Yuri S Velichko

Northwestern University, Evanston, IL, United States

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Publications (16)121.74 Total impact

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    ABSTRACT: Self-assembling peptide amphiphiles (PAs) can form hierarchically ordered membranes when brought in contact with aqueous polyelectrolytes of the opposite charge by rapidly creating a diffusion barrier composed of filamentous nanostructures parallel to the plane of the incipient membrane. Following this event, osmotic forces and charge complexation template nanofiber growth perpendicular to the plane of the membrane in a dynamic self-assembly process. In this work, we show that this hierarchical structure requires massive interfacial aggregation of PA molecules, suggesting the importance of rapid diffusion barrier formation. Strong PA aggregation is induced here through the use of heparin-binding PAs with heparin and also with polyelectrolytes of varying charge density. Small angle X-ray scattering shows that in the case of weak PA-polyelectrolyte interaction, membranes formed display a cubic phase ordering on the nanoscale that likely results from clusters of PA nanostructures surrounded by polyelectrolyte chains.
    Small 09/2013; · 7.82 Impact Factor
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    ABSTRACT: When 3D peptide amphiphile assemblies with flat and cylindrical morphologies are used as templates for mineralization, the nanoscale architecture is found to play a significant role in orienting hydroxyapatite in a bone-like fashion. Cylindrical nanostructures facilitate mineral orientation parallel to the long axis of the 1D assembly while flatter, ribbonlike architectures nucleate randomly oriented mineral. Macroscopically aligned constructs of the cylindrical nanostructures further demonstrate the ability to orient hydroxyapatite across length scales. This work by S. I. Stupp and co-workers emphasizes the importance of template morphology.
    Small 07/2012; 8(14):2194. · 7.82 Impact Factor
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    ABSTRACT: Self-assembly in the presence of external forces is an adaptive, directed organization of molecular components under nonequilibrium conditions. While forces may be generated as a result of spontaneous interactions among components of a system, intervention with external forces can significantly alter the final outcome of self-assembly. Superimposing these intrinsic and extrinsic forces provides greater degrees of freedom to control the structure and function of self-assembling materials. In this work we investigate the role of electric fields during the dynamic self-assembly of a negatively charged polyelectrolyte and a positively charged peptide amphiphile in water leading to the formation of an ordered membrane. In the absence of electric fields, contact between the two solutions of oppositely charged molecules triggers the growth of closed membranes with vertically oriented fibrils that encapsulate the polyelectrolyte solution. This process of self-assembly is intrinsically driven by excess osmotic pressure of counterions, and the electric field is found to modify the kinetics of membrane formation, and also its morphology and properties. Depending on the strength and orientation of the field we observe a significant increase or decrease of up to nearly 100% in membrane thickness, as well as the controlled rotation of nanofiber growth direction by 90 degrees, resulting in a significant increase in mechanical stiffness. These results suggest the possibility of using electric fields to control structure in self-assembly processes involving diffusion of oppositely charged molecules.
    Advanced Functional Materials 01/2012; 22(2):369-377. · 10.44 Impact Factor
  • Advanced Functional Materials 01/2012; 22(2). · 10.44 Impact Factor
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    ABSTRACT: Membranes formed by mixing high molecular weight hyluronic acid (HA) and oppositely charged peptide amphiphiles (PAs) have been shown to have a unique hierarchically ordered structure which consists of three regions: an amorphous biopolymer layer, a narrow region of PA fibers parallel to the interface and a layer of fibers perpendicular to the interface. Understanding of the structure-property relationships in these self-assembling systems is a necessary step in designing these structures for specific applications. We have formed and characterized PA/polymer self-assembled membranes using different polyelectrolytes (alginate, lambda-carrageenan, poly(acrylic acid) etc). SEM micrographs show that these assemblies have the same parallel/perpendicular fibers structure as the original HA/PA assembly. The mechanical properties and water permeability of these structures measured by membrane inflation techniques and osmotic swelling indicate that the polymer characteristics [i.e. Mw, charge density] are an important factor in determining structure formation, kinetics and final properties.
