New Frontiers in Materials and Technologies for 3D Two Photon Polymerization

Two-photon polymerization (2PP), also known as two photon lithograpy (2PL) or direct laser writing (DLW) is a microfabrication technique established in the last decade, which combines advantages of 3D-printing with sub-micron resolution.[1] Micromachinery, photonics, surface design, microrobotics, and biomedical sciences are just some fields mostly impacted by technology (see Figure 1). Recent developments both materials[2, 3] methods[4] have shown potential to realize structures unprecedented complexity, innovative functionality, dynamic functions. Great efforts been made material scientists towards development new functional photoresists encompasses nanomaterial inclusion, photoinitiators enhanced two-photon absorption biocompatibility, soft responsive hydrogels, highlight but few noteworthy examples. Concurrently, greater understanding reaction mechanisms, computational analysis, optical systems, considerable inroads extending limits resolution, fabrication speed, application. This special issue brings together host working broader field lithography includes contributions at cutting edge this field, giving occasion document recent progress, critically analyze opportunities challenges for future exciting through selected research papers, high-quality reviews, perspective articles. We thank all invited contributors that possible their wonderful contributions. Below, we identify papers name author. Lastly, Dr. Maria Ronda Lloret us opportunity be Guest Editors Special Issue. It has real pleasure her. As introduced, investigation materials, compatible approach, one most area specific topic. Enhanced functionalities, responsiveness stimuli biocompatibility targeted proposing monomers, initiators composite formulations. Four assess aspect, describing materials able respond different (e.g., chemical, temperature darkness), enabling implementation micro-sensor, micro-actuators, among other applications. Delaney co-workers introduced vapour photoresist 4D microprinting submicron 2D photonic predictable uniform colour displays, can modulated on-demand. Also, transmitted dry hydrated states accurately modelled (adfm.202211735). Nocentini presented tuneable crystals relying on elastic liquid crystalline networks environment, particular, physical deformation under variation. approach enabled highly resolved, reproducible, mechanically self-standing (adfm.202213162). Florea´s team showed novel sugar responsive, phenylboronic acid-based photoresist. system permits 3D microstructures programmable actuation (i.e., bending opening) exhibiting remarkable fast response (adfm.202213947). Barner-Kowollik´s utilized light stabilized (LSDMs) fabricate remain stable when continuously irradiated green erased exposure darkness (adfm.202206303). Additionally, Turyanska demonstrated use metal/polymer nanocomposites using polymerisation. In three complementary strategies detailed: (a) in-situ formation metal nanoparticles (NPs) single step photoreduction process, (b) integration pre-formed NPs into 2PP resin (c) site-selective decoration (adfm.202211920). Furthermore, developed specifically allow fine tuning bulk properties printed microstructure suitable post processing. Two strategy based refined nitroxide chemistry approaches. Spangenberger mediated photopolymerization (NMP). method precise modification (adfm.202211971). Blasco´s reported inclusion living bonds (alkoxyamines) printable formulations first time allowing preparation “living” microstructures. The post-polymerization processing resulted dramatic increase volume (around 8 times) microstructure, an Young's Modulus (two orders magnitude) (adfm.202207826R2). Worthy note, generation applications, included work focussed biocompatibility. proposed water soluble produce completely biocompatible Zheng anion ionic carbazole-based water-soluble initiator (TPI) 3,6-bis[2-(1-methylpyridinium)vinyl]-9-methylcarbazole ditosylate (BT) hydrogel (adfm.202210993). Magdassi´s resilin protein-based length scale ruthenium-based photoinitiator. resilient, similar native importantly, they cell growth alignment (adfm.202300293). addition, review led Van Vlierberghe discusses types applications (adfm.202212641). Innovation relates technological advancements combination others achieve advanced functionalities. Two-step lithography, holographic approaches, represent examples such advancement. original reviews report advancement from standpoint. Wegener's group recently two-step absorption[5] emerging evolution 2PP; here he his systematically explored alternatives already know one-color two-colour photoinitiators, fundamental toward inexpensive compact setups continuous-wave lasers micro printing (adfm.202212482). handling manipulation micro-structures not trivial task; Mattoli transfer arbitrary complex surfaces providing extreme level conformability. relies polymeric nano-membranes efficiently transferred onto targets (adfm.202214409). One main limitations relatively low throughput, hampered its industrial application date. Methods improve aspect so far Balena, De Vittorio co-workers, covering concepts behind high-speed Photon Lithography holography scalability (adfm.202211773). Finally, Sun's reviewed state-of-the-art techniques nano-printing directly simple polymer template-assisted printing, polymer-free others, thus cutting-edge discussing existing technical bottleneck (adfm.202211280). Concerning polymerization, it interesting underline actual trend seems driven increased interest bio-related topics, including bioinspired ones. Notably, issue, five bioinspired/biomimetic studies, spanning controlled hydrophobicity, actuation, swimming capabilities. micro-robots actuated approaches presented. Pané Vidal degradable magnetic-driven Polyvinyl alcohol (PVA), implementing morphologies stability. casting salting-out process improving PVA stability retaining (adfm.202212952). Di Leonardo's propose micro-robotic locomotion; integrating biological actuators, light-driven bacteria, propellers micro-structure. resulting hybrid micro-roots steered unbalancing intensity over micro-robot parts (adfm.202214801). Lewis Smith another principle inspired nature, demonstrating 3D-printed hydraulic actuator micro-scale. They micron-scale thickness create compliant membranes rigid encapsulated unpolymerized resist media, micro-hydraulic analogy spider's legs (adfm.202207435). Micro-devices built used mechanisms nature. regard, Mazzolai's investigated transpiration cavitation-driven dynamics observed annulus cells means synthetic structures. Specifically, fabricated prismatic microcavities, assembled PDMS microfilm, artificial micro-chambers mimicking cells, replicating evaporation-driven collapse return triggered nucleation bubbles (adfm.202214130). Moreover, Tricinci, co-worker exploited micro-contact micro-patterned morphology chemical coating hairs Salvinia Molesta leaves, reproducing wettability behaviour, contemporary high hydrophobicity roll angle (adfm.202206946). On topic, Dong Levkin micro-printing design super-repellent microstructures, focus functionalities offered possibility dimensional topographies (adfm.202213916). micro-optics, aspects 2 optic plasmonic, complete issue. Giessen's way opaque microscopic apertures contrast optics designs (adfm.202211159). With Raimondi, Chirico situ plano-convex micro-lenses non-linear imaging tissue. tested fibroblast culture, could open implanted micro-optics in-vivo inspection processes (adfm.202213926). Yang extensively fields, starting fundamentals light-matter interaction, reviewing relevant reporting technologies post-processes, analysing various (adfm.202214211). Juodkazis, Farsari analysed glass-ceramic obtained combined calcination via annealing (adfm.202215230). served mark great innovation collaboration burgeoning field. highlights researchers forefront spans several disciplines. each technologies, Polymerization reaches frontiers. V.M. L.F. acknowledge support European Union's Horizon 2020 program FET Open grant agreement 5DNanoPrinting – no. 899349. E.B. acknowledges funding German Research Council (DFG) Excellence Cluster “3D Matter Made Order” (EXC-2082/1-390761711) Carl Zeiss Foundation. authors Omar Tricinci Matteo Archimi pictures 1 composition. declare no conflict interest.