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Polymers
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Shape Memory Polymers
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Shape Memory Polymers

A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (1 December 2017) | Viewed by 68941

Special Issue Editors

Dr. Wei Min Huang

E-Mail Website
Guest Editor
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
Interests: shape memory materials and technology; sensors and actuators; 4D printing
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Andreas Lendlein

E-Mail Website
Guest Editor
1. Institute of Chemistry, University of Potsdam, Potsdam, Germany
2. Helmholtz-Zentrum Geesthacht, Institute of Biomaterial Science, Teltow, Germany
Interests: shape-memory polymers; shape-memory gels; micro and nanoscaled shape-memory systems; temperature-memory polymers; soft actuators; multifunctional polymeric materials; smart biomaterials; controlled drug release systems; medical devices
Prof. Dr. Tao Xie

E-Mail Website
Guest Editor
State Key Laboratory of Chemical Engineering,College of Chemical & Biological Engineering,Zhejiang University, Hangzhou 310027, China
Interests: shape memory polymers; stimuli-responsive polymers; dynamic covalent network; multidimensional printing; flexible electronics

Special Issue Information

Dear Colleagues,

The shape memory phenomenon refers to the ability of a material to recover its permanent shape, but only in the presence of the right stimulus, such as heat, chemical or light. Such a kind of shape memory effect (SME) has been reported in numerous polymeric materials (including many engineering polymers and newly developed ones). The polymers with the SME are termed shape memory polymers (SMPs). As a SMP is able not only to maintain the temporary shape but also to respond to the right stimulus when it is applied, via shape-shifting, a seamless integration of sensing and actuation functions is achieved within one single piece of polymer. We have seen a number of applications of SMPs, from heat shrink tube and anti-counterfeit label to comfort fitting and 4D printing. However, we believe that these applications are merely the starting point, as the SMPs are potentially able to reshape product design, fabrication and recycling in many ways.  The purpose of this Special Issue is to report the most recent progress within this rapidly developed exciting field and to address all kinds of concerns in materials design, synthesis, characterization, modelling/simulation and application. Both review and original papers are invited for this Special Issue.

Dr. Wei Min Huang
Prof. Dr. Andreas Lendlein
Prof. Dr. Tao Xie
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Shape memory polymer
  • Shape memory effect
  • Stimulus
  • Programming
  • Mechanism
  • Actuation
  • Sensing
  • Characterization
  • Simulation

Related Special Issues

Published Papers (11 papers)

