Symposium FL
Stimuli Responsive and Multifunctional Polymers: Progress in Materials and Applications


FL-1:IL01  Self-healing Copolymers via van der Waals Interactions
M.W. Urban, Clemson University, Department of Materials Science and Engineering, Clemson, SC, USA

Materials with build-in responsive components are outstanding candidates for the development of sustainable technologies. Last decade efforts have primarily focused in incorporating supramolecular chemistry and reversible covalent bonding in the development of self-healing polymers. This lecture will outline recent advances in self-healing polymers, with the primary focus on the recent advances in the development of commodity self-healable polymers. Inspired by plants, self-healing can be achieved by incorporating viscoelastic responses to their microstructures during their formation, thus enabling deformation upon mechanical damage to close a wound. This can be achieved by introducing multiphase-separated polymers composed of polycaprolactone, butanediol, and hexamethylene diisocyanate precursors copolymerized into a self-healing polymer. The presence of micro-phase separated fibrous morphologies facilitate repeatable self-healing due to stable interfacial regions between the hard and soft segments of the copolymer, thus enabling of storage of entropic energy upon mechanical damage to be recovered during self-healing. This talk will provide the framework of van der Waals interactions in acrylic-based copolymers able to self-heal upon mechanical damage. This behavior occurs when the monomer molar ratios are within a relatively narrow compositional range, forming reversible ‘key-and-lock’ interactions with preferentially alternating copolymer topologies. The unique self-healing behavior is attributed to favorable inter-chain van der Waals (vdW) forces manifested by the increased cohesive energy densities (CED) forming ‘key-and-lock’ inter-chain junctions, enabling multiple recovery upon mechanical damage without external intervention. The concept of redesigning commodity copolymers without elaborate chemical modifications will facilitate a platform for many technological opportunities and the development of new generations of sustainable copolymers with controlled chain topologies that survive repetitive damage-repair cycles.

FL-1:IL02  Multifunctional Interpenetrated Polymer Networks
K. Rohtlaid1, F. Braz Ribeiro1, T.M.G. Nguyen1, C. Soyer2, J.D.W. Madden3, E. Cattan2, F. Vidal1, C. Plesse1, 1CY Cergy Paris Université, LPPI, Cergy, France; 2Univ. Polytechnique des Hauts de France, CNRS, Univ. Lille, Yncrea, Centrale Lille, UMR 8520 - IEMN, DOAE, Valenciennes, France; 3Department of Electrical & Computer Engineering, Advanced Materials & Process Engineering Laboratory, University of British Columbia, Vancouver, Canada

Electroactive Polymers belong to the group of smart materials which respond to an electrical stimulus by undergoing large deformations and can therefore be used in biomimetic systems. Conducting polymers (CP) based actuators have several advantages compared to conventional actuators since they are soft, light weight, biocompatible, operate under low voltage and can be miniaturized. In the growing field of soft electronics, they could then fulfill tasks non possible with stiff classical technology and arise as promising candidates for the development of soft artificial muscles. Among conducting polymer actuators, conducting interpenetrating polymer network (IPN) allow, an efficient tuning of electrochemical and electromechanical properties as well as controlling the device geometry as a function of purposed application. Based on this architecture, specific choice of polymer partners and of their interpenetration, it has been possible to develop bending (micro)actuators and (micro)sensors and to develop all-solid state electrochemical devices. Furthermore the synthesis of IPNs with various shapes but also to interpenetrate functions via the combination of electrochemical CP actuation and shape memory effect.

FL-1:IL03  Shape-memory Polymer Actuators for Robotics
A. Lendlein, Institute of Biomaterial Science, Helmholtz-Zentrum Geesthacht, Teltow, Germany, & University of Potsdam, Potsdam, Germany

Shape-memory polymer actuators (SMPAs) can be programmed to bend, twist, or contract fully reversibly – and are controlled by temperature. As a soft material, these actuators might be suitable as artificial muscles. SMPAs are especially interesting for the next generation of soft robots, which attract attention with their ability to stretch, climb, be squashed, and for their soft touch. SMPAs are semi-crystalline polymer networks containing skeleton-forming units, which are crystallites that determine the geometry of the actuator’s movement, and actuation units. Actuation units cause the motion and consist of oriented crystallizable network chains. Cooling these units causes as crystallization-induced elongation in the direction of chain orientation. Upon a temperature increase, the melting of these crystallites and the strong elastic effect reverses the motion. Different material systems capable of shape-memory actuation will be introduced and the integration of additional functions such as degradability or self-healing described.
References: A. Lendlein, Sci Robot 3(18), eaat9090 (2018); A. Lendlein, O. Gould, Nat Rev Mater 4, 116-133 (2019); J. Yuan, W. Neri, C. Zakri, P. Merzeau, K. Kratz, A. Lendlein, P. Poulin, Science. 365 (6449), 155-158 (2019).

