Thermoresponsive zwitterionic poly(phosphobetaine) microgels: Effect of macro-RAFT chain length and cross-linker molecular weight on their antifouling properties

Adsorption of proteins on biological surfaces is a detrimental phenomenon that reduces the work-life of the implants in various biomedical applications. Here, we synthesized a new class of thermoresponsive zwitterionic poly(phosphobetaine) (PMPC) microgel with excellent surface antifouling property by macro-RAFT mediated thiol-epoxy click reaction. End-group modified zwitterionic PMPC homopolymers with well-defined molecular weight and narrow dispersity were grafted onto poly(N-vinylcaprolactam-co-glycidyl methacrylate) (PVG) copolymer backbone followed by addition of a cross-linker, leading to microgel formation. While no upper critical solution temperature (UCST) was found in poly(N-vinylcaprolactam-co-glycidyl methacrylate-g-2-methacryloyloxyethyl phosphorylcholine) (PVGP) graft copolymers, the corresponding microgels exhibited both UCST and lower critical solution temperature (LCST) transitions, related to the swelling and collapse of PMPC and poly (N-vinylcaprolactam) (PVCL) components respectively. An increase in the molecular chain length of the PMPC increased the shifting of UCST and LCST of the microgels to higher temperatures, due to the ability of zwitterionic groups to coordinate a large number of water molecules. The effect of the variation in the molecular weights of amphiphilic poly(ethylene glycol) diamine (PEG-NH2) cross-linker was also reflected in both temperature and salt responsiveness of the microgels. The efficacy of the microgels as potential antifouling materials was further studied by fluorescence microscopy and XPS analysis on microgel coatings treated with FITC-BSA solution and pure BSA solution respectively. Lower protein adsorption was observed for microgels grafted with higher molecular chain length of PMPC, whereas, the microgels synthesized using higher molecular weight PEG-NH2 diamine cross-linker displayed greater protein adsorption on their surfaces

Magnetorheological behavior of thermoplastic elastomeric honeycomb structures fabricated by additive manufacturing

<p><a href="https://www.sciencedirect.com/topics/materials-science/three-dimensional-printing">3D printing</a> of magnetorheological <a href="https://www.sciencedirect.com/topics/engineering/elastomer">elastomers</a> (MREs) can potentially create versatile and complex mechanical structures with reversible stiffening properties. Several additive manufacturing (AM) methods, like direct printing and <a href="https://www.sciencedirect.com/topics/materials-science/stereolithography">stereolithography</a> (SLA), have been used to achieve magnetic <a href="https://www.sciencedirect.com/topics/materials-science/thermoset-plastics">thermoset</a> and elastomer composite structures. For the first time, we demonstrate the use of MREs based on thermoplastic elastomers (TPE) in AM and we investigate their magnetorheological (MR) effect when used in lightweight honeycomb designs. Due to the low <a href="https://www.sciencedirect.com/topics/engineering/shore-hardness">shore hardness</a> of TPE, a screw extruder-based printing head is employed to print disk-shaped samples with honeycomb patterns at infill percentages varying from 15% to 50%. In order to compare the MR effect of disks with varying honeycomb infills through a <a href="https://www.sciencedirect.com/topics/engineering/compression-method">compression method</a>, we investigated the effect of different testing configurations. We observe that different permanent magnet configurations, as it has been used in literature so far, create an additional effect on the measured MR effect of the MRE samples. To eradicate this effect, a test setup with an unpaired permanent magnet configuration is proposed. MRE structures with an infill density of 20% showed, at 1% deformation range, the highest MR effect, almost four times as high as 100% infilled samples. MRE structures with an infill density between 30% and 50% showed a lower MR effect than at 20%, but were still higher than at 100%. We observe in simulations that the <a href="https://www.sciencedirect.com/topics/engineering/magnetic-flux-density">magnetic flux density</a> of 100% infilled samples was higher at the edges of the samples and lower at the center. For samples with honeycomb infill, the magnetic flux density was higher at the outer rim of the samples and edges of the walls within the sample, which causes a higher MR effect. Our work demonstrates that the MR effect can be tuned by designing a MRE structure with a honeycomb infill. The honeycomb infill results in lightweight MREs with improved MR effect useful for various downstream applications that require reversible strong stiffening while remaining comparatively lightweight.</p&gt

