites that are robustly curable under mild conditions (room temperature (RT); divalent or trivalent salt solution immersion). By selectively programming the 3D distribution of transient, ion-loaded gels into the SAA scaffolds, we prepare gradients of material behaviors within Alg-LAP nanocomposites that are inspired by aquatic organisms (i.e. sea jellies from the Cnidarian phylum) and that respond passively to water current and actively to magnetic fields. In the case of SAA scaffolds, the dynamic temporal component of import is their differential actuation capabilities that are enabled by underlying crosslinker chemistries localized during printing into 4D biomimetic gradients. The second form factor into which the 4D-printed structures are categorized is that of the micro-scaffold for the purposes of programming cellular attachment and growth. In these, the synthetic hydrogel poly-HEMA (pHEMA) is integrated with its own monomer to prepare a viscous pre-polymer material (pHH) that is amenable to high resolution filament extrusion within a DIW printing platform. pHH extrusion through pulled glass capillary printheads (~30 μm diameter) yields micro-filaments that are on the order of cellular dimensions and that present contact guidance cue-rich environments for cells cultured on them in consequence (e.g. murine fibroblast, murine preosteoblast, or dorsal root ganglia cells isolated from rats). The high-performance micro-extrusion diameters that are accessible with DIW using pHH gels allows them to be deposited in registry with 2D semiconductor or polymer nanomembrane patterns that are subsequently compressive-buckled into 3D forms. The micro-scaffolds that result from compressive-buckling assembly are described here as 3D micro-cellular frameworks (μ-CFs), and their applications are not limited to buckling hydrogel filaments into controlled aerial geometries; they are also amenable to integration into cell culture contexts wherein they support and direct cellular and tissue-level cultures with unique 3D properties. These include: curvilinear forms; true terminating edges without sidewalls; broad variations of supporting feature widths; geometrically-controllable 3D placements of features (ranging proximally to distances that only self-supporting tissue-level cell constructs can bridge); and capacities to support cell growth on the adjoined faces of the scaffold frameworks. In parallel, another type of pHH-based micro-scaffold is accessible through DIW that is composed solely of hydrogel and nanocomposite materials. In cell culture, unmodified pHH-based scaffolds and films perform as blank slate materials, which are defined by their robust resistance to cellular attachment while at the same time maintaining extremely low toxicity and high tolerance to the attachment and development of cells immediately adjacent to them. Additionally, these blank slate pHH materials can be rendered highly compliant to cellular attachment following simple protein treatments, of which poly-ʟ-lysine (PLL) is a particularly strong interaction. The physicochemical interaction between pHH and PLL is of importance for this reason, and is the subject of a volumetric kinetics study using confocal fluorescence microscopy. Through this examination, a series of spin-castable pHH films is developed that are chemically identical but compositionally distinct, leading to different degrees of bio-compliance that stem from equilibrium concentrations of PLL-loading. The result is a capacity to spin-cast films that, once treated with PLL, maintain either a robust growth positive or a growth negative response. The surface treatment-independent property of these films inspires another strategy for incorporating protein treatment-free growth compliance gradients via the incorporation of LAP silicate nanodiscs into HEMA-based ink formulations. The electrostatics and rheological outcomes present within LAP-HEMA (LH)-based materials enable 3D form factors that do not require protein treatments in order to program cellular attachment and development outcomes at the point-of-printing. LH nanocomposites enable foundational 4D scaffold development that is inspired by human dentition models. In the case of micro-scaffolds of this type, the 4D temporal dynamism originates specifically from the capacity to program spatial cellular attachment and osteodifferentiation outcomes via the material chemistries and spatial geometries of the DIW pHH hydrogel and nanocomposite gradients. Taken together, we find that is possible to load compelling material attributes into DIW ink hydrogels and nanocomposites in order to prepare a series of scaffold form factors that manifest temporally dynamics attributes that are encoded during their additive manufacture.
Issue Date:2017-07-12
Rights Information:Copyright 2017 Joselle M. McCracken
Date Available in IDEALS:2017-09-29
Date Deposited:2017-08

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