Magnetic polyurethane-based electrospun scaffolds: a linkage between magnetically enhanced bioactivity with shape memory effect for smart wound healing application

The surface-modified nanoparticle, monmorillonite (MMT), was chemically bonded to shape memory polyurethane (SMPU) to improve shape memory and mechanical properties compared to the conventional composite prepared by melt-mixing process. Cloisite 30B was selected as MMT, because the functional group on its surface, methyl tallow bis-2-hydroxyethyl ammonium group, could be used for chemical bonding with SMPU and the reduced surface hydrophilicity rendered MMT disperse better in SMPU matrix during chemical reaction compared to bare MMT. Two types of SMPU, differing according to their soft segment (PTMG) and MMT content, were compared in mechanical and shape memory properties. Maximum stress went up as high as 57 MPa, and strain remained above 1000% for all of SMPUs. Shape recovery improved up to 97%, and did not decrease after four repetitive cyclic tests. Here, results demonstrating the advantages of chemical bonding of MMT-linked SMPU, compared to MMT and PU composite made by melt-mixing method, are discussed.

By using the nanostructure and nanocomposites of shape memory polyurethane (PU), various stimulus-responsive polymer materials which can be actuated by heating, electric power, and water were prepared. For the electroactive shape memory polyurethane nanocomposites, poly(e-caprolactone) as soft segment and the functionalized carbon nanotubes(CNTs) were employed through chemical modification, grafting, surface coating, and cross-linking. The dominant enhancement in mechanical, thermal and shape memory properties were achieved in the sample of cross-linked nanocomposites of PU and CNTs. The water-triggered shape memory effect was obtained from the POSS-PU synthesized from poly(ethylene oxide) and POSS as hydrophilic and hydrophobic components in soft and hard segments, respectively. The actuation of these different stimulus-responsive polymer materials is demonstrated in this report.

Shape memory polyurethanes (SMPU) are one of the advanced materials that have potential applications in the field of biomedical particularly vascular stent. This paper studies the effect of incorporating palm oil polyol (POP) up to 40% molar ratio in place of petroleum‐based polyol in the preparation of SMPU due to environmental concern. Polycaprolactone diol was utilized as the soft segment while 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol as the hard segments. The SMPU was prepared using two‐step prepolymer method, and the fabricated samples were characterized to study the effect of POP on the thermal properties, tensile, and shape memory behavior of polyurethane. The results obtained have shown that SMPU with incorporation of POP showed good shape fixity (100%) and elongation at break (245%) up to 20% molar ratio of POP. The presence of dangling chains of fatty acid in POP was believed to enhance the flexibility of SMPU molecular chains by acting as a plasticizer. On the other hand, the shape recovery of SMPU remains high even at 40% molar ratio of POP, and the thermal stability of SMPU increased with the addition of POP. It is proposed that the synthesized POP‐based SMPU is a suitable candidate for cardiovascular stent as they possessed desired thermal, mechanical, and shape memory properties.

Bending shape memory behaviours of carbon fibre reinforced polyurethane-type shape memory polymer composites under relatively small deformation: Characterisation and computational simulation

Shape memory polyurethane (SMPU) grafted using polyethyleneimine (PEI) was tested for its electrolytic attraction in aqueous solution and shape memory effect. The PEI was connected through a second 4,4′-diphenylmethane diisocyanate anchored to the carbamate moiety of SMPU. Two series of SMPU that differed in soft segment polytetramethylene glycol and PEI content were prepared to compare their tensile and shape memory properties. Shape recovery was high as 99% and reduced only to 97% after four test cycles. The PEI group attached to the SMPU chain, if converted to the imminium salt form, was designed to work as an electrolyte during water electrolysis and was to be attracted toward the cathode to show SMPU movement in aqueous solution. The electrolytic attraction of SMPU in aqueous solution was demonstrated in an experiment in which a specimen moved to the cathode only when voltage above a minimum was applied. The mechanism and application of this finding are discussed. Open image in new window

Magnetic nanoparticle-based solder composites for electronic packaging applications

Shape memory polyurethanes are usually fabricated with low-molecular weight polyols through a two-step copolymerization, which often results in difficulty attaining both desired shape memory switch temperature and optimal thermomechanical properties. Here we present a series of shape memory polyurethane copolymers having urethane chains as soft segments. The structure and shape memory properties of copolymers were investigated with differential scanning calorimetry, dynamic mechanical analysis, small angle x-ray scattering, and thermomechanical tests. Increasing the length of the urethane soft segments enhanced phase separation, while it brought little change to the glass transition temperature (T g). Based on the urethane soft segments, some rigid chain extenders could be readily introduced into the backbone of copolymers, resulting in better phase separation. All polyurethane copolymers exhibited more than 90% of shape recovery. The shape recovery of the materials was proved to be inversely proportional to the fraction of hard phase and directly proportional to the stability of hard domains. The copolymers containing longer soft and hard segments and rigid chain extenders exhibited higher deformation stress and thus larger recovery stress. The copolymerization employing urethane chains as soft segments can greatly expand flexibility for molecular design and favor the optimization of shape memory properties.

