@article{mailen_wagner_bang_zikry_dickey_genzer_2019, title={Thermo-mechanical transformation of shape memory polymers from initially flat discs to bowls and saddles}, volume={28}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85065648786&partnerID=MN8TOARS}, DOI={10.1088/1361-665X/ab030a}, abstractNote={This paper describes the transformation of shape memory polymer (SMP) discs, from flat sheets to complex three-dimensional (3D) shapes, in response to heat generated by localized absorption of external infrared (IR) light. The gray-scale ink darkness printed on the surface of the SMP sheet determines the amount of absorbed light and the amount of heat generated on the surface of the sheet. Consequently, the lateral pattern of the ink governs the out-of-plane deformation of the SMP sheets due to variations in localized heating and shrinking. While recent studies have focused primarily on out-of-plane deformations of planar, rectangular substrates printed with linear patterns of ink and featuring either discrete or gradient ink variation, only limited studies have been performed on circular substrates with axisymmetric ink patterns. When heated by IR light, the axial symmetry of these ink designs produces unique out-of-plane deformations of the sheets, such as saddle shapes or bowl-like structures. We investigate these designs by utilizing a finite element analysis of material shrinkage and deformation, and we validate the model with experimental measurements and observations. This investigation provides insights into the mechanisms that cause axisymmetric geometries and ink patterns to form non-axisymmetric 3D structures, which can lead to the ability to program planar geometries that form complex 3D shapes when exposed to external stimuli.}, number={4}, journal={SMART MATERIALS AND STRUCTURES}, author={Mailen, Russell W. and Wagner, Catherine H. and Bang, Rachel S. and Zikry, Mohammed and Dickey, Michael D. and Genzer, Jan}, year={2019}, month={Apr} }
 @article{cooper_joshipura_parekh_norkett_mailen_miller_genzer_dickey_2019, title={Toughening stretchable fibers via serial fracturing of a metallic core}, volume={5}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.aat4600}, DOI={10.1126/sciadv.aat4600}, abstractNote={Stretchable fibers dissipate energy via the sequential fracturing of a metallic core held together by an elastomeric shell.}, number={2}, journal={SCIENCE ADVANCES}, publisher={American Association for the Advancement of Science (AAAS)}, author={Cooper, Christopher B. and Joshipura, Ishan D. and Parekh, Dishit P. and Norkett, Justin and Mailen, Russell and Miller, Victoria M. and Genzer, Jan and Dickey, Michael D.}, year={2019}, month={Feb} }
 @article{mailen_dickey_genzer_zikry_2017, title={A fully coupled thermo-viscoelastic finite element model for self-folding shape memory polymer sheets}, volume={55}, ISSN={["1099-0488"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85019544264&partnerID=MN8TOARS}, DOI={10.1002/polb.24372}, abstractNote={ABSTRACT}, number={16}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, publisher={Wiley}, author={Mailen, Russell W. and Dickey, Michael D. and Genzer, Jan and Zikry, Mohammed A.}, year={2017}, month={Aug}, pages={1207–1219} }
 @article{mailen_dickey_genzer_zikry_2017, title={Effects of thermo-mechanical behavior and hinge geometry on folding response of shape memory polymer sheets}, volume={122}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.5000040}, DOI={10.1063/1.5000040}, abstractNote={Shape memory polymer (SMP) sheets patterned with black ink hinges change shape in response to external stimuli, such as absorbed thermal energy from an infrared (IR) light. The geometry of these hinges, including size, orientation, and location, and the applied thermal loads significantly influence the final folded shape of the sheet, but these variables have not been fully investigated. We perform a systematic study on SMP sheets to fundamentally understand the effects of single and double hinge geometries, hinge orientation and spacing, initial temperature, heat flux intensity, and pattern width on the folding behavior. We have developed thermo-viscoelastic finite element models to characterize and quantify the stresses, strains, and temperatures as they relate to SMP shape changes. Our predictions indicate that hinge orientation can be used to reduce the total bending angle, which is the angle traversed by the folding face of the sheet. Two parallel hinges increase the total bending angle, and heat conduction between the hinges affects the transient folding response. IR intensity and initial temperatures can also influence the transient folding behavior. These results can provide guidelines to optimize the transient folding response and the three-dimensional folded structure obtained from self-folding polymer origami sheets that can be applied for myriad applications.}, number={19}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Mailen, Russell W. and Dickey, Michael D. and Genzer, Jan and Zikry, Mohammed}, year={2017}, month={Nov} }
 @article{morales_podolsky_mailen_shay_dickey_velev_2016, title={Ionoprinted Multi-Responsive Hydrogel Actuators}, volume={7}, ISSN={["2072-666X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84982797733&partnerID=MN8TOARS}, DOI={10.3390/mi7060098}, abstractNote={We report multi-responsive and double-folding bilayer hydrogel sheet actuators, whose directional bending response is tuned by modulating the solvent quality and temperature and where locally crosslinked regions, induced by ionoprinting, enable the actuators to invert their bending axis. The sheets are made multi-responsive by combining two stimuli responsive gels that incur opposing and complementary swelling and shrinking responses to the same stimulus. The lower critical solution temperature (LCST) can be tuned to specific temperatures depending on the EtOH concentration, enabling the actuators to change direction isothermally. Higher EtOH concentrations cause upper critical solution temperature (UCST) behavior in the poly(N-isopropylacrylamide) (pNIPAAm) gel networks, which can induce an amplifying effect during bilayer bending. External ionoprints reliably and repeatedly invert the gel bilayer bending axis between water and EtOH. Placing the ionoprint at the gel/gel interface can lead to opposite shape conformations, but with no clear trend in the bending behavior. We hypothesize that this is due to the ionoprint passing through the neutral axis of the bilayer during shrinking in hot water. Finally, we demonstrate the ability of the actuators to achieve shapes unique to the specific external conditions towards developing more responsive and adaptive soft actuator devices.}, number={6}, journal={MICROMACHINES}, publisher={MDPI AG}, author={Morales, Daniel and Podolsky, Igor and Mailen, Russell W. and Shay, Timothy and Dickey, Michael D. and Velev, Orlin D.}, year={2016}, month={Jun} }
 @article{mailen_liu_dickey_zikry_genzer_2015, title={Modelling of shape memory polymer sheets that self-fold in response to localized heating}, volume={11}, ISSN={["1744-6848"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84943141129&partnerID=MN8TOARS}, DOI={10.1039/c5sm01681a}, abstractNote={We conduct a nonlinear finite element analysis (FEA) of the thermo-mechanical shrinking and self-folding behavior of pre-strained polystyrene polymer sheets.}, number={39}, journal={SOFT MATTER}, publisher={Royal Society of Chemistry (RSC)}, author={Mailen, Russell W. and Liu, Ying and Dickey, Michael D. and Zikry, Mohammed and Genzer, Jan}, year={2015}, pages={7827–7834} }