Molecular structure of agarose chains in thermoreversible hydrogels revealed by means of a fluorescent probe technique

Structure and properties of cholesterol-based hydrogelators with varying hydrophilic terminals: biocompatibility and development of antibacterial soft nanocomposites

The present work demonstrates a rational designing and synthesis of cholesterol-based amino acid containing hydrogelators with the aim to improve the biocompatibility of these amphiphilic molecules. A thorough structure-property correlation of these hydrogelators was carried out by varying the hydrophilic terminal from a neutral amine to a quaternized ammonium chloride. The amphiphiles having a cationic polar head as the hydrophilic domain and cholesterol as the hydrophobic unit showed better water gelation efficiency (minimum gelation concentration (MGC) ∼0.9-3.1%, w/v) than the analogous free amines. Presumably, the additional ionic interactions for the quaternized amphiphiles might have played the crucial role in gelation as counterions also got involved in hydrogen bonding with solvent molecules. Hence, the attainment of desired hydrophilic-lipophilic balance (HLB) of hydrophobic cholesterol in combination with the appropriate hydrophilic terminal led to the development of efficient hydrogels. Microscopic investigations revealed the formation of various supramolecular morphologies of hydrogels due to the variation in the molecular structure of the amphiphile. Spectroscopic investigations showed the involvement of hydrogen-bonding, hydrophobic, and π-π interactions in the self-assembled gelation. Importantly, biocompatibility of all the cholesterol-based hydrogelators tested against human hepatic cancer derived HepG2 cells showed increased cell viability than the previously reported alkyl-chain-based amphiphilic hydrogelators. In order to incorporate broad spectrum antibacterial properties, silver nanoparticles (AgNPs) were synthesized in situ within the hydrogels using sunlight. The amphiphile-AgNP soft nanocomposite exhibited notable bactericidal property against both gram-positive and gram-negative bacteria.

Films of agarose enable rapid formation of giant liposomes in solutions of physiologic ionic strength

This paper describes a method to form giant liposomes in solutions of physiologic ionic strength, such as phosphate buffered saline (PBS) or 150 mM KCl. Formation of these cell-sized liposomes proceeded from hybrid films of partially dried agarose and lipids. Hydrating the films of agarose and lipids in aqueous salt solutions resulted in swelling and partial dissolution of the hybrid films and in concomitant rapid formation of giant liposomes in high yield. This method did not require the presence of an electric field or specialized lipids; it generated giant liposomes from pure phosphatidylcholine lipids or from lipid mixtures that contained cholesterol or negatively charged lipids. Hybrid films of agarose and lipids even enabled the formation of giant liposomes in PBS from lipid compositions that are typically problematic for liposome formation, such as pure phosphatidylserine, pure phosphatidylglycerol, and asolectin. This paper discusses biophysical aspects of the formation of giant liposomes from hybrid films of agarose and lipids in comparison to established methods and shows that gentle hydration of hybrid films of agarose and lipids is a simple, rapid, and reproducible procedure to generate giant liposomes of various lipid compositions in solutions of physiologic ionic strength without the need for specialized equipment.

Contact electrochemical replication of hydrophilic-hydrophobic monolayer patterns

Contact electrochemical replication (CER) is a novel pattern replication methodology advanced in this laboratory that offers the unprecedented capability of direct one-step reproduction of monolayer surface patterns consisting of hydrophilic domains surrounded by a hydrophobic monolayer background (hydrophilic @ hydrophobic monolayer patterns), regardless of how the initial "master" pattern was created. CER is based on the direct electrochemical transfer of information, through aqueous electrolyte bridges acting as an information transfer medium, between two organosilane monolayers self-assembled on smooth silicon wafer surfaces. Upon the application of an appropriate voltage bias between a patterned monolayer/silicon specimen playing the role of "stamp" and a monolayer/silicon specimen playing the role of "target", the hydrophilic features of the stamp are copied onto the hydrophobic surface of the target. It is shown that this electrochemical printing process may be implemented under a variety of experimental configurations conducive to the formation of nanometric electrolyte bridges between stamp and target; however, using plain liquid water for this purpose is, in general, not satisfactory because of the high surface tension, volatility, and incompressibility of water. High-fidelity replication of monolayer patterns with variable size of hydrophilic features was achieved by replacing water with a sponge-like hydrogel that is nonvolatile, compressible, and binds specifically to the hydrophilic features of such patterns. Since any copy resulting from the CER process can equally perform as stamp in a subsequent CER step, this methodology offers the rather unique option of multiple parallel reproduction of an initially fabricated master pattern.