Actuators are the controllable work-producing devices with an input of thermal, electrical or magnetizing stimuli and an output of mechanical energy. Regarding their widespread use, smart polymers have recently been used in producing actuators. Smart polymers are a group of neat or composite materials, which have inherent smartness along with self-adaptive capabilities against external stimuli. shape memory polymers which are also a group of smart polymers, can recover their initial and permanent shape under external stimuli. In this work an actuator was made of a shape memory cross-linked polyethylene and the effects of different factors such as the content of cross-linking agent, deformation temperature, strain ratio, strain rate, type of cooling and heating rate on final shape recovery, recovery speed and the actuator behavior between 10% and 90% of final recovery were investigated. The results show that the actuator made of cross-linked polyethylene has a controllable behavior in this range.

Smart polymers as a subset of smart materials have the ability to memorize their original form and return after reforming by inducing some stimulus. In this study, shape-memory polymers were manufactured in layers by 3D printing methods. Using this method, by controlling the percentage of each material in the sample and layer design the shape memory properties are investigated. The advantages of this method compared to other methods such as blending are the control simplicity of the impacting factors on the shape memory property, construction of complex parts, and improved shape memory property. TPU with elastic property and semicrystalline PLA materials were used to achieve shape memory property and the samples printed out in TPU-UP and PLA-UP states to investigate the layer design effect. The results of shape memory tests showed that the number of layers, their arrangement, and shape memory properties can be easily controlled and designed. The results of DMTA test indicated that the recovery temperature in layered samples is lower than the other methods and the percentage of PLA and TPU can be controlled the recovery temperature. The recovery speed of layered samples in this study is very higher than previous studies, due to the amount of saved energy in TPU and the multilayered construction. shape memory tests depicted that TPU increases the recovery ratio and the PLA increases the fixity ratio. The reason lay in the increase of the switching point percentage including crystallization, Tg, and reduction of cross-links which play the role of network cross.

In this paper, the effect of thermomechanical loading on the behavior of deflection-based harvested energies from a shape memory polymer system is experimentally investigated. Samples are created with honeycomb cells from poly-lactic acid using additive manufacturing techniques. The shape memory effect in shape recovery and force recovery paths are studied under thermomechanical tests in bending and tensile modes. The maximum recoverable strain energy is computed as well. According to the conducted thermomechanical tests, it is shown that the thermal expansion coefficient is much more dominant in the tensile mode. Some procedures are proposed to reduce the thermal expansion effect on the force recovery and arrive at higher energy harvested from a shape memory system.

In this research, using a thermomechanical constitutive model for shape memory polymers and employing the von Ká rmá n theory, a finite element analysis of a shape memory polymer beam is presented. The importance of introducing the von Ká rmá n theory for shape memory polymers is that the beam can have relatively high slopes during loading. Also, for optimization and designing processes we need to solve multiple problems and due to the high processing time the use of 3D model is not suitable. To validate the presented formulations, the reported results are compared with the 3D solution which was previously reported by the same authors. Accordingly, the effect of the hard segment volume on response of a thin beam has been investigated, and the results of the von Ká rmá n beam have been reported and compared with the 3D and Euler-Bernoulli solutions. As an example, the error of the beam response in one of the solved examples is 27% for Euler-Bernoulli beam and 1% for the von Ká rmá n solution compared to the three-dimensional solution. In general, the lower the beam thickness or the beam is longer, the Euler-Bernoulli beam error will be higher. The proposed finite element model can provide a reliable alternative response comparing to 3D modeling that requires a lot of processing time, and can be used for geometry and material parametric study.

Although there are many works published on shape memory polyurethanes, but no report is found on PCL-based polyurethane composite using PCL with molecular weight of 2000 g/mol and nanoclay particles via in-situ polymerization. In this work, we try to approach some problems concerning the chemical structure, dispersion of nanoparticles in the matrix and interaction between nanoparticles and polymer in shape memory of PCL (Mn=2000 g/mol) -based polyurethane/nanoclay composites. While PCL (Mn=2000 g/mol) polyurethane constituted the soft segments, MDI/BD formed the hard segments. The weight ratio of soft to hard segments was found to be 65/35. Composites were synthesized in presence 1 and 3 wt% of nanoclay (Cloisite®30B) via in-situ polymerization by a twostep method. Effect of nano particles on their interactions with polyurethane chains, crystallinity, mechanical properties and shape memory have been investigated using FTIR, DSC, tensile test and shape memory analysis, respectively. Phase mixing and hydrogen bonding intensified with 1 wt% nanoclay particles, whereas 3 wt% nanoclay led to phase separation. XRD, MTDSC, AFM analyses showed exfoliation of samples with 1 wt% nanoclay in the matrix and better tensile strength in comparison with pure sample and higher shape recovery compared to all other samples. Crystallinity of soft segments resulted in higher modulus and improvement of shape memory. TGA results showed a three-step degradation mechanism for PCL, MDI and BDO-based polyurethane.

