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Organic–inorganic halide perovskites feature excellent optoelectronic properties but poor chemical stability. While passivating perovskite grain boundary (GB) by polymers shows prospects on long-te...

We report on the production of a flame-resistant xanthan gum (XG)-based hydrogel formulation, which could be directly applied onto the skin for protection against burning projectiles. The hydrogel cream represents an efficient use of XG and starch, both of which are biodegradable, reusable natural materials and are also GRAS-certified. The flame-retardant agent resorcinol bis(diphenyl phosphate) (RDP) was shown to be nontoxic to cells in vitro when adsorbed directly onto the starch delivery vehicle. Three hydrogel formulations were studied, the pure XG hydrogel, commercial FireIce hydrogel, and RDP-XG/RDP-starch hydrogel. After application of a direct flame for 150 s, the RDP-XG/RDP-starch hydrogel produced a thick char layer, which was easily removed, showing undamaged chicken skin and tissue underneath. In contrast, complete burning of skin and tissue was observed on untreated control samples and those covered with FireIce and pure XG hydrogels. The thermal protective performance test was also performed, where the heat transfer was measured as a function of time for all three hydrogels. The RDP-XG/RDP-starch hydrogel was able to prolong the protection time before obtaining a second-degree burn for 103 s, which is double that for FireIce and triple that for the pure XG hydrogel. The model proposed involves endothermic reactions, producing char and burning "cold", as opposed to simply relying on the adsorbed water in the hydrogel for burn protection.

Polymer pollution from nonbiodegradable polymer blends is a source of increasing environmental concern. The obvious solution, the replacement of petroleum-based polymers with biodegradable polymers...

We have adapted the two-phase Brust method to synthesize large quantities of AuPd alloy nanoparticles with diameter of 1.86 ± 0.40 nm. When the particles were spread at the air/water interface of a Langmuir–Blodgett (LB) trough, they exhibited a distinct pressure area isotherm curve. The X-ray reflectivity (XRR) shows the formation of an incompressible monolayer with uniform thickness of 1.16 ± 0.02 nm at low pressures which collapses to form a second layer with 2.13 nm thickness at higher pressures. High resolution transmission electron microscopy (HRTEM) imaging of the monolayer indicates that the particles are highly crystalline, with well-defined atomic planes and self-assembly into a hexagonal structure. Extended X-ray absorption fine structure (EXAFS) analysis of the LB lift-off films only shows Au–Au and Au–Pd configurations, consistent with the formation of random alloy rather than core–shell structure. When the particle monolayer was lifted onto the Nafion membrane of a proton exchange membrane f...

Proton exchange membranes (PEMs), such as Nafion, are still one of the reasons for the high cost of PEMFCs. Among the alternatives, cellulose, a low cost and biodegradable material, has been considered in the form of its derivatives, such as cellulose acetate, bacterial cellulose or nanocellulose, as the PEM in fuel cells. However, its use involves more chemical synthesis steps. Here, we use low-cost 1.5-micron cellulose filter paper as the scaffold and prepare membranes for PEMFCs by simply impregnating it with a 10% Nafion solution or immersing it in resorcinol bis(diphenyl phosphate) (RDP). The prepared membranes are primarily composed of cellulose, with a cellulose to Nafion or RDP ratio of 2 : 1 or 1 : 1. The membrane electrode assemblies (MEAs) incorporating the as-prepared membranes exhibit a maximum output power of 23 mW cm−2 at 80 °C for the cellulose/Nafion membrane or 10 mW cm−2 at 60 °C for the cellulose/RDP membrane with only 0.1 mg cm−2 Pt loading on the anode and cathode, when operated in air. The stability results of the membranes after 100 hours of continuous operation indicate a loss of only 10% in power for the cellulose/Nafion membrane and 20% for the cellulose/RDP membrane. It is revealed by FTIR spectroscopy that both the Nafion polymer and RDP were hydrogen bonded to the cellulose fibers, facilitating proton conduction and stabilizing them against further dissolution.

