Organometal halide perovskite solar cells have demonstrated high conversion efficiency but poor long-term stability against ultraviolet irradiation and water. We show that rapid light-induced ...free-radical polymerization at ambient temperature produces multifunctional fluorinated photopolymer coatings that confer luminescent and easy-cleaning features on the front side of the devices, while concurrently forming a strongly hydrophobic barrier toward environmental moisture on the back contact side. The luminescent photopolymers re-emit ultraviolet light in the visible range, boosting perovskite solar cells efficiency to nearly 19% under standard illumination. Coated devices reproducibly retain their full functional performance during prolonged operation, even after a series of severe aging tests carried out for more than 6 months.
Biofabrication technologies, including stereolithography and extrusion‐based printing, are revolutionizing the creation of complex engineered tissues. The current paradigm in bioprinting relies on ...the additive layer‐by‐layer deposition and assembly of repetitive building blocks, typically cell‐laden hydrogel fibers or voxels, single cells, or cellular aggregates. The scalability of these additive manufacturing technologies is limited by their printing velocity, as lengthy biofabrication processes impair cell functionality. Overcoming such limitations, the volumetric bioprinting of clinically relevant sized, anatomically shaped constructs, in a time frame ranging from seconds to tens of seconds is described. An optical‐tomography‐inspired printing approach, based on visible light projection, is developed to generate cell‐laden tissue constructs with high viability (>85%) from gelatin‐based photoresponsive hydrogels. Free‐form architectures, difficult to reproduce with conventional printing, are obtained, including anatomically correct trabecular bone models with embedded angiogenic sprouts and meniscal grafts. The latter undergoes maturation in vitro as the bioprinted chondroprogenitor cells synthesize neo‐fibrocartilage matrix. Moreover, free‐floating structures are generated, as demonstrated by printing functional hydrogel‐based ball‐and‐cage fluidic valves. Volumetric bioprinting permits the creation of geometrically complex, centimeter‐scale constructs at an unprecedented printing velocity, opening new avenues for upscaling the production of hydrogel‐based constructs and for their application in tissue engineering, regenerative medicine, and soft robotics.
Spatially coordinated patterns of visible light tomographic projections onto cell‐laden photoresponsive hydrogels enable the rapid bioprinting of 3D tissue constructs with clinically relevant size and complex geometries. Centimeter‐scale structures are built within seconds, outperforming conventional layer‐by‐layer bioprinting approaches and demonstrating high cell viability. Stem cells retain functionality postprinting, demonstrating potential for the biofabrication of vascularized and mature tissue grafts.
The global market for 3D printing materials has grown exponentially in the last decade. Today, photopolymers claim almost half of the material sales worldwide. The lack of sustainable resins, ...applicable in vat photopolymerization that can compete with commercial materials, however, limits the widespread adoption of this technology. The development of “green” alternatives is of great importance in order to reduce the environmental impact of additive manufacturing. This paper reviews the recent evolutions in the field of sustainable photopolymers for 3D printing. It highlights the synthesis and application of biobased resin components, such as photocurable monomers and oligomers, as well as reinforcing agents derived from natural resources. In addition, the design of biologically degradable and recyclable thermoset products in vat photopolymerization is discussed. Together, those strategies will promote the accurate and waste‐free production of a new generation of 3D materials for a sustainable plastics economy in the near future.
In view of the growing demand for 3D printing materials, the availability of environmentally friendly alternatives is vital. The field of sustainable materials for vat photopolymerization is evolving rapidly from biobased resins and biodegradable photopolymers to repairable and reprocessable thermosets. This review article strives to give an overview of recent advances in the last decade.