FL-1:L04  Stress-free two-way Shape Memory Effect of Poly(caprolactone)-based Semicrystalline Networks
S. Pandini, N. Inverardi, Department of Mechanical and Industrial Engineering, University of Brescia, Brescia, Italy; M. Toselli, Department of Industrial Chemistry "Toso Montanari”, University of Bologna, Bologna, Italy; M. Messori, Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy; G. Scalet, F. Auricchio, Department of Civil Engineering and Architecture, University of Pavia, Pavia, Italy

The two-way shape memory effect is the ability of a material to change its shape between two configurations upon application and removal of a stimulus. In polymers such an effect was typically achieved with few systems (semicrystalline networks, liquid crystalline elastomers) and under specific conditions (cooling-heating cycles under a constant load). However, recent studies revealed that semicrystalline networks may also display two-way effect under completely stress-free conditions, provided a specific “training” history. In order to better explore this behaviour, two sets of crosslinked poly(caprolactone) systems were prepared: poly(caprolactone) crosslinked by a sol-gel reaction and with different crosslink densities; co-polymer based on poly(ethylene glycol) and poly(caprolactone) mixed under various ratios and photocrosslinked. In both cases, by a proper thermo-mechanical history, the stress-free two-way shape memory effect was achieved and the effects of parameters regarding the material (macromolecular architecture; composition) and the thermo-mechanical training (temperatures; strain applied) were investigated, allowing to better understand the reason behind the specific material response as well as to identify the best conditions for a self-standing actuation.

FL-1:L05  Effect of Build Orientation, Print Parameters, and Thermo-mechanical History on Performance of 3D-printed Biomedical Shape-memory Thermoplastic Polyurethane
D.L. Safranski, MedShape Inc., Atlanta, GA, USA; J.S. Consoli, Georgia Institute of Technology, Atlanta, GA, USA

Thermoplastic polyurethanes are used in a variety of biomedical devices, such as orthopaedic implants and cardiovascular devices. As a thermoplastic, they are ideal for 3D-printing via fused filament fabrication. Prior studies focused on cast or molded parts, which are monolithic and lack the numerous interfaces found between layers of 3D-printed parts. The goals of this work were to: (1) maximize failure strain by optimizing print parameters, (2) determine the effect of build orientation on shape-memory performance, and (3) determine the effect of the shape-memory cycle on the mechanical performance. At optimal print conditions, failure strain was maximized to 120% for vertical, 371% for flat, and 460% for on-side samples. Unconstrained recovery was dependent upon build orientation where shape-recovery increased from 85% to 90% to 97% for the vertical, side, and flat samples, respectively. Dogbones printed vertically lost 42% of their ultimate strength and 12% of their failure strain, while flat and on-side samples maintained their properties after a shape-memory cycle. Thus, programming and recovery should be considered along with build orientation during design of 3D-printed shape-memory devices. Also, shape-recovery via non-invasive ultra-sound will be examined.

FL-2:IL01  Stimuli-responsive Polymer-based Sensors, Muscles, and Drug Delivery Platforms
M.J. Serpe, Department of Chemistry, University of Alberta, Edmonton, Canada

The group's research is focused on the development of novel polymer-based materials for solving environmental and health-related problems. To solve these problems, the group primarily employs poly (N-isopropylacrylamide) (pNIPAm)-based spherical particles as the active component in our technologies. PNIPAm-based particles (nano or microgels, depending on their diameter) are extremely porous, and are fully water soluble and swellable. Additionally, pNIPAm-based nano/microgels are responsive to temperature, shrinking in diameter as the temperature is increased to >32 °C and reswelling when they are cooled to < 32 °C. Our group has exploited these properties for numerous applications. Today's talk will highlight the group's work on the development of these devices for sensing and biosensing, as muscles, and for controlled/triggered drug delivery.

