Functionalization of polymer optical fibers for medical application

The increasing challenges caused by the growing and aging population and the fast pace of life are calling for a change of our current medical care system towards being rapid, easy, and on-demand self-care. Empowerment with the self-caring components such as early diagnosis, treatment, and monitoring of individuals will sharply release the social burden. In this context, fibrous materials stand out for their small size, processing flexibility, designable functionalities, and the possibility to be further integrated into im-plants or wearable devices. As we know, optical fiber is widely used in the biomedical field. For example, conventional silica optical fiber has mature applications such as light guides for surgery and catheter-based endoscopy while novel types of optical fiber (hydrogel, polymer, biomedical material, and elastomer) open the door to various new application scenarios like optogenetics, active monitoring, and continuous sensing, etc. While it remains a hot topic, the use of optical fibers for drug delivery is still in lack of exploration and suggests an ideal starting point for us. Optical fiber allows light propagation and thus gives the possibility to build up a light-responsive delivery system if combined with light-responsive drug carriers. Mesoporous silica nanoparticles(MSNP) were selected to host drug substances due to their high surface area, big pore volume, and versatility of functionalization and were coated on the fiber. Optical fiber will work as a light source to trigger the release from carriers. In this thesis, we constructed the hybrid system to give an optical fiber-based release system and elucidate the interaction between light from the optical fiber and drug-hosted particles with a further expectation to integrate with sensing or monitor-ing function to have an advanced delivery device. The first part of the work involved the synthesis of mesoporous silica nanoparticles using non-surfactants as templating agents. For the first time, a systematic study has been carried out to unravel the morphogenetic mechanism of mesoporous silica nanoparticles by polyphenols. Our study has, on one side, suggested that the pKa value of the polyphenols is responsible for the particle size due to the effect on nucleation and particle growth process, and on the other side, demonstrated that the formation of the supramolecular network contributes to the porous structure by serving as the skeleton for the silica pre-cursors to polymerize around. The second part of the work is to establish a method to generate a particle-polymer optical fiber(POF) complex matrix. A robust and controlled strategy for the fabrication of particle-coated surfaces that applies to multiple genres of substrates and coating materials was proposed based on layer-by-layer(LbL) assembly. The approach enables a high drug loading as well as a low structural complexity en-dowed by a dense and homogenous monolayer coverage of particles on the substrates. The computer vision method was employed to quantitatively evaluate the particle coating, increasing dramatically the efficiency and accuracy of the coating evaluation. The final part of the work investigates the light-responsive release of photolabile coumarin-chlorambucil conjugates from optical fibers. To the best of our knowledge, it is the first study to explore the release of drugs from the side of optical fibers. Overall, this novel particle-optical fiber-based one-dimensional drug deliver

Coherent Rayleigh time domain reflectometry

Xin Lu

Owing to the advantages of the optical fibre, such as lightweight, small size, low cost and immunity to electromagnetic interferences, the fibre sensors have been applied in diverse fields and the scientific research on fibre sensing keeps improving to meet new industrial demands. In this thesis, a novel distributed fibre sensor based on coherent Rayleigh scattering is investigated to realise best accuracy measurements. Coherent Rayleigh scattering is found to be essentially assimilated to a random walk process, thus its statistical properties are theoretically analysed based on the mature theory on random walk. Then the spectral characteristics of the Rayleigh backscattered light is investigated for different incident pulse shapes. The spectral distribution of the trace amplitude turns out to be identical to the spectrum of the incident pulse. Meanwhile, a theoretical model is proposed to describe the coherent Rayleigh trace in time and frequency domains. Experiments are carried out to validate the theoretical analysis and the proposed model. Then the statistical properties and the visibility of the coherent Rayleigh traces obtained by experiment and simulation are investigated for different detection bandwidth. The minimum 3 dB bandwidth required to resolve all features of a coherent Rayleigh intensity trace is determined to be 3 times larger than the bandwidth of the incident rectangular pulse. Then coherent Rayleigh scattering is applied to distributed sensing using the optical time domain reflectometry technique. The working principle is explained by the restorability of the Rayleigh trace in time domain and by a spectral shift in frequency domain. The temperature sensitivity is calculated over a wide range from 300 K down to 4.5 K based on the thermo-optic effect and the thermal expansion of the silica fibre. The experimental results in a standard fibre with acrylate coating and a fibre specially coated with ORMOCER® confirm the high temperature sensitivity (over 1 GHz/K) and demonstrate a temperature resolution in the milliKelvin range even under cryogenic conditions. The fibre with the ORMOCER® coating exhibits a higher temperature sensitivity at room temperature than the acrylate coated fibre due to the extra strain induced by the temperate change in the coating and a more stable sensing behaviour because the polymers forming the coating stabilise the mechanical and thermal responses of the fibre. The sensors based on coherent Rayleigh scattering are also applied to retrieve the phase birefringence distribution along polarisation-maintaining and standard single mode fibres. The minimum detectable birefringence reaches 3×10¿7 when the spatial resolution is 2 m and even smaller value can be resolved using longer optical pulses. In addition, this birefringence measurement is capable of distributed temperature and strain sensing in a PANDA and an elliptical-core polarisation-maintaining fibres since the birefringence is sensitive to environmental variations. The experimental results demonstrate that this method is one order of magnitude more sensitive than a fibre sensor based on Brillouin scattering. Moreover, discriminated temperature and strain sensing is realised by a combination of this birefringence measurement and a standard COTDR sensor. This thesis is concluded by a discussion of further research directions on coherent Rayleigh scattering based distributed sensing.

