Human platelet-rich plasma improves the nesting and differentiation of human chondrocytes cultured in stabilized porous chitosan scaffolds.

The clinical management of large-size cartilage lesions is difficult due to the limited regenerative ability of the cartilage. Different biomaterials have been used to develop tissue engineering substitutes for cartilage repair, including chitosan alone or in combination with growth factors to improve its chondrogenic properties. The main objective of this investigation was to evaluate the benefits of combining activated platelet-rich plasma with a stabilized porous chitosan scaffold for cartilage regeneration. To achieve this purpose, stabilized porous chitosan scaffolds were prepared using freeze gelation and combined with activated platelet-rich plasma. Human primary articular chondrocytes were isolated and cultured in stabilized porous chitosan scaffolds with and without combination to activated platelet-rich plasma. Scanning electron microscopy was used for the morphological characterization of the resulting scaffolds. Cell counts were performed in hematoxylin and eosin-stained sections, and type I and II collagen expression was evaluated using immunohistochemistry. Significant increase in cell number in activated platelet-rich plasma/stabilized porous chitosan was found compared with stabilized porous chitosan scaffolds. Chondrocytes grown on stabilized porous chitosan expressed high levels of type I collagen but type II was not detectable, whereas cells grown on activated platelet rich plasma/stabilized porous chitosan scaffolds expressed high levels of type II collagen and type I was almost undetectable. In summary, activated platelet-rich plasma increases nesting and induces the differentiation of chondrocytes cultured on stabilized porous chitosan scaffolds.

Kinetic study of thermal degradation of chitosan as a function of deacetylation degree.

Thermal degradation of chitosan with varying deacetylation degree (DD) ranging between 50 and 85% was analyzed by dynamic thermogravimetric analysis at different heating rates. The present study focused on the temperature range between 500 and 800K, above water evaporation. Thermal degradation showed a main degradation stage in this temperature interval with a second stage that appeared in the weight derivative curves as a shoulder in the high temperature side of the main peak with increasing intensity as the DD decreased. The Kissinger and isoconversional Ozawa-Flynn-Wall models were employed to evaluate the Ea of both thermal degradation processes. Different kinetic models were tested to computer simulate the thermogravimetric traces calculating the model parameters with a non-linear least squares fitting routine. The Sestack-Berggren model allowed reproducing accurately the overlapping of the two degradation mechanisms and calculating the mass fraction lost in each of them revealing the coupling between the two degradation mechanisms.

Determining the influence of N-acetylation on water sorption in chitosan films.

Water absorption in chitosan rapidly increases when the deacetylation degree decreases between 85 and 45%. This seems to contradict the fact that water absorption in chitin is much lower than that of chitosan. The aim of this paper is to understand this feature by measuring the main parameters affecting equilibrium water content. Since swelling capacity depends on the water-polymer interaction, the Flory Huggins interaction parameter was evaluated, finding small or null dependence on the deacetylation degree. Other factor influencing elastic energy is chain stiffness related to the elastic modulus that was measured as a function of deacetylation degree. Besides, crystalline structure was measured by X-ray diffraction patterns as a characteristic of cross-linking density. These observations led us to conclude that the instability of crystals during the swelling process increases with decreasing deacetylation degree, explaining the high equilibrium water content of low deacetylation chitosans.