FL-3:IL01  How Can “Smart” Organometallic Hydrogels Learn and Forget
M.A. Hempenius, K. Zhang, X. Feng, S. Sui, G.J. Vancso, University of Twente, Enschede, The Netherlands

Stimulus responsive polymer hydrogels may exhibit several phases in response to small variations of environmental variables like temperature (T) and pH with strikingly marked hysteresis and volume expansion differences. The structure, dimensions and phase parameters depend on the pathways of varying T or pH, i.e. these systems show a non-ergodic behavior [1]. In this presentation we first focus on the synthesis and structure property relations of a novel, dual‐responsive organometallic poly(ionic liquid) (PIL), consisting of a poly(ferrocenylsilane) backbone of alternating redox‐active, silane bridged ferrocene units, and tetraalkylphosphonium sulfonate moieties in the side groups [2]. This PIL is redox responsive due to the presence of ferrocene in the backbone, and also exhibits a lower critical solution temperature (LCST)‐type thermal responsive behaviour. As the polymer can be readily cross‐linked and is easily converted into hydrogels, it represents a new dual‐responsive materials platform (T and redox). Possible applications as memory materials, electrical switches and in “smart windows” will be demonstrated.
References [1] Annaka, M., Tanaka, T., Nature 1992, 355, 430. [2] Zhang, K., Feng, X., Ye, C., Hempenius, M.A., Vancso, G.J., J. Am. Chem. Soc. 2017, 139, 10029.

FL-3:L02  Characterisation and Development of Polycationic Electro-Active Hydrogels
M. KAIKOV, A. Sort-Montenegro, E. Deasy, L. Dowling, C. Delaney, L. Florea, School of Chemistry & AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research, Trinity College Dublin, Dublin, Ireland

The development of electro-active hydrogels (EAH) has drawn considerable interest due to their ability to convert a facile, non-contact electrical stimulus into a programmable mechanical response [1]. However, while polyanionic EAH have largely been employed as electro-actuators, few examples using polycationic EAH exist to date [2]. Herein, we expand this library to include quaternised ammonium monomers, and amino-functionalised monomers with pKa values within the biological range. We characterise the effect of hydrogel thickness, polarity and magnitude of the electric field on the hydrogel’s electro-actuation response and demonstrate reproducible bending deformations of 55% with actuation times of 20s, which we monitor using an automated MATLAB code. By variation of solvents, crosslinkers, and co-monomers we make these materials suitable for use with benchtop digital light processing (DLP) printing, which enables the generation of 3D structures in the tens of micron to millimetre range. A library of achievable 3D printed structures and their resulting actuation profiles will be presented.
1. I. Ali, et.al., Mater. Sci. Eng. C, 2019, 103, 109852. 2. D. Morales, et.al., Soft Matter, 2014, 10, 9.

FL-3:L03  Stimuli Responsive Hydrogel Actuators for Microscale Cargo Transport
T. SPRATTE, C. Arndt, C. Selhuber-Unkel, Institute for Molecular Systems Engineering, Heidelberg University, Germany; R. Colaco, A. Staubitz, Institute for Organic and Analytical Chemistry, Bremen University, Germany; N. Geid, J. Rühe, IMTEK-Department of Microsystems Engineering, Freiburg University, Germany

Controlled small scale cargo transport is a challenging task due to the need of very precise and gentle handling of the transported objects, especially in the case of fragile loads, such as biological samples. Many current methods, such as microfluidics, exhibit a limited functionality due to predefined and static geometries. In our project we focus on the fabrication of a dynamically adjustable microactuator array made of thermoresponsive poly(N-Isopropylacrylamide) (pNIPAM) hydrogel pillars. For the fabrication of the pillar array, we are aiming to use both mold casting and 3D printing approaches. The hydrogel pillars (actuators) can shrink or grow in size depending on the mode of stimulation, i.e. heating or cooling respectively. By arranging the hydrogel micro pillars in a dense array (micro pin-wall), a cooperative actuation of multiple pillars could create pathways for transporting fragile microscale objects. Such a responsive structure exploits the advantages of dynamic and reversible adjustment, enabling a high degree of flexibility and manifold usage in various experimental setups. We recently discovered the potential of integrating interconnected microchannels into the hydrogel to increase the responsivity and response rate of the material.

