Drug delivery via a 3D electro-swellable conjugated polymer hydrogel.

Spatiotemporal controlled drug delivery minimizes side-effects and enables therapies that require specific dosing patterns. Conjugated polymers (CP) can be used for electrically controlled drug delivery; however so far, most demonstrations were limited to molecules up to 500 Da. Larger molecules could be incorporated only during the CP polymerization and thus limited to a single delivery. This work harnesses the record volume changes of a glycolated polythiophene p(g3T2) for controlled drug delivery. p(g3T2) undergoes reversible volumetric changes of up to 300% during electrochemical doping, forming pores in the nm-size range, resulting in a conducting hydrogel. p(g3T2)-coated 3D carbon sponges enable controlled loading and release of molecules spanning molecular weights of 800-6000 Da, from simple dyes up to the hormone insulin. Molecules are loaded as a combination of electrostatic interactions with the charged polymer backbone and physical entrapment in the porous matrix. Smaller molecules leak out of the polymer while larger ones could not be loaded effectively. Finally, this work shows the temporally patterned release of molecules with molecular weight of 1300 Da and multiple reloading and release cycles without affecting the on/off ratio.

Electrochemical modulation of mechanical properties of glycolated polythiophenes.

Electrochemical doping of organic mixed ionic-electronic conductors is key for modulating their conductivity, charge storage and volume enabling high performing bioelectronic devices such as recording and stimulating electrodes, transistors-based sensors and actuators. However, electrochemical doping has not been explored to the same extent for modulating the mechanical properties of OMIECs on demand. Here, we report a qualitative and quantitative study on how the mechanical properties of a glycolated polythiophene, p(g3T2), change in situ during electrochemical doping and de-doping. The Young's modulus of p(g3T2) changes from 69 MPa in the dry state to less than 10 MPa in the hydrated state and then further decreases down to 0.4 MPa when electrochemically doped. With electrochemical doping-dedoping the Young's modulus of p(g3T2) changes by more than one order of magnitude reversibly, representing the largest modulation reported for an OMIEC. Furthermore, we show that the electrolyte concentration affects the magnitude of the change, demonstrating that in less concentrated electrolytes more water is driven into the film due to osmosis and therefore the film becomes softer. Finally, we find that the oligo ethylene glycol side chain functionality, specifically the length and asymmetry, affects the extent of modulation. Our findings show that glycolated polythiophenes are promising materials for mechanical actuators with a tunable modulus similar to the range of biological tissues, thus opening a pathway for new mechanostimulation devices.

Flexible Organic Electronic Ion Pump for Flow-Free Phytohormone Delivery into Vasculature of Intact Plants.

Plant vasculature transports molecules that play a crucial role in plant signaling including systemic responses and acclimation to diverse environmental conditions. Targeted controlled delivery of molecules to the vascular tissue can be a biomimetic way to induce long distance responses, providing a new tool for the fundamental studies and engineering of stress-tolerant plants. Here, a flexible organic electronic ion pump, an electrophoretic delivery device, for controlled delivery of phytohormones directly in plant vascular tissue is developed. The c-OEIP is based on polyimide-coated glass capillaries that significantly enhance the mechanical robustness of these microscale devices while being minimally disruptive for the plant. The polyelectrolyte channel is based on low-cost and commercially available precursors that can be photocured with blue light, establishing much cheaper and safer system than the state-of-the-art. To trigger OEIP-induced plant response, the phytohormone abscisic acid (ABA) in the petiole of intact Arabidopsis plants is delivered. ABA is one of the main phytohormones involved in plant stress responses and induces stomata closure under drought conditions to reduce water loss and prevent wilting. The OEIP-mediated ABA delivery triggered fast and long-lasting stomata closure far away from the delivery point demonstrating systemic vascular transport of the delivered ABA, verified delivering deuterium-labeled ABA.

Long-distance turgor pressure changes induce local activation of plant glutamate receptor-like channels.

In Arabidopsis thaliana, local wounding and herbivore feeding provoke leaf-to-leaf propagating Ca2+ waves that are dependent on the activity of members of the glutamate receptor-like channels (GLRs). In systemic tissues, GLRs are needed to sustain the synthesis of jasmonic acid (JA) with the subsequent activation of JA-dependent signaling response required for the plant acclimation to the perceived stress. Even though the role of GLRs is well established, the mechanism through which they are activated remains unclear. Here, we report that in vivo, the amino-acid-dependent activation of the AtGLR3.3 channel and systemic responses require a functional ligand-binding domain. By combining imaging and genetics, we show that leaf mechanical injury, such as wounds and burns, as well as hypo-osmotic stress in root cells, induces the systemic apoplastic increase of L-glutamate (L-Glu), which is largely independent of AtGLR3.3 that is instead required for systemic cytosolic Ca2+ elevation. Moreover, by using a bioelectronic approach, we show that the local release of minute concentrations of L-Glu in the leaf lamina fails to induce any long-distance Ca2+ waves.

Polythiophene-mediated light modulation of membrane potential and calcium signalling in human adipose-derived stem/stromal cells.

