Surface Modification of Water Purification Membranes Miller, Daniel J.; Dreyer, Daniel R.; Bielawski, Christopher W. ...
Angewandte Chemie (International ed.),
April 18, 2017, Volume:
56, Issue:
17
Journal Article
Peer reviewed
Open access
Polymeric membranes are an energy‐efficient means of purifying water, but they suffer from fouling during filtration. Modification of the membrane surface is one route to mitigating membrane fouling, ...as it helps to maintain high levels of water productivity. Here, a series of common techniques for modification of the membrane surface are reviewed, including surface coating, grafting, and various treatment techniques such as chemical treatment, UV irradiation, and plasma treatment. Historical background on membrane development and surface modification is also provided. Finally, polydopamine, an emerging material that can be easily deposited onto a wide variety of substrates, is discussed within the context of membrane modification. A brief summary of the chemistry of polydopamine, particularly as it may pertain to membrane development, is also described.
Cleaning up: The efficiency of polymeric water purification membranes, which are capable of removing many impurities from water but frequently suffer from fouling, can be improved by surface modification. Common techniques used to modify membrane surfaces, including grafting, coating, chemical treatment, UV irradiation, plasma treatment, and polydopamine application, are reviewed.
In the wake of the success of modern immunotherapy, oncolytic viruses (OVs) are currently seen as a potential therapeutic option for patients with cancer who do not respond or fail to achieve durable ...responses following treatment with immune checkpoint inhibitors. OVs offer a multifaceted therapeutic platform because they preferentially replicate in tumour cells, can be engineered to express transgenes that augment their cytotoxic and immunostimulatory activities, and modulate the tumour microenvironment to optimize immune-mediated tumour eradication, both at locoregional and systemic sites of disease. Lysis of tumour cells releases tumour-specific antigens that trigger both the innate and adaptive immune systems. OVs also represent attractive combination partners with other systemically delivered agents by virtue of their highly favourable safety profiles. Rational combinations of OVs with different immune modifiers and/or antitumour agents, based on mechanisms of tumour resistance to immune-mediated attack, may benefit the large, currently underserved, population of patients who respond poorly to immune checkpoint inhibition.
Alginate is a commonly used bioink in 3D bioprinting. Matrix stiffness is a key determinant of mesenchymal stem cell (MSC) differentiation, suggesting that modulation of alginate bioink mechanical ...properties represents a promising strategy to spatially regulate MSC fate within bioprinted tissues. In this study, we define a printability window for alginate of differing molecular weight (MW) by systematically varying the ratio of alginate to ionic crosslinker within the bioink. We demonstrate that the MW of such alginate bioinks, as well as the choice of ionic crosslinker, can be tuned to control the mechanical properties (Young's Modulus, Degradation Rate) of 3D printed constructs. These same factors are also shown to influence growth factor release from the bioinks. We next explored if spatially modulating the stiffness of 3D bioprinted hydrogels could be used to direct MSC fate inside printed tissues. Using the same alginate and crosslinker, but varying the crosslinking ratio, it is possible to bioprint constructs with spatially varying mechanical microenvironments. Moreover, these spatially varying microenvironments were found to have a significant effect on the fate of MSCs within the alginate bioinks, with stiffer regions of the bioprinted construct preferentially supporting osteogenesis over adipogenesis.
Herein we propose a new structure for poly(dopamine), a synthetic eumelanin that has found broad utility as an antifouling agent. Commercially available 3-hydroxytyramine hydrochloride (dopamine HCl) ...was polymerized under aerobic, aqueous conditions using tris(hydroxymethyl)aminomethane (TRIS) as a basic polymerization initiator, affording a darkly colored powder product upon isolation. The polymer was analyzed using a variety of solid state spectroscopic and crystallographic techniques. Collectively, the data showed that in contrast to previously proposed models, poly(dopamine) is not a covalent polymer but instead a supramolecular aggregate of monomers (consisting primarily of 5,6-dihydroxyindoline and its dione derivative) that are held together through a combination of charge transfer, π-stacking, and hydrogen bonding interactions.
The synthesis and properties of the hybrid organic/inorganic germanium perovskite compounds, AGeI3, are reported (A = Cs, organic cation). The systematic study of this reaction system led to the ...isolation of 6 new hybrid semiconductors. Using CsGeI3 (1) as the prototype compound, we have prepared methylammonium, CH3NH3GeI3 (2), formamidinium, HC(NH2)2GeI3 (3), acetamidinium, CH3C(NH2)2GeI3 (4), guanidinium, C(NH2)3GeI3 (5), trimethylammonium, (CH3)3NHGeI3 (6), and isopropylammonium, (CH3)2C(H)NH3GeI3 (7) analogues. The crystal structures of the compounds are classified based on their dimensionality with 1–4 forming 3D perovskite frameworks and 5–7 1D infinite chains. Compounds 1–7, with the exception of compounds 5 (centrosymmetric) and 7 (nonpolar acentric), crystallize in polar space groups. The 3D compounds have direct band gaps of 1.6 eV (1), 1.9 eV (2), 2.2 eV (3), and 2.5 eV (4), while the 1D compounds have indirect band gaps of 2.7 eV (5), 2.5 eV (6), and 2.8 eV (7). Herein, we report on the second harmonic generation (SHG) properties of the compounds, which display remarkably strong, type I phase-matchable SHG response with high laser-induced damage thresholds (up to ∼3 GW/cm2). The second-order nonlinear susceptibility, χS (2), was determined to be 125.3 ± 10.5 pm/V (1), (161.0 ± 14.5) pm/V (2), 143.0 ± 13.5 pm/V (3), and 57.2 ± 5.5 pm/V (4). First-principles density functional theory electronic structure calculations indicate that the large SHG response is attributed to the high density of states in the valence band due to sp-hybridization of the Ge and I orbitals, a consequence of the lone pair activation.
