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Because of scarcity, vulnerability and heterogeneity in the population of circulating tumor cells (CTCs), the CTC isolation system relying on immunoaffinity interaction exhibits inconsistent efficiencies for all types of cancers...

Supported metal nanoparticles are essential components of high-performing catalysts, and their structures are intensely researched. In comparison, nanoparticle spatial distribution in powder catalysts is conventionally not quantified, and the influence of this collective property on catalyst performance remains poorly investigated. Here, we demonstrate a general colloidal self-assembly method to control uniformity of nanoparticle spatial distribution on common industrial powder supports. We quantify distributions on the nanoscale using image statistics and show that the type of nanospatial distribution determines not only the stability, but also the activity of heterogeneous catalysts. Widely investigated systems (Au-TiO2 for CO oxidation thermocatalysis and Pd-TiO2 for H2 evolution photocatalysis) were used to showcase the universal importance of nanoparticle spatial organization. Spatially and temporally resolved microkinetic modeling revealed that nonuniformly distributed Au nanoparticles suffer from local depletion of surface oxygen, and therefore lower CO oxidation activity, as compared to uniformly distributed nanoparticles. Nanoparticle spatial distribution also determines the stability of Pd-TiO2 photocatalysts, because nonuniformly distributed nanoparticles sinter while uniformly distributed nanoparticles do not. This work introduces new tools to evaluate and understand catalyst collective (ensemble) properties in powder catalysts, which thereby pave the way to more active and stable heterogeneous catalysts.

Molecular dynamics (MD) simulations of melt films of poly(alkyl methacrylate)s (PAMAs) with methyl, ethyl, and n-butyl substituents, respectively, have been performed using an all-atom model to investigate their surface and thin film properties. The applied all-atom force fields predict the bulk densities of PAMAs in good agreement with experiments. Moreover, predictions of the surface tensions of PMMA, PEMA, and Pn-BMA melts are in reasonably good agreement with experiments. The density profiles and orientational-order parameters of chain segments show atomic-scale characteristics in the air/polymer interfacial region. In the surface region, the backbone segments of PAMAs form a well-defined layer structure with the chain vectors oriented parallel to the surface, while the ester side-chains strongly segregate to the surface region and show perpendicular orientation to the surface, with the most pronounced surface segregation noted for Pn-BMA. Such surface segregations of chain segments make it difficult to apply a simple relationship between the cohesive energy density and the surface tension of polymers, for example, and should be taken into account in relating the surface/thin film characteristics to the bulk properties of polymers in general.

Proton exchange membranes (PEMs) suffer performance degradation under certain conditions—temperatures greater than 80 °C, relative humidity less than 50%, and water retention less than 22%. Novel materials are needed that have improved water retention, stability at higher temperatures, flexibility, conductivity, and the ability to function at low humidity. This work focuses on polyimide-poly(ethylene glycol) (PI-PEG) segmented block copolymer (SBC) membranes with high conductivity and mechanical strength. Membranes were prepared with one of two ionic liquids (ILs), either ethylammonium nitrate (EAN) or propylammonium nitrate (PAN), incorporated within the membrane structure to enhance the proton exchange capability. Ionic liquid uptake capacities were compared for two different temperatures, 25 and 60 °C. Then, conductivities were measured for a series of combinations of undoped or doped unannealed and undoped or doped annealed membranes. Stress and strain tests were performed for unannealed and thermally annealed undoped membranes. Later, these experiments were repeated for doped unannealed and thermally annealed. Mechanical and conductivity data were interpreted in the context of prior small angle X-ray scattering (SAXS) studies on similar materials. We have shown that varying the compositions of polyimide-poly(ethylene glycol) (PI-PEG) SBCs allowed the morphology in the system to be tuned. Since polyimides (PI) are made from the condensation of dianhydrides and diamines, this was accomplished using components having different functional groups. Dianhydrides having either fluorinated or oxygenated functional groups and diamines having either fluorinated or oxygenated diamines were used as well as mixtures of these species. Changing the morphology by creating macrophase separation elevated the IL uptake capacities, and in turn, increased their conductivities by a factor of three or more compared to Nafion 115. The stiffness of the membranes synthesized in this work was comparable to Nafion 115 and, thus, sufficient for practical applications.

Monodispersed metal and semiconductor nanocrystals have attracted great attention in fundamental and applied research due to their tunable size, morphology, and well-defined chemical composition. Utilizing these nanocrystals in a controllable way is highly desirable especially when using them as building blocks for the preparation of nanostructured materials. Their deposition onto oxide materials provide them with wide applicability in many areas, including catalysis. However, so far deposition methods are limited and do not provide control to achieve high particle loadings. This study demonstrates a general approach for the deposition of hydrophobic ligand-stabilized nanocrystals on hydrophilic oxide supports without ligand-exchange. Surface functionalization of the supports with primary amine groups either using an organosilane ((3-aminopropyl)trimethoxysilane) or bonding with aminoalcohols (3-amino-1,2-propanediol) were found to significantly improve the interaction between nanocrystals and supports achieving high loadings (>10 wt. %). The bonding method with aminoalcohols guarantees the opportunity to remove the binding molecules thus allowing clean metal/oxide materials to be obtained, which is of great importance in the preparation of supported nanocrystals for heterogeneous catalysis.

