PDMS membranes loaded with TiO2NPs for antibacterial activity

Poly (dimethyl siloxane) “PDMS” is a highly hydrophobic, thermally and mechanically stable polymer whose features are attributable to its Si-O bonds, which have higher bond strengths and larger bond lengths than average... [ view full abstract ]

Poly (dimethyl siloxane) “PDMS” is a highly hydrophobic, thermally and mechanically stable polymer whose features are attributable to its Si-O bonds, which have higher bond strengths and larger bond lengths than average C-C bonds. Therefore, PDMS is widely used in different fields, such as sealants, separating membranes and biomedical devices. In order to fit the PDMS synthesis to the electrospinning, a sol-gel route was used to synthesize PDMS elastomer. PDMS hydroxyl terminated prepolymers with two different molecular weights and therefore viscosities (20.000 e 50.000 cSt), TEOS (tetraethyl orthosilicate) as multifunctional cross-linking agent, THF as solvent and HNO₃ as acid catalyst  were used. The sol-gel route is essential for the electrospinning process, which guarantees a fibrous structure with microscale to nanoscale dimensions (fig. 1). In order to obtain the cross-linked PDMS membranes coupled with TiO₂, a Sn-based catalyst was used. Bare TiO₂ was synthesized using titanium tetraisopropoxide, 2-propanol and water (1:2:5, V/V) while N and Fe dopings were achieved using an NH₃ solution and Fe₃O₄ NPs. An amorphous gel was obtained and it was then subjected to two different thermal treatments, that are a solid-state and a hydrothermal synthesis, to get crystalline anatase TiO₂. This coupled system allows to have membrane sheets loaded with NPs TiO₂, combining the high adsorbent capacity and the macroscopic handling of the membrane with the photocatalytic antibacterial features of TiO₂. The photocatalytic activity of this system can be activated by a solar light source, whose photons have an energy at least equal to the doped TiO₂ energy gap which is lower than the bare TiO₂ energy gap. For this work, different synthetic conditions were investigated, varying the PDMS prepolymers ratio, the temperature and the time of the polymer synthesis and the electrospinning conditions (voltage, flow, distance from the electrodes). Two different amounts of the three investigated TiO₂ were loaded (5% and 10% w/w) inside the membranes, by suspending the powders or the sol in a THF solution and then electrospraying together with the PDMS membrane. The synthesized samples were characterized by means of rheological measurements and FE-SEM, while the antibacterial activity was evaluated on E.Coli abatement.