Abstract
Since the last three decades, international research interest into the shape-memory effect in polymers has been rapidly growing. The recent progresses made in the synthesis of different types of shape-memory polymers (SMPs) significantly expanded the practical potential of their applications in such fields like microelectromechanical systems, medical and biomimetic devices, sensors, actuators, self-healing systems, etc. The present chapter is focused on the classification of shape-memory polymeric materials (SMPs), as well as the current developments and most important concepts for these types of smart polymers. The recent progress in the development of shape-memory polymer composites (SMPCs) and shape-memory polymer blends (SMPBs) is also highlighted. In this chapter, different classification criteria of SMPs with a view to polymer type and structure and external stimulus are described. Particular emphasis is placed on the factors enabling shape-memory effects, especially structure–property correlations that influence shape-memory mechanisms.
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1 Introduction
Shape-memory polymers (SMPs) are a kind of very important smart polymers that have multiple shape capacities. They can be deformed and subsequently fixed into a temporary shape, which would remain stable unless they are exposed to an appropriate external stimulus such as temperature, light, pH, electric or magnetic field, and specific ion or enzyme that triggers the polymers to recover to their original shape. Usually, preparation of SMPs is conducted by conventional processing methods, e.g., injection molding or extruding. During processing, the polymer is formed into its initial permanent shape B. Afterward, the polymer specimen is deformed and fixed into the temporary shape A (Fig. 1). Polymer recovers its initial permanent shape B after application of an external stimulus [1]. In comparison with metallic shape-memory alloys, such cycle can be repeated several times in much shorter interval. Additionally, SMPs allow a much higher deformation rate between shapes A and B [2]. Apart from easy manufacturing and processing, for many applications, SMP materials are attractive substitutes to metals because of their flexibility, biocompatibility, low cost, and wide scope of modifications. Shape-memory polymer composites (SMPCs) and shape-memory polymer blends (SMPBs) have considerably enhanced the range of applications of shape-memory polymers.
Schematic representation of shape-memory effect for thermally induced process
The first shape-memory effect in polymers was described by Vernon et al. in the US patent on dental materials (methacrylic ester resin) [3, 4]. The first application of SMPs was heat-shrink tubing by Paul Cook at Raychem Company in the late 1950s [5]. The next important step in the development of SMPs was reported by Rainer et al. in [6], the utilization of heat-shrinkable polyethylenes [6]. This polymer was able to memorize its initial shape after irradiation with gamma rays. Also, George Odian with coworkers at Radiation Applications, Inc. in early 1960s, developed for NASA deployable space structures from polyethylene with radiation-induced memory. Besides these, only a few other studies were performed in the 1960s; however, industrial application was being widely explored as evidenced by patent literature on “heat-shrinkable” or “heat-recoverable” materials used in electrical engineering and packaging industry (Fig. 2) [5]. Starting in the mid-1990s, academic interest in the field of shape-memory polymers dramatically grew. Since then the research in SMPs has increased due to their possible and promising application in several fields such as smart textiles and apparels, medical devices, sensors and actuators, flexible electronic devices, high-performance water vapor permeability membranes, aerospace applications, and many others [7]. In recent years, a wide variety of polymers has been synthesized with shape-memory effects. A number of unique properties have been developed in different types of polymers like thermoplastics, elastomers, thermosets, polymeric blends and composites, hydrogels, and liquid crystals.
a Heat-shrinkable plastic tubes used to insulate wires; b Packaging shrink-wrap foil
2 Classification of SMPs
With the emergence of new types of shape-memory polymers, the basic criteria for their classification were defined. The most commonly used classification of SMPs (discussed in this review) includes the three criteria: composition and structure of polymers, the type of stimulus which triggers the shaping back to the permanent phase, and the character of shape-memory function. Such integrated insight into the classification of SMPs was proposed by Hu et al. [8]. Another division into physically and chemically cross-linked SMPs, according to the nature of their netpoints, was introduced by Liu and coworkers [9]. The combined scheme of the two above classifications is presented in Fig. 3. The chemical structure of SMPs and a type of activation trigger were the main criteria for classification showed by Mather [5]. This division includes four categories. Category I and Category II are chemically cross-linked networks that utilize, respectively, a glass transition and melting transition for their activation. Category III and Category IV represent physically cross-linked polymers activated accordingly, with a glass transition and melting transitions.
Schematic view over classification criteria of shape-memory polymers
2.1 Classification by Polymer Structure
Almost, all polymerization methods can be used to synthesize SMPs, including addition, condensation, free-radical and photochemical polymerization, and radiation reaction [9]. The shape-memory effect of the polymer can be achieved through the generation of strong interaction among the polymer chains. Usually, elastic entropic forces result from the presence of physical or chemical netpoints, which can be achieved by covalent bonds or intermolecular interactions. This kind of polymeric materials must present an adequate morphology in order to show this behavior [10]. Taking into account the cross-linking characteristics, composition, structure, morphology, and type of polymer materials, SMPs are often classified into four different polymer structures: chemically cross-linked, physically cross-linked, polymer blends, and polymer composites [11].
Generally, the molecular structure of SMPs consists of two practical parts, cross-links with chemical or physical nodes (hard segments), and switching segments. The cross-linked elements of structure allow for the memorization of the original permanent shape. The hard segments may be of physical or chemical nature, such as chemical cross-links, crystals, glassy domains, or chain entanglements [12]. The switching segments are the polymer chains between network nodes that undergo the reversible shape change (Fig. 4) [5]. The soft segments work as reversible molecular switch at transition temperatures. These segments can be either amorphous or crystalline, and therefore the transition temperature (Ttrans) is glass transition temperature (Tg) and a melting point temperature (Tm), respectively. Chemically cross-linked SMPs can be obtained by a suitable cross-linking chemistry, which are referred to as thermosets. Physically cross-linked ones require a polymer morphology consisting of segregated domains, which is typical for thermoplastics [10].
Molecular mechanism of thermally induced shape-memory effect for different types of SMPs
2.1.1 Chemically Cross-Linked Polymers
For the chemically cross-linked polymers (thermosets), the polymer network is built from the polymer chains connected by covalent bonds, which are more stable than the physical cross-linking network and show an irreversible nature [13, 14]. When the covalent bonds are introduced into polymer matrix, the programmed shape of polymer cannot be further changed. Covalent netpoints can be obtained during polymerization by the cross-linking of linear or branched polymers as well as (co)polymerization/(co)polycondensation of one or several monomers, in which one has at least trifunctional. The other methods rely on postprocessing cross-linking of polymer chains. The physicochemical properties of the network can be adjusted by the choice of monomers, their ratio and functionality, and the cross-link content. Additionally, these properties can be controlled by the curing conditions and curing time. Several types of SMPs are also synthesized by synthesis route, which involve copolymerization of monofunctional monomers with oligomeric difunctional cross-linkers [10]. Such AB copolymer networks possess increased toughness and elasticity at room temperature. AB copolymer network with Ttrans based on Tg was obtained by copolymerization of various acrylates with poly[(l-lactide-ran-glycolide)]dimethacrylate [13]. Similar covalently SMP AB copolymer network with melting transition Tm used as switching transition for the shape-memory effect was prepared by copolymerization of n-butyl acrylate with semicrystalline oligo[(ε-hydroxycaproate)-co-glycolate]dimethacrylates [15].
Typical examples of SMP networks prepared during polymerization processes are styrene copolymers, thermosetting polyurethanes, polyacrylates and polymethacrylates, PE/poly(vinyl acetate) copolymer, and epoxides. The thermosetting SMPs, like for example cross-linked styrene-based SMP and epoxy SMP, in contrast to thermoplastic SMPs with poor thermal and mechanical properties, are generally used for large-scale structural materials. Copolymerization of styrene with various co-monomers is the key to obtaining shape-memory materials with enhanced flexibility and a huge variety of network architectures [16]. For example, shape-memory effect has been reported for copolymer of styrene, corn oil and divinylbenzene [17], and trans-poly(1,4-butadiene)-polystyrene copolymer [18]. Also, polyacrylates and polymethacrylates are of interest as shape-memory materials due to their ease of preparation, their simple phase behavior, and the possibility of easily tuning their key characteristics. (Meth)acrylates with a wide variety of ester functionalities are commercially available, and many of them can be copolymerized by radical polymerization in bulk or in solution [13]. The acrylic monomers which are predominantly used for synthesis of SMP networks may have (1) network segments, (2) a switching segment, and (3) a cross-linker. For example, SMP networks were synthesized from poly(methyl methacrylate-co-butyl methacrylate) copolymer cross-linked with tetra(ethylene glycol) dimethacrylate [19]. Apart from being built up by the main chain of poly((meth)acrylates), the switching segment can also be introduced as side chains or as long-chain cross-linkers by the use of (meth)acrylic ester macromonomers based on oligo(ε-caprolactone), PEG, and poly(lactide-co-glycolide) [13]. As cross-linkers, multifunctional (meth)acrylates include (meth)acrylates of polyols (ethylene glycol, butylene glycol, glycerol), trimethylolpropane, and acrylamides which are often employed. There are several reports on the SMPs based on the polyethylene oxide (PEO), cross-linked with maleic anhydride, glycerin or dimethyl 5-isophthalates [17]. Also, interpenetrating polymer network (IPN) of polyethylene oxide/poly(methyl methacrylate) (PMMA) was reported [20]. PEO/PMMA IPN systems show shape-memory properties with two transition temperatures: Tm of PEO and Tg of IPN.
Chemically cross-linked SMPs can be also synthesized by polyaddition and polycondensation reaction. Shape-memory behaviors were observed for thermosetting polyurethanes. Hu et al. reported the influence of the molecular weight on shape-memory behavior in polyurethane films [21]. Glycerin and 1,1,1-trimethylolpropane were applied as cross-linker for polyurethanes [12, 22, 23]. A clear improvement in creep and increase in recovery temperature have been observed due to the application of cross-linking [24]. Hybrid polyurethanes, cross-linked with Si–O–Si linkages, were made by Xu and coworkers [25]. Thermosetting polyurethanes were prepared by grafting of polyacrylamides and polyacrylates or by introducing hydrophilic groups into the cross-linked polyurethane backbone. Such networks showed both shape-memory and hydrogel properties [17].
