Over the years, I have been collecting different journal publications, conference proceedings, meetings, patents, and even books that have either used or mentioned the Discov3ry Extruder. We are currently published in at least 16, scratch that, 17 publications that have directly used the Discov3ry Extruder to advance research (that's exciting) and have been mentioned in about 16 more (including 3D printing for Dummies!).
I will be sharing my entire collection with you over the following months. Last week I shared 9 academic journal publications where the Discov3ry was used in the experimentation. If you missed it, you can read all about it right here. This week's collection includes four academic dissertations that have used the Discov3ry Extruder directly to help the graduate students get experimental results and finish their thesis!
Without further ado, here are the four theses. The thesis publications range from Universities in Canada (Simon Fraser and Waterloo), South Carolina (Clemson), and even Italy (Milan Polytechnic). Here they are in reverse chronological order. I have included the abstract and keywords, but I encourage you to get a copy of the full papers directly from the host university websites (linked below).
 Design of 3D-Printable Conductive Composites for 3D-Printed Battery.
Park, J. S. (2016). Simon Fraser University. Canada. [Link]
ABSTRACT: In this research, a biocompatible nano-composite is designed for the application of 3D printed battery. The nano-composite paste is composed of an electrically conductive silver nanowire (AgNW) filler within a thixotropic carboxymethyl cellulose (CMC) matrix. Experimental demonstration and computational simulations on nano-composites with various filler fractions are performed to find the electrical percolation threshold of the nano- composite. The percolation threshold as 0.7 vol. % of AgNWs is predicted by computer simulations as well as by experiments. Also, maximum electronic conductivity is obtained as 1.19×102 S/cm from a nano-composite with 1.9 vol. % of AgNWs. Also, newly designed paste 3D printing apparatus is built by integrating a commercially available delta 3D printer with a paste extruder. Finally, the 3D printable battery facilitated by the conductive composite is demonstrated. Cathode and anode materials are formulated by addition of cathode and anode active materials to the nano-composite of AgNW and CMC. Rheology study of the cathode and anode paste is carried out and thixotropic (shear-thinning) behavior is observed which is an essential characteristic of the 3D printable paste. Lastly, the performance demonstration on the fabricated 3D printed battery is carried out. The 3D printable conductive paste is expected to contribute in additive manufacturing process for printable electronics.
KEYWORDS: CMC; Silver nanowire; lithium battery; nano-composite; paste 3D printing; percolation threshold
 Optimization and characterization of a commercial 3D printer for direct hydrogel writing.
Volino, M. (2016). Milan Polytechnic. Italy. [Link]
ABSTRACT (translated from Italian):
The concept of printing in three dimensions (3D printing) was introduced for the first time in 1983 by Charles W. Hull. It is a rapid prototyping process that allows the realization of three-dimensional structures, layer by layer, starting from a digital model of the object. The most commonly used 3D printing technologies are: Stereolithography (SLA), Digital Light Processing (DLP) technology, Fused Deposition Modeling (FDM) and the latest Direct Ink Writing (DIW). Over the years, three-dimensional printing technologies have gained greater influence in the most disparate fields: art, architecture and tissue engineering. The purpose of tissue engineering is regeneration, the restoration or replacement of living tissues or organs that have suffered injuries or insults during their lifetime. To achieve this goal, support structures, commonly called scaffolds, are used in biomedical and tissue engineering applications with the main goal of regenerating or replacing functionally and structurally the original tissues. In general, scaffolds must have some pre-eminent characteristics: internal pathways that allow cell migration and adhesion, adequate mechanical properties, shape retention during cell growth and high porosity to allow cell proliferation and differentiation but also the transport of oxygen, nutrients, growth factors and the expulsion of waste products. In this compound, 3D molding