Effective production of multifunctional magnetic-sensitive biomaterial by an extrusion-based additive manufacturing technique.

A calcium phosphate (CaP)-based scaffold used as synthetic bone grafts, which smartly combines precise dimensions, controlled porosity and therapeutic functions, presents benefits beyond those offered by conventional practices, although its fabrication is still a challenge. The sintering step normally required to improve the strength of the ceramic scaffolds precludes the addition of any biomolecules or functional particles before this stage. This study presents a proof of concept of multifunctional CaP-based scaffolds, fabricated by additive manufacturing from an innovative ink composition, with potential for bone regeneration, cancer treatment by local magnetic hyperthermia and drug delivery platforms. Highly loaded inks comprising iron-doped hydroxyapatite and ß-tricalcium phosphate powders suspended in a chitosan-based solution, in the presence of levofloxacin (LEV) as model drug and magnetic nanoparticles (MNP), were developed. The sintering step was removed from the production process, and the integrity of the printed scaffolds was assured by the polymerization capacity of the ink composite, using genipin as a crosslinking agent. The effects of MNP and LEV on the inks' rheological properties, as well as on the mechanical and structural behaviour of non-doped and iron-doped scaffolds, were evaluated. Magnetic and magneto-thermal response, drug delivery and biological performance, such as cell proliferation in the absence and presence of an applied magnetic field, were also assessed. The addition of a constant amount of MNP in the iron-doped and non-doped CaP-based inks enhances their magnetic response and induction heating, with these effects more pronounced for the iron-doped CaP-based ink. These results suggest a synergistic effect between the iron-doped CaP-based powders and the MNP due to ferro/ferrimagnetic interactions. Furthermore, the iron presence enhances human mesenchymal stem cell metabolic activity and proliferation.

A Magnetic Chameleon: Biocompatible Lanthanide Fluoride Nanoparticles with Magnetic Field Dependent Tunable Contrast Properties as a Versatile Contrast Agent for Low to Ultrahigh Field MRI and Optical Imaging in Biological Window.

A novel type of multimodal, magnetic resonance imaging/optical imaging (MRI/OI) contrast agent was developed, based on core-shell lanthanide fluoride nanoparticles composed of a ß-NaHoF4 core plus a ß-NaGdF4:Yb3+ , Tm3+ shell with an average size of ∼24 nm. The biocompatibility of the particles was ensured by a surface modification with poly acrylic acid (PAA) and further functionalization with an affinity ligand, folic acid (FA). When excited using 980 nm near infrared (NIR) radiation, the contrast agent (CA) shows intense emission at 802 nm with lifetime of 791±3 µs, due to the transition 3 H4 →3 H6 of Tm3+ . Proton nuclear magnetic relaxation dispersion (1 H-NMRD) studies and magnetic resonance (MR) phantom imaging showed that the newly synthesized nanoparticles, decorated with poly(acrylic acid) and folic acid on the surface (NP-PAA-FA), can act mainly as a T1 -weighted contrast agent below 1.5 T, a T1 /T2 dual-weighted contrast agent at 3 T, and as highly efficient T2 -weighted contrast agent at ultrahigh fields. In addition, NP-PAA-FA showed very low cytotoxicity and no detectable cellular damage up to a dose of 500 µg mL-1 .

Probing T1-T2 interactions and their imaging implications through a thermally responsive nanoprobe.

The complex and specialised diagnostic process through magnetic resonance imaging (MRI) could be simplified with the implementation of dual T1-T2 contrast agents. T1- and T2-weighted MR are compatible modalities, and co-acquisition of contrast enhanced images in both T1 and T2 will drastically reduce artefacts and provide double-checked results. To date, efforts in the development of dual MRI probes have provided inconsistent results. Here we present the preparation and relaxometric study of a dual T1-T2 MRI probe based on superparamagnetic nanoparticles, paramagnetic Gd3+ chelates and pNIPAM (poly(N-isopropylacrylamide)), in which the distance between paramagnetic and superparamagnetic species can be modulated externally via temperature variations. Such a probe alleviates traditional nanotechnology limitations (e.g. batch to batch variability) as comparisons can be established within a single probe.

Green synthesis of multimodal 'OFF-ON' activatable MRI/optical probes.

Diagnosis by MRI is frequently non-trivial due to the low sensitivity of the technique. Signal enhancing contrast agents (CAs) are used to aid in the analysis of MR images. We present here a simple protocol for the preparation of responsive CAs based on Mn nanosheets. Mn nanostructures presented here undergo a chemical and structural change in the presence of altered physiological conditions that activate their signal. This strategy allows for a reduction of background, increasing the sensitivity of the technique. The simple synthetic protocol followed allows for the combination of the nanosheets with reporter molecules for other imaging techniques, like carbon quantum dots for optical imaging.

