More Like this

1. Grayscale Digital Light Processing and Post‐Treatment for the Fabrication of 3D‐Printed Polymer Blends

   https://doi.org/10.1002/adem.202101543  

   Hergert, John E. ; Uzcategui, A. Camila ; Muralidharan, Archish ; Crespo-Cuevas, Victor ; Ferguson, Virginia L. ; McLeod, Robert R. ( February 2022 , Advanced Engineering Materials)

   3D‐printed polymer blends with programmable mechanical and compositional heterogeneity were fabricated using grayscale digital light processing by spatially modulating the intensity of light during printing and swelling the resulting part with a second monomer. A rubbery poly(ethylene glycol) diacrylate functionally graded print is variably swollen with acrylamide monomer as a function of crosslinking density. Following a secondary polymerization, a 3D‐printed functionally graded blend with regions of varying composition and stiffness was formed. A deterministic model for polymer conversion informs printing conditions to correspond with predicted material properties based upon local volume fractions of the two materials. Upon the secondary polymerization, two networks are present within the printed structure including glassy and rubbery regions. The compressive moduli of local regions within prints ranges from 76 to 200 MPa and measured moduli of the structures agree with predicted values acquired using finite element analysis. A lattice structure with prescribed local stiffness printed using grayscale exposures deforms differentially when compressed. Advantageously, local dimensional deformations caused by the removal of the unreacted printing monomer are eliminated due to the introduction of the second polymer. This method provides predictive control over local mechanical properties and high shape precision while maintaining the simplicity of vat photopolymerization.

    

   more » « less
2. 3D Printing of a Biocompatible Double Network Elastomer with Digital Control of Mechanical Properties

   https://doi.org/10.1002/adfm.201910391  

   Wang, Pengrui ; Berry, David B. ; Song, Zhaoqiang ; Kiratitanaporn, Wisarut ; Schimelman, Jacob ; Moran, Amy ; He, Frank ; Xi, Brian ; Cai, Shengqiang ; Chen, Shaochen ( February 2020 , Advanced Functional Materials)

   The majority of 3D‐printed biodegradable biomaterials are brittle, limiting their application to compliant tissues. Poly(glycerol sebacate) acrylate (PGSA) is a synthetic biocompatible elastomer and compatible with light‐based 3D printing. In this article, digital‐light‐processing (DLP)‐based 3D printing is employed to create a complex PGSA network structure. Nature‐inspired double network (DN) structures consisting of interconnected segments with different mechanical properties are printed from the same material in a single shot. Such capability has not been demonstrated by any other fabrication techniques so far. The biocompatibility of PGSA is confirmed via cell‐viability analysis. Furthermore, a finite‐element analysis (FEA) model is used to predict the failure of the DN structure under uniaxial tension. FEA confirms that the DN structure absorbs 100% more energy before rupture by using the soft segments as sacrificial elements while the hard segments retain structural integrity. Using the FEA‐informed design, a new DN structure is printed and tensile test results agree with the simulation. This article demonstrates how geometrically‐optimized material design can be easily and rapidly constructed by DLP‐based 3D printing, where well‐defined patterns of different stiffnesses can be simultaneously formed using the same elastic biomaterial, and overall mechanical properties can be specifically optimized for different biomedical applications.

    

   more » « less
3. Mechanical Recycling of 3D-Printed Thermosets for Reuse in Vat Photopolymerization

   https://doi.org/10.1021/acsapm.4c00184  

   Maines, Erin M. ; Polley, Michaela A. ; Haugstad, Greg ; Zhao, Brenda ; Reineke, Theresa M. ; Ellison, Christopher J. ( April 2024 , ACS Applied Polymer Materials)

