Tripartite entanglement from interlinked χ(2)\chi^{(2)} parametric interactions

We examine the tripartite entanglement properties of an optical system using interlinked $\chi^{(2)}$ interactions, recently studied experimentally in terms of its phase-matching properties by Bondani et al [M. Bondani, A. Allevi, E. Gevinti, A. Agliati, and A. Andreoni, arXiv:quant-ph/0604002.]. We show that the system does produce output modes which are genuinely tripartite entangled and that detection of this entanglement depends crucially on the correlation functions which are measured, with a three-mode Einstein-Podolsky-Rosen inequality being the most sensitive.Comment: 15 pages, 5 figure

Topology effects on protein–polymer block copolymer self-assembly

Bioconjugates made of the model red fluorescent protein mCherry and synthetic polymer blocks show that topology, i.e. the BA, BA2, ABA and ABC chain structure of the block copolymers, where B represents the protein and A and C represent polymers, has a significant effect on ordering transitions and the type and size of nanostructures formed during microphase separation. ABA and ABC type block copolymers were synthesized by using two site-specific bioconjugation reactions: the thiol–ene reaction with a cysteine on mCherry and maleimide functionalized polymers, and the sortase A ligation reaction with an LPETG sequence at the C-terminus on mCherry and a triglycine functionalized polymer. The phase behaviors of mCherry–poly(N-isopropylacrylamide) (PNIPAM) and mCherry–(PNIPAM)2 show that the shapes of the phase diagrams are similar overall, but mCherry–(PNIPAM)2, i.e. BA2 type, yields a narrower domain spacing than mCherry–PNIPAM, i.e. BA type. PNIPAM–mCherry–PNIPAM (ABA type) shows only lamellar phases in the range of conditions under which ordered structures appear. PDMAPS–mCherry–PNIPAM (ABC type) shows an ordered structure across the widest range of conditions in the four bioconjugates and also the widest range of different nanodomain structures. The phase behavior of the ABC type implies that the repulsive interaction between two water-soluble coil polymers can be a key factor in enhancing the self-assembly of globular protein–polymer block copolymers.Department of Energy Office of Basic Energy Sciences (Award DE-SC0007106

Controlling topological entanglement in engineered protein hydrogels with a variety of thiol coupling chemistries

Topological entanglements between polymer chains are achieved in associating protein hydrogels through the synthesis of high molecular weight proteins via chain extension using a variety of thiol coupling chemistries, including disulfide formation, thiol-maleimide, thiol-bromomaleimide and thiol-ene. Coupling of cysteines via disulfide formation results in the most pronounced entanglement effect in hydrogels, while other chemistries provide versatile means of changing the extent of entanglement, achieving faster chain extension, and providing a facile method of controlling the network hierarchy and incorporating stimuli responsivities. The addition of trifunctional coupling agents causes incomplete crosslinking and introduces branching architecture to the protein molecules. The high-frequency plateau modulus and the entanglement plateau modulus can be tuned by changing the ratio of difunctional chain extender to the trifunctional branching unit. Therefore, these chain extension reactions show promise in delicately controlling the relaxation and mechanical properties of engineered protein hydrogels in ways that complement their design through genetic engineering

Efficient Synthesis of Narrowly Dispersed Brush Copolymers and Study of Their Assemblies: The Importance of Side Chain Arrangement

Efficient, one-pot preparation of synthetically challenging, high molecular weight (MW), narrowly dispersed brush block copolymers and random copolymers in high conversions was achieved by ring-opening metathesis (co)polymerization (ROMP) of various macromonomers (MMs) using the highly active, fast-initiating ruthenium olefin metathesis catalyst (H_2IMes)(pyr)_2(Cl)_2RuCHPh. A series of random and block copolymers were prepared from a pair of MMs containing polylactide (PLA) and poly(n-butyl acrylate) (PnBA) side chains at similar MWs. Their self-assembly in the melt state was studied by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). In brush random copolymers containing approximately equal volume fractions of PLA and PnBA, the side chains segregate into lamellae with domain spacing of 14 nm as measured by SAXS, which was in good agreement with the lamellar thickness measured by AFM. The domain spacings and order−disorder transition temperatures of brush random copolymers were insensitive to the backbone length. In contrast, brush block copolymers containing approximately equal volume fractions of these MMs self-assembled into highly ordered lamellae with domain spacing over 100 nm. Their assemblies suggested that the brush block copolymer backbone adopted an extended conformation in the ordered state