technologies allow, with respect to all the other techniques used to make scaffolds, to obtain a high repeatability and control on the interconnection of the pores, on their distribution, size and volume, leading to the creation of customized support structures. Two types of scaffolds can be manufactured with the above-mentioned 3D printing technologies: cellular scaffolds, in which the cells are seeded on an appropriate 3D printed structure and bio-molded scaffolds, in which the cells and the chosen biomaterial are printed together to form the three-dimensional structure. The 3D bioprinting technology is used to obtain a controlled distribution of cells in three-dimensional structures in such a way that the cells themselves do not die or lose their functionality. The aim of the project was therefore to explore a new application of 3D printing technology in the context of tissue engineering. The project involved the optimization of a low-cost commercial 3D printer for the controlled deposition of hydrogels in order to realize accurate three-dimensional cellular cultures. The initial demonstration of the feasibility of the adaptation of the commercial printer for the controlled deposition of hydrogels in three-dimensional geometries could lead to the validation of this technique for the fabrication of cellular tissues and models. The choice and design of the material to be printed also took on great importance. The thesis project has in fact shown how it is the choice of the material and its characteristics that influence the optimization of the deposition system and not vice versa. The deposition system consists of a 3D printer, Felix 3.0 Dual extruder, and a simple system, called "pasta extruder", the Discov3ry, which is electrically connected to the printer and allows the extrusion of the material exerting a controlled pressure on the piston of a syringe. This extrusion mode is typical of filament-based DIW techniques where a highly viscous material is extruded as a continuous filament on a movable support, in this case the printer plate, through a cylindrical or conical nozzle. Experimental tests have highlighted two main problems: the not perfect control of the amount of extruded material per unit of time (flow) and the mechanical inadequacy of the support made by the company to allow the possible use of the Discov3ry tip as a second printer extruder. Regarding the latter problem, the aim was therefore to build a support that would allow to easily calibrate the tip of the pasta extruder without compromising the ability to move along the Z axis. The final support created was inspired by the design of the printer's hot-end. It is important to underline however how the fluid is not heated in any part of the extrusion system, which allows only extrusions at room temperature. Instead, it was possible to control the flow through an understanding of the mechanical and physical laws that regulate the flow of material along the system. The Discov3ry behaves like a syringe pump consisting of: a stepper motor, a transmission, two toothed wheels and a worm screw attached to the base in which the syringe is housed. Being able to control the revolutions of the stepper motor thanks to the software of the printer and known the reduction ratio of the entire system, it was possible to determine the speed of translation of the screw and therefore the flow rate exiting the syringe. The choice of material has fallen on a new type of natural hydrogel, used for a few years in tissue engineering: the silk fibroin solution. The silk fibroin solution is a natural hydrogel, extracted from the Bombyx mori silkworms, which has been shown to be highly biocompatible and possess excellent mechanical properties. Following the extraction process, the solution obtained is a 7-8 w / v% silk fibroin solution. This solution from the rheological point of view is similar to water; it has therefore been extremely useful during the comprehension and modeling of the system but not subsequently for the realization of multi-layer structures. Highly concentrated materials have shown to be particularly suitable for the realization of specific three-dimensional structures as they are capable of maintaining the filamentary form also following the extrusion. As a result, the solution was necessary to obtain a shear thinning response (shear thinning response). This means that by increasing the pressure or the extrusion speed above a certain threshold ("shear yield stress"), the