Recent Progress in Modified Polymer-Based PPE in Fight Against COVID-19 and Beyond

The increasing concerns about human-health-related microbial infections and the need for the development of personal protective equipment (PPE) is becoming a major challenge. Because of their light weight and ease of processing, polymeric materials are widely used in designing and fabricating PPE that are being used by healthcare workers and the general population. Among the available PPEs, face masks have been widely developed from polymeric materials such as polypropylene, polycarbonate, and poly(ethylene terephthalate). However, currently, many of the face masks are not antimicrobial, which can pose a great risk for cross-infection as discarded masks can be a dangerous source of microbes. To prevent the spread of microbes, researchers have prompted the development of self-sterilizing masks that are capable of inactivating microbes via different mechanisms. Hence, this review provides a brief overview of the currently available antimicrobial-modified polymer-based PPE, and it mainly focuses on the different types of nanoparticles and other materials that have been embedded in different polymeric materials. The possibility of inhaling microplastics from wearing a face mask is also outlined, and the effects of various modifications on the health of face mask users are also explored. Furthermore, the effects of the disposed masks on the environment are underlined.

Tunable Substrate Functionalities Direct Stem Cell Fate toward Electrophysiologically Distinguishable Neuron-like and Glial-like Cells

Engineering cellular microenvironment on a functional platform using various biophysical cues to modulate stem cell fate has been the central theme in regenerative engineering. Among the various biophysical cues to direct stem cell differentiation, the critical role of physiologically relevant electric field (EF) stimulation was established in the recent past. The present study is the first to report the strategy to switch EF-mediated differentiation of human mesenchymal stem cells (hMSCs) between neuronal and glial pathways, using tailored functional properties of the biomaterial substrate. We have examined the combinatorial effect of substrate functionalities (conductivity, electroactivity, and topography) on the EF-mediated stem cell differentiation on polyvinylidene-difluoride (PVDF) nanocomposites in vitro, without any biochemical inducers. The functionalities of PVDF have been tailored using conducting nanofiller (multiwall-carbon nanotube, MWNT) and piezoceramic (BaTiO₃, BT) by an optimized processing approach (melt mixing-compression molding-rolling). The DC conductivity of PVDF nanocomposites was tuned from ∼10^-11 to ∼10^-4 S/cm and the dielectric constant from ∼10 to ∼300. The phenotypical changes and genotypical expression of hMSCs revealed the signatures of early differentiation toward neuronal pathway on rolled-PVDF/MWNT and late differentiation toward glial lineage on rolled-PVDF/BT/MWNT. Moreover, we were able to distinguish the physiological properties of differentiated neuron-like and glial-like cells using membrane depolarization and mechanical stimulation. The excitability of the EF-stimulated hMSCs was also determined using whole-cell patch-clamp recordings. Mechanistically, the roles of intracellular reactive oxygen species (ROS), Ca²⁺ oscillations, and synaptic and gap junction proteins in directing the cellular fate have been established. Therefore, the present work critically unveils complex yet synergistic interaction of substrate functional properties to direct EF-mediated differentiation toward neuron-like and glial-like cells, with distinguishable electrophysiological responses.

PVDF-MWNT interactions control process induced β-lamellar morphology and orientation in the nanocomposites

The effect of methylene blue (MB) modified multiwall carbon nanotubes (MWNTs) on the nucleation and morphology of polyvinylidene fluoride (PVDF) in comparison with the effect of MWNTs was systematically assessed by DSC, 13C NMR, FT-IR, TEM, WAXS and SAXS analysis. TEM analysis of ultra-microtomed samples revealed that MB modification enhanced the dispersibility of MWNTs in PVDF. Further, the nanocomposites were subjected to mechanical rolling and the synergistic effect of processing and fillers on the PVDF morphology (before and after rolling) at different length scales was studied. Both FT-IR and WAXS analyses suggested that mechanical rolling transforms α-PVDF to β-PVDF (ca. 88%). TEM and two-dimensional WAXS analyses revealed that the MWNTs and β-crystallites are oriented preferentially along the rolling direction and the degree of orientation is not influenced by the fillers suggesting that crystallite orientation is fully controlled by mechanical rolling. On the other hand, β-lamellae showed perpendicular orientation with respect to the rolling direction. Unlike β-crystallites, the β-lamellar morphology and orientation are highly governed by the fillers as evident from SAXS analysis. Using MWNTs and the MWNT-MB π-complex, we demonstrate that the β-lamellar morphology and degree of orientation are controlled by the extent of interaction of fillers with PVDF. Interestingly, both β-lamellar morphology and degree of orientation correlate well with the mechanical properties of the rolled PVDF. More specifically, the dynamic storage modulus of the samples in the rolling direction increases with increasing β-lamellar morphology and degree of orientation. The present work demonstrates that the polymer-filler interaction plays a crucial role in regulating the processed polymer morphology and can be tuned by appropriately modifying the surface of fillers through either covalent or non-covalent interactions.

Piezoelectric Response in Electrospun Poly(vinylidene fluoride) Fibers Containing Fluoro-Doped Graphene Derivatives

Herein, graphene oxide (GO) was suitably functionalized to obtain carboxylated and fluorinated GO (GOCOOH and GOF) derivatives, respectively, via the Hunsdiecker reaction. Electrospun mats of poly(vinylidene fluoride) (PVDF)/GO, PVDF/GOCOOH, and PVDF/GOF fibers were then prepared by electrospinning from well-dispersed GO derivatives. The piezoelectric coefficient (d ₃₃), as measured using piezoelectric force measurement (PFM), enhanced by more than 2 folds with respect to the control PVDF spun mat. The piezoelectric coefficient though enhanced upon the addition of GO and GOCOOH, however, enhanced significantly in the case of GOF. For instance, a drastic increase in piezoelectric response from 30 pm V^-1(electrospun neat PVDF) to 63 pm V^-1 (for electrospun PVDF/GOF) was observed as revealed from PFM results. The phase transformation in these fibers was systematically investigated by various techniques such as Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (XRD), Raman spectroscopy, and PFM. FTIR and XRD results revealed that the electrospun fiber mats showed predominantly β-PVDF. Interestingly, the highest β content was obtained in the presence of GOF. The drastic enhancement in β phase is due to the presence of highly electronegative fluorine. The addition of GOCOOH and GOF in PVDF not only increases the polar β phase but also changes the piezoelectric response significantly. More interestingly, PVDF/GOF films exhibited higher energy density and dielectric permittivity when compared with the control PVDF samples. These findings will help guide the researchers working in this field from both theoretical understanding and practical view point for energy storing device and charge storage electronics.