The field of additive manufacturing (more commonly known as three-dimensional printing) has developed significantly in recent years, consequently increasing the need for new materials for the fabrication of functional 3D structures. It is currently being used for a variety of applications ranging from modelling to medical devices. Current methods are based on layer-by-layer fabrication of a three dimensional structure, each layer being built by one of the following methods: (1) Fuse Deposition Modelling (FDM) based on melting a material which is typically a polymer (2) Selective Laser Sintering (SLS) based on laser melting of powder particles, (3), Color Jet Printing (CJP) based on jetting a binder onto a powder, and (4),stereo lithography (SLA) which is based on selective curing of polymerizable monomers. A common method for this technique is Digital Light Processing (DLP) which is based on selective polymerization of individual pixels within a thin layer. This is done by using a digital micro mirror device (DMD) that results in small dots (tens of micrometers).
Our research is focused on developing new materials for most types of 3D printing technologies, including conductive inks, ceramic materials and metals, and shape memory polymers. Some of the research activities will be described in the following sections.
Highly Stretchable and UV Curable Elastomer for Three Dimensional Printing
We have developed compositions of highly stretchable and UV curable (SUV) elastomers that can be stretched by up to 1100%, which is more than five times the elongation at break of the existing UV curable elastomers and are suitable for UV curing based 3D printing technologies. Using DLP printing with the SUV elastomer compositions enabled the direct creation of complex 3D lattices or hollow structures that exhibit extremely large deformation. For example, we directly printed a soft actuator and a soft robotic gripper which have a complex 3D and hollow structures and can undergo large local deformations (Fig. 1). We also demonstrated a 3D Bucky ball light switch by combining the DLP printing with a silver nanoparticles coating and room temperature sintering process. Overall, the SUV elastomers will significantly enhance the capability of the DLP based 3D printing of fabricating soft and deformable 3D structures and devices including soft actuators and robots, flexible electronics, acoustic metamaterials, and many other applications (The scale bar in the figures in 10 mm). Adv. Mater. DOI: 10.1002/adma.201606000.
Figure 1. Shows different 3D printed structures such as soft actuator, gripper, spherical balloon and electronic switches using SUV elastomer
Porous structures by printing Oil-in-Water emulsions
A new ink was developed for printing porous structures that can be used for embedding various functional materials. The ink is composed of a UV polymerizable Oil-in-Water emulsion which can be converted into a solid object upon UV irradiation, forming a porous structure after evaporation of the water phase. The water phase can contain silver NP that are sintered by a chemical sintering, resulting in a 3D conductive structure (Fig.2). The surface area of the object can be controlled by changing the emulsion's droplets size and the dispersed phase fraction. see: Journal of Materials Chemistry C 1.19 (2013): 3244-3249. and Journal of Materials Chemistry C 3.9 (2015): 2040-2044.
Fig. 2: Printed 3D porous (left) and conductive objects (right)
3D and 4D printing of shape memory materials
Until now, Shape Memory Polymers (SMPs) were not used in the field of 3D printing or flexible electronics due to inadequate processing technologies. We developed a new process and inks which enables printing of oligomer melts in a DLP printer, to generate high-resolution three-dimensional (3D) shape memory structures (Fig. 3). We also demonstrated how these printed structures can be further utilized for constructing flexible electronic devices (Fig.4), see: Adv. Mater.. doi:10.1002/adma.201503132
Fig. 3: 3D printed structures changing shape upon heating due to the shape memory polymer.
Fig. 4: Printed 3D electrical circuit made of shape memory polymers, activated by heat.