Shape Memory Polymer Foams Research Articles

CFD investigations of a shape-memory polymer foam-based endovascular embolization device for the treatment of intracranial aneurysms.

The hemodynamic and convective heat transfer effects of a patient-specific endovascular therapeutic agent based on shape-memory polymer foam (SMPf) are evaluated using computational fluid dynamics studies for six patient-specific aneurysm geometries. The SMPf device is modeled as a continuous porous medium with full expansion for the flow studies and with various degrees of expansion for the heat transfer studies. The flow simulation parameters were qualitatively validated based on the existing literature. Further, a mesh independence study was conducted to verify an optimal cell size and reduce the computational costs. For convective heat transfer, a worst-case scenario is evaluated where the minimum volumetric flow rate is applied alongside the zero-flux boundary conditions. In the flow simulations, we found a reduction of the average intra-aneurysmal flow of > 85% and a reduction of the maximum intra-aneurysmal flow of > 45% for all presented geometries. These findings were compared with the literature on numerical simulations of hemodynamic and heat transfer of SMPf devices. The results obtained from this study provide a novel and practical framework for optimizing the design of patient-specific SMPf devices, integrating advanced computational models of hemodynamics and heat transfer. This framework could guide the future development of personalized endovascular embolization solutions for intracranial aneurysms with improved therapeutic outcome.

Shape Memory Polymer Foam Based on Nanofibrillar Composites of Polylactide/Polyamide.

This paper presents the novel development of a shape memory polymer foam based on polymer-polymer nanocomposites. Herein, polylactide (PLA)/biosourced polyamide (PA) foams are fabricated by in situ fibrillation of polymer blends and a subsequent supercritical CO2 foaming technique. In this system, PLA serves as a shape memory polymer to endow this foam with a shape memory effect (SME), and in situ generated PA nanofibers are employed to reinforce the PLA cell walls and provide an additional permanent phase. A concentration of PA, 5 wt.%, was chosen to form an entangled nanofibrillar network. Foams of PLA/PA nanoblends with the same content of constituents were fabricated to reveal the effect of minor phase morphology on the cell structure and shape memory behavior of polymer foams. Profiting from the reinforcing effect of PA nanofibers, the PLA/PA nanocomposite foam exhibits smaller foam cells, a narrower cell size distribution and a comparable cell concentration than the PLA/PA nanoblend foam. In addition, PA nanofibers, unlike PA nanodroplets, favor the shape fixation ratio and recovery ratio and shorten the shape recovery time.

CFD investigations of a shape-memory polymer foam-based endovascular embolization device for the treatment of intracranial aneurysms.

The hemodynamic and convective heat transfer effects of a patient-specific endovascular therapeutic agent based on shape memory polymer foam (SMPf) are evaluated using computational fluid dynamics studies for six patient-specific aneurysm geometries. The SMPf device is modeled as a continuous porous medium with full expansion for the flow studies and with various degrees of expansion for the heat transfer studies. The flow simulation parameters were qualitatively validated based on the existing literature. Further, a mesh independence study was conducted to verify an optimal cell size and reduce the computational costs. For convective heat transfer, a worst-case scenario is evaluated where the minimum volumetric flow rate is applied alongside the zero-flux boundary conditions. In the flow simulations, we found a reduction of the average intra-aneurysmal flow of > 85% and a reduction of the maximum intra-aneurysmal flow of > 45% for all presented geometries. These findings were compared with the literature on numerical simulations of hemodynamic and heat transfer of SMPf devices. The results obtained from this study can serve as a guide for optimizing the design and development of patient-specific SMPf devices aimed at personalized endovascular embolization of intracranial aneurysms.

