Alberto Riminucci

A novel route in bone tissue engineering: Magnetic biomimetic scaffolds

In recent years, interest in tissue engineering and its solutions has increased considerably. In particular, scaffolds have become fundamental tools in bone graft substitution and are used in combination with a variety of bio-agents. However, a long-standing problem in the use of these conventional scaffolds lies in the impossibility of re-loading the scaffold with the bio-agents after implantation. This work introduces the magnetic scaffold as a conceptually new solution. The magnetic scaffold is able, via magnetic driving, to attract and take up in vivo growth factors, stem cells or other bio-agents bound to magnetic particles. The authors succeeded in developing a simple and inexpensive technique able to transform standard commercial scaffolds made of hydroxyapatite and collagen in magnetic scaffolds. This innovative process involves dip-coating of the scaffolds in aqueous ferrofluids containing iron oxide nanoparticles coated with various biopolymers. After dip-coating, the nanoparticles are integrated into the structure of the scaffolds, providing the latter with magnetization values as high as 15 emu g(-)(1) at 10 kOe. These values are suitable for generating magnetic gradients, enabling magnetic guiding in the vicinity and inside the scaffold. The magnetic scaffolds do not suffer from any structural damage during the process, maintaining their specific porosity and shape. Moreover, they do not release magnetic particles under a constant flow of simulated body fluids over a period of 8 days. Finally, preliminary studies indicate the ability of the magnetic scaffolds to support adhesion and proliferation of human bone marrow stem cells in vitro. Hence, this new type of scaffold is a valuable candidate for tissue engineering applications, featuring a novel magnetic guiding option.

Electrically Programmable Magnetoresistance in Multifunctional Organic-Based Spin Valve Devices

5] In this paper we show that an electrically controlled magne-toresistance can be easily achieved in organic devices by com-bining magnetic bistability (spin valve) and electrical memory effects into an interacting multifunctional implementation. Electrical resistive switching effects in organic-based devices have recently received widespread attention

A Single-Device Universal Logic Gate Based on a Magnetically Enhanced Memristor

Memristors are one of the most promising candidates for future information and communications technology (ICT) architectures. Two experimental proofs of concept are presented based on the intermixing of spintronic and memristive effects into a single device, a magnetically enhanced memristor (MEM). By exploiting the interaction between the memristance and the giant magnetoresistance (GMR), a universal implication (IMP) logic gate based on a single MEM device is realized.

Hanle effect missing in a prototypical organic spintronic device

We investigate spin precession (Hanle effect) in the prototypical organic spintronic giant magnetoresistance device La0.7Sr0.3MnO3/tris(8-hydroxyquinoline)/AlOx/Co. The Hanle effect is not observed in measurements taken by sweeping a magnetic field at different angles from the plane of the device. As possible explanations we discuss the tilting out of plane of the magnetization of the electrodes, exceptionally high mobility, or hot spots. Our results call for a greater understanding of spin injection and transport in such devices.

Regenerable Resistive Switching in Silicon Oxide Based Nanojunctions

A nanomemristor based on SiO(2) is fabricated in situ with spatial control at the nanoscale. The proposed system exhibits peculiar properties such as the possibility to be regenerated after being stressed or damaged and the possibility to expose the metal and the oxide interfaces by removing the top electrodes.

Direct deposition of magnetite thin films on organic semiconductors

Technological procedures able to produce high quality electrodes from magnetic oxides in vertical organic-inorganic hybrid devices is a challenging task in the field of organic spintronics. Thin films of magnetite (Fe3O4) have been successfully grown directly on top of organic semiconductor layers, tris(8-hydroxyquinoline)aluminium(III) (Alq3), by pulsed-electron ablation technique. The films show ferromagnetic behavior and good structural quality, properties detected by magneto-optical Kerr effect, superconductor quantum interference device, micro-Raman spectroscopy, and Atomic Force Microscopy. The ferromagnetic behavior persists even for 10nm thick films. Charge injection at magnetite-organic interface has been finally demonstrated by detecting electroluminescence from Alq3.

Multilayered Magnetic Gelatin Membrane Scaffolds

A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 °C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial-magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications.

Pentacene thin films on ferromagnetic oxide: Growth mechanism and spintronic devices

We investigated the growth mechanism of pentacene thin films on La0.7Sr0.3MnO3. A diffusion limited, thermally activated growth was found. Pentacene molecules formed flat islands that were a few microns in size and whose growth during deposition showed a strong anisotropy. We extracted a nucleation energy of 0.65 ± 0.05 eV and a diffusion barrier energy of 0.7 ± 0.2 eV. We also estimated a critical nucleus size of three molecules. We show that vertical pentacene-based spintronic devices with La0.7Sr0.3MnO3 and Co electrodes demonstrated magnetoresistive effects up to room temperature. We also propose a route for pentacene-based spintronic devices improvement.

Electrode artifacts in low resistance organic spin valves

Artifacts can originate from the inherent shortcomings of the cross bar configuration, when the resistance of the device is small compared to that of one of the electrodes. This is particularly relevant to the field of organic spintronics, in which at least one recent work overlooked this effect. We use a simplified one-dimensional resistor model and a full three-dimensional finite element method simulation to show that an increase in the resistance of one electrode appears as a decrease of the measured resistance. We found that the model agrees qualitatively but not quantitatively with observation.

Oxygen Impurities Link Bistability and Magnetoresistance in Organic Spin Valves

Vertical crossbar devices based on manganite and cobalt injecting electrodes and a metal-quinoline molecular transport layer are known to manifest both magnetoresistance (MR) and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the MR and magnetic modulation of bistability. To explain the device functionality, we identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with the chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrate under voltage application, resulting in a modification of the electronic properties of the organic material and of the oxidation state of the interfacial layer with the ferromagnetic contacts. Variable oxygen doping of the organic molecules represents the key element for correlating bistability and MR, and our measurements provide the first experimental evidence in favor of the impurity-driven model describing the spin transport in organic semiconductors in similar devices.