A scaffold designed for tissue engineering should feature biocompatibility, tissue-like mechanical properties, and a hydrated and porous environment. To this end, hydrogels that are 3-dimensional crosslinked polymeric networks are considered excellent scaffolds for tissue engineering [1], with optimal physical and biological characteristics. Further, added functionalities can be incorporated in hydrogels such as electroconductivity, a property critical for electro-responsive tissues such as neural and cardiac tissue [2], self-healing providing the scaffold with mechanical and electronic stability under strain [3], and self-adhesion enabling the placement of the scaffold at the targeted tissue site in a minimally invasive approach [4] . Here, we report the fabrication and characterisation of an adhesive, self-healing, and conductive hydrogel. We show that the hydrogel is porous, has high swelling ratio and is physically stable. We demonstrate its rapid self-healing, and its electroactivity in physiological buffer with both ionic and electronic conduction. Further, its self-adhesion indicates a facile placement on tissues. Coupled together, these properties indicate that the hydrogel with its individual biocompatible components is a suitable scaffold for cell growth and differentiation.

Understanding and controlling the morphology of conjugated polymers is crucial for optimizing device performance in various applications such as stretchable electronics, wearable sensors, and flexible displays. Manipulating the morphology of such polymers into specific nanostructures like nanofibers or nanowires can not only maintain their electrical properties but also enhance mechanical robustness, enabling them to withstand mechanical deformations such as stretching, bending, or twisting without compromising their electrical functionality. While the majority of research on controlling conjugated polymers has focused on p-type materials, establishing an approach to precisely control diverse conjugated polymers, especially for n-type conjugated polymers, into such morphology remains a significant and elusive challenge in the field. In this work, we design a new n-type semiconducting polymer and present a pre-aggregation controlling approach that enables the morphology of the novel n-type conjugated polymer to transition from fibril into nanofibers. Utilizing the Hansen solubility parameter, we systematically screen thousands of solvents to refine our selection, thereby providing a comprehensive guideline for selecting solvents conducive to nanofiber formation. We visualize a shape change in polymer pre-aggregation within the solution state upon the addition of different anti-solvents, driven by their interaction affinities with the polymer's backbone or alkyl chain. We further establish a self-assembly nanofiber formation mechanism, discussing the effects of solvent/anti-solvent interaction and the influence of boiling points on this process and draw correlations between the pre-aggregation in the solution state and the morphology of the solid state. By extending our rules to p-type conjugated polymers, we successfully tune them into nanofibers, thereby validating our mechanism and demonstrating the universality of our guideline. The demonstrated n-type semiconductor nanofibers will offer deeper insights into the development of complementary circuits and sensors. The ability to control the morphology of conjugated polymers offers enhanced avenues for advancements in flexible and stretchable electronics and paves the way for the development and design of materials with tailored properties for next-generation electronic applications.






 

We demonstrate electroadhesion, i.e., adhesion induced by an electric field, between cationic hydrogels and animal tissues [1, 2]. When gel and tissue are placed under an electric field (DC, 10 V) for 20 s, the pair strongly adhere, and the adhesion persists indefinitely thereafter. Applying the DC field with reversed polarity reverses the adhesion. Electroadhesion works with tissues of many mammals (cow, pig, chicken, and mouse), and is especially strong in the case of the aorta, cornea, lung, and cartilage. Only cationic gels can be electroadhered to tissues, which suggests that the tissues have anionic character.

We then show the use of electroadhesion to seal cuts or tears in tissues or model anionic gels. Electroadhered gel-patches provide a robust seal over openings in bovine aorta. Moreover, a gel sleeve is able to rejoin pieces of a severed tube (this is the equivalent of a surgery called an anastomosis). These studies raise the possibility of using electroadhesion in surgery while obviating the need for sutures or staples [1, 2]. Advantages include the ability to achieve adhesion on-command, and moreover the ability to reverse this adhesion in case of error.

Conjugated   polymers   with   features   of   flexibility,   stretchability,  and  printability  have  huge  potential  applications  in  soft  robotics, health monitoring, and human-machine interface. Here, I will present our group's efforts in developing various materials for developing these functional polymers. For instance, we have developed a highly stretchable and autonomic self-healable conducting film, which exhibits stretchability as high as 630% and high electrical conductivity of 320 S cm−1, while possessing the ability to repair both mechanical and electrical breakdowns when under-going severe damage at ambient conditions.This polymer composite film is further utilized in a tactile sensor, which exhibits good pressure sensitivity of 164.5 kPa−1, near hysteresis-free, an ultrafast response time of 19 ms, and excellent endurance over 1500 consecutive presses. Additionally, an integrated 5 × 4 stretchable and self-healable organic electrochemical transistor (OECT) array with great device performance is successfully demonstrated. The developed stretchable and autonomic self-healable conducting film significantly increases the practicality and shelf life of wearable electronics, which in turn, reduces maintenance costs and build-up of electronic waste.

