Insight on the Formation of Chitosan Nanoparticles through Ionotropic Gelation with Tripolyphosphate

This work reports details pertaining to the formation of chitosan nanoparticles that we prepare by the ionic gelation method. The molecular interactions of the ionic cross-linking of chitosan with tripolyphosphate have been investigated and elucidated by means of all-electron density functional theory. Solvent effects have been taken into account using implicit models. We have identified primary-interaction ionic cross-linking configurations that we define as H-link, T-link, and M-link, and we have quantified the corresponding interaction energies. H-links, which display high interaction energies and are also spatially broadly accessible, are the most probable cross-linking configurations. At close range, proton transfer has been identified, with maximum interaction energies ranging from 12.3 up to 68.3 kcal/mol depending on the protonation of the tripolyphosphate polyanion and the relative coordination of chitosan with tripolyphosphate. On the basis of our results for the linking types (interaction energies and torsion bias), we propose a simple mechanism for their impact on the chitosan/TPP nanoparticle formation process. We introduce the β ratio, which is derived from the commonly used α ratio but is more fundamental since it additionally takes into account structural details of the oligomers

Chitosan Derivatives as Biosorbents for Basic Dyes

The scope of this study was to prepare and evaluate chitosan derivatives as biosorbents for basic dyes. This was achieved by grafting poly (acrylic acid) and poly (acrylamide) through persulfate induced free radical initiated polymerization processes and covalent cross-linking of the prepared materials. Remacryl Red TGL was used as the cationic dye. Equilibrium sorption experiments were carried out at different pH and initial dye concentration values. The experimental equilibrium data for each adsorbent-dye system were successfully fitted to the Langmuir, Freundlich and pH-dependent Langmuir-Freundlich sorption isotherms. Thermodynamic parameters of the adsorption process such as ΔG°, ΔH°, and ΔS° were calculated. The negative values of free energy reflected the spontaneous nature of adsorption. The typical dependence of dye uptake on temperature and the kinetics of adsorption indicated the process to be chemisorption. The grafting modifications greatly enhanced the adsorption performance of the biosorbents, especially in the case of powdered cross-linked chitosan grafted with acrylic acid, which exhibited a maximum adsorption capacity equal to 1.068 mmol/g. Kinetic studies also revealed a significant improvement of sorption rates by the modifications. Diffusion coefficients of the dye molecule were determined to be of the order 10-13 − 10-12 m2/s. Furthermore, desorption experiments affirmed the regenerative capability of the loaded material

Chain Conformation, Molecular Dynamics, and Thermal Properties of Poly(<i>n</i>‑methylene 2,5-furanoates) as a Function of Methylene Unit Sequence Length

