Influence of miscibility phenomenon on crystalline polymorph transition in poly(vinylidene fluoride)/ acrylic rubber/clay nanocomposite hybrid

In this paper, intercalation of nanoclay in the miscible polymer blend of poly(vinylidene fluoride) (PVDF) and acrylic rubber(ACM) was studied. X-ray diffraction was used to investigate the formation of nanoscale polymer blend/clay hybrid. Infrared spectroscopy and X-ray analysis revealed the coexistence of b and c crystalline forms in PVDF/Clay nanocomposite while a crystalline form was found to be dominant in PVDF/ACM/Clay miscible hybrids. Flory-Huggins interaction parameter (B) was used to further explain the miscibility phenomenon observed. The B parameter was determined by combining the melting point depression and the binary interaction model. The estimated B values for the ternary PVDF/ACM/Clay and PVDF/ACM pairs were all negative, showing both proper intercalation of the polymer melt into the nanoclay galleries and the good miscibility of PVDF and ACM blend. The B value for the PVDF/ACM blend was almost the same as that measured for the PVDF/ACM/Clay hybrid, suggesting that PVDF chains in nanocomposite hybrids interact with ACM chains and that nanoclay in hybrid systems is wrapped by ACM molecules

Self-powered cardiac pacemaker by piezoelectric polymer nanogenerator implant

Self-powered biomedical implants improve the life of patients and lower the risks associated with battery replacement. Piezoelectric energy harvesters that generate electricity from the cardiac motions are among the potential candidates to be used in self-powered implants, such as cardiac pacemakers. In this context, lead-based ceramic piezoelectric nanogenerators (PNGs) were emerged, which are toxic and susceptible to fatigue crack, causing harm to the patients. Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE)-based films were also developed as cardiac energy harvesters. Here, we show a battery-free heart pacemaker that is powered by the generated electricity of a biocompatible and flexible piezoelectric polymer-based nanogenerator (PNG) from the cardiac motions of the left ventricle. The PNG is comprised of composite nanofibers of poly(vinylidene fluoride) (PVDF) and a hybrid nanofiller made of zinc oxide (ZnO) and reduced graphene oxide (rGO). The composite nanofiber is optimized towards achieving a large power output. In vivo implanted optimized PNG can successfully harvest 0.487 μJ from every heartbeat, which is conveniently larger than the pacing threshold energy for the human heart. The successful demonstration of a self-powered pacemaker places the polymer-based PNGs among the viable candidates for self-powered biomedical implants.</p

Porous graphene/poly(vinylidene fluoride) nanofibers for pressure sensing

Piezoelectric polymers have emerged as promising materials for application in pressure sensing devices in particular for wearable applications, where inorganic piezoelectric materials can face limitations due to their brittleness. One of the bottlenecks for the adaptation of piezoelectric polymers is their relatively weak piezoelectric voltage coefficient. Hence there have been numerous efforts to improve the performance of the comprising devices by making composites of poly(vinylidene fluoride) (PVDF), or through making porous PVDF films, or by nanostructuring. Here, we demonstrate the fabrication of porous nanofibers with graphene/PVDF composites and investigate the suitability of the fiber for motion sensing. The nanofibers are fabricated by electrospinning from the solution phase. Guided by an experimentally validated phase diagram for PVDF/solvent/non-solvent ternary system, porous graphene/PVDF nanofibers with different porosities and pore morphologies have been produced through solidifying the fibers in the binodal or spinodal regions of the phase diagram. It is found that only by solidifying the composite fibers in the spinodal region, graphene loading of 0.1 wt% promotes the formation of the electroactive phase substantially, and the resulting fibers exhibit enhanced piezoelectric output. It is further shown that the comprising sensors are biocompatible and show high sensitivity to body motion.</p

Chemical Decellularization Methods and Its Effects on Extracellular Matrix

Background:  Extracellular matrix (ECM) produced by tissue decellularization processes as a biological scaffold due to its unique properties compared to other scaffolds for migration and implantation of stem cells have been used successfully in the field of tissue engineering and regenerative medicine in the last years. The objective of this manuscript was to provide an overview of the chemical decellularization methods, evaluation of decellularized ECM and the potential effect of the chemical decellularization agents on the biochemical composition.Methods: We searched in Google Scholar, PubMed, Scopus, and Science Direct. The literature search was done by using the following keywords: “ECM, biologic scaffold, decellularization, chemical methods, tissue engineering.” We selected articles have been published from 2000 to 2016, and 15 full texts and 97 abstracts were reviewed.Results:Employing an optimization method to minimize damage to the ECM ultrastructure as for a result of the lack of reduction in mechanical properties and also the preservation of essential proteins such as laminin, fibronectin, Glycosaminoglycans (GAGs), growth factor is required. Various methods include chemical, physical and enzymatic technics were studied. However, on each of these methods can have undesirable effects on ECM.Conclusion: It is suggested that instead of the Sodium dodecyl sulfate (SDS) which have high strength degradation, we can use zwitterionic separately or in combination with SDS. Tributyl phosphate (TBP) due to its unique properties can be used in decellularization process