Molecular dynamics simulations of free-standing thin films of neat melts of polyethylene (PE) chains up to C150H302 and their binary mixtures with n-C13H28 are performed employing a united atom model. We estimate the surface tension values of PE melts from the atomic virial tensor over a range of temperatures, which are in good agreement with experimental results. Compared with short n-alkane systems, there is an enhanced surface segregation of methyl chain ends in longer PE chains. Moreover, the methyl groups become more segregated in the surface region with decreasing temperature, leading to the conclusion that the surface-segregation of methyl chain ends mainly arises from the enthalpic origin attributed to the lower cohesive energy density of terminal methyl groups. In the mixtures of two different chain lengths, the shorter chains are more likely to be found in the surface region, and this molecular segregation in moderately asymmetric mixtures in the chain length (C13H28 + C44H90) is dominated by the enthalpic effect of methyl chain ends. Such molecular segregation is further enhanced and dominated by the entropic effect of conformational constraints in the surface for the highly asymmetric mixtures containing long polymer chains (C13H28 + C150H3020). The estimated surface tension values of the mixtures are consistent with the observed molecular segregation characteristics. Despite this molecular segregation, the normalized density of methyl chain ends of the longer chain is more strongly enhanced, as compared with the all-segment density of the longer chain itself, in the surface region of melt mixtures. In addition, the molecular segregation results in higher order parameter of the shorter-chain segments at the surface and deeper persistence of surface-induced segmental order into the film for the longer chains, as compared with those in neat melt films.

Janus graphene oxides and Janus graphenes are materials with different functionalization on opposite faces of atomically thin carbon sheets. Owing to their monolayer nature, these Janus sheets show unique properties where the functionalization on one face can modulate the properties on the opposite face. However, few general procedures to create and characterize Janus graphene oxides or Janus graphenes have been reported, and as a consequence these intriguing materials remain largely unexplored. Here we report a general synthesis of Janus graphene oxide, where particles are deposited in situ from molecular precursors on opposite faces of monolayer graphene oxide (GO). We used a silicon wafer and a polymer film to successively expose and protect alternate graphene oxide faces for asymmetric deposition of Pt and TiO2 nanocrystals, thus producing Janus graphene oxide composites (Pt|GO|TiO2). We used electron microscopy of Janus graphene oxide cross-sections to conclusively show that Pt and TiO2 particles are...

Wood products are extensively used to make furniture items and construction materials; however, the majority contain formaldehyde-based adhesives that raise serious health concerns. Here, we report a formaldehyde-free adhesive formulation comprised of two high-volume biorefinery biproducts, namely Kraft lignin (pulp and paper) and glycerol (biodiesel), and its adhesion properties as determined by ultimate shear stress as well as wood failure rates. We show that this lignin-based resin displays the same desirable characteristics as formaldehyde-based resins including water-tolerance, fast curing, and comparable adhesion performance. Chemical analysis indicates that resin curing occurs uncatalyzed via formation of ether bonds between lignin hydroxyl groups and the glycerol-derived crosslinker epoxide. We also show that different lignin and crosslinker feedstocks can be used in the formulation, in some cases with water as a cosolvent, to generate a set of lignin-derived resins with similar properties and mechanical strength. In contrast to the majority of formaldehyde-free adhesives, this lignin-epoxy formulation does not require the use of caustic base and known carcinogens. Furthermore, we demonstrate through mechanical testing and attention to processing conditions that this lignin-based resin has the potential to be a viable alternative to widely used formaldehyde resins.

United-atom molecular-dynamics computer simulations of atactic polystyrene (PS) were performed for the bulk and free-standing films of 2 nm – 20 nm thickness, for both linear and cyclic polymers comprised of 80 monomers. Simulated volumetric glass-transition temperatures (Tg) show a strong dependence on the film thickness below 10 nm. The glass-transition temperature of linear PS is 13% lower than that of the bulk for 2.5 nm-thick films, as compared to less than 1% lower for 20 nm films. Our studies reveal that the fraction of the chain-end groups is larger in the interfacial layer with its outermost region approx. 1 nm below the surface than it is in the bulk. The enhanced population of the end groups is expected to result in a more mobile interfacial layer and the consequent dependence of Tg on the film thickness. In addition, the simulations show an enrichment of backbone aliphatic carbons and concomitant deficit of phenyl aromatic carbons in the interfacial film layer. This deficit would weaken the strong phenyl-phenyl aromatic (-) interactions and, hence, lead to a lower film-averaged Tg in thin films, as compared to the bulk sample. To investigate the relative importance of the two possible mechanisms (increased chain ends at the surface or weakened - interactions in the interfacial region), the data for linear PS are compared with those for cyclic PS. For the cyclic PS the reduction of the glass-transition temperature is also significant in thin films, albeit not as much as for linear PS. Moreover, the deficit of phenyl carbons in the film interface is comparable to that observed for linear PS. Therefore, chain-end effects alone cannot explain the observed pronounced Tg dependence on the thickness of thin PS films; the weakened phenyl-phenyl interactions in the interfacial region seems to be an important cause as well.