A stenotic vessel can be opened using net-shape tubes called “ stents” leading to the restoration of the bloodstream. Compared to the commonly used stainless steel stent, self-expandable stents have some advantages. They do not suffer from the risks of damage to the vascular tissue due to the balloon expansion. Moreover, overexpansion for compensating the elastic recoil is not needed, and there is no constant force applied on the artery until the occlusion of the device by the artery stops. However, the stent cannot restore the original dimensions of the vessel in the case of calcified plaques. Self-expandable stents can be utilized for the treatment of atherosclerotic lesions in the carotid, coronary, and peripheral arteries. shape memory alloys (SMAs), mainly NiTi (nitinol), are employed for self-expandable vascular stent applications. Nitinol is widely applied for medical devices and implants due to its excellent fatigue performance, mechanical properties, and biocompatibility, which make this alloy suitable for long-term installations. Other materials used for self-expandable cardiovascular stents are shape memory polymers (SMPs). shape memory effect is triggered by the hydration of polymers or temperature change preventing the collapse of small blood vessels. This review has focused on the mechanisms and properties of SMAs and SMPs as promising materials for stent application.

The tissues in the human body comprise complex assemblages of several different types of cells that are dispersed on an extracellular matrix (ECM). In addition to biochemical and chemophysical factors, dynamic changes in the mechanical-structural properties of ECM lead to changes in cell behavior such as proliferation, differentiation, and its nature. Since any activity of the cells takes place on a dynamic substrate in the body, it is necessary to provide conditions in which the dynamic environment inside the body can be simulated. Therefore, researchers need intelligent biomaterials that can act as a powerful substrate to design smart cell culture platforms and tissue engineering scaffolds, as well as to simulate this complex environment. shape memory polymers (SMPs) and shape-changing polymers (SCPs) are the new generations of intelligent materials that can be converted from shape A to shape B in a response to a stimulus, creating new mechanical and structural properties. Although tissue engineering studies on static substrates have been performed so far, it is now clear that the fate of cells in proliferation and differentiation is influenced by the dynamic conditions of the environment. However, recent studies have been focused on designing new substrates to mimic the dynamic microenvironment. In this review article, a brief definition of cell mechanobiology is introduced and then the recent advances in the design of SMPs and SCPs used in fundamental cell mechanobiology studies were highlighted. A survey of the current review can create a more innovative perspective for researchers in this field.

NiTiHf high temperature shape memory alloys are highly popular for high temperature industrial applications due to their high transformation temperature, thermal stability and lower cost. However, they have weaker shape memory properties than NiTi binary alloys. The solution to this problem is to increase the strength of the alloy in order to prevent plastic deformation caused by slipping. Thermomechanical treatment is a method to improve the recovery strain. In this research, the Ni50Ti40Hf10 shape memory alloy was cast by vacuum arc melting and then the hot tensile test was performed on the samples with a strain rate of 0. 01 s-1 at 800, 900, 1000 and 1100 °C, also specimens were hot-rolled at 1000 °C with a reduction of thicknesses by 10, 15, 20 and 30%. To determine the amount of recovery strain and recovery ratio by bending test strains of 2. 6 to 6 were applied to the samples. The results of the hot tensile test showed that the temperature of 1000 °C is acceptable for hot rolling due to the suitable ductility of the alloy. The maximum recovery strain in the cast sample was 5. 7 with a recovery ratio of 88%. By applying 10% of hot rolling, the recovery strain and recovery ratio increased to 5. 8 and 92 respectively, while after 20% of rolling, these values increased to 5. 9 and 94. The formation of uniform and coaxial grains in the microstructure of the samples indicated the occurrence of dynamic recrystallization, which led to an increase in the recovery strain.

The TiO2 dispersed physically cross-linked polymer hydrogels were synthesized through a single step free radical addition polymerization mechanism based on acrylic acid and gum Arabic (GA) as polymer constituents, and ferric ions (Fe3+) as physical cross-linker. The effect of TiO2 powder was investigated on thermal and mechanical properties of the hydrogels by dispersion of 0. 01, 0. 02 and 0. 03 g of TiO2 in hydrogels. The prepared hydrogels were successfully characterized through FTIR, XRD, SEM and thermogravimetric analysis (TGA). For the mechanical properties, dynamic mechanical analysis and universal testing machine (UTM) were used. The DMA results showed that the storage modulus was increased with the TiO2, while UTM results showed that 0. 02 g of TiO2 powder significantly enhanced the fracture stress, elastic modulus, toughness and stretchability by 4514%, 4328%, 4124% and 20%, respectively, compared to the virgin hydrogels. Cole–, Cole plot confirmed the homogeneity and viscoelastic behavior of the system, while manual load bearing and shape memory test showed that the hydrogels bear a load of 2. 5 kg for a long time and it is recovered within 10 s to its original state. The materials can be applied for the synthesis of artificial body parts in the field of bio-engineering. The use of un-modified GA for the synthesis of hydrogels will open a new window for the researchers working in this field.