FL-3:IL04  Dually Cross-linked Stimuli-sensitive Gels
D. Kuckling1, M. RODIN1, J. Li1, 2, J. Paradies1, M. Yin21Department of Chemistry, Paderborn University, Paderborn, Germany; 2State Key Laboratory of Chemical Resource Engineering, Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China

In the last few years particular attention has been focused on stimuli-responsive polymers. This group of materials is of interest due to their ability to respond to internal and/or external chemico-physical stimuli that is often manifested by large macroscopic responses. To increase the scope of such hydrogels a novel dual cross-linking system combining photo cross-linkable covalent bonding with special molecular recognitions sites was introduced. When the noncovalent bond was broken or formed, the swelling ratio of the polymer gel will be changed significantly. A new dually cross-linked supramolecular hydrogel (DCSH) was developed by introducing a photo cross-linker for permanent crosslinking and β-cyclodextrin (β-CD) and ferrocene (Fc) as host-guest recognition pair. The DCSH showed responsive behaviors e.g. towards the target small molecule adamantane amine (Ada). Ada can break the non-covalent bonding between β-CD and Fc through competitive molecular guest interaction with β-CD. A reversible sensor was developed for specific small molecule detection of Ada by using a combination of surface plasmon resonance and optical waveguide spectroscopy. The DCSH is further used as a SPR biosensor for cancer biomarkers detection.

FL-3:IL05  Stimuli-sensitive Underwater Adhesive Gels inspired by Sandcastle Worms
M. Kamperman, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands

The underwater adhesives secreted by mussels and sandcastle worms have inspired a very active research direction over the last decades: the investigation of what is required for attachment to wet surfaces, and how this knowledge can be turned into new strategies to join wet surfaces. Early on, the presence of catecholic residues (hydroxylated tyrosine, DOPA) has been implicated to be the key component that governs adhesion and cohesion of the adhesives. More recently, other functional groups in the proteins were identified to be (equally) important. The developments evidence the potential of using the supramolecular toolbox for underwater adhesion. A picture is emerging that combinations of (noncovalent) interactions are highly important to ensure triggered solidification and good underwater adhesive performance. In other words, adhesive systems may be developed by selecting multiple supramolecular moieties, in which a combination of different types of interactions is critical: (1) to promote adhesion, (2) to adjust cohesion, and (3) to facilitate processing. In our work, we explore the versatile supramolecular interactions used in the protein-based adhesives secreted by sandcastle worms and mussels, in synthetically designed adhesive gels.

FL-4:L01  Corrosion Resistant Polymer-based Nanocomposite Coatings with High Level of Microwaves Absorption
T. PRIKHNA1, O. Prysiazhna1, V. Moshchil1, M. Monastyrov 1, 2, L. Anastasiya1, 1V. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kyiv, Ukraine; 2Open International University of Human Development «Ukraine», Kyiv, Ukraine

New non-resonant magnetic broadband radio absorbing polymer-based coatings with gradient distributed polyvalent iron oxides nanoparticles of spherical form (obtained by electroerosion dispersion), carbon black, micron sized spherical Al2O3-SiO2 shells, and basalt (or cellulose) microfibers have been developed. The main microwave absorbing component is iron oxide, and micron-sized spheres and microfibers are added as “chiral” elements helping to distribute iron oxide nanoparticles in the definite manner. Polyurethane and acrylic urethane resins are used as the polymer matrix. The absorption level of the coating of radio waves in the range of 10-70 GHz (0.03-0.0043 m) is 90-99% and reflection level of -10 dB - -23 dB (10% -0.5%). Developed coatings are resistant to UV radiation, aggressive environments (preserve the high radiophysical and physico-mechanical properties), have high mechanical properties (high damping ability, adhesion, durability, elasticity). They are corrosion stable in sea water, in oil products, etc. and can protect metal structures, vehicles, containers, building structures and facilities, road and rail transport of parts and mechanisms in conditions of all macro-climatic regions.

FL-4:IL02  Lignin as a Valuable Tool for Functional Coatings, Composites and Beyond
G. Griffini, Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”, Politecnico di Milano, Milano, Italy

Lignin represents the most abundant naturally occurring source of aromatics on Earth. Currently, most of produced lignin is used as low-cost fuel for energy and heat recovery, while only a minor fraction is employed in low-value niche markets. Such limited range of applications calls for effective approaches to enhance its full utilization as renewable component in material platforms of increased commercial and technological interest. Within this context, various approaches for lignin valorization will be discussed in this invited contribution, demonstrating some novel pathways for its direct exploitation in high value-added multifunctional polymeric materials. In particular, different chemical functionalization strategies will be introduced based on the reaction of the hydroxyl groups present in lignin with suitable functional moieties, so as to obtain polymeric precursors that find application in the fields of bio-based coatings, protective layers and composites. Similarly, physical approaches relying on size reduction of lignin particles will be presented, leading to the formation of large surface-to-volume ratio functional nano-entities to be used as bio-based fillers in novel polymer-based composites.

