Abstract
The BIOCOATCH project developed and evaluated bio-based coatings for copper and bronze substrates intended for healthcare and cultural heritage applications. Cutin extracted from tomato-peel waste was used to formulate protective coatings, including hybrid cutin/silane systems. Among the investigated formulations, CUT/PSH showed the highest anticorrosion performance, with protective efficiencies above 99% on both copper and bronze. In addition to corrosion protection, CUT/PSH exhibited antibacterial activity against selected Gram-positive bacteria while maintaining the protective function of the coating. The formulation reduced substrate-induced cytotoxicity and showed good biocompatibility in murine and human cell models. Life Cycle Assessment indicated lower environmental impacts than comparable fossil-based coatings, with reductions of up to 81%. Artificial and natural ageing tests confirmed the persistence of corrosion protection, biocompatibility and reduced metal release. Results The BIOCOATCH project focused on the development and validation of bio-based coatings for copper and bronze substrates intended for applications in healthcare and cultural heritage environments. Activities included substrate characterization, coating synthesis, corrosion testing, antibacterial characterization, biocompatibility assessment, environmental evaluation and durability testing. Characterization of substrates and coating development The metallic substrates were characterized prior to coating deposition. Chemical and microstructural analyses confirmed the composition and morphology of phosphorus-deoxidized copper (PHC Cu) and G85 bronze. Cutin extracted from tomato-peel waste was used as the starting material for the development of bio-based protective coatings. The first generation of coatings consisted of polyester/polyurethane formulations obtained from purified cutin oligomers. Electrochemical tests in simulated aggressive environments showed protective efficiencies approaching 99.9% on bronze and 99.7% on copper after seven days of immersion. Functionalization with commercial silver and zinc nanoparticles increased polarization resistance at selected concentrations; however, nanoparticle agglomeration and the absence of antibacterial activity limited their applicability. To address these limitations, new aqueous silver nanoparticle dispersions and zinc precursors were introduced and a second generation of hybrid coatings was developed by combining cutin oligomers with silane precursors. Among the investigated formulations, CUT/PSH provided the highest corrosion protection, with protective efficiencies of approximately 99.9% after room-temperature curing and 99.99% after curing at 60°C. The addition of low concentrations of silver nanoparticles and zinc precursors did not significantly affect coating performance, maintaining protective efficiencies above 99%. Phosphate-, hydroxyapatite- and β-tricalcium phosphate-based coatings were also investigated. Hydroxyapatite coatings showed cracking and limited reproducibility, while phosphate treatments provided only short-term protection. TCP coatings exhibited homogeneous morphology but limited long-term anticorrosion performance. Subsequent investigations therefore focused on the CUT/PSH formulation. Anticorrosion performance The anticorrosion properties of the coatings were evaluated by electrochemical impedance spectroscopy and polarization testing. The first-generation CUT coating reduced corrosion rates on both bronze and copper substrates, with polarization resistance values exceeding 2×10⁸ Ω·cm² for bronze and 7×10⁷ Ω·cm² for copper after seven days of exposure. Among the hybrid systems, CUT/PSH showed the highest protective performance. On bronze, the coating reduced corrosion rates by approximately three orders of magnitude compared with the bare substrate. Low concentrations of Ag nanoparticles and Zn precursors did not substantially modify the protective behaviour of the coating, whereas very high Ag concentrations reduced coating performance. In contrast, phosphate- and TCP-based coatings showed lower durability and lower protective efficiency during prolonged exposure. Antibacterial and antibiofilm activity Commercial silver and zinc nanoparticles incorporated into coatings did not exhibit antibacterial activity. Alternative Ag nanoparticles showed bactericidal activity against tested strains. At a concentration of 1.3% w/v, complete inhibition of all tested strains was observed within 30 minutes. Copper and bronze substrates showed intrinsic antibacterial and antibiofilm activity, particularly under conditions simulating surface contamination. Copper eliminated planktonic and biofilm populations of Escherichia coli and Staphylococcus aureus, whereas bronze inhibited biofilm formation by Rhodococcus spp. and Pseudomonas furukawii. This activity was associated with metal ion release from the substrates. The original cutin coating reduced the antibacterial activity of the metallic substrates, consistent with a reduction in metal ion release. Tests conducted using glass substrate for the coatignn depsotion allowed to