A. Etxabide

Chitosan as a bioactive polymer: Processing, properties and applications

Chitin is one of the most abundant natural polysaccharides in the world and it is mainly used for the production of chitosan by a deacetylation process. Chitosan is a bioactive polymer with a wide variety of applications due to its functional properties such as antibacterial activity, non-toxicity, ease of modification, and biodegradability. This review summarizes the most common chitosan processing methods and highlights some applications of chitosan in various industrial and biomedical fields. Finally, environmental concerns of chitosan-based films, considering the stages from raw materials extraction up to the end of life after disposal, are also discussed with the aim of finding more eco-friendly alternatives.

Extraction of agar from Gelidium sesquipedale (Rodhopyta) and surface characterization of agar based films

The chemical structure of the agar obtained from Gelidium sesquipedale (Rhodophyta) has been determined by (13)C nuclear magnetic resonance ((13)C NMR) and Fourier transform infrared spectroscopy (FTIR). Agar (AG) films with different amounts of soy protein isolate (SPI) were prepared using a thermo-moulding method, and transparent and hydrophobic films were obtained and characterized. FTIR analysis provided a detailed description of the binding groups present in the films, such as carboxylic, hydroxyl and sulfonate groups, while the surface composition was examined using X-ray photoelectron spectroscopy (XPS). The changes observed by FTIR and XPS spectra suggested interactions between functional groups of agar and SPI. This is a novel approach to the characterization of agar-based films and provides knowledge about the compatibility of agar and soy protein for further investigation of the functional properties of biodegradable films based on these biopolymers.

Characterization of agar/soy protein biocomposite films: Effect of agar on the extruded pellets and compression moulded films

Agar/soy protein biocomposite films were successfully processed by extrusion and compression moulding, obtaining transparent and homogeneous films. The conformational changes occurred during the extrusion process and the effect of agar on the final properties were analyzed. As shown by differential scanning calorimetry (DSC) and specific mechanical energy (SME) values, during the extrusion process protein denatured and unfolded protein chains could interact with agar. These interactions were analyzed by Fourier transform infrared spectroscopy (FTIR) and the secondary structure was determined from the amide I band. Those interactions were supported by the decrease of film solubility. Furthermore, the good compatibility between agar and soy protein was confirmed by the images from scanning electron microscopy (SEM).

Ultra thin hydro-films based on lactose-crosslinked fish gelatin for wound healing applications

This study focuses on the development and characterization of an ultra thin hydro-film based on lactose-mediated crosslinking of fish gelatin by Maillard reaction. Lactose results in the only efficient crosslinker able to produce resistant to handling hydro-films when compared to conventional crosslinkers such as glutaraldehyde or genipin (tested at 25 and 37°C in phosphate buffer saline solution (PBS)).The disappearance of the peak related to the N-containing groups (XPS) and the images obtained by SEM and AFM demonstrate the highly ordered nano-scaled structure of lactose-crosslinked gelatin, confirming the crosslinking efficiency. This dressing presents high hydrophilicity and mild occlusivity, as shown by the swelling curve (max swelling at 5min) and by the occlusion factor of 25.17±0.99%, respectively. It demonstrates high stability to hydrolysis or cell-mediated degradation. Moreover, ISO 10993-5:2009 biocompatibility assay results in undetectable cytotoxicity effects. Spreading, adhesion and proliferation assays confirm the excellent adaptability of the cells onto the hydro-film surface without invading the dressing. Finally, the hydro-film enables the controlled delivery of therapeutic factors, such as the epidermal growth factor (EGF). This study demonstrates that lactose-mediated crosslinking is able to produce ultra thin gelatin hydro-films with suitable properties for biomedical applications, such as wound healing.

Lactose-crosslinked fish gelatin-based porous scaffolds embedded with tetrahydrocurcumin for cartilage regeneration

Tetrahydrocurcumin (THC) is one of the major colourless metabolites of curcumin and shows even greater pharmacological and physiological benefits. The aim of this work was the manufacturing of porous scaffolds as a carrier of THC under physiological conditions. Fish-derived gelatin scaffolds were prepared by freeze-drying by two solutions concentrations (2.5% and 4% w/v), cross-linked via addition of lactose and heat-treated at 105 °C. This cross-linking reaction resulted in more water resistant scaffolds with a water uptake capacity higher than 800%. Along with the cross-linking reaction, the gelatin concentration affected the scaffold morphology, as observed by scanning electron microscopy images, by obtaining a reduced porosity but larger pores sizes when the initial gelatin concentration was increased. These morphological changes led to a scaffolds strength enhancement from 0.92 ± 0.22 MPa to 2.04 ± 0.18 MPa when gelatin concentration was increased. THC release slowed down when gelatin concentration increased from 2.5 to 4% w/v, showing a controlled profile within 96 h. Preliminary in vitro test with chondrocytes on scaffolds with 4% w/v gelatin offered higher metabolic activities and cell survival up to 14 days of incubation. Finally the addition of THC did not influence significantly the cytocompatibility and potential antibacterial properties were demonstrated successfully against Staphylococcus aureus.

Versatile soy protein films and hydrogels by the incorporation of β-chitin from squid pens (Loligo sp.)

This study is focused on the preparation and characterization of β-chitin reinforced soy protein films, employing compression moulding as the processing method. β-chitin was extracted from squid pens (Loligo sp.) by a simple alkaline hydrolysis, avoiding the demineralization and decolouration steps used in chitin extraction from other sources, thus reducing the processing time and the production costs of the films. β-chitin was homogenously incorporated into the soy protein matrix, indicating good compatibility between the protein and the polysaccharide. Furthermore, the tensile strength and modulus of the films were significantly improved with the β-chitin addition due to the increase in crystallinity. Regarding the water uptake of the films, equilibrium was achieved in the first four hours of immersion and film integrity was maintained during the entire immersion time, suggesting the interactions among the film forming components; additionally, film solubility decreased with β-chitin concentration. Therefore, a promising multifunctional material was developed in this study.

Extraction and incorporation of bioactives into protein formulations for food and biomedical applications

Bioactive compounds from natural resources have been pointed out as promising substances with great benefits for human health. Furthermore, new techniques for their extraction have been reviewed in order to consider a global approach taking economic and environmental issues into account. Additionally, the incorporation of these biologically active compounds into protein-based products manufactured via different processing methods, such as solution casting, compression moulding, electrospinning, freeze-drying, and 3D printing, has been assessed, since the design and manufacturing method employed have a direct influence into the final properties of the material. Hence, new opportunities to develop active biopolymeric materials with great potential in food and biomedical applications have been presented. This review aims to provide an overview of some advanced technologies employed for bioactive extraction, as well as the bioactives incorporation into protein formulations to produce biomaterials and food packaging.