The highly ordered L10 hard-magnetic phase of the equiatomic FePt alloy is of significant interest for a great number of magnetic applications, ranging from the realization of micromagnets for integrated sensors to the deposition of thin layers for vertical recording media [1]. In this context, the development of wet deposition processes able to yield high-quality layers of FePt represents a topic of considerable industrial relevance. Even though several aqueous-based electrodeposition approaches have been developed for the manufacturing of FePt, most formulations evidenced substantial technological limitations, specifically connected to the use of water as solvent (hydrogen evolution, oxygen contamination of the deposit...). From this point of view, non-aqueous electrolytes represent a promising alternative for the electrosynthesis of metallic layers. These alternative solvents are characterized by attractive applicative properties: they present wide electrochemical windows, are simple to prepare, formulated from relatively cheap components, almost unreactive with water and, in most cases, biodegradable. Thanks to these properties, they have been widely employed for the electrodeposition of metals [2], alloys [3] or composites [4]. The present work describes the deposition of FePt from a non-aqueous electrolyte based on ethylene glycol, which presents potential advantages over water-based baths in terms of gas evolution reduction and purity improvement of the obtained coatings. Deposition is carried out using Fe(III) and Pt(IV) as precursors and ammonium chloride as additive to enhance the quality of the coatings and their compositional uniformity. In this way, equiatomic FePt thin films characterized by a good morphology are easily obtained. These layers are subsequently characterized to assess their morphology, phase composition and magnetic properties. After annealing at 600 °C, the microstructure changes and the disordered face centered cubic phase present in the as-plated alloy evolves into the highly magneto-crystalline anisotropic L10 phase. As a consequence, the coercivity of the layers reaches values in excess of 10 kOe. [1] Lodder et al.; Encyclopedia of Materials: Science and Technology, pp. 1-10 (2005) [2] Abbott et al.; Phys. Chem. Chem. Phys. 8, 4265-4279 (2006) [3] Bernasconi et al.; J. Phys. Chem. B 124(47), 10739-10751 (2020) [4] Rosoiu et al.; Metals 10(11), 1455 (2020)
In the last few decades, inkjet (IJ) printing evolved from a mere graphical and visual tool to a versatile methodology able to find application in a great number of industrial fields (e.g. electronics, display production, flexible electronics). The technology is based on the controlled emission of droplets from a nozzle. Such droplets, which contain the material of interest in the form of a solution or a dispersion, are deposited on a substrate, allowing thus controlled patterning. Thanks to its flexibility and efficiency, IJ proved to be one of the most promising technologies to pattern materials on a wide variety of rigid and flexible substrates. Recently, IJ found application also in the field of microfabrication. It was employed, for example, to manufacture microelectromechanical systems (MEMS) [1] or microelectronic components and sensors [2]. Another possible application of IJ, still not developed in the existing literature, is the production of magnetically guidable microrobots [3]. These can find application in a wide variety of fields, including for example micromanipulation, cell transport and drug delivery applications.Many applications of IJ in microfabrication, and microrobots production in particular, require the presence of conductive or magnetic layers to allow actuation or sensing. By employing IJ, however, it is difficult to obtain highly conductive and mechanically stable layers. From this point of view, the variety and the performances of IJ printed conductive and magnetic materials are in many cases limited. Metals IJ printing, for example, is normally based on the use of nanoparticle suspensions or on reactive IJ deposition [4]. Both methods, however, cannot outperform bulk metallic layers. To expand IJ applicability to micromanufacturing, we developed a novel approach to indirectly pattern bulk metallic microstructures by combining IJ printing and electroforming. The technique requires the presence of a conductive substrate. Initially, a layer of SU-8 photoresist is IJ printed [5] on the substrate to form a negative of the final pattern. Subsequently, the positive pattern is growth by mean of electrodeposition inside the negative SU-8 pattern. SU-8 is then removed, leaving an indirectly printed metal pattern. It is also possible to dissolve the substrate in a suitable aggressive solution, leaving thus freestanding electroformed planar structures. Moreover, this latter approach can be employed to transfer metal patterns on nonconductive substrates [6].We applied the approach described to the microfabrication of untethered functional microdevices inspired to the shape and behavior of water-striders (Gerridae). These insects exploit water surface tension to walk on the surface of shallow lakes and ponds. They are characterized by long legs, useful to distribute their weight on the water. Taking inspiration from Gerridae, we developed micromachined devices able to run on the air-water interface (insert in Figure 1). Initially, their negative pattern was printed on an aluminum substrate. Then,...
Two of the most crucial topics in modern medicine are medicines administration routes and their relative pharmacokinetics inside human body. The largest part of conventional drug delivery methodologies, like absorption through the gastrointestinal tract or intravenous injection, are generally based on the non-selective distribution of the active substance in the whole body, mediated by blood circulation. With these delivery methodologies, however, most of the drug reaches non-target parts of the body. This implies that higher dosages must be provided to reach the optimal concentration in the target organ, lowering administration efficacy and amplifying drug side-effects.To overcome these problematics, advanced administration strategies based on targeted delivery have been recently developed [1]. More specifically, drugs are released in controlled amounts only in correspondence of the target organ. This approach requires a superior temporal and spatial control over release, which is challenging to achieve. A possible solution to control drug delivery timing can be the use of properly designed hydrogels. Indeed, release from these biocompatible materials can be controlled through a variety of approaches [2]. For example, smart hydrogels can be tailored to release drugs only under specific conditions of pH, temperature ... Release rate can be efficiently tuned by controlling the structure and the chemistry of the hydrogels. On the other side, a possible key to allow spatial control over release can be the use of magnetically controlled microrobots [3]. These remotely controlled devices are able to perform different tasks in-vivo, including for example cell transport [4] and medicine delivery applications [5]. For the latter, they can be covered with drug releasing materials and wirelessly guided inside human body to perform administration only in close proximity of the target organ. Moreover, magnetic field is harmless for humans, allowing a limited invasivity of the microrobots in conjunction with a great manipulation precision.In this context, we describe the realization of magnetically guidable microdevices integrating smart hydrogel layers specifically tailored to perform controlled drug release. The microdevices are obtained employing additive manufacturing, specifically microstereolithography, in combination with wet metallization [6]. This approach is highly scalable and flexible and can yield micrometric sized objects at relatively low cost. To allow magnetic actuation, a CoNiP layer is applied by mean of wet metallization on the 3D printed devices. The same technique is employed also to deposit a gold layer to make the surface biocompatible. Finally, the surface is coated with the hydrogel and drug release performances are evaluated in-vitro.Two different strategies are investigated to control the drug release from the hydrogel. In the first, an alginate hydrogel is modified with click chemistry, binding the drug to the biopolymer chains by mean of a pH cleavable bond. In this way, release takes place onl...
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