Adjustable wettability is important for various fields, such as droplet manipulation and controlled surface adhesion. Herein, we present high-resolution 3D stretchable structures with tunable superhydrophobicity, fabricated by a stereolithography-based printing process. The printing compositions comprise nonfluorinated monomers based on silicone urethane with dispersed hydrophobic silica particles. 3D lotus-like structures were designed and printed, having microsize pillars located at the external surfaces, with controlled dimensions and interspacing. The design of the pillars and the presence of the hydrophobic silica particles resulted in superhydrophobicity due to the surface structuring and entrapment of air between the pillars. The best structures display a contact angle of 153.3° ± 1.3° and rolling angle of 3.3° ± 0.5°, and their self-cleaning, water repellency, and buoyancy are demonstrated. The durability of the structure over time, water immersion, and heat exposure were tested, confirming the preservation of superhydrophobicity under these conditions. Upon stretching the surfaces, the interpillar distances change, thus enabling tuning the wetting properties and achieving good control over the contact and rolling angles, while the stretching-induced superhydrophobicity is reversible. This approach can expand the potential applications of superhydrophobic soft materials to fields requiring control over the wetting properties, including soft robotics, biomedical devices, and stretchable electronics.

A novel approach, i.e., Continuous Material Deposition on Filaments (CMDF), for the incorporation of active materials within 3D-printed structures is presented. It is based on passing a filament through a solution in which the active material is dissolved together with the polymer from which the filament is made. This enables the fabrication of a variety of functional 3D-printed objects by fused deposition modeling (FDM) using commercial filaments without post-treatment processes. This generic approach has been demonstrated in objects using three different types of materials, Rhodamine B, ZnO nanoparticles (NPs), and Ciprofloxacin (Cip). The functionality of these objects is demonstrated through strong antibacterial activity in ZnO NPs and the controlled release of the antibiotic Cip. CMDF does not alter the mechanical properties of FDM-printed structures, can be applied with any type of FDM printer, and is, therefore, expected to have applications in a wide variety of fields.

Piezoelectric materials have found widespread use in miniaturized sensors and actuators due to their ability of mutual conversion of mechanical and electric energy. However, current fabrication techniques for these materials are limited to either bulky structures or thin films, restricting the potential that could arise from developing devices with more intricate geometries. Here, we have developed particle-free piezoelectric ink and successfully employed in 3D printing complex barium titanate (BTO) devices using Digital Light Processing technology. The sol–gel process overcomes the viscosity and light scattering issues associated with the slurry traditionally used in 3D printing of piezoelectric ceramic materials. Printed BTO exhibits a remarkable piezoelectric coefficient of 50 pm/V and is utilized to create 3D micrometric structures for applications as both active devices, such as actuators, and passive devices, including displacement sensors and energy harvesters. Furthermore, the flexibility in device fabrication enabled us to 3D print metamaterial piezoelectric structures, designed to concentrate mechanical stress, thereby enhancing the electrical response compared to conventional bulk structures. This research not only advances the field by overcoming fabrication challenges but also opens avenues for creating innovative devices. The design freedom afforded by additive manufacturing technology further underscores the potential for groundbreaking developments in this domain.

Many optoelectronic devices, such as solar cells and LEDs, require materials that possess both transparency and conductivity. Indium tin oxide (ITO), the most commonly used transparent conductor, is limited to flat thin films and, therefore, cannot be used in 3D electronics. Herein, we present the fabrication of complex 3D ITO structures at sub-micron resolution via multiphoton absorption polymerization (MAP), a vat photopolymerization technology, by combining sol-gel chemistry and radical polymerization. Following the MAP fabrication, heat treatment is applied to convert the gel into a ceramic ITO. The sintering temperature affects the porosity, electrical conductivity, and transparency of the printed ITO structures. Electrical conductivity was measured for printed objects sintered at temperatures starting at 700 °C up to 1150 °C with a maximum bulk conductivity of 14.47 ± 1.54 S/cm at 1000 °C and maximal transparency above 90 %. Enabling the fabrication of full 3D conductive ITO micro-structures via MAP, this work unlocks new possibilities and perspectives for the fabrication of 3D optoelectronic devices with transparent and conductive components.