FL-4:IL03  Flexible Sensors Driven by Piezoionic Effect
Hidenori Okuzaki, University of Yamanashi, Kofu, Japan

In this study, fabrication and characterization of flexible sensors driven by piezoionic effect have been demonstrated. Upon bending the gel, positive electric charges are rapidly generated, whereas the equivalent negative charges are formed when the bending stops. On the other hand, the opposite phenomenon was observed when the bent gel recovers to the original straight shape, indicative of an acceleration sensor. Indeed, the electric charge increases in proportion to the acceleration, where the sensitivity was 46.8 nC/(m/s2). The value is three orders of magnitude higher than that of the commercial piezoelectric sensors. The mechanism can be explained in terms of the “piezoionic effect” based on the difference of ionic mobilities between the cations and anions. On the basis of this phenomenon, we have succeeded in fabricating a wearable sensor glove, in which the flexible acceleration sensors located on the three fingers are operating individually. Since the acceleration sensor can provide information not only the acceleration but also force, velocity, and displacement, the wet-processable, stretchable, and wearable flexible sensors based on the piezoionic effect will be available for motion sensors in a wide field of application.

FL-4:IL04  Molecular and Bulk Mechanics of Multifunctional Catecholamine Polymer Coatings
P. Delparastan1, K. Malollari2, K. Lee3, M. Park2, C. Grigoropoulos2, P.B. Messersmith1, 3, 4, 1Materials Science and Engineering Department, 2Mechanical Engineering Department, 3Bioengineering Department, University of California, Berkeley, CA, USA; 4Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

In mussels, the adhesive proteins that aid in attachment to wet surfaces are known to contain high levels of 3,4-dihydroxy-L-alanine (DOPA), and have motivated a large number of bioinspired polymer systems. For example, a number of functional thin film coatings (e.g. ‘polydopamine’ or pDA) derived from polymerization of catecholamines have been developed. Deposition is facile and the deposited coatings can be exploited for a variety of practical applications. However, the molecular features of these polymers are not well understood, and their mechanical properties are weak. Single molecule force spectroscopy (SMFS) of pDA revealed the existence of polymers with contour lengths up to 200 nm that are weakly bound to the surface through much of their contour length. Laser thermal annealing of pDA produced further polymerization of monomeric and oligomeric species leading to fundamental changes in molecular and bulk mechanical behavior, including vast improvement in scratch resistance. Laser-annealed pDA has better scratch resistance than titania and silica, while preserving the multifunctional properties of pDA that are attractive in a variety of contexts. The results of this work suggest new opportunities for the use of PDA in mechanically demanding applications.

FL-4:IL05  Carbon Nanotubes vs Graphene as Fillers for Functional Polymers
P. POULIN, Centre de Recherche Paul Pascal CNRS, University of Bordeaux, Pessac, France

1D carbon nanotubes and 2D graphene sheets are considered as remarkable nanofillers for functional polymer nanocomposites. 1D or 2D fillers are expected to similarly reinforce polymer materials under tensile load. Because of their giant aspect ratio, both fillers enjoy also a very large excluded volume resulting in a low percolation threshold. This threshold is generally expected to scale as the inverse of the particle aspect ratio. However, nanocomposites are not always deformed under uniaxial tensile load, and actual particles are not penetrable. These features can lead to dramatic differences in the efficiency of carbon nanotubes and graphene when used as polymer fillers. We show how 2D graphene sheets increase more efficiently the shear modulus of twisted polymer fibers. This greater efficiency is used to develop novel shape memory fibers with giant energy density. We also show that graphene sheets display a percolation threshold much greater than that expected from excluded volume concepts. This phenomenon is promising to make high permittivity and electrostrictive materials potentially useful for energy storage and energy conversion applications.

FL-4:L06  Optical Sensor Based on Redox-active Tetrazolium / Pluronic Nanoparticles Embedded in PDMS Films
E. Araya-Hermosilla, F. Visentin, V. Mattoli, Center for Materials Interfaces, Istituto Italiano di Tecnologia, Pontedera, Italy; R. Araya-Hermosilla, Programa Institucional de Fomento a la Investigación, Desarrollo e Innovación, Universidad Tecnológica Metropolitana, Santiago, Chile; F. Picchioni, Department of Chemical Engineering - Product Technology, University of Groningen, Groningen, The Netherlands; A. Pucci, Department of Chemistry, University of Pisa, Pisa, Italy