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Vat Photopolymerization (stereolithography, SLA), an Additive Manufacturing (AM) or 3D printing technology, holds particular promise for the fabrication of tissue scaffolds for use in ...regenerative medicine. Unlike traditional tissue scaffold fabrication techniques, SLA is capable of fabricating designed scaffolds through the selective photopolymerization of a photopolymer resin on the micron scale. SLA offers unprecedented control over scaffold porosity and permeability, as well as pore size, shape, and interconnectivity. Perhaps even more significantly, SLA can be used to fabricate vascular networks that may encourage angio and vasculogenesis. Fulfilling this potential requires the development of new photopolymers, the incorporation of biochemical factors into printed scaffolds, and an understanding of the effects scaffold geometry have on cell viability, proliferation, and differentiation. This review compares SLA to other scaffold fabrication techniques, highlights significant advances in the field, and offers a perspective on the field’s challenges and future directions.
Engineering de novo tissues continues to be challenging due, in part, to our inability to fabricate complex tissue scaffolds that can support cell proliferation and encourage the formation of developed tissue. The goal of this review is to first introduce the reader to traditional and Additive Manufacturing scaffold fabrication techniques. The bulk of this review will then focus on apprising the reader of current research and provide a perspective on the promising use of vat photopolymerization (stereolithography, SLA) for the fabrication of complex tissue scaffolds.
In the present research, a type of cycloaliphatic silicone–epoxy resin is synthesized and then compounded with acrylates as well as photoinitiators to obtain hybrid photopolymers. The photocuring ...rate of the hybrid photopolymers, the morphology, thermal and mechanical properties of the cured samples with different silicone–epoxy/acrylate ratios are studied in detail. Scanning electron microscopy images prove that interpenetrating polymer network structure is formed. To improve the mechanical properties, diglycidyl ether of bisphenol A is added and finally a type of hybrid photopolymer suitable for stereolithography 3D printing is obtained. Fourier‐transform infrared spectroscopy and photo‐differential scanning calorimeter measurements show that the hybrid photopolymer has a high curing rate, while thermal property tests prove that the cured sample has high thermal stability. Mechanical property tests show that the cured samples have a tensile strength of 40.3 MPa with a break elongation of 6.7%. The objects printed with the hybrid photopolymer exhibit high resolution and dimension accuracy.
A new type of silicone–epoxy/acrylate hybrid photopolymer is synthesized and applied in stereolithography (SL) 3D printing. Fourier‐transform infrared spectroscopy and photo‐differential scanning calorimeter measurements show that the hybrid photopolymer has high curing rate. With high thermal stability and relatively good mechanical properties, the hybrid photopolymer is applied in SL 3D printing. The printed objects exhibit high resolution and dimension accuracy.
Cyanines derived from heptamethines were investigated in combination with iodonium salts as initiators of the radical polymerization of tripropylene glycol diacrylate and epoxides derived from ...bisphenol‐A‐diglycidylether. A new near‐infrared (NIR) LED prototype emitting at 805 nm with an exposure intensity of 1.2 W cm−2 facilitated initiation of both radical and cationic polymerization using sensitizers derived from cyanines. This new light‐emitting device has brought new insight into the photochemistry of cyanines with the general structure 1 because a combination of photonic and thermal processes strongly influences reaction pathways. In particular, cationic cyanines comprising a cyclopentene moiety and diphenylamino group in the center initiated the cationic polymerization of epoxides. Selective oxidation of this unit explains why specifically these derivatives may function as initiators for cationic polymerization. In contrast, when the diphenylamino group was replaced by a barbital group at the meso‐position cationic polymerization of epoxides was not initiated.
Polymerization in a new light: New LED prototypes are used to initiate radical and cationic photopolymerization using cationic polymethine initiators derived from heptamethines. A combination of photonic and thermal processes strongly influences the reaction pathways.
Within this work, a novel acylstannane‐based photoinitiator (PI) is presented. Tetrakis(2,4,6‐trimethylbenzoyl)stannane (1) displays outstanding properties compared to state‐of‐the‐art ...acylgermane‐based initiators. Most importantly, the initiator shows absorption up to 550 nm, which allows higher penetration depths, especially in highly filled photopolymers. Besides that, 1 shows extremely high photoinitiating activity towards (meth)acrylic double bonds, as well as very fast photobleaching. Furthermore, unlike many organotin compounds, 1 shows surprisingly low cytotoxicity.