Magnetorheological behavior of thermoplastic elastomeric honeycomb structures fabricated by additive manufacturing

3D printing of magnetorheological elastomers (MREs) can potentially create versatile and complex mechanical structures with reversible stiffening properties. Several additive manufacturing (AM) methods, like direct printing and stereolithography (SLA), have been used to achieve magnetic thermoset and elastomer composite structures. For the first time, we demonstrate the use of MREs based on thermoplastic elastomers (TPE) in AM and we investigate their magnetorheological (MR) effect when used in lightweight honeycomb designs. Due to the low shore hardness of TPE, a screw extruder-based printing head is employed to print disk-shaped samples with honeycomb patterns at infill percentages varying from 15% to 50%. In order to compare the MR effect of disks with varying honeycomb infills through a compression method, we investigated the effect of different testing configurations. We observe that different permanent magnet configurations, as it has been used in literature so far, create an additional effect on the measured MR effect of the MRE samples. To eradicate this effect, a test setup with an unpaired permanent magnet configuration is proposed. MRE structures with an infill density of 20% showed, at 1% deformation range, the highest MR effect, almost four times as high as 100% infilled samples. MRE structures with an infill density between 30% and 50% showed a lower MR effect than at 20%, but were still higher than at 100%. We observe in simulations that the magnetic flux density of 100% infilled samples was higher at the edges of the samples and lower at the center. For samples with honeycomb infill, the magnetic flux density was higher at the outer rim of the samples and edges of the walls within the sample, which causes a higher MR effect. Our work demonstrates that the MR effect can be tuned by designing a MRE structure with a honeycomb infill. The honeycomb infill results in lightweight MREs with improved MR effect useful for various downstream applications that require reversible strong stiffening while remaining comparatively lightweight.ISSN:1359-8368ISSN:1879-106

Case study of a rapid prototyping method for optimizing soft gripper structures with integrated piezoresistive sensors

Closed-loop control systems and monitoring the activities of soft robots in the natural environment require sensing elements in soft actuator modules. In this study, additive manufacturing is used for sensorized soft actuator modules to investigate the influence of the Shore hardness and design aspects of an open-source tendon-based gripper structure, in a time-efficient way. Additionally, the placement of the piezoresistive sensing element (tension or compression side on the bending soft gripper) was investigated. A user-friendly method, based on thermoplastic material extrusion, has been explored to improve the future design optimization in of active soft robotic structures successfully. A higher Shore hardness resulted in a higher total deflection and a higher force to bend the gripper structure. By increasing the geometrical stiffness of the gripper printed with low Shore hardness, the total deflection was increased, but the force needed to activate the movement was higher in comparison to high Shore hardness and low geometrical stiffness. Moreover, the sensing element on the substrate of higher Shore hardness, leads to low drift, monotonic response, with good sensitivity, independent of the sampling rate. The gripper of higher Shore hardness had a larger functional range, being capable of gripping small and larger objects

3D Printable Self‐Sensing Magnetorheological Elastomer

AbstractMagnetorheological elastomers (MREs) are a category of smart materials composed of a magnetic powder dispersed in an elastomeric matrix. They are characterized by the ability to change their mechanical properties when an external magnetic field is applied, called magnetorheological (MR) effect. When a conductive filler is added to a magnetorheological elastomer, the resulting hybrid filler composite showcases both MR and piezoresistive effects. For such a reason, these composites are referred to as self‐sensing magnetorheological elastomers. In this case, the synthesized self‐sensing magnetorheological elastomers are based on styrene‐based thermoplastic elastomers (TPS), carbonyl iron particles (CIP), and carbon black (CB). The hybrid filler concept using various coated CIP and constant CB content showed that above 25 vol.% CIP the resistivity increased rapidly. This work proposes the first case of a 3D printable self‐sensing magnetorheological elastomer and cyclic mechanical compression and tensile mode analysis at high deformation (up to 20% and 10%, respectively). The results showcase a magnetoresistive change of up to 68% and a piezoresistive change of up to 42% and 98% in compression and tension, respectively. In addition, the magnetostriction of the self‐sensing samples has been characterized to be 3.6% and 5.6% in the case of CIP 15 and 30 vol.%, respectively.</jats:p