SMPs based on epoxy polymers are a high-performance thermosetting resin possessing a unique thermomechanical property together with excellent shape-memory effect [10]. The epoxy SMP was synthesized from an epoxy resin, hardener, and additional linear epoxy monomer, by Leng et al. [26]. With the increase of active linear epoxy monomer, the Tg of such tailored network ranges from 37 to 96 °C. Shape-memory network was enabled by reaction of 3-amino-1,2,4-triazole with epoxidized natural rubber catalyzed by bisphenol-A [13]. The transition temperature of this network is the Tg, which could be controlled by the 3-amino-1,2,4-triazole content in the range between 29 and 64 °C [27]. The shape-memory IPN networks can be also prepared through successive polyaddition and polymerization. The example of such IPN is a system obtained from polyethyleneglycol dimethacrylate blended with star-shaped poly[(rac-lactide)-co-glycolide], which is first photopolymerized and later, the polyesterurethane network is formed using isophorone diisocyanate [13]. Ttrans can be adjusted between −23 and 63 °C [28].
Another method of preparation of chemically cross-linked SMPs is a subsequent cross-linking of a linear or a branched polymer [14, 17, 29]. The SMPs created by postprocessing can be divided into two groups: cross-linked by means of cross-linking agent and cross-linked by electromagnetic radiation. An example of the first method is the application of peroxide to cross-link the linear polymers [11, 29,30,31]. Liu and coworkers used a dicumyl peroxide to cross-link semicrystalline polycyclooctene obtained by ring-opening metathesis polymerization containing unsaturated carbon bonds [32, 33]. The electromagnetic radiation with different wavelengths (γ-radiation, UV, neutrons, e-beam) is often used to cross-link polymers during postprocessing processes. The abovementioned polyethylene cured with gamma rays obtained by Rainer in 1964 was one of the first SMPs [6]. The γ-radiation has been also used to generate SMPs based on poly(ε-caprolactone) and its blends with poly(methyl vinyl siloxane) [11, 34]. Application of UV radiation to cross-linking SMPs requires incorporation of photo-initiators or light-sensitive monomers. For example, a covalent network with shape-memory properties was synthesized from poly(lactide-co-glycolide) and polyhedral oligomeric silsesquioxanes (POSS) using tetrathiol as cross-linking agent and 2,2-dimethoxy-2-phenylacetophenone as radical photo-initiator [35]. The use of functional, light-sensitive monomers, for example, monomers with acrylic groups, allows easy control of the initial shape and degree of cross-linking of the network formed by photo-curing [36, 37].
2.1.2 Physically Cross-Linked Polymers
For the physically cross-linked SMPs, the formation of phase segregate morphology is the fundamental mechanism behind the thermal-induced shape-memory behavior of these thermoplastic materials [10]. The molecular switch and physical cross-link are provided by separate phases of the polymer. A notable difference between physical and chemical cross-linking is that in the physically cross-linked polymers it is possible to remold the fixity phase after reaching the temperature at which the physical bonds disappear [11]. Physically cross-linked polymers can be further classified into linear polymers (block copolymers and high-molecular-weight polymers), branched polymers, and polymer complex [10]. Another classification takes into account the presence of the SMP amorphous or crystalline switching segments.
In glassy SMPs with amorphous switching segments, the hard amorphous domains act as physical cross-link via van der Waals forces, polar–polar interactions, hydrogen bonding, and other weak interactions. The Tg of the soft segments represents the transition temperature Ttrans and is responsible for SME [38]. The shape-memory behaviors of this type SMPs depend on the chain length, structure, and arrangements of soft segment. Segmented amorphous shape-memory polyurethanes (PU) are the most important class of this type of SMPs. The hard segments of linear PU are formed either from a long-chain macro-diol with a higher thermal transition temperature or from diisocyanates and chain extenders [13]. The Tg of thermoplastic polyurethanes can be controlled in a wide range by using different kinds of monomers (aromatic or aliphatic diisocyanates) and chain extenders (low-molecular-weight diols or diamines) and by adjusting their amounts [17]. Precise control of PU composition and structure of soft and hard segments are necessary for effective shape-memory effect. The glassy hard segments, except physical cross-linking, should maintain the shape of material through hydrogen bridges or polar interaction. The soft segments could freely absorb external stress by unfolding and extending PU chains in these domains. The synthetic route for long polymer polyurethane chains (soft segments) and highly polar (hard) segments is based on the two-step procedure. In the first step, a polymeric diol reacts with diisocyanate to form the prepolymer. Next, this prepolymer reacts with low-molecular-weight chain extenders, like diols or diamines [39,40,41,42]. Another method of obtaining shape-memory polyurethanes based on joining block copolymers was proposed by Lendlein et al. [43]. He prepared SMPs with tunable Ttrans between 14 and 56 °C, from copolymers of lactic acid with other monomers. Besides polyurethanes, many other SMPs with amorphous switching segments have been reported. Both homopolymers and their blends, like poly(methyl methacrylate), polynorbornene, poly(methylene-1,3-cyclopentane), poly(vinyl chloride) [17], as well as, numerous block copolymers like, for instance, poly(lactic-co-glycolic acid), allow to obtain separated phase systems [44, 45]. In the case of copolymer SMPs, the blocks from co-monomer with the highest transition temperature act as the hard segments (fixity phase), while the other ones are the soft segments (switching phase). In the case of SMPs prepared by copolymerization, the appropriate selection of monomers allows improvement in other properties like biodegradability, hydrophilicity, solvent absorption and diffusion, toughness, transition temperature, or activation shape-memory time [11].
The second group of physically cross-linked SMPs comprises polymers with crystalline switching segments. The temporary shape of these materials is fixed by crystallization of the soft domains, which occurs below Tg. The transition temperature region corresponding to Tm (melting of crystalline domains) is narrow, in contrast to the SMPs, with amorphous switching segments, which often show broad transition temperature range and usually requires difficult to achieve precise combination of soft segments [17]. Various physically cross-linked semicrystalline SMPs were reported. Typical examples are biodegradable poly(L-lactide-co-ε-caprolactone) [46], poly(ethylene oxide-co-butylene terephthalate) [47], and polystyrene-co-poly(butadiene) [38]. However, the largest group in this category are the thermoplastic segmented shape-memory semicrystalline polyurethanes. Polycaprolactone-diol (PCL-diol) has been extensively used for the synthesis of PU with crystalline soft phase [48]. The hard segments were incorporated in 4,4′-diphenylmethane diisocyanate (MDI)-based PU by application of such monomers as 1,4-butanediol [49], 4,4′-bis(2-hydroxyethoxy)biphenyl (BEBP) or 4,4′-bis(2-hydroxyhexoxy)biphenyl (BHPP) [50], and 1-octadecanol [51, 52].
2.1.3 Segmented Block Copolymers
Shape-memory effect in segmented block copolymers is based on different transition temperatures (Tg or Tm) of co-monomers [11]. The transition temperatures determine, which co-monomer will be switching phase (lower temperature) and which one will be fixity phase (higher temperature). Well-known example of switching phase co-monomer is lactic acid as PLA, but it cannot provide optimal SME without appropriate fixity phase. Only combined with ε-caprolactone as poly(l-lactide-co-ε-caprolactone) (PCLA) [46] or with glycolic acid as poly(lactic-co-glycolic acid) (PLGA) [44] shows superb SME. Similar relation between phases is also observed in polyurethanes, where reaction between diisocyanate and diol allows to obtain fixity phase with urethane groups and switching phase of oligoester [39,40,41,42,43]. Strong interactions between dipoles and hydrogen bonds ensure polarity of fixity phase, high enough to use PLA, or even polycaprolactone (PCL) as switching phase. Another example of segmented block copolymer with shape-memory effect is poly(ethylene terephthalate) (PET) as fixity phase with poly(ethylene dioxide) (PEO) as switching phase [47].
2.1.4 Cross-Linked Homopolymers
Shape-memory homopolymers have fixity phase and switching phase as block copolymers, but the difference lies in the presence of both amorphous and crystalline regions in one polymer. While crystals act as fixity phase and provide shape, physical bonds of amorphous chains (switching phase) react to appropriate temperature and reshaping occurs. Example of shape-memory homopolymer is semicrystalline PLA, which in addition to being SMP also is biocompatible and biodegradable [46, 53,54,55]. Unfortunately, shape-memory effect of PLA is limited to narrow temperature range. Also compared with the performance of polymer blends, block copolymers, and interpenetrating polymer networks, shape-memory effect of PLA homopolymer is limited.
2.1.5 Polymer Blends, Polymer IPN/Semi-iPN
There are two types of polymer blends with shape-memory effect: miscible and immiscible. Both of them are interesting for industrial applications, due to the fact that blending is easily implementable and can provide enhancement of mechanical and thermal properties. Miscible blends can be made from semicrystalline polymers like PCL and polydioxanone [56] or from semicrystalline and amorphous polymers like polyurethanes based on PCL with poly(vinyl chloride) [57] or phenolic resin [58]. Although miscibility theoretically causes one Tg of blend, different concentrations of each polymer in various regions differentiate local Tg. Immiscible blends like PCL matrix with poly(styrene-b-butadiene-b-styrene) (SBS) [59] or PLCA with PLGA [25] also represent shape-memory polymers.
Specific blends of miscible polymers with interlaced networks are known as interpenetrating polymer networks (IPNs). They can also exhibit shape-memory properties if aforementioned Tg issue is solved in similar way as for other miscible polymers. IPNs based on PLGA polyurethanes with poly(ethylene glycol) (PEG) dimethacrylates were proposed by Zhang et al. [28]. Other IPNs with acrylates were made of PMMA with PEO, where shape-memory effect was based on melting of PEO crystals, and poly(methyl methacrylate-N-vinyl-2-pyrrolidone) with PEG, where shape-memory effect was provided by hydrogen bonds [60, 61].
