Recubrimientos anti-biofilm aplicados mediante plasma-polimerización destinados a la industria de manipulación de alimentos y al sector médico stars

Abstract

Bacterial biofilms formation in food processing industries and medical applications is a matter of concern due to its ability to adhere and reproduce in different environments, materials and surfaces. Pathogenic microorganisms can easily attach to a surface, develop biofilms, survive at refrigeration temperatures or desiccation conditions and resist to disinfectants; which makes them very hard to eradicate. All these problems related to biofilms formation cause cross contamination of products, waste and food spoilage, damages of industrial equipment, economic losses for producers and health risks for consumers. Conventional methods for disinfection, in addition to employ high concentrations of toxics chemicals, are frequently inefficient because they do not achieve a complete eradication of biofilms, increasing the problems with the possible generation of bacterial resistance. Therefore, researches and companies are making great efforts to remove biofilms from production environments. Atmospheric pressure plasma technology with a Dielectric Barrier Discharge (DBD) was used in this thesis to generate anti‐biofilm coatings. In the first group of two scientific publications, the objective was to reduce bacterial biofilms formation. Plasma‐polymerized coatings based on acrylic acid (AcAc) and tetraethyl orthosilicate (TEOS) were applied on 3D printed polylactic acid (PLA) samples. The high speed development of 3D printing technology for food contact (ergonomic cutely for disabled people) and medical applications (implants, prosthesis and protection devices), make interesting the use of 3D printed PLA as a substrate. However, the use of PLA and 3D printing technology are being limited due to the ease of bacterial proliferation due to its surface roughness and the impossibility of subjecting to sterilization process because of the low fusion temperature of PLA. The influence of the precursor liquid and number of passes were characterized by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X‐Ray Photoelectron Spectroscopy (XPS) measurements and biofilm quantification. The mechanism of adhesion and bacterial proliferation were identified. The biofilm formation is caused by a combined effect of the chemical and morphological surface properties. Generally, the more hydrophilic and roughness surfaces, the better the anti‐biofilm capacity of the coatings. It was concluded that AcAc coatings are more effective than TEOS coatings. However, no specific number of passes could be defined as the best, since it depends on the shape and size of the bacteria. AcAc plasma‐polymerized coatings reduced biofilm formation more than 50% against Pseudomonas aeruginosa, Listeria monocytogenes, Escherichia coli and Staphylococcus aureus, regarding the untreated 3D printed PLA samples. In real industrial environments, multiple bacterial strains coexist, and the coated surfaces require periodical sanitization to prevent long‐term bacterial accumulation and cross‐contamination of food products. For that, in the third publication, with the purpose of taking one more step towards the industrial scaling, the aims were to analyze the anti‐biofilm character of a plasma‐polymerized coating based on (3‐Aminopropyl) triethoxysilane (APTES) and AcAc exposed to a multi‐strain cocktail of Listeria monocytogenes (one of the most difficult bacteria to control and eliminate); as well as its durability after repeated 5 cycles of sanitization with commonly used disinfectants, such as sodium hypochlorite and peracetic acid, was also assessed. The coatings were applied on stainless steel (SS) samples (material most commonly used in food industry). Coated samples achieved to reduce the biofilm production more than 85% and remained at levels of 72% after sanitization cycles with sodium hypochlorite. The anti‐biofilm effectiveness after sanitization with sodium hypochlorite was due to the high pH of this solution, which caused a deprotonation of the carboxylic acid groups of the functional coating. This fact conferred it a strong hydrophilicity and negatively charged its surface, which was favorable for preventing bacterial attachment and biofilm formation. However, this anti‐biofilm capacity lost effectivity when peracetic acid was employed as disinfection solution. It is considered that the proposed objectives have been successfully fulfilled. The coatings applied in this thesis not only reduce the biofilm generated by different bacteria present in food and clinical field, but they are also durable against disinfecting processes with alkaline sanitizers. Therefore, this demonstrates the promising applications of atmospheric pressure plasma technology in food processing and medical industries and it could be an innovative alternative to the current industrial solutions.