solution will start to flow with an ever lower viscosity and therefore will be easier to print but, as soon as it is extruded, coming back at a condition of zero stress, it will behave like a gel. It was possible to concentrate the silk fibroin solution only up to 25 w / t%; it showed an initial thinning response at the cut but a viscosity not sufficient to form a continuous filament that maintained the shape immediately after extrusion. The solution was, therefore, extruded in the form of drops. The fluid dynamics involved in the formation of the drops and their dilation following the impact with the substrate or with the other underlying layers plays a fundamental role in determining the lateral and vertical resolution of the system. The height and width of the printer lines depend on the size, the extension of the expansion and the deformation of the drops followed by solidification. The solidification of the structures takes place after the evaporation of the water content of the silk fibroin solution thanks to a printer plate temperature of 40 ° C. The best lateral resolution obtained with the system used (flat cylindrical nozzle with internal diameter of 610 μm and external of 900 μm) was 850 μm at a deposition rate of 15 mm / s. The line width does not vary depending on the flow rate at a given deposition rate but by varying the deposition rate it decreases slightly. By fixing the flow rate, with a certain line width, the height is also inversely proportional to the deposition speed. A thickness of 40 μm was obtained with the same nozzle, at a flow rate of 0.4 〖mm〗 ^ 3 / s and a deposition rate of 2 mm / s. Multilayer structures were also created. The profile of these structures was not perfectly uniform; this could be due to the round profile of the single printed lines that does not favor an adequate support or the non-perfect melting of the layer-on-layer deposited material. The lateral and vertical resolution of the deposition system is therefore determined by the rheological properties of the solution, the printing speed, the diameter and the shape of the nozzle. The system was therefore characterized in terms of deposition parameters such as the viscosity of the material, the width and the height of the line. Numerous limitations were found due to the choice of the material used and the nature of the system. In any case, it has shown good potential to be adopted in the field of 3D bioprinting; it is also easy to use and not too expensive.
KEYWORDS: 3D printing; 3D bioprinting; scaffold; hydrogel; silk fibroin; tissue engineering
 Advanced Manufacturing of Lightweight Porous Carbide Shapes Using Renewable Resources.
Islam, M. (2018). Clemson University. United States of America. [Link]
ABSTRACT: This dissertation presents an origami-inspired manufacturing and an additive manufacturing platform for the fabrication of 3D shapes of porous carbide material using renewable biopolymers as the carbon source. Porous carbide materials possess interesting properties including low density, high surface area, high chemical inertness, high oxidation resistance, adjustable electrical conductivity, and high mechanical properties. Due to such properties, they are used in different applications such as high temperature filters, catalytic support, thermal insulators and structural materials. The state-of-the-art to manufacture porous carbide materials includes direct foaming and templating methods. However, shaping of porous materials with these techniques relies on the use of molds, which restricts the shape complexity of the fabricated parts. Furthermore, most of the carbon precursors used in the current fabrication methods are polymers synthesized from non-renewable petroleum, which leads to a non-environment-friendly synthesis process of carbide materials. Different biopolymers including gelatin, chitosan and glucose have been demonstrated for a sustainable approach for the synthesis of carbide materials by previous authors. However, these synthesis approaches were limited only to the production of carbide nanoparticles. No method was reported so far for the fabrication of 3D shapes of porous carbide materials using the biopolymeric approaches. Hence, in this dissertation, I intend to develop manufacturing platforms which allow for the fabrication of 3D complex shapes of carbide materials using renewable biopolymers to achieve an environment-friendly process.
 Extrusion-based 3D Printing and Characterization of Edible Materials.
