Antonio G.B. Pereira

Superabsorbent hydrogel nanocomposites based on starch-g-poly(sodium acrylate) matrix filled with cellulose nanowhiskers

Superabsorbents hydrogel nanocomposites based on starch-g-poly(sodium acrylate) and cellulose nanowhiskers (CNWs) were synthesized. A set of experiments was performed to evaluate the influence of some factors such as NaAc/starch mass ratio, crosslinker, and nanowhiskers amount in the swelling capacity and swelling kinetics. Increasing the NaAc/starch mass ratio up to 7 leads to an increase in the water uptake at a maximum value, however, higher ratios decreased that value due to the increase of crosslinking points. Similarly, the incorporation of CNWs up to 10 wt% provided an improvement in the swelling due to the hydrophilic groups from cellobiose units. Further, the incorporation of CNWs diminishes the water uptake. Besides, the CNWs improved the mechanical properties. SEM images showed that CNWs increase the average porous size of composites. The composites presented good responsive behavior in relation to pH and salt presence allowing those materials suitable for many potential applications.

Chitosan/TPP microparticles obtained by microemulsion method applied in controlled release of heparin

This work deals with the preparation of chitosan/tripolyphosphate microparticles (CHT/TPP) using microemulsion system based on water/benzyl alcohol. The morphology of the microparticles was evaluated by scanning electron microscopy (SEM). The microparticles were also characterized through infrared spectroscopy (FTIR) and wide-angle X-ray scattering (WAXS). The morphology and crystallinity of microparticles depended mainly on CHT/TPP ratio. Studies of controlled release of HP were evaluated in distilled water and in simulated gastric fluid. Besides, the profile of HP releasing could be tailored by tuning the CHT/TPP molar ratio. Finally, these prospective results allow the particles to be employed as site-specific HP controlled release system.

N,N-Dimethyl chitosan/heparin polyelectrolyte complex vehicle for efficient heparin delivery

Polysaccharide-based device for oral delivery of heparin (HP) was successfully prepared. Previously synthesized N,N-dimethyl chitosan (DMC) (86% dimethylated by (1)H NMR spectroscopy) was complexed with HP by mixing HP and DMC aqueous solutions (both at pH 3.0). The polyelectrolyte complex (PEC) obtention was confirmed by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG) and wide-angle X-ray scattering (WAXS). In vitro controlled release assays of HP from PEC were investigated in the simulated intestinal fluid (SIF) and simulated gastric fluid (SGF). The PEC efficiently protected the HP in SGF condition in which HP is degraded. On the other hand, in SIF PEC promoted the releasing of 80 ± 1.5% of loaded HP. The promissory results indicated that the PEC based on DMC/HP presented potential as drug-carrier matrix, since biological activity of HP was improved at pH close to physiological condition.

Recentes Avanços no Design de Hidrogéis de Chitina e Derivados de Chitina e seu Impacto sobre Meio Ambiente e Agricultura: Uma Revisão

Our purpose is to show and discuss the most relevant data on the synthesis approach and the characterization of hydrogels based on chitin and chitin-derivatives, such as chitosan, as well as their applications in several materials technologies. The current and future relevance of materials based on chitin, chitosan and derivatives have been verified by the impressive number of scientific and technological publications (both papers and patents) that appears day-by-day. This review is divided into four Sections. Section 1 reports some basic concepts of hydrogels. Section 2 deals with properties of chitin, and gelation chemistries. Applications in environment and agriculture are described in Section 3. Future trends and perspectives are considered in Section 4.

Hydrogels Nanocomposites Based on Crystals, Whiskers and Fibrils Derived from Biopolymers

The advent of nanotechnology has provided new insights of applications of well-known materials due to the exceptional properties owing to the nanoscale. As an example, nanocomposites based on polymer matrix and nanoscale fillers have appeared as good candidates in a broad range of applications. Such scenery can be credited to the use of new and multifunctional fillers that provide distinct and substantial features to the nanocomposites. Recent trends on the nanocomposites field show that crystalline biopolymers , such as cellulose, chitin, and starch, are an excellent source of fillers, especially nanocrystals like fibrils , whiskers , and platelets. The incorporation of such fillers in different matrices (e.g., crosslinked polymeric network) has demonstrated outstanding improvement of several properties, such as mechanical, water uptake capacity, thermal, optical, etc. Furthermore, crystals , fibrils and whiskers can induce desirable properties in the final materials (e.g., solute retention or release, crystallinity, biodegradability, biocompatibility, antibacterial activity, etc.). This chapter condenses the relevant works regarding the preparation of polysaccharide-based crystals, whiskers, and fibrils, their application in the development of hydrogel nanocomposites as well as the future trends of this area.

