Separating Oil-Water Nanoemulsions using Flux-Enhanced Hierarchical Membranes

Membranes that separate oil-water mixtures based on contrasting wetting properties have recently received significant attention. Separation of nanoemulsions, i.e. oil-water mixtures containing sub-micron droplets, still remains a key challenge. Tradeoffs between geometric constraints, high breakthrough pressure for selectivity, high flux, and mechanical durability make it challenging to design effective membranes. In this paper, we fabricate a hierarchical membrane by the phase inversion process that consists of a nanoporous separation skin layer supported by an integrated microporous layer. We demonstrate the separation of water-in-oil emulsions well below 1 μm in size. In addition, we tune the parameters of the hierarchical membrane fabrication to control the skin layer thickness and increase the total flux by a factor of four. These simple yet robust hierarchical membranes with engineered wetting characteristics show promise for large-scale, efficient separation systems.MIT Energy InitiativeShell Oil CompanyMIT Energy Initiative (Fellowship

Enhancing droplet deposition through in-situ precipitation

Retention of agricultural sprays on plant surfaces is an important challenge. Bouncing of sprayed pesticide droplets from leaves is a major source of soil and groundwater pollution and pesticide overuse. Here we report a method to increase droplet deposition through in-situ formation of hydrophilic surface defects that can arrest droplets during impact. Defects are created by simultaneously spraying oppositely charged polyelectrolytes that induce surface precipitation when two droplets come into contact. Using high-speed imaging, we study the coupled dynamics of drop impact and surface precipitate formation. We develop a physical model to estimate the energy dissipation by the defects and predict the transition from bouncing to sticking. We demonstrate macroscopic enhancements in spray retention and surface coverage for natural and synthetic non-wetting surfaces and provide insights into designing effective agricultural sprays

Adaptive growth factor delivery from a polyelectrolyte coating promotes synergistic bone tissue repair and reconstruction

Traumatic wounds and congenital defects that require large-scale bone tissue repair have few successful clinical therapies, particularly for craniomaxillofacial defects. Although bioactive materials have demonstrated alternative approaches to tissue repair, an optimized materials system for reproducible, safe, and targeted repair remains elusive. We hypothesized that controlled, rapid bone formation in large, critical-size defects could be induced by simultaneously delivering multiple biological growth factors to the site of the wound. Here, we report an approach for bone repair using a polyelectrolye multilayer coating carrying as little as 200 ng of bone morphogenetic protein-2 and platelet-derived growth factor-BB that were eluted over readily adapted time scales to induce rapid bone repair. Based on electrostatic interactions between the polymer multilayers and growth factors alone, we sustained mitogenic and osteogenic signals with these growth factors in an easily tunable and controlled manner to direct endogenous cell function. To prove the role of this adaptive release system, we applied the polyelectrolyte coating on a well-studied biodegradable poly(lactic-co-glycolic acid) support membrane. The released growth factors directed cellular processes to induce bone repair in a critical-size rat calvaria model. The released growth factors promoted local bone formation that bridged a critical-size defect in the calvaria as early as 2 wk after implantation. Mature, mechanically competent bone regenerated the native calvaria form. Such an approach could be clinically useful and has significant benefits as a synthetic, off-the-shelf, cell-free option for bone tissue repair and restoration.National Institutes of Health (U.S.) (Grant R01 AG029601)National Institutes of Health (U.S.) (Grant R01 EB010246)National Institutes of Health (U.S.) (Grant P30 CA014051)Natural Sciences and Engineering Research Council of Canada (Fellowship

Preparation, Characterization and Performance of Poly(vinyl alcohol) based Membranes for Pervaporation Dehydration of Alcohols

