Thermotherapy shows significant potential for pain relief and enhanced blood circulation in wildlife rehabilitation, particularly for injured animals. However, the widespread adoption of this technology is hindered by the lack of biodegradable, wearable heating pads and concerns surrounding electronic waste (E-waste) in natural habitats. This study addresses this challenge by investigating an environmentally-friendly composite comprising poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), seaweed cellulose, and glycerol. Notably, this composite exhibits remarkable biodegradability, losing half of its weight within one week and displaying noticeable edge degradation by the third week when placed in soil. Moreover, it demonstrates impressive heating performance, reaching a temperature of 51 °C at a low voltage of 1.5 V, highlighting its strong potential for thermotherapy applications. The combination of substantial biodegradability and efficient heating performance offers a promising solution for sustainable electronic applications in wildlife rehabilitation and forest monitoring, effectively addressing the environmental challenges associated with E-waste.

Sensors as a composite film made from reduced graphene oxide (rGO) structures filled with a silicone elastomer are soft and flexible, making them suitable for wearable applications. The sensors exhibit three distinct conducting regions, denoting different conducting mechanisms when pressure is applied. This article aims to elucidate the conduction mechanisms in these sensors made from this composite film. It was deduced that the conducting mechanisms are dominated by Schottky/thermionic emission and Ohmic conduction.

Electronic skins have attracted significant interest due to their broad applications in our daily lives. Flexible pressure sensors form one of the essential parts of any electronic skin. Achieving high-performance electronic skins requires ways to make pressure sensor arrays with high sensitivity and good flexibility. We report on the facile fabrication of flexible piezo-resistive pressure sensor arrays with excellent mechanical stability, high sensitivity, and a wide working range (0–30 kPa) of pressure using reduced graphene oxide (rGO) on flexible PCB (FPCB). It shows a remarkable sensitivity of 0.13 kPa−1 in the pressure range < 10 kPa and 0.05 kPa−1 in the range of > 10 kPa, covering a broad spectrum of testing conditions. We demonstrated that it could provide a pressure map and intensity, giving tactile information of the pressure exerted on our prototype with a 4 × 4 array.

In this paper, the effect of strain rate on the output signal of highly stretchable interdigitated capacitive (IDC) strain sensors is studied. IDC sensors fabricated with pristine Ecoflex and a composite based on 40 wt% of 200 nm barium titanate (BTO) dispersed in a silicone elastomer (Ecoflex 00-30TM) were subjected to 1000 stretch and relax cycles to study the effect of dynamic loading conditions on the output signal of the IDC sensor. It was observed that the strain rate has no effect on the output signal of IDC sensor. To study the non-linear elastic behaviour of pristine Ecoflex and composites based on 10, 20, 30, 40 wt% of 200 nm BTO filler dispersed in a silicone elastomer, we conducted uniaxial tensile testing to failure at strain rates of ~5, ~50, and ~500 mm/min. An Ogden second-order model was used to fit the uniaxial tensile test data to understand the non-linearity in the stress-strain responses of BTO-Ecoflex composite at different strain rates. The decrease in Ogden parameters (α1 and α2) indicates the decrease in non-linearity of the stress-strain response of the composite with an increase in filler loading. Scanning electronic microscopy analysis was performed on the cryo-fractured pristine Ecoflex and 10, 20, 30, and 40 wt% of BTO-Ecoflex composites, where it was found that 200 nm BTO is more uniformly distributed in Ecoflex at a higher filler loading levels (40 wt% 200 nm BTO). Therefore, an IDC sensor was fabricated based on a 40 wt% 200 nm BTO-Ecoflex composite and mounted on an elastic elbow sleeve with supporting electronics, and successfully functioned as a reliable and robust flexible sensor, demonstrating an application to measure the bending angle of an elbow at slow and fast movement of the arm. A linear relationship with respect to the elbow bending angle was observed between the IDC sensor output signal under a 50% strain and the deflection of the elbow of hand indicating its potential as a stretchable, flexible, and wearable sensor.