2.1.6 Supramolecular Polymer Networks, Hydrogels
SMPs obtained via supramolecular chemistry are based on non-covalent interactions such as hydrogen bonds, dipole–dipole bonds, or van der Waals forces. Great numbers of these interactions can provide better stability of polymer structure and act as fixity phase [62]. Despite this, thermal-induced dissociation of hydrogen bonds also provides shape recovery of the structure [63]. Also, supramolecular SMPs have distinctive dynamics of shape change response. Most notable studies on supramolecular SMPs include solutions with ureidopyrimidinone (UPy) in polyurethane elastomers [64] or polyacrylate copolymers [63]; α-cyclodextrin (α-CD) and polyethylene glycol (PEG) in PEG-α-CD [65]; PEG and acrylates in PEG-PMMA-co-(N-vinyl-2-pyrrolidone) [60, 61], PEG–PMMA-co-acrylic acid [66], and PEG–polymethyl acrylate [20]; and pyridine in polyurethanes [21].
Hydrogels, as polymers with hydrophilic groups, are able to change their structure, thanks to ability of absorbing significant amounts of water. Temperature is a stimulus, which has important role in mechanism of shape change. There are two types of hydrogels behaving conversely: lower solution critical temperature (LSCT) hydrogels and higher solution critical temperature (HSCT) hydrogels. While LSCT hydrogels are swollen at temperatures lower than LSCT and shrunken at temperatures higher than LSCT, HSCT hydrogels have inverted characteristic (swell above HSCT and shrink below HSCT) (Fig. 5).
Swelling/shrinking mechanism of shape-memory hydrogels
First shape-memory hydrogels were obtained from stearyl acrylate [67], but shape-memory effect was not obtained immediately in both states. After achieving SMP as swollen hydrogel, exchange of stearyl acrylate to methyl acrylate was necessary to create hydrogel with shape-memory effect in both (shrunken and swollen) states [68]. Other polymers common in hydrogel synthesis are polyacrylamide (PAAm) and poly(vinyl alcohol) (PVA). While PAAm is very useful in drug delivery, shape-memory effect of PVA is hindered by cleavage of hydrogen bond above 60 °C and in consequence, unstable structure of PVA [69, 70]. Success of PAAm results from its LSCT, which is close to temperature of human body, and from modulated gel technology technique [53] using interpenetrating networks of PAAm with N-isopropylacrylamide (NIPAAm), which provides shrinkage of hydrogel at elevated temperature.
2.1.7 Composites/Nanocomposites
Shape-memory polymer composites (SMPCs) differ from other structures because of fillers and nanofillers influence on shape-memory effect. SMPs have intrinsic low mechanical strength and shape recovery stress, which have largely restricted their applications [71]. A small amount of micro/nano-sized fillers can significantly improve these properties of SMPs. SMPCs not only exhibit improved mechanical properties and shape-memory properties but also possess novel properties like multi-shape-memory effect, indirect SME, gradient SME, two-way SME, and complicated movement SME, indirectly triggering SME [71]. SMPCs can also enable or enhance thermal stimuli-active effects, include electroactive effect, magnetic-active effect, water-active effect, and photoactive effect. Zheng et al. [72] reported poly(l-lactic acid fillers) (PLLA) matrix with shape-memory effect improved by β-tricalcium. Another PLLA composites with hydroxyapatite [73] and chitosan [44] also exhibit better shape-memory effect than PLLA homopolymer. Increased stiffness and decreased recoverable strain were observed for SMPs reinforced with glass and Kevlar [17]. Conducting SMPCs were prepared by blending carbon black or a conducting polymer with the SMP [74,75,76]. Incorporation of 3.3% of carbon nanofibers resulted in 200% increase in recovery stress of the SMPCs [77]. Application of carbon nanotubes or carbon black of similar size for reinforcement of polyurethanes gave the nanocomposites with increased shape fixity [78]. SMPCs with shape-memory effect triggered by magnetic field were obtained using magnetic nanofiller like Fe2O3 with a shell of oligo(ε-caprolactone) or Ni–Zn ferrite particles [79, 126] .
2.2 Classification of Shape-Memory Function
Shape-memory polymers may have different kinds of shape-memory effect. The most common memory effects are the one-way and two-way shape-memory, multi-shape, and multifunctionality.
2.2.1 One-Way Shape-Memory Effect SMP
The procedures in one-way shape-memory effect (1W-SMPs) consist of programming and recovery of a shape. Depending on chemical structure of polymer, its behavior can differ significantly. In Fig. 6, the process of programming and recovery of a shape is shown in a schematic way. In the beginning, a programming process is carried out during which the shape-memory polymer is subjected to such action to obtain its permanent shape. In the next stage, the SMP is distorted and the intentional temporary shape is fixed. The whole this process is based on heating up the sample, deforming, and cooling the sample, or as it is possible drawing the sample at a low temperature. Shape-memory effect is inducted by heating up the sample above a transition temperature (Ttrans), and the recovery of SMP is observed. Solidification of the material is possible during cooling down the polymer below transition temperature; however, no recovery of the temporary shape is observed—what is called a one-way shape-memory effect. During next programming, including mechanical deformation, the polymer can obtain a temporary shape again but this new temporary shape is not identical as the first temporary shape. The best example of materials which have a thermo-responsive one-way shape-memory effect are hydrogels with hydrophobic, crystallizable side chains, and cross-linked poly(vinyl alcohols) [80, 81]. Hydrogels prepared from copolymerized acrylic acid and stearyl acrylate cross-linked with methylenebisacrylamide have a really strong temperature dependence in their mechanical properties. Polymers obtained in this reaction behave like tough polymers in temperature below 25 °C, but above 50 °C softening enables the materials to be extended up to 50%. 1W-SMPs behavior of poly(cyclooctene) that was cross-linked through a free-radical reaction using dicumyl peroxide was reported [32, 33]. What is important is the establishment of a provisional shape on cooling as well as quick improvement to the basic form upon heating. Besides, it was also proposed that cross-linked poly(cyclooctene) reveals crystallization-induced elongation and melting-induced contraction on heating, which can be explained by thermo-reversible actuation. The melting temperature of sample (Tm) can be customized by change of the quantity of dicumyl peroxide used for the cross-linking stage. Poly(cyclooctene) has a stable molten–rubbery plateau above the Tm, which provides effortless deformation and reacts as the transition temperature for shape-memory step, as well as a crystallization temperature (Tc) close to room temperature that lets fast crystallization process and efficient fixing of a temporary shape [82].
Schematic picture of the thermally induced one-way shape-memory effect
2.2.2 Two-Way Shape-Memory Effect SMP
Recently, two-way convertible shape-memory polymer materials (2W-SMPs) are greatly advisable for many applications [83,84,85]. Nowadays, some polymers have been investigated for two-way shape-memory properties, such as liquid crystal elastomers and photo-deformation polymers. Variety from the mechanism of 1W-SMPs, the 2W-SMPs process in liquid crystal elastomers and photo-deformation materials is imputed to the conversion of anisotropic polymer chain conformation and light-stimulated phase transitions (Fig. 7) [86,87,88,89]. Shape change gel layer is one of the samples with a thermally caused two-way shape-memory effect. Discussed gels include two types of layers: a thermosensitive control layer and a substrate layer which is not sensitive to changes in variables temperature. The first one consists of an ionic gel prepared from the N-isopropylacrylamide and sodium acrylate cross-linked with N, Nʹ-methylenebisacrylamide. During the temperature exceed of 37 °C, the control layer shrinks while the substrate layer does not change. For connecting both varied layers, one part of the control layer includes cross-linked copolymer which is exposed to an aqueous solution of acrylamide. Next, the acrylamide is polymerized by the use of a radical initiator to form diffuse chains. The pronounced variation in shape of gels is convertible, and the system can reverse between two defined shapes depending on the reaction conditions (below or above the transition temperature) [90] (Fig. 8).
Schematic showing the difference between the one-way and two-way shape-memory effects
Schematic of multi-shape-memory effect
Wang et al. reported the application of homopolymers and copolymers of ε-caprolactone and ω-pentadecalactone with cocrystallizable monomeric units for the composition of 2W-SMPs. The thiol–ene cross-linking system exposed two-way reversible 2W-effects under stress-free and stress conditions. The propulsion temperature of the two-way shape-memory effect under stress-free condition can be adapted in an extensive scope using suggested prepolymers by photo-cross-linking with a multifunctional cross-linker [91].
The shape-memory elastomer with a pre-stretched in stencil is checked. Designed material shows 2W-SM effect in reply to alterations in temperature without the need of an unchanged permanent exterior load [92]. Chen et al. prepared laminated composites with SMPs membrane and elastic polymers membrane. It is 2W-SM behavior in which the mechanism of shape-memory is ascribed to the release of elastic strain of SMP layer upon heating, and the recovery of elastic strain caused by the bending force of substratum membrane upon cooling [93].
2.2.3 Triple-Way Shape-Memory Effect SMP
Triple-way shape-memory polymers (3W-SMPs) can change forms twice and can fix two shapes compared to its permanent and initial shape. The 3W-SMPs comprise a cross-linking phase and two independent phases related to two different conversions which contain programming and recovery cycles. The programming stage of 3W-SMPs commences with heating the sample above both transitions and inducing distortion. Next, maintain the deformation while cooling the polymer to fix form at a temperature between the two conversions. Ware et al. reported a novel 3W-SM system contained both permanent covalent cross-links and supramolecular hydrogen bonding cross-links. The described effect comes into being from the connection of the glass transition of methacrylate copolymers and the dissociation of self-complementary hydrogen bonding moieties providing easy control of both glass transition temperature (Tg) and cross-link density [94]. Bellin et al. have shown the 3W-SM effect in systems containing two crystalline switching phases, while others have linked an amorphous phase with a crystalline switching phase [95]. Recently, Xie and coworkers have shown quadruple shape-memory utilizing the broad transition of perfluorosulfonic acid ionomers [96]. The composites capable of being the 3W-SMPs stand to increase the complexity of appliances utilizing the shape-memory effect by enabling multistage complex recovery profiles were prepared [97, 98]. Recently, the 3W-SM epoxy composites consisting of two layers of well-separated glass transition temperatures have been successfully synthesized. The various amounts of nanosilica particles entered into the matrix are able to cause different glass transition temperatures of the epoxy composites [99,100,101]. The application of 3-aminopropyltriethoxysilane as a chemical modifier for graphene oxide into silanized polyurethanes gives two different molecular weights and chemical compositions by sol–gel reactions. The research has proven that the materials act as multifunctional cross-links as well as supporting fillers and significantly enhanced the glassy and rubbery state moduli, glass transition temperature, and 3W-SM properties [102].
