We propel photopolymerizable liquid crystalline (LC) shape memory materials from solely elastomeric performance to the thermomechanical performance of tough, yielding thermosets. LC elastomers are at the forefront of smart, stimuli-responsive materials development. To apply their properties to mechanically superior thermosets, we demonstrate main-chain incorporation of high quantities of preordered LC motifs into a densely crosslinked network via thiol-ene photopolymerization to achieve a new material class hybridizing the advantages of LC elastomers and liquid crystalline networks. A terminal alkene mesogen with a robust LC phase is combined with multiple trithiol comonomers and selected based on resulting polymer crystallinities (13-37%). In-depth crystallinity characterization is presented (dynamic scanning calorimetry, X-ray diffraction analysis). The bulk materials exhibit high strength, stiffness and pronounced yielding under stress with elongations around 200%. Their excellent thermomechanical properties were explained by phase separation observed in atomic force microscopy. Furthermore, we demonstrate shape memory of these materials with fast, near-perfect shape imprinting (99%) and recovery (97%) over at least 20 cycles, and their light-based 3D printing at high temperature.

This work investigates the development of photopolymerization-induced phase separation (PhIPS) in methacrylate-based photopolymers. Bisphenol A ethoxylated dimethacrylate (BisEMA) was copolymerized with urethane-based diacrylate diluted in isobornyl acrylate (UI) under UV irradiation, using diphenyl-(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) as a photoinitiator. Optical changes in the cured copolymers were monitored in real time with a custom setup. NIR-photorheometry, photo-differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy, and atomic force microscopy in both topography and phase imaging modes were employed to characterize the PhIPS effect on network development and microstructure. The correlation between the microstructure of copolymers with varying BisEMA/UI ratios and their bulk properties was studied through tensile and dynstat impact tests. Results showed that up to 20% UI enhances the elongation at break of BisEMA without compromising strength. At higher monomer/oligomer ratios, phase separation led to a strength-ductility trade-off. The study also addresses the influence of AFM sample preparation on correlating phase imaging results to the local stiffness distribution.

Multi-material printing has experienced critical advances in recent years, yet material property differentiation capabilities remain limited both with regard to the accessible properties - typically hard versus soft - and the achievable magnitude of differentiation. To enhance multi-material printing capabilities, precise photochemical control during 3D printing is essential. Wavelength-differentiation is a particularly intriguing concept yet challenging to implement. Notably, dual-wavelength printing to fabricate hard and soft sections within one object has emerged, where one curing process is insensitive to visible light, while UV irradiation inevitably activates the entire resin, limiting true spatio-temporal control of the material properties. Until now, pathway-independent wavelength-orthogonal printing has not been realized, where each wavelength exclusively triggers only one of two possible reactions, independent of the order in which the wavelengths are applied. Herein, a multi-wavelength printing technique is introduced employing a tunable laser to monochromatically deliver light to the printing platform loaded with a fully wavelength-orthogonal resin. Guided by photochemical action plots, two distinct wavelengths - each highly selective toward a specific photocycloaddtion reaction - are utilized to generate distinct networks within the photoresin. Ultimately, together with the printing technique, this orthogonally addressable photoresin allows fabricating multi-material objects with degradable and non-degradable properties, in a single fabrication step.

Additive manufacturing technologies and, in particular, vat photopolymerization promise complex structures that can be made in a fast and easy fashion for highly individualized products. While the technology has upheld this promise many times already, some polymers are still out of reach or at least problematic to print reliably. High-performance epoxide-based resins, which are regulated by chain transfer via multifunctional alcohols, are a typical example of resins with late gel points, which require long irradiation times and high light intensities to print. Therefore, we have developed a dual-colour printing approach where rapid radical curing of a soft, wide-meshed polymer network facilitates fast and easy 3D structuring of the subsequently slow curing step-growth formulation at an orthogonal initiation-wavelength regime. Thereby the methacrylate system acts as a scaffold for an uncured epoxide alcohol system during the printing process, which is then cured with UV light post-printing. This way tough alcohol-regulated epoxy-systems become accessible to vat photopolymerization achieving outstanding high-resolution 3D printed parts without significant layering effects. The demonstrated wide-meshed matrix-assisted printing approach has the potential to make a multitude of slowly curing resins accessible to vat photopolymerization techniques, at low irradiation intensities and high curing speeds.