The mechanical properties and cytotoxicity of cell-laden double-network hydrogels based on photocrosslinkable gelatin and gellan gum biomacromolecules

A major goal in the application of hydrogels for tissue engineering scaffolds, especially for load-bearing tissues such as cartilage, is to develop hydrogels with high mechanical strength. In this study, a double-network (DN) strategy was used to engineer strong hydrogels that can encapsulate cells. We improved upon previously studied double-network (DN) hydrogels by using a processing condition compatible with cell survival. The DN hydrogels were created by a two-step photocrosslinking using gellan gum methacrylate (GGMA) for the rigid and brittle first network, and gelatin methacrylamide (GelMA) for the soft and ductile second network. We controlled the degree of methacrylation of each polymer so that they obtain relevant mechanical properties as each network. The DN was formed by photocrosslinking the GGMA, diffusing GelMA into the first network, and photocrosslinking the GelMA to form the second network. The formation of the DN was examined by diffusion tests of the large GelMA molecules into the GGMA network, the resulting enhancement in the mechanical properties, and the difference in mechanical properties between GGMA/GelMA single networks (SN) and DNs. The resulting DN hydrogels exhibited the compressive failure stress of up to 6.9 MPa, which approaches the strength of cartilage. It was found that there is an optimal range of the crosslink density of the second network for high strength of DN hydrogels. DN hydrogels with a higher mass ratio of GelMA to GGMA exhibited higher strength, which shows promise in developing even stronger DN hydrogels in the future. Three dimensional (3D) encapsulation of NIH-3T3 fibroblasts and the following viability test showed the cell-compatibility of the DN formation process. Given the high strength and the ability to encapsulate cells, the DN hydrogels made from photocrosslinkable macromolecules could be useful for the regeneration of load-bearing tissues.Samsung Scholarship FoundationNational Institutes of Health (U.S.) (HL092836)National Institutes of Health (U.S.) (EB02597)National Institutes of Health (U.S.) (AR057837)National Science Foundation (U.S.) (CAREER Award DMR0847287)United States. Office of Naval Research (Young Investigator Award

Site-specific conjugation of RAFT polymers to proteins via expressed protein ligation

Site-specific protein conjugates with RAFT polymers were synthesized using expressed protein ligation. Stable micelles were formed from both linear block copolymer and Y-shaped conjugates.DTRA (Project BA12PHM159

Thermoresponsive and Mechanical Properties of Poly(

Gelation of the left helical N-substituted homopolypeptide poly(l-proline) (PLP) in water was explored, employing rheological and small-angle scattering studies at different temperatures and concentrations in order to investigate the network structure and its mechanical properties. Stiff gels were obtained at 10 wt % or higher at 5 °C, the first time gelation has been observed for homopolypeptides. The secondary structure and helical rigidity of PLP has large structural similarities to gelatin but as gels the two materials show contrasting trends with temperature. With increasing temperature in D₂O, the network stiffens, with broad scattering features of similar correlation length for all concentrations and molar masses of PLP. A thermoresponsive transition was also achieved between 5 and 35 °C, with moduli at 35 °C higher than gelatin at 5 °C. The brittle gels could tolerate strains of 1% before yielding with a frequency-independent modulus over the observed range, similar to natural proline-rich proteins, suggesting the potential for thermoresponsive or biomaterial-based applications.United States. Army Research Office (W911NF-13-D-0001)United States. National Institutes of Health (NIH/NIGMS 5T32GM008334

