Extrusion-based 3D-printing is a promising manufacturing method because it can integrate various nanomaterials, including highly conductive MXenes. Nevertheless, the fabrication of both wet and dry stable 3D-printed structures with MXene has remained challenging due to the difficulty in forming mechanically stable, crosslinked networks with the required rheological properties. In this work, a MXene ink formulation incorporating cellulose nanofibers (CNFs) as rheology modifiers is developed, enhancing structural integrity and enabling a one-step freeze-induced crosslinking process to produce lightweight, porous structures. The 3D-printed structures exhibit remarkable mechanical strength, supporting up to 10,000 times their own weight, while maintaining a conductivity of over 195 S m⁻¹. Additionally, they demonstrate a specific capacitance of 240 F g⁻¹ at 5 mV s⁻¹, highlighting their potential for applications in advanced iontronic devices. A fully 3D-printed supercapacitor concept is showcased in two distinct configurations: in-plane and stacked; demonstrating their structural integrity and electrochemical stability in aqueous environments.

Paper is the largest renewable industrial substrate produced for various applications and can be recycled by disintegrating the fibers and reforming the paper. Paper and its fiber constituents lack functions such as electrical conductivity and papermaking itself has not been used for producing electronic devices. In this work, we show a potential industrially viable route for introducing cationic charges on the cellulose fibers and subsequently show how the adsorption of negatively charged ionically and electrically conductive materials onto these fibers from aqueous media can be applied at time scales relevant to industrial papermaking. This results in electroactive fibers, that can subsequently be used to prepare electroactive papers using standard papermaking procedures. Since fibers in the paper can selectively be coated with different active materials, various functions can be added into the paper. To demonstrate applications, we prepared electroactive papers using fibers with adsorbed carbon nanotubes (CNTs) and conducting polymers. We achieved conductivity of 21 S/m with only 1wt% CNT. We also prepared papers with CNTs and black phosphorus, used as paper-based lithium, and sodium ion battery (free-standing) anodes. They delivered a specific capacity of 642 mA h g⁻¹ at 100 mA g⁻¹ after 3500 cycles with 99.5% columbic efficiency. Furthermore, we recycled the papers, and as the disintegration of the fibers did not lead to removal of the ionic or electroactive materials from the fiber surface, the recycled papers showed similar electrical and mechanical properties to the original papers. This opens the path for recyclable paper-based electronics.

Two-photon polymerization (2PP) is an efficient technique to achieve high-resolution, three-dimensional (3D)-printed complex structures. However, it is restricted to photocurable monomer combinations, thus presenting constraints when aiming at attaining functionally active resist formulations and structures. In this context, metal nanoparticle (NP) integration as an additive can enable functionality and pave the way to more dedicated applications. Challenges lay on the maximum NP concentrations that can be incorporated into photocurable resist formulations due to the laser-triggered interactions, which primarily originate from laser scattering and absorption, as well as the limited dispersibility threshold. In this study, we propose an approach to address these two constraints by integrating metallic Rh NPs formed ex situ, purposely designed for this scope. The absence of surface plasmon resonance (SPR) within the visible and near-infrared spectra, coupled with the limited absorption value measured at the laser operating wavelength (780 nm), significantly limits the laser-induced interactions. Moreover, the dispersibility threshold is increased by engineering the NP surface to be compatible with the photocurable resin, permitting us to achieve concentrations of up to 2 wt %, which, to our knowledge, is significantly higher than the previously reported limit (or threshold) for embedded metal NPs. Another distinctive advantage of employing Rh NPs is their role as promising contrast agents for X-ray fluorescence (XRF) bioimaging. We demonstrated the presence of Rh NPs within the whole 2PP-printed structure and emphasized the potential use of NP-loaded 3D-printed nanostructures for medical devices.

