(356c) 3D Printing with Soft Porous Silicones By the Homocomposite Thixotropic Paste (HTP-3DP) Method

Three dimensional (3D) printing with soft materials is important for a number of applications out of which stand out biomedical materials and scaffolds. One common 3D printing method, direct ink writing, requires thixotropic inks that are flowable at high shear stress but possess high storage moduli and yield stresses. Many precursors for soft materials are liquid at room temperature before crosslinking and are made tixotropic by fillers such as fumed silica, clay nanoplatetes or cellulose nanocrystals. However, the use of fillers is problematic because it may deteriortate the mechanical properties of the resulting composite materials. We will introduce and report the results of a new method of 3D printing of soft materials with homocomposite thixotropic paste (HTP). The new 3D printing inks consist of water and two silicone-based components: crosslinked PDMS microbeads and liquid PDMS phase. Owing to the capillary binding of the microbeads, suspensions containing certain fractions of PDMS liquid precursor behave like pastes, which are flowable at high shear stress but possess the yield stress needed for direct ink writing. The Homocomposite Thixotropic Pastes (HTPs) can be directly extruded and shaped on a 3D printer. The liquid PDMS bridges are thermally crosslinked after printing, resulting in remarkably elastic and flexible structures (Adv. Mater. 2017). Their porosity and mechanical properties, such as tensile modulus, could be controlled by the fraction of liquid precursor in the original multiphasic dispersion. As the HTP-3DP inks are made of porous biocompatible silicone, they can be 3D printed under water and may find applications such as direct printing of bio-scaffolds on live tissue.