| 3D printing opens up new possibilities and techniques for individualized medicine but it also comes with inherent weaknesses. One of these drawbacks is the mechanical weakness of the structures as a result of their laminar construction. This work describes a new printing system for silk hydrogels that are stiffer than any that have been printed before, paving the way for taller structures that have smaller features. As part of this printing system, a larger printer was designed with self-contained sterility systems and a greatly increased print volume compared to current models. Additionally, light-curable inks were formulated, tested, and printed using existing 3D printers to quantify their usefulness as part of a catalogue of silk-based hydrogel inks. The long-term goal for this catalogue is to document formulae and procedures that produce hydrogels of varying mechanical and biological properties for tissue engineering. The experimental procedures presented here indicate that modest amounts of physiologically inert light are sufficient to significantly increase the stiffness of riboflavin-infused silk hydrogels. In one experiment, approximately 750J of blue light increased the young's modulus of gels by 50% from 5kPa to 7.5kPa. In a printed tower test, 5J of violet light increased the modulus of plastic deformation by 13% from 15kPa to 17kPa. Single filaments made from printed hydrogels treated with focused laser light at levels below 10mJ showed no significant increase in tensile strength, suggesting that the minimum threshold for noticeable effects in 2mM riboflavin gels is on the order of magnitude of 1-5J of light. Applying more than 1,000J of light was not found to increase the stiffness of these gels. Lastly, the current uses and the future of this technology are discussed. |
