Polydimethylsiloxane (PDMS) is a well-known and widely used viscoelastic biomaterial with applications across the tissue engineering and biomedical fields. In general, its use thus far has been limited to applications wherein casting or molding are possible. Advanced Solutions is now demonstrating PDMS bioprinting with its BioAssemblyBot to create complex shapes potentially useful in a variety of applications.
PDMS as a biomaterial
Silicone-based polymers have been used in tissue constructs since the middle of the 20th century. Their early use as a replacement bile duct and urethra exhibited the material’s useful qualities: high bio-compatibility and elasticity. Subsequent tissue constructs applications throughout the intervening 80 years have shown that silicone-based polymers, among which PDMS is the most common, are safe, broadly applicable, and economical. PDMS is characterized by its low surface tension, low modulus (contributing to its biological consistency), hydrophobicity, thermal and electrical stability. Today, PDMS is commonly used in catheter components, pacemaker leads, and contact lenses.
Due to the limited range of possible configurations of cast and molded shapes, it is desirable to 3D print with PDMS. A PDMS bioprinting ink is achieved by blending siloxane polymers SE 1700 and Sylgard 184. SE 1700 is a shear-thinning, high viscosity polymer, which gives the ink the shape fidelity needed after printing. Sylgard 184 is lower viscosity and is blended with SE 1700 to enhance the ability of the ink to run through deposition needles under pressure in 3D printing applications. To make up the printing ink, polymer base and curing agent were combined in a 10:1 ratio. Then SE 1700 and Sylgard 184 were combined in a 4:1 ratio. PDMS blends were loaded into the syringe barrel and centrifuged at 3000g for 5 min to de-gas the material. After printing, constructs were placed in an oven overnight to cure the printed construct.
The PDMS structures were printed using Advanced Solutions Life Sciences’ BioAssemblyBot. A 22GA needle was used to deposit the PDMS ink at 70PSI. Printed shapes included objects designed to test the capacity of the PDMS ink to span empty spaces, create pore spaces in solid blocks, as well as test shape fidelity after curing.
Printed PDMS adheres to well plates and coheres, supporting the printing of complex shapes and structures. Samples were examined pre- and post-curing and minimal shape deformation was seen during the curing process. Microscopic analysis of a small sample revealed that the lines in these constructs average 380 +/- 50 μm after PDMS was cured in an oven at 60oC overnight.
Hollow structures, such as those shown in the figure on the right demonstrate the ability of printed wells to be created within a PDMS print structure. These hollow structures can be used to pattern cell and tissue constructs.
Lattice structures (shown in the image at the top of this article) were used to test the ability of the PDMS bioprinting ink to span longer distances (1-2 mm) over empty space. These were largely successful, highlighting the ability of the PDMS bio-ink to cohere and maintain shape while unsupported from below. These designs illustrate that well-supported filaments of the PDMS bio-ink can easily span 2 mm gaps over empty space without sagging.
PDMS structures were printed with the Advanced Solutions BioAssemblyBot® using the preparation procedures and print parameters given above. Sample prints showed that printed lines were less than 400 mm in diameter and that inter-line spacing was as large as 1.5 – 2 mm. The utility of PDMS and other silicones now combined with the ability to form complex shapes and structures via 3D printing enables a wide variety of applications and opportunities.