Depositing a morphologically uniform monolayer film of graphene oxide (GO) single-layer sheets is an important step in the processing of many composites and devices. Conventional Langmuir-Blodgett (LB) deposition is often considered to give the highest degree of morphology control, but film microstructures still vary widely between GO samples. The main challenge is in the sensitive self-assembly of GO samples with different sheet sizes and degrees of oxidation. To overcome this drawback, here, we identify a general method that relies on robust assembly between GO and a cationic surfactant (cationic surfactant-assisted LB). We systematically compared conventional LB and cationic surfactant-assisted LB for three common GO samples of widely different sheet sizes and degrees of oxidation. Although conventional LB may occasionally provide satisfactory film morphology, cationic surfactant-assisted LB is general and allows deposition of films with tunable and uniform morphologies-ranging from close-packed to overlapping single layers-from all three types of GO samples investigated. Because cationic surfactant-assisted LB is robust and general, we expect this method to broaden and facilitate the use of GO in many applications where precise control over film morphology is crucial.

Cholesterol self-assembles into weakly ordered aggregates when tethered to a crosslinked hydrogel network of poly(ethylene glycol) (PEG). PEG-diacrylate and cholesterol-PEG-acrylamide (PEG-chol) were co-polymerized in organic solvent and transferred to water for equilibrium swelling. Small-angle x-ray scattering revealed self-assembled cholesterol structures not present during network synthesis. At lower ratios of PEG-tethered cholesterol to PEG (

Langmuir-Blodgett deposition is a popular route to produce thin films of graphene oxide for applications such as transparent conductors and biosensors. Unfortunately, film morphologies vary from sample to sample, often with undesirable characteristics such as folded sheets and patchwise depositions. In conventional Langmuir-Blodgett deposition of graphene oxide, alcohol (typically methanol) is used to spread the graphene oxide sheets onto an air-water interface before deposition onto substrates. Here we show that methanol gives rise to Marangoni flow, which fundamentally limits control over Langmuir-Blodgett depositions of graphene oxide. We directly identified the presence of Marangoni flow by using photography, and we evaluated depositions with atomic force microscopy and scanning electron microscopy. The disruptive effect of Marangoni flow was demonstrated by comparing conventional Langmuir-Blodgett depositions to depositions where Marangoni flow was suppressed by a surfactant. Because methanol is the standard spreading solvent for conventional Langmuir-Blodgett deposition of graphene oxide, Marangoni flow is a general problem and may partly explain the wide variety of undesirable film morphologies reported in the literature.

Generation of human organoids from induced pluripotent stem cells (iPSCs) offers exciting possibilities for developmental biology, disease modelling and cell therapy. Significant advances towards those goals have been hampered by dependence on animal derived matrices (e.g. Matrigel), immortalized cell lines and resultant structures that are difficult to control or scale. To address these challenges, we aimed to develop a fully defined liver organoid platform using inverted colloid crystal (ICC) whose 3-dimensional mechanical properties could be engineered to recapitulate the extracellular niche sensed by hepatic progenitors during human development. iPSC derived hepatic progenitors (IH) formed organoids most optimally in ICC scaffolds constructed with 140 μm diameter pores coated with type I collagen in a two-step process mimicking liver bud formation. The resultant organoids were closer to adult tissue, compared to 2D and 3D controls, with respect to morphology, gene expression, protein secretion, drug metabolism and viral infection and could integrate, vascularise and function following implantation into livers of immune-deficient mice. Preliminary interrogation of the underpinning mechanisms highlighted the importance of TGFβ and hedgehog signalling pathways. The combination of functional relevance with tuneable mechanical properties leads us to propose this bioengineered platform to be ideally suited for a range of future mechanistic and clinical organoid related applications.

Generation of human organoids from induced pluripotent stem cells (iPSCs) offers exciting possibilities for developmental biology, disease modelling and cell therapy. Significant advances towards those goals have been hampered by dependence on animal derived matrices (e.g. Matrigel), immortalized cell lines and resultant structures that are difficult to control or scale. To address these challenges, we aimed to develop a fully defined liver organoid platform using inverted colloid crystal (ICC) whose 3-dimensional mechanical properties could be engineered to recapitulate the extracellular niche sensed by hepatic progenitors during human development. iPSC derived hepatic progenitors (IH) formed organoids most optimally in ICC scaffolds constructed with 140 µm diameter pores coated with Collagen in a two-step process mimicking liver bud formation. The resultant organoids were closer to adult tissue, compared to 2D and 3D controls, with respect to morphology, gene expression, protein secretion, drug metabolism and viral infection and could integrate, vascularize and function following implantation into livers of immune-deficient mice. Preliminary interrogation of the underpinning mechanisms highlighted the importance of TGFβ and hedgehog signalling pathways. The combination of functional relevance with tuneable mechanical properties leads us to propose this bioengineered platform to be ideally suited for a range of future mechanistic and clinical organoid related applications.