Vanillic acid-based pro-coagulant hemostatic shape memory polymer foams with antimicrobial properties against drug-resistant bacteria

Uncontrolled bleeding is the primary cause of trauma-related death. For patients that are brought to the hospital in time to receive treatment, there is a great risk of contracting drug-resistant bacterial wound infections. Therefore, low-cost hemostatic agents with procoagulant and antibacterial properties are essential to reduce morbidity and mortality in patients with traumatic wounds. To that end, we introduced vanillic acid (VA) into shape memory polymer (SMP) foams through a dual incorporation mechanism to make dual vanillic acid (DVA) foams. The dual mechanism increases VA loading while allowing burst and sustained delivery of VA from foams. DVA foams exhibit antimicrobial and antibiofilm properties against native and drug-resistant Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis. Also, DVA foams inhibit the growth rate of both methicillin-sensitive and -resistant S. aureus colonies to limit their size and promote small colony variants. DVA SMP foams induced primary and secondary hemostasis in in vitro blood interaction studies. As a proof of concept, we demonstrated easy delivery and rapid clotting in a porcine liver injury model, indicating DVA foam feasibility for use as a hemostatic dressing. Thus, the inexpensive production of DVA SMP foams could enable a cost-effective procoagulant hemostatic dressing that is resistant to bacterial colonization to improve short- and long-term outcomes for hemorrhage control in traumatically injured patients. Statement of significanceUncontrolled bleeding is the primary cause of preventable death on the battlefield. Of patients that survive, ∼40 % develop polymicrobial infections within 5 days of injury. Drug-resistant infections are anticipated to cause more deaths than all cancers combined by 2050. Therefore, novel non-drug-based biomaterials strategies for infection control in wound care are increasingly important. To that end, we developed hemostatic polyurethane foams that include antimicrobial and pro-coagulant vanillic acid, a plant-based antimicrobial species. These foams provide excellent protection against native and drug-resistant bacteria and enhanced coagulation while remaining cytocompatible. In a pilot porcine liver injury model, vanillic acid-containing foams stabilized a bleed within <5 min. These biomaterials provide a promising solution for both hemorrhage and infection control in wound care.

Polycaprolactone-based shape memory foams as self-fitting vaginal stents

There is an urgent critical need for a patient-forward vaginal stent that can prevent debilitating vaginal stenosis that occurs after pelvic radiation treatments and vaginal reconstruction. To this end, we developed a self-fitting vaginal stent based on a shape-memory polymer (SMP) foam that can assume a secondary, compressed shape for ease of deployment. Upon insertion, the change in temperature and hydration initiates foam expansion to shape fit to the individual patient and restore the lumen of the stent to allow egress of vaginal secretions. To achieve rapid actuation at physiological temperature, we investigated the effect of architecture of two photocurable, polycaprolactone (PCL) macromers. Star-PCL-tetraacrylate displayed a reduced melting temperature as compared to a linear-PCL-diacrylate. Upon fabrication into high porosity foams with emulsion-templating, both compositions displayed shape fixity (>90 %) in a crimped, temporary shape. However, only the PCL star-foams displayed shape recovery (∼84 %) at 37 °C with expansion back to its permanent shape. A custom mold and curing system were then used to fabricate the PCL star-foams into hollow, cylindrical stents. The stent was crimped to its temporary insertion shape (50 % reduction in diameter, OD ∼ 11 mm) with a custom radial crimper and displayed excellent shape fixity for deployment (> 95 %) and shape recovery (∼ 100 %). To screen vaginal stents, we developed a custom benchtop pelvic model that simulated vaginal anatomy, temperatures, and pressures with an associated computational model. The crimped SMP vaginal stent was deployed in the model and expanded to walls of the canal (∼70 % increase in cross-sectional area) in less than 5 min after irrigation with warm water. The vaginal stent demonstrated retention of vaginal caliber with less than 10 % decrease in cross-sectional area under physiological pressures. Collectively, this work demonstrates the potential for SMP foams as self-fitting vaginal stents to prevent stenosis and provides new open-source tools for the iterative design of other gynecological devices. Statement of significanceVaginal stenosis, a painful narrowing of the vaginal canal, is a common complication after pelvic radiation therapy or reconstructive surgery. To address this clinical need, we have created a self-fitting vaginal stent from a shape-memory polymer foam. The stent compresses for easy insertion and then expands to adapt to each patient's anatomy to maintain an open vaginal canal and prevent stenosis. This innovative stent provides a patient-friendly solution that could make a significant difference for women undergoing pelvic treatments by reducing pain, aiding recovery, and improving quality of life.

