A High Cell‐Bearing Capacity Multibore Hollow Fiber Device for Macroencapsulation of Islets of Langerhans

Macroencapsulation of islets of Langerhans is a promising strategy for transplantation of insulin‐producing cells in the absence of immunosuppression to treat type 1 diabetes. Hollow fiber membranes are of interest there because they offer a large surface‐to‐volume ratio and can potentially be retrieved or refilled. However, current available fibers have limitations in exchange of nutrients, oxygen, and delivery of insulin potentially impacting graft survival. Here, multibore hollow fibers for islets encapsulation are designed and tested. They consist of seven bores and are prepared using nondegradable polymers with high mechanical stability and low cell adhesion properties. Human islets encapsulated there have a glucose induced insulin response (GIIS) similar to nonencapsulated islets. During 7 d of cell culture in vitro, the GIIS increases with graded doses of islets demonstrating the suitability of the microenvironment for islet survival. Moreover, first implantation studies in mice demonstrate device material biocompatibility with minimal tissue responses. Besides, formation of new blood vessels close to the implanted device is observed, an important requirement for maintaining islet viability and fast exchange of glucose and insulin. The results indicate that the developed fibers have high islet bearing capacity and can potentially be applied for a clinically applicable bioartificial pancreas.     

Highly alkaline stable anion exchange membranes from nonplanar polybenzimidazole with steric hindrance backbone

The anion exchange membranes (AEMs) with both high ionic conductivity and alkali stability are always the research focus of the AEM fuel cells. Here, a novel nonplanar polymer for AEMs manufacture, mPBI‐TP‐x‐R, with excellent hydroxide stability and satisfactory processability is reported for the first time. The serial mPBI‐TP‐x resins with steric hindrance were prepared by copolymerization among 3,3′,4,4′‐tetraaminobiphenyl, isophthalic acid and tetraphenyl‐terephthalic acid (TP) in different ratios under microwave condensation. The copolymers mPBI‐TP‐x were quaternized at N1/N3‐sites of benzimidazole unit in backbone with alkyl groups (R?CH₃, C₂H₅, n‐C₃H₇, or n‐C₄H₉) to prepare soluble ionomers, and the corresponding membranes in hydroxyl ion form were prepared by a solution casting method and subsequent ion‐exchange process. The chemical structure of all membranes was characterized using FTIR and ¹H NMR spectroscopy. The properties of ion exchange capacity, water uptake, swelling ratio, tensile strength, ionic conductivity, and alkaline stability were measured. Among the prepared membranes, the mPBI‐TP‐15%‐(n‐Bu) exhibited the excellent alkaline stability (only degradation ca. 5% under 1M NaOH aqueous solution at 60 °C for 800 h) and satisfactory OH^? conductivity (46.66 mS/cm at 80 °C). The current research provides a useful exploration to commercial application of alkaline fuel cell. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1087–1096     

Metal–Organic Framework/PVDF Composite Membranes with High H2 Permselectivity Synthesized by Ammoniation

Herein we report a new ammoniation‐based chemical modification strategy for synthesis of continuous and uniform metal–organic framework (MOF)/polyvinylidene fluoride (PVDF) membranes with attractive performance. Ammoniation can promote the support PVDF membrane to produce amino groups, form a nanoparticle structure, and be well cross‐linked; therefore, the high‐density heterogeneous nucleation sites for MOFs growth were provided and the thermal stability and chemical resistance of composite membranes can be greatly improved. The high‐quality layers of representative Cu‐BTC and ZIF‐8 were synthesized on the chemically modified PVDF membranes. By ammoniation, ZIF‐7 can even be grown under harsh synthetic conditions such as in DMF precursor solutions at 403 K. The fabricated MOF/PVDF composite membranes with excellent hollow fiber structures and enhanced structural stability exhibited high H₂ permselectivities for H₂/CO₂ and H₂/N₂.     

Mechanics of fish skin: A computational approach for bio-inspired flexible composites

Natural materials and structures are increasingly becoming a source of inspiration for the design novel of engineering systems. In this context, the structure of fish skin, made of an intricate arrangement of flexible plates growing out of the dermis of a majority of fish, can be of particular interest for materials such as protective layers or flexible electronics. To better understand the mechanics of these composite shells, we introduce here a general computational framework that aims at establishing a relationship between their structure and their overall mechanical response. Taking advantage of the periodicity of the scale arrangement, it is shown that a representative periodic cell can be introduced as the basic element to carry out a homogenization procedure based on the Hill-Mendel condition. The proposed procedure is applied to the specific case of the fish skin structure of the Morone saxatilis, using a computational finite element approach. Our numerical study shows that fish skin possesses a highly anisotropic response, with a softer bending stiffness in the longitudinal direction of the fish. This softer response arises from significant scale rotations during bending, which induce a stiffening of the response under large bending curvature. Interestingly, this mechanism can be suppressed or magnified by tuning the rotational stiffness of the scale-dermis attachment but is not activated in the lateral direction. These results are not only valuable to the engineering design of flexible and protective shells, but also have implications on the mechanics of fish swimming.     

