Matrix-entrapped fibers create ecological niches for gut bacterial growth.

Insoluble plant cell walls are a main source of dietary fiber. Both chemical and physical fiber structures create distinct niches for gut bacterial utilization. Here, we have taken key fermentable solubilized polysaccharides of plant cell walls and fabricated them back into cell wall-like film forms to understand how fiber physical structure directs gut bacterial fermentation outcomes. Solubilized corn bran arabinoxylan (Cax), extracted to retain some ferulate residues, was covalently linked using laccase to form an insoluble cell wall-like film (Cax-F) that was further embedded with pectin (CaxP-F). In vitro fecal fermentation using gut microbiota from three donors was performed on the films and soluble fibers. Depending on the donor, CaxP-F led to higher relative abundance of recognized beneficial bacteria and/or butyrate producers-Akkermansia, Bifidobacterium, Eubacterium halii, unassigned Lachnospiraceae, Blautia, and Anaerostipes-than free pectin and Cax, and Cax-F. Thus, physical form and location of fibers within cell walls form niches for some health-related gut bacteria. This work brings a new understanding of the importance of insoluble cell wall-associated fibers and shows that targeted fiber materials can be fabricated to support important gut microbiota taxa and metabolites of health significance.

Poly(cannabinoid)s: Hemp-Derived Biocompatible Thermoplastic Polyesters with Inherent Antioxidant Properties.

The legalization of hemp cultivation in the United States has caused the price of hemp-derived cannabinoids to decrease 10-fold within 2 years. Cannabidiol (CBD), one of many naturally occurring diols found in hemp, can be purified in high yield for low cost, making it an interesting candidate for polymer feedstock. In this study, two polyesters were synthesized from the condensation of either CBD or cannabigerol (CBG) with adipoyl chloride. Poly(CBD-Adipate) was cast into free-standing films and subjected to thermal, mechanical, and biological characterization. Poly(CBD-Adipate) films exhibited a lack of cytotoxicity toward adipose-derived stem cells while displaying an inherent antioxidant activity compared to poly(lactide) films. Additionally, this material was found to be semi-crystalline and able to be melt-processed into a plastic hemp leaf using a silicone baking mold.

Circularly Recyclable Polymers Featuring Topochemically Weakened Carbon-Carbon Bonds.

Closed-loop circular utilization of plastics is of manifold significance, yet energy-intensive and poorly selective scission of the ubiquitous carbon-carbon (C-C) bonds in contemporary commercial polymers pose tremendous challenges to envisioned recycling and upcycling scenarios. Here, we demonstrate a topochemical approach for creating elongated C-C bonds with a bond length of 1.57∼1.63 Å between repeating units in the solid state with decreased bond dissociation energies. Elongated bonds were introduced between the repeating units of 12 distinct polymers from three classes. In all cases, the materials exhibit rapid depolymerization via breakage of the elongated bond within a desirable temperature range (140∼260 °C) while otherwise remaining remarkably stable under harsh conditions. Furthermore, the topochemically prepared polymers are processable and 3D-printable while maintaining a high depolymerization yield and tunable mechanical properties. These results suggest that the crystalline polymers synthesized from simple photochemistry and without expensive catalysts are promising for practical applications with complete materials' circularity.

Roll-to-Roll Manufactured Sensors for Nitroaromatic Organophosphorus Pesticides Detection.

