Adaptive polymer fiber neural device for drug delivery and enlarged illumination angle for neuromodulation

Abstract

Objective.Optical fiber devices constitute significant tools for the modulation and interrogation of neuronal circuitry in the mid and deep brain regions. The illuminated brain area during neuromodulation has a direct impact on the spatio-temporal properties of the brain activity and depends solely on the material and geometrical characteristics of the optical fibers. In the present work, we developed two different flexible polymer optical fibers (POFs) with integrated microfluidic channels (MFCs) and an ultra-high numerical aperture (UHNA) for enlarging the illumination angle to achieve efficient neuromodulation. Approach. Three distinct thermoplastic polymers: polysulfone (PSU), polycarbonate (PC), and fluorinated ethylene propylene (FEP) were used to fabricate two step-index UHNA POF neural devices using a scalable thermal drawing process. The POFs were characterized in terms of their illumination map as well as their fluid delivery capability in phantom and adult rat brain slices. Main results. A 100-fold reduced bending stiffness of the proposed fiber devices compared to their commercially available counterparts has been found. The integrated MFCs can controllably deliver dye (trypan blue) on-demand over a wide range of injection rates spanning from 10 nL/min to 1000 nL/min. Compared with commercial silica fibers, the proposed UHNA POFs exhibited an increased illumination area by 17% and 21% under 470 and 650 nm wavelength, respectively. In addition, a fluorescent light recording experiment has been conducted to demonstrate the ability of our UHNA POFs to be used as optical waveguides in fiber photometry. Significance. Our results overcome the current technological limitations of fiber implants that have limited illumination area and we suggest that soft neural fiber devices can be developed using different custom designs for illumination, collection, and photometry applications. We anticipate our work to pave the way towards the development of next-generation functional optical fibers for neuroscience.

Opsin-free optical neuromodulation and electrophysiology enabled by a soft monolithic infrared multifunctional neural interface

“…Additionally, the large refractive index contrast between the two polymers leads to a very large numerical aperture (NA) (Fig. S1A), which is known to have an important role during neuromodulation [35]. The PSU and FEP viscosity-temperature profiles were characterized using standard rheometry and found to overlap and be suitable for fibre co-drawing (Fig.…”

“…For the modeling of standard commercial fibres, uniform silica cylindrical shapes were used as geometry, since there is almost no variation in mechanical properties between core and cladding. Similarly to the one used in [35], the numerical model is based on fixing one end of the fibre while applying a force perpendicular to the fibre’s axis to the other end. The simulated diameters were 400 µm for the SPOF and 125 and 250 µm for the silica optical fibres.…”

Mapping whole brain effects of infrared neural stimulation with positron emission tomography

“…The use of FEP, one of the softest existing thermoplastics, as a cladding strongly reduced the bending stiffness of the probes with respect to standard silica glass fibers, enhancing their long-term biocompatibility (Fig. 2D) [38]. Hollow microchannels on the side of the core allow for the integration by liquid metal injection of indium electrodes, to enable electrophysiological recording at the fiber tip.…”

Infrared neural stimulation and electrophysiology in a soft fiber-based neural interface

“…Commercially available rods of fluorinated ethylene-propylene (FEP) copolymer and polysulfone (PSU) were used as starting materials for the preform, [17][18][19] which was heated and pulled at a speed of 2 meters/minute to obtain a final fiber diameter of ∼ 400 μm (Figure 1a). Prior to the fiber fabrication, the viscosity-temperature profiles and refractive indices of both materials had been measured using a rotational rheometer (TA, Discovery Hybrid HR2) and ellipsometer (J.…”

“…The flexibility of the interfaces was evaluated numerically using a COMSOL Multiphysics model similar to the one described in our previous work. 17…”