A class of tunable, mesostructured self-assembled hydrogels has been developed based on a library of π–π stacking ABA-type telechelic triblock copolymers prepared by organocatalytic ring-opening polymerization (ROP). Poly(ethylene glycol) (PEG) served as a macroinitiator for ROP of methylene tricarbonate-benzyl ester (MTC-OBn), a benzyl-ester functionalized cyclic carbonate monomer, resulting in polymers with well-defined length and narrow polydispersity. Self-assembled hydrogels were formed by dissolving poly(MTC-OBn)-b-PEG-b-poly(MTC-OBn) copolymers in water. Physical cross-links in the hydrogels formed through hydrophobic and π–π stacking intermolecular interactions between poly(MTC-OBn) segments. The mesoscale material properties were probed using small angle X-ray scattering (SAXS) and dynamic mechanical measurements. SAXS spectra show a scattering peak, corresponding to a molecular domain spacing of 20–25 nm, which we attribute to the formation of electron-dense poly(MTC-OBn) assemblies. Results from oscillatory shear experiments were analyzed in conjunction with SAXS data in order to develop an understanding of the influence that nanoscale structure has on the mechanical properties of self-assembled gels. Modeling of scattering peaks using the Bragg spacing model demonstrated that the hydrophilic PEG network chains connecting the scattering moieties behaved as a two-dimensional self-avoiding walk. We compared the observed microstructural features with the mechanical properties of self-assembled gels and determined that the molecular weight of the polycarbonate and PEG segments controls the gel structure on both the mesoscale and macroscale. A central contribution of this work is a synthetic strategy that utilizes ROP to control polymer structure, which in turn controls both the structure and mechanical properties of these biodegradable self-assembled hydrogels.

We evaluated the biocompatibility of a poly(ethylene glycol) and poly(acrylic acid) (PEG/PAA) interpenetrating network hydrogel designed for artificial cornea in a rabbit model. PEG/PAA hydrogel measuring 6 mm in diameter was implanted in the corneal stroma of twelve rabbits. Stromal flaps were created with a microkeratome. Randomly, six rabbits were assigned to bear the implant for 2 months, two rabbits for 6 months, two rabbits for 9 months, one rabbit for 12 months, and one rabbit for 16 months. Rabbits were evaluated monthly. After the assigned period, eyes were enucleated, and corneas were processed for histology and immunohistochemistry. There were clear corneas in three of six rabbits that had implantation of hydrogel for 2 months. In the six rabbits with implant for 6 months or longer, the corneas remained clear in four. There was a high rate of epithelial defect and corneal thinning in these six rabbits. One planned 9-month rabbit developed extrusion of implant at 4 months. The cornea remained clear in the 16-month rabbit but histology revealed epithelial in-growth. Intrastromal implantation of PEG/PAA resulted in a high rate of long-term complications.

An understanding of the structure and properties of polymer electrolyte systems can be crucial to a variety of different applications. The current work performs a study of the composition, structure and properties of poly(ethylene glycol) (PEG)-aromatic polyimide systems incorporating ionic liquids that are relevant to several applications especially fuel cell membranes. Composition was varied through using different aromatic dianhydrides, aromatic diamines and in some cases synthesis solvent. Properties were characterized using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small-angle x-ray scattering, electrochemical impedance spectroscopy and cyclic voltammetry. By varying solvent, aromatic regularity and expected rigidity can be tuned, impacting average conductivity by 30%. Varying the aromatic diamine can influence the length scale and amount of aromatic regularity, which can ultimately affect the conductivity by a factor of four. The maximum conductivity reached was 83 mS/cm at 80 °C and 70 %RH. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 509–521

Micellar composite hydrogel systems represent a promising class of materials for biomolecule and drug delivery applications. In this work a system combining micellar drug delivery with supramolecular hydrogel assemblies is developed, representing an elegant marriage of aqueous hydrophobic drug delivery and next-generation injectable viscoelastic materials. Novel shear thinning and injectable micellar composite hydrogels were prepared using an amphiphilic ABA-type triblock copolymer consisting of a hydrophilic middle block and cholesterol-functionalized polycarbonates as terminal hydrophobic blocks. Varying the concentration and relative hydrophobic-hydrophilic content of the amphiphilic species conferred the ability to tune the storage moduli of these gels from 200 Pa to 3500 Pa. This tunable system was used to encapsulate drug-loaded polymeric micelles, demonstrating a straightforward and modular approach to developing micellar viscoelastic materials for a variety of applications such as delivery of hydrophobic drugs. These hydrogels were also mixed with cholesterol-containing cationic polycarbonates to render antimicrobial activity and capability for anionic drug delivery. Additionally, small-angle X-ray scattering (SAXS) and electron microscopy (EM) results probed the mesoscale structure of these micellar composite materials, lending molecular level insight into the self-assembly properties of these gels. The antimicrobial composite hydrogels demonstrated strong microbicidal activity against Gram-negative and Gram-positive bacteria, and C. albicans fungus. Amphotericin B (AmB, an antifungal drug)-loaded micelles embedded within the hydrogel demonstrated sustained drug release over 4 days and effective eradication of fungi. Our findings demonstrate that materials of different nature (i.e. small molecule drugs or charged macromolecules) can be physically combined with ABA-type triblock copolymer gelators to form hydrogels for potential pharmaceutical applications.

