Carboxymethyl chitosan microneedles patch with tunable stiffness regulates wound scar-free repair

The application of microneedles (MNs) as a mechanotherapy strategy to modulate mechanical microenvironment of wounds has garnered increasing attention. However, the influence of mechanical properties of MNs on wound healing and fibrosis remains underexplored. In this study, we developed a MNs patch composed of genipin cross-linked carboxymethyl chitosan (CMCS) and investigated relationship between variations in MN patch stiffness and their efficacy in promoting wound healing and inhibiting fibrosis. To assess mechanical environment improvement, we constructed a finite element model of MNs patch-closed wounds. The results revealed that stiff MNs patch better reduced wound area but also elevated stress in peri-wound area. Via in vivo experiments and co-culture experiments with fibroblasts, we confirmed that stiff MNs patch accelerated wound closure rate (3.55 × 10^-2 ± 8.81 × 10^-3) than soft MNs patch (5.38 × 10^-2 ± 3.68 × 10^-3, p = 0.029), but promoted fibroblast proliferation (8.70 × 10^-1 ± 9.32 × 10^-2 for stiff MNs and 6.60 × 10^-2 ± 2.28 × 10^-3 for soft MNs, p < 0.0001) and myofibroblast differentiation (0.58 ± 6.85 × 10^-3 for stiff MNs and 0.44 ± 1.14 × 10^-2 for soft MNs, p < 0.0001), contributing to fibrosis. In contrast, soft MNs patch facilitated scar-free repair. In conclusion, MNs patches promote wound healing, stiffer MNs patches are more effective during initial stages of wound healing, whereas softer patches are preferable for minimizing fibrosis in later stages. These findings underscore that MNs' mechanical properties must be carefully tailored to balance early-stage repair efficacy with long-term goal of scar-free healing.