The fabrication of highly sensitive and portable devices for the rapid detection of toxic gases and vapours is highly interesting for safety applications. In this sense, redox-switchable molecules are promising candidates for detecting toxic oxidant chemicals due to their reversible colour change. The in-situ reduction of water-soluble organic molecules in the presence of polymeric surfactants is a simple, cheap and green method for the production of colour switchable nanoparticles. In this work, pluronic F 127 was used as a stabilizer for the reduction of 2,3,5-triphenyl-2H-tetrazolium (TTC) into triphenyl formazan (TF). The TTC reduction successfully produced red-colour nanoparticles with zeta potential close to zero and hydrodynamic diameters between 138 to 253 nm as hydrophobic dispersion in aqueous media stabilized by the polymeric surfactant. Moreover, these suspensions were embedded in a film of PDMS, producing a high homogenous red colour gas-permeable elastomeric film. The latter was exposed to a nitrous vapour resulting in a fast and complete film decolouration due to the oxidation of TF. This coloured redox-switchable composite is a promising material for the fabrication of cheap and compact optical sensing devices to detect hazardous volatile chemicals.

FL-5:IL01  Biomaterials for Regenerative Engineering: Enabling Regenerative Medicine
G. Ameer, Northwestern University, Evanston, IL, USA

Regenerative engineering is the convergence of advances in materials science, physical sciences, stem cell and developmental biology, and translational medicine to develop tools that enable the regeneration and reconstruction of tissue and organ function. I will describe how materials can be engineered to play a critical role in treating tissue and organ defects and dysfunction by promoting cellular processes that are conducive to regeneration. Applications of these materials to address the complications of diabetes will be discussed.

FL-5:IL02  Oxidation-sensitive Polymers as Anti-inflammatory Agents
N. Tirelli, Laboratory of Polymers and Biomaterials, Fondazione Istituto Italiano di Tecnologia (IIT), Genova, Italy

Biologically relevant oxidants (Reactive Oxygen Species, ROS) fulfill a number of roles, which (from good to bad) include being survival factors, activators and promoters of mobility, inflammatory agents and directly cytotoxic molecules. Indeed. most inflammatory pathologies are characterized by a strongly oxidizing environment caused by high concentrations of (enzymatically produced) ROS; this feature can be exploited therapeutically, and anti-oxidant approaches often have anti-inflammatory consequences. In this communication we present therapeutic approaches based on the use of ROS-responsive polymers1, specifically polysulfides2,3 or polysulfoxides4. We will first discuss macromolecular structure – anti-oxidative activity relationships, then reporting on clinically relevant inflammatory models, such as cerebral stroke, injury after reperfusion and inflammatory bowel diseases.
1. F. El-Mohtadi et al. Macromol. Rapid Commun. 2019, 40, 1800699. 2. O. Rajkovic et al. Adv. Ther. 2019, 1900038. 3. F. El Mohtadi et al. Biomacromolecules, 2020, 21, 305 4. F. El Mohtadi et al. Int. J.Mol. Sci. 2019, 20, 4583

FL-5:IL03  Shape Memory Polymer Hydrogel Foams for Crohn’s Fistula Healing
M.B.B. Monroe1, H.T. Beaman1, B. Howes2, P. Ganesh1, 1Biomedical and Chemical Engineering, BioInspired Syracuse, Syracuse University, Syracuse, NY, USA; 2Chemistry, Lemoyne University, USA

A common complication of Crohn’s disease is fistula formation between portions of the urinary, reproductive, and digestive systems. These tunneling wounds cause pain, infections, and abscess formation and typically require surgical intervention to close. To address this clinical need, we synthesized shape memory polymer (SMP) hydrogel foams that can be easily implanted into fistula sites in a compressed shape, where they would expand to fill the wound. These cytocompatible hydrogels undergo controlled degradation by amylase produced by intestinal epithelial cells and by reducing thiol species, such as glutathione. The degradation rates can be tuned within clinically-relevant time frames based on hydrogel chemistry. The hydrogels have been modified with antimicrobial phenolic acids to reduce infection risks and to further tune thermomechanical properties. Currently, strategies for cell encapsulation into the foams during fabrication are being explored to provide a cell delivery vehicle. Overall, this highly tunable system provides a promising strategy for improving outcomes in Crohn’s fistula healing.

