Expanding Chitosan Reticular Chemistry Using Multifunctional and Thermally Stable Phosphorus-Containing Dendrimers

Abstract

Chitosan is an astonishing building block that is extracted from marine crustacean waste, features randomly distributed amino and acetamido groups in its backbone, and can be handled in different forms, giving rise to an impressive diversity of functional nanomaterials. Hitherto, its reticular chemistry, although mandatory to circumvent its main drawback of instability, has been dominated by the use of glutaraldehyde. Unfortunately, the toxicity and inherent chemistry of the latter narrow further development of such cross-linked materials and constitute an impediment for their massive spreading and real implementation, especially in nanomedicine and related healthcare applications. Prompted by the well-established advantages of dendrimers, more distinctively those containing phosphorus in their skeleton, we herein explore the use of second-and third-generation phosphoruscontaining dendrimers as cross-linkers to provide an extended covalent dendritic framework grown inside of the carbohydrate network. The presence of residual amine and aldehyde defects was explored to conjugate other chemicals (viologen-based ionic liquid and aminopropyltriethoxysilane) thereby adding more functional diversity to the assembled framework. We also leveraged on the film-forming ability of chitosan to shape the reticular network as flexible films. Despite the bulkiness of the used phosphorus dendrimers, the film-forming memory of chitosan was preserved, allowing successful preparation of highly functional, transparent, and flexible micrometer-thick bioplastics. The cross-linking seems to delay the half-weight degradation temperature of the plastics, with a significant increase in the char residue and a reduced heat release rate. Ternary objects (Congo red dye and gold nanoparticles) could also be entrapped within the transparent films without leaching or degradation, thereby expanding the usefulness of these transparent coatings as multifunctional sensors, flame retardants, biofoulants, etc.

Viologen Cross-Linked Chitosan Hydrogel as Biobased Antiseptic Surface-Coating Materials

“…47,64 These reactive building blocks are very suitable to conjugate chitosan through reticular chemistry. 42,66 We have consequently embarked to ascertain such a possibility by investigating cross-linking on chitosan powder before moving to their casting on glass surfaces and their shaping as transparent films and porous microspheres, as illustrated in Figure 1.…”

“…The intactness of the counterion demonstrates the tolerance of this reticular chemistry to cross-linkers featuring cations and anions in their structure, in consistency with the previous literature reports. 42 UV−visible spectroscopy reveals the presence of absorption bands at λ max = 253 nm typical of the π−π* transition of the viologen units (Figure S3). 42,67,68 SEM images of the crosslinked materials reveal the presence of aligned layers not seen in the native structure of chitosan (Figure S4).…”

“…72 Through deeper NMR studies, we have also validated such an approach and demonstrated that the acidic medium mandatory to dissolve chitosan does not hinder its reticular chemistry using aldehyde-terminated cross-linking candidates. 42 Practically, chitosan was first solubilized in acidified water (1% acetic acid) before adding a selected amount of 1%, 3%, or 5% molar ratio of the cross-linker (Vio 1 , Vio 2 , and Vio 3 ) relative to the -NH 2 groups. After 2 h of stirring, the resulting ink was poured into a Petri dish, for gentle removal of water from the medium.…”

“…We have previously synthesized, rigorously characterized, and meticulously isolated a set of aldehyde-terminated viologen derivatives, denoted herein as Vio 1 , Vio 2 , and Vio 3 . , These reactive building blocks are very suitable to conjugate chitosan through reticular chemistry. , We have consequently embarked to ascertain such a possibility by investigating cross-linking on chitosan powder before moving to their casting on glass surfaces and their shaping as transparent films and porous microspheres, as illustrated in Figure .…”

“…Accommodating sophisticated objects within the cross-linked network without compromising its film-forming ability, transparency, and flexibility is an important asset enabled by chitosan backbone. 42 Its inherent hydrogenbonding and film-forming properties render it an auspicious tool to shape antibacterial composition as an end-use device. SEM analysis shows a regular network typical of polysaccharide films with the presence of some roughness indicative of the occurrence of cross-linking in three dimensions (Figure S12).…”