2.2.4 Multi-Way Shape-Memory Effect SMP
In last time, it has been shown that polymers with a wide thermomechanical transition temperature range can have a multi-shape-memory effect what is related to a shape recovery process with one or more intermediate shapes between the temporary shape and permanent shape. Actually, such a condition for the multiple SME is not necessary, the use only one single transition to gain that as well. It is possible because one single transition should be considered as a combination of many small transition steps, so in fact, the multi-SME is a common property of polymers [95, 96, 103, 104].
Prathumrat and coworkers prepared benzoxazine–urethane copolymers with multiple shape-memory behaviors. These polymers exhibited great shape fixity values of 70–96% for the first temporary shape and 83–99% for the second temporary shape. Regarding shape recovery, synthesized copolymers also had significant values of 88%–96% for the first temporary shape and 97–99% for the original shape. What is important is that the proper curing conversion influences the multiple shape-memory behaviors of copolymers—curing conversion at roughly 70% was adequate for this sample to demonstrate a multi-shape-memory effect [105].
Poly(l-lactide) (PLLA)/poly(methyl methacrylate) (PMMA) blends with wide glass transitions are known as an optional matrix to design multiple shape-memory polymers. The temperature range of the symmetric 50% PLLA/50% PMMA blend softly moved from 70 to 90 °C for stretching temperatures increasing from 65 to 94 °C, and certify for a meaningful temperature memory effect. In the case of asymmetric compositions with 30 and 80% PMMA, polymer also presented a “temperature memory effect”; however, the symmetric blend greatly was revealed as the most effective composition for multiple shape-memory applications. The symmetric blend can be a really interesting material for future developments because its programming step designed with two successive stretchings within the wide glass transition provided high multi-shape-memory effect with tunable intermediate shapes [106].
2.3 Classification of Shape-Memory Polymers by Type of Stimulus
Shape-memory polymers (SMPs) as a type of significant stimuli-responsive materials can receive their original and initial shape upon exposure to external stimuli. The SMPs are stimuli-sensitive polymers with the ability to transmit a large recoverable deformation upon the application of external impulses. So far, known methods of stimulus can be generally divided into heat, electricity, light, magnetism, moisture, etc. Nowadays, SMPs are attracting increasing international research attention and there is huge progress in developing stimuli-responsive shape-memory polymers with potential applications in many fields such as biomedical devices, aerospace, textiles, bionics engineering, and energy, electronic engineering.
2.3.1 Stimulation by Temperature
The characteristic thermo-responsive SMPs are really universal, frequent, and occurring for polymers [32, 33, 107, 108, 109], in which vitrification or crystallization of polymer chains is adapted as a momentary cross-link to stabilize the change in the dimension of forms and the shape recovery is induced by heat [110]. Thermo-responsive SMPs can gain their original and initial figure and form when they are warmed above Tg for amorphous polymer and above Tm for crystalline polymers. The characteristic thermomechanical cycle of SMPs is illustrated in the following steps in Fig. 9 [60, 61, 111]. The whole process consists of formation of the SMPs into an original shape, and next stage should be heating the SMPs above the thermal transition temperature (Ttrans) (depending on the type of polymer it is a glass transition temperature (Tg), or a melting temperature (Tm)), and change of shape of the SMPs using an external force and finally cooling under Ttrans.
Schematic of shape-memory effect during a typical thermomechanical cycle
French CdF Chimie Company first developed polynorbornene with a Tg range of 35–40 °C what next was introduced to the industry by the Japan Nippon Zeon Company [13, 112]. Styrene-butadiene SMPs with Tg of about 60–90 °C were synthesized by the Asahi Company [113]. Furthermore, the Cornerstone Research Group (CRG), Inc. has expanded some thermosetting SMPs [114], which comprising a one-part epoxy SMP with a Tg of about 90 °C, a two-part epoxy SMP with a Tg of about 104 °C, and also a cyanate ester SMP with a high Tg range from 135 to 230 °C. Moreover, Composite Technology Development (CTD), Inc. has proceeded a thermosetting epoxy SMP with a Tg of about 113 °C. In addition, it is known that a series of thermoplastic polyurethane SMPs is commercially available from Mitsubishi Heavy Industry, with the Tg ranging from 40 to 55 °C. Lamm et al. prepared sustainable epoxy resins derived from plant oils with thermo- and chemo-responsive SM maintenance which were obtained using plant oils and cellulose nanocrystals (CNCs). Epoxidized soybean polymers (PESBMA) were grafted from CNCs using surface-initiated atom transfer radical polymerization (SI-ATRP) where the polymer was combined with P(ESBMA-co-SBMA) copolymer. P(ESBMA-co-SBMA) has a Tg of 13 °C, versus 20 °C for CNC-g-PESBMA [115]. Truong et al. [116] prepared thermo-responsive SM poly(ε-caprolactone) (PCL) networks with multiple pendant double chains at both link ends which are used to cross-link with multi-thiol compounds via photo-initiated thiol–ene reactions. SM features can be also changed through modification in the number of alkene side groups at the poly(ε-caprolactone) and thiol cross-linker structure. The developed thermoset materials exhibit great thermo-responsive shape-memory efficiency by changing the operating temperature below or above the melting temperature of crystalline poly(ε-caprolactone) segments, which changes in the range of 34–40 °C, and the highest shape retention and recovery factors can get 98–100% [117].
2.3.2 Stimulation by PH Changes
In this section, shape-memory material-stimulated pH change will be shown. The change of polymer properties occurs when in present ionizable functional groups’ material gets ionized and obtains charge in certain pH. The shape-memory polymer chains between like-charged groups lead to repulsion force and from here widen their dimension and finally at the moment when the pH changed, the repulsion disappears and the materials come to the original shape and position. The reversibility and changes to this material can be treated as a disadvantage that comes into being with the use of pH-responsive materials because it commonly needs solvent replacement, which is not good for the environment. Despite these restrictions, pH-responsive polymers have shown promise in many areas such as drug delivery and microprocessing [82]. pH-sensitive SMPs were prepared by cross-linking the β-cyclodextrin-modified alginate (β-CD-Alg) and diethylenetriamine-modified alginate (DETA-Alg). The pH reversible β-CD-DETA inclusion complexes operate as a convertible phase, and the cross-linked alginate serves as a fixing phase. It is shown that this material can be processed into temporary shape at pH 11.5 and recover to its initial shape at pH 7. The recovery relation and the fixity ratio were accordingly 95.7 ± 0.9% and 94.8 ± 1.1% [118]. Han et al. proposed to use pH as a stimulus for SMPs for its convenience and safety in medical applications because the shape transition pH value is almost to that of our body fluid and this pH-triggered shape‐memory effect is convenient and safe to use. It is also indicated a polyurethane with a pH-sensitive SM effect. First, a series of polyurethanes were successfully synthesized through solution polymerization of polyethylene glycol, dimethylolpropionic acid (DMPA), and 4,4′-diphenylmethane diisocyanate (MDI). These polymers PEG-i-MDI-DMPA (i = 20, 30, 40%) and i represent the weight content of PEG in the polymers. The results of SM testing showed that the PEG-30%-MDI-DMPA has both the 3-SM effects. In PEG-30%-MDI-DMPA, the glass transition of PEG and the association and disassociation of carboxylic dimers act as two switches to control the 3-SM conversion, while the carboxylic dimer is affected by pH values to associate in acidic solutions (at pH 2) and dissociate in alkaline solutions (at pH 9) to induce the pH-sensitive shape-memory [119], which developed pH-responsive SMPs by blending poly(ethylene glycol)-poly(ε-caprolactone)-based polyurethane (PECU) with functionalized cellulose nanocrystals (CNCs). CNCs were functionalized with pyridine (CNC-C6H4NO2) through hydroxyl substitution of CNCs with pyridine-4-carbonyl chloride and with carboxyl groups (CNC-CO2H) via 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) conjunctived surface oxidation. At a high pH, the CNC–C6H4NO2 had inviting interactions from the hydrogen bonding between pyridine groups and hydroxyl moieties at a low pH, the interplays reduced, or disappeared due to the protonation of pyridine groups, which are a Lewis base. The shape-memory function of the nanocomposite network was only dependent on the pH variation of the environment [99,100,101]. Xiao et al. reported novel multi-responsive polyacrylamide-(PAAm)-based cross-linked copolymer (PAAm-TSMP) hydrogel which is characterized by pH-sensitive and photo-sensitive at the same time. pH-sensitive of hydrogel is possible by adding active group in the structure (positively and negatively ionized). Polyacids and polybases are the only available groups because the first ones accept protons at low pH, producing gel shrinkage, while polybases donate protons at high pH (Fig. 10) [120].
