Zn and Al vapour-phase metalation of polyamide-6 via ALD: structural, functional, and biomedical insights

This study reports the effect of diethylzinc (DEZ) and trimethylaluminium (TMA) functionalization on polyamide-6 (PA6) films using the vapour-phase metalation (VPM) process within an atomic layer deposition (ALD) chamber. The resulting zinc- and aluminium-functionalized films are referred to henceforth as PA6-Zn and PA6-Al, respectively. Biocompatibility was preliminarily assessed via C2C12 cytotoxicity testing. Reaction mechanisms were examined using density functional theory, electrostatic potential maps, Mulliken charge distribution, and X-ray photoelectron spectroscopy, revealing interactions between metal precursors and PA6 amide groups. DFT confirmed alpha-PA6 as the dominant structure and identified reactive sites influencing functionalization pathways. Structural and morphological changes were analysed via environmental scanning electron microscopy and X-ray diffraction. ESEM showed Zn-functionalized PA6 forming strand-like structures, while Al-functionalized PA6 developed pore-like cavities. XRD indicated increased crystallinity upon metalation, with the alpha/gamma crystallite size ratio following the trend: PA6-Al > PA6-Zn > PA6. Spectroscopic analysis using infrared and Raman microscopy, along with UV-visible spectroscopy, highlighted modifications in chemical bonding and polymorphism, aligning with DFT predictions. Al functionalization had a stronger influence on PA6's spectroscopic and some mechanical properties, whereas Zn functionalization notably enhanced failure strain. Barrier and mechanical properties were evaluated, showing that Zn-functionalized PA6 exhibited superior oxygen permeability, while both metal-modified films improved water vapour transmission rates compared to bare PA6. Cytotoxicity testing revealed enhanced C2C12 cell proliferation in the order PA6-Al > PA6-Zn > PA6, suggesting VPM-modified PA6 as a promising material for biomedical applications.