Enhanced Piezoelectricity of Electrospun Polyvinylidene Fluoride Fibers for Energy Harvesting

Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the β-phase and piezoelectric properties of PVDF fibers. We shed new light on β-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectric performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d33 piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 μW·cm-2 from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with β-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications

Production of electrospun fast-dissolving drug delivery systems with therapeutic eutectic systems encapsulated in gelatin

Fast-dissolving delivery systems (FDDS) have received increasing attention in the last years. Oral drug delivery is still the preferred route for the administration of pharmaceutical ingredients. Nevertheless, some patients, e.g. children or elderly people, have difficulties in swallowing solid tablets. In this work, gelatin membranes were produced by electrospinning, containing an encapsulated therapeutic deep-eutectic solvent (THEDES) composed by choline chloride/mandelic acid, in a 1:2 molar ratio. A gelatin solution (30% w/ v) with 2% (v/v) of THEDES was used to produce electrospun fibers and the experimental parameters were optimized. Due to the high surface area of polymer fibers, this type of construct has wide applicability. With no cytotoxicity effect, and showing a fast-dissolving release profile in PBS, the gelatin fibers with encapsulated THEDES seem to have promising applications in the development of new drug delivery systems.The research leading to these results has received funding from Fundação para a Ciência e a Tecnologia (FCT) through the projects ENIGMA - PTDC/EQU-EPR/ 121491/2010 and UID/CTM/50025/2013, LAQVREQUIMTE: UID/QUI/50006/2013, UCIBIO-REQUIMTE: UID/Multi/04378/2013 (co-financed by the ERDF under the PT2020 Partnership Agreement [POCI-01-0145-FEDER- 007728]) and by FEDER through the COMPETE 2020 Programme. Marta Martins is grateful for financial support from FCT through the grant BIM/PTDC/EQUEPR/121491/ 2010/ENIGMA. This research has also received funding from the European Union Seventh Framework Programme (FP7/ 2007-2013) under grant agreement number REGPOTCT2012-316331-POLARIS and from the project BNovel smart and biomimetic materials for innovative regenerative medicine approaches^ RL1 - ABMR - NORTE-01-0124- FEDER-000016) co-financed by North Portugal Regional Operational Programme (ON.2 – O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF).info:eu-repo/semantics/publishedVersio

Investigations of polycaprolactone/gelatin blends in terms of their miscibility

Synthetic and natural polymers blends represent a new brand of materials with application in wound healing, scaffolds or drug delivery systems. Polycaprolactone/gelatin (PCL/Gt) blends were analyzed in terms of their miscibility. The PCL structure was investigated as a function of Gt content. Changes in the PCL spherulitic structure with Gt content were investigated by a polarizing-interference microscope. The analysis of the glass transition temperature (Tg) of both components as a function of PCL/Gt ratio by differential scanning calorimetry indicates that the system of polycaprolactone/gelatin belongs to a type of s.c. compatible system, being intermediate between miscible and immiscible systems. There is possibility of very limited miscibility of both components. Supplementary wide angle X-ray scattering results are presented

Investigations of polycaprolactone/gelatin blends in terms of their miscibility

Synthetic and natural polymers blends represent a new brand of materials with application in wound healing, scaffolds or drug delivery systems. Polycaprolactone/gelatin (PCL/Gt) blends were analyzed in terms of their miscibility. The PCL structure was investigated as a function of Gt content. Changes in the PCL spherulitic structure with Gt content were investigated by a polarizing-interference microscope. The analysis of the glass transition temperature (Tg) of both components as a function of PCL/Gt ratio by differential scanning calorimetry indicates that the system of polycaprolactone/gelatin belongs to a type of s.c. compatible system, being intermediate between miscible and immiscible systems. There is possibility of very limited miscibility of both components. Supplementary wide angle X-ray scattering results are presented

The preliminary studies of a structure and electrospinning of new polyurethanes based on synthetic atactic poly[(R, S)-3-hydroxybutyrate]

Novel polyurethanes based on synthetic, atactic poly[(R, S)-3-hydroxybutyrate] (a-PHB) and polycaprolactone (PCL) or polyoxytetramethylene (PTMG) diols were synthesized. It was shown that the presence of a-PHB within soft segments reduces crystallinity of PUR. Because of the low melting temperature for polyurethanes with PCL in soft segments, at this stage of work, electrospinning was limited to polyurethanes containing PTMG and a-PHB. Polyurethane containing 80% of PTMG and 20% of a-PHB was electrospun at various parameters from hexafluoro-2-propanole solution, resulting in formation of fibers with the average diameter ca. 2 μm. The fiber diameter decreased with decreasing polymer concentration in a solution and was practically insensitive to the needle-collector distance in the applied range of distances

The preliminary studies of a structure and electrospinning of new polyurethanes based on synthetic atactic poly[(R, S)-3-hydroxybutyrate]

Novel polyurethanes based on synthetic, atactic poly[(R, S)-3-hydroxybutyrate] (a-PHB) and polycaprolactone (PCL) or polyoxytetramethylene (PTMG) diols were synthesized. It was shown that the presence of a-PHB within soft segments reduces crystallinity of PUR. Because of the low melting temperature for polyurethanes with PCL in soft segments, at this stage of work, electrospinning was limited to polyurethanes containing PTMG and a-PHB. Polyurethane containing 80% of PTMG and 20% of a-PHB was electrospun at various parameters from hexafluoro-2-propanole solution, resulting in formation of fibers with the average diameter ca. 2 μm. The fiber diameter decreased with decreasing polymer concentration in a solution and was practically insensitive to the needle-collector distance in the applied range of distances