Swelling and shrinkage properties in ionic-based hydrogel by change in pH
2.3.3 Stimulation by Water/Solvent
Yang et al. discovered this particular effect. The glass transition temperature (equal to 35 °C) of an ether-based polyurethane shape-memory polymer (SMP) has been found to decrease significantly after immersion in water. The results reveal that the hydrogen bonding between N–H and CO groups is weakened by the absorbed water. Moreover, the H2O absorbed into the SMP can be in two forms (free water and the bound water). Bound water notably reduces the Tg in a linear way and has an influence on the uniaxial tensile behavior, while the effect of free water is negligible [121]. Also, Du and coworkers studied recovery time of poly(vinyl alcohol) in different solvents, and the results presented that the best recovery time for water is immersed. This kind of stimulation of shape-memory polymers is very interesting because it does not need to apply heat to obtain shape-memory conversion [122]. Diffusion of water, acetone, and ethanol into a polyether urethane matrix has been studied by Ghobadi et al. It was revealed that even after 1 week, putting the samples in the corresponding solvent baths, neither enthalpy relaxation nor monomer release could occur because of the lack of hydrophilic groups. Dry and physically (hydrolytically) aged samples have been conducted to different maximum strains and different holding times. It could be indicated that the shape fixation of physically (hydrolytically) aged polymers do not differ from dry samples. However, physical (hydrolytic) aging resulted in an obvious better and faster shape recovery ratio as a result of additional physical cross-links [123].
2.3.4 Stimulation by Magnetic Field
Magnetic field-sensitive polymer can be achieved by preparing nanocomposites loaded with specific magnetic nanoparticles. The magnetic nanofillers produce heat when they are subjected to magnetic field. The shape of nanocomposites is obtained in the same way as that in the thermally inducted one. Recovery of shape is fixed by the Joule effect at a time when the sample is exposed to exterior magnetic field. Via magnetic fields can induce internal heating within SMP composites containing magnetic nanoparticles (Fe2O3, Fe3O4, Ni, etc.) [47, 79, 124] which are known as ferromagnetic shape-memory polymers. This type of composites can actuate at higher frequencies (up to 1 kHz) because the actuation energy is transmitted via magnetic fields and is not hindered by the relatively slow heat transfer mechanism [125]. Iron oxide (Fe3O4) particles are known as magnetic fillers which induce heating when exposed to a magnetic field. Incorporating them into an SMP is a known practice to fabricate a shape-memory composite for which the shape recovery can be actuated remotely via magnetic field. Leng et al. analyzed that the micro-sized Ni powder formed chains under a weak external magnetic field, which can strengthen significantly the electrical conductivity in the chain direction. Schmidt et al. and Zrinyi et al. added magnetite to poly(butyl acrylate), polylactide, and polycaprolactone matrixes [126,127,128]. For instance, Fuhrer and coworkers used magnetosensitive particles in shape-memory hydrogels [129]. One class of biodegradable polymer composite was elaborated with an electrospinning process using poly(ε-caprolactone) (c-PCL) as the basis and carbon nanotubes as the supplement coated with Fe3O4. The fibers showed an excellent SM behavior stimuli by hot water and by an alternating magnetic field [130].
2.3.5 Stimulation by Light
Light stimuli shape-memory polymer has meaningful advantage in comparison with the thermal stimuli shape-memory polymer which results from the fact that photoactivation does not produce tissue damage as could be produced by heat treatments. Thanks to this behavior, light activation is very attractive for biomedical application. Jiang et al. reported that there are three kinds of photoresponsive molecules [131]. The division created by them is as follows: molecules which have ability to change their configuration from trans to cis and contrariwise at the time when they are exposed to UV light, and molecules obtained by cationic inducted polymerization and photoresponsive molecules. The configuration capable of producing shape-memory effect with photo-reactive molecules is presented in Fig. 11. Black dots in Fig. 11 mean molecules which are the switch phase and the covalent bonds between polymer chains are the fixity phase. When the sample is in the presence of electromagnetic radiation λ > λtrans, the photo-reactive molecules form dimers that are accountable to fix the temporary shape and dimension. At the moment when the shape-memory polymer is exposed to another radiation λ < λtrans, it can recover its original shape (Fig. 12). Lu et al. developed a photoactive SMP by incorporating boron nitride and carbon nanotube, which reportedly have a synergistic effect, into an epoxy-based SMP. The use of these additives improves the thermal conductivity of the material and its infrared light absorption, while the transferred nitrides aided in the heat transfer to the SMP matrix, resulting in faster shape-memory recovery [132]. Inam and coworkers reported that infrared light can be used to produce indirect shape-memory polymer matrix with addition of carbon black or carbon nanotubes. These reinforced nanofillers increase the thermal conductivity of the polymer. The behavior of these polymers is analogous to the thermal-induced shape-memory mechanism but the recovery appears when the polymer is irradiated with infrared light [133]. Shou et al. also developed near-infrared (near-IR) light-responsive SMPs by incorporating gold nanorods (AuNRs) into a poly(ε-caprolactone) matrix [134]. The second method, as reported by Lendlein et al., involves the introduction of cinnamic groups, which can be set in motion by ultraviolet light (UV). In research applied, two other configurations of cinnamic acid in polymer matrix permitted obtained SM network stimulated by light [135].
Occurring processes in shape-memory polymer stimulated by magnetic field
Molecular mechanism of photoinduced shape-memory effect at various states
2.3.6 Stimulation by Oxidation/Reduction
SM effect in hydrogels is mostly stimulated with use of a redox reaction [136]. Aoki et al. prepared cellulose derivatives by esterification of cellulose acetate (CA) with mercaptoacetic acid (MA). The CA-MA samples thus synthesized showed a sol–gel transition in solution and a shape-memory behavior formed through adequate redox treatments due to the reversible, cross-linking association and dissociation between mercapto groups [137]. Studies showed that host (poly(acrylic acid) (pAA) modified with beta-cyclodextrins (pAA-β-CDs))—guest (ferrocene (pAA-Fc)) are complementarity and multipoint cross-links have cooperative roles in forming the supramolecular polymer hydrogel. The reversible gel–sol transitions were achieved by adding an oxidant (NaClO aq.) and then a reductant (glutathione, GSH). What is more interesting is that the self-healing property of the hydrogel can be controlled by redox reactions. This study represents the first example of self-healing of supramolecular polymeric materials based on host–guest interactions and will further prompt the applications of host–guest recognition motifs in advanced supramolecular polymeric materials [138]. Moreover, redox‐stimuli shape‐memory matrix was obtained by cross-linking β‐cyclodextrin-modified chitosan (β‐CD‐CS) and ferrocene-modified ethyleneimine polymer (Fc‐PEI). The obtained β‐CD‐CS/Fc‐PEI has two cross-links: convertible redox‐sensitive β‐CD‐Fc complexes and covalent cross-links as fixing stages. The analyses showed that studied system can be processed into interim forms as needed in the reduced state and recovers its initial shape after oxidation reaction. In both cases, the recovery ratio and the fixity relation are more than 70% [139].
2.3.7 Multifunctionality
Multifunctionality is a set of material properties, which contains shape-memory effect and at least one other functionality (e.g., optical, permeable, thermal chromic, biodegradable) non-linked with SME [140]. Combining SME with phase-changing materials (PCM) can result in wrinkle-free textiles. Addition of active fillers like carbon black or carbon nanotubes to SMP will provide actuation through electric field [75, 76]. Similar actuation in magnetic field can be obtained with magnetically active fillers like iron oxide [79, 107]. Also, drug delivery systems made of SMP and drug are examples of multifunctionality. Radio-opacity of medical can be obtained via adding barium sulfate or zirconium oxide [141]. All types of modifications can provide attractive multifunctional SMP. The variety of multifunctional SMPs results from unique requirements, which are designed for certain applications.
3 Main Applications of SMP
Shape-memory polymers possess great functionality in shape-memory effect, and natural consequence is their wide range of possible applications. Most notable of them are in four fields: spacecraft, medical, textile, and engineering. Medical applications benefit from functions of SMP such as deployment, fixation, and actuation.
Deployment function plays an important role in SMP foams, which can be useful in treatment of aneurysms, especially embolic treatment [142]. Idea of SMP foam usage as device is still in the test phase, but delivery of compressed foam and its size increase after laser stimulation are still interesting solutions. Another application of deployment function in medicine is SMPs as cardiovascular stents [143]. They provide protection of small blood vessels from collapse, thanks to SME triggered by temperature change or polymer’s hydration [144, 145]. On the other hand, intracranial aneurysms can be treated with special SMP coils as blood flow reducers, which are able to help in formation of thrombus [146].
Fixation function of SMPs is useful in SMPU-PCL orthodontic wires, which are competitive alternative for traditional, metallic wires [147]. Their main advantage is better aesthetic appearance in comparison with metallic ones. SMP wires also provide low density, transparency, easy processing and, of course, high shape recovery. Another application, which benefits from fixation function of SMPs, is medical casts. Rousseau et al. proposed SMP medical cast with adjustable diameter and ability to fit the shape to broken limbs. These casts also provide easy and low-cost processing, recyclability, permeability, and lightweight [148]. Actuation function is usually related to artificial muscles, which in case of SMPs can be used in endovascular thrombectomy. Takashima and coworkers [149] obtained nitinol-core/SMP-shell artificial muscle with preprogrammed and thermally activated corkscrew form. This kind of micro-actuator can be very promising for clot and thrombus removal. SMPs with actuation function are versatile solutions, similarly attractive for spacecraft and engineering fields. Harris et al. reported liquid crystal elastomers (LCE) with shape-memory effect allowing to obtain mechanical energy from light energy [150]. These SMP actuator devices are obtained from azobenzene units in twisted and densely cross-linked structure, which results in high elastic modulus (≈1 GPa) at room temperature. Other possible applications attractive for spacecraft and other engineering fields are systems like micro-valves and micro-transducers [151, 152] which are microelectromechanical systems (MEMS) providing temperature-adjustable flow through the tube. Also, stimuli-responsive SMPs can be suitable in applications such as antennas in spacecraft, morphing wing structures, or wrinkle-free fabrics [153].
Self-healing is another SMPs function, which can be widely applicable. Self-healing mechanism of SMPs can be based on reverse plasticity [154] or combination of different shape-memory effects in two-component blends called SMASH (shape-memory assisted self-healing) [155].
Group of SMPs dedicated for textile industry is based on special fibers—shape-memory fibers (SMFs). The SMFs can be obtained via different spinning methods (melt, dry, and wet) and their uniqueness results from outstanding temperature-response performance in their elastic modulus and recovery parameters [51, 52]. These properties allow to use SMFs in many textile applications, which are presented in Fig. 13.