Eventhough it is well established that materials can promote stem cell differentiation, hard tissue formation is a templated process for which little is known regarding the in vitro process. We have found that surface curvature enables self-assembly of triple helical collagen fibrils into banded bundle structures from rat tail and human collagen secreted by dental pulp stem cells. Collagen fibrils were adsorbed at 4 °C on spun cast flat P4VP films and electrospun fibers. Protein adsorption was observed on both surfaces, but large banded bundles with a uniform spacing of approximately 55 nm were present only on the fiber surfaces. SEM/EDS mapping showed that dental pulp stem cells plated on the same surfaces biomineralized copiously only along the electrospun fibers. Raman spectroscopy indicated that despite the presence of adsorbed collagen on the flat surfaces, only the deposits present on the fibrous surface had a protein to hydroxyl apatite ratio similar to natural dentin from human teeth. RT-PCR indicated up regulation of collagen, osteocalcin and dental sialophosphate protein, confirming that odontogenic differentiation is promoted only on the fiber scaffolds. Taken together the results indicate that, in addition to surface chemistry, the supermolecular structure of ECM collagen, which is essential in directing DPSCs differentiation and templating biomineralization, can be modified by the underlying surface morphology. Statement of Significance The past decade has been focused efforts in the use of dental pulp stem cells (DPSC) for dental regeneration. Eventhough the factors required for DPSCs differentiation have been well studied, actual mineral deposition, positively identified as dentin, has not been achieved in vitro. Hard tissue is known to be a templated process in vivo where the mineral to protein ratio is tightly controlled via proteins which aid in collagen conformation and mineral sequestration. Here we show that one can mimic this process in vitro via the combination of materials selection and morphology. The material chemistry is shown to induce genetic upregulation the genes responsible for collagen and osteocalcin, while Raman spectroscopy confirms the translation and adsorption the proteins on the substrate. But, we show that the simple presence of collagen is not enough to template actual biomineral deposition similar to that found in vivo. Mineral deposition is a complicated process templated on collagen bundles and mediated by specific sibling proteins that determine the protein to mineral ratio. Here we show that surface curvature can reduce the barrier to collagen bundle formation, directing DPSC differentiation along odontogenic lineage, and subsequently templating actual dentin, comparable to that found in vivo in human teeth.

We have designed and engineered an environmentally sustainable ternary polymer blend with the mechanical properties comparable to high impact resistant conventional polymers under the guidance of the lattice self-consistent field model. In this blend system, poly(methyl methacrylate) (PMMA) was used as the compatibilizer for the poly(lactic acid) (PLA)/poly(butylene adipate-co-butylene terephthalate) (PBAT) blend. We characterized the compatibility of those components and found PMMA was miscible with PLA and partially compatible with PBAT, which allowed it to self-assemble to a nanoscale interfacial layer on the PLA/PBAT interface. This PMMA layer can significantly decrease the interfacial energy and strongly entangle with either PLA or PBAT, resulting in the strengthening of the interface and dramatically enhancement of the impact resistance of the ternary blend. The optimal mechanical performance was achieved when the total PMMA concentration was less than 10 wt %. Higher PMMA content embrittled the ble...

Three-dimensional printing (3DP) technology offers unique advantages for pharmaceutical applications. However, most of current 3D printing methods and instrumentations are not specifically designed and developed for pharmaceutical applications. To meet the needs in pharmaceutical applications for precision, compatibility with a wide range of pharmaceutical excipients and drug materials without additional processing, high throughput and GMP compliance, an extrusion-based 3D printer based on Melt Extrusion Deposition (MED™) 3D printing technology was developed in this study. This technology can process powder pharmaceutical excipients and drugs directly without the need of preparing filament as required by FDM 3D printing. Six different tablet designs based on compartment models were used to demonstrate the precision and reproducibility of this technology. The designed tablets were fabricated using the GMP-compliant MED™ 3D printer and were evaluated in vitro for drug release and in vivo for selected designs using male beagle dogs. Tablet designs with one or more compartments showed versatile release characteristics in modulating the release onset time, release kinetics, duration of release and mode of release. Multiple drugs or formulations were fabricated into a single tablet to achieve independent release kinetics for each drug or to fine-tune the pharmacokinetic profile of a drug. Building upon the theoretical analysis of models, precision and reproducibility of MED™ 3D printing technology, a novel product development approach, 3D printing formulation by design (3DPFbD®) was developed to provide an efficient tool for fast and efficient pharmaceutical product development. The MED™ 3D printing represents a novel and promising technology platform encompassing design and development of modified drug release products and has potential to impact the drug delivery and pharmaceutical product development.

We have engineered an environmentally sustainable, biodegradable, and flame retardant poly (lactic acid) (PLA) based composite by introducing resorcinol bis (diphenyl phosphate) (RDP) coated cellulose fibers at a mass fraction of only 8%. Mechanical testing showed that formation of the composite significantly improved the impact strength, dynamic and elastic moduli, and tensile strength relative to neat PLA. The composite self-extinguished in less than 2 s and had greatly reduced dripping, hence easily passing the UL-94 V0 criteria. Fourier Transform Infrared Spectroscopy (FTIR) was used to elucidate the chemical mechanism responsible for these effects, which were interpreted in terms of a dehydration process of cellulose in the presence of RDP. This has an overall cooling effect and reduction of the combustion, which can be observed in the reduction of heat release rate (HRR) by cone calorimetry and increase in limiting oxygen index (LOI) value.

