Weak Polyelectrolytes as Nanoarchitectonic Design Tools for Functional Materials: A Review of Recent Achievements.

The ionization degree, charge density, and conformation of weak polyelectrolytes can be adjusted through adjusting the pH and ionic strength stimuli. Such polymers thus offer a range of reversible interactions, including electrostatic complexation, H-bonding, and hydrophobic interactions, which position weak polyelectrolytes as key nano-units for the design of dynamic systems with precise structures, compositions, and responses to stimuli. The purpose of this review article is to discuss recent examples of nanoarchitectonic systems and applications that use weak polyelectrolytes as smart components. Surface platforms (electrodeposited films, brushes), multilayers (coatings and capsules), processed polyelectrolyte complexes (gels and membranes), and pharmaceutical vectors from both synthetic or natural-type weak polyelectrolytes are discussed. Finally, the increasing significance of block copolymers with weak polyion blocks is discussed with respect to the design of nanovectors by micellization and film/membrane nanopatterning via phase separation.

Oligomer Sensor Nanoarchitectonics for "Turn-On" Fluorescence Detection of Cholesterol at the Nanomolar Level.

Sensitive and rapid monitoring of cholesterol levels in the human body are highly desirable as they are directly related to the diagnosis of cardiovascular diseases. By using the nanoarchitectonic approach, a novel fluorescent conjugated oligofluorene (OFP-CD) functionalized with ß-cyclodextrin (ß-CD) was assembled for "Turn-On" fluorescence sensing of cholesterol. The appended ß-CD units in OFP-CD enabled the forming of host-guest complexes with dabsyl chloride moieties in water, resulting in fluorescence quenching of the oligofluorene through intermolecular energy transfer. In the presence of cholesterol molecules, a more favorable host-guest complex with stoichiometry 1 cholesterol: 2 ß-CD units was formed, replacing dabsyl chloride in ß-CD's cavities. This process resulted in fluorescence recovery of OFP-CD, owing to disruption of energy transfer. The potential of this nanoarchitectonic system for "Turn-On" sensing of cholesterol was extensively studied by fluorescence spectroscopy. The high selectivity of the sensor for cholesterol was demonstrated using biologically relevant interfering compounds, such as carbohydrates, amino acids, metal ions, and anions. The detection limit (LOD value) was as low as 68 nM, affirming the high sensitivity of the current system.

Recent Developments in Artificial Super-Wettable Surfaces Based on Bioinspired Polymeric Materials for Biomedical Applications.

Inspired by nature, significant research efforts have been made to discover the diverse range of biomaterials for various biomedical applications such as drug development, disease diagnosis, biomedical testing, therapy, etc. Polymers as bioinspired materials with extreme wettable properties, such as superhydrophilic and superhydrophobic surfaces, have received considerable interest in the past due to their multiple applications in anti-fogging, anti-icing, self-cleaning, oil-water separation, biosensing, and effective transportation of water. Apart from the numerous technological applications for extreme wetting and self-cleaning products, recently, super-wettable surfaces based on polymeric materials have also emerged as excellent candidates in studying biological processes. In this review, we systematically illustrate the designing and processing of artificial, super-wettable surfaces by using different polymeric materials for a variety of biomedical applications including tissue engineering, drug/gene delivery, molecular recognition, and diagnosis. Special attention has been paid to applications concerning the identification, control, and analysis of exceedingly small molecular amounts and applications permitting high cell and biomaterial cell screening. Current outlook and future prospects are also provided.

Block Copolymer Derived Vertically Coupled Plasmonic Arrays for Surface-Enhanced Raman Spectroscopy.

A surface-enhanced Raman spectroscopy sensing template consisting of gold-covered nanopillars is developed. The plasmonic slab consists of a perforated gold film at the base of the nanopillars and a Babinet complementary dot array on top of the pillars. The nanopillars were fabricated by the incorporation of an iron salt precursor into a self-assembled block copolymer thin film and subsequent reactive ion etching. The preparation is easy, scalable, and cost-effective. We report on the increase in surface-enhanced Raman scattering efficiency for smaller pillar heights and stronger coupling between the dot array and perforated gold film with average enhancement factors as high as 107. In addition, the block copolymer-derived templates show an excellent relative standard deviation of 8% in the measurement of the Raman intensity. Finite difference time domain simulations were performed to investigate the nature of the electromagnetic near-field enhancement and to identify plasmonic hot spots.

Bioactive supra decorated thiazolidine-4-carboxylic acid derivatives attenuate cellular oxidative stress by enhancing catalase activity.