Pervaporation (PV), a non-porous membrane separation process, is gaining considerable attention for solvent separation in a variety of industries ranging from chemical to food and pharmaceutical to petrochemicals. The most successful application has been the dehydration of organic liquids, for which hydrophilic membranes are used. However, during pervaporation, excessive affinity of water towards hydrophilic membranes leads to undesirable swelling (water absorption) of the membrane matrix. To control swelling, often hydrophilic membranes are crosslinked to modify physicochemical (surface and bulk) properties. Since the transport of species in pervaporation is governed by sorption (affected by surface and bulk properties) and diffusion (affected by bulk properties), it is essential to study the effect of crosslinking on the surface and bulk physicochemical properties and their effects on separation performance. This thesis focuses on the effect of crosslinking on the physicochemical properties (e.g., crystallinity, hydrophilicity, surface roughness) of hydrophilic polymeric membranes and their dehydration performance alcohol-water mixtures. Poly(vinyl alcohol), PVA was used as the base polymer to prepare membranes with various morphologies such as homogeneous, blended (with Chitosan, CS) and composite (with poly(sulfone), PSf) structures. Before applying the crosslinked membranes for the PV dehydration of alcohols, the physicochemical characterization were carried out using Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), tensile testing, contact angle and swelling experiments. The crosslinked membranes showed an increase in surface hydrophobicity from the contact angle measurements as compared to the uncrosslinked membranes. AFM surface topography showed that the membrane surfaces have nodular structures and are rough at the nanometer scale and affected by the crosslinking conditions such as concentration and reaction time. Surface hydrophobicity and roughness was found to increase with increasing degree of crosslinking. DSC measurements showed an increase in melting temperature of the polymer membranes after crosslinking. For the PV dehydration of ethanol, a decrease in flux and an increase in selectivity were observed with increase in the degree of crosslinking. Effects of membrane thickness (of PVA layer) for crosslinked PVA-PSf composite membranes were studied on PV dehydration of ethanol. Total flux and selectivity were statistically analyzed as a function of the membrane thickness. In general, the outcome agrees with the solution-diffusion (S-D) theory: the total flux was found to be significantly affected by the PVA layer thickness, while the selectivity remains nearly unaffected. Using the S-D theory, the mass transfer resistance of the selective layers was calculated and found to increase with thickness. The relatively small change observed for selectivity has been related to the crosslinking of the PVA layer that increases the surface hydrophobicity of the membrane. Chitosan-Poly(vinyl alcohol), or CS-PVA, blended membranes were prepared by varying the blending ratio to control membrane crystallinity and its effect on the PV dehydration of ethylene glycol. The blended membranes were crosslinked interfacially with trimesoyl chloride (TMC)/hexane. The crystallinity of the membrane was found to decrease with increasing CS wt% in the blend. Although the crosslinked CS-PVA blend membranes showed improved mechanical strength, they became less flexible as detected in tensile testing. The resulting crosslinked CS-PVA blended membranes showed high flux and selectivity simultaneously, for 70-80wt% CS in the blend. The effect of feed flow-rate was studied to find the presence of concentration polarization for 90wt% EG in feed mixture as well. The crosslinked blend membrane with 75wt% CS showed a highest total flux of 0.46 kg/m2/h and highest selectivity of 663 when operating at 70oC with 90wt% EG in the feed mixture. Effects of crosslinking concentration and reaction time of trimesoyl chloride (TMC) were studied on poly(vinyl alcohol)-poly(sulfone) or PVA-PSf composite membranes. Results showed a consistent trend of changes in the physicochemical properties: the degree of crosslinking, crystallinity, surface roughness, hydrophilicity and swelling degree all decrease with increasing crosslinking agent (TMC) concentration and reaction time. The crosslinked membrane performance was assessed with PV dehydration of ethylene glycol-water mixtures at a range of concentrations (30 to 90wt% EG). The total flux of permeation was found to decrease, while the selectivity to increase, with increasing TMC concentration and reaction time. The decrease in flux was most prominent at low EG concentrations in the feed mixtures. A central composite rotatable design (CCRD) of response surface methodology was used to analyze PV dehydration performance of crosslinked poly(vinyl alcohol) (PVA) membranes. Regression models were developed for the flux and selectivity as a function of operating conditions such as, temperature, feed alcohol concentration, and flow-rate. Dehydration experiments were performed on two different alcohol-water systems: isopropanol-water (IPA-water) and ethanol-water (Et-water) mixtures around the azeotrope concentrations. Judged by the lack-of-fit criterion, the analysis of variance (ANOVA) showed the regression model to be adequate. The predicted flux and selectivity from the regression models were presented in 3-D surface plots over the whole ranges of operating variables. For both alcohol-water systems, quadratic effect of temperature and feed alcohol concentration showed significant (p < 0.0001) influence on the flux and selectivity. A strong interaction effect of temperature and concentration was observed on the selectivity for the Et-water system. For the dehydration of azeotropic IPA-water mixture (87.5wt% IPA), the optimized dehydration variables were found to be 50.5oC and 93.7 L/hr for temperature and flow-rate, respectively. On the other hand for azeotropic Et-water mixture (95.5wt% Et), the optimized temperature and flow-rate were found to be 57oC and 89.2 L/hr, respectively. Compared with experiments performed at optimized temperature and feed flow-rate, the predicted flux and selectivity of the azeotropic mixtures showed errors to be within 3-6 %

