This paper reports on what differentiates the field of soft (i.e. soft-bodied) robotics from the conventional hard (i.e. rigid-bodied) robotics. The main difference centres on seamlessly combining the actuation, sensing, motion transmission and conversion mechanism elements, electronics and power source into a continuum body that ideally holds the properties of morphological computation and programmable compliance (i.e. softness). Another difference is about the materials they are made of. While the hard robots are made of rigid materials such as metals and hard plastics with a bulk elastic modulus of as low as 1 GPa, the monolithic soft robots should be fabricated from soft and hard materials or from a strategic combination of them with a maximum elasticity modulus of 1 GPa. Soft smart materials with programmable mechanical, electrical and rheological properties, and conformable to additive manufacturing based on 3D printing are essential to realise soft robots. Selecting the actuation concept and its power source, which is the first and most important step in establishing a robot, determines the size, weight, performance of the soft robot, the type of sensors and their location, control algorithm, power requirement and its associated flexible and stretchable electronics. This paper outlines how crucial the soft materials are in realising the actuation concept, which can be inspired from animal and plant movements.

We have developed high affinity Molecularly Imprinted Polymers (MIPs) for neurotransmitters such as dopamine, noradrenaline and caffeine. These polymer particles are mixed within the bulk of screen-printed ink allowing masss-producible bulk modified MIP Screen-Printed Electrodes (MIP-SPEs) to be realised. We have explored different SPE supporting surfaces, such as polyester, tracing paper and household-printing paper. The performance of those MIP-SPEs is studied using the Heat-Transfer Method (HTM), a patented thermal method. With the combination of screen-printing techniques and thermal detection, it is possible to develop a portable sensor platform that is capable of low-cost and straightforward detection of biomolecules on-site. In the future, this unique sensor architecture holds great promise for the use in biomedical devices.

Inkjet printing, of the researched techniques for printing of hydrogels, gives perhaps the best potential control over the shape and composition of the final hydrogel. It is, however, fundamentally limited by the low viscosity of the printed ink, which means that crosslinking of the hydrogel must take place after printing. This can be particularly problematic for hydrogels as the slow diffusion of the crosslinking species through the gel results in very slow vertical printing speeds, leading to dehydration of the gel and (if simultaneously deposited) cell death. Previous attempts to overcome this limitation have involved the sequential printing of alternating layers to reduce the diffusion distance of reactive species. In this work we demonstrate an alternative approach where the crosslinker and gelator are printed so that they collide with each other before impinging upon the substrate, thereby facilitating hydrogel synthesis and patterning in a single step. Using a model system based upon sodium alginate and calcium chloride a series of 3D structures are demonstrated, with vertical printing speeds significantly faster than previous work. The droplet collision is shown to increase advective mixing before impact, reducing the time taken for gelation to occur, and improving definition of printed patterns. With the facile addition of more printing inks, this approach also enables spatially varied composition of the hydrogel, and work towards this will be discussed.

Macroscopic assembling of responsive hydrogels has been used to construct soft actuators that transform their shape upon external stimuli. It remains a challenge to establish a robust assembling interface between gels. Here, we demonstrate a fabrication of bilayered hydrogel actuators assembled by host-guest recognition at the interface. The supramolecular recognition enabled efficient, rapid, and robust macroscopic assembling of hydrogels, which was utilized to create gel bilayers that were actuated upon unbalanced swelling/deswelling.

The effect of ions on the structure and dynamics of aggracan solutions was investigated using a variety of scattering techniques (neutron spin echo, small angle neutron scattering, static and dynamic light scattering). The results show that aggrecan forms microgel-like assemblies which remain stable in the presence of counter-ions. As opposed to many synthetic polyelectrolytes which exhibit a great sensitivity to ion concentration and charge valency, it was found that aggrecan solutions are remarkable insensitive to charge valence. This property of aggrecan is consistent with its biological role as an ion reservoir mediating calcium metabolism and maintaining dimensional stability in cartilage and bone.

We propose a 3D-printable soft, stretchable, and transparent hydrogel-elastomer device that is able to detect simulated ‘nerve’ signals. The signal is passed to a conductive hydrogel electrode through a non-contact method of capacitive coupling through polydimethylsiloxane (PDMS). We demonstrate that the device is able to detect sinusoidal waveforms passed through a simulated ‘nerve’ made from conductive hydrogel over a range of frequencies (1 kHz – 1 MHz). Analysis of signal detection showed a correlation to the electrode contact area and a Vin/Vout of larger than 10%. This provides the framework for the future development of a soft, 3D-printable, capacitive coupling device that can be used as a cuff electrode for detecting peripheral nerve signals.

Recent strategy in the electronics sector is to ascertain the ways to make cheap, flexible and environmentally friendly electronic devices. The 3D inkjet printing technology is based on the Additive Manufacturing concept and it is with no doubt capable of revolutionising the whole system of manufacturing electronic devices including: material selection; design and fabrication steps and device configuration and architecture. Thus, 3D inkjet printing technology (IJP) is not only one of the most promising technologies to reduce the harmful radiation/ heat generation but also achieve reductions in manufacturing cost. Here, we explore the potential of 3D – inkjet printing technology to provide an innovative approach for electronic devices in especially information storage elements by seeking to manufacture and characterise state-of-art fully inkjet printed two terminal electronic memory devices. In this work, ink-jettable materials (Ag and PEDOT:PSS) were printed by a piezoelectric Epson Stylus P50 inkjet printing machine on a flexible substrate. All components of the memory cells of a simple metal/active layer/metal structure were deposited via inkjet printing. The quality of the printed layers was first assessed by Nikon LABOPHOT-2 optical microscope, fitted with Nikon Camera DS-Fi1. Furthermore, an in-depth electrical characterisation of the fabricated memory cells was carried out using HP4140B picoammeter.