Polyurethane Shape Memory Polymer Foams Research Articles

Effect of multi-layer prosthetic foam liner on the stresses at the stump–prosthetic interface

The prosthetic liner plays a significant role in the redistribution of the pressure between the stump and the socket, as it adding a cushioning layer between the stump and the socket which relieves pain and makes the prosthesis more comfortable. This study employed nonlinear finite element analyses to investigate the peak pressure and shear stress at stump–prosthetic interface in the case of multi-layer prosthetic foam liner, this liner having an inner polymeric foam layer Surrounded by another type of polymeric foam layer, we used three different types of foams in different order to define this liner (flexible polyurethane foam, polyurethane-shape memory polymer foam, and natural rubber latex foam). That’s allows comparing 6 deferent configuration of multi-layer prosthetic foam liner.

Nonlinear Finite Element Modelling of Thermo-Visco-Plastic Styrene and Polyurethane Shape Memory Polymer Foams

This paper presents nonlinear finite element (FE) models to predict time- and temperature-dependent responses of shape memory polymer (SMP) foams in the large deformation regime. For the first time, an A SMP foam constitutive model is implemented in the ABAQUS FE package with the aid of a VUMAT subroutine to predict thermo-visco-plastic behaviors. A phenomenological constitutive model is reformulated adopting a multiplicative decomposition of the deformation gradient into thermal and mechanical parts considering visco-plastic SMP matrix and glass microsphere inclusions. The stress split scheme is considered by a Maxwell element in parallel with a hyper-elastic rubbery spring. The Eyring dashpot is used for modelling the isotropic resistance to the local molecular rearrangement such as chain rotation. A viscous flow rule is adopted to prescribe shear viscosity and stress. An evolution rule is also considered for the athermal shear strengths to simulate macroscopic post-yield strain-softening behavior. In order to validate the accuracy of the model as well as the solution procedure, the numerical results are compared to experimental responses of Styrene and Polyurethane SMP foams at different temperatures and under different strain rates. The results show that the introduced FE modelling procedure is capable of capturing the major phenomena observed in experiments such as elastic and elastic-plastic behaviors, softening plateau regime, and densification.

Enhanced X-ray Visibility of Shape Memory Polymer Foam Using Iodine Motifs and Tantalum Microparticles

Shape memory polymer (SMP) foams are porous materials with high surface area and large volumetric expansion capabilities that are well suited for endovascular occlusion applications, including brain aneurysm embolization. However, many polyurethane SMP foams are inherently radiolucent when X-ray visibility is required to ensure the safe delivery of the foam to the targeted aneurysm site using fluoroscopy. Here, highly radio-dense tantalum microparticles were added to a previously reported triiodobenzene-containing SMP foam (ATIPA foam) premix to fabricate ATIPA foam-tantalum composites (AT_T). The AT_T foams showed comparable glass transition temperatures, faster expansion profiles, increased X-ray visibility, good cytocompatibility, and faster oxidative degradation compared to the control ATIPA foam without tantalum. The mechanical properties were improved up to 4 vol% tantalum and the X-ray visibility was most appropriate for the 2 vol% (AT_2%T) and 4 vol% (AT_4%T) tantalum foams. E-beam sterilization did not impair the critical properties of the ATIPA foams. Overall, AT_2%T was the optimal foam composition for neurovascular prototypes due to its high oxidative stability in vitro compared to previous low-density SMP foams. The AT_T foams are very promising materials with high toughness and sufficient X-ray visibility for use as neurovascular embolization devices.

Thermomechanical Properties of Polyurethane Shape-Memory Polymer Foam

The thermomechanical properties of polyurethane-shape memory polymer foam were investigated by the compressive tests. The results are summarized as follows. (1) The material contracts uniformly in the axial direction with the ratio of lateral strain to axial strain 0.4 in the early stage, but about 0.15 thereafter. (2) The deformation resistance is large at low temperature and at high strain rate. (3) In the case of thermomechanical loading, strain is recovered at temperatures in the vicinity of Tg. The rate of strain recovery is 99%. The rate of strain fixity is 100%.

611 ポリウレタン系形状記憶ポリマーフォームの形状固定後の変形特性

611 ポリウレタン系形状記憶ポリマーフォームの形状固定後の変形特性

Shape Fixity and Shape Recovery of Polyurethane-Shape Memory Polymer Foam.

