Shape Memory Gels Research Articles

Hofmeister-Effect-Driven Hybrid Glycerogels for Perfect Wide-Temperature Shape Fixity and Shape Recovery in Soft Robotics Applications.

Shape memory gels have emerged as crucial elements in soft robotics, actuators, and biomedical devices; however, several problems persist, like the trade-off between shape fixity and shape recovery, and the limited temperature range for their application. This article introduces a new class of shape memory hybrid glycerogels (GGs) designed to address these limitations. The well-modulated internal structure of the GGs, facilitated by the Hofmeister salting-out effect, strategically incorporates a higher crystallite content, abundant crosslinking points, and a high elastic modulus. Unlike reported shape memory gels, the GG exhibits a perfect triple-step shape memory behavior in air with 100% shape fixity in a wide programming temperature range (75-135°C) and simultaneously achieves 100% shape recoverability. The gel recovers its shape at -40°C under near-infrared light across a wide programming temperature range (25-135°C), showing unexpected initiation even at subzero temperatures. Inspired by the mechanics of composite structures, a method is proposed to integrate the GG seamlessly with a shape memory alloy, which further expands the temperature range that yields perfect shape memory properties. Finally, two light-controlled fluttering and crawling soft robot prototypes are engineered to illustrate the versatility and potential applications of the composite gel in soft robotics.

Natural Oleanolic Acid-Tailored Eutectogels Featuring Multienvironment Shape Memory Performance.

Shape memory gels, one of the primary modern smart materials, hold great promise in a myriad of applications spanning from soft robotics to medical devices. Nevertheless, most shape memory gels rely on water, organic solvents, and ionic liquids as dispersion mediums, posing the risks of freezing, dehydration, and toxicity to humans or environment. Herein, we have developed a thermoresponsive shape memory eutectogel by introducing an oleanolic acid-modified polyacrylamide network into a deep eutectic solvent (DES). The resulting eutectogel shows a fracture strength of 4.46 MPa along with elongation of 345%, Young's modulus of 14.83 MPa, and toughness of 9.51 MJ m-3. Thanks to the low freezing point and low volatility inherited from DES, this eutectogel possesses good antifreezing and long-term storage stability, which facilitate the shape memory behavior both in silicone oil and in air. The shape fixity and shape recovery ratios of this eutectogel maintain almost 90% during 10 cycles in silicone oil and more than 70% during four cycles in air that cannot be realized in hydrogels. By virtue of shape memory effect and conductivity, the eutectogel can be further used as a thermoswitch. This work presents a simple approach to fabricating shape memory eutectogels and imparts exciting prospects to smart eutectogels.

Three-Dimensional Printed Shape Memory Gels Based on a Structured Disperse System with Hydrophobic Cellulose Nanofibers.

Inks for 3D printing were prepared by dispersing bacterial cellulose nanofibers (CNF) functionalized with methacrylate groups in a polymerizable deep eutectic solvent (DES) based on choline chloride and acrylic acid with water as a cosolvent. After 3D printing and UV-curing, the double-network composite gel consisting of chemically and physically crosslinked structures composed from sub-networks of modified CNF and polymerized DES, respectively, was formed. The rheological properties of inks, as well as mechanical and shape memory properties of the 3D-printed gels, were investigated in dynamic and static modes. It was shown that the optimal amount of water allows improvement of the mechanical properties of the composite gel due to the formation of closer contacts between the modified CNF. The addition of 12 wt% water results in an increase in strength and ultimate elongation to 11.9 MPa and 300%, respectively, in comparison with 5.5 MPa and 100% for an anhydrous system. At the same time, the best shape memory properties were found for an anhydrous system: shape fixation and recovery coefficients were 80.0 and 95.8%, respectively.

Antioxidant, Anti-Inflammatory and Attenuating Intracellular Reactive Oxygen Species Activities of Nicotiana tabacum var. Virginia Leaf Extract Phytosomes and Shape Memory Gel Formulation.