Surface functionalization superparamagnetic nanoparticles conjugated with thermoresponsive poly(epsilon-lysine) dendrons tethered with carboxybetaine for the mild hyperthermia-controlled delivery of VEGF.

UNLABELLED: Vascular endothelial growth factor (VEGF) is the growth factor responsible for the triggering of angiogenesis, the process of blood vessel formation supporting the long-term viability of any repaired or regenerated tissue. As the growth factor is effective only when concentration gradients are generated, new shuttles need to be developed that ensure both the control of gradients at the site of tissue repair and the release of VEGF at physiological levels. Magnetic hyperthermia is the production of heat induced by magnetic materials through their exposure to an external oscillating magnetic field. In this paper, magnetic nanoparticles capable of generating controllable hyperthermia were functionalised with hyperbranched poly(epsilon-lysine) peptides integrating in their core parallel thermoresponsive elastin-like peptide sequences and presenting an uppermost branching generation tethered by the zwitterionic amino acid carboxybetaine. The results show that these functionalised magnetic nanoparticles avidly bind VEGF and release it only upon generation of mild-hyperthermic pulses generated by oscillating magnetic filed. The VEGF release occurred in a temperature range at which the elastin-like peptides collapse. It is proposed that, through the application of an external magnetic field, these magnetic carriers could generated gradients of VEGF in vivo and allow its tuned delivery in a number of clinical applications. STATEMENT OF SIGNIFICANCE: The present paper for the first time reveals the possibility to control the delivery of VEGF through mild hyperthermia stimuli generated by a oscillating magnetic field. To this purpose, magnetic nanoparticles of high size homogeneity and coated with a thin coating of poly(acrylic acid) were functionalised with a novel class of poly(epsilon lysine) dendrimers integrating in their structure a thermoresponsive amino acid sequence mimicking elastin and exposing at high density a zwitterionic modified amino acid, the carboxybetaine, known to be able to bind macromolecules. Physicochemical and biochemical characterisation elegantly show the link between the thermal properties of the nanoparticles and of the dendrimer change of conformation and how this enable the release of VEGF at temperature values compatible with the growth factor stability.

Effect of magnetic hyperthermia on the structure of biofilm and cellular viability of a food spoilage bacterium.

This work evaluated the effect of magnetic hyperthermia (MH) on planktonic cells and biofilms of a major food spoilage bacterium Pseudomonas fluorescens and its performance compared to a conventional direct heating (DH) technique. The results showed that MH had a greater and faster bactericidal effect, promoting a significant reduction in cell viability (≥3 Log CFU) in planktonic and biofilm cells, and leading to a complete eradication of planktonic cells at 55 °C (after only ~8 min). Accordingly, when comparing the same final temperatures, MH was more harmful to the integrity of cell membranes than DH, as observed in confocal laser scanning microscope images. Additionally, scanning electron microscope images revealed that exposure to MH had promoted modifications of the bacterial cell surface as well as of the structure of the biofilm. These results present the possibility of using MH out of the biomedical field as a potential disinfection method in food-related environments.

Magnetic poly(ε-caprolactone)/iron-doped hydroxyapatite nanocomposite substrates for advanced bone tissue engineering.

In biomedicine, magnetic nanoparticles provide some attractive possibilities because they possess peculiar physical properties that permit their use in a wide range of applications. The concept of magnetic guidance basically spans from drug delivery and hyperthermia treatment of tumours, to tissue engineering, such as magneto-mechanical stimulation/activation of cell constructs and mechanosensitive ion channels, magnetic cell-seeding procedures, and controlled cell proliferation and differentiation. Accordingly, the aim of this study was to develop fully biodegradable and magnetic nanocomposite substrates for bone tissue engineering by embedding iron-doped hydroxyapatite (FeHA) nanoparticles in a poly(ε-caprolactone) (PCL) matrix. X-ray diffraction analyses enabled the demonstration that the phase composition and crystallinity of the magnetic FeHA were not affected by the process used to develop the nanocomposite substrates. The mechanical characterization performed through small punch tests has evidenced that inclusion of 10 per cent by weight of FeHA would represent an effective reinforcement. The inclusion of nanoparticles also improves the hydrophilicity of the substrates as evidenced by the lower values of water contact angle in comparison with those of neat PCL. The results from magnetic measurements confirmed the superparamagnetic character of the nanocomposite substrates, indicated by a very low coercive field, a saturation magnetization strictly proportional to the FeHA content and a strong history dependence in temperature sweeps. Regarding the biological performances, confocal laser scanning microscopy and AlamarBlue assay have provided qualitative and quantitative information on human mesenchymal stem cell adhesion and viability/proliferation, respectively, whereas the obtained ALP/DNA values have shown the ability of the nanocomposite substrates to support osteogenic differentiation.