Effective reinforcement of plasticized starch by the incorporation of graphene, graphene oxide and reduced graphene oxide.

Plasticized starch (PLS) nanocomposite films using glycerol and reinforced with graphene (G) and graphene oxide (GO) were prepared by solvent casting procedure. On one hand, the influence of adding different G contents into the PLS matrix was analyzed. In order to improve the stability of G nanoflakes in water, Salvia extracts were added as surfactants. The resulting nanocomposites presented improved mechanical properties. A maximum increase of 287 % in Young's modulus and 57 % in tensile strength was achieved for nanocomposites with 5 wt% of G. However, it seemed that Salvia acted as co-plasticizer for the PLS. Moreover, the addition of the highest G content led to an improvement of the electrical conductivity close to 5 × 10-6 S/m compared to the matrix. On the other hand, GO was also incorporated as nanofiller to prepare nanocomposites. Thus, the effect of increasing the GO content in the final behavior of the PLS nanocomposites was evaluated. The characterization of GO containing PLS nanocomposites showed that strong starch/GO interactions and a good dispersion of the nanofiller were achieved. Moreover, the acidic treatment applied for the reduction of the GO was found to be effective, since the electrical conductivity was 150 times bigger than its G containing counterpart.

Integral Valorization of Grape Pomace for Antioxidant Pickering Emulsions.

Full harnessing of grape pomace (GP) agricultural waste for the preparation of antioxidant Pickering emulsions is presented herein. Bacterial cellulose (BC) and polyphenolic extract (GPPE) were both prepared from GP. Rod-like BC nanocrystals up to 1.5 µm in length and 5-30 nm in width were obtained through enzymatic hydrolysis (EH). The GPPE obtained through ultrasound-assisted hydroalcoholic solvent extraction presented excellent antioxidant properties assessed using DPPH, ABTS and TPC assays. The BCNC-GPPE complex formation improved the colloidal stability of BCNC aqueous dispersions by decreasing the Z potential value up to -35 mV and prolonged the antioxidant half-life of GPPE up to 2.5 times. The antioxidant activity of the complex was demonstrated by the decrease in conjugate diene (CD) formation in olive oil-in-water emulsions, whereas the measured emulsification ratio (ER) and droplet mean size of hexadecane-in-water emulsions confirmed the physical stability improvement in all cases. The synergistic effect between nanocellulose and GPPE resulted in promising novel emulsions with prolonged physical and oxidative stability.

Tailor-Made 3D Printed Meshes of Alginate-Waterborne Polyurethane as Suitable Implants for Hernia Repair.

Hernia injuries are the main condition where mesh implants are needed to provide a suitable reinforcement of the damaged tissue. Mesh implants made of polypropylene (PP) are widely used for this application, however complications related to lack of flexibility, elasticity, and mesh infection have been reported. The development of mesh implants from safer materials adaptable to patient necessities can suppose an alternative for conventional PP meshes. In this work, personalized mesh implants made of alginate and waterborne-polyurethane (A-WBPU) are developed using 3D printing technology. For that purpose, five waterborne polyurethane ink formulations with different amounts of alginate are developed and rheologically characterized. All ink formulations are 3D printed showing good printability, manufacturing surgical mesh implants with suitable morphological characteristics customizable to patient injury through computer-aided design (CAD) mesh model adaptation. A calcium chloride (CaCl2 ) coating is applied after 3D printing as mesh reinforcement. Mechanical analysis revealed that CaCl2 coated meshes containing 6 wt % of alginate in their formulation are the most suitable to be used as implants for small and groin hernias under physiological tensile strength value of 16 N cm-1 , and presenting proper elasticity to cover physiological corporal movements (42.57 %). Moreover, an antibiotic-loaded A-WBPU formulation suitable for 3D printing of meshes are developed as strategy to avoid possible mesh infection.

3D printing of customized all-starch tablets with combined release kinetics.

Starch-based tablets with tailored releases were prepared by 3D printing using a hydrophobic drug. The importance of the origin of the excipient in the inks and tablets was analyzed. Besides, the effect of the geometry of the tablet on the drug release profile was also evaluated. The rheological properties of the inks was influenced by the botanic origin of the starch. Consequently, tablets presented different microporous structure and particular compression and swelling behaviors. Normal maize starch showed a non-well-defined porous morphology, not being able to form a stable structure whereas, waxy maize and potato starches exhibited a well-defined porous structure and were both able to maintain their integrity after long time immersion. Finally, tablets combining different starches and geometries were printed tailoring the drug release from 10 min to 6 h and designing two-steps profiles. The applicability of the developed 3D printed drug release systems in personalized therapies was demonstrated.