A pharmacophoric motif decorated with supramolecular functionalities (TZT) was designed for potential interaction with biological targets. Main insights of this work include the correlation of supra functionalities of TZT with its binding ability to proteins leading to the modulation of their structure and bioactivity as a promising perspective in the field of cellular protection from oxidative stress. To investigate the role of TZT in obliterating oxidative stress at a molecular level, its binding propensity with bovine serum albumin (BSA) and bovine liver catalase (BLC) was characterized using various biophysical methods. The binding constants of TZT with BSA (Kb = 2.09 × 105 M-1) and BLC (Kb = 2.349 × 105 M-1) indicate its considerable interaction with these proteins. TZT efficiently triggers favourable structural changes in BLC, thereby enhancing its enzyme activity in a dose dependent manner. The enzyme kinetics parameters of TZT binding to BLC were quantified using the Michaelis-Menten model. Both in silico and experimental results suggest that an increased substrate availability could be the reason for enhanced BLC activity. Furthermore, physiological relevance of this interaction was demonstrated by investigating the ability of TZT to attenuate oxidative stress. Treatment with TZT was found to mitigate the inhibition of A549 cell proliferation in the presence of high concentrations of vitamin C. This finding was confirmed at a molecular level by PARP cleavage status, demonstrating that TZT inhibits apoptotic cell death induced by oxidative stress.

Carbon fiber doped thermosetting elastomer for flexible sensors: physical properties and microfabrication.

We have developed conductive microstructures using micropatternable and conductive hybrid nanocomposite polymer. In this method carbon fibers (CFs) were blended into polydimethylsiloxane (PDMS). Electrical conductivities of different compositions were investigated with various fiber lengths (50-250 µm), and weight percentages (wt%) (10-60 wt%). Sample composites of 2 cm × 1 cm × 500 µm were fabricated for 4-point probe conductivity measurements. The measured percolation thresholds varied with length of the fibers: 50 wt% (307.7 S/m) for 50 µm, 40 wt% (851.1 S/m) for 150 µm, and 30 wt% (769.23 S/m) for 250 µm fibers. The conductive composites showed higher elastic modulus when compared to that of PDMS.

An organoferroelasticity driven by molecular conformational change.

A single crystal of adipic acid shows twinning ferroelasticity by the reversible molecular conformational change. The flexible nature of components in molecular solids raises the efficiency of energy dissipation using organoferroelasticity.

Enhancement of dissipated energy by large bending of an organic single crystal undergoing twinning deformation.

We demonstrate exceptional twinning deformation in a molecular crystal upon application of mechanical stress. Crystal integrity is preserved and the deformation is associated with a large bending angle (65.44°). This is a new strategy to increase the magnitude of the dissipated energy in an organic solid comparable to that seen in alloys. By X-ray crystallographic analysis it was determined that a large molecular rearrangement at the twinning interface preserves the crystal integrity. Drastic molecular rearrangement at the twinning interface helps to preserve hydrogen bonding in the molecular rotation, which facilitates the large bending angle. The maximum shear strain of 218.81% and dissipated energy density of 1 MJ m-3 can significantly enhance mechanical damping of vibrations.

Ferroelasticity in an Organic Crystal: A Macroscopic and Molecular Level Study.

Ferroelasticity has been relatively well-studied in mechanically robust inorganic atomic solids but poorly investigated in organic crystals, which are typically inherently fragile. The absence of precise methods for the mechanical analysis of small crystals has, no doubt, impeded research on organic ferroelasticity. The first example of ferroelasticity in an organic molecular crystal of 5-chloro-2-nitroaniline is presented, with thorough characterization by macro- and microscopic methods. The observed cyclic stress-strain curve satisfies the requirements of ferroelasticity. Single-crystal X-ray structure analysis provides insight into lattice correspondence at the twining interface, which enables substantial crystal bending by a large molecular orientational shift. This deformation represents the highest maximum strain (115.9 %) among reported twinning materials, and the associated dissipated energy density of 216 kJ m-3 is relatively large, which suggests that this material is potentially useful as a mechanical damping agent.

Development of Hierarchical Polymer@Pd Nanowire-Network: Synthesis and Application as Highly Active Recyclable Catalyst and Printable Conductive Ink.

A facile one-pot approach for preparing hierarchical nanowire-networks of hollow polymer@Pd nanospheres is reported. First, polymer@Pd hollow nanospheres were produced through metal-complexation-induced phase separation with functionalized graft copolymers and subsequent self-assembly of PdNPs. The nanospheres hierarchically assembled into the nanowire-network upon drying. The Pd nanowire-network served as an active catalyst for Mizoroki-Heck and Suzuki-Miyaura coupling reactions. As low as 500 µmol % Pd was sufficient for quantitative reactions, and the origin of the high activity is ascribed to the highly active sites originating from high-index facets, kinks, and coalesced structures. The catalyst can be recycled via simple filtration and washing, maintaining its high activity owing to the micrometer-sized hierarchical structure of the nanomaterial. The polymer@Pd nanosphere also served as a printable conductive ink for a translucent grid pattern with excellent horizontal conductivity (7.5×10(5) S m(-1)).