3D Printable Self‐Sensing Magnetorheological Elastomer

Abstract Magnetorheological elastomers (MREs) are a category of smart materials composed of a magnetic powder dispersed in an elastomeric matrix. They are characterized by the ability to change their mechanical properties when an external magnetic field is applied, called magnetorheological (MR) effect. When a conductive filler is added to a magnetorheological elastomer, the resulting hybrid filler composite showcases both MR and piezoresistive effects. For such a reason, these composites are referred to as self‐sensing magnetorheological elastomers. In this case, the synthesized self‐sensing magnetorheological elastomers are based on styrene‐based thermoplastic elastomers (TPS), carbonyl iron particles (CIP), and carbon black (CB). The hybrid filler concept using various coated CIP and constant CB content showed that above 25 vol.% CIP the resistivity increased rapidly. This work proposes the first case of a 3D printable self‐sensing magnetorheological elastomer and cyclic mechanical compression and tensile mode analysis at high deformation (up to 20% and 10%, respectively). The results showcase a magnetoresistive change of up to 68% and a piezoresistive change of up to 42% and 98% in compression and tension, respectively. In addition, the magnetostriction of the self‐sensing samples has been characterized to be 3.6% and 5.6% in the case of CIP 15 and 30 vol.%, respectively

Soft Magnetoactive Morphing Structures with Self-Sensing Properties, Using Multi-Material Extrusion Additive Manufacturing

&lt;p&gt;Material extrusion-based additive manufacturing (MEX-AM) processes&lt;br&gt;have enabled the fabrication of multi-material structures. Commercially&lt;br&gt;available 3D printers already consist of more than two extruders to print structures&lt;br&gt;with different materials. However, the fabrication of structures with both&lt;br&gt;actuation and sensing (ActSense), in one single process by MEX-AM has been&lt;br&gt;scarcely explored. In this work, we use a multi-material extrusion-based additive&lt;br&gt;manufacturing process to couple magnetic actuation and strain-sensing into one&lt;br&gt;AQ1 additively manufactured structure. The ActSense multi-functional structure was&lt;br&gt;achieved with a composite based on styrenic block copolymer type thermoplastic&lt;br&gt;elastomer (TPE), soft ferromagnetic and carbon black filler particles. For comparison,&lt;br&gt;elastomeric structures were printed with a composite comprising TPE and&lt;br&gt;soft ferromagnetic filler particles only. In order to achieve improved efficiency,&lt;br&gt;30 vol% of carbonyl iron particles (CIP) were mixed with the elastomeric matrix.&lt;br&gt;Owing to the fact that CIP and carbon black filler have different densities and&lt;br&gt;a conductive network must be achieved, 15 vol% of each CIP and carbon filler&lt;br&gt;was added to realize the ActSense composites. Morphing membranes with an&lt;br&gt;elastomeric substrate and integrated ActSense elements were analyzed with an&lt;br&gt;additively manufactured custom test setup based on a laser displacement sensor&lt;br&gt;and an electromagnet.With the customized test setup a magnetic field was applied&lt;br&gt;from underneath, and the deformation of the soft structure was analyzed by the&lt;br&gt;AQ2 laser. Due to the low deformation range, the change in resistance was small, and&lt;br&gt;a diminished piezoresistive behavior of the self-sensing, magnetic composites&lt;br&gt;was obtained. Thereby, to detect the small deformation, a piezoresistive sensing&lt;br&gt;element was extruded separately on top of the magnetoactive part. With this approach,&lt;br&gt;a change in relative resistance at low deformation could be successfully&lt;br&gt;determined. As established by the results, the customized electromagnet-laser&lt;br&gt;sensor setup is an interesting tool for the investigation of soft magnetic materials&lt;br&gt;and structures for shape morphing structures.&lt;/p&gt;&lt;p&gt;The deformation measurements shown in Figure 9, is also included in Figure 10. Thereby, to avoid repetition, raw data of only Figure 10 has been added.&lt;/p&gt