In vitro assessment of small-diameter synthetic vascular grafts usually uses standard cell culture conditions with early-passage cells. However, these conduits are mainly implanted in elderly patients and are subject to complex cellular interactions influenced by age and inflammation. Understanding these factors is central to the development of vascular grafts tailored to the specific needs of patients. In this study, the effects of aged endothelial cells subjected to pro- and anti-inflammatory agents and cultivated on a newly developed biodegradable electrospun thermoplastic polyurethane/poly(urethane-urea) blend (TPU/TPUU), on clinically available expanded polytetrafluorethylene (ePTFE), and on decellularized extracellular matrix (dECM) grafts were investigated. Young and aged endothelial cells were exposed to pro- and anti-inflammatory agents and characterized by morphology, migration capacity, and gene expression. In addition, the cells were seeded onto the various graft materials and examined microscopically alongside gene expression analyses. When exposed to pro-inflammatory cytokines, young and aged cells demonstrated signs of endothelial activation. Cells seeded on ePTFE showed reduced attachment and increased expression of pro-inflammatory genes compared with the other materials. dECM and TPU/TPUU substrates provided better support for endothelialization with aged cells under inflammatory conditions compared with ePTFE. Moreover, TPU/TPUU showed positive effects on reducing pro-thrombotic and pro-inflammatory gene expression in endothelial cells. Our results thus emphasize the importance of developing new synthetic graft materials as an alternative for clinically used ePTFE.

We demonstrate light-based 3D printing of pure poly(ether carbonate) networks free of shrinkage stress. Expanding the recently pioneered concept of pure cationic double ring-opening photopolymerization of spiro-orthoesters at elevated temperatures, we herein investigate spiro-orthocarbonates. Thereof resulting poly(ether carbonate) networks could find manyfold applications in biological and medical settings as well as in applications searching for more sustainable material solutions. We have determined the dependence of single and double ring-opening and the presence of backbiting side reactions for three synthesized spiro-orthocarbonate monomers in combination with an oxetane crosslinker on the ring size and photopolymerization temperature to optimize the photogenerated network and thus material properties. The absence of residual stresses in the polymer network was confirmed by tracking the decrease of sample birefringence with increasing spiro-carbonate monomer content of the sample. Based on this fundamental study, the best-performing monomer was printed in combination with an oxetane crosslinker.

Photopolymers have been optimized as protective and decorative coating materials for decades. However, with the rise of additive manufacturing technologies, vat photopolymerization has unlocked the use of photopolymers for three-dimensional objects with new material requirements. Thus, the originally highly cross-linked, amorphous architecture of photopolymers cannot match the expectations for modern materials anymore, revealing the largely unanswered question of how diverse properties can be achieved in photopolymers. Herein, we review how microstructural features in soft matter materials should be designed and implemented to obtain high performance materials. We then translate these findings into chemical design suggestions for enhanced printable photopolymers. Based on this analysis, we have found microstructural heterogenization to be the most powerful tool to tune photopolymer performance. By combining the chemical toolbox for photopolymerization and the analytical toolbox for microstructural characterization, we examine current strategies for physical heterogenization (fillers, inkjet printing) and chemical heterogenization (semicrystalline polymers, block copolymers, interpenetrating networks, photopolymerization induced phase separation) of photopolymers and put them into a material scientific context to develop a roadmap for improving and diversifying photopolymers' performance.

Employing two colors of light to 3D print objects holds potential for accessing advanced printing modes, such as the generation of multi-material objects from a single print. Thus, dual-wavelength-driven photoreactive systems (reactions that require or utilize two wavelengths) and their exploitation as chemo-technological solutions for additive manufacturing technologies have experienced considerable development over the last few years. Such systems saw an increase in printing speeds, a decrease in resolution thresholds, and─perhaps most importantly─the actual generation of multi-material objects. However, the pace at which such reactive systems are developed is moderate and varies significantly depending on the fashion in which the two colors of light are employed. Herein, we address for the first time the varying logic conjugations of light-activated chemical compounds in dual-wavelength photochemical processes in a systematic manner and consider their implications from a photochemical point of view. To date, four dual-wavelength reaction types have been reported, termed synergistic (λ1 AND λ2), antagonistic (reversed λ1 AND λ2), orthogonal (λ1 OR λ2), and─most recently─cooperative (λ1 AND λ2 or λ1 OR λ2). The progress of their implementation in additive manufacturing is assessed individually, and their concurrent and individual chemical challenges are identified. These challenges need to be addressed for future dual-wavelength photochemical systems to progress multi-wavelength additive manufacturing technologies beyond their current limitations.

