Thermoresponsive shape memory polymers (SMPs) are a type of stimuli-sensitive materials that switch from a temporary shape back to their permanent shape upon exposure to heat. While the majority of SMPs have been fabricated in the solid form, porous SMP foams exhibit distinct properties and are better suited for certain applications, including some in the biomedical field. Like solid SMPs, SMP foams have been restricted to a limited group of organic polymer systems. In this study, we prepared inorganic-organic SMP foams based on the photochemical cure of a macromer comprised of inorganic polydimethylsiloxane (PDMS) segments and organic poly(ε-caprolactone) (PCL) segments, diacrylated PCL(40)-block-PDMS(37)-block-PCL(40). To achieve tunable pore size with high interconnectivity, the SMP foams were prepared via a refined solvent-casting/particulate-leaching (SCPL) method. By varying design parameters such as degree of salt fusion, macromer concentration in the solvent and salt particle size, the SMP foams with excellent shape memory behavior and tunable pore size, pore morphology, and modulus were obtained. 相似文献
Polymeric blend shape memory polymers (SMPs) can be constructed from two immiscible polymeric matrices. The shape recovery behavior of these composite systems can be easily controlled by varying the ratio of the polymer blends. It has been recently discovered that the functionality of SMPs can be further enhanced with electroactive ability through the use of conductive fillers. However, the fillers may negatively interact with the SMPs and cause a reduction in the elongation at failure thereby diminishing the shape recovery performance. It is proposed that a plasticizer can be utilized to alter the microstructure of the SMPs with conductive fillers. In this study, a new hybrid SMP is developed by combining single‐walled carbon nanotubes (SWCNT) into a poly(lactic acid) (PLA) and thermoplastic polyurethane (TPU) SMP system containing poly(ethylene glycol) (PEG) plasticizer. The incorporation of PEG is able to lower the activation temperature, while enhancing dispersion of SWCNT. The presence of SWCNT can stabilize the SMP system and significantly enhance the shape‐fixing capability after deformation at room temperature conditions. By carefully controlling the formulation, an electroactive SMP can be created by optimizing the amount of SWCNT and PEG plasticizer. 相似文献
Shape memory polymers (SMPs)are widely used owing to their ability to change shapes under external stimuli. Conventional covalently crosslinked SMPs have limitations in biomedical applications. This article presents a linear shape memory biodegradable polyester without chemical crosslinks or multiblock structures. A new programming protocol is developed to split the crystals into two parts with different melting transitions through partial melting/recrystallization. The split crystals play different roles in fixation and recovery process to complete a shape memory cycle. The ratio between the partitioned crystals affects the fixed rate and recovery rate. The shape memory performance can be optimized by controlling the partial melting temperature and pre-stretching of the sample. Examples of complicated shape changes demonstrate the effectiveness of the proposed technique. The method is applicable to crystallizable linear polymers and has potential applications in implantation devices. 相似文献
The rapidly expanding field of shape memory polymers (SMPs) is driven by a growing number of potential applications, such as biomaterials, optics, and electronics. The basic concept involves polymers that can be trapped in a thermodynamically-unfavorable shape, then triggered by an external stimulus to return to their original shape, doing useful work in the process. Part of the attraction of using SMPs is that the energy released during actuation is stored in the polymer itself, rather than requiring an external force to change shape. This approach is beneficial for applications where external actuation is impossible or inconvenient. Polymers are also advantageous over shape memory metal alloys or ceramics in that there are endless combinations of functional groups and material properties to suit a variety of purposes, based on the monomers and polymerization conditions chosen. This advantage of SMPs is of particular interest in the development of materials with additional, desirable physicochemical attributes that are not necessarily coupled to the shape memory (SM) behavior itself. The SM behavior is quantitatively measured to facilitate comparison of various polymer systems, and researchers have used a number of defining parameters to guide the development and characterization of materials with extremely precise and reliable SM responses. In this review, recent trends in the structural or chemical characteristics of SMPs are explored, with an emphasis on how the molecular structure and functionality of each polymer affects its mechanical response. 相似文献
A novel styrene-butadiene-styrene tri-block copolymer (SBS) and poly(?-caprolactone) (PCL) blend were introduced for its shape memory properties. Compared to the reported shape memory polymers (SMPs), this novel elastomer and switch polymer blend not only simplified the fabrication process but also offer a controllable approach for the study of mechanisms and the optimization of shape memory performances. Microstructures of this blend were characterized by differential scanning calorimetry (DSC), AFM microscope observation and tensile test. DSC results demonstrated the immiscibility between SBS and PCL. AFM images and stress-strain plot further confirmed the two-phase morphology within the blend. It was found that the SBS and PCL continuous phases contributed to the shape recovery and shape fixing performances, respectively. A detailed shape memory mechanism for this type of SMP system was then concluded and an optimized SMP system with both good recovery and fixing performances was designed from this mechanism. 相似文献
Porous and bulk water‐responsive urethane‐based shape memory polymers (SMPs) containing poly(ethylene glycol) (PEG), poly(caprolactone), and poly(dimethylsiloxane) are fabricated. The copolymers are processed by electrospinning to achieve porous structures. Shape fixation and recovery are achieved via the solvation and recrystallization of the hydrophilic PEG switching segment. Mechanical testing is performed to determine the SMP functionality. Water uptake rate for porous SMP is found to be higher than bulk SMP partly due to higher surface area for water contact. This enables porous structure water‐responsive SMPs to recover faster compared to bulk SMPs. The water‐responsive SMP exhibits good extents of shape fixity and shape recovery when immersed in water (≈35 °C). Different actuation times can be achieved based on the total surface area and efficiency of water‐entry into the polymer.
Thermally stimulated shape memorypolymers (SMP) are defined by their ability to store and recoverstrains when subjected to a particular thermo-mechanical cycle. The thermo-mechanical behavior of SMPs can be tailored by modifying the molecular structure of the polymer. In this article, the shape memory behavior of thermoplastic segmented polyurethane (TSPU) as a function of hard segment (HS) has been reported. The experimental results showed that tailoring of hard and soft segment is extremely necessary for TSPU showing shape memory behavior. The thermo-mechanical properties of TSPU with four different concentrations of hard segment viz. 58.7, 47.9, 37.5, and 31.0% have been studied in this article. TSPU with 58.7% of hard segment content would not able to elongate even up to 30% in experimental condition. However, all other three samples show good shape memory behavior. 相似文献