Superabsorbent bacterial cellulose spheres biosynthesized from winery by-products as natural carriers for fertilizers.

Soil contamination, sustainable management of water resources and controlled release of agrochemicals are the main challenges of modern agriculture. In this work, the synthesis of sphere-like bacterial cellulose (BC) using agitated culture conditions and Komagateibacter medellinensis bacterial strain ID13488 was optimized and characterized from grape pomace (GP). First, a comparative study was carried out between agitated and static cultures using different nitrogen sources and applying alternative GP treatments. Agitation of the cultures resulted in higher BC production yield compared to static culture conditions. Additionally, Water holding capacity (WHC) assays evidenced the superabsorbent nature of the BC biopolymer, being positively influenced by the spherical shape as it was observed an increase of 60% in contrast to the results obtained for the BC membranes under static culture conditions. Moreover, it was found that sphere-like BCs were capable of retaining urea up to 375% of their dry weight, rapidly releasing the fertilizer in the presence of water. According to our findings, sphere-like BCs represent suitable systems with great potential for actual agricultural hazards and grape pomace valorisation.

Morphological Analysis of Several Bamboo Species with Potential Structural Applications.

Bamboo constitutes a family of plants that are very promising and interesting as renewable materials for both large and small structure construction. To be used as an alternative to traditional materials; the understanding of its morphology and mechanical behavior is of crucial importance. As the distribution of fibers and vascular bundles differs for each type of bamboo; several bamboo types have been characterized: Phyllostachys aurea (PA), Arundinaria amabilis (AA) and Dendrocalamus strictus (DS). Morphological analysis has been performed by optical (OM) and scanning electron microscopy (SEM). Differences in density; surface morphology and wall thickness have been found. In fact; PA and AA have shown a great morphological regularity; while DS presents the greatest thickness; to the point that it can be considered full culm. The plant's own ducts constitute a very important factor for future impregnations and the optimization of mechanical properties for structure construction.

Design of a Waterborne Polyurethane-Urea Ink for Direct Ink Writing 3D Printing.

In this work, polycaprolactone-polyethylene glycol (PCL-PEG) based waterborne polyurethane-urea (WBPUU) inks have been developed for an extrusion-based 3D printing technology. The WBPUU, synthesized from an optimized ratio of hydrophobic polycaprolactone diol and hydrophilic polyethylene glycol (0.2:0.8) in the soft segment, is able to form a physical gel at low solid contents. WBPUU inks with different solid contents have been synthesized. The rheology of the prepared systems was studied and the WBPUUs were subsequently used in the printing of different pieces to demonstrate the relationship between their rheological properties and their printing viability, establishing an optimal window of compositions for the developed WBPUU based inks. The results showed that the increase in solid content results in more structured inks, presenting a higher storage modulus as well as lower tan δ values, allowing for the improvement of the ink's shape fidelity. However, an increase in solid content also leads to an increase in the yield point and viscosity, leading to printability limitations. From among all printable systems, the WBPUU with a solid content of 32 wt% is proposed to be the more suitable ink for a successful printing performance, presenting both adequate printability and good shape fidelity, which leads to the realization of a recognizable and accurate 3D construct and an understanding of its relationship with rheological parameters.

Light-driven assembly of biocompatible fluorescent chitosan hydrogels with self-healing ability.

Nitrile imine-mediated tetrazole-ene cycloaddition (NITEC) was successfully used to cross-link complementary tetrazole and maleimide chitosan derivatives into hydrogel networks using irradiation. The photo-click reaction resulted in the formation of robust fluorescent hydrogels with an emission signal at around 530 nm. The degree of cross-linking and the resulting hydrogel properties such as pH sensitivity and swelling were influenced by the tetrazole/maleimide ratio and the length of irradiation. Interestingly, rheological studies demonstrated self-healing character of the novel hydrogels as indicated by instantaneous recovery of the storage modulus to the initial values under different oscillatory strains without any additional external trigger. Finally, in addition to their photo-tuneable and self-healing properties, the novel chitosan hydrogels were also found to be biocompatible and susceptible to in vitro enzymatic degradation, making them suitable for design of traceable biomaterials for biomedical applications.

ß-Glycerol phosphate/genipin chitosan hydrogels: A comparative study of their properties and diclofenac delivery.