In this paper, the creep behaviour of stretchable interdigital capacitive (IDC) large strain sensors is studied. A generalized Kelvin-Voigt (GKV) model is used to study the creep behaviour of the sensor's substrate material, manufactured from silicone elastomer (Ecoflex 00-30) with barium titanate (BTO) filler. Creep experiments are performed on sensors with 10, 20, 30 and 40 wt% BTO nanoparticles with dimensions of 100 nm and 200 nm dispersed in the elastomer. The BTO was used to increase the overall permittivity of the substrate, hence raising the capacitance of the IDC sensor. The effect of BTO on the GKV model parameters was studied in detail through analysis of the creep response. The pristine Ecoflex silicone elastomer is predominately a hyperelastic material, which shows negligible creep, while the addition of BTO particles led to the composite exhibiting creep such that the composite behaves like a visco-hyperelastic material. Hence, this behaviour results in the creep affecting the electrical sensing performance of the capacitive strain sensors during static loading conditions. This information provides insights on the impact of composite composition on creep-resistance and output signal of the sensor (capacitance). Crown Copyright (C) 2021 Published by Elsevier B.V. All rights reserved.

Multi-material in-air coalescence inkjet printing technique and the patterned COF using this printing method.

The stress relaxation behaviour of barium titanate (BTO) - elastomer (Ecoflex) composites used in a large strain sensor is studied using a generalized Maxwell-Wiechert model. In this paper, we examine the stress relaxation behaviour of ceramic polymer composites, by conducting stress relaxation tests on samples prepared with varying the particle loading by 0, 10, 20, 30 and 40 wt% of 100 nm or 200 nm BTO ceramic particles embedded in a Ecoflex silicone based hyperelastic elastomer. The influence of BTO on spring-dashpot coefficients of the Maxwell-Wiechert model is studied through the stress relaxation experiments. While a pristine Ecoflex silicone is predominantly a hyperelastic material, the addition of BTO made the composite behave as a visco-hyperelastic material. However, this behaviour has negligible effect on the electrical performance of the large strain sensor.

Reactive inkjet printing holds great prospect as a multimaterial fabrication process because of its unique advantages involving customization, miniaturization, and precise control of droplets for patterning. For inkjet printing of hydrogel structures, a hydrogel precursor (or cross-linker) is printed onto a cross-linker (or precursor) bath or a substrate. However, the progress of patterning and design of intricate hydrogel structures using the inkjet printing technique is limited by the erratic interplay between gelation and motion control. Accordingly, microreactive inkjet printing (MRIJP) was applied to demonstrate a spontaneous 3D printing of hydrogel microstructures by using alginate as the model system. In addition, a printable window within the capillary number-Weber number for the MRIJP technique demonstrated the importance of velocity to realization of in-air binary droplet collision. Finally, systematic analysis shows that the structure and diffusion coefficient of hydrogels are important factors that affect the shape of printed hydrogels over time. Based on such a fundamental understanding of MRIJP of hydrogels, the fabrication process and the structure of hydrogels can be controlled and adapt for 2D/3D microstructure printing of any low-viscosity (<40 cP) reactive inks, with a representative tissue-mimicking structure of a similar to 200 mu m diameter hollow tube presented in this work.

Additive manufacturing (AM) is becoming increasingly popular because of its unique advantages. However, AM still suffers from support material waste during the fabrication process when overhanging features exist. Plenty of research has been carried out for minimising support usage. However, former studies only focused on the optimisation for a single part fabrication. In this paper, a four-step strategy of multi-part production for reducing support consumption in AM is proposed. When printing a group of parts in the same build vat or chamber, the proposed strategy optimises the print orientation for each part, combines every two parts based on the geometries, proposes several possible multi-part combinations, and then selects the optimal part positions for fabrication. Two case studies are carried out for verification. The results show that the four-step strategy can significantly reduce the support waste and total fabrication time.