Oxidative stress is one of the major causes of skin aging. In this study, the shape memory gels containing phytosomes were developed as a delivery system for Nicotiana tabacum var. Virginia fresh (VFL) and dry (VDL) leaf extracts. The extracts were loaded in the phytosomes by a solvent displacement method. The physical and chemical characteristics and stability of phytosomes were evaluated by dynamic light scattering and phytochemistry, respectively. The in vitro antioxidant activity and intracellular reactive oxygen species reduction of phytosomes and/or extracts were investigated by the DPPH and ABTS radical scavenging assays, FRAP assay, and DCFH-DA fluorescent probe. The cytotoxicity and anti-inflammatory activity of VDL and VFL phytosomes were studied by an MTT and a nitric oxide assay, respectively. Here, we first reported the total phenolic content in the dry leaf extract of N. tabacum var. Virginia was significantly greater than that of the fresh leaf extract. The HPLC analysis results revealed that VDL and VFL extracts contained 4.94 ± 0.04 and 3.13 ± 0.01 µg/mL of chlorogenic acid and 0.89 ± 0.00 and 0.24 ± 0.00 µg/mL of rutin, respectively. The phytosomes of the VDL and VFL extracts displayed stable size, polydispersity index, zeta potential values, and good chemical stability. VDL and VDL phytosomes showed higher phenolic and flavonoid contents which showed stronger DPPH and ABTS radical scavenging effects and reduced the intracellular ROS. The results suggested that the phenolic compounds are the main factor in their antioxidant activity. Both VDL and VFL phytosomes inhibited nitric oxide production induced by LPS, suggesting the anti-inflammatory activity of the phytosomes. The shape memory gel containing VDL and VFL phytosomes had good physical stability in terms of pH and viscosity. The VDL and VFL phytosomes dispersed in the shape memory gels can be considered as a promising therapeutic delivery system for protecting the skin from oxidation and reactive oxygen species.

Highly Stable and Nonflammable Hydrated Salt-Paraffin Shape-Memory Gels for Sustainable Building Technology

Hydrated salts (salt hydrates) are highly promising low-temperature phase change materials (PCMs) due to their high cohesive energy density and low cost. However, they exhibit phase separation, liq...

Light Scattering and Rheological Studies of 3D/4D Printable Shape Memory Gels Based on Poly (N,N-Dimethylacrylamide-co-Stearyl Acrylate and/or Lauryl Acrylates).

In this work, we present the structural analysis of 3D/4D printable N,N-dimethylacrylamide (DMAAm)-co-stearyl acrylate (SA) and/or lauryl acrylate (LA)-based shape memory gels (SMGs). We characterized these gels by scanning microscopic light scattering technique (SMILS) where a time- and space-averaged correlation function is obtained to overcome the inhomogeneous media. Thus, the characteristic size of the gel internal network (mesh size, ξ) and crosslinking densities are estimated from the Einstein–Stokes formula. The rheological study of the SMGs revealed information about their mechanical strength and transition temperature. From the experimental storage modulus measured by rheological study, crosslinking density and mesh size of the network were also calculated. Both the techniques suggest that SMG with high crystalline content of SA monomer in the gel network contain smaller mesh size (1.13 nm for SMILS and 9.5 nm for rheology study) and high crosslinking density. The comparative study between the light scattering technique and rheological analysis through the quantitative analysis of crosslinking densities will be important to understand the structural properties of the SMGs.

Transparency of Temperature-responsive Shape-memory Gels Tuned by a Competition between Crystallization and Glass Transition

Transparency is often an important property in the practical applications of temperature-responsive shape-memory gels. We investigated the mechanism of significant transparency improvement upon a change in two copolymer gels with their molar ratios between stearyl acrylate and N, N-dimethylacrylamide from 1:1 to 0.75:1. By means of Flash DSC measurement, we made the thermal analysis characterization of crystallization and glass transition in two copolymer gels and compared the results to the parallel experiments of corresponding homopolymers. The results showed that the slightly lower content of stearyl acrylate sequences suppresses crystallization in their side chains due to the chemical confinement of comonomers on copolymer crystallization; meanwhile it shifts up the glass transition temperature of the backbone N, N-dimethylacrylamide sequences. Eventually on cooling, crystallization gives its priority position to glass transition in copolymer gels, resulting in a higher transparency of the gel without losing the shape-memory performance. To confirm the chemical confinement, we further compared the isothermal crystallization kinetics of stearyl acrylate side chains in the copolymer gel to that of their homopolymer. Our observations facilitate the rational design of the temperature-responsive shape-memory gels for the transparency property.

