National Institute Of Materials Physics - Romania

A methodology for the quantitative estimation of the drug loading of iron oxide-based magnetic nanoparticles by corroborating magnetometry and M & ouml;ssbauer spectroscopy investigations is reported. The proposed methodology is exemplified in the case of two series of nanoparticles, namely Fe3O4 nanoparticles covered with citric acid molecules and further functionalized with doxorubicin, and Fe3O4 nanoparticles covered with L-Cysteine molecules and further functionalized with doxorubicin. The general idea of the proposed methodology is to probe the real magnetic structure of the magnetic core via low-temperature M & ouml;ssbauer spectroscopy for the correct estimation of the spontaneous magnetization of the magnetic core. It subsequently uses the ratio between the spontaneous magnetization of the covered nanoparticles and that of the magnetic core for the reliable and nondestructive evaluation of the nanoparticle loading by organic molecules. Although the methodology is exemplified in the case of magnetite-based nanoparticles, it can be successfully considered for a large class of medicine-loaded Fe-containing magnetic nanoparticles where 57Fe M & ouml;ssbauer spectroscopy can be applied.

Biodegradable templates are sought for targeted antibiotic administration/delivery in bone infections to avoid detrimental reactions during bone regeneration. We investigated two key-aspects in this direction: 1) the optimal antibiotic delineation, with thermal stability equivalent to the temperature involved for templates preparation and 2) the antibacterial templates development by a two-step homogenization process. The selected antibiotic - ampicillin (AMP) was mechanically and then thermally mixed with the prime materials: poly(lactic acid) (PLA) - the polymeric matrix, biogenic bovine bone-derived hydroxyapatite (HA, particles <40 mu m), and graphene nanoplatelets (GnP, micrometric range). For the first time, all materials were used in simultaneous modulated ratios for the synthesis of PLA/AMP (1-5 wt.%)/HA (0-30 wt.%)/GnP (0-3 wt.%) composites. The influence of the concomitant materials modulation was surveyed through several assays. The FTIR-ATR spectroscopy depicted a three-level model of overlapping structures asserting the solid molecular cross-linking between all materials, without structural alterations induced to any material (XRD analysis). The addition of AMP to the PLA matrix caused a slight particle conglomeration, alleviated through GnP addition. The microporous HA particles supported the adhesion to the PLA matrix and promoted the AMP particles' entrapment/attachment. Linked to the enhanced wettability of the composite materials, the phosphate buffered saline solution (PBS) degradation profiles revealed a pronounced burst during the first 14-28 days of incubation and a long-term, low-level process hereafter. Thus, the formation of pores and cavities were signalled along with the HA particles' fragmentation. The released AMP (percentage) pictured an ascending trendline during the 24 h of analysis, at all targeted ratios. The preservation of AMP features at 200 degrees C was endorsed by the strong antibacterial activity of composite materials against Staphylococcus aureus (S. Aureus) growth and the medium response against Escherichia coli (E. Coli) - the higher the drug release, the higher the inhibitory effect on bacteria evolution.

In this work, we report for the first time the development and complex characterization of new bioceramics based on hydroxyapatite (HAp, Ca10(PO4)6(OH)2). On the other hand, the lyophilization process was used for the first time in this research. The samples were obtained by a modified coprecipitation method and were dried by lyophilization (lyophilized hydroxyapatite (HApLF) and lyophilized zinc-doped hydroxyapatite (5ZnHApLF)). Valuable information about the HApLF and 5ZnHApLF stability was obtained through nondestructive ultrasound measurements. The X-ray diffraction (XRD) studies revealed the phase and the effects of the incorporation of Zn ions into the HAp structure. The chemical composition of the samples was evaluated by energy dispersive X-ray analysis (EDS) and X-ray photoelectron spectroscopy (XPS). Information about the functional groups present in the HApLF and 5ZnHApLF was obtained using Fourier Transform Infrared Spectroscopy (FTIR) studies. The morphology of HApLF and 5ZnHApLF pellets was observed by scanning electron microscopy (SEM). The surface topography of HApLF and 5ZnHApLF pellets was studied with the aid of atomic force microscopy (AFM). Details regarding the roughness of the samples were also obtained using AFM topographies and SEM images. A complementary study was also carried out on a larger analysis surface using a Scanning Acoustic Microscope (SAM). The SAM was used for the first time to analyze the surface of HAp and 5ZnHAp pellets. The biological properties of the HApLF and 5ZnHApLF pellets was investigated with the aid of MG63 and human gingival fibroblasts (HGF-1) cell lines. The results of the cell viability assay highlighted that both the HApLF and 5ZnHApLF pellets exhibited good biological activity. Moreover, SEM and AFM studies were conducted in order to emphasize the development of MG63 and HGF-1 cells on the pellet's surface. Both SEM and AFM images depicted that the pellets' surface favored the cell attachment and development of MG63 and HGF-1 cells. Furthermore, the antimicrobial properties of the HApLF and 5ZnHApLF were evaluated against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Candida albicans ATCC 10231. The results of the antimicrobial assays highlighted that the 5ZnHApLF exhibited a strong antimicrobial activity against the tested microbial strains. The results of the biological assays suggested that the samples show great potential for being used in the development of novel materials for biomedical applications.

