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Three New Peer Reviewed Studies Explore Extrusion 3D Printing for Composites, Bioprinting and Manufacturing

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As 3D printing technologies and materials rapidly expand, more and more research is being conducted in order tu fully understand the possibilities that even the most accessible and basic 3D printing processes can offer. Ever since open source plastic extrusion 3D printing (generally known as fused filament fabrication or FFF) became accessible to university labs, the unique opportunities that it offered to science labs in just about every research field – from mechanical engineering to bioarchitecture – became clear. Just yesterday (June 15th) three peer reviewed studies were published that explore the possibilities offered by extrusion 3D printing in the most varied fields, from composite manufacturing, to bioengineering materials to an analysis of 3D printing for end part manufacturing.

The first of these studies, titled Fabrication of Continuous Carbon, Glass and Kevlar fibre reinforced polymer composites using Additive Manufacturing, was conducted by Andrew N. DicksonJames N. BarryKevin A. McDonnell, and Denis P. Dowling of the School of Mechanical and Materials engineering, University College Dublin, Belfield, Dublin 4, Ireland. It was received 4 August 2016, revised 19 May 2017, accepted 14 June 2017, and is available online as of 15 June 2017.

This study evaluated the performance of continuous carbon, Kevlar and glass fibre reinforced composites manufactured using the fused deposition modelling (FDM) additive manufacturing technique. These nylon composites were fabricated using a Markforged Mark One 3D printing system. The mechanical performance of the composites was evaluated both in tension and flexure. The influence of fibre orientation, fibre type and volume fraction on mechanical properties were also investigated. The results were compared with that of both non-reinforced nylon control specimens, and known material property values from literature. It was demonstrated that of the fibres investigated, those fabricated using carbon fibre yielded the largest increase in mechanical strength. Its tensile strength values were up to 6.3 times that obtained with the non-reinforced nylon polymer. As the carbon and glass fibre volume fraction increased so too did the level of air inclusion in the composite matrix, which impacted on mechanical performance. As a result, a maximum efficiency in tensile strength was observed in glass specimen as fibre content approached 18%, with higher fibre contents (up to 33%), yielding only minor increases in strength.

The second study that was also published on June 15th is titled Poly-l-lactic Acid: Pellets to Fiber to Fused Filament Fabricated Scaffolds, and Scaffold Weight Loss Study. It was conducted by Prashanth RaviPanos S. Shiakolas and Tré R. Welch from the Department of Mechanical and Aerospace Engineering, The University of Texas at Arlington, United States, and the Division of Pediatric Cardiovascular and Thoracic Surgery, The University of Texas Southwestern Medical Center, Dallas, United States. The research was received 16 June 2016, revised 25 May 2017, accepted 14 June 2017 and is available online 15 June 2017.

This study explore the use of Poly-l-lactic acid (PLLA), which is a bioresorbable polymer used in a variety of biomedical applications. Many 3D printers employ the fused filament fabrication (FFF) approach with the ubiquitous low-cost poly-lactic acid (PLA) fiber. However, use of the FFF approach to fabricate scaffolds with medical grade PLLA polymer remains largely unexplored. In this study, high molecular weight PL-32 pellets were extruded into ∼1.7 mm diameter PLLA fiber. Melt rheometric data of the PLLA polymer was analyzed and demonstrated pseudo-plastic behavior with a flow index of n = 0.465 ( < 1). Differential scanning calorimetry (DSC) was conducted using samples from the extruded fiber to obtain thermal properties. DSC of the 3D printed struts was also analyzed to assess changes in thermal properties due to FFF. The DSC and rheometric analysis results were subsequently used to define appropriate FFF process parameters.

Constant porosity scaffolds were FFF 3D printed with 4 distinct laydown patterns; 0/90° rectilinear (control), 45/135° rectilinear, Archimedean chords, and honeycomb using the in-house developed custom multi-modality 3D bioprinter (CMMB). The effect of laydown pattern on scaffold bulk erosion (weight loss) was studied by immersion in phosphate-buffered saline (PBS) over a 6-month period and measured monthly. A repeated measures analysis of variance (ANOVA) was performed to identify statistically significant differences between mean percent weight loss of the four laydown patterns at each time point (1-6 months). The resulting data follows distinct temporal trends, but no statistically significant differences between means at individual time points were found. Cross-sectional scanning electron microscope (SEM) images of the 6-month degraded scaffolds showed noticeable structural deterioration. The study demonstrates successful processing of PLLA fiber from PL-32 pellets and FFF-based 3D printing of bioresorbable scaffolds with pre-defined laydown patterns using medical grade PLLA polymer which could prove beneficial in biomedical applications.

The third research that was published on the same day compares FFF printed parts to injection molded parts. The work is titled Investigation of Mechanical Anisotropy of the Fused Filament Fabrication Process via Customized Tool Path Generation and was conducted by Carsten KochLuke Van Hulle and Natalie Rudolph of the University of Wisconsin-Madison in Madison, USA. It was received on 2nd February 2017, revised 9 May 2017, accepted 14 June 2017, and is available online as of 15 June 2017

The goal of the study is to aid in the transition of 3D printed parts from prototypes to functional products, which requires investigating the mechanical anisotropy induced by the Fused Filament Fabrication (FFF) process. Since the mechanical properties of an FFF part are most greatly affected by the bead orientation and printed density, or solidity ratio, techniques to precisely control these variables are required. An open source Python program, SciSlice, was developed to create the desired tool paths/layer orientations and convert them into machine commands (e.g. G-Code). SciSlice was then used to develop tool paths which either directly printed tensile specimens or printed sheets from which specimens could be water-jet cut. The effects of proper bed leveling and feed wheel adjustment are noted and a careful analysis of both bead orientation and solidity ratio are presented. Printing artifacts related to turns made at the part edges are discussed having been found to have strong effects on the measure strength in the weakest orientation. Finally, it is shown that with proper bead orientation, low layer heights, and a maximum solidity ratio, tensile strengths within 3% of injection molded parts are achievable.


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