A new cure: A novel acylstannane‐based visible‐light photoinitiator, tetrakis(2,4,6‐trimethylbenzoyl)stannane (1), shows absorption at wavelengths up to 550 nm, which results in higher penetration depths, especially in highly filled photopolymers. Photoinitiator 1 also shows extremely high photoinitiating activity towards (meth)acrylic double bonds, very fast photobleaching and surprisingly low cytotoxicity.
The reaction of thiols and anhydrides to form ring opened thioester/acids is shown to be highly reversible and it is accordingly employed in the fabrication of covalent adaptable networks (CANs) that ...possess tunable dynamic covalent chemistry. Maleic, succinic, and phthalic anhydride derivatives were used as bifunctional reactants in systems with varied stoichiometries, catalyst, and loadings. Dynamic characteristics such as temperature‐dependent stress relaxation, direct reprocessing and recycling abilities of a range of thiol–anhydride elastomers, glasses, composites and photopolymers are discussed. Depending on the catalyst strength, 100 % of externally imposed stresses were relaxed in the order of minutes to 2 hours at mild temperatures (80–120 °C). Pristine properties of the original materials were recovered following up to five cycles of a hot‐press reprocessing technique (1 h/100 °C).
On the move: Thiol–anhydride networks were fabricated and assessed for their dynamic reversible characteristics. Three anhydrides (maleic, succinic, and phthalic) were used to create dynamic thermosets of diverse propensities for thioester anhydride link reversion. An impressive degree of control over their dynamic responsiveness was achieved.
Holographic photopolymers are a new technology to create passive diffractive optical elements by a pure laser interference recording. In this review, we explain the chemistry concepts of light ...harvesting in an interference pattern and the subsequent grating formation as chemical response. Using the example of the newly developed Bayfol
HX film we discuss the reaction-diffusion driven photo-polymerization process for an index modulation formation to create volume phase gratings. Further we elucidate the selection of monomer chemistry and discuss details of the recording conditions based on the concept of exposure dosage and exposure time. Influences ranging from high dosage recording to low power recording are explained and how to affect the desired diffraction efficiency. Finally, we outline and demonstrate the process to mass manufacturing of volume phase gratings.
Additive manufacturing (AM) of complex three‐dimensional (3D) metal oxides at the micro‐ and nanoscales has attracted considerable attention in recent years. State‐of‐the‐art techniques that use ...slurry‐based or organic–inorganic photoresins are often hampered by challenges in resin preparation and synthesis, and/or by the limited resolution of patterned features. A facile process for fabricating 3D‐architected metal oxides via the use of an aqueous metal‐ion‐containing photoresin is presented. The efficacy of this process, which is termed photopolymer complex synthesis, is demonstrated by creating nanoarchitected zinc oxide (ZnO) architectures with feature sizes of 250 nm, by first patterning a zinc‐ion‐containing aqueous photoresin using two‐photon lithography and subsequently calcining them at 500 ºC. Transmission electron microscopy (TEM) analysis reveals their microstructure to be nanocrystalline ZnO with grain sizes of 5.1 ± 1.6 nm. In situ compression experiments conducted in a scanning electron microscope show an emergent electromechanical response: a 200 nm mechanical compression of an architected ZnO structure results in a voltage drop of 0.52 mV. This photopolymer complex synthesis provides a pathway to easily create arbitrarily shaped 3D metal oxides that could enable previously impossible devices and smart materials.
Fabrication of 3D nanoarchitected multifunctional metal oxides is performed through a facile method using a metal‐ion‐containing aqueous photoresin, which is polymerized using two‐photon lithography and calcined to give the metal oxide structure. Zinc oxide microstructures, with sub‐micrometer features, fabricated using this technique exhibit an electromechanical response that could enable the production of previously impossible 3D smart devices.
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