Abstract
Polysaccharide-based hydrogels are very promising materials for a wide range of medical applications, ranging from tissue engineering to controlled drug delivery for local therapy. The most interesting property of this class of materials is the ability to be injected without any alteration of their chemical, mechanical and biological properties, by taking advantage of their thixotropic behavior. It is possible to modulate the rheological and chemical-physical properties of polysaccharide hydrogels by varying the cross-linking agents and exploiting their thixotropic behavior. We present here an overview of our synthetic strategies and applications of innovative polysaccharide-based hydrogels: hyaluronan-based hydrogel and new derivatives of carboxymethylcellulose have been used as matrices in the field of tissue engineering; while guar gum-based hydrogel and hybrid magnetic hydrogels, have been used as promising systems for targeted controlled drug release. Moreover, a new class of materials, interpenetrating hydrogels (IPH), have been obtained by mixing various native thixotropic hydrogels.
Highlights
Hydrogels are materials constituted by physically interacting or chemically cross-linked hydrophilic polymer chains, capable of absorbing a high amount of water
Some polysaccharides used for the preparation of hydrogels are shown in Figure 1: carboxymethylcellulose (CMC) [9,10], hyaluronic acid (HYAL) [11,12,13], guar gum (GG) and chitosan (CHT) [14,15,16,17,18]
Two methods have been successfully used in order to obtain such information: (I) potentiometric titrations, which allow the verification of the number of carboxylate groups or amine groups of the polysaccharide not involved in the cross-linking reaction, i.e., remaining free in the network and which can be titred by OH− or H+, and (II) 13C nuclear magnetic resonance (NMR) spectroscopy, by comparing the areas of specific NMR signals belonging to the polymer functional groups in the free or cross-linked form [19]
Summary
Hydrogels are materials constituted by physically interacting or chemically cross-linked hydrophilic polymer chains, capable of absorbing a high amount of water. In addition to covalent cross-linking, every chemical hydrogel present physical interactions, due to the aggregation of hydrophobic cross-linking agents and/or parts of the polymer This implies that a certain degree of dishomogeneity is present in chemical hydrogels; unlike physical ones, their mechanical properties are highly reproducible, offering the possibility to modulate their cross-linking degree. In both cases, the density of cross-links is crucial in determining both properties and applications of the gels, as it is responsible for the swelling behavior and for the combined solid-like and liquid-like characteristics. Chemical hydrogels appear more attractive than physical hydrogels
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