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Research

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15 pages, 2920 KiB  
Article
Extractable Free Polymer Chains Enhance Actuation Performance of Crystallizable Poly(ε-caprolactone) Networks and Enable Self-Healing
by Muhammad Farhan, Tobias Rudolph, Ulrich Nöchel, Karl Kratz and Andreas Lendlein
Polymers 2018, 10(3), 255; https://doi.org/10.3390/polym10030255 - 01 Mar 2018
Cited by 10 | Viewed by 4011
Abstract
Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(ε-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5–60 wt [...] Read more.
Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(ε-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5–60 wt % of non-crosslinked polymer chains, which freely interpenetrate the crosslinked network, were achieved leading to differences in the resulting phase of the bulk material. This can be described as “sponge-like” with open or closed compartments depending on the amount of interpenetrating polymer. The crosslinking density and the average network chain length remained in a similar range for all network structures, while the theoretical accessible volume for reptation of the free polymer content is affected. This feature could influence or introduce new functions into the material created by thermomechanical treatment. The effect of interpenetrating PCL in cPCLs on the reversible actuation was analyzed by cyclic, uniaxial tensile tests. Here, high reversible strains of up to ∆ε = 24% showed the enhanced actuation performance of networks with a non-crosslinked PCL content of 30 wt % resulting from the crystal formation in the phase of the non-crosslinked PCL and co-crystallization with network structures. Additional functionalities are reprogrammability and self-healing capabilities for networks with high contents of extractable polymer enabling reusability and providing durable actuator materials. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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16 pages, 5617 KiB  
Article
Shape Memory Behavior of PET Foams
by Loredana Santo, Denise Bellisario and Fabrizio Quadrini
Polymers 2018, 10(2), 115; https://doi.org/10.3390/polym10020115 - 25 Jan 2018
Cited by 18 | Viewed by 5752
Abstract
Shape memory properties of PET (polyethylene-terephthalate) foams have been evaluated for two different foam densities. Samples were subjected to multiple memory-recovery cycles along three different directions to measure the effect of foam anisotropy on static mechanical and shape memory properties. The memory cycle [...] Read more.
Shape memory properties of PET (polyethylene-terephthalate) foams have been evaluated for two different foam densities. Samples were subjected to multiple memory-recovery cycles along three different directions to measure the effect of foam anisotropy on static mechanical and shape memory properties. The memory cycle was performed by uniaxial compression tests at room temperature. Despite these severe conditions, PET foams demonstrated very good shape memory behavior with shape recovery always higher than 90%. Due to cycling, the mechanical performance of foam samples is partially reduced, mainly along the extrusion direction of the foam panels. Despite this loss of static performance, shape memory properties are only partially affected by thermo-mechanical cycles. The maximum reduction is 10% for shape fixity and 3% for shape recovery. The experimental results are particularly interesting considering that compression tests were undertaken at room temperature. Indeed, PET foams seem to be optimal candidates for self-repairing structures. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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24 pages, 8798 KiB  
Article
Demonstrating the Influence of Physical Aging on the Functional Properties of Shape-Memory Polymers
by Ehsan Ghobadi, Mohamed Elsayed, Reinhard Krause-Rehberg and Holger Steeb
Polymers 2018, 10(2), 107; https://doi.org/10.3390/polym10020107 - 23 Jan 2018
Cited by 5 | Viewed by 4854
Abstract
Polymers that allow the adjustment of Shape-Memory properties by the variation of physical parameters during programming are advantageous compared with their counterparts requiring synthesis of new material. Here, we explored the influence of hydrolytic (physical) aging on the Shape-Memory properties of the polyetherurethane [...] Read more.
Polymers that allow the adjustment of Shape-Memory properties by the variation of physical parameters during programming are advantageous compared with their counterparts requiring synthesis of new material. Here, we explored the influence of hydrolytic (physical) aging on the Shape-Memory properties of the polyetherurethane system Estane, programmed in repeated thermomechanical cycles under torsional load. We were able to demonstrate that physical aging occurred through water adsorption influencing the existing free volume of the samples as well as the functional properties of Estane. Dynamic Mechanical Thermal Analysis determined the glass transition temperatures of dry and hydrolytically aged samples. According to our results, Estane takes up to 3 wt % water for two weeks (at an ambient temperature of θ = 20 °C). The glass transition temperatures of dry samples decreased within this period from 55 to 48 °C as a consequence of a plasticization effect. Next, for both samples, six subsequent thermomechanical cycles under torsional loading conditions were performed. We were able to confirm that hydrolytically aged samples showed higher shape recovery ratios of Rr ≥ 97%, although dry samples revealed better shape fixity values of about 98%. Moreover, it was observed that the shape fixity ratio of both dry and hydrolytically (physically) aged samples remained almost unchanged even after six successive cycles. Besides this, the shape recovery ratio values of the aged samples were nearly unaltered, although the shape recovery values of the dry samples increased from Rr = 81% in the first cycle to 96% at the end of six repeated cycles. Further, the evolution of the free volume as a function of temperature was studied using Positron Annihilation Lifetime Spectroscopy. It was shown that the uptake of two other organic solvents (acetone and ethanol) resulted in much higher specific free volume inside the samples and, consequently, a softening effect was observed. We anticipate that the presented approach will assist in defining design criteria for self-sufficiently moving scaffolds within a knowledge-based development process. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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5895 KiB  