In this paper, we present the development of magnesium-doped hydroxyapatite in chitosan matrix (MHA_Ch) powder by an adapted coprecipitation method. The MHA_Ch powder was then deposited as thin layers by radio frequency magnetron sputtering. The MHA_Ch layers were exposed to various irradiation doses and immersed in Dulbecco's Modified Eagle's Medium (DMEM) for various time intervals. We report, for the first time, the effects of DMEM on irradiated layers of magnesium-doped hydroxyapatite in a chitosan matrix. The surface morphology of the layers before and after irradiation and immersion in DMEM was evaluated by SEM, AFM, and MM studies. Additionally, data about the functional groups present in the layers and the changes induced by exposure of the layers to irradiation and DMEM were obtained by FTIR studies. In vitro biological assays were conducted using an MG63 cell line (ATCC CRL1427). Our results suggest that the magnesium-doped hydroxyapatite in chitosan matrix layers may be suitable candidates for applications in the biomedical domain.

Magnesium-doped hydroxyapatite/chitosan composite coatings produced by the radio-frequency magnetron sputtering technique were exposed to 5 MeV electron beams of 8 and 30 Gy radiation doses in a linear electron accelerator. The surfaces of unirradiated layers are smooth, while the irradiated ones exhibit nano-structures with sizes that increase from 60 nm at a 8 Gy dose to 200 nm at a 30 Gy dose. Young's modulus and the stiffness of the layers decrease from 58.9 GPa and 10 mu N/nm to 5 GPa and 2.2 mu N/nm, respectively, when the radiation doses are increased from 0 to 30 Gy. These data suggest the diminishing of the contribution of the chitosan to the elasticity of the magnesium-doped hydroxyapatite/chitosan composite layers after electron beam irradiation. The biological capabilities of the coatings were assessed before and after their immersion in RPMI-1640 cell culture medium for 7 and 14 days, respectively, and further cultured with a MG63 cell line (ATCC CRL1427) in Dulbecco's Modified Eagle Medium supplemented with fetal bovine serum, penicillin-streptomycin, and L-glutamine. Thus, 1 mu m spherical structures were developed on the surfaces of the layers exposed to a 30 Gy radiation dose and immersed for 14 days in the RPMI-1640 biological medium. The molecular structures of all the RPMI-1640 immersed samples were modified by the growth of a carbonated hydroxyapatite layer characterized by a B-type substitution, as Fourier Transform Infrared Spectroscopy revealed. The biological assay proved the increased biocompatibility of the layers kept in RPMI-1640 medium and enhanced MG63 cell attachment and proliferation. Atomic force microscopy analysis indicated the elongated fibroblastic cell morphology of MG63 cells with minor alteration at 30 Gy irradiation doses as a result of layer biocompatibility modifications.

In the last decade, it has been observed that the field of biomaterials has gained the attention of the researchers. This study presents the physicochemical and biological properties of coatings based on chromium-doped hydroxyapatite (CrHAp) and chromium-doped hydroxyapatite enriched with amoxicillin (CrHApAx). The coatings were obtained for the first time using the dip coating technique, beginning from dense suspensions of CrHAp and CrHApAx. The obtained layers were then analyzed by various methods in order to have a comprehensive overview of their physicochemical properties. Stability studies performed using ultrasound measurements showed that the CrHAp suspension has very good stability (S = 6.8610-6 s-1) compared to double-distilled water. The CrHApAx suspension (S = 0.00025 s-1) shows good but weaker stability compared to that of the CrHAp suspension. Following XRD studies, a single hydroxyapatite-specific phase was observed in the CrHAp sample, while in the case of the CrHApAx sample, an amoxicillin-specific peak was also observed. The AFM results showed that the CrHAp coatings had a surface topography of a homogenous and uniform layer, with no significant cracks and fissures, while the CrHApAx coatings exhibited a surface morphology of homogenous layers formed of particles conglomerates. The biocompatibility of CrHAp and CrHApAx coatings was assessed using the MG63 cell line. The cytotoxicity of the coatings was evaluated by measuring cell viability with the aid of an MTT assay after 24, 48, and 72 h of incubation with the CrHAp and CrHApAx coatings. The results demonstrated that both CrHAp and CrHApAx coatings exhibited good biocompatibility for all the tested time intervals. The in vitro antibacterial activity of the coatings was also assessed against Pseudomonas aeruginosa 27853 ATCC (P. aeruginosa) bacterial cells. The potential of P. aeruginosa bacterial cells to adhere and develop on the surfaces of CrHAp and CrHApAx coatings was also investigated using AFM analysis. The findings of the biological assays suggest that CrHAp and CrHApAx coatings could be considered as promising candidates for biomedical applications, including the development of novel antimicrobial materials.

