1 School of Environmental and Natural Resources, Zhejiang University of Science and Technology, Hangzhou 310023, PR China.
2 School of Biological & Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, PR China. Electronic address: Wubz_314@163.com.
3 School of Pharmaceutical and Chemical Engineering, Taizhou University, Taizhou 318000, China. Electronic address: xiaosw@tzc.edu.cn.
4 Key Laboratory of Advanced Textile Materials and Manufacturing Technology and Engineering Research Center for Eco-Dyeing & Finishing of Textiles, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, China. Electronic address: zhengsijia@zstu.edu.cn.
5 School of Biological & Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310023, PR China.
6 Department of Chemical and Materials Engineering, Concordia University, Montreal, Quebec H3G 1M8, Canada.
7 School of Environmental and Natural Resources, Zhejiang University of Science and Technology, Hangzhou 310023, PR China; School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China. Electronic address: qilinga@126.com.

Wet-strength resins are fundamentally important for papers as they provide water resistance and wet strength, allowing papers to complete tasks before incurring wet damage. Resins currently in use are primarily petroleum-based substances that pose inherently environmental and health risks due to the release of hazardous organochlorine or formaldehyde compounds during production and use. While bio-based resins provide a more sustainable alternative, they typically present insufficient wet-strength performance. Yet, the ever-growing demand for paper products calls for more sustainable and greener resins. Herein, guanidinylated cluster-modified chitosan (3.44 mmol/g cationic charge content) has been obtained as an alternative wet-strength resin. The strategy is based on grouping cations into ion clusters which interact with cellulosic fibers, thereby enhancing the electrostatic force and facilitating a robust and multifaceted interactive physical network. As a result, the fabricated benign papers display ~57 MPa dry strength and ~ 3 MPa wet strength at 1 wt% dosage. The values are 3 and 10 times higher than control papers (17.3 and ~ 0.35 MPa, respectively), and are comparable to those of 1 wt%-PAE-reinforced papers. In addition, re-exposing papers to water enabled us to observe their good dispersibility and antibacterial behavior. Overall, this work presents an alternative biomass-derived wet-strength resin.