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Mammalian cells are widely used in biotechnology and regenerative medicine applications, including recombinant protein production, cell therapy, 3D bioprinting, and ex vivo engineering of tissues and organs. Unlike unicellular organisms, fungi, or plants, animal cells lack a protective cell wall, and therefore are more sensitive to processing conditions, particularly mechanical forces. Hydrodynamic forces during capillary flow can damage the plasma membrane and impact cell viability and functions, limiting the yields of protein production or the success of injection-based cell delivery and 3D bioprinting of artificial tissues and organs. Here, we present nanocoating individual murine fibroblasts as a model organism with silk-based artificial cell walls to protect against mechanical stress. Cells were coated with three bilayers of silk polyelectrolytes through layer-by-layer electrostatic deposition and subjected to mechanical stress by extrusion through needles with small inner diameters or shearing using a rheometer. The silk nanocoatings preserved membrane integrity, cell survival, and proliferation after exposure to stress in viscous polyethylene glycol solution, providing a useful strategy for cytoprotection during cell delivery and 3D bioprinting applications. Use of mammalian cells is a necessity in the industrial production of biopharmaceuticals because of proper protein folding through chaperone systems and post-translational modifications such as glycosylation being essential for functional products. Moreover, transplantation of human cells holds great promise in regeneration of serious injuries in the bone, brain, or spinal cord as well as debilitating diseases such as stroke, diabetes, arterial dysfunctions, and cancers. Cell delivery by direct injection or within 3D-printed scaffolds with well-defined, patient-specific geometry and composition has potential in filling the gap of insufficient organ transplantation. Both the delivery of mammalian cells into a bioreactor through transfer pipes or cell extrusion through fine needles or nozzles for injection-based delivery or bioprinting, however, may expose the cells to extremes of mechanical stress that impair cell viability and reduce the yield of production or overall success of the transplantation therapy. The silk nanocoatings on individual cells demonstrated in this study acted as artificial cell walls for mammalian cells and provided protection against mechanical stress during capillary flow or exposure to a constant shear force and significantly limited the loss of membrane integrity and necrotic or apoptotic cell death. The safety and simplicity of the approach involving protein-based, biocompatible silk fibroin processed through organic solvent-free, nature-friendly modification pathways allows for rapid translation in biotechnology and regenerative medicine to improve cell delivery applications.

Here, we report a previously unreported low-temperature curable barium strontium titanate (BaXSr1−XTiO3) or BST dielectric nanoparticle ink which shows a high dielectric tunability for printed electronics/additive manufacturing applications. The newly formulated BST ink is optimized to print in aerosol jet printers and can be cured at 150°C, which will allow the fabrication of tunable radio-frequency (RF) and microwave (MW) devices on a wide range of flexible substrates. Characterization of high-frequency dielectric properties showed a high dielectric tunability (~ 15% at 10 GHz with 10 V/µm) and a high dielectric constant (~ 16 at 10 GHz). The linear-reversible tunability, which is very important for tunable devices, was confirmed by the tunability testing at 10 GHz. Characterization of temperature-dependent dielectric properties found < 10% variations of the dielectric constant at 10 GHz from −50°C to 125°C for this BST ink. Detailed information on BST nanoparticle characterization, ink formulation and characterization of dielectric properties is discussed.

Polyamides (PAs) are repeatedly exposed to environments of varying humidity throughout their service life. Due to their hygroscopic nature, moisture diffusion can alter the polymer properties, some...

The free radical functionalization of immiscible blends of polybutylene succinate (PBS) and polypropylene carbonate (PPC) was successfully achieved on a novel quad screw extruder. A premade compatibilizer, PPC-grafted-maleic anhydride (gPPC), was added in various amounts to trigger the chemical compatibilization and tailor the properties of the final blend. Titration of acid groups on the functionalized blends showed that the grafting efficiency increases with the addition of gPPC. Proton NMR corroborated the formation of new graft copolymers in the reactive blends. A change in the rheological behavior of the formulations evidenced the grafting reactions occurring at the interphase of the components. Also, gPPC suppressed droplet coalescence as seen in the SEM images. Finally, the addition of compatibilizer increased the tensile strain at break by more than 100%, improved up to 50% the impact resistance, and produced a small increase on flexural and elastic modulus.

