Aqueous Multiphase Systems of Polymers and Surfactants Provide Self-Assembling Step-Gradients in Density

Charles R. Mace†, Ozge Akbulut†, Ashok A. Kumar‡, Nathan D. Shapiro†, Ratmir Derda†, Matthew R. Patton†, and George M. Whitesides*†§

J. Am. Chem. Soc., 2012, 134 (22), pp 9094–9097

DOI: 10.1021/ja303183z

Publication Date (Web): May 17, 2012

Copyright © 2012 American Chemical Society

This Communication demonstrates the generation of over 300 phase-separated systems—ranging from two to six phases—from mixtures of aqueous solutions of polymers and surfactants. These aqueous multiphase systems (MuPSs) form self-assembling, thermodynamically stable step-gradients in density using a common solvent, water. The steps in density between phases of a MuPS can be very small (Δρ ≈ 0.001 g/cm³), do not change over time, and can be tuned by the addition of co-solutes. We use two sets of similar objects, glass beads and pellets of different formulations of Nylon, to demonstrate the ability of MuPSs to separate mixtures of objects by differences in density. The stable interfaces between phases facilitate the convenient collection of species after separation. These results suggest that the stable, sharp step-gradients in density provided by MuPSs can enable new classes of fractionations and separations based on density.

Analog modeling of Worm-Like Chain molecules using macroscopic beads-on-a-string†

Simon Tricard *a, Efraim Feinstein b, Robert F. Shepherd a, Meital Reches a, Phillip W. Snyder a, Dileni C. Bandarage a, Mara Prentiss b and George M. Whitesides *ac
Current computational simulations can not accurately quantify the very large number of interactions and conformations required to describe molecular phenomena (for example, polymer dynamics, solvation, crystal nucleation and growth, molecular recognition, etc.). Descriptions of the kinetics of dynamic phenomena are mostly unapproachable without drastic simplifications. Assumptions and approximations – some major – are required to make aspects of static and equilibrium problems tractable for theoretical modeling or simulation. Although we applaud the value of digital, computational models, we also believe that analog, physical methods1–4 have a role to play in understanding molecular (and supramolecular) phenomena, and we are exploring such models as a complement to theory and in silico simulation.

Behaviour of polydiacetylene vesicles under different conditions of temperature, pH and chemical components of milk

• Cristiane Patrícia de Oliveira^a, , 
• Nilda de Fátima Ferreira Soares^b, , , 
• Edimar Aparecida Filomeno Fontes^b, , 
• Taíla Veloso de Oliveira^b, , 
• Antônio Manoel Maradini Filho^b, 

• Received 21 February 2012. Revised 17 May 2012. Accepted 20 May 2012. Available online 28 May 2012.
• 
  

Abstract

Blue polydiacetylene vesicles were studied with regard to their behaviour under variations in storage temperature, heating, potentiometric titration and in the presence of chemical components of milk, to evaluate their application as a sensor in the food industry. Vesicles were prepared using 10,12-pentacosadienoic acid (PCDA)/1,2- dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). Their changes were monitored using UV-Vis absorption. Temperatures not exceeding 25 °C did not cause colour change in PCDA/DMPC vesicles for a period of up to 60 days of storage. Heating for 10 minutes at 60 and 90 °C, exposure to pH higher than 9.0 and the simulant solutions of the whey proteins, β-lactoglobulin and α-lactalbumin, promoted colour change from blue to red for the vesicles studied. The effects of routine factors on the characteristics and stability of polydiacetylene vesicles is important in defining the parameters related to their application as a sensor for the food industry.