4D-Printed Tool for Compressing a Shape Memory Polyurethane Foam during Programming.

Although several force application concepts are known that can be used to deform shape memory polymers (SMPs) within the scope of programming, controlled deformation is challenging in the case of samples with a cylinder-like shape, which need to be homogeneously compressed starting from the lateral surface. To solve this problem, this contribution follows a material approach that takes advantage of four-dimensional (4D) printing. Fused filament fabrication (FFF) was used as an additive manufacturing (AM) technique to produce a thermoresponsive tool in a cylindrical shape from a polyether urethane (PEU) having a glass transition temperature (Tg) close to 55 °C, as determined by differential scanning calorimetry (DSC). Once it was 4D-printed, a sample of laser cut polyester urethane urea (PEUU) foam with a cylindrical wall was placed inside of it. Subsequent heating to 75 °C and keeping that temperature constant for 15 min resulted in the compression of the foam, because the internal stresses of the PEU were transferred to the PEUU, whose soft segments were completely molten at 65 °C as verified by DSC. Upon cooling to -15 °C and thus below the offset temperature of the soft segment crystallization transition of the PEUU, the foam was fixed in its new shape. After 900 days of storage at temperatures close to 23 °C, the foam recovered its original shape upon reheating to 75 °C. In another experiment, a 4D-printed cylinder was put into hibernation for 900 days before its thermoresponsiveness was investigated. In the future, 4D-printed tools may be produced in many geometries, which fit well to the shapes of the SMPs to be programmed. Beyond programming SMP foams, transferring the forces released by 4D-printed tools to other programmable materials can further expand technical possibilities.

Degrees of macrophage-facilitated healing in aneurysm occlusion devices.

Insufficient healing of aneurysms following treatment with vascular occlusion devices put patients at severe risk of fatal rupture. Therefore, promoting healing and not just occlusion is vital to enhance aneurysm healing. Following occlusion device implantation, healing is primarily orchestrated by macrophage immune cells, ending with fibroblasts depositing collagen to stabilize the aneurysm neck and dome, preventing rupture. Several modified occlusion devices are available currently on-market. Previous in vivo work demonstrated that modifications of occlusion devices with a shape memory polymer foam had enhanced aneurysm healing outcomes. To better understand cellular response to occlusion devices and improve aneurysm occlusion device design variables, we developed an in vitro assay to isolate prominent interactions between devices and key healing players: macrophages and fibroblasts. We used THP-1 monocyte derived macrophages and human dermal fibroblasts in our cell culture models. Macrophages were allowed device contact with on-market competitor aneurysm occlusion devices for up to 96 h, to allow for any spontaneous device-driven macrophage activation. Macrophage secreted factors were captured in the culture media, in response to device-specific activation. Fibroblasts were then exposed to device-conditioned macrophage media (with secreted factors alone), to determine if there were any device-induced changes in collagen secretion. Our in vitro studies were designed to test the direct effect of devices on macrophage activation, and the indirect effect of devices on collagen secretion by fibroblasts to promote aneurysm healing and stabilization. Over 96 h, macrophages displayed significant migration toward and interaction with all tested devices. As compared to other devices, shape memory polymer foams (SMM, Shape Memory Medical) induced significant changes in gene expression indicating a shift toward an anti-inflammatory pro-healing M2-like phenotype. Similarly, macrophages in contact with SMM devices secreted more vascular endothelial growth factor (VEGF) compared with other devices. Macrophage conditioned media from SMM-contacted macrophages actively promoted fibroblast secretion of collagen, comparable to amounts observed with exogenous stimulation via VEGF supplementation. Our data indicate that SMM devices may promote good aneurysm healing outcomes, because collagen production is an essential step to ultimately stabilize an aneurysm.