Author Correction: Enhancing droplet deposition through in-situ precipitation

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Osteophilic Multilayer Coatings for Accelerated Bone Tissue Growth

Osteophilic modular nanostructured multilayers containing hydroxyapatite nanoparticles complexed with a natural polymer chitosan create an osteoconductive surface for mesenchymal stem cells (MSCs). Coupled with the sustained release of physiological amounts of osteoinductive bone morphogenetic protein over several days from degradable poly(β-amino ester) based multilayers, this single coating results in a synergistic accelerated and upregulated differentiation of MSCs into osteoblasts laying down new bone tissue on orthopedic implants. Copyright ©2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.NIH-NIA (5R01AG029601-04)U.S. Army Research Office (contract no. W911NF-07-D-0004)NCI grant (2P30CA014051-39

Carbon nanotube–polyaniline core–shell nanostructured hydrogel for electrochemical energy storage

Conductive polymer hydrogels, which synergize the advantageous features of hydrogels and conductive materials, have been utilized in many electrochemical energy storage applications. Here, we introduce phytic acid as (1) a dispersing agent for pristine multi-walled carbon nanotubes (MWNTs) in aqueous solution containing aniline and as (2) a gelator to form polyaniline (PANI)-based hydrogels after polymerization. The PANI-based hydrogels exhibit nanowire-based mesoporous networks with high surface area and electrical conductivity. The nanostructured core (MWNT)–shell (PANI) hydrogels show an improvement on the electrical conductivity from 0.21 to 1.54 S cm[superscript −1] as the loading of MWNTs increases from 0 to 5.0 wt%. The conducting nanowire-based networks with MWNT loadings of 3.0 wt% in the hydrogel provide efficient electron transport pathways that exhibit a maximal specific capacity of 609 F g[superscript −1]. The scalable and facile synthesis demonstrates excellent electrochemical performance, rendering it attractive for sensing, energy conversion, and energy storage applications.Eni S.p.A. (Firm) (Eni-MIT Energy Fellowship)National Science Foundation (U.S.). Center for Chemical Innovation (CHE-1305124)United States. Army Research Office. Institute for Collaborative BiotechnologiesNatural Sciences and Engineering Research Council of Canada (Postgraduate Scholarship

Synthetic nanoscale electrostatic particles as growth factor carriers for cartilage repair

The efficient transport of biological therapeutic materials to target tissues within the body is critical to their efficacy. In cartilage tissue, the lack of blood vessels prevents the entry of systemically administered drugs at therapeutic levels. Within the articulating joint complex, the dense and highly charged extracellular matrix (ECM) hinders the transport of locally administered therapeutic molecules. Consequently, cartilage injury is difficult to treat and frequently results in debilitating osteoarthritis. Here we show a generalizable approach in which the electrostatic assembly of synthetic polypeptides and a protein, insulin-like growth factor-1 (IGF-1), can be used as an early interventional therapy to treat injury to the cartilage. We demonstrated that poly(glutamic acid) and poly(arginine) associated with the IGF-1 via electrostatic interactions, forming a net charged nanoscale polyelectrolyte complex (nanoplex). We observed that the nanoplex diffused into cartilage plugs in vitro and stimulated ECM production. In vivo, we monitored the transport, retention and therapeutic efficacy of the nanoplex in an established rat model of cartilage injury. A single therapeutic dose, when administered within 48 hours of the injury, conferred protection against cartilage degradation and controlled interleukin-1 (IL-1) mediated inflammation. IGF-1 contained in the nanoplex was detected in the joint space for up to 4 weeks following administration and retained bioactivity. The results indicate the potential of this approach as an early intervention therapy following joint injury to delay or even entirely prevent the onset of osteoarthritis. Keywords: compounds/materials; drug delivery; nanoparticles; regenerative medicine; osteoarthritisUnited States. Department of Defense (Contract W81XWH-14-1-0544