We have engineered a flame retardant ethylene-vinyl acetate (EVA) composite which has the similar mechanical properties as polyvinyl chloride (PVC) and therefore may prove to be an alternative material for cable sheathing. Four composites were studied, EVA with aluminum hydroxide (ATH), EVA with ATH and molybdenum disulfide (MoS 2 ), EVA with ATH and graphene nanoplatelets (GNPs), and EVA with all three components. Tensile testing showed nearly identical results for the EVA/ATH and EVA/ATH/MoS 2 compounds, while the EVA/ATH/GNPs compound had higher mechanical properties. The compound containing all three components showed further enhanced mechanical properties, indicating that a synergy was established. This was further confirmed using Scanning Electron Microscopy (SEM) where GNPs were seen to increase the dispersion of the MoS 2 and ATH components within the polymer matrix. Cone calorimetry test clearly showed a large decrease in heat release rate when GNPs were added, which was further enhanced by adding GNPs and MoS 2 together. Application of the UL-94 test showed that only the compound containing 36 wt% of ATH and 2 wt% each of MoS 2 and GNPs can achieve the UL-94 V0 rating.

Flame retardant, environmentally sustainable nanocomposites were made by melt blending poly (lactic acid) (PLA) with melamine polyphosphate (MPP) and Cloisite 30B (C-30B). The composition of the nanocomposite was highly specific and guided by interfacial energy minimization principals which balanced enthalpic and mechanical contributions. In this critical range, even small changes in the filler concentration can have a large impact on the performance of the material. We showed that while addition of 17% MPP can increase the flame resistance of PLA, (achieving a UL-94 V2 rating) the mechanical properties were significantly degraded. Addition of only 1% C-30B reversed these effects and yielded a nanocomposite with enhanced mechanical properties and passing the UL-94 V0 flame test. This compound was able to be extruded and fed into a Makerbot Replicator 2X Fused Deposition Modeling (FDM) 3D printer, where the printed samples were indistinguishable mechanically from their molded counterparts and also achieved the UL-94 V0 rating. The enhanced performance occurred only within a very narrow composition window. Cone calorimetry revealed that while a significant decrease in the heat release rate, accompanied by the formation of an intumescent char, was achieved by the addition of 1% C-30B to the MPP/PLA blend, a very poor char, corresponding the increase in the heat release rate, was obtained with addition of 2% C-30B. These results were explained in view of the altered phase morphology observed in Transmission Electron Microscopy (TEM).

Local anesthetics, which cause temporary loss of pain by inhibiting the transmission of nerve impulses, have been widely used in clinical practice. However, neurotoxicity and short half-lives have significantly limited their clinical applications. To overcome those barriers, numerous drug delivery systems (DDS) have been designed to encapsulate local anesthetic agents, so that large doses can be released slowly and provide analgesia over a prolonged period. So far, multiple classes of local anesthetic carriers have been investigated, with some of them already on the market. Among those, polymer-based delivery platforms are the most extensively explored, especially in the form of polymeric nanoparticle carriers. This review gives a specific focus on the most commonly used natural and synthetic polymers for local anesthetics delivery, owing to their excellent biocompatibility, biodegradability and versatility. State-of-the-art studies concerning such polymer delivery systems have been discussed in depth. We also highlight the impact of those delivery platforms as well as some key challenges that need to be overcome for their broader clinical applications. STATEMENT OF SIGNIFICANCE: Currently, local anesthetics have been widely used in clinically practices to prevent transmission of nerve impulses. However, the applications of anesthetics are greatly limited due to their neurotoxicity and short half-lives. Moreover, it is difficult to maintain frequent administrations which can cause poor compliance and serious consequences. Numerous drug delivery systems have been developed to solve those issues. In this review, we highlight the recent advances in polymer-based drug delivery systems for local anesthetics. The advantages as well as shortcomings for different types of polymer-based drug delivery systems are summarized in this paper. In the end, we also give prospects for future development of polymer drug delivery systems for anesthetics.