Multiscale modeling of shape memory polymers foams nanocomposites

Shape memory polymer foams (SMPFs) are defined as lightweight cellular materials with the ability to recover their undeformed shape by applying an external stimulus like light, temperature, magnetic field, etc. Reinforcement of the material with nano-clay filler leads to a significant improvement in its physical properties. As a result, a wide range of applications is occupied by SMPFs, especially in industry and biomedical applications. Because of the heterogeneous nature of the SMPFs at different scale levels, modeling the material with one scale numerical model which able to capture all the effects of the lower scale material structure is really a complex task. Within this work, a full multiscale modeling approach is employed to investigate the thermomechanical response of the SMPFs. Furthermore, a combination of the 3D Representative Volume Element (RVE) and finite element method is used to explore the effects of the nano-filler weight fractions and the material's cellular structure at different length scales on the material dynamics. The multiscale modeling process gives great and promising results with good agreement with the experimental results. Moreover, the model shows relatively high sensitivity parameters that are initiated from the lower scale level.

Toward the Development of a Shape Memory Polymer for Individualized Endovascular Therapy of Intracranial Aneurysms Using a 3D‐Printing/Leaching Method

Endovascular treatment of intracranial aneurysms (ICA) aims to occlude the aneurysm space to prevent ICA growth/rupture. Modern endovascular techniques are still limited by relatively low complete occlusion rates, frequently leading to aneurysm growth, rupture, and reoperation. Herein, shape memory polymer (SMP)‐based embolic devices are proposed to advance the effectiveness of ICA therapy by facilitating individualized ICA occlusion. Specifically, a 3D‐printing/leaching method for the fabrication of 3D‐SMP devices that can be tailored to patient‐specific aneurysm geometries obtained from computed tomography angiography is developed. It is demonstrated that this method allows the fabrication of highly porous, compressible foams with unique shape memory properties and customizable microstructure. In addition, the SMP foams exhibit great shape recovery, anisotropic mechanical properties, and the capability to occlude in vitro models with individualized geometries. Collectively, this study indicates that the proposed method will have the potential to advance the translation of coil‐ and stent‐free embolic devices for individualized treatment of saccular ICAs, targeting complete and long‐term durable aneurysm occlusion.

Out-of-autoclave molding of carbon fiber laminates by consolidation with shape memory polymer foams

Carbon fiber reinforced (CFR) laminates have been manufactured by an innovative out-of-autoclave (OOA) process thanks to the use of smart materials. In this study, for the first time, a shape memory polymer (SMP) foam has been used into a pressure dome to apply the consolidation pressure to the laminate. Heat for resin curing was supplied by a thermal blanket between the laminate and the SMP foam. In order to test the OOA molding process, 24-ply CFR laminates were manufactured and tested. For comparison and reference, CFR laminates were also molded by traditional vacuum bagging and autoclave curing. Samples for bending tests were extracted from OOA and autoclave molded plates. Results show that the SMP-OOA process is able to provide optimal laminate consolidation, despite of the low applied pressure (about 1 bar). A comparable density and ply thickness was measured on samples by the innovative and the conventional molding process, whereas a higher bending strength (+5%) was found on OOA samples. A higher dispersion was also observed for the properties of SMP-OOA molded laminates in comparison with autoclave, probably due to the prototyping nature of the molding technique in comparison with the well-known autoclave practice. Nevertheless, the final quality of the molded laminates is very high, and the SMP-OOA process is a very promising candidate as a technology to repair CFR structures.

Dual Burst and Sustained Release of p-Coumaric Acid from Shape Memory Polymer Foams for Polymicrobial Infection Prevention in Trauma-Related Hemorrhagic Wounds.