A major challenge for studying authentic liver cell function and cell replacement therapies is that primary human hepatocytes rapidly lose their advanced function in conventional, 2-dimensional culture platforms. Here, we describe the fabrication of 3-dimensional hexagonally arrayed lobular human liver tissues inspired by the liver’s natural architecture. The engineered liver tissues exhibit key features of advanced differentiation, such as human-specific cytochrome P450–mediated drug metabolism and the ability to support efficient infection with patient-derived inoculums of hepatitis C virus. The tissues permit the assessment of antiviral agents and maintain their advanced functions for over 5 months in culture. This extended functionality enabled the prediction of a fatal human-specific hepatotoxicity caused by fialuridine (FIAU), which had escaped detection by preclinical models and short-term clinical studies. The results obtained with the engineered human liver tissue in this study provide proof-of-concept determination of human-specific drug metabolism, demonstrate the ability to support infection with human hepatitis virus derived from an infected patient and subsequent antiviral drug testing against said infection, and facilitate detection of human-specific drug hepatotoxicity associated with late-onset liver failure. Looking forward, the scalability and biocompatibility of the scaffold are also ideal for future cell replacement therapeutic strategies. NMRC (Natl Medical Research Council, S’pore) NRF (Natl Research Foundation, S’pore) Published version

Polymer electrolyte membrane (PEM) fuel cells can provide alternatively sourced energy, but current PEMs lose performance under certain conditions. The current work examines composition, structure and properties of poly (ethylene glycol)-aromatic polyimide-ionic liquid systems for PEM applications, as poly (ethylene glycol) (PEG) is an ion conductor and polyimides are stable. To evaluate polymer interactions, different PEG concentrations (0–50% by weight) and different PEG molecular weights (990–6000 g/mole) were examined. Characterization techniques included Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small-angle x-ray scattering, electrochemical impedance spectroscopy and cyclic voltammetry. By increasing the PEG amount, PEG domains and polymer flexibility are increased, which increases conductivity by two to three orders of magnitude. By increasing PEG molecular weight, PEG segmental motion and PEG-polyimide interface quality are decreased, which decreases conductivity by a factor of two. The maximum conductivity was 64 mS/cm at 80 °C and 70 %RH.

In this laboratory experiment, students work in pairs to synthesize a simple aliphatic polycarbonate via ring-opening polymerization of trimethylene carbonate using 1,8-diazabicyclo[5.4.0]undec-7-ene and thiourea as organocatalysts. Following polymer isolation, students cool the material in a dry ice/acetone bath to observe its glass-transition behavior. This experiment is convenient to perform under teaching laboratory conditions and reinforces key concepts learned in second-year undergraduate organic chemistry, for example, nucleophilic acyl substitution, transesterification reactions, and Lewis acidity–basicity. Additionally, the experiment introduces students to polymer chemistry, heterocycles, materials science, and green chemistry. It also covers interesting concepts that are less frequently encountered at the undergraduate level such as biomimetic chemistry, bifunctional catalysis, and polymer–glass transitions.

A small molecule nucleating agent, orotic acid (OA), was investigated to enhance crystallinity and crystallization kinetics in poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) for the purpose of addressing embrittlement and reducing solidification time after thermal processing. In particular, the effectiveness of monohydrated (OA-m) and anhydrous (OA-a) forms of OA as nucleating agents for isothermal and non-isothermal crystallization of PHBV films was investigated and compared. Both forms of OA were able to increase crystallization temperature of PHBV as well as form more uniform crystal structures, based on differential scanning calorimetry. It was found that OA-a at 1–2 wt% was most effective in PHBV crystal nucleation because of the increase in overall polymer crystallinity and faster crystallization rate. Additionally, the faster crystallization of OA-a led to fibrillar film morphology of the PHBV/OA blends.

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) was melt-foamed using a single screw extrusion process and found to be susceptible to cell coalescence at the higher processing temperatures used for achieving low bulk density. The addition of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) allowed for the generation of a range of crystallization temperatures much broader than can be achieved through small molecular crystal nucleation agents. This broader range can induce solidification to occur earlier during cooling and so can be used to minimize cell coalescence. Several PHBHHx/PHBV blend compositions were produced and characterized; initial understanding of the crystallinity and impact of blending miscible crystallizable polymers was gained through thermal analysis. PHBHHx and PHBV appeared to be fully miscible across all compositions used in this study. The impacts of blend composition and extruder temperature profile on foam properties were investigated. It was found that just 2% PHBV consi...