Poly (butylene succinate) (PBS) is an important bio-based and biodegradable polymer and attracts lots of attention stemming from its good mechanical properties that are complementary to other biobased polyesters. PBS has relatively slow biodegradation due to its high degree of crystallinity, which limits its utility in targeted applications. It is known that enzymatic degradation depends on polymer chemistry, solid-state morphology (i.e. crystallinity), molecular weight and other structural factors. In this paper, PBS-based copolyesters were synthesized through a melt polycondensation process and enzymatic degradation was carried out using lipase from Candida rugosa. Rate of enzymatic degradation and thermal properties were found to vary depending on the ratio of butanediol to hexanediol in the copolymer. The combined analysis of the enzymatic degradation rate and change in the morphology and molecular weight of a series of PBS-based copolyesters demonstrated the relative contributions of polymer chemistry, thermal properties and crystallinity. PBS-based copolyesters with tunable enzymatic degradation show promise as a more sustainable substitute for non-biodegradable plastics in agriculture and packaging industries.

In this work, biodegradable polymers were melt compounded with urea phosphate to fabricate &ldquo, smart fertilizers&rdquo, for sustainable agriculture. Urea phosphate (UP) is typically applied as a water-soluble fertilizer to treat phosphorus deficiency in high pH soils. Due to the low diffusion rate of phosphate through slow-release fertilizer coatings, phosphate supply has been considered the &ldquo, bottleneck&rdquo, for nitrogen&ndash, phosphorous&ndash, potassium (NPK) nutrients supply. We study the influence of polymer matrix structure on release kinetics in deionized water using novel polyesters including poly (hexamethylene succinate) (PHS), poly (30% butylene succinate-co-70% hexamethylene succinate) (PBHS 30/70), and PBHS 70/30. Melt processed composites of UP and polyester were analyzed to determine UP loading efficiency and dispersion and distribution of the salt in the polymer matrix. A combined empirical model involving diffusion and erosion mechanisms was found have a good agreement with the experimental release curve. This work provides a solution for environmentally friendly controlled release phosphate fertilizer with good release performance using bio-based and biodegradable polymers.

The immiscible bio-plastic blend of poly(lactic acid) (PLA) and polyamide11 (PA11 or Nylon11) was compatibilized, using a catalyzed the ester-amide interchange chemical reaction during reactive extrusion. The effects of screw configuration on mixing and reaction optimization were explored. It was found that effective mixing and minimized degradation were achieved when kneading elements were installed only near the die end of the extruder rather than near the beginning of the melt section. However, significant degradation of PLA could not be avoided during processing, which led to a decrease in mechanical strength of blend. To prevent the molecular weight reduction, tris(nonylphenyl) phosphite (TNPP) stabilizer was introduced to improve the thermal stability of PLA matrix. Improvement to both tensile strength and elongation were achieved in the resulting PLA/PA11/TsOH/TNPP blend.

Twin screw extrusion at speeds exceeding several thousand rotations per minute (RPM) has the potential to provide extreme shear typically required to break up aggregates and provide good dispersion in polymer nanocomposites. In this work, a novel twin screw extruder with ultra-high screw speed capability has been used to compound the polystyrene (PS) with organically modified nanoclay without using any compatibilizer. The rheological properties and the morphology of the nanocomposites were investigated and compared with simulation after compounding. Screw profiles imparting more and less aggressive mixing were compared over a range of screw speeds from 400 to 4000 RPM. Morphological characterization revealed the necessity of intense shear stress for achieving intercalation and exfoliation when chemical interactions between filler and matrix are unfavorable. The nanocomposites exhibited greater elasticity indicating reinforcement up to a critical screw speed for each screw profile, but further increasing the screw speed resulted in significant polymer degradation, and thus lower viscosity and storage modulus. Moreover, based on calculations of the theoretical adhesion force between the organoclay layers and the shear stress imparted through mixing, the optimized screw speed for a specific screw profile was determined that would overcome lamellar adhesion to form exfoliated nanocomposites, while minimizing the effect of degradation. The resulting model could be extended to any well-defined extruder system as well as other agglomerated nanofillers.