Thermosensitive hydrogels based on polysaccharides are suitable candidates for the design of biodegradable and biocompatible injectable drug delivery systems. Thus, the combination of chitosan (CHI) and ß-glycerol phosphate disodium salt (ß-GP) has been intensively investigated to develop thermo-induced physical gels. With the aim of exploring the possibilities of optimization of these hydrogels, in this work, chitosan, ß-GP and naturally extracted crosslinking agent, genipin (GEN), have been successfully combined, obtaining co-crosslinked hydrogels with both in situ physical and covalent crosslinking. A wide range of ß-GP concentrations have been selected in order to analyze its influence on a variety of properties, including gelation time, pore size, water uptake ability, in vitro hydrolytic and enzymatic degradation, mucoadhesion and mechanical and rheological properties. Furthermore, the potential application of the developed systems for the administration and controlled release of an anti-inflammatory anionic drug, such as diclofenac, has been successfully demonstrated.

Tailoring the in situ conformation of bacterial cellulose-graphene oxide spherical nanocarriers.

Bacterial cellulose (BC)/graphene oxide (GO) sphere-like hydrogels have been biosynthesized by in situ route in dynamic cultivation. The GO concentration during BC biosynthesis (0.01 and 0.05 mg mL-1) was the determining factor for the conformation of the final hydrogels: encapsulation (BC/GO 0.01) or distribution through all the body of the spheres (BC/GO 0.05). The as-prepared sphere hydrogels were characterized in terms of physico-chemical properties, thermal stability, microstructure, and swelling capacity in different media. In addition, a chemical treatment with ascorbic acid was performed in order to obtain reduced graphene oxide (rGO) into the spheres (BC/rGO). After the chemical treatment, electrostatic force microscopy (EFM) revealed electrical interactions due to the presence of rGO inside the spheres and resistivity values in the range of semiconductive materials were obtained (106 Ω·cm), making BC/rGO spheres promising for the development of electro-stimulated systems. The in vitro release study of ibuprofen (IB), showed that the reduction process led to an increase of 73 and 92% of drug release with respect to BC/GO 0.05 and BC/GO 0.01 spheres, respectively. Moreover, the encapsulation conformation showed more homogeneous porous structure and thus, a cumulative drug release of 63% was reached after 6 h.

Influence of Process Parameters in graphene oxide Obtention on the Properties of mechanically strong alginate nanocomposites.

Sodium alginate, a biopolymer extracted from brown algae, has shown great potential for many applications, mainly due to its remarkable biocompatibility and biodegradability. To broaden its fields of applications and improve material characteristics, the use of nanoreinforcements to prepare nanocomposites with enhanced properties, such as carbonaceous structures which could improve thermal and mechanical behavior and confer new functionalities, is being studied. In this work, graphene oxide was obtained from graphite by using modified Hummers' method and exfoliation was assisted by sonication and centrifugation, and it was later used to prepare sodium alginate/graphene oxide nanocomposites. The effect that different variables, during preparation of graphene oxide, have on the final properties has been studied. Longer oxidation times showed higher degrees of oxidation and thus larger amount of oxygen-containing groups in the structure, whereas longer sonication times and higher centrifugation rates showed more exfoliated graphene sheets with lower sizes. The addition of graphene oxide to a biopolymeric matrix was also studied, considering the effect of processing and content of reinforcement on the material. Materials with reinforcement size-dependent properties were observed, showing nanocomposites with large flake sizes, better thermal stability, and more enhanced mechanical properties, reaching an improvement of 65.3% and 83.3% for tensile strength and Young's modulus, respectively, for a composite containing 8 wt % of graphene oxide.

The role of cellulose nanocrystals in biocompatible starch-based clicked nanocomposite hydrogels.

Starch-based nanocomposite hydrogels were successfully prepared by the Diels-Alder click cross-linking reaction between furan-functionalized starch derivative and a water-soluble tetrafunctional maleimide compound, adding cellulose nanocrystals (CNC) as nanoreinforcement. The effect of increasing the CNC content on rheological and swelling properties as well as on the morphology of the hydrogels was analyzed. Besides, in order to evaluate the applicability of the as-prepared hydrogels as delivery systems, drug release measurements and in vitro cytotoxicity assays were also performed. It was found that the prepared nanocomposite hydrogels presented higher stiffness as the CNC content increased. The incorporation of the nanocrystals modified the internal porous microstructure of the hydrogels, affecting consequently both the swelling capacity and the drug-delivery kinetics. Moreover, the prepared nanocomposite hydrogels showed non-toxic behavior, demonstrating their potential applicability in the biomedical field, especially as sustained drug delivery systems.

Starch/graphene hydrogels via click chemistry with relevant electrical and antibacterial properties.