The gelation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has gained popularity for its potential applications in three dimensions, while possessing tissue-like mechanical properties, high conductivity, and biocompatibility. However, the fabrication of arbitrary structures, especially via inkjet printing, is challenging because of the inherent gel formation. Here, microreactive inkjet printing (MRIJP) is utilized to pattern various 2D and 3D structures of PEDOT:PSS/IL hydrogel by in-air coalescence of PEDOT:PSS and ionic liquid (IL). By controlling the in-air position and Marangoni-driven encapsulation, single droplets of the PEDOT:PSS/IL hydrogel as small as a diameter of ≈260 μm are fabricated within ≈600 μs. Notably, this MRIJP-based PEDOT:PSS/IL has potential for freeform patterning while maintaining identical performance to those fabricated by the conventional spin-coating method. Through controlled deposition achieved via MRIJP, PEDOT:PSS/IL can be transformed into different 3D structures without the need for molding, potentially leading to substantial progress in next-generation bioelectronics devices.

In traditional directed energy deposition (DED) processes, post-processing involving laser cutting or wire electrical discharge machining is necessary for removing printed parts from the substrate, which is time consuming and labor intensive. In this letter, a support interface method for DED is proposed for direct part removal without additional machining operations. A strut array is first printed as a sacrificial layer, upon which the actual part is then deposited. This letter demonstrates the method feasibility with a customized DED setup. It is expected that the proposed strategy will be beneficial in various DED processes to enhance process efficiency and automation.

Self-folding, whereby a 2D net autonomously folds into a pre-ordained 3D shape when exposed to a stimulus, shows potential, in a manner similar to 3D printing, as a means of easily customisable digital manufacture. It also presents some inherent advantages over conventional additive manufacturing techniques, such as the low cost associated with mass-production of polymer sheets and coatings, the compatibility with most planar manufacturing techniques, and the ease of storage and transportation. A self-folding mechanism was developed by inkjet printing silver nanoparticle suspensions onto polyethylene terephthalate (PET) sheets. By providing sufficient electrical power to the printed tracks, resistive heating causes folding to occur along the printed silver lines. A bilayer strip model was adapted to analyse the steady-state fold angle of the PET substrate, which shows good qualitative agreement, and reasonable quantitative agreement, with the experimental data. Furthermore, inkjet-printed silver tracks are known for a significant reduction in resistivity as the sintering temperature increases. Therefore, a power control system that utilises a real-time resistance sensor was developed to enable power reference tracking. The developed mechanism was able to achieve folds up to 90° and a fast actuation time of 35 s when 2.25 W was provided to a 3 mm by 40 mm silver track.

The micro-reactive inkjet printing technique and the patterned conductive PANI on a glass substrate using this printing method.

This work investigates the performance of a Barium-Titanate (BTO) elastomer composite interdigital capacitive based large strain sensor. The high strain interdigital capacitive sensor examined here is fabricated using a ceramic polymer composite substrate with different sizes of BTO’s nanoparticles based on 100 nm or 200 nm BTO ceramic particles dispersed uniformly in an Ecoflex™ 00-30 silicone based elastomer. While BTO particles with a 100 nm particle size offers a higher relative permittivity and slightly higher change in capacitance with strain, it is demonstrated to be less reliable than those formed with 200 nm BTO nanoparticles.

The emergence of additive manufacturing (AM) technologies (also known as 3D printing) promotes the reduction of material consumption in terms of avoiding the repeated fabrication of dies as well as comparatively high material efficiency. However, despite widespread application and evident advantages over traditional manufacturing techniques, AM still suffers from redundant support material usage when printing parts with overhanging features. In this article, a support generation method through print path planning is proposed for the first time, with the aim of reducing support material consumption in AM of parts with flat features. Print path can significantly influence the support usage when considering the longest printable bridge length. Two parts are printed by our new method with much less support consumption than general line and grid support generation methods. The results show the effectiveness of this new support generation method in terms of both reducing the support consumption and finish surface deterioration, enabling AM to be a more environmental friendly and sustainable manufacturing technique.