"Green" polymer nanocomposites were made by melt blending biodegradable poly(lactic acid) (PLA) and poly(butylene adipate-co-butylene terephthalate) (PBAT) with either montmorillonite clays (Cloisite Na(+)), halloysite nanotubes (HNTs), the resorcinol diphenyl phosphate (RDP)-coated Cloisite Na(+), and coated HNTs. A technique for measuring the work of adhesion (Wa) between nanoparticles and their matrixes was used to determine the dispersion preference of the nanoparticles in the PLA/PBAT blend system. Transmission electron microscopy (TEM) images of thin sections indicated that even though both RDP-coated nanotubes and clay platelets segregated to the interfacial regions between the two immiscible polymers, only the platelets, having the larger specific surface area, were able to reduce the PBAT domain sizes. The ability of clay platelets to partially compatibilize the blend was further confirmed by the dynamic mechanical analysis (DMA) which showed that the glass transition temperatures of two polymers tended to shift closer. No shift was observed with either coated or uncoated HNTs samples. Izod impact testing demonstrated that the rubbery PBAT phase greatly increased the impact strength of the unfilled blend, but addition of only 5% of treated clay decreased the impact strength by nearly 50%. On the other hand, an increase of 9% relative to the unfilled blend sample was observed with the addition of 5% treated nanotubes. TEM cross-section analysis confirmed that the RDP-coated clay platelets covered most of the interfacial area. On one hand, this enabled them to reduce the interfacial tension effectively; on the other hand, it prevented chain entanglements across the phase boundary and increased the overall brittleness, which was confirmed by rheology measurements. In contrast, the RDP-coated HNTs were observed to lie perpendicular to the interface, which made them less effective in reducing interfacial tension but encouraged interfacial entanglements across the interface, resulting in "stitching" of the interface and an increase in the Izod impact of the blend.

Environmental concerns have resulted in the increased use of biodegradable polymers and their nanocomposites. We have developed a facile method for measuring the work of adhesion ( W a ) between nanoparticles and their matrix, which we showed can be used to determine their degree of intercalation within the matrix. This method was then applied to Poly (lactic acid) (PLA) nanocomposites with either sodium montmorillonite clays (C-Na+), organically modified clays (C-30B), resorcinol di (phenyl phosphate) (RDP) coated C-Na+ (C-RDP), Halloysite nanotubes (HNTs) and RDP coated HNTs (H-RDP). The C-30B showed the highest W a within the PLA matrix, followed by the C-RDP and the C-Na+. X-ray diffraction and TEM indicated that the C-30B platelets were highly exfoliated, the C-RDP were intercalated, while the C-Na+ were aggregated in the PLA matrix. Oxygen gas permeability measurements showed the largest decrease in permeability for the C-30B nanocomposites, followed by the C-RDP, and the C-Na+ nanocomposites. The values of the particle aspect ratios obtained using Nielsen model were consistent with the TEM images. In contrast to clay platelets, HNTs and H-RDP were not effective in decreasing oxygen gas permeability of PLA matrix, which was in excellent agreement with the model we derived. Despite the higher degree of exfoliation, the C-30B nanocomposites had a significantly lower Izod impact than the C-RDP nanocomposites. SEM images showed numerous micro-voids on the Izod impact fracture surface of C-30B nanocomposites. On the other hand, the nanotubes were much more effective in reinforcing the mechanical properties, with RDP coated tubes having the better performance, consistent with their higher value of W a with PLA matrix. These results showed that RDP coated silicate nanoparticles can provide environmentally safe alternatives for modifying the mechanical and gas barrier properties of PLA.

We have developed a flame retardant poly(lactic acid) (PLA) composite with the addition of only 2 wt% of ammonium polyphosphate (APP) and 0.12 wt% of resorcinol bis(diphenyl phosphate) (RDP), which achieved the V-0 rating of UL-94 test and could be drawn into filaments for Fused Deposition Modeling (FDM) 3D printing. The composite was designed by analyzing the work of adhesion ( W a ) between RDP/PLA, RDP/APP and PLA/APP, where RDP was found to act as the compatibilizer to improve the dispersion of APP particles within PLA matrix, resulting in enhanced flame retardant efficiency. These results were confirmed by thermal imaging of the UL-94 burning process and cone calorimetry. Scanning electron microscopy imaging and EDS mapping also confirmed the better dispersion of APP particles and the reduced particle size with the addition of RDP. Furthermore, with RDP localized on the PLA/APP interface, the relatively high W a between RDP/PLA and RDP/APP minimized the negative effect of APP and RDP on mechanical properties. Impact and tensile testing showed that the PLA/APP/RDP composite has mechanical properties comparable to those of neat PLA, which enabled the composite to be drawn into thin filaments for 3D printing application.

