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1. Optimizing the Tensile Strength for 3D Printed PLA Parts

   Novoa, C; Flores, A. (November 2019, Solid Freeform Fabrication 2019: Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference)

   This research investigates on how extruder nozzle temperature, model infill rate (i.e. density) and number of shells affect the tensile strength of three-dimensional polylactic acid (PLA) products manufactured with the fused deposition model technology. Our goal is to enhance the quality of 3D printed products using the Makerbot Replicator. In the last thirty years, additive manufacturing has been increasingly commercialized, therefore, it is critical to understand properties of PLA products to broaden the use of 3D printing. We utilize a Universal Tensile Machine and Quality Engineering to comprehend tensile strength characteristics of PLA. Tensile strength tests are performed on PLA specimens to analyze their resistance to breakage. Statistical analysis of the experimental data collected shows that extruder temperature and model infill rate (i.e. density) affect tensile strength. 

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2. Impact of the Fused Deposition (FDM) Printing Process on Polylactic Acid (PLA) Chemistry and Structure

   https://doi.org/10.3390/app7060579  

   Cuiffo, Michael Arthur; Snyder, Jeffrey; Elliott, Alicia M.; Romero, Nicholas; Kannan, Sandhiya; Halada, Gary P. (June 2017, Applied Sciences)

   null (Ed.)
3. Confinement and Composition Effects on the Degradation Profile of Extruded PLA/PCL Nonwoven Fiber Blends

   https://doi.org/10.1021/acsapm.1c00454  

   Van de Voorde, Kristian M.; Korley, LaShanda T.; Pokorski, Jonathan K. (August 2021, ACS Applied Polymer Materials)
4. The influence of porosity, crystallinity and interlayer adhesion on the tensile strength of 3D printed polylactic acid (PLA)

   https://doi.org/10.1108/rpj-08-2020-0205  

   von Windheim, Natalia; Collinson, David W.; Lau, Trent; Brinson, L. Catherine; Gall, Ken (July 2021, Rapid Prototyping Journal)

   null (Ed.)

   Purpose The purpose of this study is to understand how printing parameters and subsequent annealing impacts porosity and crystallinity of 3D printed polylactic acid (PLA) and how these structural characteristics impact the printed material’s tensile strength in various build directions. Design/methodology/approach Two experimental studies were used, and samples with a flat vs upright print orientation were compared. The first experiment investigates a scan of printing parameters and annealing times and temperatures above the cold crystallization temperature ( T cc ) for PLA. The second experiment investigates annealing above and below T cc at multiple points over 12 h. Findings Annealing above T cc does not significantly impact the porosity but it does increase crystallinity. The increase in crystallinity does not contribute to an increase in strength, suggesting that co-crystallization across the weld does not occur. Atomic force microscopy (AFM) images show that weld interfaces between printed fibers are still visible after annealing above T cc , confirming the lack of co-crystallization. Annealing below T cc does not significantly impact porosity or crystallinity. However, there is an increase in tensile strength. AFM images show that annealing below T cc reduces thermal stresses that form at the interfaces during printing and slightly “heals” the as-printed interface resulting in an increase in tensile strength. Originality/value While annealing has been explored in the literature, it is unclear how it affects porosity, crystallinity and thermal stresses in fused filament fabrication PLA and how those factors contribute to mechanical properties. This study explains how co-crystallization across weld interfaces is necessary for crystallinity to increase strength and uses AFM as a technique to observe morphology at the weld. 

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5. Prolonged Release and Functionality of Interleukin-10 Encapsulated within PLA-PEG Nanoparticles

   https://doi.org/10.3390/nano9081074  

   Duncan, Skyla A.; Dixit, Saurabh; Sahu, Rajnish; Martin, David; Baganizi, Dieudonné R.; Nyairo, Elijah; Villinger, Francois; Singh, Shree R.; Dennis, Vida A. (August 2019, Nanomaterials)

   Inflammation, as induced by the presence of cytokines and chemokines, is an integral part of chlamydial infections. The anti-inflammatory cytokine, interleukin (IL)-10, has been reported to efficiently suppress the secretion of inflammatory cytokines triggered by Chlamydia in mouse macrophages. Though IL-10 is employed in clinical applications, its therapeutic usage is limited due to its short half-life. Here, we document the successful encapsulation of IL-10 within the biodegradable polymeric nanoparticles of PLA-PEG (Poly (lactic acid)-Poly (ethylene glycol), to prolong its half-life. Our results show the encapsulated-IL-10 size (~238 nm), zeta potential (−14.2 mV), polydispersity index (0.256), encapsulation efficiency (~77%), and a prolonged slow release pattern up to 60 days. Temperature stability of encapsulated-IL-10 was favorable, demonstrating a heat capacity of up to 89 °C as shown by differential scanning calorimetry analysis. Encapsulated-IL-10 modulated the release of IL-6 and IL-12p40 in stimulated macrophages in a time- and concentration-dependent fashion, and differentially induced SOCS1 and SOCS3 as induced by chlamydial stimulants in macrophages. Our finding offers the tremendous potential for encapsulated-IL-10 not only for chlamydial inflammatory diseases but also biomedical therapeutic applications. 

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