Shape memory polyurethanes (SMPUs) are typically synthesized using polyols of low molecular weight (MW~2,000 g/mol) as it is believed that the high density of cross-links in these low molecular weight polyols are essential for high mechanical strength and good shape memory effect. In this study, polyethylene glycol (PEG-6000) with MW ~6000 g/mol as the soft segment and diisocyanate as the hard segment were used to synthesize SMPUs, and the results were compared with the SMPUs with polycaprolactone PCL-2000. The study revealed that although the PEG-6000-based SMPUs have lower maximum elongations at break (425%) and recovery stresses than those of PCL-based SMPUs, they have much better recovery ratios (up to 98%) and shape fixity (up to 95%), hence better shape memory effect. Furthermore, PEG-based SMPUs showed a much shorter actuation time of < 10 s for up to 90% shape recovery compared to typical actuation times of tens of seconds to a few minutes for common SMPUs, demonstrated their great potential for applications in microsystems and other engineering components.

Shape memory polyurethane - Amorphous molecular mechanism during fixation and recovery

A series of PCL-based shape memory polyurethanes was synthesized via bulk pre-polymerization. Their thermal, mechanical properties, shape memory properties, softening and hardening processes were investigated by the experimental approach and made comparison with a commercially available orthotic material. The cytotoxicity of the low-temperature thermoplastic polyurethane was tested. The results suggest that the soft segment phase of the shape memory polyurethanes has a melting transition at about 36–46°C, which makes them possible low-temperature thermoplastic materials. The hard segment phase has a two-fold effect on the shape memory polyurethane as a low-temperature thermoplastic orthotic material: increasing tensile mechanical strength at room temperature, which enables it to be used in circumstances where high tensile strength is required; and reducing low-temperature malleability and fixity ratio, which make it difficult to fabricate orthortic devices. To obtain a shape memory polyurethane with excellent low-temperature thermoplastic properties for orthopaedical surgical use, the hard segment content should not be above 22 wt%. At last, a prototype wrist orthosis was easily fabricated at 60°C with hand using a shape memory polyurethane with 16 wt% hard segment content. Cytotoxicity tests indicate that the wrist orthotic material is not cytotoxic.

A flexibly cross-linked shape memory polyurethane (SMPU) was converted to a magnetic polymer by making a composite with a ferromagnetic particle (Fe3O4). The flexibly cross-linked SMPU has already displayed excellent mechanical and shape memory properties; the design of a magnetically responsive material allowed for a unique and novel SMPU. Among the three different composite preparation methods (melt-mixing, solvent blending, and in situ reaction mixing), the melt-mixing method was the best and attained even distribution of magnetic particles and high mechanical and shape memory properties. Differential scanning calorimetric and infrared results showed that the polymer structure was not affected by melt-mixing. In tensile testing, the maximum stress of the composite reached 39 MPa, and the strain at break also increased to 2495%. Shape recovery exhibited maximums as high as 99% and displayed similar values after repetitive shape recovery test cycles. Finally, the magnetic property of SMPU was characterized by a superconducting quantum interference device magnetometer and demonstrated in the magnetic attraction test. The potential applications of the magnetic and flexible SMPU are discussed.

Evaluation of nanoparticulate fillers for development of shape memory polyurethane nanocomposites

The development and large-scale implementation of multifunctional advanced materials with smart and intelligent properties like shape memory are very topical. In the present work, we report the development of multifunctional graphene nanoplatelets (GNPs)-reinforced thermo-responsive shape memory composites, in ether type shape memory polyurethane (SMPU) matrix. A unique twin screw co-rotating microcompounder with a back flow channel was operated to ensure proper dispersion of GNPs in the SMPU matrix for developing different compositions of nanocomposites, namely SMC0, SMC1, SMC2, and SMC3, respectively. The detailed characterizations and properties of the above developed nanocomposites were studied using various complementary techniques for spectroscopy, morphology, mechanical, thermal, shape memory, DMA, etc. The dynamic thermomechanical properties of all the developed nanocomposites were studied at 0.1 and 10 Hz, respectively. Structure of SMP and developed composite were also analyzed using various spectroscopic methods. The addition of GNPs to the SMP matrix improved the mechanical and shape memory properties, although a noticeable impact on thermal property is also reported. The fractured microphotographs reveal the uniform dispersion of GNP in SMPU. Addition of 1 phr GNPs increased storage modulus of SMPU from 3.14 to 4.11 GPa and the value of tan δ peak was decreased from 0.81 to 0.53, respectively. The GNPs in SMPU matrix influences the shape recovery, which is improved with the addition of GNPs in the experimental range.

Preparation of electroactive shape memory polyurethane/graphene nanocomposites and investigation of relationship between rheology, morphology and electrical properties

Shape memory polyurethanes (SMPUs) are typically synthesized using polyols of low molecular weight, Mw, and high hydroxyl number as it is believed that high density of cross-links in these polyols are essential for high performance shape memory polymers. In this study, polyethylene glycol (PEG-6000) with Mw ~ 6000 g/mol and low hydroxyl number (OH ~ 18 mg K OH/g) as the soft segment and diisocyanate as the hard segment were used to synthesize SMPUs. It revealed that although the PEG-6000 based SMPUs have lower maximum elongation at break (425%) and recovery stress than those of PCL-2000 polyol based SMPUs, they have much better shape recovery ratio (98%) and shape fixity (95%). Furthermore, these SMPUs showed a much shorter actuation time of <10sec for up to 85% shape recovery, much shorter than those low Mw SMPUs, clearly demonstrated their great potential for applications.