Article
Elastic Shape Memory Hybrids Programmable at Around Body-Temperature for Comfort Fitting
by Tao Xi Wang, Chris Renata, Hong Mei Chen and Wei Min Huang
Polymers 2017, 9(12), 674; https://doi.org/10.3390/polym9120674 - 04 Dec 2017
Cited by 13 | Viewed by 4251
Abstract
A series of silicone based elastic shape memory hybrids are fabricated. Their shape memory performance, mechanical behaviors at room temperature with/without programming and during fitting at 37 °C are investigated. It is found that these materials have good shape memory effect and are [...] Read more.
A series of silicone based elastic shape memory hybrids are fabricated. Their shape memory performance, mechanical behaviors at room temperature with/without programming and during fitting at 37 °C are investigated. It is found that these materials have good shape memory effect and are always highly elastic. At 37 °C, there are 10 min or more for fitting. Thus, it is concluded that this type of material has great potential as an elastic shape memory material for comfort fitting. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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9616 KiB  
Article
The Study of Thermal, Mechanical and Shape Memory Properties of Chopped Carbon Fiber-Reinforced TPI Shape Memory Polymer Composites
by Zhenqing Wang, Jingbiao Liu, Jianming Guo, Xiaoyu Sun and Lidan Xu
Polymers 2017, 9(11), 594; https://doi.org/10.3390/polym9110594 - 10 Nov 2017
Cited by 41 | Viewed by 8636
Abstract
Trans-l,4-polyisoprene (TPI) shape memory polymer composites with different chopped carbon fiber mass fractions were prepared to study the effects of different chopped carbon fiber mass fractions and temperatures on the TPI shape memory polymer composites in this paper. While guaranteeing the shape memory [...] Read more.
Trans-l,4-polyisoprene (TPI) shape memory polymer composites with different chopped carbon fiber mass fractions were prepared to study the effects of different chopped carbon fiber mass fractions and temperatures on the TPI shape memory polymer composites in this paper. While guaranteeing the shape memory effect of TPI shape memory polymers, the carbon fiber fillers also significantly enhanced the mechanical properties of the polymers. The thermodynamic properties and shape memory properties of TPI shape memory polymers were studied by a differential scanning calorimeter (DSC) test, dynamic mechanical analysis (DMA) test, thermal conductivity test, static tensile test, mechanical cycle test, thermodynamic cycling test and shape memory test. Furthermore, the tensile fracture interface of TPI shape memory polymer composites was analyzed by scanning electron microscopy. The experimental results show that when the chopped carbon mass fraction fiber is 8%, TPI shape memory polymers have good shape memory properties and the best mechanical properties. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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4375 KiB  
Article
Shape Memory Polymers Containing Higher Acrylate Content Display Increased Endothelial Cell Attachment
by Tina Govindarajan and Robin Shandas
Polymers 2017, 9(11), 572; https://doi.org/10.3390/polym9110572 - 03 Nov 2017
Cited by 7 | Viewed by 4544
Abstract
Shape Memory Polymers (SMPs) are smart materials that can recall their shape upon the application of a stimulus, which makes them appealing materials for a variety of applications, especially in biomedical devices. Most prior SMP research has focused on tuning bulk properties; studying [...] Read more.
Shape Memory Polymers (SMPs) are smart materials that can recall their shape upon the application of a stimulus, which makes them appealing materials for a variety of applications, especially in biomedical devices. Most prior SMP research has focused on tuning bulk properties; studying surface effects of SMPs may extend the use of these materials to blood-contacting applications, such as cardiovascular stents, where surfaces that support rapid endothelialization have been correlated to stent success. Here, we evaluate endothelial attachment onto the surfaces of a family of SMPs previously developed in our group that have shown promise for biomedical devices. Nine SMP formulations containing varying amounts of tert-Butyl acrylate (tBA) and Poly(ethylene glycol) dimethacrylate (PEGDMA) were analyzed for endothelial cell attachment. Dynamic mechanical analysis (DMA), contact angle studies, and atomic force microscopy (AFM) were used to verify bulk and surface properties of the SMPs. Human umbilical vein endothelial cell (HUVEC) attachment and viability was verified using fluorescent methods. Endothelial cells preferentially attached to SMPs with higher tBA content, which have rougher, more hydrophobic surfaces. HUVECs also displayed an increased metabolic activity on these high tBA SMPs over the course of the study. This class of SMPs may be promising candidates for next generation blood-contacting devices. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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8082 KiB  
Article
Shape Memory Polyurethanes Based on Zwitterionic Hard Segments
by Shuqin Fu, Huanhuan Ren, Zaochuan Ge, Haitao Zhuo and Shaojun Chen