Analysis of Methylation and Expression Profile of Foxp3 Gene in Patients with Behçet’s Syndrome

Forkhead box P3 (Foxp3) gene is an important means in the Treg cells function, in both maintenances of immune tolerance and regulation of response. Epigenetic modifications of the foxp3 gene at its regulatory regions control the chromatin accessibility for the transcription factors and other transcriptional regulators in order to control Foxp3 expression. In addition, the methylation status of CpG islands within the Foxp3 promoter and regulatory elements regulate the expression of Foxp3. This study was performed to assess the role of the foxp3 gene in patients with Behçet’s syndrome (BS). Venous blood samples were collected from all participants and peripheral blood mononuclear cells (PBMC) were extracted through Ficoll-Hypaque method. Genomic DNA was randomly sheared by sonication and immunoprecipitated with a monoclonal antibody. The status methylation of the foxp3 gene was estimated in 108 blood samples of active BS patients and healthy individuals (controls); using methylation DNA immunoprecipitation (MeDIP) technique. Expression analysis was carried out; using Real-time PCR. The expression of foxp3 gene in the patients' group (mean±SD: 1.79±1.12) was significantly lower than the healthy group (mean±SD: 2.73±1.33) (p<001). Also, the methylation levels of Foxp3 promoter showed that its level in patients (mean±SD: 2.3±1.16) was higher than the healthy group (mean±SD: 1.85±0.59). However, this increase was not statistically significant (p>0.05). Also, these results indicated that increasing the amount of methylation of the foxp3 gene by reducing its expression leads to an increase and intensifying of the disease. The decrease in Foxp3 expression is possibly associated with hypermethylation of the gene, and it can be considered as a risk factor for BS. Future studies may be needed to identify the capability of specific DNA methylation alterations in this syndrome

Beyond 17% stable perovskite solar module via polaron arrangement of tuned polymeric hole transport layer

Operational stability of perovskite solar cells (PSCs) is rapidly becoming one of the pressing bottlenecks for their upscaling and integration of such promising photovoltaic technology. Instability of the hole transport layer (HTL) has been considered as one of the potential origins of short life-time of the PSCs. In this work, by varying the molecular weight (MW) of doped poly(triarylamine)(PTAA) HTL, we improved by one order of magnitude the charge mobility inside the HTL and the charge transfer at the perovskite/HTL interface. We demonstrate that this occurs via the enhancement of polaron delocalization on the polymeric chains through the combined effect of doping strategy and MW tuning. By using high MW PTAA doped combining three different dopant, we demonstrate stable PSCs with typical power conversion efficiencies above 20%, retain more than 90% of the initial efficiency after 1080 h thermal stress at 85 °C and 87% of initial efficiency after 160 h exposure against 1 sun light soaking. By using this doping-MW strategy, we realized perovskite solar modules with an efficiency of 17% on an active area of 43 cm2, keeping above 90% of the initial efficiency after 800 h thermal stress at 85 °C. These results, obtained in ambient conditions, pave the way toward the industrialization of PSC-based photovoltaic technology.</p

A facile method to enhance ferroelectric properties in PVDF nanocomposites

Poly(vinylidene fluoride) (PVDF)/nanoclay composites were prepared using melt compounding. The effect of acrylic rubber (ACM) as a compatibilizer on different polymorph formation and on the ferroelectric properties of nanocomposites were investigated. The intercalation and morphological structure of the samples were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The infrared spectroscopy and X-ray analysis revealed the coexistence of beta and gamma crystalline forms in PVDF-clay nanocomposite, while in partially miscible PVDF/ACM/clay hybrids, three polymorphs of alpha, beta and g coexisted. The coefficients of electric field-polarization (E-P) Taylor expansion were calculated based on the Lorentz theory. Using a genetic algorithm, complex dielectric susceptibilities as well as the dielectric constants for each sample were calculated and optimized. The predicted dielectric constants were found to be in good agreement with the experimental results. A dielectric constant of 16 (10 Hz) was obtained for PVDF/ACM/clay (90/10/5), which was 40% higher than that of the PVDF-clay (100/5) nanocomposite without ACM. The improved dielectric performance of the nanocomposites can be attributed to the compatibilizing effect of ACM, which facilitated the growth of b polymorph in the sample