    03/2010;
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    ABSTRACT: The mechanical properties and water permeability of hierarchical self-assembling membranes and sacs formed from oppositely charged high molecular weight hyaluronic acid (HA) and small molecule peptideamphiphiles (PAs) were studied. Techniques to make reproducible 2D planar membranes and 3D spherical sacs from these materials were developed while membrane inflation and osmotic swelling were used to quantify the mechanical properties and water permeability of these structures. It was found that incubation time and concentration of HA used had an effect on the area modulus and water permeability of the membranes. These factors also affected the kinetics of membranegrowth as evidenced in SEM micrographs, which showed differences in the structure. Area modulus of membranes changed from about 6 N m−1 for the lower weight percent HA system at the shortest incubation time of 3 minutes, up to 12 N m−1 for the higher weight percent HA system at the longest incubation time of 60 minutes. Water permeability decreased with incubation time, but the lower weight percent HA system showed a lower water permeability when compared to the higher weight percent HA system at the same incubation time. This type of characterization and understanding of the structure–property relationships in self-assembling systems are necessary steps in both using these structures for specific applications and applying this knowledge to design new and better materials in the future.
    Soft Matter 01/2010; 6(8). · 4.15 Impact Factor
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    ABSTRACT: We report here crystallization at long range in networks of like-charge supramolecular peptide filaments mediated by repulsive forces. The crystallization is spontaneous beyond a given concentration of the molecules that form the filaments but can be triggered by x-rays at lower concentrations. The crystalline domains formed by x-ray irradiation, with interfilament separations of up to 320 angstroms, can be stable for hours after the beam is turned off, and ions that screen charges on the filaments suppress ordering. We hypothesize that the stability of crystalline domains emerges from a balance of repulsive tensions linked to native or x-ray-induced charges and the mechanical compressive entrapment of filaments within a network. Similar phenomena may occur naturally in the cytoskeleton of cells and, if induced externally in biological or artificial systems, lead to possible biomedical and lithographic functions.
    Science 12/2009; 327(5965):555-9. · 31.20 Impact Factor
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    ABSTRACT: We investigate the formation of charged patterns on the surface of cylindrical micelles from co-assembled cationic and anionic amphiphiles. The competition between the net incompatibility chi (which arises from the different chemical nature of oppositely charged molecules) and electrostatic interactions (which prevent macroscopic segregation) results in the formation of surface domains. We employ Monte Carlo simulations to study the domains at thermal equilibrium. Our results extend previous work by studying the effect of the Bjerrum length l(B) at different values of the cylinder's radius R and chi and analyze how it affects the transition between helical, ring, and isotropic patterns. A critical surface in the space (l(B), R, chi) separating these three phases is found, and we show how it corresponds to a first-order phase transition. This confirms that the Bjerrum length l(B) is a significant parameter in the control of the helical-ring transition; the ring pattern is strongly associated with short-range forces, whereas the helical pattern develops from dominant long-range electrostatic interactions.
    The Journal of Physical Chemistry B 06/2008; 112(17):5423-7. · 3.61 Impact Factor
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    ABSTRACT: We study ion condensation on a patterned surface with stripes of alternating charge. The competition between adsorbed ion-ion and adsorbed ion-surface interactions leads to the formation of different strongly correlated structures of condensed ions in the low-temperature limit (LTL). We consider two types of arrangements which have lowest energy in the LTL: (1) ions adsorbed onto the stripe center lines and (2) arrays of dipoles at the interfaces between charged domains. We determine the preferred arrangement as a function of surface charge density, the chemical potential of the ions in the surrounding medium, and the geometric parameters of the system. We determine the conditions for the appearance of more complex ionic patterns by considering simple perturbations of the stripe-centered and dipolar array structures.
    The Journal of Chemical Physics 05/2008; 128(14):144706. · 3.12 Impact Factor
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    ABSTRACT: We report here the self-assembly of macroscopic sacs and membranes at the interface between two aqueous solutions, one containing a megadalton polymer and the other, small self-assembling molecules bearing opposite charge. The resulting structures have a highly ordered architecture in which nanofiber bundles align and reorient by nearly 90 degrees as the membrane grows. The formation of a diffusion barrier upon contact between the two liquids prevents their chaotic mixing. We hypothesize that growth of the membrane is then driven by a dynamic synergy between osmotic pressure of ions and static self-assembly. These robust, self-sealing macroscopic structures offer opportunities in many areas, including the formation of privileged environments for cells, immune barriers, new biological assays, and self-assembly of ordered thick membranes for diverse applications.