Traditional printing compositions for stereolithography (SLA), a vat photopolymerization technology, rely on light-sensitive photoinitiators (PIs) to initiate cross-linking reactions. Here, we propose a new approach for printing in which the polymerisation occurs locally with carbon nanotubes (CNTs), which function as photothermal converters combined with low-cost thermal initiators (TIs). The irradiation is performed at near-infrared (NIR), which enables deep light penetration, and polymerisation in black compositions, thus increasing the printing throughput. We demonstrate the control over polymerisation kinetics, printing resolution and cure depth, achieving very large printable layer thickness. The CNT photoconvertors can be used in both nonaqueous and aqueous systems, while the latter addresses the limited availability of water-soluble PIs for printing in water. The CNT enables dual use, initiating polymerisation and printing composite materials. This approach presents an advancement in SLA-based technologies, avoiding the use of conventional PIs and thus broadening the scope of 3D printing applications.

A novel method is presented for fabricating 3D-printed Cr³⁺-doped α-Al₂O₃ complex structures, known as Ruby, using digital light processing (DLP) 3D printing and sol-gel reactions based on solutions only. The aqueous printing solution comprises aluminum and chromium chloride as the sol-gel precursor and acrylic acid (AA) as the polymerizable component. After photopolymerization, aging, and sintering at 1150°C, structures shrink up to 28±7%, achieving a final printing resolution of 55.7±0.7 μm, surpassing the nominal printer’s resolution of 200 μm. Characterization includes X-ray diffraction, scanning electron microscopy, UV-Vis, and fluorescence measurements, revealing crystalline Cr:α-Al₂O₃ composition emitting at 693 nm. The structures exhibit maximum compression stress of 89±3 MPa and microhardness of 340-500 HV, showcasing potential applications in thermal insulation, jewelry, and mechanical uses.

Fabrication of glass with complex geometric structures by digital additive manufacturing (3D printing) presents a paradigm shift in glass design and molding processes. Till now, 3D printing glasses have suffered from limited printed glass materials and the low resolution of particle-based or fused glass technologies. Herein, a high-resolution 3D printing of transparent nanoporous glass is presented, by the combination of transparent photo-curable sol-gel printing compositions and vat photopolymerization technology (Digital Light Processing, DLP). Multi-component transparent glass, including binary, ternary, and quaternary oxide nanoporous glass objects with complex shapes, high spatial resolutions, and multi-oxide chemical compositions are fabricated, by DLP printing and subsequent sintering process. We successfully demonstrated the photoluminescence and hydrophobic modification of 3D printed glass objectives. This work extends the scope of 3D printing to transparent nanoporous glasses with complex geometry and facile functionalization, making them available for a wide range of applications.

Rapid deployment of automation in today's world has opened up exciting possibilities in the realm of design and fabrication of soft robotic grippers endowed with sensing capabilities. Herein, a novel design and rapid fabrication by 3D printing of a mechano-optic force sensor with a large dynamic range, sensitivity, and linear response, enabled by metamaterials-based structures, is presented. A simple approach for programming the metamaterial's behavior based on mathematical modeling of the sensor under dynamic loading is proposed. Machine learning models are utilized to predict the complete force–deformation profile, encompassing the linear range, the onset of nonlinear behavior, and the slope of profiles in both bending and compression-dominated regions. The design supports seamless integration of the sensor into soft grippers, enabling 3D printing of the soft gripper with an embedded sensor in a single step, thus overcoming the tedious and complex and multiple fabrication steps commonly applied in conventional processes. The sensor boasts a fine resolution of 0.015 N, a measurement range up to 16 N, linearity (adj. R²–0.991), and delivers consistent performance beyond 100 000 cycles. The sensitivity and range of the embedded mechano-optic force sensor can be easily programmed by both the metamaterial structure and the material's properties.