Complementary techniques were applied to characterize the structure property relationships of FDM printed isotactic polypropylene/graphene nanocomposites. Raman spectroscopy indicated that graphene was mostly exfoliated during the nozzle extrusion process. Rheological measurements of the viscosity indicated that the presence of graphene induced shear thinning during extrusion. Azimuthal scans of wide angle x-ray scattering indicate correlated thermal fluctuations of the graphene platelets which stops abruptly at the onset of transcrystallization, or templating of the iPP chains on the graphene. X-ray microbeam SAXS analysis show the formation of ‘shish-kebab’ structures at the core of the unfilled filaments, where the ‘kebab’ component vanishes at the fiber-fiber interface enabling interdiffusion. Weak lamellar structure, and a corresponding decrease in the storage modulus are observed with the addition of 5% graphene. The lamellar structure disappears entirely with the addition of 10% graphene, while the storage modulus is decreased by nearly 50%. Thermal imaging of heat flux dissipation across molded and printed samples shows no orientational effects in pure iPP despite differences in crystal structure. Thermal conductivity increases dramatically in the samples with 10% graphene, and strong orientational effects are observed where the thermal coefficients differ by 180% between samples printed parallel or perpendicular to the heat flux.

There is an urgent demand for producing biodegradable polymer based composites with good thermal and/or electrical conductivity to mitigate the plastic pollution introduced by electronic waste. Here, we have designed and engineered a mechanically strong, melt processable, biodegradable polymer based nanocomposite with excellent thermal and electrical conductivity using filler dispersion principle and the work of adhesion ( W a ) as guides. In the design, graphene nano-platelets (GNPs) were dispersed into a highly ductile biodegradable polymer - poly (butylene adipate-co-butylene terephthalate) (PBAT). Blending with another biodegradable polymer, poly (lactic acid) (PLA) that has low affinity to GNPs, confined the dispersion of GNPs within PBAT matrix, thereby facilitating the formation of a percolated network. As a result, high thermal conductivity ( 3.15 W / m ⋅ K ) and electrical conductivity ( 338 S / m ) were achieved for the nanocomposite at 40 wt% of GNPs loading, and the mechanical performance remained strong even at such filler loading due to the strong interaction between GNPs and PBAT. This study provides a new strategy for effectively producing high thermally and/or electrically conductive polymer nanocomposites.

Proton exchange membrane fuel cells (PEMFCs) are one of the most promising energy solutions in meeting the soaring global energy demand and relieving the environmental concerns associated with greenhouse emissions. Cost and durability are two main obstacles hindering the successful commercialization of PEMFCs. Here, we propose a solution which could significantly enhance durability, reduce PGM catalyst, and increase tolerance to impure hydrogen sources thereby reducing cost and increasing convenience by allowing operation in ambient conditions. We show that applying a coating of 1 μg/cm2 of graphene oxide (GO) directly onto the Nafion membrane or electrodes enabled a 60% enhancement of the maximum power output to 0.78 or 0.76 W/cm2, using only a total of 0.15 mg/cm2 Pt catalyst. Durability tests were carried out complying with the DOE2020 protocols, indicating that the enhancement persisted even after 30k cycles, where the maximum power decrease was only 9%, as compared with 18% in the control sample, and the decrease in voltage at 1.5 A/cm2 was only 13%, as compared with 70% of the control sample. In addition, blending of 0.1% CO gas into the input H2 stream reduced the power by 72% in the control, while only 26% power reduction was observed in the coated PEMFCs. Also, electrochemical impedance spectroscopy (EIS) measurements exhibited a decrease in resistance of only 13%, while the active Pt surface area of the electrode with GO coating after 30k cycles was 17.5% higher than the control and the minimal DOE requirement.

Using known parameters for the surface and interfacial tension, the work of adhesion of PMMA with PLA and styrenic polymers has been calculated. The results indicated that PMMA, an abundant and economical homopolymer, could serve as an effective compatibilizer, rivaling complex and costly block copolymers for PLA/styrenic blends. Blends of PLA with either SAN or ABS were produced with added 1%–10% PMMA. Tensile and impact toughness data show that the blends display properties comparable to those of PP with only 4% added PMMA. Deuterated-secondary ion mass spectrometry (DSIMS) performed with deuterated PMMA indicated that this corresponded to the formation of an interfacial layer approximately 2Rg thick, as the optimal thickness for integrating two polymers, without the formation of a third brittle layer. Blends with ABS showed an increase of nearly 300% in impact toughness compared to that for polymer containing no PMMA, while blends with SAN formed ideal extruded filaments, which produced 3-D printed structures at least 58% stronger and more ductile than molded PS.