During this reporting period, corresponding to months 17–20 of the project, GAiA worked mainly within WP4, with activities involving both the University Campus Bio-Medico of Rome and the University of Modena and Reggio Emilia. The goal was to translate the knowledge generated in the previous work packages into manufacturing procedures capable of producing electrospun fibres loaded with antimicrobial particles. This step was essential because GAiA’s final ambition is not simply to develop promising materials in isolation, but to create active fibrous layers that can be integrated into future filtering face piece systems.

The work started from the polymer solution already selected in WP2 and from the bioactive glass formulations developed and validated in WP3. The antimicrobial charge was introduced by dispersing the bioactive glass powders into the polymer solution before electrospinning. This was a delicate step: the particles had to be distributed homogeneously without altering their structural and chemical properties, and without compromising the ability of the polymer solution to form continuous fibres.

One of the important technical outcomes of this phase was the confirmation that a standard single-needle electrospinning process was sufficient to obtain loaded fibres. A coaxial needle had been considered as a possible mitigation strategy to improve particle entrapment, but the report states that this approach proved unnecessary because the standard process produced fibres with well-distributed particles in the nonwoven fabrics. SEM and EDS analyses then confirmed the homogeneous incorporation of the antimicrobial charge and the correct fabrication of the electrospun materials.

The electrospinning process was also revised to take into account the presence of bioactive glasses in the starting solution. Compared with the process used for the unloaded polymer system, the parameters were adjusted and a new E-Fiber EF100 Electrospinning system was used. This equipment allowed the electric field to be modulated between spinneret and target, improving fibre collection, stabilising the process and reducing defects in the nonwoven fabric.

The fibres produced in this phase were not treated only as experimental samples. They were characterised as candidate materials for the next step of GAiA: integration into prototype filter structures and functional validation. The fifth-period technical report states that the WP4 activities covered T4.1, T4.2, T4.3 and T4.4, and that the period covered deliverables D4.1 and D4.2. Their completion constituted the third GAiA milestone, confirming the validated design of composite antimicrobial fibres and their morphological and mechanical characterisation.

Morphological characterisation was central to this result. The project evaluated whether the antimicrobial charge was distributed inside or on the surface of the fibres, whether particle clusters were present, and whether the fibre network preserved the structural quality required for filtration applications. The SEM micrographs showed fibres without surface defects and with high dimensional homogeneity. They also demonstrated that non-water-soluble PVA/PAA nonwoven fibres loaded with antimicrobial bioactive glasses had been successfully produced.

This result was particularly important for the sustainability profile of GAiA. The nonwoven materials were produced from two polymers that are easily soluble in water, avoiding toxic solvents and reducing risks for health and the environment. At the same time, the bioactive glass particles appeared well immobilised within the layers of the nonwoven fabric, reducing the risk of complete particle release. The report also notes that the fabrics showed homogeneous porosity, with pore dimensions consistent with their potential use as filtering substrates for airway protection.

The team also assessed the mechanical behaviour of the loaded fibres. This was necessary because the introduction of inorganic particles into polymer fibres can reduce strength if the particle-matrix interface is weak or if the resistant polymer phase is disrupted. Mechanical tests were therefore performed on esterified, non-aligned electrospun fabrics using tensile testing methods consistent with ASTM D882-10. The results were reported as compatible with those obtained for systems without bioactive glass, supporting the feasibility of using the loaded nonwoven materials as layers for face-mask filters.

By the end of the fifth phase, GAiA had therefore achieved a decisive bridge between material research and prototype development. The project had moved beyond individual components — polymer solutions, electrospinning parameters and antimicrobial powders — and had combined them into composite nonwoven fibres with controlled morphology, embedded antimicrobial particles and mechanical properties suitable for the next validation stage.

This phase did not yet represent the final validation of the complete filter system. Instead, it created the material basis required for that validation. The subsequent WP5 activities were planned to test these fibres as active components in facial filters, assessing their performance, antimicrobial function, stability and user safety. In this sense, the fifth reporting period transformed GAiA from a project centred on material design into a project ready to evaluate functional filter prototypes.

The fifth-period report also confirms that the WP4 activities expected by month 20 were completed, and that no substantial variation from the approved project plan was recorded. Earlier small delays were addressed through corrective measures and did not lead to deviations from the original planning or expected results.

For GAiA, this milestone was more than a technical achievement. It showed that sustainable electrospinning, antimicrobial bioactive glasses and fibre-level material engineering could be integrated into a coherent platform for safer and greener respiratory protection. The composite fibres developed in this phase became the practical link between laboratory discovery and the future demonstration of active, environmentally responsible mask-filter materials.