The thermomechanical properties of polyurethane-shape memory polymer foam were investigated experimentally. The results obtained are summarized as follows. (1) By cooling the foam after deformation at high temperature, stress decreases and the deformed shape is fixed. Stress decreases markedly in the region of temperature below the glass transition temperature Tg during the cooling process. (2) By heating the shape-fixed foam under no-load, the original shape is recovered. Strain is recovered markedly at the temperature region in the vicinity of Tg. (3) The ratio of shape fixity is 100% and that of shape recovery 98%. Both ratios do not depend on the number of cycles. (4) Recovery stress increases by heating under constraint of the fixed shape. Recovery stress is about 80% of maximum stress. Relaxed stress at high temperature is not recovered. (5) The shape deformed at high temperature is maintained for six months at Tg-60 K under no-load without depending on maximum strain, and the original shape is recovered by heating. (6) If the deformed shape is kept at high temperature, the original shape is not recovered. The factors to influence the shape irrecovery are strain, temperature and time during keeping the deformed shape.

Creep and Stress Relaxation of Polyurethane-Shape Memory Polymer Foam.

The compressive deformation properties of polyurethane-shape memory polymer foam depending on time were investigated experimentally. The results obtained are summarized as follows. (1) The compressive deformation of the foam initiates at a certain local part and progresses from that part. During the unloading process, the shape recovery starts from the part which is deformed at the end of the loading process. (2) Creep deformation is large if the initial deformation is small. Both creep strain and creep recovery strain are large at temperatures below the glass transition temperature Tg. (3) Relaxed stress after a certain time is proportional to initial stress. The ratio of stress relaxation is large below Tg but is small above Tg. (4) The amount of stress relaxation is large if strain rate is high during the loading process. (5) If large strain is applied, followed by keeping the stress constant above Tg, irrecoverable strain appears. If large strain is kept constant above Tg, stress almost relaxes and the strain is fixed.

Influence of long-term storage in cold hibernation on strain recoveryand recovery stress of polyurethane shape memory polymer foam

In this paper, the effects of long-term storage in compressed coldhibernated elastic memory (CHEM) polyurethane foam, a kind of shape memorypolymer, are investigated experimentally. The foams were pre-strained at ahigh temperature, which was above the glass transition temperature, to 80%and 93.4%, respectively, and then cooled back to room temperature. Aftervarious periods of cold hibernation (up to two months), they were heated up atfixed length or against different constant loads. It is found that: (1) themaximum stress that the foam could exert at fixed length depends heavily onthe amount of pre-strain; (2) expansion rates of 380 and 1273% from thehibernated size against a 1 N load (pre-strained by 80 and 93.4%,respectively) are achievable. However, upon further increases in load, theexpansion is reduced dramatically. It appears that the tested CHEMpolyurethane foam retains its shape memory properties even after being storedin a compacted state for a long period. Complete strain recovery is attainablefor a hibernation period of up to two months.

Thermomechanical Properties of Polyurethane-Shape Memory Polymer Foam

The thermomechanical properties of polyurethane-shape memory polymer foam were investigated by the compressive tests. The results are summarized as follows. (1) The material contracts uniformly in the axial direction with the ratio of lateral strain to axial strain 0.4 in the early stage, but about 0.15 thereafter. (2) The deformation resistance is large at low temperature and at high strain rate. (3) In the case of thermomechanical loading, strain is recovered at temperatures in the vicinity of Tg. The rate of strain recovery is 99%. The rate of strain fixity is 100%.

105 ポリウレタン系形状記憶ポリマーフォームの変形特性

The thermomechanical properties of polyurethane-shape memory polymer foam were investigated. The main results are summarized as follows. (1) Strain is recovered at temperatures around the glass transition temperature during heating. The temperature at which strain is recovered decreases with an increase in maximum strain. (2) The rate of strain recovery is 99% and does not change under cyclic deformation. (3) The rate of strain fixity is 100%. (4) Stress diminished during cooling. Stress decreases markedly at temperatures below the glass transition temperature. (5) Because large deformation and large variation in volume are obtained in shape-memory polymer foam, shape-memory polymer foam has excellent functional performance for large elements of mechanics and structures.

Thermomechanical properties of polyurethane-shape memory polymer foam.

The thermomechanical properties of polyurethane-shape memory polymer foam were investigated by the compressive tests. The results are summarized as follows. (1) The material contracts uniformly in the axial direction with the ratio of lateral strain to axial strain 0.4 in the early stage but about 0.15 thereafter. (2) The deformation resistance is large at low temperature and at high strain rate. (3) In the case of thermomechanical loading, strain is recovered at temperatures in the vicinity of Tg. The rate of strain recovery is 99%. The rate of strain fixity is 100%.