Study of Sensing Behavior of Conductive Hydrogels

Hydrogels having shape memory behavior are one of the smart materials with numerous possible application in sensor, optical and biomedical field. Thermo-responsive gels have the ability to show reversible shape transformation due to the melting induced order-disordered transitions of the molecular constituent. Our group has developed poly(dimethyl acrylamide-co-stearyl acrylate (DMAAm-co-SA) based shape memory gels (SMG) [1] with high mechanical strength, very good transparency and biocompatibility having potential application in different sectors [2]. Introduction of conductive properties in hydrogels can create high potential in the field of medical treatment (drug release), electrochemistry (bioactive electrode coating), sensors and actuators. In this work we have focused to combine the tunable physical and mechanical properties of the SMGs with the electrical activity of an electroactive component in order to bring out new prospects in material engineering. However, conductivity is not part of the inherent characteristics of the hydrogels, it can be provided by other materials or particles that are incorporated within the network of the hydrogels (e.g., conductive particles, conjugated polymers, etc.). Fully swollen hydrogels with conducting particles, such as graphite, carbon nanotubes or metallic particles incorporated in their structure typically show conductivity but conductivity is inversely affected by the swelling ratio, and the hydrogels exhibit brittle mechanical behavior [3]. In this work conductivity of the SMGs has been achieved by chemically polymerizing EDOT (with PSS as the molecular dopant) within the network of fully swollen SMG. A wide variety of conductive SMG with tunable mechanical elasticity, softness and swelling degree has been developed by varying crystalline monomer (SA) ratio and comparative study with pristine SMG revealed that conductive network did not affected their swelling degree and mechanical properties extremely. Conductive SMGs with low SA content has been found to be highly conductive with high swelling degree compared to the SMG with high SA content. We studied their electric resistance as a function of applied pressure or strain and developed an Arduino based systems for application in force sensing resistor devices.

4D Printed Soft Robot

Hydrogels are capable of absorbing large amounts of liquid or biological fluids in three-dimensional polymeric networks. The properties of smart gels can be controlled or tuned by external stimuli such as heat, optics, solvent, and pH. Shape-memory gels (SMGs) are kind of smart material that have the ability to demonstrate reversible shape transformation induced by an external stimulus like in our present study: temperature sensitivity. Mechanically strong along with good flexibility and transparency, Poly(dimethyl acrylamide-co-stearyl acrylate) (DMMA-co-SA)-based SMGs [1] show thermoresponsive shape memory behavior above 40 °C. DMMA-co-SA SMGs have been fabricated by stereolithographic process using our customized 3D printer named as SWIM-ER. Using SWIM-ER we were able to print sample models like gel sheets, tubes, fingers etc. of SMGs that were transparent, flexible and strong. To successfully print SMG samples, we critically maintained all required conditions like polymerization inhibition, turbidity, light scattering etc. during printing and confirmed that printed SMGs exhibited similar properties like conventionally synthesized SMG. In this contribution, we presented 3D printed smart hydrogels that can morph according to the desired shapes. Utilizing this phenomenon we have made soft robots like soft gripper, smart capsule etc. Both the temperature responsiveness and swelling property of the hydrogels has been utilized as stimuli for shape transformation. Finally, we analyzed the limitation and potential of 3D printing process and discussed a possible approach for application of 4D printed SMGs in soft robotics. Reference: [1] Amano, Y; Hidema, R; Gong, J; Furukawa, H. Chem Lett.,41, 1029-1031 (2012)

Gel Transistor By Chemically Tunable Hydrogels

The transport of liquid in the polymeric network of Hydrogels have been discussed for a decade because the gel membrane may use as chemical separator [1]. Here we demonstrate a system that control the flux of solvents by a combination of three types of gels of different swelling behavior as a gel transistor. Poly(dimethyl acrylamide-co-stearyl acrylate and/or Lauryl Acrylate) (PDMMAm-co-SA and/or LA)-based shape memory gels (SMGs) swelling behavior has been observed for different solvents and binary solvent mixtures. It was found that SMGs at all composition showed increased swelling when ethanol composition was increased. On the other hand, when an anionic copolymer was introduced in the DMAA network, swelling behavior was reversed in the presence of high ethanol composition. These oppositely responsive gels were tested for permeability of solvents through them and we successfully developed the gel diode [2]. The unidirectional solvent flow was achieved just like in diode. Information about the gel diode has been utilized to develop a system that simulate a transistor to more sophistically control the flow of liquid mixtures. This findings are expected to create positive impact to develop the gel membrane solvent separator, a hot topic for rectifier, calculator and separator in chemical systems. References Tanaka, Phys. Rev. Lett. 40, 820–823 (1978).Arai, M., Gong, J., Makino, M., KABIR, M.,H., Furukawa, H. SPIE Proc. 9430, 94302A-1

