Optical Quality Resorbable Calcium-Phosphate Glasses for Biophotonic Applications

Recently developed calcium-phosphate glass formulations are proposed in this chapter as a new class of materials for biomedical optics and photonics. The glasses have been designed and carefully prepared in our laboratory to be dissolvable in biological fluids while being optically transparent, mechanically reliable both in dry and humid environments, and suitable for both preform extrusion and fiber drawing. Optical fibers have been drawn from these glasses using our custom-made induction heated drawing tower and showed attenuation loss values from one to two orders of magnitude lower than the counterpart polymeric-based bioresorbable devices reported in literature. In addition, the optical fibers have been implanted in living rats for several weeks and no clinical signs of any adverse effect have been found. Results on the inscription and characterization of different types of fiber Bragg grating-based optical filters will be also shown, together with the demonstration of the suitability of the above-mentioned bioresorbable optical fibers for time-domain diffuse optical spectroscopy

High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers

In recent years, the increasing need of airborne LIght Detection And Ranging (LIDAR) systems for environmental monitoring and surveillance has noticeably boosted the development of compact eye-safe optical amplifiers. In this scenario, multi-component phosphate glasses can be regarded as ideal candidate materials as they can be doped with a large amount of rare-earth (RE) ions without clustering, thus enabling the realization of few-cm long optical amplifier sections featured by high optical gain per unit length. In this work we will report the ongoing activities and the recent results obtained by our research group on the design, processing and characterization of a series of Yb-Er co-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The physical, thermo-mechanical, optical and spectroscopic properties of the prepared glasses have been thoroughly investigated

Phosphate glass fibrous scaffolds: tailoring of the properties and improvement of the bioactivity through the incorporation of mesoporous glasses

Introduction. Synthetic bone scaffolds are proposed as an alternative to the use of bone grafting technique for bone regeneration. Porous scaffold obtained from glass fibres randomly arranged into a mould shows an interconnected porosity generated by the free space between fibres and they do not need of any further material or processing step before sintering. In this work, a resorbable phosphate glass was selected for the fibre drawing and bioactive mesoporous glasses with different morphology and size were incorporated into the fibrous scaffold to combine the resorption property of the fibres with the bioactivity of the mesoporous powders. Materials and methods. Fibres of a TiO2-containing phosphate glass (TiPS2.5) were fabricated following the preform drawing approach as described elsewhere [1]. A dense silica-based bioactive glass (CEL2) [2] was produced by melt quenching as reference sample. Spherical micro-sized mesoporous glass based on SiO2-CaO system (SD_MBG) was produced by an aerosol-assisted spray-drying technique [3]. Cu-containing (85SiO2-13CaO-2CuO, % mol, referred as Cu_BGn2%) mesoporous glass nanoparticles were synthetized by an ultra-sound assisted sol-gel method to impart antibacterial properties. To fabricate the fibrous scaffolds, the selected powder and phosphate glass fibres, cut at precise length, were placed in a beaker containing 2 ml of ethanol. After ethanol evaporation, the powder/fibre mixture was randomly placed inside a zirconia cylindrical mould [4]. After the thermal treatment, the scaffolds were analyzed through micro-CT in order to investigate their inner structure. Furthermore, their ability to form hydroxyapatite was studied by soaking them in a simulated body fluid (SBF). The scaffold morphology before and after immersion in SBF was studied by FESEM. Results and discussion. FESEM micrographs show that CEL2 are not well incorporated into the fibre surface. On the contrary, SD-MBG (Figure 1.a, Figure 1.b and Figure 1.d) and Cu_BGn2% particles homogeneously cover the whole surface. Micro-CT analysis did not reveal the presence of powder agglomerates for all the observed scaffolds and showed a homogeneous porosity of 58 vol.% for CEL2/fibre scaffold, 53 vol.% for SD_MBG/scaffold (Figure 1.c) and 33% for Cu_BGn2%/scaffold. In CEL2/fibre scaffolds, glass particles were removed during soaking in SBF, leaving some pits on the fibre surface: FESEM analysis revealed few particles still anchored to the scaffold surface after 7 days. On the contrary, after 7 days in SBF, SD-MBG and Cu_BGn2% particles were clearly visible on the surface of the scaffolds and after 1 day of soaking in SBF, they appeared (Figure 2) fully covered with a HA layer, showing the typical "cauliflower-like" morphology. Conclusion. The incorporation of mesoporous bioactive glass powder in the phosphate glass fibrous scaffold resulted to be a very interesting strategy to impart multifunctional properties to the scaffold. These promising results encourage further investigation in order to fully exploit the ability of mesoporous particles to act as a system for smart release of therapeutic ions and drugs

Multifunctional bioresorbable phosphate glass optical fibers for theranostics

We report on the design and development of microstructured phosphate glass optical fibers for minimally invasive diagnosis and therapy. We discuss preliminary results of fiber drawing and characterization

Single-frequency, pulsed Yb3+-doped multicomponent phosphate power fiber amplifier

