Bioresorbable phosphate glass optical fiber for biomedical applications Nadia G. Boetti1*, Diego Pugliese2, Antreas Theodosiou3, Kyriacos Kalli3, Edoardo Ceci-Ginistrelli2, Davide Janner2, Daniel Milanese2,4 1
Istituto Superiore Mario Boella, Via P. C. Boggio 61, 10134 Torino, Italy *Tel: +39 011 2276312, Fax: +39 011 2276299, e-mail:
[email protected] Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino and RU INSTM, C.so Duca degli Abruzzi 24, 10129 Torino, Italy 3 Nanophotonics Research Laboratory, Cyprus University of Technology, Lemesos 3036, Cyprus 4 Consiglio Nazionale delle Ricerche, Istituto di Fotonica e Nanotecnologie, Via alla Cascata 56/C, 38123 Trento, Italy 2
Abstract: We report on recent developments in the field of bioresorbable phosphate optical fibers for biomedicine. Preliminary results for fiber Bragg grating inscription in a single-mode bioresorbable fiber, using femtosecond laser system, are presented and discussed. OCIS codes: (160.1435) Biomaterials; (160.2290) Fiber materials; (060.2280) Fiber design and fabrication; (060.3735) Fiber Bragg gratings. 1. Introduction Optical fibers and fiber-based sensors are widely employed for a variety of invasive and non-invasive biomedical applications, such as diagnosis, monitoring and therapy. The advantages of fiber optic technology reside in the intrinsic physical characteristics of optical fibers: small size, low weight, flexibility, immunity to electromagnetic interference and capability to perform multi-point and multi-parameter sensing remotely [1]. Several biomedical applications, that require insertion of optical fibers into the human body, will take advantage of the availability of bioresorbable fibers able to be gradually resorbed by the tissue eliminating the need for followup explant surgery. Fibers could be implanted after an operation and left in place for imaging and monitoring of the healing process, in addition to delivering light to a deep wound to stimulate healing by a process called photochemical tissue bonding (PTB) [2]. Finally, they could be used for long-term photodynamic therapy (PDT) for cancer treatment [3]. Research efforts have mainly focused so far on the use of polymers [4] and silk [5] based materials for the realization of bioresorbable waveguides. We recently proposed calcium-phosphate glass compositions able to combine solubility in a simulated biological environment, transparency window from UV to near IR region, low intrinsic attenuation loss and sufficient thermal stability for fiber drawing [6]. By selecting suitable core and cladding glass pairs, multi-mode (MM) and singlemode (SM) fibers were manufactured by preform drawing, with the preform produced using the rod-in-tube technique. Preliminary results of potential applications of these fibers have been obtained for time-domain diffuse optical spectroscopy [7], Bragg gratings inscriptions by UV irradiation [8] and drug release from hollow glass fibers [9]. In this work we report on recent advances in the inscription of Bragg gratings in a bioresorbable phosphate glass SM optical fiber using the plane-by-plane (Pl-by-Pl) femtosecond (fs) laser inscription method [10]. 2. Fiber Bragg Gratings inscription by fs laser system A suitable core and cladding bioresorbable glass pair was designed and synthesized in order to obtain an adequate value of numerical aperture (NA) with the aim to fabricate a SM optical fiber. The glasses were fabricated by conventional melt-quenching technique. The core glass was cast into a cylindrical mold to form a rod, whereas rotational casting was carried out to obtain the cladding glass tube. The core-cladding preform was realized by rod-in-tube technique and then the optical fiber was manufactured by preform drawing using a drawing tower developed in-house. The optical fiber drawn had diameters of 15 and 120 µm for the core and the cladding, respectively, with a NA of 0.07, thus exhibiting a single-mode behavior at 1550 nm. A good quality of the core/cladding interface was obtained and an attenuation loss of 2 dB/m was measured at 1300 nm using the cut-back technique. The Bragg grating inscription set-up consisted of a fs laser system (HighQ Laser femtoREGEN) operating at 517 nm, with a 220-fs pulse duration, a 1-kHz repetition rate and a nm-accuracy air-bearing translation stage system (Aerotech) for controlled and accurate two-axis motion during the inscription. The laser beam was focused from above using a third stage and a long working distance microscope objective (Mitutoyo, x50, NA 0.42). A fiber Bragg grating (FBG) was inscribed in the SM bioresorbable phosphate glass fiber using the Pl-by-Pl fs laser inscription method. The grating was written to operate at around 1560 nm and the grating period was set to ~ 2 μm.