Analysis of Internal Structural of 3D Printed Shape Memory Gels

Understanding the internal structure of the gels is important to comprehend their physico-chemical properties and propose better utilization in practical application. The scanning microscopic light scattering (SMILS) is one of the powerful tools to nondestructively characterize the internal structure of gels. The SMILS is a typical dynamic light scattering (DLS) system, which can be used to characterize the internal structure of gels by observing the diffusion process [1]. In our previous study we studied internal structures of Poly (N-N-dimethylacrylamide (PDMAAm) gels and different inter-crosslinking network (ICN) gels and compared their crosslinking density with ionic gels [2]. We also determined the soft to hard transition temperature of PDMAAm-co Stearyl acrylate (SA) shape memory gels SMGs prepared by mold techniques by carrying out temperature dependent SMILS measurements [3]. In this work, we present the structural analysis of 3D printed transparent SMGs containing two different hydrophobic crystalline monomers SA and Lauryl acrylate (LA) fabricated by optical stereolithography technique. By SMILS we can obtain a time- and space-averaged correlation function i.e., an ensemble-averaged correlation function to overcome the inhomogeneous media. For each sample, the time-averaged homodyne correlation functions g(2)(q,τ) were determined at several points, where q is scattering vector and τ is correlation time. Then the ensemble-averaged correlation function g(1)(q,τ) was calculated. Thus, the characteristic size of diffusing objects (mesh size) ξ can be estimated from the Einstein-Stokes formula. In the measurement of the SMGs, we controlled the angle of PMT and relaxation time distribution was calculated for every angle. We have correlated their internal structures with mechanical properties to understand their internal structures and made justified assumption on their structural homogeneities. H., Horie, K., Nozaki, R., Okada, M. Phys Rev E 68:031406-1-14 (2003)Ahmed, K., Watanabe, Y., Higashihara, T. Arafune, H. Kamijo, T., Morinaga, T. Sato, T., Makino, M. Kawakami, M., Furukawa, H. Microsyst Technol., 22, 17 (2016)Kabir, M., H., Gong, J., Watanabe, Y., Makino, M., Furukawa, H. Lett., 108, 239–242 (2013)

3D Printing of Smart Gels

Various kind of gel materials for example tough double network hydrogels [1], shape memory hydrogels [2] and ionic gels [3] have been developed with potential in numerous sectors. The transparent, flexible and low friction properties of these gels have added different prospects in scientific and technological areas. Utilization of 3D printing in fabrication of gel materials is still in its infancy and thus hindering rapid prototyping and design freedom. In this work, we have fabricated smart gels like thermos-responsive gels and conductive gels etc. using both customized optical gel 3D printers named SWIM-ER and commercial printer named Acculas. This process of 3D printing enabled rapid and moldless fabrication of smart gels with variety of 3D design from macro to micro scale. Robust thermos-responsive Poly (dimethyl acrylamide-co-stearyl acrylate and/or Lauryl Acrylate) (PDMMAm-co-SA and/or LA)-based shape memory gels (SMGs) with tunable mechanical, thermal, swelling, and optical properties are obtained by optimizing their critical conditions during 3d printing. The superior physiochemical properties of such smart gels widen the range of applications for soft robotics, biomedicine, flexible electronics, mimicking organ structure, bioinspired lens and sensing applications. References Gong, J. P., Katsuyama, Y., Kurokawa, T., Osada, Y., “Double-Network Hydrogels with Extremely High Mechanical Strength,” Adv. Mater., 15, 1155-1158 (2003).Kabir, M.H., Ahmed, K. Furukawa, H., Microelectron. Eng. 150, 43–46 (2016).Ahmed, K., Watanabe, Y., Higashihara, T. Arafune, H. Kamijo, T., Morinaga, T. Sato, T., Makino, M. Kawakami, M., Furukawa, H. Microsyst Technol 22, 17 (2016).