A fully roll-to-roll manufactured electrochemical sensor with high sensing and manufacturing reproducibility has been developed for the detection of nitroaromatic organophosphorus pesticides (NOPPs). This sensor is based on a flexible, screen-printed silver electrode modified with a graphene nanoplatelet (GNP) coating and a zirconia (ZrO2) coating. The combination of the metal oxide and the 2-D material provided advantageous electrocatalytic activity toward NOPPs. Manufacturing, scanning electron microscopy-scanning transmission electron microscopy image analysis, electrochemical surface characterization, and detection studies illustrated high sensitivity, selectivity, and stability (∼89% current signal retention after 30 days) of the platform. The enzymeless sensor enabled rapid response time (10 min) and noncomplex detection of NOPPs through voltammetry methods. Furthermore, the proposed platform was highly group-sensitive toward NOPPs (e.g., methyl parathion (MP) and fenitrothion) with a detection limit as low as 1 µM (0.2 ppm). The sensor exhibited a linear correlation between MP concentration and current response in a range from 1 µM (0.2 ppm) to 20 µM (4.2 ppm) and from 20 to 50 µM with an R2 of 0.992 and 0.991, respectively. Broadly, this work showcases the first application of GNPs/ZrO2 complex on flexible silver screen-printed electrodes fabricated by entirely roll-to-roll manufacturing for the detection of NOPPs.

Anisotropic phase-separated morphology of polymer blends directed by electrically pre-oriented clay platelets.

We describe a general pathway to prepare an anisotropic phase-separated polystyrene (PS) - poly(vinyl methyl ether) (PVME) blend morphology by using electrically pre-orientated clay platelets. The clay platelets were oriented in a PS/PVME blend by means of an externally applied AC electric field while the blend is in one phase. Following orientation step, phase separation of the blends was induced by a temperature jump above their lower critical solution temperature (LCST) in the presence of the oriented clay platelets. In this process, an early stage co-continuous PS/PVME morphology coarsened and turned anisotropic phase-separated morphology parallel to the direction defined by clay planes oriented by AC electric field. The degree of anisotropy of PS/PVME phase-separated morphology was characterized by image analysis and that was found to be linearly proportional to the degree of orientation of clay platelets obtained by a 2D Wide Angle X-ray Scattering (WAXS). Transmission Electron Microscope (TEM) image of the blend morphology revealed that clay platelets oriented to AC field direction were located in a PVME phase. The electrically ordered column structures of clay platelets in the PVME phase yielded anisotropic PS diffusion during the phase separation. This process provides a unique new way to develop directionally organized phase-separated morphology from partially miscible binary blends using nanoparticles in combination with an external electric field.

Anisotropic hydrogels formed by magnetically-oriented nanoclay suspensions for wound dressings.

Anisotropic hydrogels are produced, by magnetic alignment of magnetically sensitized nanoclays followed by polymerization of the hydrogel to freeze the developed oriented structure. The anisotropy in these hydrogels is quantitatively investigated using birefringence and 2D small angle X-ray scattering (SAXS) techniques. The oriented nanoclays being intrinsically birefringent provide optical anisotropy to the hydrogel and this orientation increases with the increase of the applied magnetic field strength. Moreover, 2D SAXS patterns also confirm that the nanoclays are oriented parallel to the permanent magnetic field in the hydrogel with an orientation order parameter of up to 0.67. The field-induced birefringence and 2D SAXS orientation results exhibit a linear correlation over the range of 0 to 9 tesla (T). The resultant anisotropic hydrogels exhibit substantial swelling anisotropy, making them suitable for wound dressings where the out of plane swelling is substantially higher than in-plane swelling to minimize in-plane stress damage to the wounds during healing.

Tunable Piezoresistivity from Magnetically Aligned Ni(Core)@Ag(Shell) Particles in an Elastomer Matrix.

Core-shell (Ni@Ag) particles are aligned through the thickness of a poly(dimethylsiloxane) (PDMS) film using a magnetic field in a continuous roll-to-roll process. The alignment of the particles dramatically decreases the percolation threshold for electrical conductivity through the thickness of the film by nearly an order of magnitude from 28 vol % without the field to ≈1 vol % with a 52 mT magnetic field during curing. However, the magnetic forces lead to rough surface topography for intermediate Ni@Ag loadings, but confining the Ni@Ag/PDMS composite by a glass constraint provides a smooth surface. This difference in geometry changes the morphology of the vertically aligned "chains" of Ni@Ag particles where the chains are more aggregated when the film is unconstrained. As the Ni@Ag concentration is decreased below 3.6% for the constrained film, breaks in the aligned particles evident from X-ray tomography lead to pressure sensitive resistance across that film with a large decrease in resistance above a threshold pressure. The threshold pressure is demonstrated to be controllable from ≈15 to ≈290 kPa through the loading of aligned Ni@Ag in the PDMS, but this threshold pressure decreases on cyclic loading. These magnetically aligned composites represent a facile route to mechanically responsive films that could be used in a variety of applications where cyclic loading above and below the threshold pressure is not required, such as disposable pressure sensors for ensuring reliability of products through transportation and embedded structural health monitoring for identifying critical displacements.

