Optical fibers have been employed for several years in biomedicine and mainly used for light delivery and collection with high efficiency and selectivity. So far most of the research effort has been devoted to the optical configurations and the functions of the fibers rather than on the materials employed. Indeed, this aspect has been mainly considered to assure biocompatibility with tissues and non-toxic behavior limiting the choice mostly to silicate fibers.
We report on the recent advances in engineering inorganic glass optical and hollow fibers fabricated with optical glasses which are also resorbable in body fluids. Suitable phosphate glass compositions were designed to combine resorbability and optical transparency. Glasses were fabricated by melt-quenching inside a chamber furnace under a flux of dried air and cast into preheated brass molds. The fibers were obtained by preform drawing, with the core rod fabricated by melt quenching whilst the cladding tube by rotational casting. Extrusion techniques were also applied to obtain more complex cross sections with increased functionalities.
Glasses and fibers were characterized in their physical and optical properties. The materials showed high stability toward crystallization and a wide optical transmission window, ranging from the ultraviolet to the near infrared wavelength regions. Hollow fibers were employed to demonstrate multifunctional fiber probes, able to provide drug delivery and light excitation in the prospect of developing resorbable endoscopes for intravital monitoring and therapy, such as photodynamic therapy. Optimization of drug delivery was carried out using functionalization procedures on the surface of both bulk glasses and hollow fibers, aiming to modify the release kinetics: a silanization protocol was developed and successfully tested using different organic compounds. The modification of the surface roughness was monitored using atomic force microscopy, while surface energy changes verified using contact angle measurements. The possibility of performing drug excitation was assessed by guiding light through the capillary using optical beams produced by different wavelength sources covering the visible spectrum. Finally, mechanical characterization of the prepared optical fibers and hollow fibers was carried out to measure the elastic moduli, the tensile strength and the minimum radius of curvature attainable. The overall results allowed to demonstrate the reliability of the proposed optical fibers and hollow fibers for biomedical applications.
We report on the employment of a biodegradable phosphate-based optical fiber as a pH sensing probe in physiological environment. The phosphate-based optical fiber preform was fabricated by the rod-in-tube technique. The fiber biodegradability was first tested in-vitro and then its biodegradability and toxicity were tested in-vivo. Optical probes for pH sensing were prepared by the immobilization of a fluorescent dye on the fiber tip by a sol-gel method. The fluorescence response of the pH-sensor was measured as a ratio of the emission intensities at the excitation wavelengths of 405 and 450 nm.
A hollow bioresorbable phosphate glass fiber was developed and used for drug and light delivery.
The interaction between organic molecules and the fiber’s internal surface was studied. Promising
results for the release of Rose Bengal were obtained.
We show for the first time the aptness of Calcium Phosphate Glass-based bioresorbable fibers for time-domain diffuse optics using tests described by a standardized protocol and we also present a spectroscopic measurement on a chicken breast.
A theoretical and experimental analysis of group velocity reduction in periodic super-structured Bragg gratings
is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the 1.5 μm wavelength of optical communications is reported using either a 20-cm-long Moire and a periodically-spaced πphase shift fiber gratings. Time delays up to approximately 690 ps for 250-ps-duration optical pulses have been achieved leading to the realization of an optical buffer.