Tunable Shape Memory Polymer with Adhesive Property at Body Temperature for Shape Conformable Wearable Sensor Skins

Previously our group has developed poly(dimethyl acrylamide-co-stearyl acrylate (DMAAm-co-SA) based shape memory gels (SMG) [1] with high mechanical strength, very good transparency and biocompatibility having potential application in different sectors [2]. Most commonly used polymers in order to fabricate sensor skins is Polydimethylsiloxane (PDMS), but has a major drawback that it is not adhesive in nature [3, 4, 5]. In order to over come this problem, in this work we have incorporated adhesive properties by copolymerizing lauryl acrylate along with DMAAm and SA. The developed gels at body temperature had high transparency, good adhesive properties and wearability. Composition and temperature dependent adhesive properties of DMAAM-co-SA-co-LA has been investigated along with their mechanical, swelling and thermal properties and best suited adhesive SMG has been utilized to develop wearable skin sensor.

Conductive Shape Memory Gels for Sensing Application

In this work we have combined the physical and mechanical properties of the thermo-responsive poly (N,N-dimethyl acrylamide-co-Stearyl acrylate) (PDMAAm-co-SA) shape memory gels (SMGs) with the electrical activity of an electroactive component in order to develop a hybrid material named conductive SMG (C-SMG) that can sense their shape transformation through electrical properties. The conductivity of the SMGs was achieved by chemically polymerizing EDOT (with PSS as the molecular dopant) within the tough SMGs fully swollen network. We critically optimized the composition to achieve conductive SMG (C-SMG) with tunable swelling and mechanical toughness. Finally, we demonstrated the sensing behavior of C-SMG by measuring their electric signal as a function of applied pressure or strain which can be applied in sensor devices like pressure sensor or strain sensor.

Conductive Shape Memory Gels for Sensing Application

Shape memory gels (SMGs) are one of the interesting and unique classes of soft and wet materials having wide application in actuator, sensor, optical and biomedical field. Thermal responsive SMGs have the ability to return from a temporary deformed state to its original shape under the influence of heat thus having the limitation of quick and proper control. On the other hand, conductive hydrogels have high potential in the field of medical treatment (drug release), electrochemistry (bioactive electrode coating), sensors and actuators. Our group has developed DMAAm-co-SA SMG with high mechanical strength, very good transparency and biocompatibility having potential application in different sectors [1]. Thus, we are motivated to combine the physical and mechanical properties of the SMGs with the electrical activity of an electroactive component in order to create unique prospects for the next generation materials. However, conductivity is not part of the inherent characteristics of the hydrogels, it can be provided by other materials or particles that are incorporated within the network of the hydrogels (e.g., conductive particles, conjugated polymers, etc.). Fully swollen hydrogels with conducting particles, such as graphite, carbon nanotubes or metallic particles incorporated in their structure typically show conductivity but conductivity is inversely affected by the swelling ratio, and the hydrogels exhibit brittle mechanical behavior [2]. In this work conductivity of the SMGs was achieved by chemically polymerizing EDOT (with PSS as the molecular dopant) within the tough SMGs fully swollen network. Here we could achieve conductive SMG with high swelling ratio and good mechanical toughness and studied their electric signal as a function of applied pressure or strain for application in sensor devices like pressure sensor or strain sensor.

3D Printed Shape Memory Hydrogels for Soft Robotics

Hydrogels possess three-dimensional polymeric networks and capable of absorbing large amounts of water or biological fluids. Due to their high water content, porosity and low friction they closely simulate natural living tissue. The properties of a polymer gel depend on the chemical structures of the component molecule and can be controlled or tuned by external stimuli such as heat, optics, solvent, and pH. Shape-memory gels (SMGs) are unique materials that have the ability to return from a temporary deformed state to their permanent i.e. original shape induced by an external stimulus like temperature change. Poly(dimethyl acrylamide-co-stearyl acrylate) (DMMA-co-SA)-based SMGs [1] show thermoresponsive shape memory behavior when temperature was raised above 40 °C. Although being a hydrogel they are mechanically very strong along with good flexibility and transparency. In this work, we applied stereolithographic (SLA) process to fabricate DMMA-co-SA SMGs using our customized 3D printer named as SWIM-ER. Using SWIM-ER we were able to print sample models like gel sheets and tubes of SMGs that were transparent, flexible and strong. However, printing of SMGs was not an easy task due a number of issues like sample polymerization inhibition, turbidity, swelling during printing and shape deformation. We critically maintained these conditions and resulted SMGs were compared with that of conventionally synthesized SMGs to find out the effect of printing on the mechanical and swelling properties. Finally, we analyzed the limitation and potential of 3D printing process and discussed a possible approach for application of 3D printed SMGs in soft actuators and sensors. Reference: [1] Amano, Y; Hidema, R; Gong, J; Furukawa, H. Chem Lett.,41, 1029-1031 (2012)