The temporospatial regulation of axon outgrowth is useful for guiding de novo connectivity or re-connectivity of neurons in neurological injury or disease. Here we report the successful construction of a biocompatible guidance device, in which a linear propagation of IGF-1 gradient sequentially directs axon outgrowth. We observe the extensive in vitro axonal extension over 5 mm with a desired growth rate of ∼ 1 mm/day.

Biodegradable polymer foams have the potential to lessen environmental burdens caused by traditional petroleum-based plastics. One such family of alternatives, poly(hydroxyalkanoates), have tremendous potential in this regard, but have poor foamability owing to a narrow thermal processing window. Of particular interest for this study is poly(hydroxybutyrate-co-valerate) (PHBV). Two chemical blowing agents were tested for their ability to create low density, closed-cell PHBV foams, and it is shown here that sodium bicarbonate decreases the bulk density compared to azodicarbonamide blowing agents but with the loss of a closed-cell structure. To counter this, PHBV foams were quenched with water, leading to faster crystalline formation in the polymer matrix. As a result of faster solidification, a more uniform, closed-cell bubble morphology was entrapped in the final foam product, leading to high-expansion ratio foam. Thus, PHBV, a material with poor melt strength, has enhanced melt properties for foaming applications when crystallization is induced on the same time scale as cell coalescence. POLYM. ENG. SCI., 54:2877–2886, 2014. © 2014 Society of Plastics Engineers

The introduction and subsequent removal of highly elastic solutions from surfaces has recently allowed industry to effectively remove colloidal, particulate contaminants from high-grade silicon. The substrate is first coated with the polymeric cleaning solution, and then the solution is removed either by simply rinsing the surface using an impinging water jet or by siphoning the cleaning fluid from the surface. The advantage of this continuous process over conventional techniques is the noninvasive removal while generating limited nonhazardous aqueous waste. Our group investigated the use of polymeric liquids that effectively eliminate particles without damaging the delicate surfaces. To investigate this removal, we studied two different flow types (siphoning and rinsing) of various rheological fluids to understand the governing physics that allow for removal. In this publication, we show that the presence of local shear flows of a viscoelastic fluid having a large elongational viscosity can create polymer stresses that are much larger than the associated Newtonian shear stresses. The onset of this added polymer stress in the flow field correlates well to the increase in particle removal.

Alkaline exchange membranes (AEMs) are a promising class of polyelectrolytes whose alkaline operating environment enables the use of non-precious metal catalysts in low-temperature fuel cells. However, their poor ionic conductivities, which are often an order of magnitude lower than traditional acidic membranes (e.g., Nafion), have limited their practicality. The performance problem can partially be ascribed to the poorly-defined morphologies of typical random copolymer AEMs, leading to tortuous ion transport pathways. Here, we show the ability to form nanoscale (5 to 10 nm diameter) anion transport channels by grafting hydrophilic poly(ethylene glycol) side-chains along a model benzyltrimethylammonium polysulfone-based AEM. Concomitant with the structure formation is a 100% increase in the IEC-normalized hydroxide conductivity from 20.2 mS g cm−1 mmol−1 to 40.3 mS g cm−1 mmol−1 as well as a 50% increase in the peak power density from 118 mW cm−2 to 180 mW cm−2 when incorporated into a fuel cell.

Foaming studies on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were performed to evaluate the potential impact of nitrogen gas solubility on foam microstructure and properties. It was found that there was a step change from low to high cell density below and above a specific pressure threshold. This pressure threshold, which is associated with nitrogen gas solubility in PHBV, was calculated in order to inform processing requirements for extrusion foaming of PHBV. In the process, the PVT properties of PHBV were also calculated to account for polymer swelling at high temperature and pressure. To validate the predictive method applied in this work, gas solubility of nitrogen was also determined for polypropylene (PP) and poly(lactic acid) (PLA), which have similar thermal and rheological properties to PHBV. Predicted PVT properties for PP were found to be similar to experimental values in the literature, with the predicted solubility having a 10–14% error for PP and 20–24% error for PLA. Application of the same error range to the solubility predicted for PHBV aligned well with experimental observations. POLYM. ENG. SCI., 54:2683–2695, 2014. © 2013 Society of Plastics Engineers

The need for renewable alternatives to traditional petroleum-derived plastics has driven recent interest in biobased composite materials that are sourced from carbon-neutral feedstocks. Lignin, an ...