Poly­(n-methylene 2,5-furanoates) is a family of biobased polymers with outstanding gas barrier and mechanical properties and with the potential to frame the future in certain applications (e.g., food packaging, fibers, and engineering thermoplastics). Herein, we used combined efforts by density functional theory calculations and experiments to explore in detail the conformational properties, the thermodynamics, and the molecular dynamics in the poly­(n-methylene 2,5-furanoate) series as a function of n in the range from 2 poly­(ethylene furanoate) (PEF) to 12 poly­(dodecylene furanoate). The computational study employed the conformers suggested earlier [Macromolecules 2018, 51, 3515–3526] but used additional functionals and investigated, in addition to the monomer and trimer, the PEF nonamer with respect to conformations pertinent to the amorphous state. Depending on the conformer, variable dipole moments were obtained in the range from 2.1 to 6.1, 3.0 to 8.2, and 1.8 to 7.1 debye, respectively, for the monomer, the trimer, and the nonamer. Strikingly, both the trimer and more importantly, the nonamer exhibited very compact helical structures stabilized by π–π interactions of the furan rings. We suggest that the helical motifs within the amorphous state contribute to the barrier improvement for carbon dioxide in PEF as compared to PET. The distinct structural motifs of poly­(n-methylene 2,5-furanoate)­s exerted an influence on the sub-Tg and the segmental dynamics (average relaxation times and distribution of relaxation times, fragility, and dielectric strength). The segmental process shows Vogel–Fulcher–Tammann temperature dependence with distinctly different behaviors in the amorphous and crystalline states with Tg dependencies following an approximate linear dependence with n–1 as Tgcr = 249 ± 5 + (231 ± 18/n) and Tgam = 240 ± 5 + (232 ± 17/n). The large Tg reduction is compared with another homologous series, namely, poly­(n-alkyl methacrylates), where the internal plasticization takes place at the side group. Internal plasticization is more efficient in the latter because of the mobile free end. Apart from Tg reduction, they show (i) subglass dynamics with activation energies that decrease with increasing alkyl length [from 57.8 kJ/mol in PEF (n = 2) to 47 kJ/mol in PNF (n = 9)], revealing the unlocking of local dipolar motions by the flexible spaces, (ii) a narrow distribution within the segmental process, αam, (corresponding Kohlrausch–Williams–Watts stretching exponent of 0.48, i.e., among the narrower for amorphous polymers), (iii) segments with locally nearly antiparallel dipolar orientation correlations, and (iv) a constant fragility in the amorphous state independent of alkyl chain length. We suggest that pertinent to these dynamic features is the local packing of chains composed of compact helical segments

3D-printed hydrogels based on amphiphilic chitosan derivative loaded with levofloxacin for wound healing applications

Skin wounds not only cause physical pain to patients but also pose an economic burden to society. Consequently, effective approaches to promote skin repair remain a challenge. Specifically, chitosan-based hydrogels are ideal candidates to promote wound healing at different stages and while diminishing the factors that impede this process (such as excessive inflammatory and chronic wound infection). Furthermore, the unique biological properties of a chitosan-based hydrogel enable it to serve as both a wound dressing and a drug delivery system (DDS). In the present work, chitosan (CS) graft copolymer with [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (CS-MTAC), a cationic monomer with promising antibacterial properties, was synthesized. The successful synthesis of the copolymer was confirmed, while it was studied for its swelling ability and water absorption capacity, as well as for its biocompatibility and antibacterial properties. Expecting to improve its printability, the copolymer was blended with elastin (EL), collagen (COL), and increasing concentrations of gelatin (GEL). The hydrogel with 6% w/v CS, 4% w/w EL, 4% w/w COL and 1% w/v GEL was selected for its potential to be 3D-printed and was neutralized with ammonia vapors or ethanol/sodium hydroxide solution and loaded with levofloxacin. The feasibility of CS-MTAC/EL/COL/GEL bioink, loaded with Levo, as a suitable candidate for wound healing and drug delivery applications, has been demonstrated.</p

3D-Printed Chitosan-Based Hydrogels Loaded with Levofloxacin for Tissue Engineering Applications

Herein, we demonstrate the feasibility of a three-dimensional printed chitosan (CS)–poly­(vinyl alcohol) (PVA)–gelatin (Gel) hydrogel incorporating the antimicrobial drug levofloxacin (LEV) as a potential tissue engineering scaffold. Hydrogels were prepared by physically cross-linking the polymers, and the printability of the prepared hydrogels was determined. The hydrogel with 3% w/v of CS, 3% w/v of PVA, and 2% w/v of Gel presented the best printability, producing smooth and uniform scaffolds. The integrity of 3D-printed scaffolds was improved via a neutralization process since after testing three different neutralized agents, i.e., NH3 vapors, EtOH/NaOH, and KOH solutions. It was proved that the CS/PVA/Gel hydrogel was formed by hydrogen bonds and remained amorphous in the 3D-printed structures. Drug loading studies confirmed the successful incorporation of LEV, and its in vitro release continued for 48 h. The cytotoxicity/cytocompatibility tests showed that all prepared scaffolds were cytocompatible

Factors Controlling the Enhanced Mechanical and Thermal Properties of Nanodiamond-Reinforced Cross-Linked High Density Polyethylene