Classification of shape-memory fibers’ applications with examples
4 Conclusion
Shape-memory polymers are one of the most intensively developing areas of materials science and technology providing excellent opportunities for scientific discoveries in the field of molecular design, polymer synthesis, functionalization and processing of polymer blends, copolymers, composites, and nanocomposites. The properties of SMPs, such as easy processing, large recoverable strains, tunability, low weight, different types of external switching stimulus, easy to control a wide range of transition temperatures, switching at body temperature, biocompatibility, and biodegradability, makes them superior in comparison to shape-memory alloys. Due to these excellent properties and the low-cost and commercial availability of most of the polymers used as shape-memory materials, the applications of SMPs will increase in near future, within the numerous, new fields, like, for example, biomedical smart materials, advanced mechanical sectors, mechatronic, and power generation. However, great research efforts are still required to obtain SMPs with precisely controlled response and better durability and reliability over those offered by currently available technologies. In order to increase the versatility of SMPs, it is necessary to solve the major drawbacks of SMPs, which are associated with their relatively lower recovery stress/forces, long response time, lower cycle life, and weak material stability.
In this chapter, the literature reports on shape-memory polymers have been reviewed highlighting the classification of shape-memory polymeric materials and most important concepts for these types of smart materials. The main emphasis was put on the development of many types of SMPs categorized by the different classification criteria, with particular regard to polymer type and structure, shape-memory function, and external stimulus.
References
Behl M, Lendlein A (2007) Shape-memory polymers. Mater Today 10(4):20–28
Hornbogen E (2006) Comparison of shape memory metals and polymers. Adv Eng Mat 14:101–106
Hager MD, Bode S, Weber C, Schubert US (2015) Shape memory polymers: past, present and future developments. Prog Polym Sci 45–50:3–33
Lester B, Vernon B, Vernon HM (1941) Process of manufacturing articles of thermoplastic synthetic resins. US 2234993
Safranski DL, Griffis JC (2017) Shape-memory polymer device design. Elsevier, Oxford
Rainer WC, Redding EM, Hitov JJ, Sloan AW, Steward WD (1964) Heat-shrinkable polyethylene. US 3144398
Pilate F, Toncheva A, Dubois P, Raquez J-M (2016) Shape-memory polymers for multiple applications in the material world. Europ Polym J 80:268–294
Hu J, Zhu Y, Huang H, Lu J (2012) Recent advances in shape-memory polymers: Structure, mechanism, functionality, modeling and applications. Prog Polym Sci 37:1720–1763
Liu C, Qin H, Mather PT (2007) Review of progress in shape-memory polymers. J Mat Chem 17:1543–1558
Leng J, Lan X, Liu Y, Du S (2011) Shape-memory polymers and their composites: Stimulus methods and applications. Prog Mater Sci 56:1077–1135
Aguilar MR, Roman JS (2014) Smart polymers and their applications. Woodhead Publishing, Cambridge
Lee SH, Kim JW, Kim BK (2004) Shape memory polyurethanes having crosslinks in soft and hard segments. Smart Mater Struc 13:1345–1350
Leng JS, Du SY (2010) Shape memory polymer and multifunctional composite. CRC Press, Taylor & Francis Group, New York
Naga N, Tsuchiya Toyata A (2006) Synthesis and properties of polyethylene and polypropylene containing hydroxylated cyclic units in the main chain. Polymer 47:520–526
Kelch S, Steuer S, Schmidt AM, Lendlein A (2007) Shape-memory polymer networks from oligo[(epsilon-hydroxycaproate)-co-glycolate]dimethacrylates and butyl acrylate with adjustable hydrolytic degradation rate. Biomacromol 8:1018–1027
Meng Q, Hu J (2009) A review of shape memory polymer composites and blends. Composites:Part A 40:1661–1672
Ratna D, Karger-Kocsis (2008) Recent advances in shape memory polymers and composites:a review. J Mater Sci 43:254–269
Sakurai K, Shirakawa Y, Kashiwagi T, Takahashi T (1994) Crystal transformation of styrene–butadiene block-copolymer. Polymer 35:4238–4239
Lui C, Mather PT (2002) Thermomechanical characterization of a tailored series of shape memory polymers. J Appl Med Polym 6:47–52
Liu G, Ding X, Cao Y, Zheng Z, Peng Y (2005) Novel shape-memory polymer with two transition temperatures. Macromol Rapid Commun 26(8):649–652
Chen SJ, Hu JL, Liu YQ, Liem HM, Zhu Y, Meng QH (2007) Effect of molecular weight on shape memory behavior in polyurethane films. Polym Int 56:1128–1134
Hu J, Yang Z, Yeung L, Ji F, Liu Y (2005) Dependency of the shape memory properties of a polyurethane upon thermomechanical cyclic conditions. Polym Int 54:600–605
Zouohong Y, Jinlian H, Yeqiu L, Lapyan Y (2006) The study of crosslinked shape memory polyurethanes. Mater Chem Phys 98:368–372
Buckley CP, Prisacariu C, Caraculacu A (2007) Novel triol-crosslinked polyurethanes and their thermorheological characterization as shape-memory materials. Polymer 48:1388–1396
Xu J, Shi W, Pang W (2006) Synthesis and shape memory effects of Si–O–Si cross-linked hybrid polyurethanes. Polymer 47:457–465
Leng JS, Wu XL, Liu YJ (2009) Effect of linear monomer on thermomechanical properties of epoxy shape-memory polymer. Smart Mater Struct 18(095031):1–6
Chang YW, Mishra JK, Cheong JH, Kim DK (2007) Thermomechanical properties and shape memory effect of epoxidized natural rubber crosslinked by 3-amino-1,2,4-triazole. Polym Int 56:694–698
Zhang SF, Feng YK, Zhang L, Sun JF, Xu XK, Xu YS (2007) Novel interpenetrating networks with shape-memory properties. J Polym Sci Part A Polym Chem 45:768–775
Li F, Zhu W, Zhang X, Zhao C, Xu M (1999) Shape memory effect of ethylene–vinyl acetate copolymers. J Appl Polym Sci 71:1063–1070
Helminen AO, Korhonen H, Seppala JV (2002) Cross-linked poly(epsiloncaprolactone/D, L-lactide) copolymers with elastic properties. Macromol Chem Phys 203:2630–2639
Morshedian J, Khonakdar HA, Mehrabzadeh M, Eslami H (2003) Preparation and properties of heat-shrinkable cross-linked low-density polyethylene. Adv in Polym Tech 22:112–119
Liu C, Chun S, Mather P, Zheng L, Haley E, Coughlin B (2002) Chemically cross-linked polycyclooctene: synthesis, characterization, and shape memory behavior. Macromol 35:9868–9874
Liu C, Chun SB, Mather PT, Zheng L, Haley EH, Coughlin EB (2002) Chemically cross-linked polycyclooctene: synthesis, characterization, and shape memory behavior. Macromol 35:9868–9874
Zhu G, Liang G, Xu Q, Yu Q (2003) Shape-memory effects of radiation crosslinked poly(epsilon-caprolactone). J Appl Polym Sci 90:1589–1595
Knight PT, Lee KM, Chung T, Mather PT (2009) PLGA-POSS end-linked networks with tailored degradation and shape memory behavior. Macromol 42:6596–6605
Schoener CA, Weyand CB, Murthy R, Grunlan MA (2010) Shape memory polymers with silicon-containing segments. J Mater Chem 20:1787–1793
Wischke C, Lendlein A (2010) Shape-memory polymers as drug carriers - a multifunctional system. Pharma Research 27:527–529
Kalita H (2018) Shape memory polymers. De Gruyter, Berlin
Cao Q, Liu PS (2006) Structure and mechanical properties of shape memory polyurethane based on hyperbranched polyesters. Polymer Bull 57:889–899
Nagahama K, Ueda Y, Ouchi T, Ohya Y (2009) Biodegradable shape-memory polymers exhibiting sharp thermal transitions and controlled drug release. Biomacromol 10:1789–1794
Wang WS, Ping P, Chen X, Jing X (2006) Polylactide-based polyurethane and its shape-memory behavior. Eur Polymer J 42:1240–1249
Xue LA, Dai SY, Li Z (2010) Biodegradable shape-memory block co-polymers for fast self-expandable stents. Biomaterials 31:8132–8140
Lendlein A, Zotzmann J, Feng Y, Altheld A, Kelch S (2009) Controlling the switching temperature of biodegradable, amorphous, shape-memory poly(rac-lactide)urethane networks by incorporation of different comonomers. Biomacromol 10:975–982
Meng QH, Hu J, Ho KC, Ji F, Chen S (2009) The shape memory properties of biodegradable chitosan/poly(l-lactide) composites. J Poly and Envi 17:212–224
Min CC, Cui W, Bei J, Wang S (2005) Biodegradable shape-memory polymer polylactide-co- poly(glycolide-co-caprolactone) multiblock copolymer. Polym for Advan Tech 16:608–615
Lu XL, Sun ZJ, Cai W, Gao ZY (2008) Study on the shape memory effects of poly(L-lactide-co-epsilon-caprolactone) biodegradable polymers. J Mat Sci Mat Med 19:395–399
Luo XL, Zhao MC, Wang MZ, Ding LN, Ma DZ (2000) Thermally stimulated shape memory behavior of (ethylene oxide-butylene terephthalate) segmented copolymer. Chin J Polym Sci 18:357–361