Polymers 2017, 9(10), 465; https://doi.org/10.3390/polym9100465 - 21 Sep 2017
Cited by 16 | Viewed by 5488
Abstract
This work aimed at elucidating the influence of zwitterionic hard segments on the structures and properties of shape memory polyurethanes (SMPUs). A series of zwitterionic SMPUs was successfully prepared with N-methyldiethanolamine (MDEA), 1,3-propanesultone (1,3-PS), 1,6-hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG6000). The [...] Read more.
This work aimed at elucidating the influence of zwitterionic hard segments on the structures and properties of shape memory polyurethanes (SMPUs). A series of zwitterionic SMPUs was successfully prepared with N-methyldiethanolamine (MDEA), 1,3-propanesultone (1,3-PS), 1,6-hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG6000). The influence of MDEA-PS-based zwitterionic hard segment on structure, morphology, thermal property, shape memory property and cytocompatibility were systematically investigated. The results demonstrated that the PEG-based zwitterionic SMPUs (PEG-ZSMPUs) formed phase separation structure consisting of crystalline soft phase and amorphous hard phase. The MDEA-PS zwitterionic segments showed a tendency to form ionic clusters in hard segments, which served as reinforced net points. Shape memory analysis showed that zwitterionic PEG-ZSMPUs containing a high content of zwitterionic segments had thermal-induced shape memory effects. Finally, cytotoxic assays demonstrated that MDEA-PS zwitterionic segment improved the biocompatibility of PEG-ZSMPUs. The zwitterionic PEG-ZSMPUs could thus have a promising application in smart biomedical fields. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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4203 KiB  
Article
Increased X-ray Visualization of Shape Memory Polymer Foams by Chemical Incorporation of Iodine Motifs
by Landon D. Nash, Mary Beth Browning Monroe, Yong-Hong Ding, Kendal P. Ezell, Anthony J. Boyle, Ramanathan Kadirvel, David F. Kallmes and Duncan J. Maitland
Polymers 2017, 9(8), 381; https://doi.org/10.3390/polym9080381 - 20 Aug 2017
Cited by 10 | Viewed by 6097
Abstract
Shape memory polymers can be programmed into a secondary geometry and recovered to their primary geometry with the application of a controlled stimulus. Porous shape memory polymer foam scaffolds that respond to body temperature show particular promise for embolic medical applications. A limitation [...] Read more.
Shape memory polymers can be programmed into a secondary geometry and recovered to their primary geometry with the application of a controlled stimulus. Porous shape memory polymer foam scaffolds that respond to body temperature show particular promise for embolic medical applications. A limitation for the minimally invasive delivery of these materials is an inherent lack of X-ray contrast. In this work, a triiodobenzene containing a monomer was incorporated into a shape memory polymer foam material system to chemically impart X-ray visibility and increase material toughness. Composition and process changes enabled further control over material density and thermomechanical properties. The proposed material system demonstrates a wide range of tailorable functional properties for the design of embolic medical devices, including X-ray visibility, expansion rate, and porosity. Enhanced visualization of these materials can improve the acute performance of medical devices used to treat vascular malformations, and the material porosity provides a healing scaffold for durable occlusion. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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4631 KiB  
Article
A New Type of Photo-Thermo Staged-Responsive Shape-Memory Polyurethanes Network
by Jinghao Yang, Hao Wen, Haitao Zhuo, Shaojun Chen and Jianfeng Ban
Polymers 2017, 9(7), 287; https://doi.org/10.3390/polym9070287 - 19 Jul 2017
Cited by 22 | Viewed by 5437
Abstract
In this paper, we developed a photo-thermo staged-responsive shape-memory polymer network which has a unique ability of being spontaneously photo-responsive deformable and thermo-responsive shape recovery. This new type of shape-memory polyurethane network (A-SMPUs) was successfully synthesized with 4,4-azodibenzoic acid (Azoa), hexamethylenediisocyanate (HDI) and [...] Read more.
In this paper, we developed a photo-thermo staged-responsive shape-memory polymer network which has a unique ability of being spontaneously photo-responsive deformable and thermo-responsive shape recovery. This new type of shape-memory polyurethane network (A-SMPUs) was successfully synthesized with 4,4-azodibenzoic acid (Azoa), hexamethylenediisocyanate (HDI) and polycaprolactone (PCL), followed by chemical cross-linking with glycerol (Gl). The structures, morphology, and shape-memory properties of A-SMPUs have been carefully investigated. The results demonstrate that the A-SMPUs form micro-phase separation structures consisting of a semi-crystallized PCL soft phase and an Azoa amorphous hard phase that could influence the crystallinity of PCL soft phases. The chemical cross-linking provided a stable network and good thermal stability to the A-SMPUs. All A-SMPUs exhibited good triple-shape-memory properties with higher than 97% shape fixity ratio and 95% shape recovery ratio. Additionally, the A-SMPUs with higher Azoa content exhibited interesting photo-thermo two-staged responsiveness. A pre-processed film with orientated Azoa structure exhibited spontaneous curling deformation upon exposing to ultraviolet (UV) light, and curling deformation is constant even under Vis light. Finally, the curling deformation can spontaneously recover to the original shape by applying a thermal stimulus. This work demonstrates new synergistically multi-responsive SMPUs that will have many applications in smart science and technology. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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Review