Herein, aqueous suspensions of poly(3-hexylthiophene)/poly(styrene) (P3HT/PS) blended colloids with varied ratios were prepared using a miniemulsion process. The effects of composition and marginal solvent amount on the aggregates, optical and hole-transport properties of P3HT/PS blended colloids were investigated. Both PS and THF promoted P3HT chain aggregation and electronic coupling, resulting in a red-shift and increased absorbance intensity at the 0-0 and 0-1 vibronic peaks in aqueous suspensions. But, PS prevented further chain packing and aggregation during thermal annealing in solid-state of P3HT/PS blended colloid films, compared to pure P3HT colloids. The crystal lattice spacing in alkyl packing direction of P3HT was not affected by either PS or THF. Additionally, the hole mobility of FETs using pure P3HT colloids was 9.08 × 10−5 cm2/Vs, which decreased when P3HT/PS blended colloids were used. However, incorporation of THF enhanced the hole mobility of FETs using P3HT/PS(2/8) blended colloids, from 0.76 × 10−5 cm2/Vs for FETs using blended colloids made from solvent without THF to 1.24 × 10−5 cm2/Vs for FETs using blended colloids made from solvent mixture with 10 vol% THF. These performance improvements will enable greener, more industrially-relevant water-processing of polymers for emerging organic electronics.

The key approach to achieve high performance field effect transistor fabricated from semiconducting/insulating polymer blends with majority insulating polymer phase is the formation of connected fibrous structures of semiconducting polymer and good interfacial interaction of semiconducting polymer with the dielectric layer. Herein, tetrahydrofuran (THF) as a marginal solvent was used as an additive in marginal/good solvent mixtures to control the crystallite structure, phase segregation, and hole transport properties of poly(3-hexylthiophene)/poly(styrene) (P3HT/PS; weight ratio: 1/4) blends, with the advantage that marginal/good solvent mixture gives P3HT sufficient time for phase segregation and relatively better solvent quality to aggregate to more stable structures compared to other reported strategies as bad/good solvent mixtures or directly marginal solvents. Incorporation of THF reduces the P3HT solubility, forming connected fibrous structures as observed in both neat P3HT and blend films; it appea...

Immiscible PLA/PA11 of 80/20 and 50/50 wt% were compatibilized through addition of p-toluenesulfonic acid (TsOH) catalyst in reactive ultra-high speed twin-screw extrusion. Two mixing screw designs were compared for their ability to disperse the PA11 droplets in the PLA matrix as a function of screw speed up to 2000 rpm. The size and polydispersity of droplets of dispersed PA11 decreased when a high shear (HS) screw was used, whereas broad droplet size distribution was produced in the low shear (LS) screw. Two models predicting the droplet size dependence on shear rate, viscosity ratio and interfacial tension were fit to the experimental data. The Serpe model including volume fraction effects produced a better fit compared to the Wu model, which does not include volume fraction effects. Mechanical testing indicated that the compatibility of PLA/PA11 blends was improved through addition of TsOH catalyst for 50/50 wt% blends due to ester – amide exchange reactions at the interfaces in the immiscible PLA and PA11 phases. The enhancement of ductility was greater after processing with the LS screw configuration than the HS screw configuration. The inferior properties after high shear mixing were likely due to molecular weight degradation during processing. While the aggressive shear in the HS screw design resulted in fine dispersion, care should be taken to minimize degradation, especially for shear sensitive polymers.

In this article, a kinetic model is introduced in conjunction with experimental extrusion results to predict the evolution of depolymerization reaction at various operating conditions during ultra-high speed twin screw extrusion (TSE). A commercially available flow simulation software (LUDOVIC®) was used to calculate thermomechanical flow parameters for various screw profiles. The simulated local material temperature and mechanical shear rate were used as inputs to develop a kinetic model that separately describes the effects of temperature and shear on the extent of degradation reaction due to extruding at very high speeds. The model is validated through comparison with experimental gel permeation chromatography (GPC) results on extruded samples. A good agreement was found between theoretical and experimental results. This validation makes the model practically useful for processing optimization, which is a considerable challenge for realizing compounding benefits in ultra-high speed TSE.