Reinforcement of Shear Thinning Protein Hydrogels by Responsive Block Copolymer Self-Assembly

Shear thinning hydrogels are promising materials that exhibit rapid self-healing following the cessation of shear, making them attractive for applications including injectable biomaterials. Here, self-assembly is demonstrated as a strategy to introduce a reinforcing network within shear thinning artificially engineered protein gels, enabling a responsive transition from an injectable state at low temperatures with a low yield stress to a stiffened state at physiological temperatures with resistance to shear thinning, higher toughness, and reduced erosion rates and creep compliance. Protein-polymer triblock copolymers capable of the responsive self-assembly of two orthogonal networks are synthesized. Midblock association forms a shear-thinning network, while endblock aggregation at elevated temperatures introduces a second, independent physical network into the protein hydrogel. These reversible crosslinks introduce extremely long relaxation times and lead to a five-fold increase in the elastic modulus, significantly larger than is expected from transient network theory. Thermoresponsive reinforcement reduces the high temperature creep compliance by over four orders of magnitude, decreases the erosion rate by at least a factor of five, and increases the yield stress by up to a factor of seven. Combined with the demonstrated potential of shear thinning artificial protein hydrogels for various uses, this reinforcement mechanism broadens the range of applications that can be addressed with shear-thinning physical gels

Effect of polymer chemistry on globular protein–polymer block copolymer self-assembly

Bioconjugates of the model red fluorescent protein mCherry and synthetic polymer blocks with different hydrogen bonding functionalities show that the chemistry of the polymer block has a large effect on both ordering transitions and the type of nanostructures formed during bioconjugate self-assembly. The phase behaviours of mCherry-b-poly(hydroxypropyl acrylate) (PHPA) and mCherry-b-poly(oligoethylene glycol acrylate) (POEGA) in concentrated aqueous solution show that changes in polymer chemistry result in increase in the order–disorder transition concentrations (C[subscript ODT]s) by approximately 10–15 wt% compared to a previously studied globular protein–polymer block copolymer, mCherry-b-poly(N-isopropylacrylamide) (PNIPAM). The C[subscript ODT]s are always minimized for symmetric bioconjugates, consistent with the importance of protein–polymer interactions in self-assembly. Both mCherry-b-PHPA and mCherry-b-POEGA also form phases that have not previously been observed in other globular protein–polymer conjugates: mCherry-b-PHPA forms a cubic phase that can be indexed to Ia[bar over 3]d and mCherry-b-POEGA displays coexistence of lamellae and a cubic Ia[bar over 3]d structure over a narrow range of concentration and temperature. Several common behaviours are also revealed by comparison of different polymer blocks. With increasing concentration and temperature, ordered phases always appear in the order lamellar, cubic/PL, and hexagonal, although not all phases are observed in all materials. High concentration solutions (near 80 wt%) also undergo a re-entrant order–disorder transition to form nematic liquid crystalline phases, regardless of the polymer block chemistry.United States. Air Force Office of Scientific Research (Award FA9550-12-0259)United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0007106

Tripartite entanglement and threshold properties of coupled intracavity downconversion and sum-frequency generation

The process of cascaded downconversion and sum-frequency generation inside an optical cavity has been predicted to be a potential source of three-mode continuous-variable entanglement. When the cavity is pumped by two fields, the threshold properties have been analysed, showing that these are more complicated than in well-known processes such as optical parametric oscillation. When there is only a single pumping field, the entanglement properties have been calculated using a linearised fluctuation analysis, but without any consideration of the threshold properties or critical operating points of the system. In this work we extend this analysis to demonstrate that the singly pumped system demonstrates a rich range of threshold behaviour when quantisation of the pump field is taken into account and that asymmetric polychromatic entanglement is available over a wide range of operational parameters.Comment: 24 pages, 15 figure