Starch-based hydrogels were performed by Diels-Alder cross-linking reactions between furan-modified starch and a water soluble bismaleimide, with improving conducting properties by using graphene layers as active nanofillers. The characterization results demonstrated that the Diels-Alder reaction and the corresponding conditions for the hydrogel formation were appropriate. The effect of increasing the furan/maleimide ratio on the architecture of the hydrogels and on the morphological, rheological and swelling properties were thoroughly evaluated. Effective network structure was obtained by increasing the cross-linker content leading to decreasing pore size and increasing storage modulus value of the final material. It was shown that the swelling behavior of hydrogels was mainly governed by the hydrophilic character of bismaleimide. Graphene nanosheets were added for the synthesis of nanocomposite hydrogel and it was characterized in terms of rheological properties, electrical conductivity and antimicrobial activity. The nanocomposite hydrogel presented enhanced mechanical performance, antimicrobial activity and increased conductivity values, up to a decade, indicating that conductive and active hydrogels could be satisfactory obtained, for a large range of potential applications such as biomed.

Design of reusable novel membranes based on bacterial cellulose and chitosan for the filtration of copper in wastewaters.

This study has been carried out to design novel, environmentally friendly membranes by in situ and ex situ routes based on bacterial cellulose (BC) as a template for the chitosan (Ch) as functional entity for the elimination of copper in wastewaters. Two routes led to bionanocomposites with different aspect and physico-chemical properties. The mechanical behaviour in wet state, strongly related to crystallinity and water holding capacity, resulted to be very different depending on the preparation route although the Ch content was very similar: 35 and 37 wt% for the in situ and ex situ membranes, respectively. The morphological characterization suggested a better incorporation of the Ch into BC matrix through the in situ route. The cooper removal capacity of these membranes was analyzed and in situ prepared membrane showed the highest values, about 50%, for initial concentrations of 50 and 250 mg L-1. Moreover the reusability of the membranes was assessed. This is the first time that the whole 3D nano-network BC membrane is used to provide physical integrity for chitosan to develop eco-friendly membranes with potential applications in heavy metal removal.

Modification of Pea Starch and Dextrin Polymers with Isocyanate Functional Groups.

Pea starch and dextrin polymers were modified through the unequal reactivity of isocyanate groups in isophorone diisocyanate (IPDI) monomer. The presence of both urethane and isocyanate functionalities in starch and dextrin after modification were confirmed by Fourier transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (13C NMR). The degree of substitution (DS) was calculated using elemental analysis data and showed higher DS values in modified dextrin than modified starch. The onsets of thermal degradation and temperatures at maximum mass losses were improved after modification of both starch and dextrin polymers compared to unmodified ones. Glass transition temperatures (Tg) of modified starch and dextrin were lower than unmodified control ones, and this was more pronounced in modified dextrin at a high molar ratio. Dynamic water vapor sorption of starch and dextrin polymers indicated a slight reduction in moisture sorption of modified starch, but considerably lower moisture sorption in modified dextrin as compared to that of unmodified ones.

Biocompatible hydrogel nanocomposite with covalently embedded silver nanoparticles.

Bionanocomposite materials, combining the properties of biopolymers and nanostructured materials, are attracting interest of the wider scientific community due to their potential application in design of implants, drug delivery systems, and tissue design platforms. Herein, we report on the use of maleimide-coated silver nanoparticles (Ag NPs) as cocross-linkers for the preparation of a bionanocomposite gelatin based hydrogel. Diels-Alder cycloaddition of benzotriazole maleimide (BTM) functionalized Ag NPs and furan containing gelatin in combination with additional amide coupling resulted in stable and biocompatible hybrid nanocomposite. The storage moduli values for the hydrogel are nearly three times higher than that of control hydrogel without NPs indicating a stabilizing role of the covalently bound NPs. Finally, the swelling and drug release properties of the materials as well as the biocompatibility and toxicity tests indicate the biomedical potential of this type of material.

Starch and cellulose nanocrystals together into thermoplastic starch bionanocomposites.

In the present work, thermoplastic maize starch based bionanocomposites were prepared as transparent films, plasticized with 35% of glycerol and reinforced with both waxy starch (WSNC) and cellulose nanocrystals (CNC), previously extracted by acidic hydrolysis. The influence of the nanofiller content was evaluated at 1 wt.%, 2.5 wt.% and 5 wt.% of WSNC. The effect of adding the two different nanoparticles at 1 wt.% was also investigated. As determined by tensile measurements, mechanical properties were improved at any composition of WSNC. Water vapour permeance values maintained constant, whereas barrier properties to oxygen reduced in a 70%, indicating the effectiveness of hydrogen bonding at the interphase. The use of CNC or CNC and WSNC upgraded mechanical results, but no significant differences in barrier properties were obtained. A homogeneous distribution of the nanofillers was demonstrated by atomic force microscopy, and a shift of the two relaxation peaks to higher temperatures was detected by dynamic mechanical analysis.