3D food printing sectors require comprehensive knowledge on viscoelastic and mechanical properties of diverse food materials in order to effectively utilize them in rapid and customized 3D production for supply and manufacturing chains. In this work, we present mechanical and rheological properties of Agar and Konjac based edible gels at different Agar and Konjac weight ratio and discuss their 3D printing performance. Gel samples with higher Konjac content positively contributed to the viscoelastic properties of the gel samples which in return has been found viable for extrusion-based 3D printing. By choosing appropriate printing parameters, different shapes are printed to demonstrate printing resolution. We expect, this study will add potential scope for evaluating and optimizing soft-gel materials for 3D food printing sector.

Utilization of soft material like hydrogels for task-specific applications such as in soft robotics requires freedom in the manufacturing process and designability. Here, we have developed highly robust thermoresponsive poly(dimethyl acrylamide-co-stearyl acrylate and/or lauryl acrylate) (PDMAAm-co-SA and/or LA)-based shape memory gels (SMGs) using a customized optical 3D gel printer. This process enabled rapid and moldless fabrication of SMGs with a variety of shapes and sizes. By varying the compositions of the constituent monomers, a wide variety of SMGs with tunable mechanical, thermal, optical and swelling properties have been obtained. Printed SMGs with excellent fixity and recovery ratios have exhibited a wide range of values of Young's modulus (0.04–17.35 MPa) and strain (612–2363%) at room temperature when the acrylate co-monomer (SA and LA) content was varied and the value of strain has been found to be enhanced at elevated temperatures. Thermogravimetric analysis (TGA) of the SMGs shows one step peak degradation (407–417 °C) regardless of composition after an initial mass loss due to water evaporation. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) revealed variable transition temperatures (29–49.5 °C) depending on the SA and LA content. SMGs with all of the composition ratios possess high transparency with variable swelling degrees in water and different organic solvents and exhibit refractive index values in the range of intraocular lenses, making them suitable for applications in the optical field. These unique properties of 3D printed SMGs with free formability and tunable properties are expected to generate rapid demand in a variety of sectors in biomedicine, robotics and sensing applications.

4D printing is based on 3D printing technology with an added dimension, where the printed structure evolves as a function of time. Materials that are stimuli-responsive are used for 4D printing such as shape memory alloys and polymers etc. Once these materials are 3D printed, they can morph into complex geometries on being exposed to external stimuli such as heat, temperature, pH etc. Among various stimuli responsive materials, gels are of great interest to soft robotics community because of their toughness and flexibility. Designing of complex 4D printed gel objects that are preprogrammed to morph into otherwise unattainable geometries opens the door for numerous applications in every field of science and technology. This paper presents a comprehensive review of current trends, prospects and challenges in 4D printing of gel materials with a focus towards their applications in soft robotics and bionic devices.