Mechanistic Understanding and Control of Adhesion and Lubrication by Coacervate Hydrogels for Advanced Manufacturing

This award supports research addressing the challenge of engineering hydrogel materials with dynamically controllable adhesive and lubricious interfaces. Advances in biomimetic robotics, biomedical implants, and human–machine interfaces are driving the demand for soft materials with enhanced performance. While hydrogels are promising candidates, a key challenge remains: combining mechanical durability with responsiveness to external stimuli. Coacervate hydrogels can retain the dynamic behavior of traditional coacervates while offering the mechanical strength required for load-bearing applications, making them attractive for emerging soft-matter technologies. Precise knowledge of structure–property-function relationships and the mechanisms underlying adhesion and lubrication reduces reliance on trial-and-error approaches and facilitates scalable fabrication of soft interfaces, accelerating the translation of laboratory innovations to industrial production. By integrating dynamic interactions, these materials offer responsive behavior and adaptability. This capability supports the development of multifunctional hydrogels, catalyzing industrial sectors like soft wearable devices, soft robotics, tissue engineering, and sensing. Moreover, enabling function control lowers material costs, aligning with national goals for economic manufacturing and accelerating US advanced manufacturing. The project also contributes to US workforce development by training two graduate research assistants. Education plans further enhance the broader impacts of the project. The project hypothesis is that the interfacial structure and rheology of coacervate hydrogels can be tuned by modulating the balance between inter-chain interactions; and that this can serve to enable active control of adhesion and friction in response to external stimuli as well as switchable functionality between adhesive and lubricious states. The intellectual merit of this research includes advancing the fundamental understanding of the effects of physical interactions –(a) electrostatic attraction vs. repulsion, (b) hydrogen bonding and electrostatic, and (c) hydrophobic attraction and electrostatic– on the network properties of three classes (a-c) of coacervate hydrogels, and on the mechanisms underlying lubrication and adhesion. First, phase diagrams for representatives of the three hydrogel classes are established using turbidity and zeta potential measurements and gelation protocols are developed. The influence of physical interactions on microstructure and network dynamics is then studied using infrared spectroscopy, rheology, and scanning electron microscopy; while interfacial responsiveness is investigated using chemically sensitive imaging methods based on atomic force microscopy. Tribo-rheometry, adhesion measurements, microscopy friction visualization as well as modeling are used to understand and quantify the tunability of interfacial forces. This approach aims to achieve tunable and controllable aqueous lubrication and stiction using physically cross-linked, coacervate-based hydrogels and paves the way for scalable approaches and enhanced cost-efficiency in manufacturing hydrogel systems. 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. NSF Award ID: 2535887 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Rosa Espinosa-Marzal | Institution: University of Illinois at Urbana-Champaign, URBANA, IL | Award Amount: $550,000 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2535887 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2535887.html