Membrane fouling is often characterized in the laboratory by flux decline experiments, where an increase in transport resistance due to accumulation of foulants on and/or in a membrane is manifested ...as a decrease in permeate flux with filtration time at fixed transmembrane pressure. However, many industrial microfiltration and ultrafiltration applications operate at constant permeate flux, and there are few reports comparing these modes of operation. In this study, emulsified oil fouling of polysulfone ultrafiltration membranes was studied using both constant permeate flux and constant transmembrane pressure experiments. Mass transfer resistance changes during fouling were compared between constant flux experiments and constant transmembrane pressure experiments performed at an initial flux equal to the flux imposed during the constant flux experiment. At low fluxes, the transport resistance and its change with permeate volume per unit area agreed within experimental error regardless of operational mode. In contrast, at high fluxes, the change in membrane resistance with permeate volume per unit area was much higher in constant flux than in constant transmembrane pressure experiments. The threshold flux, defined recently as the flux at which the rate of fouling begins to increase rapidly, separates the regimes of good and poor agreement between the two types of experiments. The weak form of the critical flux, below which spontaneous adsorption is the only significant resistance imposed by foulant, was also observed.
Establishing reliable intravenous catheterization in mice with optical implants allows the combination of neural manipulations and recordings with rapid, time-locked delivery of pharmacological ...agents. Here we present a procedure for handmade jugular vein catheters designed for head-mounted intravenous access and provide surgical and postoperative guidance for improved survival and patency. A head-mounted vascular access point eliminates the need for a back-mounted button in animals already receiving neural implants, thereby reducing sites of implantation. This protocol, which is readily adoptable by experimenters with previous training and experience in mouse surgery, enables repeated fiber photometry recordings or optogenetic manipulation during drug delivery in adult mice that are awake and behaving, whether head fixed or freely moving. With practice, an experienced surgeon requires ~30 min to perform catheterization on each mouse. Altogether, these techniques facilitate the reliable and repeated delivery of pharmacological agents in mouse models while simultaneously recording at high temporal resolution and/or manipulating neural populations.
A commercial polyamide reverse osmosis (RO) membrane was surface-modified with polydopamine deposited from buffered, aqueous dopamine solution at ambient conditions. The influence of various ...modification conditions (i.e., dopamine solution concentration, polydopamine deposition time, and initial pH of Tris–HCl buffer) on pure water flux, flux during filtration of an oil/water emulsion, and NaCl rejection was investigated. Dead-end filtration results showed decreased pure water flux with increasing dopamine solution concentration and polydopamine deposition time. Membranes modified at a pH of 5 exhibited no change in pure water flux or flux during fouling experiments compared to the native membranes, suggesting that polydopamine was not deposited under such acidic coating conditions. All polydopamine-modified membranes, except those coated at a pH of 5, had higher fluxes when filtering an oil/water emulsion than that of unmodified membranes. NaCl rejection values in all membranes were within the manufacturer's specification. The increased flux when filtering an oil/water emulsion was not sensitive to dopamine concentration, coating time greater than 60min, or alkaline buffer pH value. Short deposition times slightly reduced the fouling resistance of coated membranes, and membranes modified at acidic pH values showed no improvement in fouling.
► Polydopamine was deposited on polyamide reverse osmosis membrane to improve fouling resistance. ► Effect of dopamine concentration, deposition time, and pH on membrane properties was studied. ► Polydopamine coating could improve membrane fouling resistance.
Significant progress has been made in the field of cartilage and bone tissue engineering over the last two decades. As a result, there is real promise that strategies to regenerate rather than ...replace damaged or diseased bones and joints will one day reach the clinic however, a number of major challenges must still be addressed before this becomes a reality. These include vascularization in the context of large bone defect repair, engineering complex gradients for bone-soft tissue interface regeneration and recapitulating the stratified zonal architecture present in many adult tissues such as articular cartilage. Tissue engineered constructs typically lack such spatial complexity in cell types and tissue organization, which may explain their relatively limited success to date. This has led to increased interest in bioprinting technologies in the field of musculoskeletal tissue engineering. The additive, layer by layer nature of such biofabrication strategies makes it possible to generate zonal distributions of cells, matrix and bioactive cues in 3D. The adoption of biofabrication technology in musculoskeletal tissue engineering may therefore make it possible to produce the next generation of biological implants capable of treating a range of conditions. Here, advances in bioprinting for cartilage and osteochondral tissue engineering are reviewed.
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