Polymeric materials hold several advantages over metal components in heat exchangers such as cost savings, lighter weight and corrosion resistance. However, it is challenging to engineer plastics with good heat transfer characteristics, processability and required strength. Neat polymer resins have inferior mechanical and thermal properties relative to metals, requiring careful consideration of the entire heat exchanger system from materials to system design, to achieve sufficient performance. This review summarizes the physical parameters governing polymer and composite thermal conductivity, as well as the latest research on augmenting thermal conductivity. Highly filled composites containing carbon or metal have achieved thermal conductivity an order of magnitude higher than that of neat polymers. The effects of critical additive characteristics, such as interfacial compatibility, filler shape factor, loading level and processing technique, are reviewed. In addition to lower material costs, high volume processing technologies such as injection molding and extrusion are responsible for the cost savings of polymers over metals. Thus, the manufacturing considerations for the most promising high thermal conductivity polymer composites are also reviewed.

Biobased aliphatic polyesters are of interest for their biodegradability and potential to offset the use of unsustainable fossil resources. In addition, many of the bio-sourced monomers are inherently less toxic than those used in conventional polymers. In this work, biobased poly(butylene succinate-co-hexamethylene succinate) (P(BS-co-HS)) copolyesters with butylene succinate (BS)/hexamethylene succinate (HS) molar ratios over the entire compositional range were synthesized from succinic acid, butanediol and 1,6-hexanediol using direct melt polycondensation. The chemical and crystalline structure, thermal properties, solubility and mechanical properties of P(BS-co-HS) copolyesters were investigated. The results confirmed successful synthesis of all copolymers, and the melting temperature, glass transition temperature and crystallization temperature of P(BS-co-HS) copolyesters were tunable depending on BS/HS composition. The crystallinity of P(BS-co-HS) copolyesters decreased to a minimum of 6.0% when the BS/HS ratio was close to 1. Moreover, the incorporation of HS altered the tensile failure mechanism from brittle failure for neat PBS to ductile for P(BS-co-HS) copolyesters with HS content higher than 30 mol%. The solubility of these biobased copolymers and their thermal, mechanical and crystallization behavior over the full compositional range are disclosed for the first time. The polyesters show promise as greener coatings for biodegradable paper packaging.

Poly(ether ether ketone) (PEEK) is increasingly used in selective laser sintering (SLS) due to its superior mechanical and thermal properties and biocompatibility. It is well known that the properties of selective laser sintering (SLS) powder govern the processability and quality of the parts. The SLS printing process exposes the PEEK bed/feedstock to variable elevated temperatures (above 300 °C) for a prolonged time. The effect of this thermal history on the part quality is unknown. This work evaluates the changes that occur in thermally treated PEEK powder through spectroscopic, morphological, and rheological characterizations. It was found that crystallinity increased marginally within the first two hours, but particle size and shape remained virtually unchanged. The thermal treatment also resulted in a significant increase in the melt viscosity of the PEEK powder, and its flowability slightly improved. Understanding these changes could help to reduce waste through recycling of some portion of PEEK powders used in SLS printing.

This article characterizes a novel twin screw extrusion (TSE) process with the capability of rotating at speeds up to 4500 rpm. The resulting extreme high shear rate is expected to result in molecular weight changes due to thermomechanical degradation of the polymeric materials being extruded, polystyrene (PS) in this case. In order to differentiate between mechanical and thermal factors affecting degradation of PS running at ultrahigh speeds and also to evaluate the relative importance of the two mechanisms, PS has been extruded at different screw speeds and different barrel temperatures with corresponding melt temperatures. Viscosity measurements and size exclusion chromatography measurements show the extent of degradation due to mechanical stress as a result of high screw rotational speeds. Furthermore, through analyzing the kinetics of PS depolymerization, the reaction rate and hypothetical apparent temperatures at each screw speed have been calculated. All results support the idea that the mechanical shear stress can be considered as the controlling factor of polymer degradation in ultrahigh speed TSE. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

In this work, aqueous suspensions of poly(3-hexylthiophene) (P3HT) colloids were fabricated using three different surfactants with varied degrees of conjugation. The morphology, crystalline structure and optical properties of these colloids were characterized by scanning electron microscopy, wide angle X-ray diffractometry and UV–vis spectrometry, respectively. Results indicated that the morphology and crystalline were similar for all the colloids, while the optical properties and aggregation could be tuned by surfactant conjugation. Increasing conjugation in surfactant corresponded to increased chain order, conjugation length, and red-shifted absorbance spectrum in P3HT colloids. Field effect transistors (FETs) made from these colloids showed a hole mobility on the order of 10 −3 cm 2 /Vs, also tunable by surfactant conjugation and comparable to FETs made from P3HT solution.