Xu M, Li F (1999) Thermally stimulated shape memory behavior of polymers with physical crosslinks. Chin J Polym Sci 17:203–213
Lendlein A, Kelch S, Kratz K (2006) Kunststoffe mit programmiertem Gedächtnis. Kunstoffe 2:54–59
Jeong HM, Kim BK, Choi YJ (2000) Synthesis and properties of thermotropic liquid crystalline polyurethane elastomers. Polymer 41:1849–1855
Zhu Y, Hu JL, Yeung KW, Liu YQ, Lien HM (2006) Influence of ionic groups on the crystallization and melting behavior of segmented polyurethane ionomers. J Appl Polym Sci 100:4603–4613
Zhu Y, Hu JL, Yeung LY, Liu Y, Ji FL, Yeung KW (2006) Development of shape memory polyurethane fiber with complete shape recoverability. Smart Mater Struct 15:1385–1394
Li Y, Hu ZB, Chen YY (1997) Shape memory gels made by the modulated gel technology. J Appl Polym Sci 63(9):1173–1178
Lu XL, Cai W, Gao Z, Tang WJ (2007) Shape memory effects of poly(Llactide) and its copolymer with poly(epsilon-caprolactone). Polym Bull 58(2):381–391
Wong YS, Venkatraman SS (2010) Recovery as a measure of oriented crystalline structure in poly(L-lactide) used as shape memory polymer. Acta Mater 58(1):49–58
Behl M, Bellin I, Kelch S, Wagermaier W, Lendlein A (2009) One-step process for creating triple-shape capability of AB polymer networks. Adv Funct Mat 19(1):102–108
Jeong HM, Song JH (2001) Miscibility and shape memory property of poly(vinyl chloride)/thermoplastic polyurethane blends. J Mater Sci 36(22):5457–5463
Jeong HM, Ahn BK, Kim BK (2001) Miscibility and shape memory effect of thermoplastic polyurethane blends with phenoxy resin. Eur Polym J 37(11):2245–2252
Zhang H, Wang H, Zhong W, Du Q (2009) A novel type of shape memory polymer blend and the shape memory mechanism. Polymer 50(6):1596–1601
Liu GQ, Guan CL, Xia H, Guo F, Ding X, Peng Y (2006) Novel shape-memory polymer based on hydrogen bonding. Macromol Rapid Comm 27(14):1100–1104
Liu YP, Gall K, Dunn ML, Greenberg AR, Diani J (2006) Thermomechanics of shape memory polymers: uniaxial experiments and constitutive modeling. Int J Plast 22:279–313
Hu J (2014) Shape memory polymers: fundamentals, advances and applications. Smithers Rapra, Shawbury
Li J, Viveros JA, Wrue MH, Anthamatten M (2007) Shape memory effects in polymer networks containing reversibly associating side-groups. Adv Mater 19(19):2851–2855
Zhu Y, Hu J, Liu Y (2009) Shape memory effect of thermoplastic segmented polyurethanes with self-complementary quadruple hydrogen bonding in soft segments. Eur Phys J E 28(1):3–10
Zhang S, Yu Z, Govender T, Luo H, Li B (2008) A novel supramolecular shape memory material based on partial α-CD–PEG inclusion complex. Polymer 49(15):3205–3210
Liu G, Ding X, Cao Y, Zheng Z, Peng Y (2004) Shape memory of hydrogen-bonded polymer network/poly (ethylene glycol) complexes. Macromol 37(6):2228–2232
Osada Y, Matsuda A (1995) Shape memory in hydrogels. Nat 376:219–220
Kagami Y, Gong JP, Osada Y (1996) Shape memory behaviors of crosslinked copolymers containing stearyl acrylate. Macromol Rapid Comm 17(8):539–543
Hirai T, Matuyama H, Suzuki T, Hayashi S (1992) Effect of chemical crosslinking under elongation on shape restoring of poly(vinyl alcohol) hydrogel. J Appl Polym Sci 46(8):1449–1451
Hirai T, Matuyama H, Suzuki T, Hayashi S (1992) Shape memorizing properties of a hydrogel of poly(vinyl alcohol). J Appl Polym Sci 45(10):1849–1855
Meng H, Li G (2013) A review of stimuli-responsive shape memory polymer composites. Polymer 54:2199–2221
Zheng XT, Zhou S, Yu X, Li X, Feng B, Qu S, Weng J (2008) Effect of in vitro degradation of poly(D, L-lactide)/beta-tricalcium composite on its shape memory properties. J Biomed Mater Res B 86B(1):170–180
Zhou SB, Zheng X, Yu X, Wang J, Weng J, Li X, Feng B, Yin M (2007) Hydrogen bonding interaction of poly(D, L-lactide)/hydroxyapatite nanocomposites. Chem Mater 19(2):247–253
Ni QQ, Zhang CS, Fu Y, Dai G, Kimura T (2007) Shape memory effect and mechanical properties of carbon nanotube/shape memory polymer nanocomposites. Compos Struct 81:176–184
Cho JW, Kim JW, Jung YC, Goo NS (2005) Electroactive shape-memory polyurethane composites incorporating Carbon Nanotubes. Macromol Rapid Commun 26:412–416
Cho JW, Kim JW, Jung YC, Goo NS (2005) Electroactive shape-memory polyurethane composites incorporating carbon nanotubes. Macromol Rapid Comm 26:412–416
Sahoo NG, Jung YC, Goo NS, Cho JW (2005) Conducting shape memory polyurethane-polypyrrole composites for an electroactive actuator. Macromol Mater Eng 290:1049–1055
Koerner H, Price G, Pearce NA, Alexander M, Vaia R (2004) Remotely actuated polymer nanocomposites - stress-recovery of carbon-nanotube-filled thermoplastic elastomers. Nature Mater 3:115–120
Mohr R, Kratz K, Weigel T, Lucka-Gabor M, Moneke M, Lendlein A (2006) Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers. Proc Natl Acad Sci 103:3540–3545
Bilici C, Can V, Nöchel U, Behl M, Lendlein A, Okay O (2016) Melt-processable shape-memory hydrogels with self-healing ability of high mechanical strength. Macromol 49(19):7442–7449
Lee YM, Kim SH, Cho CS (1996) Synthesis and swelling characteristics of pH and thermoresponsive interpenetrating polymer network hydrogel composed of poly(vinyl alcohol) and poly(acrylic acid). J Appl Polym Sci 62:301–311
Chung T, Romo-Uribe A, Mather PT (2008) Two-way reversible shape memory in a semicrystalline network. Macromol 41:184–192
Huang W, Toh W (2000) Training two-way shape memory alloy by reheat treatment. J Mater Sci Lett 19:1549–1550
Liu Y, Liu Y, Humbeeck JV (1999) Two-way shape memory effect developed by martensite deformation in NiTi. Acta Mater 47(1):199–209
Tokuda M, Sugino S, Inaba T (2001) Two-way shape memory behavior obtained by combined loading training. J Intell Mater Syst Struct 12:289–292
Ahir SV, Tajbakhsh AR, Terentjev EM (2006) Self-assembled shape-memory fibers of triblock liquid-crystal polymers. Adv Funct Mater 16:556–560
Li MH, Keller P, Li B, Wang X, Brunet M (2003) Light-driven side on nematic elastomer actuators. Adv Mater 15:569–572
Naciri J, Srinivasan A, Jeon H, Nikolov N, Keller P, Ratna BR (2003) Nematic elastomer fiber actuator. Macromol 36(2003):8499–8505
Yu Y, Nakano M, Ikeda T (2003) Photomechanics: directed bending of a polymer film by light. Nat 425:145–145
Hu Z, Zhang X, Li Y (1995) Synthesis and application of modulated polymer gels. Science 269:525–526
Wang K, Jia YG, ZhuXX (2017) Two-way reversible shape memory polymers made of cross-linked cocrystallizable random copolymers with tunable actuation temperatures. Macromol 50(21):8570–8579
Westbrook K, Mather PT, Parakh V, Dunn ML, Ge Q, Lee BM, Qi HJ (2011) Two-way reversible shape memory effects in a free-standing polymer composite. Smart Mat and Struct 20(6):1–9
Chen SJ, Hu JL, Zhuo H, Zhu Y (2008) Two-way shape memory effect in polymer laminates. Mat Let 62:4088–4090
Ware T, Hearon K, Lonnecker A, Wooley KL, Maitland DJ, Voit W (2012) Triple-shape memory polymers based on self-complementary hydrogen bonding. Macromol 45(2):1062–1069
Bellin I, Kelch S, Langer R, Lendlein A (2006) Polymeric triple-shape materials. Proc Natl Acad Sci USA 103(48):18043–18047
Xie T (2010) Tunable polymer multi-shape memory effect. Nat 464(7286):267–270
Luo X, Mather P (2010) Conductive shape memory nanocomposites for high speed electrical actuation. Soft Matter 6:2146–2149
Luo X, Mather PT (2010) Triple-Shape Polymeric Composites (TSPCs). Adv Funct Mater 20(16):2649–2656
Li G, Zhang H, Fortin D, Xia H, Zhao Y (2015) Poly(vinyl alcohol)-poly(ethylene glycol) double-network hydrogel: a general approach to shape memory and self-healing functionalities. Langmuir 27,31(42):11709–11716
Li Y, Chen H, Liu D, Wang W, Liu Y, Zhou S (2015) pH-responsive shape memory poly(ethylene glycol)-poly(ε-caprolactone)-based polyurethane/cellulose nanocrystals nanocomposite. ACS Appl Mater Interfaces 17:7(23):12988-12999
Li Xixi, Zhu Yaofeng, Dong Yubing, Liu Meng, Ni Qingqing, Yaqin Fu (2015) Epoxy resin composite bilayers with triple-shape memory effect. J Nanomat 475316:1–8
Kim YJ, Park HC, Kim BK (2015) Triple shape-memory effect by silanized polyurethane/silane-functionalized graphene oxide nanocomposites bilayer. High Perform Polym 27(7):886–897
Behl M, Ridder U, Feng Y, Kelch S, Lendlein A (2009) Shape-memory capability of binary multiblock copolymer blends with hard and switching domains provided by different components. Soft Matter 5(3):676–684
Sun L, Huang WM (2010) Mechanisms of the multi-shape memory effect and temperature memory effect in shape memory polymers. Soft Matter 6(18):4403–4406
Prathumrat P, Tiptipakorn S, Rimdusit S (2017) Multiple-shape memory polymers from benzoxazine–urethane copolymers. Smart Mater Struct 26(9):1–9
