Research

The complexed interactions among different components of water borne coatings are studied.

Water pores/channels form inside lipid bilayers and are one of the important processes for many biological phenomena. We are trying to explain the formation of water pores inside lipid bilayers from molecular level using a combination of modeling and computer simulation.

Using coarse-grained molecular dynamic simulations based on the MARTINI force field, we study the self-assembly of free dipalmitoylphosphatidylcholine (DPPC) lipids onto PEGylated lipids tethered to a solid substrate. We show that upon increasing lipid concentration, structural transitions occur from tethered spherical nanoparticles, to tethered cylinders and bicelles, to a tethered lipid bilayer with pores, to an unporated tethered lipid bilayer, and finally to a tethered lipid bilayer with liposomes on top of it. The simulation results compare well with structures inferred from experimental observations. In addition, we also demonstrate the structural stability and local fluidity of the tethered lipid bilayer.

We systematically studied the influence of different design parameters of a spherical nanoparticle tethered with monovalent ligands on its efficiency of targeting planar cell surfaces containing mobile receptors. We investigate how the nanoparticle affinity can be affected by changing the binding energy, the percent of functionalization by ligands, tether length, grafting density, and nanoparticle core size. We also discuss the selectivity of nanoparticle targeting of cells with a high receptor density.

We analyze the efficiency in targeting mobile receptors on cell surfaces by nanoparticles carrying multivalent (divalent, tetravalent) ligands. We identify a few cases when using multivalent ligands innanoparticle targeting can be beneficial, especially for a high binding energy of ligand-receptor interactions and large receptor densities. We demonstrate that for nanoparticles with longer tether length or larger core size, using multivalent ligands becomes favorable. We also show that multivalent ligands can enhance the selectivity of nanoparticletargeting by increasing the nanoparticles affinity to cells with a high density of mobile receptors.

Selectivity of interactions between nanoparticles functionalized by tethered ligands and cell surfaces with different densities of receptors plays an essential role in biorecognition and its implementation in nanobiomedicine. We show that the onset of nanoparticle adsorption has a universal character for a range of nanoparticles: the onset receptor density decreases exponentially with the energy of ligand-receptor binding and inversely with the ligand density. We demonstrate that a bimodal tether distribution, which permits shielding ligands by longer nonfunctional tethers, leads to extra loss of entropy at the adsorption onset, enhancing the selectivity.

We studied how the polydispersity of the chains influences the targeting affinity and selectivity o nanoparticles.

Formation of reversible metallo-supramolecular networks based on 3 : 1 ligand–metal complexes between end-functionalized oligomers and metal ions was studied. The formation of different ligand-metal complexes was investigated. The average molecular weight and molecular weight distribution were calculated. The formation of gel under critical condition was identified and the gel properties, i.e., mesh size, plateau modulus, were calculated.

We studied the effect of cis-trans isomerization of 2:1 ligand–metal complexes on self-assembly and network formation of metallo-supramolecular polymersin a good solvent. We show that trans-cis isomerization of ligand-metal complexes can significantly increase the average molecular weight as well as trigger formation of reversible metallosupramolecular network based on 3:1 ligand-metal complexes acting as cross-linkers. We predict conditions when trans- to cis- isomerization can trigger the sol-network transition and/or result in a significant change in materials properties, such as molecular weight and especially elastic plateau modulus. We discuss the molecular mechanisms of network transformation upon cis-trans isomerization, which vary with metal-to-oligomer ratio and originate from different morphologies of the reversible network.

We show that the equilibrium properties of metallo-supramolecular micelles are determined by the competition of 2:1 and 1:1 metal–ligand complexation in the bulk and on the surface as well as steric interactions between the neighboring corona blocks attached to the surface. We predict that by increasing the association energy for the second metal–ligand bond, or decreasing the corona block length one can achieve a larger core surface coverage for metallo-supramolecular micelles. Compared to covalently bonded block copolymer micelles, we show that metallo-supramolecular micelles have smaller monomer and end group density, especially in the vicinity of the core, which may lead to experimentally observed aggregation.

Polymer micelles with two different core-forming blocks, poly(D,L -lactide) (PLA) and poly(ε-caprolactone) (PCL), but the same coronal material, poly(ethylene glycol) (PEG), were investigated in this study as nanoscopic drug carriers. The release of two different drugs, doxorubicin (DOX) and β-lapachone (β-lap), from PEG(5k)-b-PCL(5k) and PEG(5k)-b-PLA(5k) micelles was studied at pH 5.0 and 7.4. Mathematical solutions of both Higuchi’s model and Fickian diffusion equations were utilized to elucidate the differences between the micelle core materials for the two drugs.