Scalable liquid-based manufacturing of new classes of particles with special shape and enhanced functionality

We will first discuss a number of scalable, rapid and cost-effective processes for the synthesis of new classes of particles and functional nanomaterials via antisolvent-induced biphasic polymer precipitation from solution under shear. The ultralow interfacial tension between the droplets and the medium enables the formation of high surface area liquid structures, which can serve as templates for the formation of diverse classes of polymer and biopolymer materials, at least one characteristic dimension of which may be on the nanoscale. Our “shear nanospinning” technique that operates on these principles opens the way to scalable manufacture of nanofibers and nanoribbons (Adv. Mater., 27, 2642, 2015). The fibers are formed in the bulk of liquid medium by the combined action of shear and phase separation. The corresponding patented technology commercialized as XanoShear™ may revolutionize the scale and scope of nanofiber application in consumer and industrial products. After introducing the method principles, we will discuss two classes of novel particles made by this technique in Velev group, which could find applications in a broad range of consumer products. The method was originally used to make dispersions of polymer rods that can act as superstabilizers of Pickering foams and emulsions. Modifications of the technique allowed making new types of sheet-like and ribbon-like particles, which exhibit extraordinary strong jamming in suspension and can be used as highly efficient viscosity modifiers and matrixes for gels and aerogels. Finally, we present the making and properties of new class of environmentally-benign nanoparticles (EbNPs) with cores made of biodegradable lignin. These particles are fabricated by liquid shear process including water-only pH-jump precipitation. They can serve as highly potent microbicidal substitutes of common silver nanoparticles after being loaded with an optimal amount of silver in the form of adsorbed Ag+ ions (Nature Nanotech., 10, 817, 2015). The high antimicrobial efficiency of the EbNPs stems from a cationic surface modification of the particles that facilitates their adsorption onto bacterial membranes and triggers a targeted release of active Ag+ ions. These environmentally-benign nanoparticles illustrate how green chemistry principles can be applied to design more sustainable nanomaterials with increased activity and decreased environmental footprint. Please click Additional Files below to see the full abstract

Large scale fabrication of environmentally benign nanoparticles from lignin for use as delivery vehicles of active ingredients

Our group previously introduced a new class of environmentally-benign nanoparticles (EbNPs) with cores made of biodegradable lignin (Nature Nanotech., 10, 817, 2015). Unlike traditional inorganic nanoparticles, the environmentally benign nanoparticles made of lignin can degrade after they have been used, so there is no potential for toxic impact on the environment or humans. The lignin core nanoparticles are synthesized through flash precipitation, but until recently they were only produced in mL-scale batches. We have developed a semi-continuous system featuring a recycle loop, making it possible to produce such nanoparticles in practical quantities for industrial applications. We investigated the role of each variable in our process to determine how we can control the size of our EbNPs and the final concentration of the EbNP suspensions. Because of the turbulent flow in the system, we found that the range of possible flow rates did not have any impact on our final size. The amount of anti-solvent added to the medium also had no effect on our final EbNP size distribution, revealing that we have continuous nucleation throughout each run instead of the LaMer mechanism, which would result in growth of existing particles with the addition of more lignin. This allows effective control of the resulting nanoparticle size through the starting concentration of lignin in acetone. Then, by altering our anti-solvent volume, we can control the final NP concentration of our solution. Please click Additional Files below to see the full abstract

Conference Program

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Generic model for tunable colloidal aggregation in multidirectional fields

Based on Brownian Dynamics computer simulations in two dimensions we investigate aggregation scenarios of colloidal particles with directional interactions induced by multiple external fields. To this end we propose a model which allows continuous change in the particle interactions from point-dipole-like to patchy-like (with four patches). We show that, as a result of this change, the non-equilibrium aggregation occurring at low densities and temperatures transforms from conventional diffusion-limited cluster aggregation (DLCA) to slippery DLCA involving rotating bonds; this is accompanied by a pronounced change of the underlying lattice structure of the aggregates from square-like to hexagonal ordering. Increasing the temperature we find a transformation to a fluid phase, consistent with results of a simple mean-field density functional theory

Transparent and soft elastomeric composites and oil/water biphasic systems with stimuli-triggered release of “invisible” liquid

The synthesis, principles, and properties of a new class of stimuli-responsive soft matter biphasic composites will be introduced. The soft composite consists of more than 30% of aqueous solution emulsion (of micron-sized droplets) optically hidden in a matrix of silicone or hydrocarbon gel. Through delicate adjustment of the refractive index (RI) of the internal aqueous phase, the composite is completely transparent to visible light and the internally dispersed aqueous droplet phase is invisible to the naked eye. Multiple phases can be included in the form of gelled multiple emulsion. The composite exhibits unique stimuli-response capabilities, such as changing its optical transmittance upon mechanical, thermal, osmotic and other stresses. Intrusion damage causes the composite to release the RI matched aqueous phase, which causes change in transparency of color. In addition, when the composite is present in an aqueous medium where salinity is different from the dispersed phase, the osmotic pressure in the droplets causes instantaneous transparency change triggered by osmotic pressure. This enables us to measure osmotic pressure of the aqueous medium quickly. The new composites and gels could find many applications including a number of cosmetics and other consumer products with attractive and unusual appearance and stimulus-triggered active ingredients delivery. Please click Additional Files below to see the full abstract

A new class of dendrimeric gecko legs polymer particles with extraordinary structure- building, gelation and adhesive capabilities

