There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

/pdf/hydrogels-in-regenerative-medicine-lx1cllc4g8.pdf

Hydrogels in regenerative medicine

Cells are organized on length scales ranging from angstrom to micrometres. However, the mechanisms by which angstrom-scale molecular properties are translated to micrometre-scale macroscopic properties are not well understood. Here we show that interactions between diverse synthetic, multivalent macromolecules (including multi-domain proteins and RNA) produce sharp liquid-liquid-demixing phase separations, generating micrometre-sized liquid droplets in aqueous solution. This macroscopic transition corresponds to a molecular transition between small complexes and large, dynamic supramolecular polymers. The concentrations needed for phase transition are directly related to the valency of the interacting species. In the case of the actin-regulatory protein called neural Wiskott-Aldrich syndrome protein (N-WASP) interacting with its established biological partners NCK and phosphorylated nephrin, the phase transition corresponds to a sharp increase in activity towards an actin nucleation factor, the Arp2/3 complex. The transition is governed by the degree of phosphorylation of nephrin, explaining how this property of the system can be controlled to regulatory effect by kinases. The widespread occurrence of multivalent systems suggests that phase transitions may be used to spatially organize and biochemically regulate information throughout biology.

/pdf/phase-transitions-in-the-assembly-of-multivalent-signalling-1407v3k58p.pdf

Phase transitions in the assembly of multivalent signalling proteins

Novel emulsions stabilized by pH and temperature sensitive microgels

Surfactant-free oil-in-water emulsions prepared with temperature and pH sensitive poly(N-isopropylacrylamide)(PNIPAM) microgel particles offer unprecedented control of emulsion stability.

https://absimage.aps.org/image/MAR06/MWS_MAR06-2005-004393.pdf

High internal phase emulsions (HIPEs) are often defined as very concentrated emulsions in which the volume fraction of the internal phase exceeds 0.74. Conventional HIPEs consisting of a continuous organic phase and an internal aqueous phase (water-in-oil, w/o emulsion) are commonly stabilized by large amounts of surfactant. If the continuous phase contains one or more monomeric species that are polymerizable, HIPEs can be used as templates for the fabrication of highly porous materials. Highly porous materials have proven to be useful in a variety of applications, including filtration membranes for molten metals and hot gases, bioreactors, catalyst carriers, and scaffolds for bone replacement and tissue engineering. In addition to surfactants, colloidal particles have also been used to stabilize HIPEs and produce macroporous materials after drying and sintering. 8] The concept of using particle-stabilized, or Pickering, emulsions as templates to manufacture porous materials provides a number of benefits that are not achievable using low-molecular-weight surfactants. Firstly, the particles used as stabilizers in Pickering emulsions are irreversibly adsorbed at the interface of emulsions because of their high energy of attachment, which makes the resultant Pickering emulsions extremely stable with shelf-life stabilities of months or even years. Secondly, the use of Pickering emulsion droplets as templates can functionalize the cell walls of the porous materials with a layer of solid particles, which could, for example, contain functional groups and lead to a variety of further applications. The stability and type of Pickering emulsions depend on the hydrophilicity of the particles. While considerable progress has been made on the fabrication of porous materials by Pickering HIPE templating, one important limitation has still remained. All previous reports on Pickering emulsions deal with emulsions for which the volume fractions of the dispersed phases are less than 0.70. On the basis of the developed thermodynamic model, Kralchevsky et al. have predicted that Pickering emulsions will phase-invert above an internal phase volume fraction of 0.5. In practice, phase inversion is usually observed at a volume fraction of 0.70 after kinetic factors are considered. Binks and co-workers 12] have experimentally demonstrated that Pickering emulsions phase-invert between volume fractions of 0.65 and 0.70, which means that the majority phase becomes the continuous phase. The formation of HIPEs stabilized solely by solid particles seems to be impossible. Menner et al. reported on the first successful preparation of an HIPE stabilized solely by carbon nanotubes with 60% internal phase volume. Akartuna et al. also reported on the preparation of macroporous materials from Pickering HIPE templates stabilized by inorganic particles, but about 35 vol% particles were needed to stabilize the emulsions with internal phase fractions of 72–78%. Recently, using titania or silica particles, stable Pickering HIPEs with an internal phase volume fraction greater than 90% could be prepared. However, the hydrophilicity of the particles should be tailored through prior chemical treatment. Furthermore, to avoid the collapse of the emulsion structure during the production of porous materials, consolidation of the HIPEs by gelation of the continuous phase requires additional strict control over the reaction chemistry, which may be challenging. Hence, the fabrication of porous materials using the Pickering HIPE templating approach that would not need chemical reactions and could be easily extended to a wide variety of chemical compositions is highly desirable. We report herein the stabilization of Pickering hexane-inwater (o/w) HIPEs with volume fractions as high as 0.9 by soft poly(N-isopropylamide)-co-(methacrylic acid) (PNIPAM-coMAA) microgel particles at concentrations as low as 0.05 wt %. Microgel particles are adsorbed at the oil–water interface to hinder extensive droplet coalescence. Excess microgel particles simultaneously form a gel in the continuous phase to trap oil droplets in the gel matrix, which in turn can inhibit creaming of the oil droplets and enhance the emulsion stability. Evaporation in air of the gelled continuous phase of the HIPEs directly leads to porous materials without any chemical reactions. Furthermore, the porosity of the final structure can be tailored by simply changing the microgel particle concentration. Fluorescent PNIPAM-co-MAA microgel particles were synthesized using surfactant-free precipitation polymerization as described before. The details are provided in the Supporting Information (Figures S1–S4). The resultant microgel particles have an average hydrodynamic diameter of 248 nm at room temperature with a solution pH value of 7.5, as determined by dynamic laser light scattering (see the [*] Z. F. Li, Prof. T. Ngai Department of Chemistry, The Chinese University of Hong Kong Shatin, N.T., Hong Kong (China) E-mail: tongai@cuhk.edu.hk Homepage: http://www.chem.cuhk.edu.hk/faculty_ngai_to.htm

