STIMULI RESPONSIVE ACTUATING HYDROGELS BY STEREOLITHOGRAPHY 3D PRINTING

Hydrogels are three-dimensional polymer networks that uptake a large amount of water but do not dissolve in water. They form the basis of an attractive class of materials for many biomedical applications, ranging from scaffolds for tissue engineering to drug delivery reservoirs to wound dressings. Hydrogels that are composed of stimuli responsive polymers can undergo macroscopic volume changes that can be utilized to generate movement. Stereolithographic 3D printing is an additive manufacturing technique that builds 3D structures layer-by-layer, by sequentially polymerizing a liquid resin. We have modified a temperature responsive polymer with a sol-gel transition temperature below 37 °C that can be 3D printed. As a result of this technique, hydrogels can be created to form structures that are only accessible by 3D printing.

This multiblock polymer of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) is characterized by a tunable lower critical solution temperature. It is soluble at low temperatures but above the critical temperature, phase separation occurs between the hydrophilic and hydrophobic domains. In the case where the hydrogel is covalently cross-linked, the hydrophobic domains undergo dehydration leading to isotropic deswelling. A 20% (w/w) aqueous solution of cross-linked PEO-PPO-PEO undergoes a weight change of 900% below the critical temperature and only 400% at 37 °C. We further report on the swelling and deswelling response time, the dimensional changes, rheology and mechanical behavior of 3D printed hydrogels. As well, we demonstrate the implementation of a proof-of-concept hydrogel actuator based on swelling-deswelling triggered by changes in temperature.