Recent progress in the fields of regenerative medicine and tissue engineering has been strongly fostered both by the investigation of crucial cues, able to trigger the regeneration of damaged tissues, and by the development of ad hoc functional materials, capable of selectively (re-)activating relevant physiological pathways. In parallel to the successful realization of biochemical cues and the optimization of delivery protocols, the use of biophysical stimuli has been emerging as an alternative, highly effective strategy. Techniques based on electrical, magnetic and mechanical stimulation have been reported to efficiently direct differentiation of stem cells and modulate cell physiology at different developmental stages. In this framework, the use of optical stimulation represents a valuable approach, possibly overcoming current limitations of chemical cues, like limited spatial and temporal resolution and poor control over the extracellular environment. Surprisingly, the effects of light on the physiological properties (light toxicity, cell membrane potential, and cell ionic trafficking) of undifferentiated cells, as well as on their differentiation pathways, were investigated to a very limited extent and rarely quantified in a systematic way. In this work, we aim at clarifying the effects of optical excitation on the physiological behaviour of undifferentiated human adipose-derived stem cells (hASC), cultured on top of a light-sensitive conjugated polymer, region-regular poly-3-hexyl-thiophene (P3HT). Interestingly, we observe statistically significant modulation of the cell membrane potential, as well as noticeable effects on intracellular calcium signalling, triggered by P3HT excitation upon green light stimuli. Possible mechanisms involved in the signal transduction pathways are considered and critically discussed. The capability to modulate the physiological response of hASC upon photoexcitation, in a highly controlled and selective manner, provides a promptly available and non invasive diagnostic tool, thus contributing to the understanding of the complex machinery behind stem cells and material interfaces. Moreover, it may open the route to novel techniques to drive the differentiation path with unprecedented versatility and operational easiness.

Light-Triggered Electron Transfer between a Conjugated Polymer and Cytochrome C for Optical Modulation of Redox Signaling.

Protein reduction/oxidation processes trigger and finely regulate a myriad of physiological and pathological cellular functions. Many biochemical and biophysical stimuli have been recently explored to precisely and effectively modulate intracellular redox signaling, due to the considerable therapeutic potential. Here, we propose a first step toward an approach based on visible light excitation of a thiophene-based semiconducting polymer (P3HT), demonstrating the realization of a hybrid interface with the Cytochrome c protein (CytC), in an extracellular environment. By means of scanning electrochemical microscopy and spectro-electrochemistry measurements, we demonstrate that, upon optical stimulation, a functional interaction between P3HT and CytC is established. Polymer optical excitation locally triggers photoelectrochemical reactions, leading to modulation of CytC redox activity, either through an intermediate step, involving reactive oxygen species formation, or via a direct photoreduction process. Both processes are triggered by light, thus allowing excellent spatiotemporal resolution, paving the way to precise modulation of protein redox signaling.

Use of Exogenous and Endogenous Photomediators as Efficient ROS Modulation Tools: Results and Perspectives for Therapeutic Purposes.

Reactive Oxygen Species (ROS) play an essential dual role in living systems. Healthy levels of ROS modulate several signaling pathways, but at the same time, when they exceed normal physiological amounts, they work in the opposite direction, playing pivotal functions in the pathophysiology of multiple severe medical conditions (i.e., cancer, diabetes, neurodegenerative and cardiovascular diseases, and aging). Therefore, the research for methods to detect their levels via light-sensitive fluorescent probes has been extensively studied over the years. However, this is not the only link between light and ROS. In fact, the modulation of ROS mediated by light has been exploited already for a long time. In this review, we report the state of the art, as well as recent developments, in the field of photostimulation of oxidative stress, from photobiomodulation (PBM) mediated by naturally expressed light-sensitive proteins to the most recent optogenetic approaches, and finally, we describe the main methods of exogenous stimulation, in particular highlighting the new insights based on optically driven ROS modulation mediated by polymeric materials.

Photocatalytic Activity of Polymer Nanoparticles Modulates Intracellular Calcium Dynamics and Reactive Oxygen Species in HEK-293 Cells.

Optical modulation of living cells activity by light-absorbing exogenous materials is gaining increasing interest, due to the possibility both to achieve high spatial and temporal resolution with a minimally invasive and reversible technique and to avoid the need of viral transfection with light-sensitive proteins. In this context, conjugated polymers represent ideal candidates for photo-transduction, due to their excellent optoelectronic and biocompatibility properties. In this work, we demonstrate that organic polymer nanoparticles, based on poly(3-hexylthiophene) conjugated polymer, establish a functional interaction with an in vitro cell model (Human Embryonic Kidney cells, HEK-293). They display photocatalytic activity in aqueous environment and, once internalized within the cell cytosol, efficiently generate reactive oxygen species (ROS) upon visible light excitation, without affecting cell viability. Interestingly, light-activated ROS generation deterministically triggers modulation of intracellular calcium ion flux, successfully controlled at the single cell level. In perspective, the capability of polymer NPs to produce ROS and to modulate Ca2+ dynamics by illumination on-demand, at non-toxic levels, may open the path to the study of biological processes with a gene-less approach and unprecedented spatio-temporal resolution, as well as to the development of new biotechnology tools for cell optical modulation.