Polymer micelles that are self-assembled from biocompatible amphiphilic polymers in water have emerged as one of the most promising nanocarrier systems for various hydrophobic drugs. These systems offer several advantages, such as significantly enhancing drug water solubility, decreasing side effects, and improving drug delivery to tumor tissues via the enhanced permeability and retention (EPR) effect. Recent advances in polymer micelles for drug delivery have led to systems showing “triggered” release on demand which allows restricting drug release at the targeted location by an external stimulus. Among external stimulations, light, especially when two-photon activation is used, is attractive as it can be remotely applied with a high temporal and spatial precision. In two-photon excitation, near-infrared (NIR) - infrared (IR) stimuli (700–1300 nm) are within the range of the transparency window of tissues in which the absorption and scattering of photons by tissues are low and enable deeper penetration with less photodamage to tissue in comparison to UV or visible light excitation. Although several methods have been developed for the synthesis of photoresponsive polymer micelles, most of these carrier systems have been designed from synthetic polymer backbones and were not explored in studies on whole animals. Therefore, substantial efforts in the development of light sensitive biocompatible and biodegradable polymer assemblies for future clinical applications are needed. The aim of this project is to engineer and to study a new class of NIR-light sensitive biocompatible polymer carrier systems consisting of hyaluronic acid (HA)-based nanogels that exhibit photoinduced swelling and degradation properties for remote-controlled drug release. Thermosensitive copolymer chains possessing NIR two-photon cleavable units (coumarin ester derivative) and crosslinker precursors (pyridyl disulfide (PDS) moieties or 2-ureido-4-pyrimidone (UPy) units), will be introduced on the HA backbone to produce HA derivatives that can self-assemble into multi-stimuli responsive nanogels (also considered as micelles) above the lower critical solution temperature (LCST) of the copolymer. The reversible crosslinking bonds formed from the PDS or Upy groups (disulfide bonds or quadruple H-bonds, respectively) will ensure stability of nanogels before reaching the target site in which they will be dissociated. Here, the nanogels will undergo a rapid swelling induced by the photolysis of the coumarin ester, resulting in the burst release of the drug payload. In these systems, the coumarin derivatives, having large two-photon absorption cross-sections, act as photoremovable protecting groups inducing a shift in the LCST of the copolymer due to the conversion of coumarin esters into carboxylate groups upon light irradiation. The amount of coumarin moieties in the copolymer chains will be thus adjusted in such a way that the LCST will change from a temperature below the body temperature (~ 25 °C) to a temperature higher than 37 °C (~ 45 °C), allowing for triggered drug release at body temperature. After releasing their cargo, the nanogels will disintegrate completely inside the cells, because the disulfide bonds have the propensity to be degraded in the intracellular redox environment and H-bonds between Upy units are destabilized in a highly hydrophilic environment. The originality of this approach lies in the synergistic combination of thermosensitivity and NIR-light sensitivity which will induce an important volume phase transition of the nanogels allowing efficient drug release. To obtain functional HA nanogels for photocontrolled delivery applications, we will conduct fundamental studies of their light responsiveness and release processes, and assess their performance in vivo on a mouse brain tumor model.

Dysfunctions of the central nervous system are a major economic and social issue. Neural prostheses and brain-computer interfaces offer promising perspectives to restore motor functions and communication capabilities in patients suffering from severe paralysis. These approaches require the implantation of arrays of microelectrodes offering the possibility to record brain activity with stability on the long term. However, to date, the fabrication of brain implants housing a large number of microelectrodes and offering a stable connection with the neural tissue on the long term remains impaired by two major limitations. The first one stems from the electrode material itself when the size of the electrodes becomes small. Noble metals such as Platinum or Iridium have been used for decades to make macroscopic electrodes, which are now used in routine for neural recording and stimulation in several clinical applications such as cochlear implants, deep brain stimulation for Parkinson disease, and also the pre-surgical functional evaluation of epilepsy. However, thanks to the development of microfabrication technologies, the past decades have seen the development of new types of implants housing tens or even hundreds of microelectrodes on the micrometer scale. Yet, when the size of the electrodes diminishes, two problems arise: The intrinsic (thermal) noise level of the electrodes increase, and their safe charge injection limits decrease, which prevents delivering sufficient currents to activate neural networks without inducing lesions due to electrochemical reactions at the electrode/tissue interface. In this context, the first goal of the NeuroMeddle project will be to consider new types of materials based on the electrodeposition of pure or doped PEDOT/PSS to develop electrodes with improved performance and stable on the long term. A second main problem of existing brain implants (for instance like the Utah array) is the instability over days and even the loss of neural signals along time after a few weeks or months. This is especially the case for action potential signals, either of single or multiple units. This instability is mostly due to the combined effect of the movements of the brain and the inadequacy of the rigidity of implant materials versus the soft properties of the brain tissue. For this reason, an important line of research worldwide is the development of flexible implants matching the geometry and the mechanical properties of the brain, while still compatible with intracortical recordings. In this quest, an important open challenge remains to find strategies to insert flexible microelectrodes so that they meddle into the brain to create intimate and stable connections with individual neurons on the long term. Hence, the second goal of the NeuroMeddle project will be to develop implants offering such conformational stability, based on transient rigidification of flexible electrodes using biodegradable embedding materials (PEG, PLA, Chitosan, Silk fibroin) for the time of implantation. We will particularly focus on silk fibroin, which offers high rigidity and is not yet used in Europe for this type of application, while well mastered by one of the NeuroMeddle partner. The new electrode materials based on PEDOT/PSS, as well as biodegradable materials will first be tested in vivo in the rat. In a second step, we will consider another model closer to the human brain in order to face similar problems of stability of implants. We will use a paradigm for cortical recordings underlying vocalization in the awake mini pig, which allows to test the stability of long term recordings of unit and multiunit signals using the new conformational implants developed in the project.