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In this work, chitosan nanoparticles were prepared by ionotropic gelation of chitosan with tripolyphosphate (TPP). The effects of the ionic strength of the solvent employed in the particle preparation on the average size and compactness of the particles were investigated. In addition, the effects of the chitosan concentration and the crosslinker to polymer ratio on the particle characteristics were studied. The chitosan-TPP nanoparticles were characterized by dynamic light scattering, zeta potential, and turbidity measurements. The compactness of the nanoparticles was estimated with a method based on the size of the nanoparticles and the turbidity of the nanoparticle suspension. All the investigated preparation parameters, i.e., the ionic strength of the solvent, the chitosan concentration, and the TPP to chitosan ratio, affected the particle characteristics. For instance, smaller and more compact particles were formed in saline solvents, compared to particles formed in pure water. Further, the addition of monovalent salt rendered it possible to prepare particles in the nanometer size range at a higher polymer concentration. Solvent salinity is thus an important parameter to address in the preparation of chitosan nanoparticles crosslinked with TPP.

The evolution of viscoelasticity during the gelation reactions of semidilute solutions of poly(vinyl alcohol) (PVA) in the presence of cross-linker (glutaraldehyde) has been monitored through the sol−gel transition with dynamic mechanical experiments. The gelation time of the system decreased with increasing PVA and cross-linker concentrations. At the gel point, a power law frequency dependence of the dynamic storage modulus (G‘ ∝ ω n ‘) and loss modulus (G‘‘ ∝ ω n ‘‘) was observed with n‘ = n‘‘ = n. The power law exponent is lower than that predicted (0.7) from the percolation model. The value of n decreases with increasing polymer and cross-linker concentrations. The critical gel strength parameter (S) rises with increasing polymer and cross-linker concentrations. Some stress relaxation measurements on gelling PVA systems were also carried out. At the gel point, a power law time dependence of the relaxation modulus was detected, but the relaxation exponent was lower than the corresponding one obtained from oscillatory shear measurements. The fractal dimension (d f) was determined for the incipient PVA gels. The value of d f increased with increasing polymer concentration and cross-linking density. This trend of d f suggests a more “tight” structure of the network at higher polymer concentrations and cross-linking densities.

amount of cross-linked solid. According to the nature of solvents, gels are categorized into hydrogel and organogel to indicate whether the solvent is water or organic solvent(s), respectively. As to the gelation driving forces, gels can be classified into physical gels in which intermolecular interactions are responsible for gel formation, and chemical gels in which the gel skeleton is cross-linked by covalent bonds.Incorporation of metal components (metal ions, metal-organic molecules, and metal nanoparticles) is an effective way to locally establish extra interactions among the building blocks and consequently trigger gel formation, [2][3][4] weaken [5] or enhance [6] gel strength, and modify gel morphology. [7,8] Moreover, addition of metal components is a straightforward way to integrate the specific properties of metals with the properties of organic matrix, therefore to tune properties like conductivity, [9] color, [10,11] rheological behavior, [12] adsorption, [13] emission, [14] photophysical properties, [15] magnetism, [16,17] antibacterial activities, [18,19] catalytic activities, [20][21][22][23] redox activities, [24,25] and selfhealing properties. [26][27][28] Therefore, a broad response range to physical and chemical stimuli can be achieved. For instance, the incorporation of multivalence ions such as Fe 2+ /Fe 3+ , [25,29] Co 2+ / Co 3+ , [30] Cu + /Cu 2+ , [31] results in redox reactive hydrogels; the incorporation of magnetic nanoparticles like Fe 3 O 4[17] causes the gel to respond to external magnetic fields. In addition to the abovementioned intrinsically functional superiorities, metallogels can also serve as ideal templates to generate new materials, [13,22,23,32,33] such as 3D networks, [34] porous structures, [35] chiral materials, [36][37][38] quantum dots, [39] and nanorods. [40] Following the rapid advancement of exploration on the knowledge acquisition toward the major roles that metallogels are playing in catalysis, sensing, biomedicine, electronics, and optical devices, the focus of research has been transferred to the design principles of metallogels in the last decade. Owing to the advancements in the instrumental characterizations and theoretical calculations, [41] a number of pioneering efforts on metallogel design have been made and several innovative reviews have summarized these inspiring contributions. [32,[42][43][44] Despite their extensively acknowledged application advantages in many fields, the discovery of new metallogels with expected functionalities is still highly dependent on experimental screening and serendipity. The challenge stems from the susceptible balance among those complicated intermolecular interactions and the elaborate structure requirements of metallogels.Another research niche that needs to be clarified before discussing recent development of metallogels is: how to sort Introducing metal components into gel matrices provides an effective strategy to develop soft materials with advantageous properties such as: optical activity, conductivity, magn...

The physical stability of chitosan nanoparticles cross-linked with sodium tripolyphosphate (TPP) was investigated over a period of 1 month. Special emphasis was placed on changes in the particle size and the particle compactness, which are two important physicochemical parameters of nanoparticulate drug delivery systems. The chitosan-TPP particles were prepared at different ionic strengths, chitosan chloride concentrations, and TPP-to-chitosan ratios. In the presence of monovalent salt, the positive ζ potential of the particles was reduced. In spite of this, the particles were more stable when prepared and stored under saline conditions compared to water. This could be attributed to the smaller particle sizes found in the presence of sodium chloride. Most of the particles prepared in saline solvents were stable with respect to changes in the size and the compactness of the particles. However, instability was observed at the highest cross-linker-to-polymer ratios. Generally, a reduction in the ζ potential and an increase in the particle compactness were observed at increasing TPP-to-chitosan ratios. This combined with the size increase induced by a high concentration of chitosan, increased the aggregation and sedimentation tendency of the particles and reduced the colloidal stability of the particles.