The governing kinetic behavior of water transport in a biopolymeric composite material derived from poly(β-hydroxybutyrate)-co-poly(β-hydroxyvalerate) and lignocellulosic wood flour were investigated along with the influence of temperature, wood flour content, and chemical modification (silane, maleic anhydride) on polymer and composite diffusivity. The water absorption process in both untreated and treated composites was found to follow the kinetics of Fickian diffusion theory. Diffusion coefficients for neat polymer and composite samples were experimentally determined, and the thermodynamics of diffusive water transport were observed to exhibit Arrhenius rate-law behavior. A model for predicting equilibrium moisture content in wood-polymer composites is presented and substantiated by obtained results and cited experimental data. Isodiffusion plots are presented to evaluate the effectiveness of chemical modifications, which were found to reduce the rates of water uptake. Both in- and out-of-plane dimensional changes were monitored during the absorption process, permitting the determination of moisture-dependent hydroexpansion coefficients.

Extrusion foaming of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and two blends of PHBV with cellulose acetate butyrate (CAB) were studied using an azodicarbonamide (AZ) blowing agent and a single-screw extruder. The concentration of the blowing agent was systematically varied from 0 to 4.0 phr to achieve maximum density reduction reaching 41%, as well as to obtain information on the dependence of cell growth on blowing agent concentration. Extruded foams were characterized in terms of their bulk densities and cellular morphologies. Stereological and statistical methods permitted full characterization of the three-dimensional cell size distributions, assessing the average cell diameters (ranging from 58 to 290 μm) and cell densities (ranging from 650 to 180,000 cm−3). The variation in cellular morphology among foams consisting of different polymer matrix or blowing agent concentration was compared. The results were analyzed by considering the influence of viscoelastic properties of the polymer matrix on the bubble growth during foaming. Significantly higher melt viscosity and elasticity and reduced gas solubility of the PHBV/CAB blends are believed to retard cell coalescence and collapse during foam expansion, resulting in more uniform cell size distribution and better homogeneity of cellular morphology. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Fully biobased composite materials were fabricated using a natural, lignocellulosic filler, namely oak wood flour (OWF), as particle reinforcement in a biosynthesized microbial polyester matrix derived from poly(β-hydroxybutyrate)- co -poly(β-hydroxyvalerate) (PHBV) via an extrusion injection molding process. The mechanisms and effects of processing, filler volume percent (vol%), a silane coupling agent, and a maleic anhydride (MA) grafting technique on polymer and composite morphologies and tensile mechanical properties were investigated and substantiated through calorimetry testing, scanning electron microscopy, and micromechanical modeling of initial composite stiffness. The addition of 46 vol% silane-treated OWF improved the tensile modulus of neat PHBV by 165%. Similarly, the tensile modulus of MA-grafted PHBV increased 170% over that of neat PHBV with a 28 vol% addition of untreated OWF. Incorporation of OWF reduced the overall degree of crystallinity of the matrix phase and induced embrittlement in the composites, which led to reductions in ultimate tensile stress and strain for both treated and untreated specimens. Deviations from the Halpin–Tsai/Tsai–Pagano micromechanical model for composite stiffness in the silane and MA compatibilized specimens are attributed to the inability of the model both to incorporate improved dispersion and wettability due to fiber–matrix modifications and to account for changes in neat PHBV and MA-grafted PHBV polymer morphology induced by the OWF.

The orientation of a monoclonal, anti-streptavidin human IgG1 antibody on a model hydrophobic, CH(3)-terminated surface (1-dodecanethiol self-assembled monolayer on gold) was studied by monitoring the mechanical coupling between the adsorbed layer and the surface as well as the binding of molecular probes to the antibodies. In this study, the streptavidin antigen was used as a probe for the Fab portions of the antibody, while bacteria-derived Protein G' was used as a probe for the Fc region. Bovine serum albumin (BSA) acted as a blocking protein. Monolayer coverage occurred around 468 ng/cm(2). Below 100 ng/cm(2), antibodies were found to adsorb flat-on, tightly coupled to the surface and unable to capture their antigen, whereas the Fc region was able to bind Protein G'. At half-monolayer coverage, there was a transition in the mechanism of adsorption to allow for vertically oriented antibodies, as evidenced by the binding of both Protein G' and streptavidin as well as looser mechanical coupling with the surface. Monolayer coverage was characterized by a reduced level in probe binding per antibody and an even less rigid coupling to the surface.

Aims: To determine the rate of diffusion of myoglobin and bovine serum albumin (BSA) through the human cornea. These small proteins have hydrodynamic diameters of approximately 4.4 and 7.2 nm, and molecular weights of 16.7 and 66 kDa, for myoglobin and BSA, respectively. Meth ods: Diffusion coefficients were measured using a diffusion chamber where the protein of interest and balanced salt solution were in different chambers separated by an ex vivo human cornea. Protein concentrations in the balanced salt solution chamber were measured over time. Diffusion coefficients were calculated using equations derived from Fick’s law and conservation of mass in a closed system. Results: Our experiments demonstrate that the diffusion coefficient of myoglobin is 5.5 ± 0.9 × 10–8 cm2/s (n = 8; SD = 1.3 × 10–8 cm2/s; 95% CI: 4.6 × 10–8 to 6.4 × 10–8 cm2/s) and the diffusion coefficient of BSA is 3.1 ± 1.0 × 10–8 cm2/s (n = 8; SD = 1.4 × 10–8 cm2/s; 95% CI: 2.1 × 10–8 to 4.1 × 10–8 cm2/s). Conclusions: Our study suggests that molecules as large as 7.2 nm may be able to passively diffuse through the human cornea. With applications in pharmacotherapy and the development of an artificial cornea, further experiments are warranted to fully understand the limits of human corneal diffusion and its clinical relevance.