Technology and application of shape memory polymers in textiles

PurposeShape memory polymers (SMPs) respond with a change in their shape against a specific stimulus by memorizing their original shape and are reformed after deformation most often by changing the temperature of the surrounding without additional mechanical efforts. In the coming years, these polymers indeed will be in limelight to manufacture textile materials which will retain their shape even after prolonged use under disturbed conditions. This study aims at defining shape memory materials and polymers as well as their technological characteristics and also highlights application in various fields of textiles.Design/methodology/approachThe methodology used to explain these SMPs have been carried out starting with the discussion on their properties, their physical nature, types, viz., shape memory alloys (SMAs), shape memory ceramics, shape memory hybrid, magnetic shape memory alloy, shape memory composites, shape memory gels and SMP along with properties of each type. Other related details of these polymers, such as their advantages, structure and mechanism, shape memory functionality, thermally responsive SMPs and applications, have been detailed.FindingsIt has been observed that the SMPs are very important in the fields of wet and melt-spun fibers to offer novel and functional properties, cotton and wool fabric finishing, to produce SMP films, foams and laminated textiles, water vapor permeable and breathable SMP films, etc.Originality/valueThe field of SMPs is new, and very limited information is available to enable their smooth production and handling.

Evaluation of internal network structure of transparent shape memory gels and application of T-SMG to develop gel devices

Gels, soft and wet materials, have unique properties such as biocompatibility, low friction, and material permeability which are hardly found in hard and dry materials. In recent years, gels are expected to industrial applications, because the various high-strength gels, functional gels, and 3D gel printer that enabled free form fabrication of gels have been developed. Our research group succeeded in developing transparent gels with shape memory properties (T-SMG). In this study, we aimed at free form fabrication of T-SMG with to apply T-SMG’s new medical materials, optical devices, and robot joints and so on. We also examined the internal network structure of T-SMG, since it is very important to know the internal network structure of the gels in order to improve the gels. We study the internal network structure of T-SMG through the dynamic light scattering, uniaxial tensile test, and swelling test. As a result, we found that T-SMG is a unique material that changes the internal structure considerably depending on the presence or absence of crystal components. The state of chemical components changes physical properties such as mechanical properties and swelling behavior, without changing the synthesis ratio. In addition, even though the crystals were melted, it showed a higher Young ‘s modulus than the amorphous gels, it was suggested that the crystal components contributes to the Young’ s modulus even though it melted. We tried free form fabrication of T-SMG using 3D printing system. As T-SMG become cloudy at the time of printing, the modeling accuracy become worse. However, by mixing UV absorbers, it was possible to improve the accuracy and suppression of clouding of gels. We successfully made the fine and complicated shaping of T-SMG which was difficult in the past processes. Based on this technology, we hope that T-SMG will be applied in various fields.

185 形状記憶ゲルを活用したGel Chemical Transistorの開発

185 形状記憶ゲルを活用したGel Chemical Transistorの開発

Structural Analysis of Shape Memory Gel

The determination of structural properties of a material is important before its practical application. The analysis data provide us some information whether the material is suitable for application or not. The prospective applications of soft and wet materials explore the new era in the material science as an industrial material especially for medical applications. Shape memory gels (SMGs) are one kind of unique soft and wet materials having shape recovery property which is suitable for medical application such as bandages for broken bones or making optical lens and so on. In the present study, scanning microscopic light scattering (SMILS) is used to characterize the internal structure of shape memory gels. It is observed that the SMGs are transparent at room temperature, mechanically elastic and ductile as well as thermoresponsive despite the high water contents. We confirm the mesh size in nanometer scale of the internal network structure and the critical behavior of the SMG by dynamic light scattering (DLS). The mechanical properties also have been characterized by dynamic mechanical analysis (DMA).