Size effects of graphene nanoplatelets on the properties of high-density polyethylene nanocomposites: morphological, thermal, electrical, and mechanical characterization

High-density polyethylene (HDPE)-based nanocomposites incorporating three different types of graphene nanoplatelets (GnPs) were fabricated to investigate the size effects of GnPs in terms of both lateral size and thickness on the morphological, thermal, electrical, and mechanical properties. The results show that the inclusion of GnPs enhance the thermal, electrical, and mechanical properties of HDPE-based nanocomposites regardless of GnP size. Nevertheless, the most significant enhancement of the thermal and electrical conductivities and the lowest electrical percolation threshold were achieved with GnPs of a larger lateral size. This could have been attributed to the fact that the GnPs of larger lateral size exhibited a better dispersion in HDPE and formed conductive pathways easily observable in scanning electron microscope (SEM) images. Our results show that the lateral size of GnPs was a more regulating factor for the above-mentioned nanocomposite properties compared to their thickness. For a given lateral size, thinner GnPs showed significantly higher electrical conductivity and a lower percolation threshold than thicker ones. On the other hand, in terms of thermal conductivity, a remarkable amount of enhancement was observed only above a certain filler concentration. The results demonstrate that GnPs with smaller lateral size and larger thickness lead to lower enhancement of the samples' mechanical properties due to poorer dispersion compared to the others. In addition, the size of the GnPs had no considerable effect on the melting and crystallization properties of the HDPE/GnP nanocomposites.

Polydopamine-based Implantable Multifunctional Nanocarpet for Highly Efficient Photothermal-chemo Therapy

We report a design and fabricate multifunctional localized platform for cancer therapy. Multiple stimuli-responsive polydopamine (PDA) was used for surface modification of electrospun doxorubicin hydrochloride (DOX) loaded polycaprolactone (PCL) fibers to make a designated platform. Photothermal properties such as photothermal performance and stability of the resulting composite mats were studied under the irradiation of the near-infrared (NIR) laser of 808 nm. With the incorporation of PDA into the fiber, a remarkable increase of local temperature was recorded under NIR illumination in a concentration-dependent manner with excellent stability. Drug released assay results revealed PDA coated PCL-DOX mats showed pH and NIR dual responsive behavior thereby exhibiting improved drug release in an acidic medium compared to physiological pH condition (pH 7.4) which is further increased by NIR exposure. The cancer activity in vitro of the mats was evaluated using cell counting (CCK) and live and dead cell assays. The combined effect of NIR mediated hyperthermia and chemo release resulting improved cells death has been reported. In summary, this study presents a major step forward towards a therapeutic model to cancer treatment utilizing pH and NIR dual responsive property from PDA alone in a fibrous mat.

pH/NIR-Responsive Polypyrrole-Functionalized Fibrous Localized Drug-Delivery Platform for Synergistic Cancer Therapy

Localized drug-delivery systems (LDDSs) are a promising approach for cancer treatment because they decrease systematic toxicity and enhance the therapeutic effect of the drugs via site-specific delivery of active compounds and possible gradual release. However, the development of LDDS with rationally controlled drug release and intelligent functionality holds great challenge. To this end, we have developed a tailorable fibrous site-specific drug-delivery platform functionalized with pH- and near-infrared (NIR)-responsive polypyrrole (PPy), with the aim of cancer treatment via a combination of photothermal ablation and chemotherapy. First, a paclitaxel (PTX)-loaded polycaprolactone (PCL) (PCL-PTX) mat was prepared by electrospinning and subsequently in situ membrane surface-functionalized with different concentrations of PPy. The obtained PPy-functionalized mats exhibited excellent photostability and heating property in response to NIR exposure. PPy-coated mats exhibited enhanced PTX release in a pH 5.5 environment compared to pH 7.4. Release was further accelerated in response to NIR under both conditions; however, superior release was observed at pH 5.5 compared to pH 7.4, indicating a dual stimuli-responsive (pH and NIR) drug-delivery platform. More importantly, the 808 nm NIR irradiation enabled markedly accelerated PTX release from PPy-coated PCL-PTX mats and slowed and sustained release following termination of laser irradiation, confirming representative stepwise drug-release properties. PPy-coated PCL-PTX mats presented significantly enhanced in vitro and in vivo anticancer efficacy under NIR irradiation compared to PPy-coated PCL-PTX mats not exposed to NIR or uncoated mats (PCL-PTX). This study has thus developed a promising fibrous site-specific drug-delivery platform with NIR- and pH-triggering that notably utilizes PPy as a dopant for synergistic photothermal chemotherapy.

Cellulose Nanowhiskers Templating in Conductive Polymer Nanocomposites Reduces Electrical Percolation Threshold 5-Fold

The creation of conducting networks within composite materials is very important to reduce the generally expensive conducting polymer content, to create conducting/nonconducting domains, and to adjust conductivity of the final composite. We developed cellulose/poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS)-based polystyrene (PS) composites with an extremely low percolation threshold of the conductive polymer. The percolation threshold of PEDOT:PSS in PEDOT:PSS/PS blends, being 2.2 wt % (2.31 vol%), was lowered to 0.4 wt % (0.42 vol%) by adding 0.8 wt % (0.56 vol%) of cheap, nonconducting cellulose nanowhiskers. Such a low percolation threshold of PEDOT:PSS is attributed to the templating effect of the cellulose nanowhiskers: the conducting PEDOT:PSS is thought to adsorb onto the cellulose surface and by doing that (at least partly) covers the network formed by the percolating, high aspect ratio cellulose whiskers in the PS matrix. UV-vis experiments indeed point to an interaction between PEDOT:PSS and the cellulose whiskers, confirming the templating of PEDOT:PSS onto the nanowhiskers during processing and film formation. This approach can be applied to other conducting composites to reduce the required conducting polymer content and increase the ease of processing as electrical percolation is directly achieved.

In situ polymerization of polyaniline in wood veneers

The present study describes the possibility to polymerize aniline within wood veneers to obtain a semi-conducting material with solid wood acting as the base template. It was determined that it is possible to synthesize the intrinsically conductive polymer (ICP) polyaniline in situ within the wood structure of Southern yellow pine veneers, combining the strength of the natural wood structure with the conductivity of the impregnated polymer. It was found that polyaniline is uniformly dispersed within the wood structure by light microscopy and FT-IR imaging. A weight percent gain in the range of 3-12 wt % was obtained with a preferential formation in the wood structure and cell wall, rather than in the lumen. The modified wood was found to be less hydrophilic with the addition of phosphate doped polyaniline as observed by equilibrium water swelling studies. While wood itself is insulating, the modified veneers had conductivities of 1 × 10(-4) to 1 × 10(-9) S cm(-1), demonstrating the ability to tune the conductivity and allowing for materials with a wide range of applications, from anti-static to charge-dispersing materials. Furthermore, the modified veneers had lower total and peak heat releases, as determined by cone calorimetry, because of the char properties of the ICP. This is of interest if these materials are to be used in building and furniture applications where flame retardance is of importance.