Material degradation stands as a paramount concern for both material scientists and engineers. The repercussions of degradation extend beyond mere failure, often necessitating costly repair efforts. Consequently, there exists a keen interest in the development of self-healing materials to render maintenance obsolete. Unlike their inorganic semiconductor counterparts, organic semiconducting materials exhibit notably low Young's moduli, rendering them exceptionally suited for deployment in wearable electronic devices that can be directly applied to human skin [1]. However, wearable electronics are particularly vulnerable to a host of environmental stressors, including mechanical wear, chemical exposure, temperature fluctuations, and radiation. The relentless impact of these stressors can lead to the deterioration of the chemical structure, resulting in the degradation and eventual loss of the material's physical properties.

In this context, we will delve into our strategy for mitigating the loss of physical properties through the development of intrinsically self-healing polymers. This accomplishment was made possible by harnessing the principles of supramolecular chemistry, particularly the utilization of intramolecular hydrogen bonds [2-4]. To gain a comprehensive understanding of the impact of hydrogen bonding on the viscoelastic and electrical characteristics of organic semiconductors, we formulated two distinct material sets: Firstly, a conjugated polymer with incorporated hydrogen bonding functionality and seondly a composite material comprising a conjugated polymer embedded within a self-healing polysiloxane matrix.

Our discussion will encompass the effects of these diverse approaches on charge transport and self-healing capabilities. Furthermore, we will outline how we can exploit the observed disparities to tailor not only the electronic properties but also the self-healing and mechanical attributes of the material to suit specific applications and their unique demands.

Materials able to regenerate after damage have attracted a great deal of attention since the ancient times. For instance, self-healing concretes, able to resist earthquakes, aging, weather, and seawater are known since the times of ancient Rome and are still the object of research.

While several mechanically healable materials have been reported, self-healing conductors are still relatively rare, and are attracting enormous interest for applications in electronic skin, wearable and stretchable sensors, actuators, transistors, energy harvesting, and storage devices, such as batteries and supercapacitors.1 Self-healable and recyclable conducting materials have the potential to reduce electronic waste by enabling the repair and reuse of electronic components, which can extend the lifespan of electronic devices. Furthermore, they can be used for wearable electronic and biomedical devices, which are often subject to mechanical stress causing damage to their components.

Conducting polymers exhibit attractive properties that makes them ideal materials for bioelectronics and stretchable electronics, such as mixed ionic-electronic conductivity, leading to low interfacial impedance, tunability by chemical synthesis, ease of process via solution process and printing, and biomechanical compatibility with living tissues. However, they show typically poor mechanical properties and are therefore not suitable as self-healing materials.

In our group, we produced several self-healing and stretchable conductors by mixing aqueous suspensions of the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with other materials providing the mechanical characteristics leading to self-healing, like for instance polyvinyl alcohol (PVA), polyethylene glycol, polyurethanes and tannic acid. 2-10 In this talk, various types of self-healing will be presented and correlated with the electrical ad mechanical properties of the materials. The use of the self-healing gels and films as epidermal electrodes and other devices will be also discussed.

REFERENCES

Y. Li, X. Zhou, B. Sarkar, F. Cicoira et al., Adv. Mater. 2108932, 2022.

Y. Li, X. Li, S. Zhang, F. Cicoira et al., Adv. Funct. Mater. 30, 2002853, 2020.

Y. Li, X. Li, R. N., S. Zhang, F. Cicoira, et al. Flexible and Printed Electronics 4, 044004, 2019.

N. Rossetti, F. Cicoira et al., ACS Appl. Bio Mater. 2, 5154-5163, 2019.

C. Bodart, N. Rossetti, F. Cicoira et al. ACS Appl. Mater. Interfaces,11, 17226-17233, 2019.

S. Zhang, Y. Li, F. Cicoira et al. Adv. Electron. Mater 1900191, 2019.

S. Zhang, F. Cicoira, Adv. Mater. 29, 1703098, 2017.

X. Zhou, G. A. Lodygensky, F. Cicoira et al., Acta Biomaterialia 139, 296-306, 2022.

X. Zhou et al, Advanced Sensor Research, in press, 2023

P. Kateb et al., Flexible and Printed Electronics, in press.