Vignesh Muthuvijayan

A novel method of preparing chitosan gels using in situ generated negatively-charged colloidal salts of a variety of metal ions is described. Their potential as scaffolds for tissue-engineering and as recoverable catalysts in aza-Michael addition is demonstrated here. Given their wide range of properties, they have broad scope for applications.

Poor haemocompatibility of material surfaces is a serious limitation that can lead to failure of blood-contacting devices and implants. In this work, we have improved the haemocompatibility of polyethylene terephthalate (PET) surfaces by immobilizing apyrase/ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) on to the carboxylated PET. NTPDase immobilized PET surfaces scavenge the ADP released by activated platelets, which prevents further platelet activation and aggregation. The surface properties of the modified PET were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDAX), and contact angle measurement. The enzyme attachment and stability on the modified PET surfaces were evaluated. The kinetics of free enzyme and immobilized enzyme were studied and fitted using the Michaelis-Menten kinetic model. Both free and immobilized NTPDase followed Michaelis-Menten kinetics with similar Michaelis-Menten constants (K m ). This suggests that the activity of NTPDase was unchanged upon immobilization. Protein adsorption and %hemolysis was significantly reduced for carboxylated PET and NTPDase immobilized PET surfaces compared to unmodified PET. Lactate dehydrogenase assay showed that the number of adhered platelets reduced by more than an order of magnitude for the NTPDase immobilized PET surface compared to unmodified PET. These results clearly indicate that NTPDase immobilization significantly enhances the haemocompatibility of PET surfaces.

Fluorophores are used for sensing biologically relevant ions, toxic metals or pathogenic markers. However, the mode of entry of such fluorophores into the cell greatly depends on their size, shape, surface charge, functional groups, and hydrophobicity. In particular, the influence of hydrophobicity on the intracellular uptake of fluorophores is poorly investigated. Self-assembly is a recent strategy to tune the intracellular uptake of fluorophores, facilitating increased intracellular sensing and fluorescence. Herein, self-assembly of three novel poly(aryl ether) dendron derivatives that contain rhodamine units was used to investigate the effect of hydrophobicity on the intracellular uptake of self-assembled fluorophores. The results suggest that monomer hydrophobicity plays an important role in the uptake. The dendron-based fluorophores, which upon self-assembly, formed stable spherical aggregates ranging from 300 to 500 nm. The rhodamine-based dendrons could selectively sense Hg 2+ ions in the presence of other competing metal cations. Intracellular imaging of the dendron-based fluorophores displayed bright red fluorescence in human embryonic kidney cells. The rate of intracellular uptake of the three dendron-based fluorophores was analyzed by flow cytometry. The results establish the importance of the hydrophilic-lipophilic balance of the self-assembled amphiphiles for tuning the intracellular uptake.

The increased threat of bacterial resistance against conventional antibiotics has warranted the need for development of membrane targeting antibacterial agents. Several self-assembled cationic amphiphiles with different supramolecular structures have been reported in recent years for potent antibacterial activity with increased specificity. In this study, we describe the self-assembly and antibacterial activity of four lower generation poly(aryl ether)-based amphiphilic dendrimers (AD-1, AD-2, AD-3, and AD-4) containing terminal amine (PAMAM-based), ester, and hydrazide functional groups with varied hydrophobicity. Among the four dendrimers under study, the amine-terminated dendrimer (AD-1) displayed potent antibacterial activity. The ratio of surface cationic charge to hydrophobicity had a significant effect on the antibacterial activity, where AD-3 dendrimer with increased surface cationic charges exhibited a higher minimum inhibitory concentration (MIC) than AD-1. AD-2 (ester terminated) and AD-4 (hydrazide terminated) dendrimers did not show any bactericidal activity. The amphiphilic dendrimer-bacteria interactions, further validated by binding studies, also showed significant changes in bacterial morphology, effective membrane permeation, and depolarization by AD-1 in comparison with AD-3. Molecular dynamics simulations of AD-1 and AD-3 on bacterial membrane patches further corroborated the experimental findings. The structural conformation of AD-1 dendrimer facilitated increased membrane interaction compared to AD-3 dendrimer. AD-1 also displayed selectivity to bacterial membranes over fibroblast cells (4× MIC), corroborating the significance of an optimal hydrophobicity for potent antibacterial activity with no cytotoxicity. The self-assembled (poly(aryl ether)-PAMAM-based) dendrimer (AD-1) also exhibited potent antibacterial activity in comparison with conventional higher generation dendrimers, establishing the implication of self-assembly for bactericidal activity. Moreover, the detailed mechanistic study reveals that optimal tuning of the hydrophobicity of amphiphilic dendrimers plays a crucial role in membrane disruption of bacteria. We believe that this study will provide valuable insights into the design strategies of amphiphilic dendrimers as antibacterial agents for efficient membrane disruption.

