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Title:Freeform, direct-write assembly of thermoplastics and glasses: Theory, practice, and applications
Author(s):Gelber, Matthew K.
Director of Research:Bhargava, Rohit
Doctoral Committee Chair(s):Bhargava, Rohit
Doctoral Committee Member(s):Kilian, Kris; Underhill, Gregory H.; White, Scott R.
Department / Program:Bioengineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Direct-write assembly
Freeform 3D-printing
Carbohydrate glass
Assembly planning
Abstract:Additive manufacturing has received considerable attention in recent years for applications ranging from tissue engineering to architecture. Conventional approaches deposit material layer by layer, so that the final structure is a discretized approximation of the design along at least one dimension. There is a subset of additive manufacturing, broadly termed direct-write assembly, in which material is deposited through a translating nozzle onto a curved surface, across spanning gaps, into a fluid reservoir, or in free space. The latter approach, referred to here as freeform assembly, is particularly well-suited to fabricating sparse, free-standing frames comprising a network of connected filaments. These structures can be used as sacrificial molds, enabling the construction of networks of cylindrical channels in diverse media, which have applications in tissue engineering, microfluidics, and functional materials. The challenge is developing a freeform assembly process that can produce high-fidelity, topologically complex sacrificial molds that can be removed under biocompatible conditions. This problem is solved here using amorphous isomalt, a common pharmaceutical excipient, which is extruded above its glass transition temperature and solidifies by rapid cooling. The material properties and processing requirements for isomalt are discussed first. The physics of extrusion through a translating, heated nozzle, including heat transfer and fluid dynamics, are considered theoretically, and the shape of the extruded beams as well as the forces caused by the viscous flow are characterized experimentally. The problem of translating a design into a sequence of assembly steps is formalized and it is proved that deciding the existence of a feasible sequence is NP-complete. A graph-search approach to finding an optimal sequence, which maximizes the frame fidelity and minimizes the probably of assembly failure, is developed, implemented and validated by printing designs comprising thousands of beams. The freeform assembly process is applied to create a highly efficient helical micromixer in a material that is refractive-index-matched to water, enabling complete imaging with multiphoton microscopy. Freeform assembly also is shown to be a viable method for making polymeric medical devices, including polylactide stents and polycarbonate urethane elastomeric surgical mesh. Finally, a protocol is proposed for using an isomalt sacrificial mold to create a tissue-engineered model of the kidney proximal tubule.
Issue Date:2017-10-10
Rights Information:Copyright 2017 Matthew K. Gelber
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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