Highly biocidal poly(vinyl alcohol)-hydantoin/starch hybrid gels: A "Trojan Horse" for Bacillus subtilis.

HYPOTHESIS: Poly (vinyl alcohol) (PVA) cryogels can be functionalized with n-Halamines to confer biocidal features useful for their application as wound-dressing tools. Their efficacy can be boosted by stably embedding a polymeric bacterial food source (e.g., starch) in the gel matrix. The bioavailability of the food source lures bacteria inside the gel network via chemotactic mechanisms, promoting their contact with the biocidal functionalities and their consequent inactivation. EXPERIMENTS: The synthesis of a novel hydantoin-functionalized PVA (H-PVA-hyd) is proposed. The newly synthesized H-PVA-hyd polymer was introduced in the formulation of H-PVA-based cryogels. To promote the cryogelation of the systems we exploited phase-separation mechanisms employing either a PVA carrying residual acetate groups (L-PVA) or starch as phase-segregating components. The permanence of the biocidal functionality after swelling was investigated via proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) microscopy. The activated H-PVA-hyd cryogels have been tested against bacteria with amylolytic activity (Bacillus subtilis) and the outcomes were analyzed by direct observation via confocal laser scanning microscopy (CLSM). FINDINGS: The cryogels containing starch resulted in being the most effective (up to 90% bacterial killing), despite carrying a lower amount of hydantoin groups than their starch-free counterparts, suggesting that their improved efficacy relies on a "Trojan Horse" type of mechanism.

Role of amylose and amylopectin in PVA-starch hybrid cryo-gels networks formation from liquid-liquid phase separation.

HYPOTHESIS: The role of amylose and amylopectin in the formation of cryogels based on Poly(vinyl alcohol) (PVA) and starch is poorly understood. A systematic investigation of simplified systems containing PVA, amylose, and/or amylopectin constitutes the basis to predict the final features of PVA/starch cryogels by knowing their composition, and the amylose content of the employed raw starches. EXPERIMENTS: Pre-gel solutions and cryogels containing PVA/amylose, PVA/amylopectin, and PVA/amylose/amylopectin in variable ratios were investigated employing small-angle X-ray scattering (SAXS), confocal laser scanning microscopy (CLSM), differential scanning calorimetry (DSC), and rheological measurements. The gel fraction (G%) of 23 samples with variable compositions was calculated and plotted to predict the G% (the gel fraction) of any PVA/amylose/amylopectin mixing ratio. FINDINGS: We report on how the PVA, amylose, and amylopectin composition affect the properties of the final polymer blend and cryogel formation. In particular, PVA/amylose and PVA/amylopectin show different behaviors with respect to cryogel formation. We show that is possible to predict cryogel formation by using the simple G% parameter for any PVA/amylose/amylopectin mixing ratio, ruling out the starch botanical origin in the gel formation. The results reported in this work represent a simple tool, able to predict the formation of high-quality biobased materials that can replace fully synthetic materials with a significantly positive impact on our ecosystem.

"Green" biocomposite Poly (vinyl alcohol)/starch cryogels as new advanced tools for the cleaning of artifacts.

HYPOTHESIS: Gels made from synthetic polymers have improved the cleaning of artifacts, but there is the strong need to elaborate new systems through an all-green approach, developing materials with higher eco-compatibility while retaining optimal efficacy. Rice starch (RS) is a renewable biopolymer with high potential for formulating sustainable gels from composites with synthetic polymers, but its interaction with the latter in composite structures is poorly understood. EXPERIMENTS: Poly (vinyl alcohol) (PVA) and RS were used to obtain biocomposite hydrogels through a robust and "green" freeze-thawing route. For the first time, extensive understanding of these composites was tackled by investigating their gel structure and rheological behavior. The cleaning effectiveness of the PVA/RS gels was assessed on soiled modern painting mock-ups, whose water-sensitiveness makes their cleaning too risky using traditional tools. FINDINGS: The composites behave as strong gels whose structure and viscoelastic response are controlled tuning the PVA/RS ratio. X-ray scattering and thermal analysis suggested the formation of hybrid PVA-RS links. Starch amylopectin likely acts as a porogen, while amylose forms hydrogen bonds with PVA. The gels adhere to rough paint layers and remove soil effectively without detectable residues. Overall, the PVA/RS composites are highly effective and provide a significant step forward in the formulation of eco-sustainable cleaning formulations.