Recently, SUSTech Associate Professor Qi Ge (Department of Mechanical and Energy Engineering) collaborated with Professor Shaoxing Qu from Zhejiang University made substantial progress in the field of 3D printing hydrogel-polymer hybrids, with the results published in Science Advances (IF=13.117), entitled “3D printing of highly stretchable hydrogel with diverse UV curable polymers” (cover article). The team reported a simple yet versatile multimaterial 3D printing approach to fabricate complex hydrogel-polymer hybrid structures, overcoming the poor bonding between the hydrogel and other polymers.
Hydrogels, water-containing polymer networks, have found numerous applications in biomedicals, flexible electronics and others. In many applications, hydrogels are combined with other polymers to form hybrid structures, which are used to protect, reinforce, or add new functionalities to hydrogel structures. However, the polymers that hydrogels could be firmly bonded with are mainly restricted to silicone rubbers, and the geometries of hydrogel-polymer hybrids are mostly constrained to laminate structures, which greatly limit the functionality and performance of hydrogel-polymer-based devices and machines. Therefore, it is desired to develop an effective approach that fabricates hydrogel-polymer-based hybrid structures with high design freedom and rich material choice.
Digital light processing (DLP)-based 3D printing is an ideal technology to fabricate highly complex 3D structures with high resolution. However, the capability of using DLP-based 3D printing to fabricate hydrogel-polymer hybrid structures has not yet been achieved, due to the limited choice of highly efficient DLP-based multimaterial 3D printing system and the lack of a universal approach that forms robust bonding between high-performance hydrogels with diverse UV curable polymers.
Qi Ge collaborated with Professor Shaoxing Qu’s team have developed a simple yet versatile multimaterial 3D printing approach to fabricate highly complex hybrid 3D structures consisting of highly stretchable and high-water content acrylamide-PEGDA (AP) hydrogels that are covalently bonded with diverse water-insoluble UV curable polymers including elastomer, rigid polymer, ABS-like polymer, shape memory polymer (SMP), and other (meth)acrylate-based UV curable polymers. Covalent bonding between AP hydrogel and other polymers are realized by using the incomplete polymerization of AP hydrogel initiated by the water-soluble photoinitiator TPO nanoparticles. The hybrid structures are printed on a self-built DLP-based multimaterial 3D printer (Figure 1). Three application cases have demonstrated that the proposed new method can greatly enrich the design freedom and material choice of the hydrogel-polymer hybrid structures and devices, and further improve their functions and performances.
Figure 1. Multimaterial 3D printing hydrogel with other polymers.
As shown in Figure 2, the rapid prototyping of the hydrogel-polymer hybrid structures can be achieved by multimaterial 3D printing technology. Through the rigid polymer-reinforced microstructure design, the tensile modulus of the hydrogel-polymer hybrids can be increased by ~30 times, and the compressive modulus can be increased by more than 700 times. Moreover, the local stiffness of the hydrogel-polymer hybrids can be modulated by tuning the local size of the microstructure.
Figure 2. 3D printed rigid polymer-reinforced hydrogel composites.
Figure 3 shows the printed shape memory polymer (SMP) stent with drug releasing function . The stent has the shape memory effect. It can be squeezed into a compacted shape at the programming temperature, and the compacted shape can be fixed after cooling to a lower temperature, which is lower than the glass transition temperature (Tg of 30℃) of the SMP. The compacted SMP stent would recover to its original shape in the body temperature of 37℃ and expand the blood vessel with stenosis. The drug releasing function is imparted into the cardiovascular SMP stent by integrating hydrogel into the SMP stent. The drug-loaded hydrogel releases 3, 16, and 30% of the total drugs within 2 min, 30 min, and 1 hour, respectively. After 3 hours, the cumulative release saturates at about 90%. The drug could be released completely after 24 hours.
Figure 3. Printed SMP stent with drug releasing function.
Figure 4 shows the printed soft pneumatic actuator with hydrogel strain sensor. The strain sensing function can be directly assigned to the soft pneumatic actuator through the multimaterial 3D printing of ion conductive hydrogel and photosensitive elastomer, realizing the rapid integration of driving and sensing of the soft robot.
Figure 4. Printed soft pneumatic actuator with hydrogel strain sensor.
This research has broadened the forming methods and capabilities of hydrogel-polymer hybrid structures, and has great application potential in the development of new multifunctional soft devices and machines.
Southern University of Science and Technology is the first unit of this research article. Southern University of Science and Technology, Northwestern Polytechnical University and Zhejiang University are the corresponding units of this paper. This research was funded by the Key-Area Research and Development Program of Guangdong Province and the National Natural Science Foundation of China.
Paper link: https://advances.sciencemag.org/content/7/2/eaba4261
