Abstract
Shape memory polymers (SMPs) are a promising class of materials for biomedical applications due to their favorable mechanical properties, fast response, and good biocompatibility. However, it is difficult to achieve controllable sequential shape change for most SMPs due to their high deformation temperature and the simplex deformation process. Herein, shape memory composites based on polylactic acid (PLA) matrix and semi-crystalline linear polymer polycaprolactone (PCL) are fabricated using 4D printing technology. Compared with pure PLA, with the rise of PCL content, the 4D-printed PLA/PCL composites show decreased glass transition temperature (Tg) from 67.2 to 55.2 °C. Through the precise control of the deformation condition, controllable sequential deformation with an outstanding shape memory effect can be achieved for the PLA/PCL shape memory composites. The response time of shape recovery is less than 1.2 s, and the shape fixation/recovery rates are above 92%. In order to simulate sequential petal opening and sequential drug releasing effects, a double-layer bionic flower and a drug release device, respectively, are presented by assembling PLA/PCL samples with different PLA/PCL ratios. The results indicate the potential applications of 4D-printed PLA/PCL composites in the field of bio-inspired robotics and biomedical devices.
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Acknowledgements
This work was supported by the Project of National Key Research and Development Program of China (Nos. 2018YFB1105100 and 2018YFC2001300), the National Natural Science Foundation of China (Nos. 5167050531, 51822504, 91848204, 91948302, and 52021003), the Key Scientific and Technological Project of Jilin Province (No. 20180201051GX), the Program for JLU Science and Technology Innovative Research Team (No. 2017TD-04), and the Scientific Research Project of Education Department of Jilin Province (No. JJKH20211084KJ).
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SQM and ZYJ performed the experiments and wrote the draft of manuscript; MW and LZ analyzed the data; YHL and LR proposed the project and critical comments on the writing of the manuscript; ZHZ and LQR provided some additional suggestions on experiments. SQM, ZYJ, MW, LZ, YHL, ZHZ, LR, and LQR contributed to the general discussion.
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This study does not contain any studies with human or animal subjects performed by any of the authors.
Appendix
Appendix
DW 3D printer
The homemade DW 3D printer is illustrated in Fig. A1. The printing head of the DW printer is a syringe with nozzle diameter of 640 μm. The printing route is controlled by a three-dimensional moving stage, and the printing platform is a Teflon plate with a smooth surface.
Material preparation
The material components of the printing ink are shown in Table A1. The PLA/PCL composites are named as PLA1−x/PCLx, where x is the mass ratio of PCL in PLA and PCL, respectively. The PLA/PCL powder and nano-silica were added to CH2Cl2 solvent with a mass ratio of PLA/PCL:nano-silica:CH2Cl2 = 1:0.0005:3.
Molding method for PLA sample preparation
The schematic of molding is depicted in Fig. A2. For pure PLA samples, the solution was prepared according to the material content of PLA1.00/PCL0.00. The molding method includes the following steps: (1) pour the PLA solution into a Teflon mold and scrape the top of the solution to be flat; (2) shake the mold to get rid of air bubbles; (3) dry the PLA solution at room temperature for 36 h; (4) peel the PLA samples off the Teflon mold.
Shape fixation/recovery rate of U-shape
The shape fixation rate (Rf) is calculated according to the following equation:
The shape recovery rate (Rr) is calculated according to the following equation:
where θ0 represents the angle with external force once the sample has been fixed to the temporary U-shape, θ1 represents the angle after cooling down the sample and releasing the external force, and θ2 represents the angle after heating the sample up again and recovering it to the original shape.
Shape fixation/recovery rate of helical shape
The shape fixation rate (Rf) is calculated according to the following equation:
where d0 represents the outer diameter of the helical shape with external force once the sample has been fixed to the temporary helical shape, and d1 represents the outer diameter after cooling down the sample and releasing the external force.
The shape recovery rate (Rr) is calculated according to the following equation:
where S0 represents the original rectangle area of the sheet-like sample, and S1 represents the projected area of the recovered sample.
Shape memory properties when fixed to a helical shape
The shape memory properties, including the shape fixation rate, shape recovery rate, and shape recovery time of the 4D-printed PLA/PCL samples fixed to a helical shape, are summarized in Table A2.
Force measurement of drug release devices
The force measurement was performed on a one-dimensional force transducer (500 mN, NBIT, Nanjing, China). As shown in Fig. A3a, the samples with a temporary “closed” state were placed on a hot plate 2 mm away from the force transducer, with one end pasted on the hot plate. When the samples were heated above Tg, they tended to recover to their original “open” state and then touch the force transducer, which could record the forces generated by the samples. The measured forces shown in Fig. A3b can be transferred into the mass of the pellets according to the equation of F = mg, where F denotes the force, m represents the mass, and g is 9.8 N/kg.
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Ma, S., Jiang, Z., Wang, M. et al. 4D printing of PLA/PCL shape memory composites with controllable sequential deformation. Bio-des. Manuf. 4, 867–878 (2021). https://doi.org/10.1007/s42242-021-00151-6
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DOI: https://doi.org/10.1007/s42242-021-00151-6