Despite of additive manufacturing technologies being rapidly developed with wide applications in the fields of aerospace, engineering, medical application and marine, support structures are still unavoidable for many printed products with overhangs, resulting in extended build time and expensive post-processing, material waste, and sometimes failure to fabricate the part of the required quality. The threshold overhang angle that can be self-supported is generally set at 45° for FDM printers. However, different process parameters such as extrusion temperature and print speed can also have a great impact on printable threshold overhang angle (PTOA). In this paper, the influence of extrusion temperature on PTOA is studied theoretically and experimentally for the achievement of the lowest possible PTOA. First, theoretical analysis of overhang with regard to extrusion temperature is carried out. Then experiments of overhangs with 20°, 30°, 40° and 50° in extrusion temperatures of 175 °C, 190 °C, 205 °C and 220 °C are conducted on an FDM printer. According to the results, PTOA can be quite different under various extrusion temperatures and the theoretical analysis can be used for predicting the lowest PTOA. The findings can also provide some references for future research in high-precision printing by adjusting relevant print parameters.

Wearable electronics and soft robotics are emerging fields utilizing soft and stretchable sensors for a variety of wearable applications. In this paper, the fabrication of a highly stretchable capacitive sensor with a printed carbon black/Ecoflex interdigital capacitor is presented. The highly stretchable capacitive sensor was fabricated on a substrate made from barium titanate–EcoflexTM 00-30 composite, and could withstand stretching up to 100%. The designed highly stretchable capacitive sensor was robust, and showed good repeatability and consistency when stretched and relaxed for over 1000 cycles.

Among the available additive manufacturing technologies, extrusion based 3D printing (otherwise known as fused deposition modelling or fused filament fabrication) is among the most commonly used due to low cost and relative simplicity. However, such printers still suffer from redundant support material waste (both interior and exterior) when printing large-volume solid objects or objects with overhangs. The support material can also be a significant cause of long part production time and higher energy consumption during manufacture. Hence, we propose a new support generation strategy considering both interior and exterior support via AM process planning to reduce the total amount of material consumption, production time and energy consumed for manufacturing an object. Print path and print orientation are both considered as significant factors and are both optimized for achieving the lowest consumption of material. The areas to be filled on each layer are determined according to the printable threshold overhang angle (PTOA) and the longest printable bridge length (LPBL). The characteristics of LPBL and PTOA are fully considered for saving more material. Several tests are used to verify the proposed strategy and the results show that this strategy can considerably reduce material waste, production time and energy consumed compared with conventional strategies, enabling AM to be a more environmentally friendly and sustainable manufacturing technique.

In recent years, additive manufacturing has been developing rapidly mainly due to the ease of fabricating complex components. However, complex structures with overhangs inevitably require support materials to prevent collapse and reduce warping of the part. In this paper, the effects of process parameters on printable bridge length (PBL) are investigated. An optimisation is conducted to maximise the distance between support points, thus minimising the support usage. The orthogonal design method is employed for designing the experiments. The samples are then used to train a neural network for predicting the nonlinear relationships between PBL and process parameters. The results show that the established neural network can correctly predict the longest PBL which can be integrated into support generation process in additive manufacturing for maximising the distance between support points, thus reducing support usage. A framework for integrating the findings of this paper into support generation process is proposed.

Additive manufacturing (AM) has developed rapidly since its inception in the 1980s. AM is perceived as an environmentally friendly and sustainable technology and has already gained a lot of attention globally. The potential freedom of design offered by AM is, however, often limited when printing complex geometries due to an inability to support the stresses inherent within the manufacturing process. Additional support structures are often needed, which leads to material, time and energy waste. Research in support structures is, therefore, of great importance for the future and further improvement of additive manufacturing. This paper aims to review the varied research that has been performed in the area of support structures. Fifty-seven publications regarding support structure optimization are selected and categorized into six groups for discussion. A framework is established in which future research into support structures can be pursued and standardized. By providing a comprehensive review and discussion on support structures, AM can be further improved and developed in terms of support waste in the future, thus, making AM a more sustainable technology.