Thermoresponsive zwitterionic poly(phosphobetaine) microgels:Effect of macro-RAFT chain length and cross-linker molecular weight on their antifouling properties

Adsorption of proteins on biological surfaces is a detrimental phenomenon that reduces the work-life of the implants in various biomedical applications. Here, we synthesized a new class of thermoresponsive zwitterionic poly(phosphobetaine) (PMPC) microgel with excellent surface antifouling property by macro-RAFT mediated thiol-epoxy click reaction. End-group modified zwitterionic PMPC homopolymers with well-defined molecular weight and narrow dispersity were grafted onto poly(N-vinylcaprolactam-co-glycidyl methacrylate) (PVG) copolymer backbone followed by addition of a cross-linker, leading to microgel formation. While no upper critical solution temperature (UCST) was found in poly(N-vinylcaprolactam-co-glycidyl methacrylate-g-2-methacryloyloxyethyl phosphorylcholine) (PVGP) graft copolymers, the corresponding microgels exhibited both UCST and lower critical solution temperature (LCST) transitions, related to the swelling and collapse of PMPC and poly (N-vinylcaprolactam) (PVCL) components respectively. An increase in the molecular chain length of the PMPC increased the shifting of UCST and LCST of the microgels to higher temperatures, due to the ability of zwitterionic groups to coordinate a large number of water molecules. The effect of the variation in the molecular weights of amphiphilic poly(ethylene glycol) diamine (PEG-NH2) cross-linker was also reflected in both temperature and salt responsiveness of the microgels. The efficacy of the microgels as potential antifouling materials was further studied by fluorescence microscopy and XPS analysis on microgel coatings treated with FITC-BSA solution and pure BSA solution respectively. Lower protein adsorption was observed for microgels grafted with higher molecular chain length of PMPC, whereas, the microgels synthesized using higher molecular weight PEG-NH2 diamine cross-linker displayed greater protein adsorption on their surfaces

Thermoresponsive zwitterionic poly(phosphobetaine) microgels : Effect of macro‐RAFT chain length and cross‐linker molecular weight on their antifouling properties

Adsorption of proteins on biological surfaces is a detrimental phenomenon that reduces the work-life of the implants in various biomedical applications. Here, we synthesized a new class of thermoresponsive zwitterionic poly(phosphobetaine) (PMPC) microgel with excellent surface antifouling property by macro-RAFT mediated thiol-epoxy click reaction. End-group modified zwitterionic PMPC homopolymers with well-defined molecular weight and narrow dispersity were grafted onto poly(N-vinylcaprolactam-co-glycidyl methacrylate) (PVG) copolymer backbone followed by addition of a cross-linker, leading to microgel formation. While no upper critical solution temperature (UCST) was found in poly(N-vinylcaprolactam-co-glycidyl methacrylate-g-2-methacryloyloxyethyl phosphorylcholine) (PVGP) graft copolymers, the corresponding microgels exhibited both UCST and lower critical solution temperature (LCST) transitions, related to the swelling and collapse of PMPC and poly (N-vinylcaprolactam) (PVCL) components respectively. An increase in the molecular chain length of the PMPC increased the shifting of UCST and LCST of the microgels to higher temperatures, due to the ability of zwitterionic groups to coordinate a large number of water molecules. The effect of the variation in the molecular weights of amphiphilic poly(ethylene glycol) diamine (PEG-NH2) cross-linker was also reflected in both temperature and salt responsiveness of the microgels. The efficacy of the microgels as potential antifouling materials was further studied by fluorescence microscopy and XPS analysis on microgel coatings treated with FITC-BSA solution and pure BSA solution respectively. Lower protein adsorption was observed for microgels grafted with higher molecular chain length of PMPC, whereas, the microgels synthesized using higher molecular weight PEG-NH2 diamine cross-linker displayed greater protein adsorption on their surfaces