Samuel C, Barrau S, Lefebvre JM, Raquez JM, Dubois P (2014) Designing multiple-shape memory polymers with miscible polymer blends: evidence and origins of a triple-shape memory effect for miscible PLLA/PMMA blends.Macromol 47(19):6791–6803
Buckley PR, McKinley GH, Wilson T, Small W, Benett J, McElfresh M, Maitland D (2006) Inductively heated shape memory polymer for the magnetic actuation of medical devices. IEEE Trans Biomed Eng 53(10):2075–2083
Tobushi H, Hashimoto T, Hayashi S, Yamada E (1997) Thermomechanical constitutive modeling in shape memory polymer of polyurethane series. J Intell Mater Syst Struct 8:711–718
Tobushi H, Okumura K, Hayashi S, Ito N (2001) Thermomechanical constitutive model of shape memory polymer. Mech Mater 33(10):545–554
Lu W, Le X, Zhang J, Huang Y, Chen T (2017) Supramolecular shape memory hydrogels: a new bridge between stimuli-responsive polymers and supramolecular chemistry. Chem Soc Rev 46:1284–1294
Lan X, Wang XH, Liu YJ, Leng JS (2009) Fiber reinforced shape-memory polymer composite, its application in a deployable hinge. Smart Mater Struct 8(024002):1–6
Liang C, Rogers CA, Malafeew E (1997) Investigation of shape memory polymers and their hybrid composites. J Intell Mater Syst Struct 8:380–386
Wei ZG, Sandstroum R, Miyazaki S (1998) Shape memory materials and hybrid composites for smart systems: part II shape memory hybrid composites. J Mater Sci 33(15):3763–3783
Simkevitz S, Naguib HE (2008) Development of two part porous shape memory polymer nanocomposites. Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS2008 1:453–460
Lamm M, Wang Z, Zhou J, Yuan L, Zhang X, Tang C (2018) Sustainable epoxy resins derived from plant oils with thermo- and chemo-responsive shape memory behavior. Polymer 111:121–127
Truong TT, Thai SH, Nguyen HT (2018) Poly(ε-caprolactone) networks with tunable thermoresponsive shape memory via a facile photo-initiated thiol–ene pathway. J Mater Sci 53:2236–2252
Kalita H, Karak N (2014) Biobased hyperbranched shape-memory polyurethanes: effect of different vegetable oils. J Appl Polym 131:1–8
Han XJ, Dong ZQ, Fan MM, Liu Y, li JH, Wang YF, Yuan QJ, Li BJ, Zhang S (2012) pH-induced shape-memory polymers. Macromol Rapid Commun 27:33(12):1055–1060
Song Q, Chen H, Zhou S, Zhao K, Wang B, Hu P (2016) Thermo- and pH-sensitive shape memory polyurethane containing carboxyl groups. Polym Chem 7:1739–1746
Xiao Y, Gong X, Kang Y, Jiang Z, Zhang S, Li B (2016) Light-, pH- and thermal-responsive hydrogels with the triple-shape memory effect. Chem Commun 52:10609–10612
Yang B, Huang W, Li C, Li L (2006) Effects of moisture on the thermomechanical properties of a polyurethane shape memory polymer. Polymer 47(4):1348–1356
Du H, Zhang J (2010) Shape memory polymer based on chemically cross-linked poly(vinyl alcohol) containing a small number of water molecules. J Colloid Polym Sci 288:15–24
Ghobadi E, Marquardt A, Zirdehi E, Neuking K, Varnik F, Eggeler G, Steeb H (2018) The influence of water and solvent uptake on functional properties of shape-memory polymers. Inter J Poly Sci 7819353:15–30
Leng JS, Lv H, Liu Y, Du SY (2007) Electroactivate shape-memory polymer filled with nanocarbon particles and short carbon fibers. Appl Phys Lett 91(144105):1–3
Leng J, Lan X, Liu Y, Du S, Huang W, Liu N, Phee S, Yuan Q (2008) Electrical conductivity of thermoresponsive shape-memory polymer with embedded micron sized Ni powder chains. Appl Phys Lett 92(014104):1–2
Schmidt AM (2006) Electromagnetic activation of shape memory polymer networks containing magnetic nanoparticles. Macromol Rapid Commun 27:1168–1172
Schmidt AM (2006) Electromagnetic activation of shape memory polymer networks containing magnetic nanoparticles. Macromol Rapid Commun 27(14):1168–1172
Zrínyi M (2000) Intelligent polymer gels controlled by magnetic fields. Colloid Polym Sci 278(2):98–103
Fuhrer R, Athanassiou EK, Luechinger NA, Stark WJ (2009) Crosslinking metal nanoparticles into the polymer backbone of hydrogels enables preparation of soft, magnetic field-driven actuators with muscle-like flexibility. Small 5(3):383–388
Gong T, Li W, Chen H, Wang L, Shao S, Zhou S (2012) Remotely actuated shape memory effect of electrospun composite nanofibers. Acta Biomater 8(3):1248–1259
Jiang H, Kelch S, Lendlein A (2006) Polymers move in response to light. Ad Mat 18(11):1471–1475
Lu H, Yao Y, Huang WM, Leng J, Hui D (2014) Significantly improving infrared light-induced shape recovery behavior of shape memory polymeric nanocomposite via a synergistic effect of carbon nanotube and boron nitride. Compos Part B 62:256–261
Inam F, Wong D, Kuwata M, Peijs T (2010) Multiscale hybrid micro-nanocomposites based on carbon nanotubes and carbon fibers. J of Nanomat 453420:12–24
Shou Q, Uto K, Iwanaga M, Ebara M, Aoyagi T (2014) Nearinfrared light-responsive shape-memory poly([epsiv]-caprolactone) films that actuate in physiological temperature range. Polym J 46(8):492–498
Lendlein A, Jiang H, Junger O, Langer R (2005) Light-induced shape-memory polymers. Nat 434(7035):879–882
Miyamae K, Nakahata M, Takashima Y, Harada A (2015) Self-healing, expansion − contraction, and shape memory properties of a preorganized supramolecular hydrogel through host guest interactions. Angew Chem 127(31):9112–9115
Aoki D, Teramoto Y, Nishio Y (2007) SH-containing cellulose acetate derivatives: preparation and characterization as a shape memory-recovery material. Biomacromol 8(12):3749–3757
Xuzhou Y, Feng W, Bo Z, Feihe H (2012) Stimuli-responsive supramolecular polymeric materials. Chem Soc Rev 41:6042–6065
Dong Z, Cao Y, Yuan Q, Wang Y, Li J, Li B, Zhang S (2013) Redox and glucose induced shape memory polymers. Macromol Rapid Comm 34(10):867–872
Behl M, Razzaq MY, Lendlein A (2010) Multifunctional shape-memory polymers. Adv Mater 22(31):3388–3410
Kruft MAB, Benzina A, Blezer R, Koole LH (1996) Studies on radio-opaque polymeric biomaterials with potential applications to endovascular prostheses. Biomat 17:1803–1812
Small W, Buckley PR, Wilson TS, Benett WJ, Hartman J, Saloner D, Maitland DJ (2007) Shape memory polymer stent with expandable foam: a new concept for endovascular embolization of fusiform aneurysms. IEEE T Bio-Med Eng 54(6):1157–1160
Yakacki CM, Shandas R, Lanning C, Rech B, Eckstein A, Gall K (2007) Unconstrained recovery characterization of shape-memory polymer networks for cardiovascular applications. Biomat 28(14):2255–2263
Baer GM, Wilson TS, Small W, Hartman J, Benett WJ, Matthews DL, Maitland DJ (2009) Thermomechanical properties, collapse pressure, and expansion of shape memory polymer neurovascular stent prototypes. J Biomed Mater Res B Appl Biomater 90(1):421–429
Wache HM, Tartakowska DJ, Hentrich A, Wagner MH (2003) Development of a polymer stent with shape memory effect as a drug delivery system. J Mater Sci-Mater Med 14(2):109–112
Hampikian JM, Heaton BC, Tong FC, Zhang ZQ, Wong CP (2006) Mat Sci Eng C Mater 26(8):1373–1379
Jung YC, Cho JW (2010) Application of shape memory polyurethane in orthodontic. J Mater Sci Mater Med 21(10):2881–2886
Rousseau LA, Berger E, Owens J, Kia H (2012) Shape memory polymer medical cast. US 8100843B2
Takashima K, Rossiter J, Mukai T (2010) McKibben artificial muscle using shape-memory polymer. Sensor Actuat A-Phys 164(1–2):116–124
Harris KD, Cuypers R, Scheibe P, van Oosten CL, Bastiaansen CWM, Lub J, Broer DJ (2005) Large amplitude light-induced motion in high elastic modulus polymer actuators. J Mater Chem 15(47):5043–5048
Gall K, Dunn ML, Liu Y, Finch D, Lake M, Munshi NA (2002) Shape memory polymer nanocomposites. Acta Mater 50(20):5115–5126
Gall K, Kreiner P, Turner D, Hulse M (2004) Shape-memory polymers for microelectromechanical systems. J Microelectromech S 13(3):472–483
Serrano MC, Ameer GA (2012) Recent insights into the biomedical applications of shape-memory polymers. Macromol Biosci 12(9):1156–1171
Xiao XC, Xie T, Cheng YT (2010) Self-healable graphene polymer composites. J Mater Chem 20(17):3508–3514
Rodriguez ED, Luo XF, Mather PT (2011) Linear/network poly(ε-caprolactone) blends exhibiting shape memory assisted self-healing (SMASH). ACS Appl Mater Inter 3(2):152–161
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Strzelec, K., Sienkiewicz, N., Szmechtyk, T. (2020). Classification of Shape-Memory Polymers, Polymer Blends, and Composites. In: Parameswaranpillai, J., Siengchin, S., George, J., Jose, S. (eds) Shape Memory Polymers, Blends and Composites. Advanced Structured Materials, vol 115. Springer, Singapore. https://doi.org/10.1007/978-981-13-8574-2_2
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