High Internal Phase Emulsions Stabilized Solely by Microgel Particles

Using stimulus-sensitive microgel particles as an emulsifier, we have prepared a new type of emulsion responsive to pH, ionic strength, and temperature changes. Each of these environmental changes can trigger a volume phase transition in poly(N-isopropylacrylamide) (PNIPAM) microgel particles containing some carboxylic groups. Depending on their hydrophobicity and charging state, such PNIPAM microgel particles can adsorb to the droplets of an octanol-in-water emulsion and provide excellent stability against coalescence and ripening. We have studied in detail the correlation between the particles' response to changes in the solution conditions and the corresponding response of particle-decorated emulsion droplets. In their swollen, hydrophilic state, the microgel particles consistently stabilize the octanol droplets, but inducing a microgel collapse usually results in a destabilization of the emulsion and eventually in phase separation. A notable exception was found at high pH where particles are highly ch...

Environmental Responsiveness of Microgel Particles and Particle-Stabilized Emulsions

In this paper, we report for the first time the use of a well-dispersed gelatin particle as a representative of natural and biocompatible materials to be an effective particle stabilizer for high internal phase emulsion (HIPE) formulation. Fairly monodispersed gelatin particles (∼200 nm) were synthesized through a two-step desolvation method and characterized by dynamic light scattering, ζ-potential measurements, scanning electron microscopy, and atomic force microscopy. Those protein latexes were then used as sole emulsifiers to fabricate stable oil-in-water Pickering HIPEs at different concentrations, pH conditions, and homogenization times. Most of the gelatin particles were irreversibly adsorbed at the oil-water interface to hinder droplet coalescence, such that Pickering HIPEs can be formed by a small amount of gelatin particles (as low as 0.5 wt % in the water phase) at pH far away from the isoelectric point of the gelatin particles. In addition, increasing homogenization time led to narrow size distribution of droplets, and high particle concentration resulted in more solidlike Pickering HIPEs. In vitro controlled-release experiments revealed that the release of the encapsulated β-carotene can be tuned by manipulating the concentration of gelatin particles in the formulation, suggesting that the stable and narrow-size-distributed gelatin-stabilized HIPEs had potential in functional food and pharmaceutical applications.

To Ngai

Papers

Novel emulsions stabilized by pH and temperature sensitive microgels

Novel emulsions stabilized by pH and temperature sensitive microgels

High Internal Phase Emulsions Stabilized Solely by Microgel Particles

Environmental Responsiveness of Microgel Particles and Particle-Stabilized Emulsions

Gelatin Particle-Stabilized High Internal Phase Emulsions as Nutraceutical Containers