Effect of ammonium groups on the properties and alkaline stability of poly(arylene ether)‐based anion exchange membranes

Five kinds of ammonium groups functionalized partially fluorinated poly(arylene ether) block copolymer membranes were prepared for investigating the structure–property relationship as anion exchange membranes (AEMs). Consequently, the pyridine (PYR)‐modified membrane showed the highest alkaline and hydrazine stability in terms of the conductivity, water uptake, and dry weight. The chloromethylated precursor block copolymers were reacted with amines, such as trimethylamine, N‐butyldimethylamine, 1‐methylimidazole, 1,2‐dimethylimidazole, and PYR to provide the target quaternized poly(arylene ether)s. The structures of the polymers, as well as model compounds and oligomers were well characterized by ¹H NMR spectra. The obtained AEMs were subjected to water uptake and hydroxide ion conductivity measurements and stabilities in aqueous alkaline and hydrazine media. The pyridinium‐functionalized quaternized polymers membrane showed the highest alkaline and hydrazine stability with minor losses in the conductivity, water uptake, and dry weight. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 383–389     

Evaluating the impact of functional groups on membrane-mediated CO2/N2 gas separations using a common polymer backbone

Polymeric membranes have shown tremendous promise for the separation of CO₂ from flue gas streams. However, few systematic studies have been conducted to better understand the impact that chemical functionalities have on membrane-based gas separation performance. To address this gap, we herein describe the synthesis and gas separation performance of a series of vinyl-addition polynorbornenes bearing various CO₂-philic functional groups. To facilitate direct comparison between functional groups, each material was designed to maintain a common polymer backbone. Though the incorporation of CO₂-philic moieties within a dense polymeric membrane is frequently hypothesized to enhance CO₂ solubility, and thereby increase CO₂/N₂ selectivity, our results demonstrate that the incorporation of CO₂-philic groups onto a common polymer backbone do not necessarily result in increased gas separation performance. Experimental and computational results demonstrate that the incorporation of amidoxime groups onto a polynorbornene backbone increase CO₂/N₂ selectivity, whereas commonly employed ethereal side chains only increased permeability.     

Etched ZIF-8 as a Filler in Mixed-Matrix Membranes for Enhanced CO2/N2 Separation

Zeolite ZIF-8 has been etched with acid to form microporous ZIF-8-E crystals. These were then introduced into a polyethersulfone (PES) membrane matrix to enhance its CO₂/N₂ separation performance. Open through pores of size about 100 nm formed in the ZIF-8 crystals allow the ingrowth of polyethersulfone chains, ensuring a reduction in the number of nonselective voids, thereby achieving better interaction between ZIF-8-E and PES. As a result, the CO₂/N₂ separation performance of the ZIF-8-E/PES membrane increased significantly, showing a CO₂ permeability of 15.7 Barrer and a CO₂/N₂ ideal selectivity of 6.5.     

Interactive Thermal Effects on Metal–Organic Framework Polymer Composite Membranes

Polymeric membranes are important tools for intensifying separation processes in chemical industries, concerning strategic tasks such as CO₂ sequestration, H₂ production, and water supply and disposal. Mixed‐matrix and supported membranes have been widely developed; recently many of them have been based on metal–organic frameworks (MOFs). However, most of the impacts MOFs have within the polymer matrix have yet to be determined. The effects related to thermal behavior arising from the combination of MOF ZIF‐8 and polysulfone have now been quantified. The catalyzed oxidation of the polymer is strongly affected by the MOF crystal size and distribution inside the membrane. A 16 wt % 140 nm‐sized ZIF‐8 loading causes a 40 % decrease in the observed activation energy of the polysulfone oxidation that takes place at a temperature (545 °C) 80 °C lower than in the raw polymer (625 °C).     

Comb‐shaped guanidinium functionalized poly(ether sulfone)s for anion exchange membranes: Effects of the spacer types and lengths

A series of poly(ether sulfone)‐based anion exchange membranes (AEMs), tethering with guanidinium side chains with different spacers, were synthesized via azide‐alkyne cycloaddition, deprotection, and the subsequent ion exchange reactions. The designed polymer structures were verified by the ¹H NMR spectra. Because of the appropriate water uptake and formation of interconnected ionic clusters, the GPES‐3C with propyl spacer showed higher conductivity than the GPES‐1C and GPES‐9C, with methylene and nonyl spacers, respectively. Comparatively, the GPES‐EO AEM with two ethylene oxide (EO) spacers exhibited even higher conductivity, these can be interpreted by interconnectivity of ionic channels and hydrophilicity nature of the EO spacer. Additionally, although the GPES membranes displayed sufficient thermal stability, the chemical stability of as‐prepared materials needs to be much improved for fuel cell applications. Overall, these results demonstrated that the properties of “pendent‐type” AEM can be tuned facilely by the spacer types and lengths. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1313–1321