Recent Trends in Advanced Contact Lenses.

Exploiting contact lenses for ocular drug delivery is an emerging field in the area of biomedical engineering and advanced healthcare materials. Despite all the research conducted in this area, still, new technologies are in their early stages of the development, and more work must be done in terms of clinical trials to commercialize these technologies. A great challenge in using contact lenses for drug delivery is to achieve a prolonged drug release profile within the therapeutic range for various eye-related problems and diseases. In general, desired release kinetics to avoid the initial burst release is the zero-order kinetics within the therapeutic range. This review highlights the new technologies developed to achieve efficient and extended drug delivery. It also provides an overview of the materials and methods for fabrication of contact lenses and their mechanical and optical properties.

Laser-Enabled Processing of Stretchable Electronics on a Hydrolytically Degradable Hydrogel.

Degradable electronics represent a rapidly emerging field of science and technology with the potential to serve short-term medical implantation applications where the device disappears once its function is complete. Despite many efforts in developing new types of degradable electronics, many of such systems are nonelastic and incompatible with the dynamic motion of native soft/elastic biological tissues. Herein, a photo-crosslinkable hydrogel with integrated electronics that are highly stretchable and degradable in liquid environments is demonstrated. The fabrication process takes advantage of facile laser micromachining of conductive patterns directly onto the hydrogel under ambient conditions and permanent hydrogel-hydrogel bonding. The robustness and degradation rate of hydrogel and the laser-processed encapsulated stretchable circuits is systematically investigated in different solutions under various conditions. Biocompatibility tests with non-neoplastic cells (HMT 3522 S1) and cancer cells (T4-2 and MDA-MB-231) are performed in 2D and 3D cell culture systems to confirm instead of evaluate the safety of the hydrogel and its byproducts during degradation as well as the zinc metal used in this technology. As a proof of concept, a stretchable hydrogel-based device that can be used for remote/wireless delivery of thermal energy into the tissue in contact with the hydrogel is fabricated.

Anisotropic swelling wound dressings with vertically aligned water absorptive particles.

A multi-layer solution casting method was utilized to fabricate a three-layer wound dressing film consisting of a wound contact layer, an absorbing layer and a backing layer. The absorbing layer, whose function is to absorb and retain the exudate thus providing a moist environment for wound healing, was made of superabsorbent particles and a thermoplastic polyurethane matrix. In this study, the superabsorbent particles were aligned into chains whose axes oriented along the thickness direction of the film by an external electric field. This structure could minimize the lateral swelling of the absorbing layer while preferentially expanding in the thickness direction during the water absorption process, and therefore eliminate the lateral stress or shear induced friction between the films and the wound. When compared to the wound dressing films with non-aligned particles, the films with aligned particles could achieve up to 33% smaller lateral expansion. The effect of particle shape on anisotropic swelling was also investigated, and the rod-like particles with higher aspect ratio were more effective at improving the anisotropic swelling and reducing lateral expansion compared to irregular-shaped particles. Additionally, the imprinted patterns on the contact layer resulting from the electric field alignment process promoted the efficiency of absorbing and transporting the exudate into the absorbing layer.

Three-Dimensional Printed Shape Memory Objects Based on an Olefin Ionomer of Zinc-Neutralized Poly(ethylene-co-methacrylic acid).