Separation of Nanoparticles in Aqueous Multiphase Systems through Centrifugation

Ozge Akbulut, Charles R. Mace, Ramses V Martinez, Ashok A. Kumar, Zhihong Nie, Matthew R. Patton, and George M Whitesides

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/nl301452x

Publication Date (Web): June 5, 2012

Copyright © 2012 American Chemical Society

Abstract

This paper demonstrates the use of aqueous multiphase systems (MuPSs) as media for rate-zonal centrifugation to separate nanoparticles of different shapes and sizes. The properties of MuPSs do not change with time or during centrifugation; this stability facilitates sample collection after separation. A three-phase system demonstrates the separation of the reaction products (nanorods, nanospheres and large particles) of a synthesis of gold nanorods, and enriches the nanorods from 48% to 99% in less than ten minutes using a benchtop centrifuge.

Sterilizable Gels from Thermoresponsive Block Copolymer Worms

Adam Blanazs†, Robert Verber†, Oleksandr O. Mykhaylyk†, Anthony J. Ryan†, Jason Z. Heath‡, C. W. Ian Douglas‡, and Steven P. Armes*†

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja3024059

Publication Date (Web): May 14, 2012

Copyright © 2012 American Chemical Society

Biocompatible hydrogels have many applications, ranging from contact lenses to tissue engineering scaffolds. In most cases, rigorous sterilization is essential. Herein we show that a biocompatible diblock copolymer forms wormlike micelles via polymerization-induced self-assembly in aqueous solution. At a copolymer concentration of 10.0 w/w %, interworm entanglements lead to the formation of a free-standing physical hydrogel at 21 °C. Gel dissolution occurs on cooling to 4 °C due to an unusual worm-to-sphere order–order transition, as confirmed by rheology, electron microscopy, variable temperature ¹H NMR spectroscopy, and scattering studies. Moreover, this thermo-reversible behavior allows the facile preparation of sterile gels, since ultrafiltration of the diblock copolymer nanoparticles in their low-viscosity spherical form at 4 °C efficiently removes micrometer-sized bacteria; regelation occurs at 21 °C as the copolymer chains regain their wormlike morphology. Biocompatibility tests indicate good cell viabilities for these worm gels, which suggest potential biomedical applications.

Real-Time Imaging of Pt3Fe Nanorod Growth in Solution

1. Science 25 May 2012: 
   Vol. 336 no. 6084 pp. 1011-1014 
   DOI: 10.1126/science.1219185

1. 
   

1. Hong-Gang Liao¹, 
2. Likun Cui¹, 
3. Stephen Whitelam¹,², 
4. Haimei Zheng¹,*

ABSTRACT

The growth of colloidal nanocrystal architectures by nanoparticle attachment is frequently reported as an alternative to the conventional growth by monomer attachment. However, the mechanism whereby nanoparticle attachment proceeds microscopically remains unclear. We report real-time transmission electron microscopy (TEM) imaging of the solution growth of Pt₃Fe nanorods from nanoparticle building blocks. Observations revealed growth of winding polycrystalline nanoparticle chains by shape-directed nanoparticle attachment followed by straightening and orientation and shape corrections to yield single-crystal nanorods. Tracking nanoparticle growth trajectories allowed us to distinguish the force fields exerted by single nanoparticles and nanoparticle chains. Such quantification of nanoparticle interaction and understanding the growth pathways are important for the design of hierarchical nanomaterials and controlling nanocrystal self-assembly for functional devices.

Designing Cell-Compatible Hydrogels for Biomedical Applications

Science 1 June 2012: 
Vol. 336 no. 6085 pp. 1124-1128 
DOI: 10.1126/science.1214804

1. Dror Seliktar

Hydrogels are polymeric materials distinguished by high water content and diverse physical properties. They can be engineered to resemble the extracellular environment of the body’s tissues in ways that enable their use in medical implants, biosensors, and drug-delivery devices. Cell-compatible hydrogels are designed by using a strategy of coordinated control over physical properties and bioactivity to influence specific interactions with cellular systems, including spatial and temporal patterns of biochemical and biomechanical cues known to modulate cell behavior. Important new discoveries in stem cell research, cancer biology, and cellular morphogenesis have been realized with model hydrogel systems premised on these designs. Basic and clinical applications for hydrogels in cell therapy, tissue engineering, and biomedical research continue to drive design improvements using performance-based materials engineering paradigms.