FL-5:IL04  A New Class of Submolecular Switches based on the DBCOD Conformational Change
W. Fu1, T. Alam2, R. Adams3, J.C. Li4, W. Yang4, JENNIFER LU1, 1Materials Science and Engineering, University of California at Merced, Merced, CA, USA; 2Sandia National Laboratory, USA; 3Chemistry Department, University of Manchester, UK; 4Chemistry Department, Duke University, USA

Dibenzocyclooctadiene (DBCOD), a flexible eight‐membered ring fused into two rigid phenyl rings, can be regarded as the simplest submolecular structure. The DBCOD conformational change from“boat” (open) to“chair”(close) leads to thermal contraction. We have incorporated this contractile unit in polyamides and observed negative thermal expansion from 273 K to 360 K. Furthermore, we have demonstrated that the coefficient of thermal expansion of a linear polyamide can be adjusted by the number of DBCOD incorporated onto the polymer backbone. This has laid the foundation for the development of electronic packaging polymers with low thermal expansion. We have fabricated a bilayer system with a layer of DBCOD-containing polymer chains oriented along the longitudinal direction of aligned CNTs. This system offers power-efficient controlled actuation, i.e., directional bending and twisting. Recently, we have synthesized a series of single-molecule DBCODs with different substitutions. Through structure-property relationship investigation, we have revealed that substitution plays an influential role in conformation preference and stability. With proper substitution, DBCOD conformational transition can be served as a low-energy driven switch that operates under ambient conditions reliably.

FL-5:IL05  Biodegradable Injectable Polymer Systems Exhibiting Temperature-responsive Irreversible Gelation
YUICHI OHYA, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Japan

Aqueous solutions of some amphiphilic block copolymers are known to exhibit temperature-responsive sol-gel transitions. Such systems have attracted considerable attention as injectable polymers (IPs) for biomedical applications [1]. Most of the thermo-gelling systems exhibit sol-gel transitions to form hydrogels by the physical cross-linking. One of the practical problems for these systems is the short duration of the gel in the body. The formed hydrogel tends to revert to the sol state within a short period where a large amount of body fluid exists. This property is one of the obstacles of biodegradable IP systems for clinical application. We recently reported biodegradable temperature-triggered covalent gelation systems exhibiting longer and controllable duration time of the gel state utilizing thiol-ene reaction [2]. The obtained formulation showed temperature-responsive irreversible sol-gel transition and a longer duration of the gel. We investigated the potential utility of the system as sustained drug-releasing devices [3], anti-adhesive materials [4], and stem cell delivery devices [5].
1) React. Funct. Polym. 2013, 73, 979. 2) Biomat. Sci. 2017, 5, 1304. 3) Gels 2017, 3, 38. 4) ACS Appl. Bio Mater. 2021, 4, 3079. 5) Sci. Technol. Adv. Mater. 2021, 22, 627.

FL-6:IL02  Building Multifunctional, Morphing 3D Structures
T.H. Ware,  Department of Biomedical Engineering, Department of Materials Science and Engineering, Texas A&M University, College Station, TX, USA

Coordinated processing methods and materials formulation strategies are needed to enable the printing 3D objects that change shape reversibly to heat and light. In this work, shear during printing is used to orient a nematic liquid crystal elastomer (LCE), which undergoes programmed shape change on exposure to stimulus. Thermally-responsive materials are limited in applications by the need to heat the area around the actuator. Here, we describe the synthesis, processing, and properties of LCE-liquid metal composites. 3D-printed composites with greater than 88wt% liquid metal are highly conductive and thus can be actuated with <5 VDC. 3D printing of LCEs can also be used to fabricate photo-switchable objects, where shape change persists for indefinite periods of time after a stimulus but can be recovered by exposure to another stimulus. Printable LCEs with an azobenzene comonomer and self-complementary hydrogen bonding side-chains act as photo-switches. These materials undergo UV-induced deformation that is then fixed (>90%) by the physical crosslinks. The original shape can then be recovered by thermally breaking the physical crosslinks. Soft robots may be enabled by the use of light and electrical current to drive shape change in 3D printed structures.

FL-6:IL04  Advancing 4D Fabrication and Computational Analysis of Shape-Memory Polymers
J.H. Henderson, BioInspired Syracuse: Institute for Material and Living Systems, Syracuse Biomaterials Innovation Facility, Syracuse University, Syracuse, NY, USA

Manufacturing with shape-memory polymers (SMPs) has the potential to enable paradigm-shifting advances across diverse fields through creation of devices possessing spatially varying material functionality that cannot be achieved by any current approach. Yet gaps in fundamental understanding at the interface of materials processing and materials science currently impede progress. To address these limitations and transcend the domains involved, we are studying fundamental materials processing and science to achieve new approaches for fabrication of fully 3D, solid or porous devices with uniform or spatially varying functionality from individual, rather than composite, SMPs using off-the-shelf 3D printers. Here we will present integrated, interdisciplinary experimentation and simulation to achieve and study these approaches.