A series of poly[4-(4-cyanoazobenzene-4′-oxy)alkyl methacrylate]s, side-chain liquid crystalline polymers (azoLCPs) were synthesized with methylene groups as spacers varying from 5 to 12. The thermal properties and phase transition temperatures of the polymers were characterized with differential scanning calorimetry and polarized optical microscopy and a relationship between spacer lengths, glass transition (Tg) and clearing temperatures (Tc) of the polymers was established. The Tg decreased with increasing spacer length, while the Tc exibited an odd–even effect with varying spacer length. X-ray diffraction was used to determine the degree crystallinity above and below Tc. The azoLCPs exhibited smectic ↔ nematic ↔ isotropic phases. Increasing crystallinity correlated linearly with decreasing gas permeability as measured using an oxygen permeation analyzer, which was used to measure the films’ permeability to oxygen (O2) gas. Switching of the azoLCPs from a liquid crystalline to an isotropic state was accomplished by heating the films above their Tc, which resulted in at least a 10-fold increase in the O2 permeability coefficient (PO2). Increasing the methylene spacer length of the azoLCP had little or no effect on gas permeability however it did decrease the Tc, allowing fine control of the temperature at which the switch in PO2 takes place by tuning the mesophase between nematic and isotropic states.

Herein, aqueous suspensions of poly (3-hexylthiophene) (P3HT) colloids with tunable particle size were fabricated using a miniemulsion process followed by solvent evaporation. The effects of solvent evaporation temperature, sonication time and surfactant amount on colloid properties and field effect transistor performance were investigated. The particle size distribution and morphology of the colloids were characterized by dynamic light scattering and atomic force microscopy. It was found that increasing solvent evaporation temperature leads to larger particle size; longer sonication leads to smaller particle size and careful selection of these variables along with controlled surfactant amount can be used to tune colloid sizes. Organic field-effect transistors (FETs) prepared using P3HT colloids displayed increasing hole mobility and decreasing threshold voltage as the colloidal particle size decreased. The trend in performance can be explained by considering the geometric factors governing carrier density and carrier transport.

Polymer blends are of significant interest for reinforcing bioplastics via addition of a second polymer and a blend compatibilizer or in situ reaction. However, increased costs associated with additional materials and extra processing steps can limit the viability of this solution. Here, a simple, continuous reactive extrusion processing method was examined for producing tougher bioplastic blends. p-Toluenesulfonic acid (TsOH) catalyst was added to two immiscible biobased polymers, poly(lactic acid) (PLA) and polyamide11 (PA11), to induce ester-amide exchange reaction. The mechanical properties of PLA were improved through mixing with PA11 by introducing copolymers at the interface thereby reducing interfacial tension. The morphology, chemical structure analysis, and tensile testing supported that copolymerization reaction occurred resulting in improved bonding between PLA and PA11 with 0.5 wt % TsOH catalyst in the batch mixing, but depolymerization dominated at higher shear stress (2000 rpm) and catalyst loading (over 2 wt %). The PLA/PA11 blend with 0.5 wt % TsOH catalyst displayed around 50% improvement in elongation at break in twin-screw extruder blending (around 5 min mixing time) at 250 rpm screw speed, which was similar to the improvement using batch mixing (20 min mixing time). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43350.

Poly(propylene carbonate) (PPC) is a promising new sustainable polymer produced from carbon dioxide. PPC has inferior thermal stability which could be enhanced by synergistic blending with other polymers. Blends of PPC and the engineering thermoplastic polyoxymethylene are produced by melt compounding in various weight ratios. The compatibility of the blends is investigated using thermogravimetric analysis (TGA), differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), density measurements, and scanning electron microscopy (SEM). TGA reveals that thermal stability of the blends increases dramatically in comparison to the neat PPC. A small shift in the glass transition temperature demonstrates the immiscibility of the blends but also indicates some compatibility, attributed to potential dipole–dipole interactions which are also corroborated with the FTIR results. A deviation of the rule of mixtures for density is found for some of the blends. SEM analysis of the blends shows two phase morphology; however, the interfacial adhesion appeared to be enhanced with increasing PPC content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45823.