In recent years, the design and synthesis of bio-compatible coatings leading to hybrid nanoparticles (NPs) as the contrast agents have gained substantial relevance. Furthermore, the addition of several functionalities for bio-imaging applications represents a key step for non-invasive bio-diagnostics. In this context, we design and utilize hybrid nanostructures for X-ray fluorescence computed tomography (XFCT). The combination of a ceramic or metallic core–based on MoO2, Rh or Ru–with a protective shell allows the generation of bio-compatible nanohybrids for dual mode bio-imaging, where the core NPs constitute the X-ray fluorescence (XRF) contrast agents [1]–[3]. Core NPs are synthesized via polyol, hydrothermal or microwave-assisted hydrothermal methods, yielding uniform shape and high dispersibility in aqueous media. Different approaches have been pursued for the fabrication of a bio-compatible shell coating. A modified sol-gel based silica coating process, doped with a commercial fluorophore (Cy5.5), was developed and shown to be applicable to both ceramic and metallic NPs [4], forming core-shell NPs with both optical and X-ray fluorescence properties. Alternatively, carbon quantum dots (CQDs) were synthesized via citrate pyrolysis using microwave-assisted hydrothermal method, exhibiting uniform size distribution (1.6±0.4 nm) and excitation-independent emission (440 nm). Conjugation of these CQDs, via cross-linking, with Rh NPs led to excitation-independent hybrid NPs, with a red-shifted emission wavelength (520 nm), attributed to the reduction of pyrrolic nitrogen on CQDs [5]. These hybrid NPs exhibit improved in vitro biocompatibility in comparison with bare XRF contrast agents. Furthermore, the optical fluorescence–provided by Cy5.5 or CQDs–allows the localization of the NPs in the intracellular environment while the XRF signal from the core NPs is utilized for XFCT, in small animals, leading to both a microscopic and macroscopic bio-imaging contrast agent.

Multimodal contrast agents in biomedical imaging enable the collection of more comprehensive diagnostic information. In the present work, we design hybrid ruthenium-decorated superparamagnetic iron oxide nanoparticles (NPs) as the contrast agents for both magnetic resonance imaging (MRI) and X-ray fluorescence computed tomography (XFCT). The NPs are synthesized via a one-pot polyol hot injection route, in diethylene glycol. In vivo preclinical studies demonstrate the possibility of correlative bioimaging with these contrast agents. The complementarity allows accurate localization, provided by the high contrast of the soft tissues in MRI combined with the elemental selectivity of XFCT, leading to NP detection with high specificity and resolution. We envision that this multimodal imaging could find future applications for early tumor diagnosis, improved long-term treatment monitoring, and enhanced radiotherapy planning.

Nanoparticle (NP)-based contrast agents enabling different imaging modalities are sought for non-invasive bio-diagnostics. A hybrid material, combining optical and X-ray fluorescence is presented as a bioimaging contrast agent. Core NPs based on metallic rhodium (Rh) have been demonstrated to be potential X-ray Fluorescence Computed Tomography (XFCT) contrast agents. Microwave-assisted hydrothermal method is used for NP synthesis, yielding large-scale NPs within a significantly short reaction time. Rh NP synthesis is performed by using a custom designed sugar ligand (LODAN), constituting a strong reducing agent in aqueous solution, which yields NPs with primary amines as surface functional groups. The amino groups on Rh NPs are used to directly conjugate excitation-independent nitrogen-doped carbon quantum dots (CQDs), which are synthesized through citrate pyrolysis in ammonia solution. CQDs provided the Rh NPs with optical fluorescence properties and improved their biocompatibility, as demonstrated in vitro by Real-Time Cell Analysis (RTCA) on a macrophage cell line (RAW 264.7). The multimodal characteristics of the hybrid NPs are confirmed with confocal microscopy, and X-ray Fluorescence (XRF) phantom experiments.

Scalable synthetic strategies for high-quality and reproducible thermoelectric (TE) materials is an essential step for advancing the TE technology. We present here very rapid and effective methods for the synthesis of nanostructured bismuth telluride materials with promising TE performance. The methodology is based on an effective volume heating using microwaves, leading to highly crystalline nanostructured powders, in a reaction duration of two minutes. As the solvents, we demonstrate that water with a high dielectric constant is as good a solvent as ethylene glycol (EG) for the synthetic process, providing a greener reaction media. Crystal structure, crystallinity, morphology, microstructure and surface chemistry of these materials were evaluated using XRD, SEM/TEM, XPS and zeta potential characterization techniques. Nanostructured particles with hexagonal platelet morphology were observed in both systems. Surfaces show various degrees of oxidation, and signatures of the precursors used. Thermoelectric transport properties were evaluated using electrical conductivity, Seebeck coefficient and thermal conductivity measurements to estimate the TE figure-of-merit, ZT. Low thermal conductivity values were obtained, mainly due to the increased density of boundaries via materials nanostructuring. The estimated ZT values of 0.8-0.9 was reached in the 300-375 K temperature range for the hydrothermally synthesized sample, while 0.9-1 was reached in the 425-525 K temperature range for the polyol (EG) sample. Considering the energy and time efficiency of the synthetic processes developed in this work, these are rather promising ZT values paving the way for a wider impact of these strategic materials with a minimum environmental impact.