Due to their conductive properties and optoelectronic tunability, MXenes have revolutionized the area of electrocatalysis and active materials in supercapacitors. In comparison, there are only a few reports on MXenes as thermal catalysts for general organic reactions. Herein, the unprecedented catalytic activity of Ti3C2 MXene for the hydroamination of alkynes is reported, overcoming the limitations of poor activity, lack of selectivity, and stability, which are generally encountered in the solid catalysts known so far. In the case of Ti3C2, hydroamination exhibits almost complete selectivity for the anti-Markovnikov regioisomer, for both aliphatic amines and less-reactive aromatic amines. Ti3C2 also efficiently catalyzes intramolecular hydroamination, leading to the formation of indol heterocycles. The catalytic hydroamination of C-C multiple bonds is a reaction with complete atom efficiency that may form C-N bonds from convenient reagents. The maximum number of hydroamination sites on the Ti3C2 nanosheets is quantified by thermoprogrammed NH3 desorption. The measured TOF values are on the order of 102 h-1, with the highest TOF value being 350 h-1 for 1-hexyne hydroamination by n -butylamine. Therefore, Ti3C2 is among the few heterogeneous hydroamination catalysts studied, with its activity per site being comparable to the best hydroamination catalysts reported so far. Density functional theory calculations on the models indicate the cooperation of neighboring Ti atoms in the mechanism. Considering the compositional and structural versatility of MXenes, the present findings open the door for further application of MXenes in other general organic reactions.

Tungsten-copper (W-Cu) composites have a wide range of engineering applications, from arc-resistant electrodes and high-voltage electrical contacts to heat sinks for integrated circuits and plasma-facing components for fusion reactors. They combine high corrosion and erosion resistance, very good thermal and electrical conductivity, low thermal expansion, with good mechanical properties. However, the fabrication of such materials is limited in terms of shape complexity and the internal distribution of the individual phases. Furthermore, the dissimilar thermo-mechanical properties (melting temperature, thermal conductivity, coefficient of thermal expansion) of the constituent phases impose severe constraints on the fabrication and use of W-Cu composites. To overcome the challenges of component design and enable greater freedom in terms of composition, W-Cu composites were produced by a combination of additive manufacturing and liquid-melt infiltration (LMI). Porous W-lattice structures were manufactured by laser powder-bed fusion (LPBF) followed by infiltration with molten Cu. A series of composites was produced with Cu contents from 3 to 75 vol% and evaluated in terms of thermal, electrical, and mechanical properties. The LPBF-LMI W-Cu composites exhibited comparable thermo-mechanical properties to W-Cu materials manufactured using powder-metallurgical processing, but with an expanded composition range and shape complexity. Lower thermal expansion coefficients (4.5-5.8 x 10-6 K- 1) and an improved thermal stability of the Young's modulus, only a 27-33 GPa decline in the range 27-827 degrees C, were observed for all the compositions, which was ascribed to the W-phase connectivity in all the W-Cu composites, independent of the volume fraction of Cu.

Polymorphism determines significant variations in materials' properties by lattice symmetry variation. If they are stacked together into multilayers, polymorphs may work as an alternative approach to the sequential deposition of layers with different chemical compositions. However, selective polymorph crystallization during conventional thin film synthesis is not trivial; changes of temperature or pressure when switching from one polymorph to another during synthesis may cause degradation of the structural quality. The present work reports on the single-step ion-beam-assisted fabrication of multilayered polymorph structures while applying the disorder-induced ordering approach. The dynamic annealing of disorder may be tuned, during ion irradiation, toward self-assembling of several polymorph interfaces. Gallium oxide multilayers with two polymorph interface repetitions are obtained. The single-crystal structure of the polymorphs is maintained between interfaces, exhibiting repeatable crystallographic relationships and optical properties. These data pave the way for enhancing materials' functionalities using not previously conceived capabilities of ion beam technology.

We show in theory and experiment that in periodically patterned spintronic terahertz emitters (STEs), charge dynamics can modify the emission spectrum in a well-controlled way. Characterization of nanopatterned STEs at frequencies up to 30 THz shows that the STE emission spectrum systematically changes with emitter size. The spectral intensity exhibits significant reductions at frequencies below 4 THz, accompanied by pronounced dips at around 15 and 24 THz. While reduction of the STE size enhances the modulation of all features, it does not alter the dip frequencies. The effect originates from the charging of the structure's edges by terahertz currents, causing a backflow that interferes with the initially induced current pulse. An analytical model quantitatively reproduces these results and agrees well with the findings of control experiments. Our findings enable a detailed investigation of the charge dynamics in STEs and provide additional means for controlled shaping of STE emission spectra by nanopatterning.