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3723 KiB  
Review
Review of Progress in Shape Memory Epoxies and Their Composites
by József Karger-Kocsis and Sándor Kéki
Polymers 2018, 10(1), 34; https://doi.org/10.3390/polym10010034 - 29 Dec 2017
Cited by 101 | Viewed by 10629
Abstract
Shape memory polymer (SMP) is capable of memorizing one or more temporary shapes and recovering successively to the permanent shape upon various external stimuli. Beside of the above mentioned one-way variants, also two-way shape memory polymers (SMPs) and shape memory (SM) systems exist [...] Read more.
Shape memory polymer (SMP) is capable of memorizing one or more temporary shapes and recovering successively to the permanent shape upon various external stimuli. Beside of the above mentioned one-way variants, also two-way shape memory polymers (SMPs) and shape memory (SM) systems exist which feature a reversible shape change on the basis of “on-off switching” of the external stimulus. The preparation, properties and modelling of shape memory epoxy resins (SMEP), SMEP foams and composites have been surveyed in this exhaustive review article. The underlying mechanisms and characteristics of SM were introduced. Emphasis was put to show new strategies on how to tailor the network architecture and morphology of EPs to improve their SM performance. To produce SMEPs novel preparation techniques, such as electrospinning, ink printing, solid-state foaming, were tried. The potential of SMEPs and related systems as multifunctional materials has been underlined. Added functionality may include, among others, self-healing, sensing, actuation, porosity control, recycling. Recent developments in the modelling of SMEPs were also highlighted. Based on the recent developments some open topics were deduced which are merit of investigations in future works. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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2778 KiB  
Review
Systematic Development Strategy for Smart Devices Based on Shape-Memory Polymers
by Andrés Díaz Lantada
Polymers 2017, 9(10), 496; https://doi.org/10.3390/polym9100496 - 10 Oct 2017
Cited by 29 | Viewed by 7570
Abstract
Shape-memory polymers are outstanding “smart” materials, which can perform important geometrical changes, when activated by several types of external stimuli, and which can be applied to several emerging engineering fields, from aerospace applications, to the development of biomedical devices. The fact that several [...] Read more.
Shape-memory polymers are outstanding “smart” materials, which can perform important geometrical changes, when activated by several types of external stimuli, and which can be applied to several emerging engineering fields, from aerospace applications, to the development of biomedical devices. The fact that several shape-memory polymers can be structured in an additive way is an especially noteworthy advantage, as the development of advanced actuators with complex geometries for improved performance can be achieved, if adequate design and manufacturing considerations are taken into consideration. Present study presents a review of challenges and good practices, leading to a straightforward methodology (or integration of strategies), for the development of “smart” actuators based on shape-memory polymers. The combination of computer-aided design, computer-aided engineering and additive manufacturing technologies is analyzed and applied to the complete development of interesting shape-memory polymer-based actuators. Aspects such as geometrical design and optimization, development of the activation system, selection of the adequate materials and related manufacturing technologies, training of the shape-memory effect, final integration and testing are considered, as key processes of the methodology. Current trends, including the use of low-cost 3D and 4D printing, and main challenges, including process eco-efficiency and biocompatibility, are also discussed and their impact on the proposed methodology is considered. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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