According to a team of Penn State researchers, integrating two different polymer forms can switch manufacturing of silicone parts from molding, casting and spin coating basic forms, to 3D printing intricate geometries, with improved mechanical characteristics and better biological adhesion.

« So far, PDMS (polydimethylsiloxane, or silicone) has limitations in formability and manufacturing of devices, » said Ibrahim T. Ozbolat, Hartz Family Associate Professor of Engineering Science and Mechanics and Bioengineering. « Most research is done using casting or micro molding, but this fabrication yields materials with weak mechanical properties and also weak cell adhesion. Researchers often use extracellular proteins like fibronectin to make cells adhere. »

PDMS is used to produce lab-on-a-chip devices, two- and three-dimensional cell culture platforms, organ-on-a-chip devices and biological machines. The material is more commonly used in flexible baking pans and heat-resistant silicone spatulas, but these are geometrically simple and can be effortlessly molded. If the material is used for growing tissue cultures or testing, the geometries become much smaller and more multifaceted.

For any material to serve as « ink » in a 3D printer, it must be able to pass through the printing nozzle and maintain shape once it is deposited. The material cannot seep, spread or flatten, otherwise the integrity of the design vanishes. Sylgard 184, an elastomer of PDMS, is not adequately viscose to use in 3D printing – the material just flows out of the nozzle and puddles. However, when it is blended with SE 1700, another PDMS elastomer, in the proper ratio, the mixture is printable.

« We optimized the mixture for printability, to control extrusion and fidelity to the original pattern being printed, » said Ozbolat.

The researchers improve the mixture to exploit a materials property known as « shear thinning. » They report their results in the January edition of ACS Biomaterials Science & Engineering.

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