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 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. This work investigates the changes in the mechanical properties of glycolated polythiophenes induced by electrochemical addressing and by electrolyte concentration, due to its ability to stabilize water.

Electrochemically induced volume changes in organic mixed ionic-electronic conductors (OMIECs) are particularly important for their use in dynamic microfiltration systems, biomedical machinery, and electronic devices. Although significant advances have been made to maximize the dimensional changes that can be accomplished by OMIECs, there is currently limited understanding of how changes in their molecular structures impact their underpinning fundamental processes and their performance in electronic devices. Herein, a series of ethylene glycol functionalized conjugated polymers is synthesized, and their electromechanical properties are evaluated through a combined approach of experimental measurements and molecular dynamics simulations. As demonstrated, alterations in the molecular structure of OMIECs impact numerous processes occurring during their electrochemical swelling, with sidechain length shortening decreasing the number of incorporated water molecules, reducing the generated void volumes and promoting the OMIECs to undergo different phase transitions. Ultimately, the impact of these combined molecular processes is assessed in organic electrochemical transistors, revealing that careful balancing of these phenomena is required to maximize device performance.

Volume changes are the foundation for a wide range of phenomena and applications, ranging from the movement of plants to valves and drug delivery devices. Therefore, it does not come as a surprise that controlled volume changes are an interesting topic of research. In this thesis, volume changes in polymers are the object of investigation. Polymers are a class of macromolecules that comprise repetitive units. Owing to the wide variety of such units, polymers can exhibit manifold properties, including but not limited to strong water attraction and electrical conductivity. The former is the defining property in polymer hydrogels while the latter is a core property of conducting polymers. Both the water attracting properties and conductivity are closely linked to transport events on a molecular level. In the case of hydrogels, it is predominantly water uptake, while in the case of conducting polymers it is a complex interplay between charges, ionic charge balancing entities and water. However, in either case the transport events lead to volume changes. Despite the similarities, the properties of the materials differ greatly. On the one hand volume changes in hydrogels are very large but hard to control. On the other hand, volume changes in conducting polymers are much smaller than in hydrogels, but the control is easier due to the electronic addressing.   

P(gXTX) polymers combine a conducting polymer backbone with hydrogel sidechains. As described in publication 1, this combination of molecular entities was found to enabled unique properties of an electrically controllable giant volume change and concomitant solid-gel transition. In the second publication, the effect of the side chain lengths on the volume change properties of the polymers were explored. The knowledge acquired from these studies helped us to develop an electroactive filter based on p(gXTX) polymers which enabled electrochemical modulation of flow (publication 3). The aim of the fourth publication was to study the complex electronic-ionic transport processes and volume changes in a model conducting polymer, PEDOT:Tos. 

The understanding of fundamental processes and properties of controllable volume changes may pave the way for advances in various applications, including electroactive meshes, actuators and drug delivery devices.