Hemorrhage is the primary cause of trauma-related death. Of patients that survive, polymicrobial infection occurs in 39% of traumatic wounds within a week of injury. Moreover, traumatic wounds are susceptible to hospital-acquired and drug-resistant bacterial infections. Thus, hemostatic dressings with antimicrobial properties could reduce morbidity and mortality to enhance traumatic wound healing. To that end, p-coumaric acid (PCA) was incorporated into hemostatic shape memory polymer foams by two mechanisms (chemical and physical) to produce dual PCA (DPCA) foams. DPCA foams demonstrated excellent antimicrobial and antibiofilm properties against native Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis; co-cultures of E. coli and S. aureus; and drug-resistant S. aureus and S. epidermidis at short (1 h) and long (7 days) time points. Resistance against biofilm formation on the sample surfaces was also observed. In ex vivo experiments in a porcine skin wound model, DPCA foams exhibited similarly high antimicrobial properties as those observed in vitro, indicating that PCA was released from the DPCA foam to successfully inhibit bacterial growth. DPCA foams consistently showed improved antimicrobial properties relative to those of clinical control foams containing silver nanoparticles (AgNPs) against single and mixed species bacteria, single and mixed species biofilms, and bacteria in the ex vivo wound model. This system could allow for physically incorporated PCA to first be released into traumatic wounds directly after application for instant wound disinfection. Then, more tightly tethered PCA can be continuously released into the wound for up to 7 days to kill additional bacteria and protect against biofilms.

Development of Biopsy Tract Sealants Based on Shape Memory Polymer Foams.

Lung biopsies are often used to aid in the diagnosis of cancers. However, the procedure carries the dual risk of air (pneumothorax) or blood (hemothorax) filling the pleural cavity, increasing the risk of a collapsed lung and chest intubation. This work demonstrates the effectiveness of a polyurethane-based shape memory polymer foam as a biopsy tract sealant. The impact of diameter, length, pore size, and shape memory effect was evaluated to determine the ideal device design for tract sealing. Characterization in an in vitro benchtop lung model identified that diameter had the largest influence on sealing efficacy, while the length of the device had little to no impact. Finally, evaluation of deployment force demonstrated that devices fabricated from the shape memory polymer foams were easier to deploy than elastic foams. Following characterization, down-selected device designs were combined with radiopaque markers for use in image-guided based procedures. Furthermore, the introduction of the markers or sterilization did not impact the ability of the devices to seal the biopsy tract and led to a decrease in the deployment force. Overall, these results demonstrate the potential for polyurethane-based shape memory foam devices to serve as biopsy tract sealant devices that aim to reduce complications, such as pneumothorax, from occurring.

Swellable and Thermally Responsive Hydrogel/Shape Memory Polymer Foam Composites for Sealing Lung Biopsy Tracts.

Lung tissue biopsies can result in a leakage of blood (hemothorax) and air (pneumothorax) from the biopsy tract, which threatens the patient with a collapsed lung and other complications. We have developed a lung biopsy tract sealant based on a thiol-ene-crosslinked PEG hydrogel and polyurethane shape memory polymer (SMP) foam composite. After insertion into biopsy tracts, the PEG hydrogel component contributes to sealing through water-driven swelling, whereas the SMP foam contributes to sealing via thermal actuation. The gelation kinetics, swelling properties, and rheological properties of various hydrogel formulations were studied to determine the optimal formulation for composite fabrication. Composites were then fabricated via vacuum infiltration of the PEG hydrogel precursors into the SMP foam followed by thermal curing. After drying, the composites were crimped to enable insertion into biopsy tracts. Characterization revealed that the composites exhibited a slight delay in shape recovery compared to control SMP foams. However, the composites were still able to recover their shape in a matter of minutes. Cytocompatibility testing showed that leachable byproducts can be easily removed by washing and washed composites were not cytotoxic to mouse lung fibroblasts (L929s). Benchtop testing demonstrated that the composites can be easily deployed through a cannula, and the working time for deployment after exposure to water was 2 min. Furthermore, testing in an in vitro lung model demonstrated that the composites were able to effectively seal a lung biopsy tract and prevent air leakage. Collectively, these results show that the PEG hydrogel/SMP foam composites have the potential to be used as lung biopsy tract sealants to prevent pneumothorax post-lung biopsy.

Designable Electrical/Thermal Coordinated Dual-Regulation Based on Liquid Metal Shape Memory Polymer Foam for Smart Switch.

