Fig. 3: Adhesion performance and mechanisms of nanowhisker glues.

a Controlled deacetylation of chitin nanocrystals leads to ChsNWs with a varied degree of deacetylation and amine content. b Adhesion energy as a function of amine content. L, M, and H refer to low (32%), medium (52%), and high (66%) degrees of deacetylation (DDA), respectively. c Adhesion energy as a function of amine content for nanoparticles deployed using microneedles. d Schematic showing the cyclic peeling test to measure interfacial fatigue threshold and depicting the “crack-pinning” behavior of ChsNWs. The inset is the loading profile. e Representative curves of the crack growth as a function of the number of cycles for ChsNWs and chitosan adhesives under G = 267 J m⁻². f The crack growth as a function of the number of cycles at several values of G for nanowhisker glues. g Crack growth rate (dc/dN) versus applied energy release rate G. The last three data points were linearly extrapolated to obtain the fatigue threshold (i.e., the intercept of the x-axis). h Ashby plot showing adhesion energy and fatigue threshold relationships for previous nanoparticle adhesives^15,30 polymeric adhesives^6,29, and this work. The interfacial fatigue threshold of nanoparticle adhesives is approximated by their adhesion energies due to the lack of data reported. i Mechanisms of fatigue fracture of nanowhisker glue and polymer glue at the interface between hydrogel and tissue. Red arrows indicate the crack path. Data in (b, c) are presented as mean ± SD (n = 3 independent biological replicates). Statistical significance and P- values in (b, c) were determined by two-sided ANOVA.