Huang, C. Y. (2018). University of Waterloo. Canada [Link]
ABSTRACT: 3D printing food offers the ability to customize shapes, texture, as well as nutritional content. In addition, it can automate the cooking process to save time and produce meals on-demand to minimize waste. One potential application is to 3D print food for those suffering from dysphagia, a condition that affects one’s ability to swallow. Texture modified food products for dysphagia often lose their shape and have limited visual appeal. 3D printing could provide shape to these texture modified food products and ultimately improve nutrient intake. One of the limitations that are currently preventing wider adaption of this technology is the lack of understanding of how food properties affect the 3D printing process and quality of the printed object. In this thesis, room temperature extrusion-based 3D printing was investigated using a desktop 3D printer with a syringe extrusion system. Two hydrocolloids, modified starch and xanthan gum, were used as model material to study room temperature extrusion-based 3D printing. The relationship between the 3D printer settings and the extrusion process variables, extrusion rate and nozzle speed, was obtained by investigating the machine command (G-code). The nozzle speed could be controlled by the extrusion multiplier while the extrusion rate could be controlled by the stepper motor speed. In addition, extrusion tests showed that the syringe extrusion system displayed a lag time around 2 to 5 minutes before stable extrusion rate was reached. The extrusion lag time increased with increased material yield stresses and decreased with increased syringe motor speed. Xanthan gum paste, modified starch pastes, and puréed carrot were selected as model inks. Oscillatory rheology measurements including strain and frequency sweep were conducted to study the range of properties suitable for 3D printing. The range of yield stress suitable for extrusion was between 60-730 Pa and around 0.1-0.2 for the loss tangent (tan δ). The printable range of complex modulus (G*) was from 320 to 1200 Pa. Furthermore, data from the frequency sweep of xanthan gum and modified starch pastes was fitted to power law models and compared to published data of foods to assess their potential suitability as food inks for 3D printing. Puréed carrot had higher G* compared to xanthan gum and modified starch pastes but had lower elasticity. Puréed carrot was suitable for 3D printing because of its stiffness and low elasticity. In addition, food texture measurements based on the methods described in the International Dysphagia Diet Standardisation Initiative (IDDSI) were also conducted. Printable inks were able to retain its shape on a fork without dripping through the prongs and slide off a spoon with minimal residue. Two printed objects were considered, a line and a cylinder. The line printing was conducted to find the optimal settings of volumetric extrusion rate, nozzle speed, and layer height. The cylinder printing was conducted to assess the effects of ink rheology and infill levels, the fraction of the interior of the object to be filled with material when printed, on maximum build height. Continuous lines and sharp angles were able to be 3D printed when the line diameter was 130% of the nozzle diameter. Slightly thicker lines ensure proper layer adhesion. The layer height of the printed line, determined from the aspect ratio (height over width), ranged from 50% to 80% of the nozzle diameter. Lower aspect ratio indicated spreading of the ink. The cylinder printing experiments indicated that an ink with storage modulus (G’) around 300 Pa produced cylinder up to 20 mm height before collapse, while an ink with G’ around 900 Pa produced a cylinder up to twice the height. Increasing infill levels from 0 to 50% provided additional internal support to the structure but subjected the object to more stress due to nozzle movement. The work presented in this thesis generated information on how rheological characteristics affect the food’s suitability for room temperature extrusion-based 3D printing as well as the quality of the printed object. The relationships between the 3D printer, slicer setting, and G-code were investigated to understand how extrusion rates and nozzle speeds can be controlled for 3D printing paste type inks. Food texture measurements based on the methods described in the International Dysphagia Diet Standardisation Initiative (IDDSI) were conducted with fork and spoon to assess the ink’s consistency and adhesiveness. Rheological characterization of the inks provided upper and lower limit of a printable ink. Power law models were used to analyze the rheology data and the models parameters of the inks were compared to published data of foods to assess their potential suitability as food inks for 3D printing.
KEYWORDS: 3D Food Printing; 3D Printing; Chemical Engineering; Master Thesis; Rheology; Starch; Texture Modified Food; Xanthan Gum
- Park, J. S. (2016). Design of 3D-Printable Conductive Composites for 3D-Printed Battery. Simon Fraser University. Retrieved from http://summit.sfu.ca/item/16545
- Volino, M. (2016). Optimization and characterization of a commercial 3D printer for direct hydrogel writing. Milan Polytechnic. Retrieved from https://www.politesi.polimi.it/handle/10589/131568
- Islam, M. (2018). Advanced Manufacturing of Lightweight Porous Carbide Shapes Using Renewable Resources. Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/2138
- Huang, C. Y. (2018). Extrusion-based 3D Printing and Characterization of Edible Materials. University of Waterloo. Retrieved from https://uwspace.uwaterloo.ca/handle/10012/12899