Natural Polymers-Based Materials: A Contribution to a Greener Future

Abstract

Natural polymers have emerged as promising candidates for the sustainable development of materials in areas ranging from food packaging and biomedicine to energy storage and electronics. In tandem, there is a growing interest in the design of advanced materials devised from naturally abundant and renewable feedstocks, in alignment with the principles of Green Chemistry and the 2030 Agenda for Sustainable Development. This review aims to highlight some examples of the research efforts conducted at the Research Team BioPol4fun, Innovation in BioPolymer-based Functional Materials and Bioactive Compounds, from the Portuguese Associate Laboratory CICECO-Aveiro Institute of Materials at the University of Aveiro, regarding the exploitation of natural polymers (and derivatives thereof) for the development of distinct sustainable biobased materials. In particular, focus will be given to the use of polysaccharides (cellulose, chitosan, pullulan, hyaluronic acid, fucoidan, alginate, and agar) and proteins (lysozyme and gelatin) for the assembly of composites, coatings, films, membranes, patches, nanosystems, and microneedles using environmentally friendly strategies, and to address their main domains of application.

Keywords: composites and hybrid materials; films and membranes; green chemistry; microneedles; nanosystems; natural polymers; patches; polysaccharides; proteins; sustainability.

Figure 1

Examples of the natural polymers and derivatives used for materials design by the BioPol4fun research group.

Figure 2

(A) Illustration of the preparation of nanocomposites of modified cellulose nanofibers (CNFs) and thermoplastic matrices, in this case poly(ε-caprolactone) (PCL). Plots of Young’s Modulus (B) and the flexural modulus (C) of PCL and the nanocomposites, showing the improvement of mechanical properties, while retaining flexibility (inset photograph of (C). (D) Micrographs of the surface of PLC and one of the composites after 10 weeks of enzymatic degradation at 37 °C. Reproduced with permission from [98]. Copyright John Wiley and Sons, 2018.

Figure 3

(A) Illustration of the grafting of chitosan and 5,10,15-tris(pentafluorophenyl)corrol (TPFC) and inset of a digital photograph of the corrole-grafted chitosan after 48 h reaction. Digital photographs (B) and fluorescence lifetime images (C) of the neat (CH) and corrole-grafted chitosan films prepared via solvent casting. (D) Antibacterial activity of chitosan, TPFC and the corrole grafted-chitosan films against S. aureus. Reproduced with permission from [72]. Copyright American Chemical Society, 2016.

Figure 4

(A) Schematic illustration of the incorporation of hydroalcoholic extracts from chestnut spiny burs (CSB) and roasted hazelnut skins (RHS) in a pullulan (PL) matrix via a solvent casting technique and photographs of the prepared films. UV–vis spectra (B) and antioxidant activity (C) of the PL, PL/CSB, and PL/RHS-based films. Reproduced with permission from [75]. Copyright Elsevier, 2020.

Figure 5

(A) Schematic illustration of the preparation of fully biobased bacterial nanocellulose (BNC) and fucoidan (Fuc) membranes with tannic acid as a crosslinker. (B) Photographs and micrographs of the nanocellulose surface and cross-section before (BNC) and after (BNC/Fuc_75) inclusion of the sulfated polysaccharide (Fuc) (scale bar: 2 µm). (C) Moisture uptake capacity of the membranes. (D) Arrhenius-type plot of the through-plane protonic conductivity of the BNC/Fuc_75 membrane. Reproduced with permission from [81]. Copyright Elsevier, 2020.

Figure 6

(A) Schematic illustration of the preparation of the BNC/HA/DFC patches and photographs of the dried patches. (B) Photographs of the adhesion of BNC/HA/DCF patch in an agarose hydrogel skin model. (C) Release profile of the drug-loaded patches. Reproduced with permission from [78]. Copyright MDPI, 2020.

Figure 7

(A) Schematic illustration of the production of insulin-loaded pullulan microneedles. (B) Force–displacement curves of neat (PL 24%) and drug-loaded (PL 24% + insulin) microneedles. (C) SEM micrograph (scale bar: 500 μm) and (D) histological cross-sections of human abdominal skin after insertion of the pullulan microneedle patch with insulin. Reproduced with permission from [76]. Copyright Elsevier, 2020.