M13 Virus-Enabled Synthesis of Titanium Dioxide Nanowires for Tunable Mesoporous Semiconducting Networks

Mesoporous semiconducting networks exhibit advantageous photoelectrochemical properties. The M13 virus is a versatile biological scaffold that has been genetically engineered to organize various materials into nanowire (NW)-based mesoporous structures. In this study, high-aspect ratio titanium dioxide NWs are synthesized by utilizing M13 viruses as templates, and the NWs are assembled into semiconducting mesoporous networks with tunable structural properties. To understand the effects of different morphologies on the photovoltaic performance, the as-fabricated networks are employed as photoanodes in liquid-state dye-sensitized solar cells (DSCs). Compared with traditional nanoparticle-based photoanodes, the NW-based DSC photoanodes demonstrate much higher electron diffusion lengths while maintaining a comparable light harvesting capacity, thus leading to improved power conversion efficiencies. In addition, the NW-based semiconducting mesoporous thin films are able to load sufficient organolead iodide perovskite materials into the interconnected pores, and the perovskite-coated films are utilized as efficient photoanodes for solid-state organolead iodide perovskite hybrid solar cells and achieve power conversion efficiencies superior to those of liquid-state DSCs.Eni S.p.A. (Firm) (Eni-MIT Energy Fellowship)Natural Sciences and Engineering Research Council of Canada (Postgraduate Scholarship

Surface-Mediated Bone Tissue Morphogenesis from Tunable Nanolayered Implant Coatings

The functional success of a biomedical implant critically depends on its stable bonding with the host tissue. Aseptic implant loosening accounts for more than half of all joint replacement failures. Various materials, including metals and plastic, confer mechanical integrity to the device, but often these materials are not suitable for direct integration with the host tissue, which leads to implant loosening and patient morbidity. We describe a self-assembled, osteogenic, polymer-based conformal coating that promotes stable mechanical fixation of an implant in a surrogate rodent model. A single modular, polymer-based multilayered coating was deposited using a water-based layer-by-layer approach, by which each element was introduced on the surface in nanoscale layers. Osteoconductive hydroxyapatite (HAP) and osteoinductive bone morphogenetic protein–2 (BMP-2) contained within the nanostructured coating acted synergistically to induce osteoblastic differentiation of endogenous progenitor cells within the bone marrow, without indications of a foreign body response. The tuned release of BMP-2, controlled by a hydrolytically degradable poly(β-amino ester), was essential for tissue regeneration, and in the presence of HAP, the modular coating encouraged the direct deposition of highly cohesive trabecular bone on the implant surface. In vivo, the bone-implant interfacial tensile strength was significantly higher than standard bioactive bone cement, did not fracture at the interface, and had long-term stability. Collectively, these results suggest that the multilayered coating system promotes biological fixation of orthopedic and dental implants to improve surgical outcomes by preventing loosening and premature failure.David H. Koch Institute for Integrative Cancer Research at MIT (Koch Institute Swanson Biotechnology Center)National Institutes of Health (U.S.) (NIH R01 AG029601)United States. Army Research Office. Institute for Soldier Nanotechnologies (contract no.W911NF-07-D-0004)David H. Koch Institute for Integrative Cancer Research at MIT (NCI grant P30 CA014051)Natural Sciences and Engineering Research Council of Canada (Fellowship)National Science Foundation (U.S.) (Fellowship)David H. Koch Institute for Integrative Cancer Research at MIT (David H. Koch (1962) Chair Professorship in Engineering