Abstract
Natural polymers are of great interest in the biomedical field due to their intrinsic properties such as biodegradability, biocompatibility, and non-toxicity. Layer-by-layer (LbL) assembly of natural polymers is a versatile, simple, efficient, reproducible, and flexible bottom-up technique for the development of nanostructured materials in a controlled manner. The multiple morphological and structural advantages of LbL compared to traditional coating methods (i.e., precise control over the thickness and compositions at the nanoscale, simplicity, versatility, suitability, and flexibility to coat surfaces with irregular shapes and sizes), make LbL one of the most useful techniques for building up advanced multilayer polymer structures for application in several fields, e.g., biomedicine, energy, and optics. This review article collects the main advances concerning multilayer assembly of natural polymers employing the most used LbL techniques (i.e., dipping, spray, and spin coating) leading to multilayer polymer structures and the influence of several variables (i.e., pH, molar mass, and method of preparation) in this LbL assembly process. Finally, the employment of these multilayer biopolymer films as platforms for tissue engineering, drug delivery, and thermal therapies will be discussed.
Highlights
Over the last decades, polymers obtained from biomass, known as natural polymers, have been widely employed for a variety of biomedical applications due to their intrinsic properties such as biocompatibility and non-toxicity
When CHI was assembled with ALG, the study of the buildup’s process at different concentrations, pH, and ionic strength allowed to conclude that the fastest film growth took place for chitosan and alginate concentrations of 1.0 and 5.0 mg/mL and pH 5 and 3, respectively, conditions under which alginate is in high concentration and only partially ionized in a way that its negative charge interacts weakly with the positively charged amino groups of CHI [47,58]
The results showed an increase in the adhesion strength from 3.4 MPa for hyaluronic acid (HA)-based films to 8.6 MPs for HA with dopamine (HA–DN)-based films, highlighting the enhanced adhesive properties of CHI/HA–DN films
Summary
Polymers obtained from biomass, known as natural polymers, have been widely employed for a variety of biomedical applications due to their intrinsic properties such as biocompatibility and non-toxicity. Polysaccharides are constituted by monosaccharide units linked by O-glycosidic bonds including cellulose, chitin, chitosan, alginate, hyaluronic acid, chondroitin sulphate, dextran, and agarose [2] Proteins, such as collagen and gelatin, are polymer structures formed by 20 different amino acids linked by amide (or peptide) bonds [3]. A strategy to increase the biostability of natural polymers in physiological conditions without compromising their biocompatibility is the formation of polyelectrolyte complexes (PECs) formed by electrostatic interactions between natural polycations and polyanions In this regard, layer-by-layer (LbL) assembly, based on the sequential deposition of interacting species onto a substrate, emerged as a versatile, simple, efficient, reproducible, and flexible bottom-up technique, that allows a precise control over the thickness and compositions at the nanoscale [7]. The employment of multilayers derived from natural polymers as bioactive functional coatings and platforms for tissue engineering or drug delivery and thermal therapies will be discussed
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