Particulate rheology modifiers are important component of many cosmetics, food, and pharmaceutical formulations. The efficiency of rheology modifiers is usually determined by the interplay between surface area and shape of suspended particles. We will present a new class of nanofibrilated dendrimeric polymer particles (DPPs) with very high surface area and morphology engineered for applications in rheology modifiers and adhesives. The DPPs are fabricated in a novel efficient and scalable process for liquid-based synthesis of nanomaterials by antisolvent precipitation in turbulently sheared medium. The process allows for a variety of polymers to be readily made into DPPs which are hierarchically structured, with a big branched corona of nanofibers spreading out in all directions. The hierarchical structure endows DPPs with high excluded volume. They build a stable three-dimensional network leading to gel-like behavior at fractions as low as 1-2 vol.% of DPPs in various liquids. In addition, the biomimetic similarity of their structure to the gecko lizards’ setae endows the DPPs with excellent adhesion and cohesion properties. Our results demonstrate that this strong adhesion and cohesion are attributed to the contact splitting and van der Waals interactions of their nanofibrous structures. This new class of polymeric particles opens new ways to make strong non-covalent binding coatings, new types of dry adhesives, nonwovens and fluid-gels. They could have a transformative role as rheology modifiers and nano-adhesives to hair and skin in many cosmetics formulations. Please click Additional Files below to see the full abstract

Artificial leaf device for hydrogen generation from immobilised C. reinhardtii microalgae

We developed a fully biomimetic leaf-like device for hydrogen production which allows incorporated fabric-immobilised microalgae culture to be simultaneously hydrated with media and harvested from the produced hydrogen in a continuous flow regime without the need to replace the algal culture. Our leaf device produces hydrogen by direct photolysis of water resulting from redirecting the photosynthetic pathways in immobilised microalgae due to the lack of oxygen. In contrast to the many other reports in the literature on batch photobioreactors producing hydrogen from suspension culture of microalgae, we present the first report where this is done in a continuous manner from a fabric-immobilised microalgae culture. The reported artificial leaf device maximises the sunlight energy utilisation per gram of algae and can be upscaled cheaply and easily to cover large areas. We compared the production of hydrogen from both immobilised and suspended cultures of C. reinhardtii microalgae under sulphur, phosphorus and oxygen deprived conditions. The viability and potential of this approach is clearly demonstrated. Even though this is a first prototype, the hydrogen yield of our artificial leaf device is twenty times higher per gram of algae than in previously the reported batch reactors. Such leaf-like devices could potentially be made from flexible plastic sheets and installed on roofs and other sun-exposed surfaces that are inaccessible by photovoltaic cells. The ability to continuously produce inexpensive hydrogen by positioning inexpensive sheets onto any surface could have an enormous importance in the field of biofuels. The proposed new concept can provide a cleaner and very inexpensive way of bio-hydrogen generation by flexible sheet-like devices

Leveraging a deeper understanding of Poloxamer188 to improve cell culture processes

The industry-wide use of Poloxamer188 (P188) underwent severe scrutiny as a result of lot variability discovered within the past few years. While screening methods have been developed to ensure lot consistency and the root cause of the variability has likely been identified, a fundamental understanding of surfactant-cell interactions has not yet been achieved. As industry continues to push culture densities higher to maximize product yield, higher aeration and agitation are required to supply sufficient oxygen transfer rate. The harsher environment in the bioreactor, depletion of shear protectants, and possible cell physiology change leads to the need of improved shear protection strategies to minimize shear damage in the cell culture process. In this project, novel concentric cylinder mixer (CCM) assay was developed to quantify the relative shear sensitivity of mAb producing Chinese Hamster Ovary (CHO) cell lines in production bioreactors. Compared with other methods to characterize shear sensitivity, the CCM assay requires low sample volume and minimal processing time. Various concentrations of P188 were evaluated using CCM assay to improve shear protection strategies in 3L and 300L bioreactors. Results indicate that cell shear sensitivity dramatically increases upon reaching the cell culture stationary phase, coinciding with viability decline and exponential LDH increase in the bioreactor. With a simple shift in shear protectant concentration, we were able to increase harvest viability resulting in decreased cellular debris, decreased foam stability, and reduction in LDH upon harvest. A strong dose dependent correlation between membrane rigidity and surfactant concentration was also discovered through the studies which provided possible mechanism of how surfactant reinforces cell membrane by decreasing membrane fluidity. The knowledge of cell membrane fluidity combined with the CCM assay contributes to our understanding of cell shear sensitivity and surfactant-cell interactions. These tools can be used to optimize process parameter set points, evaluate media formulation effects on cell sensitivity, and select shear resistant cell lines to improve cell culture process robustness

Phase diagram of two-dimensional systems of dipole-like colloids

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Based on Discontinuous Molecular Dynamics (DMD) simulations we present a phase diagram of two-dimensional nano-particles with dipole-like short-ranged interactions. Similar to systems with true, long-ranged dipolar interactions the present system undergoes a transition from an isotropic fluid phase into a polymer-like fluid, characterized by an association of most particles into clusters. Further decrease of the temperature leads to a percolated system which, moreover, displays dynamical properties reminiscent of a gel. Specifically, we find a plateau in the mean-squared displacement and a non-gaussian behavior of the self-part of the van Hove correlation function. In the high density region we observe crystallization from the isotropic fluid into a solid phase with hexagonal order. Surprisingly, the crystallization is accompanied by a global parallel ordering of the dipole moments, i.e., a ferroelectric phase. This behavior is in marked contrast to what is found in 2D systems with long-ranged dipolar interactions. Our results allow insights into the design of gel-like or highly ordered structures at interfaces, shells around droplets and bubbles and new-sheet like materials.DFG, GRK 1524, Self-Assembled Soft-Matter Nanostructures at Interface