Soft grippers are garnering increasing attention for their adeptness in conforming to diverse objects, particularly delicate items, without warranting precise force control. This attribute proves especially beneficial in unstructured environments and dynamic tasks such as food handling. Human hands, owing to their elevated dexterity and precise motor control, exhibit the ability to delicately manipulate complex food items, such as small or fragile objects, by dynamically adjusting their grasping configurations. Furthermore, with their rich sensory receptors and hand-eye coordination that provide valuable information involving the texture and form factor, real-time adjustments to avoid damage or spill during food handling appear seamless. Despite numerous endeavors to replicate these capabilities through robotic solutions involving soft grippers, matching human performance remains a formidable engineering challenge. Robotic competitions serve as an invaluable platform for pushing the boundaries of manipulation capabilities, simultaneously offering insights into the adoption of these solutions across diverse domains, including food handling. Serving as a proxy for the future transition of robotic solutions from the laboratory to the market, these competitions simulate real-world challenges. Since 2021, our research group has actively participated in RoboSoft competitions, securing victories in the Manipulation track in 2022 and 2023. Our success was propelled by the utilization of a modified iteration of our Retractable Nails Soft Gripper (RNSG), tailored to meet the specific requirements of each task. The integration of sensors and collaborative manipulators further enhanced the gripper’s performance, facilitating the seamless execution of complex grasping tasks associated with food handling. This article encapsulates the experiential insights gained during the application of our highly versatile soft gripper in these competition environments.

Vertical farming has emerged as a sustainable, efficient, and climate-resilient food production method, which can improve food security. In most commercial vertical farms, harvesting is carried out manually, which are labor-intensive and costly. Numerous robotic grippers solutions have been developed for harvesting. However, they have limitations like restricted adaptivity, excessive mechanical stress on target, and poor accessibility, hindering their adoption for harvesting. Here, we present a tendon-driven gripper equipped with a capacitance-based contact sensor array. The proposed gripper can grow and twine around the target vegetable and adjust the tightness of its grip based on number of contacts. The proposed gripper can generate 4 to 10 N pulling force on bok choy and can also grip various gourds, leafy and podded vegetables. This work paves the way for harvesting automation in vertical farms. Apart from agriculture field, the smart gripper can also be used to grasp objects with various size, shape and weight in warehouse, and food & beverage industry.

Hybrid perovskites show piezoelectric properties due to polarization and centro-symmetry breaking of PbX₆ pyramids (X = I-, Br-, Cl-). This study examines the piezoelectric response of quasi-2D perovskites using various barrier molecules: benzyl amine (BzA), phenylethyl amine (PEA), and butyl diamine (BuDA). Utilizing piezoelectric force microscopy measurements, we determine the piezoelectric coefficient (d₃₃) where BuDA exhibits a substantial response with values of 147 pm V^–1 for n = 5, better than the other quasi-2D and 3D perovskite counterparts. Density functional theory calculations reveal distorted bond angles in the PbBr₆ pyramids for quasi-2D perovskites, enhancing symmetry breaking. Additionally, polarizabilities and dielectric constants, derived from ab initio many-body perturbation theory, are highest for BuDA, followed by PEA and BzA, aligning with experimental results. We demonstrate pressure sensor performance, emphasizing the quicker capacitance decay time of the quasi-2D perovskite based on BuDA. This research underscores the impact of perovskite dimensionality on piezoelectricity, paving the way for the development of sensitive and wide-ranging pressure sensors.

Additive manufacturing technologies based on stereolithography rely on initiating spatial photopolymerization by using photoinitiators activated by UV-visible light. Many applications requiring printing in water are limited since water-soluble photoinitiators are scarce, and their price is skyrocketing. On the contrary, thermal initiators are widely used in the chemical industry for polymerization processes due to their low cost and simplicity of initiation by heat at low temperatures. However, such initiators were never used in 3D printing technologies, such as vat photopolymerization stereolithography, since localizing the heat at specific printing voxels is impossible. Here we propose using a thermal initiator for 3D printing for localized polymerization processes by near-infrared and visible light irradiation without conventional photoinitiators. This is enabled by using gold nanorods or silver nanoparticles at very low concentrations as photothermal converters in aqueous and non-aqueous mediums. Our proof of concept demonstrates the fabrication of hydrogel and polymeric objects using stereolithography-based 3D printers, vat photopolymerization, and two-photon printing.