Jawad Naciri

Interpenetrating networks based on gelatin methacrylamide and PEG formed using concurrent thiol click chemistries for hydrogel tissue engineering scaffolds.

The integration of biological extracellular matrix (ECM) components and synthetic materials is a promising pathway to fabricate the next generation of hydrogel-based tissue scaffolds that more accurately emulate the microscale heterogeneity of natural ECM. We report the development of a bio/synthetic interpenetrating network (BioSINx), containing gelatin methacrylamide (GelMA) polymerized within a poly(ethylene glycol) (PEG) framework to form a mechanically robust network capable of supporting both internal cell encapsulation and surface cell adherence. The covalently crosslinked PEG network was formed by thiol-yne coupling, while the bioactive GelMA was integrated using a concurrent thiol-ene coupling reaction. The physical properties (i.e. swelling, modulus) of BioSINx were compared to both PEG networks with physically-incorporated gelatin (BioSINP) and homogenous hydrogels. BioSINx displayed superior physical properties and significantly lower gelatin dissolution. These benefits led to enhanced cytocompatibility for both cell adhesion and encapsulation; furthermore, the increased physical strength provided for the generation of a micro-engineered tissue scaffold. Endothelial cells showed extensive cytoplasmic spreading and the formation of cellular adhesion sites when cultured onto BioSINx; moreover, both encapsulated and adherent cells showed sustained viability and proliferation.

Anisotropic actuation in electroclinic liquid crystal elastomers

The macroscopic mechanical response of a freestanding, electroclinic liquid crystal elastomer to an applied electric field is described. Contraction strains and shearing were observed upon e-field application when 60-μm-thick elastomer films were tested normal and parallel to smectic layers, respectively. The anisotropic response observed in the two orthogonal directions with respect to the smectic layers correlate calculated from mechanical studies with the induced tilt of the molecules. The electrostrictive and electroclinic coefficients agree well with the values calculated from optical tilt angle measurements.

Fast switching ferroelectric side-chain liquid-crystalline polymer and copolymer

Abstract New ferroelectric side-chain liquid-crystalline polymers, a copolymer and a homopolymer, with siloxane backbone and a triaromatic mesogen as the side group have been synthesized. The materials exhibit a chiral smectic C phase over a large temperature range extending to room temperature. They possess high values of spontaneous polarization: 105 nC cm−2 for the homopolymer and 180 nC cm−2 for the copolymer. The electro-optic switching time in the chiral smectic C phase is extremely fast (150 μs). In the smectic A phase, an electroclinic effect with switching times less than 100 μs and with field induced tilt angles of 18° is observed.

Understanding Charge Transport in Molecular Electronics

Abstract: For molecular electronics to become a viable technology the factors that control charge transport across a metal‐molecule‐metal junction need to be elucidated. We use an experimentally simple crossed‐wire tunnel junction to interrogate how factors such as metal‐molecule coupling, molecular structure, and the choice of metal electrode influence the current‐voltage characteristics of a molecular junction.

Multifunctional Liquid Crystal Nanoparticles for Intracellular Fluorescent Imaging and Drug Delivery

A continuing goal of nanoparticle (NP)-mediated drug delivery (NMDD) is the simultaneous improvement of drug efficacy coupled with tracking of the intracellular fate of the nanoparticle delivery vehicle and its drug cargo. Here, we present a robust multifunctional liquid crystal NP (LCNP)-based delivery system that affords facile intracellular fate tracking coupled with the efficient delivery and modulation of the anticancer therapeutic doxorubicin (Dox), employed here as a model drug cargo. The LCNPs consist of (1) a liquid crystal cross-linking agent, (2) a homologue of the organic chromophore perylene, and (3) a polymerizable surfactant containing a carboxylate headgroup. The NP core provides an environment to both incorporate fluorescent dye for spectrally tuned particle tracking and encapsulation of amphiphilic and/or hydrophobic agents for intracellular delivery. The carboxylate head groups enable conjugation to biologicals to facilitate the cellular uptake of the particles. Upon functionalization of the NPs with transferrin, we show the ability to differentially label the recycling endocytic pathway in HEK 293T/17 cells in a time-resolved manner with minimal cytotoxicity and with superior dye photostability compared to traditional organic fluorophores. Further, when passively loaded with Dox, the NPs mediate the rapid uptake and subsequent sustained release of Dox from within endocytic vesicles. We demonstrate the ability of the LCNPs to simultaneously serve as both an efficient delivery vehicle for Dox as well as a modulator of the drugs cytotoxicity. Specifically, the delivery of Dox as a LCNP conjugate results in a ∼40-fold improvement in its IC50 compared to free Dox in solution. Cumulatively, our results demonstrate the utility of the LCNPs as an effective nanomaterial for simultaneous cellular imaging, tracking, and delivery of drug cargos.