Hydrogels with high modulus and fracture strength are obtained by interpenetrating a tightly cross-linked poly(ethylene glycol) (PEG) network with a loosely cross-linked poly(acrylic acid) (PAA) network. Small-angle X-ray and neutron scattering (SAXS/SANS) are used in conjunction with swelling measurements to determine the structure of PEG/PAA interpenetrating polymer networks (IPNs) and to measure the average PEG chain extension within the IPN. At pH 7.4, the PEG chains within the IPN are extended to 45–70% of their maximum achievable length as a result of expansion of the ionized PAA network within the IPN. Near these high extension ratios, the force required to further strain the PEG chains is increased due to the entropic effects of finite chain extensibility. This leads to PEG/PAA IPN hydrogels with a 3-fold increase in both compressive modulus and fracture strength compared to PEG single networks with the same polymer volume fraction. The structure, mechanical properties, and mechanisms of strength ...

Films of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB-co-3HHx) containing 3.8–10 mol% of 3-hydroxyhexanoate (3HHx) comonomer were subjected to anaerobic biodegradation to explore the effects of copolymer composition, crystallinity, and morphology on biodegradation. As biodegradation proceeded, samples with higher HHx fraction tended to have faster weight loss; on Day 7 of the degradation experiment, P3HB-co-10 mol%-3HHx lost 80% of its original weight, while P3HB-co-3.8 mol%-3HHx lost only 28%. Scanning electron microscopy (SEM) images revealed that the anaerobic biodegradation proceeded at the surface of the samples, with preferential erosion of the amorphous regions, exposing the crystalline spherulites formed inside the copolymer films. It was observed that copolymers with higher HHx fraction had smaller diameter spherulites, ranging from roughly 40 μm for P3HB-co-3.8 mol%-3HHx to 10 μm for P3HB-co-10 mol%-3HHx. A banded spherulite morphology was observed for P3HB-co-6.9 mol%-3HHx and P3HB-co-10 mol%-3HHx, with much wider band spacing (2 μm) for the former than the latter (0.3 μm). Different thermal history seemed to affect the morphological properties and, thus, the biodegradability of the P3HB-co-3HHx samples as well. When comparing copolymers with the same copolymer composition, P3HB-co-3HHx annealed at 70 °C had 5–30% more weight loss after the same duration of incubation in active sludge compared to the quenched samples. We suggest that annealing of P3HB-co-3HHx likely induces void formation in the semi-crystalline structure, facilitating the movement of water or perhaps enzymes to a higher degree of penetration into the sample and subsequently enhancing microbial degradation.

This study examines the influence of electrostatic interactions on enzyme surface diffusion and the contribution of diffusion to interfacial biocatalysis. Surface diffusion, adsorption, and reaction were investigated on an immobilized bovine serum albumin (BSA) multilayer substrate over a range of solution ionic strength values. Interfacial charge of the enzyme and substrate surface was maintained by performing the measurements at a fixed pH; therefore, electrostatic interactions were manipulated by changing the ionic strength. The interfacial processes were investigated using a combination of techniques: fluorescence recovery after photobleaching, surface plasmon resonance, and surface plasmon fluorescence spectroscopy. We used an enzyme charge ladder with a net charge ranging from -2 to +4 with respect to the parent to systematically probe the contribution of electrostatics in interfacial enzyme biocatalysis on a charged substrate. The correlation between reaction rate and adsorption was determined for each charge variant within the ladder, each of which displayed a maximum rate at an intermediate surface concentration. Both the maximum reaction rate and adsorption value at which this maximum rate occurs increased in magnitude for the more positive variants. In addition, the specific enzyme activity increased as the level of adsorption decreased, and for the lowest adsorption values, the specific enzyme activity was enhanced compared to the trend at higher surface concentrations. At a fixed level of adsorption, the specific enzyme activity increased with positive enzyme charge; however, this effect offers diminishing returns as the enzyme becomes more highly charged. We examined the effect of electrostatic interactions on surface diffusion. As the binding affinity was reduced by increasing the solution ionic strength, thus weakening electrostatic interaction, the rate of surface diffusion increased considerably. The enhancement in specific activity achieved at the lowest adsorption values is explained by the substantial rise in surface diffusion at high ionic strength due to decreased interactions with the surface. Overall, knowledge of the electrostatic interactions can be used to control surface parameters such as surface concentration and surface diffusion, which intimately correlate with surface biocatalysis. We propose that the maximum reaction rate results from a balance between adsorption and surface diffusion. The above finding suggests enzyme engineering and process design strategies for improving interfacial biocatalysis in industrial, pharmaceutical, and food applications.