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. 2016 Aug 8:6:31110.
doi: 10.1038/srep31110.

Multimaterial 4D Printing with Tailorable Shape Memory Polymers

Qi Ge  1   2 , Amir Hosein Sakhaei  1 , Howon Lee  2 , Conner K Dunn  3 , Nicholas X Fang  2 , Martin L Dunn  1
Affiliations

Multimaterial 4D Printing with Tailorable Shape Memory Polymers

Qi Ge et al. Sci Rep. .

Abstract

We present a new 4D printing approach that can create high resolution (up to a few microns), multimaterial shape memory polymer (SMP) architectures. The approach is based on high resolution projection microstereolithography (PμSL) and uses a family of photo-curable methacrylate based copolymer networks. We designed the constituents and compositions to exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior. We used a high resolution, high contrast digital micro display to ensure high resolution of photo-curing methacrylate based SMPs that requires higher exposure energy than more common acrylate based polymers. An automated material exchange process enables the manufacture of 3D composite architectures from multiple photo-curable SMPs. In order to understand the behavior of the 3D composite microarchitectures, we carry out high fidelity computational simulations of their complex nonlinear, time-dependent behavior and study important design considerations including local deformation, shape fixity and free recovery rate. Simulations are in good agreement with experiments for a series of single and multimaterial components and can be used to facilitate the design of SMP 3D structures.

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Figures

Figure 1
Figure 1. Schematics of multimaterial additive manufacture system.
(a) A workflow illustrates the process of fabricating a multimaterial structure based on PμSL (b) Photo-curable shape memory polymer network is constructed by mono-functional monomer, Benzyl methacrylate (BMA) as linear chain builder (LCB), and multi-functional oligomers, Poly (ethylene glycol) dimethacrylate (PEGDMA), Bisphenol A ethoxylate dimethacrylate (BPA), and Di(ethylene glycol) dimethacrylate (DEGDMA) as crosslinkers.
Figure 2
Figure 2. Experimental characterization of methacrylate SMP networks.
Highly tailorable glass transition temperature (a), rubbery modulus (b), and failure strain (c) are controlled by either changing the mixing LCB/crosslinker ratio or using different crosslinkers. (d) The temperature effect on the failure strain of the SMP consisting of 90% BMA and 10% BPA. (e) The normalized exposure energy to cure a thin layer varies with the crosslinker concentration as well as the molecular weight of crosslinker. (f) The investigation on the interface bonding of a printed composite with two components arranged in series (inset).
Figure 3
Figure 3. SM behavior of the (meth)acrylate based copolymer SMP network.
(a) The SM behavior has been investigated by following a typical SM cycle: at Step I, a sample is deformed by emax at a programming temperature TD; at Step II, the temperature is decreased from TD to TL while keeping the sample deformed by emax; at Step III, after unloading, there is a deformation bounce back Δe; at Step IV, the free recovery is performed by heating the sample to a recovery temperature TR. (b) The representative SMP strain-time curves achieved by stretching a SMP sample (80% BMA and 20% P750) at 63 °C, unloading at 25 °C, and heating to 63 °C, 50 °C, 40 °C and 35 °C, respectively. (c) Shape fixity as a function of programming temperature. (d) Shape recovery time (t0.95) as a function of recovery temperature.
Figure 4
Figure 4. 3D printed shape memory structures with single material.
(a) A 3D printed shape memory spring (I) was programmed to a straight strand temporary configuration (II), and then recovered to its original shape upon heating (III–V). (b) Experimental characterization and FE simulation were performed to investigate the nonlinear deformation. (c) Experiments and simulations of the free recovery at different temperatures. (d) 3D printed SM Eiffel tower. (e) 3D printed SM stents.
Figure 5
Figure 5. 3D printed multimaterial grippers.
(a) Multimaterial grippers were fabricated with different designs. (b) The demonstration of the transition between as printed shape and temporary shape of multimaterial grippers. (c) The snapshots of the process of grabbing an object.
Figure 6
Figure 6. The sequential recovery of a multimaterial flower.
The multimaterial flower in the original shape (c) was first programmed into the temporary bud state at 20 °C (a). The outer petals opened first after heating to 50 °C (b) and then, the flower fully bloomed at 70 °C (c). (d)–(f) represent the FE simulations of the corresponding flower blooming process.
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