The authors regret not including the following statement in the original paper. Kindly include the following text: “CONFIDENTIAL - PATENT PENDING - <201741017579>” The authors would like to apologise for any inconvenience caused.

This study explores the potential of gallic acid incorporated chitosan (CS/GA) 3D scaffolds for tissue engineering applications. Scaffolds were prepared by freezing and lyophilization technique and characterized. FTIR spectra confirmed the presence of GA in chitosan (CS) gel. DSC and TGA analysis revealed that the structure of chitosan was not altered due to the incorporation of GA, but thermal stability was significantly increased compared to the CS scaffold. SEM micrographs showed smooth, homogeneous, and microporous architecture of the scaffolds with good interconnectivity. CS/GA scaffolds exhibited approximately 90% porosity on average, increased swelling (600-900%) and controlled biodegradation (15-40%) in PBS (pH 7.4 at 37°C) with 1 mg/mL of lysozyme. CS/GA scaffolds showed 2-4 fold decrease in CFUs (p < 0.05) for both gram positive and gram negative bacteria compared to the CS scaffold. Cytotoxicity of these scaffolds was evaluated using NIH 3T3 L1 fibroblast cells. CS/GA 0.25% scaffold showed similar viability with CS scaffold at 24 and 48 h. CS/GA scaffolds (0.5-1.0%) showed 60-75% viability at 24 h and 90% at 48 h. SEM images showed that an increased cell attachment was observed for CS/GA scaffolds compared to CS scaffolds. These findings authenticate that CS/GA scaffolds were cytocompatible and would be useful for tissue engineering applications.

A single step method for encapsulation of clinically relevant proteins viz., Bovine Serum Albumin (BSA), Lysozyme and Insulin molecules, inside core-sheath structured polymer fibres using coaxial electrospinning technique, is described. Transmission electron microscopic pictures show the formation of core-sheath structure. The secondary structure of the proteins was characterized through CD spectroscopy. The secondary conformation was retained with a minor decrease in β-conformation and an increase in the random and turn conformations after coaxial electrospinning. This method of encapsulation is simple and requires little or no harsh treatment of sensitive biomolecules like insulin. Thus, the core-sheath structure of the fibres might apparently help protect the biomolecules during and after electrospinning, in addition to providing a high interactive surface area for controlled release. This scheme will be suitable for applications in cell culture and tissue regeneration. © 2013 American Scientific Publishers, All rights reserved.

Herein, we describe the design, synthesis and drug release kinetics of a low molecular weight gel based on an aryl ether dendron, under in vitro conditions. The first generation dendron self-assembles and forms gels, resulting in a robust three-dimensional fibrous network, to facilitate controlled release of molecules. While aryl ether dendrons are known for their enhanced self-assembling propensity, these systems have not been used for drug release studies. The self-assembled system was characterized using SEM, TEM, rheology and PXRD experiments. In vitro cytotoxicity of the dendron gel was studied and the results show that the dendron gel is biocompatible. The effect of gel leaching and the exposure time on NIH/3T3 cells is also studied. Further, the gel based on poly aryl ether dendron derivative (D1) is capable of entrapping model hydrophilic dyes and a local anaesthetic drug (prilocaine hydrochloride), where the D1 gel could effectively entrap about 1.5 mg of prilocaine hydrochloride per 5 mg of gelator. The in vitro drug release suggests that the release kinetics is inversely proportional to the gelator wt%, and the lowest release rate obtained is 1.75 min-n with 0.7 gelator wt%. The release profiles of prilocaine hydrochloride are fitted with the Peppas-Korsmeyer model, and the results depict a non-Fickian diffusion mechanism. These studies indicate that the poly aryl ether dendron based gel shows desirable characteristics and also displays promising possibilities of expanding dendron based drug delivery systems for transdermal applications.

Bacterial infection and biofilm formation are serious concerns in the wound healing process and with biomedical implants and devices. Different methods for engineering of surfaces have been studied over the years to mitigate biofilm formation. The major factors controlling biofilm formation are environmental, material, and bacterial properties. Out of these, engineering of the material surface is the most viable option for improving the antibacterial activity and controlling implant-related biofilm infections. These surface engineering strategies focus on altering physicochemical properties of the material surface, developing antiadhesive surfaces, coating with bioactive organic and inorganic molecules, and adding antimicrobial moieties to inhibit bacterial adhesion or express bacteriostatic or bactericidal effects. This chapter discusses the mechanism of biofilm formation and the surface engineering approaches applied to prevent biofilms.