Three-dimensional printing enables the net shape manufacturing of objects with minimal material waste and low tooling costs, but the functionality is generally limited by available materials, especially for extrusion-based printing, such as fused deposition modeling (FDM). Here, we demonstrate shape memory behavior of 3D printed objects with FDM using a commercially available olefin ionomer, Surlyn 9520, which is zinc-neutralized poly(ethylene-co-methacrylic acid). The initial fixity for 3D printed and compression-molded samples was similar, but the initial recovery was much lower for the 3D printed sample (R = 58%) than that for the compression-molded sample (R = 83%). The poor recovery in the first cycle is attributed to polyethylene crystals formed during programming that act to resist the permanent network recovery. This effect is magnified in the 3D printed part due to the higher strain (lower modulus in the 3D printed part) at a fixed programming stress. The fixity and recovery in subsequent shape memory cycles are greater for the 3D printed part than for the compression-molded part. Moreover, the programmed strain can be systematically modulated by inclusion of porosity in the printed part without adversely impacting the fixity or recovery. These characteristics enable the direct formation of complex shapes of thermoplastic shape memory polymers that can be recovered in three dimensions with the appropriate trigger, such as heat, through the use of FDM as a 3D printing technology.

Transport-Limited Adsorption of Plasma Proteins on Bimodal Amphiphilic Polymer Co-Networks: Real-Time Studies by Spectroscopic Ellipsometry.

Traditional hydrogels are commonly limited by poor mechanical properties and low oxygen permeability. Bimodal amphiphilic co-networks (ß-APCNs) are a new class of materials that can overcome these limitations by combining hydrophilic and hydrophobic polymer chains within a network of co-continuous morphology. Applications that can benefit from these improved properties include therapeutic contact lenses, enzymatic catalysis supports, and immunoisolation membranes. The continuous hydrophobic phase could potentially increase the adsorption of plasma proteins in blood-contacting medical applications and compromise in vivo material performance, so it is critical to understand the surface characteristics of ß-APCNs and adsorption of plasma proteins on ß-APCNs. From real-time spectroscopic visible (Vis) ellipsometry measurements, plasma protein adsorption on ß-APCNs is shown to be transport-limited. The adsorption of proteins on the ß-APCNs is a multistep process with adsorption to the hydrophilic surface initially, followed by diffusion into the material to the internal hydrophilic/hydrophobic interfaces. Increasing the cross-linking of the PDMS phase reduced the protein intake by limiting the transport of large proteins. Moreover, the internalization of the proteins is confirmed by the difference between the surface-adsorbed protein layer determined from XPS and bulk thickness change from Vis ellipsometry, which can differ up to 20-fold. Desorption kinetics depend on the adsorption history with rapid desorption for slow adsorption rates (i.e., slow-diffusing proteins within the network), whereas proteins with fast adsorption kinetics do not readily desorb. This behavior can be directly related to the ability of the protein to spread or reorient, which affects the binding energy required to bind to the internal hydrophobic interfaces.

Zero-Order Antibiotic Release from Multilayer Contact Lenses: Nonuniform Drug and Diffusivity Distributions Produce Constant-Rate Drug Delivery.

A novel approach to zero-order constant-rate drug delivery from contact lenses is presented. Quasi-Case II non-Fickian transport is achieved by nonuniform drug and diffusivity distributions within three-layer bimodal amphiphilic conetworks (ß-APCNs). The center layer is a highly oxygen permeable ß-APCN matrix, which contains the drug and exhibits a high drug diffusivity. The outer ß-APCN layers contain no-drug and are loaded with vitamin E, which slows diffusion. In contrast to single-layer neat-polymer and vitamin E-loaded films that display first-order "burst" kinetics, it is demonstrated experimentally and by modeling that the combined effect of nonuniform distribution of drug loading and diffusion constants within the three-layer lens maintains low local drug concentration at the lens-fluid interface and yields zero-order drug delivery. The release rates of topical antibiotics provide constant-rate therapeutic-level delivery with appropriate oxygen permeability for at least 30 h, at which time ≈25% of the drug was released.

Real-Time Monitoring of Chemical and Topological Rearrangements in Solidifying Amphiphilic Polymer Co-Networks: Understanding Surface Demixing.

