Chitosan macro- and micro/nano-gels have gained increasing attention in recent years, especially in the biomedical field, given the well-documented low toxicity, degradability, and non-immunogenicity of this unique biopolymer. In this review we aim at recapitulating the recent gelling concepts for developing chitosan-based physical gels. Specifically, we describe how nowadays it is relatively simple to prepare networks endowed with different sizes and shapes simply by exploiting physical interactions, namely (i) hydrophobic effects and hydrogen bonds—mostly governed by chitosan chemical composition—and (ii) electrostatic interactions, mainly ensured by physical/chemical chitosan features, such as the degree of acetylation and molecular weight, and external parameters, such as pH and ionic strength. Particular emphasis is dedicated to potential applications of this set of materials, especially in tissue engineering and drug delivery sectors. Lastly, we report on chitosan derivatives and their ability to form gels. Additionally, we discuss the recent findings on a lactose-modified chitosan named Chitlac, which has proved to form attractive gels both at the macro- and at the nano-scale.
The present paper describes an original method to form under physiological conditions homogeneous lactose-modified chitosan (CTL) gels avoiding syneresis. Specifically, combination of boric acidi.e., the cross-linkerand mannitoli.e., a polyol competitor for boron bindingwere exploited to reduce the very fast kinetics of CTL/boron self-assembly. Resulting gels were homogeneous as proved by scattering analyses. An indepth rheological characterization was undertaken to identify the correct mannitol-to-boron ratio at which gels showed homogeneity without weakening. Stress sweep and frequency sweep tests were performed to investigate the viscoelastic properties of these dynamic networks, highlighting a marked strain-hardening behavior, which is pivotal in native tissues. Notably, herein we report for the first time that CTL−boric acid gels are multiresponsive systems, whose mechanics can be tailored by different stimuli such as the presence of small molecules like glucose. Moreover, we demonstrate that these networks spontaneously self-heal after breakage. The biocompatibility of such gels was studied under 2D and 3D conditions toward three different cell models, namely, pig primary chondrocytes, human Dental Pulp Stem Cells (hDPSCs), and mouse fibroblasts. Giving the peculiar mechanical performance of selected systems and considering the wellknown bioactivity of the chitosan derivative, CTL−boric acid networks are promising candidates as multiresponsive gels to be used in the field of tissue engineering, especially for articular cartilage regeneration.
The necessity to continuously and seamlessly monitor human health is calling for compliant, comfortable, and safe wearables. The employment of piezoelectric biopolymers in form of thin film perfectly matches with these needs due to their inherent flexibility, sensitivity, and biocompatibility. Among them, chitosan is a low cost, highly sustainable, and biocompatible material with a great potential for applications in compliant wearables. However, chitosan and biopolymers in general show relatively low piezoelectric coefficients and processing difficulties. Here, it is shown a facile approach to increase more than twice the piezoelectric coefficient of thin chitosan film and to process this promising biomaterial for the fabrication of the first set of thin chitosan film‐based ultrasound transducers. This work leverages the exploitation of environmental‐friendly biopolymers in the development of compliant wearable transducers and thus represents a step forward in the development of completely biodegradable, transparent, thin, and flexible piezoelectric macro‐ and microtransducers.
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