Electronic components with tunable resistance, especially with synergistic regulation of thermal conductivity, play important roles in the fields of electronics, smart switch, soft robots, and so on. However, it is still a challenge to get the material with various resistance and thermal conductivity stably without lasting external force. Herein, a liquid metal shape memory polymer foam (LM-SMF) is developed by loading electrically and thermally conductive liquid metal (LM) on deformable foam skeleton. Based on thermal response shape memory effect, the foam skeleton can be reversibly pressed, the process of which enables LM to transfer between connected and disconnected states. As a result, obtained LM-SMF shows that the resistance stably changes from 0.8 Ω (conductor) to 200 MΩ (insulator), and the thermal conductivity difference is up to 4.71 times (0.108 to 0.509W m-1 K-1 ), which indicates that LM-SMF can achieve the electrical and thermal dual-regulation. Moreover, LM-SMF can be used as a designable self-feedback/-warning integrated smart switch or tunable infrared stealth switch. This work proposes a novel strategy to get the material with electrical-thermal coordinated dual-regulation, which is possibly applied in intelligent heating system with real-time monitoring function, electrothermal sensor in the future.

Poly(β‐hydroxythioether)s as shape memory polymer foams for oil sorption in aquatic environments

AbstractOil spills in aquatic environments represent a significant ongoing threat to aquatic life due to the persistence of oil films or slick. While many methods are available for open ocean waterways, interior waterways represent a different set of challenges. To that end, we propose the use of poly(β‐hydroxythioether) (PBHTE) shape memory polymer foams as a highly porous, low density solid for environmental remediation through oil collection. PBHTE foams are produced through thiol‐epoxy “click” reactions in the presence of an organobase, with gas blown foaming producing the highly porous scaffold with tunable pore sizes and salt‐leaching yielding smaller pore sizes (~400 μm). The different porosities are used here for studying the oil sorption as functions of time and environmental temperature for different pore sizes and compositions. The PBHTE material demonstrated two different Tgs when dry versus wet to compare against environmental differences. While dry the foam showed a Tgof 51.5°C and conversely when wet the Tgwas at 25°C. The foams were compared to see how the pore size will affect the oil sorption of the material and how it can be optimized for oil spills in interior water ways. The pore sizes analyzed were 400 μm, 800 μm, and 1100 μm. The relationship of pore size, temperature of the oil system during sorption, and time in the oil system seemed to have the largest impact on the sorption of oil during this study. The peak conditions for maximum oil sorption yielded the best performer being the 800 μm foam at 10°C after 15 h of sorption yielding a 2250% sorption, comparable with graphene and other low density sorption materials. Ultimately, the role of density in scavenging, along with a literature review, is used to assemble a density vs sorption Ashby chart to provide insight into the different materials available for such environmental remediation. In this context, PBHTE foams represent a new, promising class of material capable of absorbing oil in aquatic environments.

Shape Memory Polymer Foam for Autonomous Climate-Adaptive Building Envelopes

Reducing the continuously growing cooling energy demand of buildings is an important part of achieving global emission targets. Here, we present an innovative scenario of how the integration of a programmable material into a climate-adaptive building envelope (CABE) can create an energy-efficient thermal management system inherent to the material. This novel concept is based on a thermoresponsive shape memory polymer foam (SMP) and is designed to regulate the flow of ambient air through the building envelope in order to enable natural cooling of the structure. Hygrothermal simulation data obtained by the software WUFI® Plus indicate that significant cooling energy saving potential may be accessible with this type of concept. As a possible material basis for a corresponding adaptive element, a reactive foamed polyurethane-based SMP foam is proposed, which is capable of executing a thermoreversible shape change of more than 20% while having a suitable switching temperature range. Finally, the ecological impact of such a functional foam element is evaluated in detail as well as its influence on the overall balance of a façade construction by means of a life cycle assessment (LCA).