    Science 04/2008; 319(5871):1812-6. · 31.20 Impact Factor
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    ABSTRACT: We study the self-assembly of peptide amphiphile (PA) molecules, which is governed by hydrophobic interactions between alkyl tails and a network of hydrogen bonds between peptide blocks. We demonstrate that the interplay between these two interactions results in the formation of assemblies of different morphology, in particular, single beta-sheets connected laterally by hydrogen bonds, stacks of parallel beta-sheets, spherical micelles, micelles with beta-sheets in the corona, and long cylindrical fibers. We characterize the size distribution of the aggregates as a function of the molecular interactions. Our results suggest that the formation of nanofibers of peptide amphiphiles obeys an open association model, which resembles living polymerization.
    The Journal of Physical Chemistry B 03/2008; 112(8):2326-34. · 3.61 Impact Factor
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    ABSTRACT: Small-molecule self-assembly has proven to be a rich field for the controlled synthesis of supramolecular objects with the size scale of polymers and interesting properties. Using several recent examples from our laboratory, we discuss the development of chemical structure codes for supramolecular self-assembly objects with defined shapes. The resulting materials formed by these objects are promising for electronic functions and biological functions for regenerative medicine.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 07/2007; 365(1855):1417-33. · 2.89 Impact Factor
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    ABSTRACT: We study ion condensation onto a patterned surface of alternating charges. The competition between self-energy and ion-surface interactions leads to the formation of ionic crystalline structures at low temperatures. We consider different arrangements of underlying ionic crystals, including single ion adsorption, as well as the formation of dipoles at the interface between charged domains. Molecular dynamic simulation illustrates existence of single and mixed phases. Our results contribute to understanding pattern recognition, and molecular separation and synthesis near patterned surfaces. Comment: 3 figures
    04/2007;
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    ABSTRACT: We analyze the structure and mechanical properties of self-assembled gels formed by anionic peptide amphiphiles (PA) in the presence of cationic peptides and polyion salt. The PA molecules, which are composed of a hydrophobic alkyl tail, a beta-sheet forming region, and a hydrophilic epitope region, self-assemble into cylindrical micelles in water with multivalent salt. The fibers grow in one dimension by forming an internal beta sheet along the middle segment; the hydrophobic tail hides inside the fiber and the epitope region is exposed on the surface. Rheology and electron microscopy are used to investigate the physical properties of the resulting PA gels. The PA-fibers form a self-supporting gel at a concentration of one weight percent. Our experimental results show a strong dependence on the nature and valency of the polyions. We will present a theoretical model that incorporates both PA self-assembly and gelation of PA-fibers in the presence of polyion salt.
    03/2007;
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    Y S Velichko, M Olvera de la Cruz
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    ABSTRACT: Electrostatics play a key role in biomolecular assembly. Oppositely charged biomolecules, for instance, can be coassembled into functional units, such as DNA and histone proteins into nucleosomes and actin-binding protein complexes into cytoskeleton components, at appropriate ionic conditions. These cationic-anionic coassemblies often have surface charge heterogeneities that result from the delicate balance between electrostatics and packing constraints. Despite their importance, the precise role of surface charge heterogeneities in the organization of cationic-anionic coassemblies is not well understood. We show here that coassemblies with charge heterogeneities strongly interact through polarization of the domains. We find that this leads to symmetry breaking, which is important for functional capabilities, and structural changes, which is crucial in the organization of coassemblies. We determine the range and strength of the attraction as a function of the competition between the steric and hydrophobic constraints and electrostatic interactions.
    The Journal of Chemical Physics 07/2006; 124(21):214705. · 3.12 Impact Factor
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    Y S Velichko, M Olvera de la Cruz
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    ABSTRACT: Charged pattern formation on the surfaces of self-assembled cylindrical micelles formed from oppositely charged heterogeneous molecules such as cationic and anionic peptide amphiphiles is investigated. The net incompatibility chi among different components results in the formation of segregated domains, whose growth is inhibited by electrostatics. The transition to striped phases proceeds through an intermediate structure governed by fluctuations, followed by states with various lamellar orientations, which depend on cylinder radius Rc and chi. We analyze the specific heat, susceptibility S(q*), domain size Lambda = 2pi/q*, and morphology as a function of Rc and chi.
    Physical Review E 11/2005; 72(4 Pt 1):041920. · 2.31 Impact Factor