EPFL2016

Design and Fabrication of Stretchable Photonic Fibers

Nicola Bartolomei

Optical fibers have reshaped the technological landscape, from optical networks and high-speed data communication to in situ imaging and non-invasive surgery methods. The revolution allowed by these fibers has been made possible by its fabrication method, the thermal drawing process, which combines high scalability and nanoscale fabrication accuracy. Despite tremendous successes, silica step-index and photonic crystal fibers have held intrinsic limitations due to their mechanical rigidity and fragility, limiting their possible applications . There is however an increasing demand for optical fibers that could guide light efficiently while sustaining large deformations in fields like robotics, smart textiles and the automotive world. Other fields in sensing, helath care or advanced textiles could benefit from soft fibers that could display tunable optical effects. Techniques like lithography and molding have proven valuable to fabricate complex elastomeric photonic fibers, but their limited scalability intrinsically limits their use in several fields of application. On the other hand, scalable fabrication techniques like extrusion guarantee the desired throughput but fail to deliver the architectural complexity required to realize softfibers advanced optical properties. In this thesis, we propose to exploit the thermal drawing process to realize different types of soft and highly stretchable optical fibers, from the classic step-index architecture to 1D photonic crystal fibers, liquid core fibers and 2D photonic crystal fibers. To achieve this overall objective, we first establish a theoretical framework to evaluate the material requirements from the rheological, optical and mechanical point of view. After selecting the materials, we develop a step-by-step fabrication process that starts from the material pellets and ends with the fabrication of meters of elastomeric photonic fiber via thermal drawing. We then move on to fully characterize the optical and mechanical properties of the fibers and design several fiber-based devices with specific optical effects. More specifically in Chapter 2, we demonstrate the materials selection, innovative fabrication process, and the optical and mechanical characterizations to realize a soft optical wave-guide based on a step-index design. To highlight its optical and mechanical performance, we demonstrate a strain sensing sport gear that integrates this newly developed fiber. In chapter 3, we go one step further in the control over feature size by going about a similar demonstration for a 1D photonic crystal fibers based on all-elastomeric materials, with feature sizes down to sub-100 nm. We show in particular a mechanochromic fiber that can reversibly change color upon stretching. In Chapter 4, we propose a series of other fiber architectures based on our scientific and technological achievements that include a multicore stretchable step-index fiber that form the basis of an advanced demonstrator of a soft fiber with multiple channels and functionalities found in endoscopes. We also present preliminary results on a liquid-core step index fiber, and a stretchable 2D photonic crystal fiber, that pave the way towards highly complex and high-performance soft optical fiber devices.

EPFL2021

Sol-gel processes applied to micro- and nanotechnology

Jean-Baptiste Robert Orhan

In this thesis, we intend to develop the sol-gel technology (a chemical way to make glass) from the traditional "raw" materials side to a novel technology allowing realization of innovative products in the field of micro- and nanotechnology. We first present the development of a process for the realization of 60 µm thick and 100 µm wide microlens arrays in sol-gel glass, based on an innovative photoresist replication and softening method. We synthesize and characterize our hybrid organic/inorganic sol-gel glass solution. The structural and optical characterizations indicate the reproducibility and high optical quality of our sol-gel glass micro-lens arrays. Then, we demonstrated a novel non-aqueous synthesis route to obtain a borosilicate solution used for the in situ modification of a poly dimethylsiloxane (PDMS) microchannel. Our modification process is producing a covalently bonded smooth and sub-micron thick (800 nm) crack-free borosilicate glass coating. The efficiency of the coating is demonstrated by a negligible diffusion of fluorescent Rhodamine B in the PDMS, when flowing water- and toluene-based solutions through the microchannel. Moreover, the coating prevents swelling and consequent structural damage of the PDMS when exposed to harsh chemicals like toluene. Finally, we discovered and report on an original process for the generation of borosilicate nanoparticles by mixing a non-aqueous Si-B binary oxide solution with water. Our experiments allow us to assess the borosilicate nature of the generated particles, and also to propose a novel formation mechanism via exothermic phase separation. Our discovery has high potential; not only for life science applications, but monodisperse borosilicate particles could be key to the realization of photonic bandgap devices with high optical contrast, contrast agents for ultrasonic microscopy or chemical filtration membranes. To sum up, our work demonstrates the possibility of innovative and versatile use of the sol-gel process in the micro- and nanotechnology field.

EPFL2008