To prepare a filament, coarse-grained branched polymers with a backbone length of 80 beads were randomly dispersed into a simulation box with a height of 75σ to achieve a bead density of 0.85/σ 3 . We implemented periodic boundary conditions in the xy dimension and a shrink-wrap boundary condition in the z-dimension to create a free surface. All systems were equilibrated by constraining bead displacements within 0.1σ per step, employing a Langevin thermostat at a reduced temperature of T* = 1.0, which is above the glass transition temperature, and a timestep of 0.005τ for 2,000τ. Following the initial equilibration step, we carried out MD simulations with an isothermal-isobaric ensemble (NpT) at T* = 1.0 for 20,000τ with a timestep of 0.01τ. A Berendsen barostat was applied at the reduced pressure p* = 0.0 on the xy boundaries, allowing them to move freely, whereas the shrink-wrap boundary condition was maintained on the z dimension. Subsequently, we replicated the filament in the z dimension by shifting the coordinates by the box height, generating two contacting filaments, which underwent interfilamentous diffusion. The temperature of the CGMD systems was kept at T* = 1.0 with a Langevin thermostat. The damping coefficient of the Langevin thermostat was set at 0.1τ -1 for all CGMD simulations unless otherwise noted. To evaluate the mechanical properties of solidified filaments after welding for tw, we rapidly quenched the system to T* = 0.2 at a rate of -2 × 10 -4 τ -1 , below the glass transition temperature of T* = 0.35. Subsequently, an engineering strain of 𝜖̇= 2 × 10 -4 τ -1 was applied to the z dimension, slow enough to ensure the failure mode was not affected. Simultaneously, zero pressure was applied on the xy boundaries. The stress was calculated by averaging the sum of per-atom tensors every 100 MD steps. The temperature was controlled using a Langevin thermostat (damping coefficient Γ = 1 τ -1 ), applied only to the z dimension to avoid biasing the flow.