where h(t) indicates the thickness of the PMMA film at process time t and h0 the thickness of the PMMA film at the beginning of the process, i. Interestingly, the swelling of the PLA matrix is much faster than that of PMMA with a much steeper swelling variation during the initial stages of the TMA exposure step, indicating that diffusivity of TMA is higher in PLA than in PMMA. This is clearly highlighted in figure and showing the evolution of the normalized swelling ε(t)/εMAX as a function of t 1/2 /h0 for PLA and PMMA thin films, respectively. Previous studies demonstrated that TMA diffusion into PMMA is governed by Fickian diffusion during the initial stages of the TMA exposure step, with a progressive increase of the ε(t)/εmax that is perfectly described by the following equation: