Surface modification and polysaccharide deposition on BisGMA/TEGDMA thermoset.

Bisphenol A glycidylmethacrylate (BisGMA)/triethyleneglycol dimethacrylate (TEGDMA) thermosets and composites are well-known examples of biomaterials for dental applications that are receiving growing interest for orthopedic applications. While mechanical bulk properties are guaranteed by the presence of reinforcing fibers, in vitro and in vivo performances of these materials are ultimately driven by their ability to establish proper interactions between their surface and the surrounding tissues. Hence, the development of novel chemical processes enabling the introduction of bioactive molecules on the surface of these methacrylate-based thermosets is of particular interest. In the present work, we have devised a chemical strategy to expose carboxylic groups on the surface of the BisGMA/TEGDMA thermoset. The presence of negative charges was confirmed by Fourier transform infrared-attenuated total reflectance and by UV-vis spectrophotometry. Bulk mechanical properties and surface morphology of the thermoset were only slightly affected upon chemical functionalization. The activated material was further refined by the deposition of a lactose-modified chitosan (chitlac) driven by strong electrostatic interactions. The presence of the bioactive polysaccharide was confirmed by fluorescence spectroscopy and by confocal laser scanning microscopy measurements. Scratch tests were performed to evaluate the mechanical behavior of the coating. Finally, in vitro tests revealed that the presence of chitlac led to a slight enhancement of cell proliferation with respect to the unmodified BisGMA/TEGDMA thermoset. This effect was more pronounced when chitlac decorated with an arginine-glycine-aspartic acid (RGD) peptide was used in the preparation of the coating. In the latter case, the in vitro performance of the coated BisGMA/TEGDMA thermoset became comparable with that of clinically used roughened titanium.

Non-cytotoxic silver nanoparticle-polysaccharide nanocomposites with antimicrobial activity.

In this work we study (i) the formation and stabilization of silver nanoparticles in a bioactive chitosan-derived polysaccharide solution, (ii) the antimicrobial properties, either in solution or in 3D hydrogel structures, obtained by mixtures with the polysaccharide alginate, and (iii) the cytotoxicity of the latter nanocomposite materials on different eukaryotic cell lines. Antimicrobial results show that these nanocomposite systems display a very effective bactericidal activity toward both Gram+ and Gram- bacteria. However, the hydrogel does not show any cytotoxic effect toward three different eukaryotic cell lines. This is due to the fact that the nanoparticles, immobilized in the gel matrix, can exert their antimicrobial activity by simple contact with the bacterial membrane, while they can not be uptaken and internalized by eukaryotic cells. This novel finding could advantageously contribute to responding to the growing concerns on the toxicity of nanoparticles and facilitate the use of silver-biopolymer composites in the preparation of biomaterials.

Polyol synthesis of silver nanoparticles: mechanism of reduction by alditol bearing polysaccharides.

Alditol bearing chitosans have shown the ability to reduce silver ions in mild conditions and without addition of exogenous reducing agents. The ion reduction induces the formation of a lactone moiety on the polysaccharide (Fetizon reaction) without causing C-C bond cleavage on the polyol. The close and multivalent arrangement of the endogenous reducing agent (alditols) on the polysaccharide backbone resulted in the formation of silver nanoparticles (phi < 10 nm), which induced a considerable SERS effect and led to hydrogel formation.

Synergistic effects in semidilute mixed solutions of alginate and lactose-modified chitosan (chitlac).

The present study specifically aimed at preparing and characterizing semidilute binary polymer mixtures of alginate and chitlac which might find an application in the field of cell encapsulation. A polyanion, alginate, and a polycation, a lactose-modified chitosan, were mixed under physiological conditions (pH 7.4 and NaCl 0.15) and at a semidilute concentration avoiding associative phase separation. The mutual solubility was found to be dependent on the charge screening effect of the added NaCl salt, being prevented below 0.05 M NaCl. A comparison with the behavior of the polyanion (alginate) under the same experimental conditions revealed that both the viscosity and the relaxation times of the binary polymer solutions are strongly affected by the presence of the polycation. In particular, the occurrence of electrostatic interactions between the two oppositely charged polysaccharides led to a synergistic effect on the zero-shear viscosity of the solution, which showed a 4.2-fold increase with respect to that of the main component of the solution, i.e., alginate. Moreover, the relaxation time, calculated as the reciprocal of the critical share rate, markedly increased upon reducing the alginate fraction in the binary polysaccharide solution. However, the formation of the soluble complexes and the synergistic effect are reduced upon increasing the concentration of the 1:1 electrolyte. By containing a gel-forming polyanion (alginate, e.g., with Ca(2+) ions) and a bioactive polycation (chitlac, bearing a beta-linked D-galactose), the present system can be regarded as a first step toward the development of biologically active scaffold from polysaccharide mixtures.