Moreover, to ensure a high FBG reflectivity, the grating consisted of 1000 planes. A bright field microscope image of the inscribed grating, as captured with a CCD camera during the inscription, is shown in Fig. 1a. The image shows the extent of the fiber diameter and the grating location, which has been designed to completely cover the core region. Following the inscription, the phosphate fiber sample was spliced and illuminated with a broadband light source (Thorlabs ASE730) and the reflection spectrum was recovered using a commercial spectrometer through a circulator (see Fig. 1b). The splicing of the phosphate fiber to the standard telecom SM fiber (Corning, SMF28E) was carried out by setting the intensity of the electric arc at a very low value and by shifting the relative position of the splicing location 700 μm towards the silica fiber. a)
b)
10 µm Fig. 1. a) Microscope picture of a FBG inscribed in the bioresorbable phosphate glass fiber using the Pl-by-Pl inscription method. b) Reflection spectrum of the FBG as recovered with a commercial spectrometer.
4. Conclusion We presented preliminary results of FBGs inscription on a bioresorbable calcium-phosphate optical fiber using the Pl-by-Pl femtosecond laser inscription method. The combination of a bioresorbable optical fiber with reliable and high quality FBGs could pave the way towards the fabrication of novel biomedical devices able to integrate several health diagnostic functionalities in compact format and eliminate the need for follow-up explant surgery. Acknowledgements The authors acknowledge the COST Action MP1401 “Advanced Fibre Laser and Coherent Source as tools for Society, Manufacturing and Lifescience” for the partial support of this research effort. 5. References [1] A. Mendez, "Specialty Optical Fibers in Biomedical Applications: Needs & Applications," in Workshop on Specialty Optical Fibers and their Applications, (Optical Society of America, Washington, D.C., 2013), paper T3.1. [2] S. Nizamoglu, M. C. Gather, M. Humar, M. Choi, S. Kim, K. S. Kim, S. K. Hahn, G. Scarcelli, M. Randolph, R. W. Redmond, and S. H. Yuna, “Bioabsorbable polymer optical waveguides for deep-tissue photomedicine,” Nat. Commun. 7, 10374 (2016). [3] L. Brancaleon and H. Moseley, “Laser and non-laser light sources for photodynamic therapy,” Lasers Med. Sci. 17, 173-186 (2002). [4] A. Dupuis, N. Guo, Y. Gao, N. Godbout, S. Lacroix, C. Dubois, and M. Skorobogatiy,“Prospective for biodegradable microstructured optical fibers,” Opt. Lett. 2, 109-111 (2007). [5] S. T. Parker, P. Domachuk, J. Amsden, J. Bressner, J. A. Lewis, D. L. Kaplan, and F. G. Omenetto, “Biocompatible Silk Printed Optical Waveguides,” Adv. Mater. 21, 2411-2415 (2009). [6] E. Ceci-Ginistrelli, D. Pugliese, N. G. Boetti, G. Novajra, A. Ambrosone, J. Lousteau, C. Vitale-Brovarone, S. Abrate, and D. Milanese, “Novel biocompatible and resorbable UV-transparent phosphate glass based optical fiber,” Opt. Mater. Express 6, 2040-2051 (2016). [7] L. Di Sieno, N. G. Boetti, A. Dalla Mora, D. Pugliese, A. Farina, S. Konugolu Venkata Sekar, E. Ceci-Ginistrelli, D. Janner, A. Pifferi, and D. Milanese, “Towards the use of bioresorbable fibers in time-domain diffuse optics,” J. Biophotonics, accepted for publication. [8] M. Konstantaki, S. Pissadakis, D. Pugliese, E. Ceci-Ginistrelli, N. G. Boetti, and D. Milanese, "Bragg grating UV inscription in a bioresorbable phosphate glass optical fiber," 18th International Conference on Transparent Optical Networks, (IEEE, New York, 2016) pp. 01-04. [9] E. Ceci-Ginistrelli, C. Pontremoli, D. Pugliese, N. Barbero, N. G. Boetti, C. Barolo, S. Visentin, and D. Milanese, “Drug release kinetics from biodegradable UV-transparent hollow calcium-phosphate glass fibers, Mater. Lett. 191, 116-118 (2017). [10] A. Theodosiou, A. Lacraz, M. Polis, K. Kalli, M. Tsangari, A. Stassis, and M. Komodromos, “Modified fs-laser inscribed FBG array for rapid mode shape capture of free-free vibrating beams”, IEEE Photonics Technol. Lett. 28, 1509-1512 (2016).
