Conjugated polymers (CP), as exemplified by polypyrrole (PPy), are intrinsically conducting polymers with potential for development as soft actuators or 'artificial muscles' for numerous applications. Significant progress has been made in our understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g. low driving potential, easy to miniaturise) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns and textiles, operating in liquids as well as in air for, ready for use by engineers. This review initially highlights the milestones made in understanding these unique materials and their development as actuators. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials possessing a wealth of multifunctional properties.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Micro-actuators have been developed that exploit the electrochemically induced volume change of the electro-active polymer polypyrrole. The strain regime is inherently complex at a physical level and whilst volume change can be estimated indirectly using, for instance, bending beam theory, such methods become unreliable for large deflections owing to limitations in the mathematical model. A new non-contact measuring technique based on laser micrometry is presented to characterize the timedependent expansion of electro-active films such as polypyrrole. Measurements have been made which demonstrate that the observed strain is dependent on film thickness. The new measurement technique is straightforward to perform and it is anticipated that it can be used for future materials development and performance assessment, including long term stability evaluations and operational failure studies of the films.

Conducting polymers such as polypyrrole are biocompatible materials used in bioelectronic applications and microactuators for mechanobiology and soft microrobotics. The materials are commonly electrochemically synthesised from an electrolyte solution comprising pyrrole monomers and a salt, which is incorporated as the counter ion. This electrosynthesis results in polypyrrole forming a threedimensional network with extensive cross-linking in both the alpha and beta positions, which impacts the electro-mechanical performance. In this study we adopt a 'blocking strategy' to restrict and control cross-linking and chain branching through beta substitution of the monomer to investigate the effect of crosslinking on the electroactive properties. Methyl groups where used as blocking groups to minimise the impact on the pyrrole ring system. Pyrrole, 3-and 3,4-methyl substituted pyrrole monomers were electro-polymerised both as homo-polymers and as a series of co-polymer films. The electroactive performance of the films was characterised by measuring their electrochemical responses and their reversible and non-reversible film thickness changes. This showed that altering the degree of crosslinking through this blocking strategy had a large impact on the reversible and irreversible volume change. These results elaborate the importance of the polymer structure in the actuator performance, an aspect that has hitherto received little attention.