   Additive manufacturing, otherwise known as three-dimensional (3D) printing, is a rapidly growing technique that is increasingly used for the production of polymer products, resulting in an associated increase in plastic waste generation. Waste from a particular class of 3D-printing, known as vat photopolymerization, is of particular concern, as these materials are typically thermosets that cannot be recycled or reused. Here, we report a mechanical recycling process that uses cryomilling to generate a thermoset powder from photocured parts that can be recycled back into the neat liquid monomer resin. Mechanical recycling with three different materials is demonstrated: two commercial resins with characteristic brittle and elastic mechanical properties and a third model material formulated in-house. Studies using photocured films showed that up to 30 wt% of the model material could be recycled producing a toughness of 2.01 ± 0.55 MJ/m3, within error of neat analogues (1.65 ± 0.27 MJ/m3). Using dynamic mechanical analysis and atomic force microscopy-based infrared spectroscopy, it was determined that monomers diffuse into the recycled powder particles, creating interpenetrating networks upon ultraviolet (UV) exposure. This process mechanically adheres the particles to the matrix, preventing them from acting as failure sites under a tensile load. Finally, 3D-printing of the commercial brittle material with 10 wt% recycle content produced high quality parts that were visually similar. The maximum stress (46.7 ± 6.2 MPa) and strain at break (11.6 ± 2.3%) of 3D-printed parts with recycle content were within error the same as neat analogues (52.0 ± 1.7 MPa; 13.4 ± 1.8%). Overall, this work demonstrates mechanical recycling of photopolymerized thermosets and shows promise for the reuse of photopolymerized 3D-printing waste. 

   more » « less
4. Suitability of 3D-Printed devices for low-temperature geochemical T experiments

   https://doi.org/doi.org/10.1016/j.apgeochem.2018.08.012  

   Kletetschka, K ; Rimstidt, J Donald ; Long, Timothy E ; Michel, F Marc ( August 2018 , Applied geochemistry)

   Desktop 3D printing stereolithography (SLA) is a fabrication technique based on photopolymerization that can be used to efficiently create novel reaction devices for laboratory geochemistry with complex features (e.g. internal channels, small volumes) that are beyond the capabilities of traditional machining methods. However, the stability of 3D printed parts for low-temperature aqueous geochemical conditions has not been carefully evaluated. Furthermore, it is unclear what criteria should be used when attempting to optimize the mechanical and chemical properties during post-processing steps. Addressing these challenges is important for determining the suitability of 3D printed devices for laboratory investigations such as mineral precipitation/dissolution ex- periments. Here, we use thermogravimetric analysis (TGA) profiles, dynamic mechanical analysis (DMA), and chemical extraction of leachables to show how ultraviolet (UV) post-curing can optimize properties of a com- mercial photo-reactive resin (Formlabs Standard Clear). The mechanical and chemical stability of the post-cured material was enhanced and a working temperature of up to 80 °C was determined. We further provide data showing the stability and compatibility of the material in aqueous conditions of pH 0, 5.7 and 12. As SLA 3D printing is still an emerging and rapidly developing technology, the method presented here will provide a fra- mework for assessing how new printer types and materials (i.e. resins) impact the suitability of SLA printed devices for future experimental studies. 

   more » « less
5. Additive manufacture of lightly crosslinked semicrystalline thiol–enes for enhanced mechanical performance

   https://doi.org/10.1039/c9py01452g  

   Childress, Kimberly K. ; Alim, Marvin D. ; Hernandez, Juan J. ; Stansbury, Jeffrey W. ; Bowman, Christopher N. ( January 2020 , Polymer Chemistry)

   Photopolymerizable semicrystalline thermoplastics resulting from thiol–ene polymerizations were formed via fast polymerizations and achieved excellent mechanical properties. These materials have been shown to produce materials desirable for additive manufacturing (3D printing), especially for recyclable printing and investment casting. However, while well-resolved prints were previously achieved with the thiol–ene thermoplastics, the remarkable elongation at break ( ε max ) and toughness ( T ) attained in bulk were not realized for 3D printed components ( ε max,bulk ∼ 790%, T bulk ∼ 102 MJ m −3 vs. ε max,print < 5%, T print < 0.5 MJ m −3 ). In this work, small concentrations (5–10 mol%) of a crosslinker were added to the original thiol–ene resin composition without sacrificing crystallization potential to achieve semicrystalline, covalently crosslinked networks with enhanced mechanical properties. Improvements in ductility and overall toughness were observed for printed crosslinked structures, and substantial mechanical augmentation was further demonstrated with post-manufacture thermal conditioning of printed materials above the melting temperature ( T m ). In some instances, this thermal conditioning to reset the crystalline component of the crosslinked prints yielded mechanical properties that were comparable or superior to its bulk counterpart ( ε max ∼ 790%, T ∼ 95 MJ m −3 ). These unique photopolymerizations and their corresponding monomer compositions exhibited concurrent polymerization and crystallization along with mechanical properties that were tunable by changes to the monomer composition, photopolymerization conditions, and post-polymerization conditioning. This is the first example of a 3D printed semicrystalline, crosslinked material with thermally tunable mechanical properties that are superior to many commercially-available resins. 

   more » « less