High-power, single-frequency, pulsed fiber amplifiers are required in light detection and ranging, coherent laser detection, and remote sensing applications to reach long range within a short acquisition time. However, the power-scaling of these amplifiers is limited by nonlinearities generated in the optical fibers, in particular by stimulated Brillouin scattering (SBS). In this regard, the use of multicomponent phosphate glasses maximizes the energy extraction and minimizes nonlinearities. Here, we present the development of a single-stage, hybrid, pulsed fiber amplifier using a custom-made multicomponent Yb-doped phosphate fiber. The performance of the phosphate fiber was compared to a commercial Yb-doped silica fiber. While the latter showed SBS limitation at nearly 6.5 kW for 40 cm length, the maximum achieved output peak power for the multicomponent Yb-doped phosphate fiber was 11.7 kW for 9 ns pulses using only 20 cm with no sign of SBS

Bioresorbable optical fiber Bragg gratings

We demonstrate, for the first time, an inscription and wet dissolution study of Bragg gratings in a bioresorbable calcium-phosphate glass optical fiber. Bragg gratings, with average refractive index changes of 5.8 × 10^−4, were inscribed using 193 nm excimer laser radiation. Results on the dissolution of the irradiated fiber in simulated physiological conditions are presented after immersing a tilted Bragg grating in a phosphate buffered saline solution for 56 h; selective chemical etching effects are also reported. The investigations performed pave the way toward the use of such phosphate glass fiber Bragg gratings for the development of soluble photonic sensing probes for the efficient in vivo monitoring of vital mechanical or chemical parameters

Structural and spectral characterisation of Er3+ and Nd3+ doped Ga-La-S-Se glasses

In this work, the spectroscopy of Er3+ and Nd3+ doped Se-GLS glasses was studied. A structural comparison between doped and non-doped samples was done to assess the differences between the glasses. For this comparison, Raman spectroscopy and thermal analysis were employed. The spectral properties of the samples were studied in order to identify the mechanisms responsible for quenching the fluorescence lifetime of the dopants. In particular, cross-relaxation and concentration quenching were observed in Nd3+ doped samples, whilst co-operative upconversion, radiation trapping and concentration quenching were observed in Er3+ doped samples. The results obtained demonstrated the fundamental role of the phonon energy in the mechanism of fluorescence. The low phonon energy of chalcogenides decreased the rate of non-radiative processes promoting co-operative upconversion. This effect could be exploited to design new lasers and sensitizers for solar energy harvesters

High-power laser testing of calcium-phosphate-based bioresorbable optical fibers

Silica optical fibers are employed in endoscopy and related minimally invasive medical methods thanks to their good transparency and flexibility. Although silicon oxide is a biocompatible material, its use involves a serious health risk due to its fragility and the fact that potential fiber fragments can freely move inside the body without the possibility of being detected by conventional methods such as X-ray imaging. A possible solution to this issue can be the development of optical fibers based on bioresorbable (i.e., biodegradable and biocompatible) materials, which exhibit the important benefit of not having to be explanted after their functionality has expired. The optical power transmission tests of recently developed single-mode (SM) and multi-mode (MM) bioresorbable optical fibers based on calcium-phosphate glasses (CPGs) are here reported. A continuous-wave (CW) fiber laser at 1080 nm with output power up to 13 W and picosecond laser sources at 515 and 1030 nm with MW pulse peak power were used to test the transmission capabilities of the CPG fibers. No degradation of the CPG fibers transmission under long-term illumination by CW laser was observed. A laser-induced damage threshold (LIDT) at a fluence higher than 0.17 J/cm2 was assessed with the picosecond laser sources

Characterization of sub-nanosecond pulsed laser amplification with Er:Yb co-doped phosphate glass fibers

We present an experimental characterization of the amplification of sub-nanosecond duration laser pulses at a wavelength of 1538 nm in short custom-made Er:Yb phosphate glass fibers with different core diameters. The fibers vary in their diameter from 100 µm (highly multi-mode) down to 12 µm (single-mode). The peak power, energy per pulse, and spectral shape of the amplified signal are presented. With our input pulses, the measurements show that the large core diameter fibers do not increase the amplification of the 1538 nm signal. We believe this is due to the high re-absorption of the Er3+ ions in the phosphate fiber. The optimal fiber geometry was found to have a core diameter of 20 µm with a length of 14 cm. The maximum peak power is 8.25 kW, corresponding to a net gain of 10.9 dB, with a pulse duration of 0.7 ns and a repetition rate of 40 kHz. © 2020 Optical Society of Americ

The future of Cybersecurity in Italy: Strategic focus area

This volume has been created as a continuation of the previous one, with the aim of outlining a set of focus areas and actions that the Italian Nation research community considers essential. The book touches many aspects of cyber security, ranging from the definition of the infrastructure and controls needed to organize cyberdefence to the actions and technologies to be developed to be better protected, from the identification of the main technologies to be defended to the proposal of a set of horizontal actions for training, awareness raising, and risk management