Cellulose nanowhiskers decorated with silver nanoparticles as an additive to antibacterial polymers membranes fabricated by electrospinning

Antimicrobial films based on distinct polymer matrices, poly (vinyl alcohol) (PVA) or poly (N-isopropylacrylamide) (PNIPAAm), and silver nanoparticles (AgNPs) immobilized onto cellulose nanowhiskers (CWs) were successfully prepared by either casting or electrospinning. CWs were first functionalized with carboxylate groups (labeled as CWSAc) and later they were immersed in a silver nitrate solution (AgNO3). After Ag+ ions anchored in the COO- groups are chemically reduced to produce AgNPs. The CWSAc/AgNPs biological activity was evaluated against Staphylococcus aureus (S. aureus), Bacillus Subtilis (B. subtilis), Escherichia coli (E. coli), and Candida albicans (C. albicans). The materials were more effective against C. albicans that showed a MIC of 15.6 µg/mL. In the process of AgNPs synthesis, the activity of the stabilizing agent (gelatin) and concentration of precursor and reducing agents were evaluated. The synthesized polymeric films displayed good antimicrobial activity against S. aureus, E. coli, and Pseudomonas aeruginosa (P. aeruginosa) bacteria. The PVA films with CWSAc/AgNPs showed diameter of the inhibition halo of up to 11 mm. The results obtained displayed that the films obtained have a potential application to be used in different fields such as packaging, membrane filtration, wound dressing, clothing and in different biomedical applications.

Preparation of Polymeric Mats Through Electrospinning for Technological Uses

Although the electrospinning (ES) is known for almost 80 years, only in the last two decades this technique has been widely used for obtaining micro- and/or nanofibers. Several aspects contributed for spreading the electrospinning, for instance, the easy operational aspects, affordable equipment, and highly versatile design setup, among others. So, in view of materials chemistry, the electrospinning is one of paramount techniques for processability of polymers and product development at submicrometric scales. This chapter presents the basic concepts of electrospinning of polymeric solutions as well as experimental arrangements commonly employed for different materials. Recent results toward the development of polymer mats published in the literature are discussed as well as the structure/properties relationship. Different applications of electrospun mats are discussed in this chapter. A very large window of opportunities remains opened for developing mats as absorbents for industrial effluent treatments. Solid-phase microextraction analysis is another field in which electrospun mats find the enormous potential of application. The high surface area to volume ratio allows electrospun mats to work as an efficient drug-releasing device even as scaffolds for cell growth and tissue engineering. This chapter is divided in the following sections: The Introduction (in Sect. 1) deals with the basic aspects of electrospinning such as the experimental devices used and the parameters that may influence the morphology and properties of mats; chemical and physical characterization of electrospun mats are discussed in Sect. 2; Sect. 3 shows the most relevant technological applications of electrospun fibers. More than 260 references are provided.

Chapter 7:Outstanding Features of Starch-based Hydrogel Nanocomposites

Starch-based hydrogel nanocomposites are a very important issue in both academic and industrial fields owing to their availability, renewable sources, chemical structure and potential applications in several technologies. In the light of this, the incorporation of submicron- or nano-sized materials into starch-based hydrogel formulations has been explored as a very attractive strategy to improve properties and applications. This chapter is devoted to recent aspects of the development of starch-based hydrogel nanocomposites focused on the formulation of functional materials with enhanced properties for more suitable applications in different fields. The main aspects discussed are those based on structure–property relationships and also specific functionalities for a given application. Further comprehensive studies will broaden the understanding of structure–property relationships. Some future trends are highlighted – breakthroughs are necessary for improving the boundaries of knowledge of the materials science field.