Amphiphilic polymer co-networks provide a unique route to integrating contrasting attributes of otherwise immiscible components within a bicontinuous percolating morphology and are anticipated to be valuable for applications such as biocatalysis, sensing of metabolites, and dual dialysis membranes. These co-networks are in essence chemically forced blends and have been shown to selectively phase-separate at surfaces during film formation. Here, we demonstrate that surface demixing at the air-film interface in solidifying polymer co-networks is not a unidirectional process; instead, a combination of kinetic and thermodynamic interactions leads to dynamic molecular rearrangement during solidification. Time-resolved gravimetry, low contact angles, and negative out-of-plane birefringence provided strong experimental evidence of the transitory trapping of thermodynamically unfavorable hydrophilic moieties at the air-film interface due to fast asymmetric solvent depletion. We also find that slow-drying hydrophobic elements progressively substitute hydrophilic domains at the surface as the surface energy is minimized. These findings are broadly applicable to common-solvent bicontinuous systems and open the door for process-controlled performance improvements in diverse applications. Similar observations could potentially be coupled with controlled polymerization rates to maximize the intermingling of bicontinuous phases at surfaces, thus generating true three-dimensional, bicontinuous, and undisturbed percolation pathways throughout the material.

Poly(dimethyltin glutarate) as a prospective material for high dielectric applications.

Poly(dimethyltin glutarate) is presented as the first organometallic polymer, a high dielectric constant, and low dielectric loss material. Theoretical results correspond well in terms of the dielectric constant. More importantly, the dielectric constant can be tuned depending on the solvent a film of the polymer is cast from. The breakdown strength is increased through blending with a second organometallic polymer.

Rationally designed polyimides for high-energy density capacitor applications.

Development of new dielectric materials is of great importance for a wide range of applications for modern electronics and electrical power systems. The state-of-the-art polymer dielectric is a biaxially oriented polypropylene (BOPP) film having a maximal energy density of 5 J/cm(3) and a high breakdown field of 700 MV/m, but with a limited dielectric constant (∼2.2) and a reduced breakdown strength above 85 °C. Great effort has been put into exploring other materials to fulfill the demand of continuous miniaturization and improved functionality. In this work, a series of polyimides were investigated as potential polymer materials for this application. Polyimide with high dielectric constants of up to 7.8 that exhibits low dissipation factors (<1%) and high energy density around 15 J/cm(3), which is 3 times that of BOPP, was prepared. Our syntheses were guided by high-throughput density functional theory calculations for rational design in terms of a high dielectric constant and band gap. Correlations of experimental and theoretical results through judicious variations of polyimide structures allowed for a clear demonstration of the relationship between chemical functionalities and dielectric properties.

A novel macroencapsulating immunoisolatory device: the preparation and properties of nanomat-reinforced amphiphilic co-networks deposited on perforated metal scaffold.

This paper describes the design and preparation of the non-biological components (the "hardware") of a conceptually novel bioartificial pancreas (BAP) to correct diabetes. The key components of the hardware are (1) a thin (5-10 microm) semipermeable amphiphilic co-network (APCN) membrane [i.e., a membrane of cocontinuous poly(dimethyl acryl amide) (PDMAAm)/polydimethylsiloxane (PDMS) domains cross-linked by polymethylhydrosiloxane (PMHS)] expressly created for macroencapsulation and immunoisolation of a tissue graft; (2) an electrospun nanomat of PDMS-containing polyurethane to reinforce the water-swollen APCN membrane; and (3) a perforated hollow-ribbon nitinol scaffold to stiffen and provide geometric stability to the construct. The reinforcement of water-swollen hydrogels with an electrospun nanomat is a generally applicable new method for hydrogel reinforcement. Details of device design and preparation are discussed. The advantages and disadvantages of micro- and macro-immunoisolation are analyzed, and the requirements for the ideal immunoisolatory membrane are presented. Burst pressure, and glucose and insulin permeabilities of representative devices have been determined and the effect of device composition and wall thickness on these properties is discussed.