Low transition temperature organosiloxane liquid crystals displaying a de Vries smectic A phase

The synthesis, phase properties and electro-optic response of two new chiral low molar mass organosiloxane liquid crystalline materials are presented. The structure of the molecule contains a short (three silicon atoms) siloxy chain attached via a hydrocarbon chain to the non-chiral end of a chiral mesogenic moiety. The materials have low melting points (< -20°C) and broad smectic phase ranges (≈80°C wide) extending to below room temperature. Both materials are electroclinic at room temperature. A 30° tilt of the optic axis can be achieved in fields of the order of 25 V μ;m -1. The data presented indicate that in these materials the smectic phase is a de Vries-type smectic A phase. The electroclinic effect arises because the electric field produces a bias in the distribution of the direction of the tilt.

Synthesis and photodimerization in self-assembled monolayers of 7-(8-trimethoxysilyloctyloxy)coumarin

We report a synthesis of 7-(8-trimethoxysilyloctyloxy)coumarin that can self-assemble into optically active monolayers on substrates. Atomic force microscopy and UV–vis spectroscopy have been used to characterize the self-assembly processes and photochemical reaction of the coumarin silane on substrates. We also show that when irradiated with linearly polarized UV light, the self-assembled coumarin monolayer can induce a homogeneous alignment of nematic liquid crystals.

Influence of the electric field on the quasibookshelf stripe deformation in an electroclinic liquid crystal

A quantitative study of the effect of electric field on the stripe domains formed by layer deformation in chiral smectic A liquid crystals is presented. X‐ray diffraction studies reveal that the angle between the layer normals in adjacent stripe domains increases with increasing electric field. A simple model is presented to derive the true molecular tilt angle from optical transmission measurements. The relationship between the optical tilt angle and the tilt angle evaluated from x‐ray measurements of the smectic layer thickness indicates that the molecules are tilting as rigid rods.

Tuning the physical properties of a nematic liquid crystal elastomer actuator

In this report we demonstrate the ability to tune the physical properties of a liquid crystal elastomer (LCE) by varying the amount and type of crosslinking within the elastomer network. LCE films composed of a single mesogenic compound were capable of uniaxial contraction when thermally actuated through the nematic to isotropic phase of the material. We probed the physical properties of the LCE films while varying the amount and concentration of two crosslinking agents and measured actuation strains of 10–35%, elastic moduli of 3–14 MPa, and transition temperatures ranging between 75 and 60°C. The viscous losses of the elastomers and the estimated work capable of being produced by the films were also evaluated. The ability to tune the physical properties of the LCE films allows for a wide range of applications including robotics, microelectromechanical systems (MEMS), shape‐changing membranes, and/or microfluidics.

Photo-dimerized monolayer (PDML) versus rubbed polyimide (RPI): a comparison of electro-optic properties

Electro-Optic response characteristics as well as polar anchoring energies of liquid crystal cells prepared using a new photo-alignment technique i.e., photo-dimerized monolayer, have been measured. These data are compared with those for cells that use a rubbed polyimide alignment layer. The two alignment methods yield comparable electro-optic properties showing thereby that the new photo-alignment technique is a viable alternative to the rubbed alignment technique for display applications.