The adhesion of hydrogels on solid and soft surfaces, such as human skin, biological tissues, and metal substrates, is important in many practical applications, such as robust artificial tissues, smart robots, electronic skins, and motion/damage sensors. These broad application areas indicate their importance to developing key sectors of the US economy including health care and defense systems. The generation of hydrogels with the appropriate level of adhesion, and the need to re-adhere to a surface once removed, however, has been very challenging. This research will focus on creation of a new family of physically-based tough hydrogels and hydrogel adhesives with integrated superior mechanical, self-healing, and stimuli-responsive properties in bulk and on solid substrates. The use of two polymer networks in the hydrogel, with the networks intertwined and possessing differing properties key to the performance of the material, is a novel feature of the approach. One network could provide mechanical toughness while the other network could lead to reformable adhesive bonds to a surface leading to the incorporation of typically incompatible properties. Once developed, the two polymer networks can also be used in the fabrication of strain sensors for human motion detection in medical applications. New knowledge, techniques, and materials derived from this project will be important in the engineering and design of other soft materials and in advancing the manufacture and performance of new smart materials. The project will provide research opportunities to all-level students, particularly from underrepresented groups, learning hands-on skills from polymer physics/chemistry, lab-on-chip design, and ergonomic engineering, thus promoting the next-generation of STEM education.
Most of hydrogel adhesives adhere weakly to diverse surfaces with very low adhesion energy, easily lose adhesive capacity after multiple on-and-off peeling tests, and lack self-recovery and self-healing functions to recover their adhesive and mechanical properties. The current materials design strategy prevents both bulk and interfacial toughness to be presented in the same hydrogel, because the bulk and interfacial toughness of hydrogels stem from different origins. To overcome these scientific barriers, this research strives to design a new family of physically-linked double network hydrogels by understanding, coupling, and engineering the interactions between different networks and the associated energy mechanisms to achieve multiple force-activated functionalities, including high bulk/interfacial toughness, multiple-stimuli self-healing property, and reversible adhesion both in bulk and on solid substrates, as well as to fabricate the hydrogel adhesives into strain sensors with integrated multi-functions for human motion detection. The function and performance of this new class of physically-linked hydrogels will be controlled by tuning their network components and structures in a programmable way. This research will advance fundamental knowledge and practical principles for rational design of new smart materials, better understanding of component-structure-property-performance interrelationship of the materials, and improvement of materials multi-functionality, processing, and fabrication.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.