Supramolecular polymers can substantially influence the dynamic mechanical properties in slightly crosslinked polymer networks. One prominent example of supramolecular building blocks is 2-ureido-4[1H]-pyrimidinones (UPy). Combining UPy-terminated supramolecular segments with classical covalent-reactive monomers implements dynamic behavior in photopolymerizable systems. In this work, a UPy-based methacrylic monomer (up to 20 mol%) was introduced in a classical photopolymerizable methacrylate matrix. The influence of the UPy-motif on the reactivity and (thermo)mechanical properties was investigated via RT-NIR photorheology, DMTA, and tensile testing. The dynamic behavior was characterized via stress relaxation and reprocessing studies to demonstrate the dynamic effects of photopolymers containing the UPy building block compared to difunctional photopolymers with similar structural features. In a final step, the UPy-based photopolymerizable system was applied in bulk in a Hot Lithography printing process at elevated temperatures yielding complex 3D-printed parts with high resolution and precision.

Clinically available small-diameter synthetic vascular grafts (SDVGs) have unsatisfactory patency rates due to impaired graft healing. Therefore, autologous implants are still the gold standard for small vessel replacement. Bioresorbable SDVGs may be an alternative, but many polymers have inadequate biomechanical properties that lead to graft failure. To overcome these limitations, a new biodegradable SDVG is developed to ensure safe use until adequate new tissue is formed. SDVGs are electrospun using a polymer blend composed of thermoplastic polyurethane (TPU) and a new self-reinforcing TP(U-urea) (TPUU). Biocompatibility is tested in vitro by cell seeding and hemocompatibility tests. In vivo performance is evaluated in rats over a period for up to six months. Autologous rat aortic implants serve as a control group. Scanning electron microscopy, micro-computed tomography (µCT), histology, and gene expression analyses are applied. TPU/TPUU grafts show significant improvement of biomechanical properties after water incubation and exhibit excellent cyto- and hemocompatibility. All grafts remain patent, and biomechanical properties are sufficient despite wall thinning. No inflammation, aneurysms, intimal hyperplasia, or thrombus formation are observed. Evaluation of graft healing shows similar gene expression profiles of TPU/TPUU and autologous conduits. These new biodegradable, self-reinforcing SDVGs may be promising candidates for clinical use in the future.

Aliphatic polycarbonates are highly regarded due to their potential as sustainable, biodegradable and inherently biocompatible materials. Therefore, much effort has been directed towards implementation of aliphatic poly -carbonates into network structures. To date, these efforts have relied on incorporation of main-or sidechain functional groups into carbonate-containing monomers or oligomeric precursors, with pure polycarbonate net-works remaining inaccessible. Here we show that recently developed thermally stable photobase generators have now made cyclic carbonates available for light-induced anionic ring-opening polymerization for the first time to form pure aliphatic polycarbonate networks at elevated temperatures. To gain insights into the polymerization mechanism, the reactivity of synthesized aromatically and aliphatically substituted cyclic carbonates was investigated utilizing photo-DSC and photorheology between 70 and 120 degrees C. A bifunctional cyclic carbonate was synthesized as crosslinker and tested for network formation with varying amounts of the monofunctional cyclic carbonate as reactive diluent. Tensile tests and DMTA measurements revealed tough, highly tunable (thermo-) mechanical properties of the obtained materials, depending on the ratio of reactive diluent to crosslinker.

We demonstrate stereolithographic 3D printing of pure aliphatic poly(ether esters) from spiro-orthoesters with near-net-zero shrinkage and significantly reduced shrinkage stress.