A systematic investigation of the factors influencing the notable enhancement of the mechanical and thermal properties of nanodiamonds (NDs)-reinforced cross-linked high density polyethylene (PEX) is presented in this work. The effects of crystal structure and molecular conformation as well as filler dispersion and adhesion with the matrix were found to govern the mechanical properties of the final composites. A considerable increase in the strength, toughness, and elastic modulus of the materials was found for the composites with filler content below 1 wt %. For higher NDs concentrations, the properties degraded. When filler concentration does not exceed 1 wt %, enhanced adhesion with the matrix is achieved, allowing a more successful load transfer between the filler and the matrix, thus enabling an effective reinforcement of the composites. The higher degree of crystallinity along with larger crystal size are also positively influencing the mechanical properties of PEX. Higher filler concentrations, on the other hand, lead to the formation of larger aggregates, which lead to lower adhesion with the matrix, while they also constitute stress concentrators and therefore reduce the positive reinforcement of the matrix. The thermal conductivity of the composites was also found to be significantly increased for low-filler concentrations. This enhancement was less significant for higher NDs concentrations. It is concluded that this reinforcement is due to the heat capacity increase that NDs incorporation causes in PEX. Additionally, a thermal stability enhancement was found for the composite with minimum filler content

Amino-Functionalized Multiwalled Carbon Nanotubes Lead to Successful Ring-Opening Polymerization of Poly(ε-caprolactone): Enhanced Interfacial Bonding and Optimized Mechanical Properties

In this work, the synthesis, structural characteristics, interfacial bonding, and mechanical properties of poly­(ε-caprolactone) (PCL) nanocomposites with small amounts (0.5, 1.0, and 2.5 wt %) of amino-functionalized multiwalled carbon nanotubes (<i>f</i>-MWCNTs) prepared by ring-opening polymerization (ROP) are reported. This method allows the creation of a covalent-bonding zone on the surface of nanotubes, which leads to efficient debundling and therefore satisfactory dispersion and effective load transfer in the nanocomposites. The high covalent grafting extent combined with the higher crystallinity provide the basis for a significant enhancement of the mechanical properties, which was detected in the composites with up to 1 wt % <i>f</i>-MWCNTs. Increasing filler concentration encourages intrinsic aggregation forces, which allow only minor grafting efficiency and poorer dispersion and hence inferior mechanical performance. <i>f</i>-MWCNTs also cause a significant improvement on the polymerization reaction of PCL. Indeed, the in situ polymerization kinetics studies reveal a significant decrease in the reaction temperature, by a factor of 30–40 °C, combined with accelerated the reaction kinetics during initiation and propagation and a drastically reduced effective activation energy

Poly(itaconic acid)-Grafted Chitosan Adsorbents with Different Cross-Linking for Pb(II) and Cd(II) Uptake

Two novel chitosan (CS) adsorbents were prepared in powder form, after modification with the grafting of itaconic acid (CS-<i>g</i>-IA) and cross-linking with either glutaraldehyde (CS-<i>g</i>-IA­(G)) or epichlorohydrin (CS-<i>g</i>-IA­(E)). Their adsorption properties were evaluated in batch experiments for Cd­(II) or Pb­(II) uptake. Characterization techniques were applied to the prepared adsorbents as swelling experiments, TGA, SEM, XRD, and FTIR. Adsorption mechanisms were suggested for different pH conditions. Various adsorption parameters were determined as the effect of pH, contact time, and temperature. The maximum adsorption capacities for Cd­(II) uptake were 405 and 331 mg/g for CS-<i>g</i>-IA­(G) and CS-<i>g</i>-IA­(E), respectively, revealing the capacity enhancement after grafting (124 and 92 mg/g were the respective values before grafting, respectively). A similar grafting effect was observed for Pb­(II) uptake, proving its adsorption effectiveness on the CS backbone. The reuse of adsorbents was tested with 20 adsorption–desorption cycles