3D Printing PDMS Elastomer in a Hydrophilic Support Bath via Freeform Reversible Embedding

Abstract

Polydimethylsiloxane (PDMS) elastomer is used in a wide range of biomaterial applications including microfluidics, cell culture substrates, flexible electronics, and medical devices. However, it has proved challenging to 3D print PDMS in complex structures due to its low elastic modulus and need for support during the printing process. Here we demonstrate the 3D printing of hydrophobic PDMS prepolymer resins within a hydrophilic Carbopol gel support via freeform reversible embedding (FRE). In the FRE printing process, the Carbopol support acts as a Bingham plastic that yields and fluidizes when the syringe tip of the 3D printer moves through it, but acts as a solid for the PDMS extruded within it. This, in combination with the immiscibility of hydrophobic PDMS in the hydrophilic Carbopol, confines the PDMS prepolymer within the support for curing times up to 72 h while maintaining dimensional stability. After printing and curing, the Carbopol support gel releases the embedded PDMS prints by using phosphate buffered saline solution to reduce the Carbopol yield stress. As proof-of-concept, we used Sylgard 184 PDMS to 3D print linear and helical filaments via continuous extrusion and cylindrical and helical tubes via layer-by-layer fabrication. Importantly, we show that the 3D printed tubes were manifold and perfusable. The results demonstrate that hydrophobic polymers with low viscosity and long cure times can be 3D printed using a hydrophilic support, expanding the range of biomaterials that can be used in additive manufacturing. Further, by implementing the technology using low cost open-source hardware and software tools, the FRE printing technique can be rapidly implemented for research applications.

3D Printing of Transparent and Conductive Heterogeneous Hydrogel–Elastomer Systems

“…For applications where a higher resolution is required, many techniques and products are available to adjust the rheological behavior of the PDMS precursor. [5,24,[43][44][45][46][47] The development of the hydrogel precursor for our extrusion printing was more demanding and required a balance between conductivity, stability, and rheological characteristics.…”

Support Structures for Additive Manufacturing: A Review

“…Then, the whole liquid structure is solidified in situ by applying suitable cross-linking mechanisms [74,75]. Hinton et al [76] demonstrated a new method of 3D printing polydimethylsiloxane (PDMS) using a hydrophilic Carbopol support bath. Carbopol support acts as a Bingham plastic that yields and fluidizes when the syringe tip of the 3D printer moves through it, but acts as a solid for the PDMS extruded within it.…”

Current developments in 3D bioprinting for tissue engineering

“…After the printing is completed, the fugitive inks are transformed from a gel to a liquid by simply altering the temperature and then the resulting liquid can be drained away leaving the bioprinted structure behind. Fugitive inks are used in two ways, either around the structure (in the form of a supporting bath) to support its creation in free space [1][2][3] or inside the structure to enable the creation of internal channels [4].…”

“…Previously when printing within a hydrogel, filler material is required to restore the resulting voids and crevasses left by the nozzle as it travels through the hydrogel material [1]. However, a new technique called Freeform Reversible Embedding of Suspended Hydrogels (FRESH) [2], or more simply Freeform Reversible Embedding (FRE) [3], has been developed which uses a supporting bath composed of a material that exhibits a Bingham plastic rheology, flowing as a viscous fluid at high shear stresses but behaving as a rigid body at lower shear stresses. Due to this property of the bath, the syringe nozzle can travel through the supporting material with negligible resistance while the extruded material is supported and the geometry of the printed structure is maintained.…”

“…In FRESH the supporting material is composed of a slurry of gelatin microparticles which is melted and washed away by simply raising the temperature to 37 °C when the structure is completed [2]. While FRE utilised a hydrophilic Carbopol gel to support the 3D printing of hydrophobic PDMS prepolymer resins; after the PDMS print is cured, it can be released by liquefying the Carbopol in the presence of ionic solutions such as phosphate buffered saline solution [3].…”