A photoresist-based on a light-stabilized dynamic material driven by an out-of-equilibrium photo-Diels-Alder reaction of triazolinediones with naphthalenes-whose ability to intrinsically degrade postprinting can be tuned by a simple adjustment of laser intensity during 3D laser lithography is introduced. The resist's ability to form stable networks under green light irradiation that degrade in the dark is transformed into a tunable degradable 3D printing material platform. In-depth characterization of the printed microstructures via atomic force microscopy before and during degradation reveals the high dependency of the final structures' properties on the writing parameters. Upon identifying the ideal writing parameters and their effect on the network structure, it is possible to selectively toggle between stable and fully degradable structures. This simplifies the direct laser writing manufacturing process of multifunctional materials significantly, which typically requires the use of separate resists and consecutive writing efforts to achieve degradable and nondegradable material sections.

Independently addressing photoreactive sites within one molecule with two colours of light is a formidable challenge. Here, we combine two sequence independent λ-orthogonal chromophores in one heterotelechelic dilinker molecule, to exploit their disparate reactivity utilizing the same reaction partner, a maleimide-containing polymer. We demonstrate that polymer network formation only proceeds if two colours of light are employed. Upon single colour irradiation, linker-decorated post-functionalized polymers are generated at either wavelength and in either sequence. Network formation, however, is only achieved by sequential or simultaneous two colour irradiation. The herein introduced photoreactive system demonstrates the power of wavelength orthogonal chemistry in macromolecular synthesis.

AbstractDie unabhängige Aktivierung von lichtreaktiven Funktionalitäten innerhalb eines Moleküls stellt eine besondere Herausforderung dar. Wir nutzen die Kombination von zwei sequenzunabhängigen λ‐orthogonalen Chromophoren innerhalb eines heterotelechelen Quervernetzer‐Moleküls und ihre gegenläufigen Reaktivitäten mit demselben Reaktionspartner, einem Copolymer mit Maleimid‐Seitengruppen, um Netzwerkbildung exklusiv durch die Bestrahlung mit zwei Lichtfarben zu induzieren. Bestrahlunge mit nur einer der beiden Lichtfarben führt zur einseitigen Reaktion des Quervernetzers und somit zur Postfunktionalisierung des Polymers. Die Netzwerkbildung hingegen wird ausschließlich durch sequenzielle oder simultane zweifarben Bestrahlung erzielt. Dieses lichtreaktive System zeigt exemplarisch den Nutzen von Wellenlängen‐orthogonaler Chemie in der makromolekularen Synthese.

The ability of light to remotely control the properties of soft matter materials in a dynamic fashion has fascinated material scientists and photochemists for decades. However, only recently has our ability to map photochemical reactivity in a finely wavelength resolved fashion allowed for different colors of light to independently control the material properties of polymer networks with high precision, driven by monochromatic irradiation enabling orthogonal reaction control. The current concept article highlights the progress in visible light-induced photochemistry and explores how it has enabled the design of polymer networks with dynamically adjustable properties. We will explore current applications ranging from dynamic hydrogel design to the light-driven adaptation of 3D printed structures on the macro- and micro-scale. While the alternation of mechanical properties via remote control is largely reality for soft matter materials, we herein propose the next frontiers for adaptive properties, including remote switching between conductive and non-conductive properties, hydrophobic and hydrophilic surfaces, fluorescent or non-fluorescent, and cell adhesive vs. cell repellent properties.

The terpolymer acrylonitrile-butadiene-styrene (ABS) is a widely used thermoplastic material due to its excellent mechanical properties, especially high toughness. However, the monomer system of ABS cannot be feasibly photopolymerized due to its reactivity, opacity and monomer volatility. We show the transfer of an ABS microstructure to photopolymers via monomer systems designed to mimic ABS while remaining photopolymerizable. Acrylonitrile was substituted by more reactive and less volatile maleimides, of which the N substituent influences crosslinking considerably. Instead of styrene, less volatile derivatives were utilized as comonomers. Poly(butadiene) was introduced as cheap, readily available and non-volatile rubber. The resulting maleimide-styrene-poly(butadiene) networks exhibit varying microphase separations and simultaneous transparency. While optimized materials cannot quite exhibit the yield strain of hot-pressed ABS filament, their toughness partly exceeds that of ABS. Superior thermal stabilities and glass transition temperatures up to 190 degrees C were observed. Finally, stereolithographic printing of one tuned monomer system was conducted. (c) 2021 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.