determine that the CUT/PSH coating had antibacterial activity against Gram-positive bacteria while partially preserving the antimicrobial properties of the underlying metals. Functionalization with silver nanoparticles or zinc precursors did not consistently enhance antibacterial performance once incorporated into the coating matrix. Bacterial response to metal exposure The response of bacterial cells to metal exposure was investigated using media conditioned with copper and bronze substrates. Copper-conditioned media produced stronger inhibitory effects than bronze-conditioned media. Exposure to both metals induced changes in glucose consumption, ATP production and reactive oxygen species generation, indicating activation of stress-response mechanisms. Biocompatibility The biocompatibility of metallic substrates and coatings was assessed using conditioned media and in vitro cell models. Bare copper and bronze substrates induced cytotoxic effects in BALB/3T3 fibroblasts, including altered morphology, reduced spreading and lower viability. CUT-PE/PU coatings reduced these effects, and subsequent analyses demonstrated that both room-temperature and 60°C-cured CUT/PSH formulations mitigated the cytotoxicity associated with copper and bronze substrates. Additional experiments performed on primary human dermal fibroblasts and A549 lung epithelial cells confirmed lower cytotoxicity and oxidative stress in coated samples compared with uncoated substrates. Functionalization with Ag nanoparticles did not induce additional cytotoxic effects and maintained biocompatibility levels comparable to those of the non-functionalized coating. Environmental assessment Life Cycle Assessment (LCA) models were developed to evaluate the environmental impacts associated with coating production and application. For CUT-PE/PU formulations, cutin extraction and solvent use represented the main contributors to environmental impacts. For phosphate-based coatings, diammonium phosphate was the principal contributor to the carbon footprint. An additional LCA scenario was developed for the CUT/PSH formulation. Comparative analyses against commercial fossil-based coatings showed lower environmental impacts for both CUT-based systems. Climate change impacts were estimated at 4.71 kg CO₂ eq/FU for CUT-PE/PU and 2.97 kg CO₂ eq/FU for CUT/PSH, compared with 9.71 and 21.07 kg CO₂ eq/FU for the corresponding commercial alternatives. Overall environmental scores were reduced by 54% for CUT-PE/PU and 81% for CUT/PSH relative to fossil-based reference systems. Ageing, durability and post-ageing performance The durability of the coatings was evaluated through artificial and natural ageing protocols. Bronze samples were exposed to climatic chamber cycles, UVA irradiation and artificial rain runoff, while copper samples underwent artificial sweat exposure and sanitation cycles. Compared with uncoated substrates, coated specimens showed lower mass loss, lower metal release and improved colour stability. During runoff testing, coated bronze exhibited 90% lower copper release than uncoated samples. Electrochemical characterization after ageing indicated some reduction in polarization resistance; however, the CUT/PSH coating maintained protective efficiencies above 98% under most artificial ageing conditions. Natural ageing was conducted at the Certosa Monumental Cemetery in Bologna. After five months of exposure, coated bronze showed lower colour variation and less extensive corrosion than uncoated specimens, although localized coating defects and cracking were observed. Antibacterial activity was generally maintained after artificial and natural ageing. Bare copper and bronze retained antibacterial activity, while coated samples continued to modulate bacterial growth depending on coating degradation and exposure conditions. Similar microbial communities were detected on coated and uncoated naturally aged bronze surfaces. Methylobacterium spp. were isolated from biodeteriorated bronze and confirmed by sequencing analyses. The biocompatibility of aged samples was assessed using conditioned media obtained from coated and uncoated substrates after artificial and natural ageing. The protective effect of the CUT/PSH coating against substrate-induced cytotoxicity was maintained after climatic chamber ageing, runoff exposure and sanitation cycles. Although a partial reduction in protection was observed after natural ageing, coated bronze and copper samples remained more biocompatible than the corresponding uncoated substrates. Overall, the results identified the CUT/PSH formulation as the coating showing the highest anticorrosion performance together with good biocompatibility, durability and lower environmental impacts among the investigated systems.
Dettagli del progetto
Responsabile scientifico: Martina Cappelletti
Strutture Unibo coinvolte:
Dipartimento di Farmacia e Biotecnologie
Coordinatore:
ALMA MATER STUDIORUM - Università di Bologna(Italy)
Contributo totale di progetto: Euro (EUR) 224.847,00
Contributo totale Unibo: Euro (EUR) 157.728,00
Durata del progetto in mesi: 24
Data di inizio
30/11/2023
Data di fine:
28/02/2026
