No abstract

3D printing of silicone has been a challenge for medical applications for several years. The main property of medical silicone (mostly polydimethylsiloxane) is its mechanical similitude with human tissues. The very soft tissues as prostate, skin, liver, etc, are of Young's modulus lower than 100 kPa. 3D printing for such soft materials is not as obvious as printing thermoplastic polymers. In this work, the goal is to elaborate formulations of room‐temperature‐vulcanizing (RTV) silicone leading to final materials of Young's modulus down to 25 kPa while being processable by liquid deposition modeling, a layer by layer deposit of extruded filament. The main challenge is keeping the material with a sufficient firmness during the process to maintain the shape of the object but without increasing its final rigidity. Therefore, a RTV silicone is mixed with a hydrophilic liquid to create an emulsion of high yield stress behavior. Different emulsions are tested to optimize the composition on the basis of rheological measurements carried out to determine the yield stress variation and compare it to an emulsion model. Then, after printing and curing, the hydrophilic liquid is removed to create a material of fine porosity and consequently of low Young's modulus.

For manufacturing parts of very soft materials by liquid deposition modeling (e.g., to mimic living soft tissues), formulations of 3D‐printable polydimethylsiloxane have been developed, with the aim of increasing the yield stress of the liquid and reducing the final mechanical modulus. In the present work, suspensions of solid‐like hydrogel particles, which are easily 3D‐printable, are prepared in order to generate yield stress, and the suspended phase is removed after manufacturing by taking advantage of the thermo‐reversibility of the hydrogel behavior, resulting in porosity, which reduces the final rigidity. The reported approach is even more efficient than a previous approach based on emulsion formulations.