FL-7:L03  Direct Laser Writing of Responsive Polymer Microstructures - Towards Soft Robotics at the Micro-scale
L. FLOREA, T. Faraone, S. Kolagatla, A. Ennis, L. Lavelle, Colm Delaney School of Chemistry & AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research, Trinity College Dublin, Ireland

By merging the advantages of direct laser writing (DLW) enabled micro-fabrication with stimuli-responsive polymers, we demonstrate the realisation of complex 3D micro-structures that can switch or change characteristics in response to desired stimuli. Using DLW, fine control of mechanical properties can be achieved in 3D through control of laser parameters (laser power, writing speed, slicing and hatching distance), to achieve structures which can undergo anisotropic and programmable shape change upon stimulation. This is achieved by combining 3D design with prediction of the real-time response via Finite Element Analysis (FEA). Herein, we demonstrate a range of 3D/4D micro-structures based on hydrogels and liquid crystal elastomers, that can respond to external stimulation, actuate on demand, sense and report on their local chemical environment.[1,2] Such microstructures have a wide range of applications in the soft micro-robotics arena, for the development of micro-actuators, micro-swimmers, micro-grippers and smart delivery micro-systems.
1. M. Del Pozo, C. Delaney, C.W. Bastiaansen, D. Diamond, A.P. Schenning, L. Florea, 2020, ACS Nano 2020, 14(8), 9832. 2. C. Delaney, J. Qian, X. Zhang, R. Potyrailo, A.L. Bradley, L. 2021, J. Mater. Chem. C, 2021, 9, 11674.

FL-7:IL04  HASEL Artificial Muscles
C. Keplinger, Max Planck Institute for Intelligent Systems, Stuttgart, Germany

Robots today rely on rigid components and electric motors based on metal and magnets, making them heavy, unsafe near humans, expensive and ill-suited for unpredictable environments. Nature, in contrast, makes extensive use of soft materials and has produced organisms that drastically outperform robots in terms of agility, dexterity, and adaptability. To create a new generation of soft, life-like robots that reproduce the vast capabilities of biological systems, we need to develop actuators that replicate the astonishing all-around actuation performance of biological muscle. Hydraulically Amplified Self-healing ELectrostatic (HASEL) transducers are a new class of self-sensing, high-performance muscle-mimetic actuators, which are electrically driven and harness a mechanism that couples electrostatic and hydraulic forces to achieve a wide variety of actuation modes. Current designs of HASEL artificial muscles exceed actuation stress of 0.3 MPa, linear strain of 100%, specific power of 600W/kg, efficiency of 30% and bandwidth of 100Hz; all these metrics match or exceed the capabilities of biological muscle. This talk gives an overview over the latest developments, including modeling, new designs of actuators, fabrication techniques, and creation of untethered soft robotic devices.

FL-7:IL06  Plants as Concept Generators for the Development of New Materials Systems for Soft-robotics
T. Speck1, 2, 3, M. Thielen1, 2, F. Esser1, 2, 3, B. Mazzolai4, 1Botany: Functional Morphology & Biomimetics, Botanic Garden of the University of Freiburg, Freiburg, Germany; 2Freiburg Materials Research Centre (FMF) and Freiburg Institute for Interactive Materials & Bioinspired Technologies (FIT), Germany; 3Cluster of Excellence Living, Adaptive and Energy-autonomous Materials Systems (livMatS @ FIT); 4Italian Institute of Technology (IIT), Italy

During the last decades biomimetics has attracted increasing attention from basic and applied research and especially from soft robotics. The huge number of organisms with the specific structures and functions they have developed during evolution in adaptation to differing environments represents the basis for all biomimetic projects. Animals with their fascinating movement processes have long attracted interest in biomimetics and especially in soft robotics, but more recently also plants have been recognized as valuable concept generators for biomimetic research in general and soft robotics in particular. The potential of plant-inspired materials development for soft robotics is demonstrated by some of the Plant Biomechanics Group's research projects. Examples include bioinspired adaptive (anti-)attachment and self-repairing materials systems. Special emphasis is laid on embodied energy and intelligence found in moving plant organs which offer a huge potential for a new generation of materials systems for soft robots and technical applications in general. Such materials systems are major field of research within the Cluster of Excellence Living, Adaptive and Energy-autonomous Materials Systems (livMatS).


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