Introduction to foam induced shape memory effect: non-contact loading to program shape memory polymers

The challenge to bring up new methods for programming and stimulating smart materials is an unstoppable global trend, with particularly strong momentum toward facilitating them. The external contact loading conventionally employed to induce strain (to form a temporary shape) is replaced with a non-contact loading resulting from bubbles growth during the foaming process. The obtained results confirmed that the induced internal strain during the foaming process was fully applicable to program shape memory polymer foams. It was revealed that by using this method, the significant volumetric strain (up to 80%) is attainable in the shape memory polymer foams. Executing the shape recovery process on the foam-induced shape memory polymers indicated that the higher values of the shape recovery ratios (up to 90% in the case of high volumetric strains) are achievable. Moreover, variation of programming parameters caused significant differences in volumetric strain (from 10 up to 80%) and shape recovery ratios (from 60 up to 100%). Finally, performing actuation stress measurement in different foam-induced shape memory polymers discovered that meaningful promotion (more than two times) in actuation stress is attainable as the saturation time and foaming temperature increase.

A Fast-Responding Electro-Activated Shape Memory Polymer Composite with Embedded 3D Interconnected Graphene Foam.

Shape memory polymers (SMPs) have gained increasing attention as intelligent morphing materials. However, due to the inherent electrical insulation and poor thermal conductivity of polymers, deformation and temperature control of SMPs usually require external heating devices, bringing about design inconveniences and fragility of interfaces. Herein, we report a shape memory composite that integrates reliable temperature and shape control functions into the interior. The composite is comprised of resin-based SMP and three-dimensional interconnected graphene foam (3DGF), exhibiting a high recovery rate and thermal/electrical conductivity. With only 0.26 wt% of graphene foam, the composite can improve electrical conductivity by 15 orders of magnitude, thermal conductivity by 180%, tensile strength by 64.8%, and shape recovery speed by 154%. Using a very simple Joule heating scheme, decimeter-sized samples of the composite deformed to their preset shapes in less than 10 s.

Controlling Morphology and Physio-Chemical Properties of Stimulus-Responsive Polyurethane Foams by Altering Chemical Blowing Agent Content.

Amorphous shape memory polymer foams are currently used as components in vascular occlusion medical devices such as the IMPEDE and IMPEDE-FX Embolization Plugs. Body temperature and moisture-driven actuation of the polymeric foam is necessary for vessel occlusion and the rate of expansion is a function of physio-chemical material properties. In this study, concentrations of the chemical blowing agent for the foam were altered and the resulting effects on morphology, thermal and chemical properties, and actuation rates were studied. Lower concentration of chemical blowing agent yielded foams with thick foam struts due to less bubble formation during the foaming process. Foams with thicker struts also had high tensile modulus and lower strain at break values compared to the foams made with higher blowing agent concentration. Additionally, less blowing agent resulted in foams with a lower glass transition temperature due to less urea formation during the foaming reaction. This exploratory study provides an approach to control thermo-mechanical foam properties and morphology by tuning concentrations of a foaming additive. This work aims to broaden the applications of shape memory polymer foams for medical use.

Shape memory polymer foams with tunable interconnectivity using off-the-shelf foaming components.

The ability to easily and safety tune pore structures of gas-blown polyurethane shape memory polymer (SMP) foams could improve their outcomes as hemostatic dressings or tissue engineering scaffolds and enable overall commercialization efforts. Incorporating physical blowing agents into the polymer mix can be used to tune pore size and interconnectivity without altering foam chemistry. Enovate (HFC-254fa) is a commonly used physical blowing agent in gas-blown foams, but the Environmental Protection Agency (EPA) considers its use unacceptable because it is a hydrofluorocarbon that contributes to global warming. Here, off-the-shelf solvents accepted for use by the EPA, acetone, dimethyoxymethane (methylal), and methyl formate, were used as physical blowing agents by adding small volumes during foam fabrication. Increasing the physical blowing agent volume resulted in greater pore interconnectivity while maintaining SMP foam chemical and thermal properties. Pore size and interconnectivity also impacted cell and blood interactions with the foams. This work provides a safe and easy method for tuning SMP foam interconnectivity to aid in future commercialization efforts in a range of potential biomedical applications.