Recent advances in paraffin-based actuation: A pathway to multifunctional systems

Around the turn of the century, paraffin as a phase change material demonstrated great potential in the field of microactuators due to its high thermal expansion and high mechanical work capacity. Since then, paraffin actuator research has vastly expanded as new applications in bioengineering, soft robotics and self-tracking systems have emerged. Despite this progress, the most recent comprehensive review was published over a decade ago, leaving a comparatively huge gap in the literature. This review addresses that gap by examining the recent advances and latest developments over the past 10 years, while also including earlier studies not covered in the previous review. In addition to classical microactuators in which the phase change of paraffin triggers the actuation, new concepts for building alternative actuators are presented. These concepts exploit the synergy with other materials and achieve actuation without the use of phase change. We also describe the use of paraffin actuators as switches for smart surface adaptation in terms of stiffness, transparency and adhesion. The scope of this work is to demonstrate the potential of combining diverse properties of paraffin across different applications to develop autonomous multifunctional systems. These systems hold the promise of consolidating functionality into a single device, thereby reducing complexity, energy consumption, and maintenance requirements.