Mechanical and structural response of a hybrid hydrogel based on chitosan and poly(vinyl alcohol) cross-linked with epichlorohydrin for potential use in tissue engineering.

The development and characterization of a hybrid hydrogel based on chitosan (CS) and poly(vinyl alcohol) (PVA) chemically cross-linked with epichlorohydrin (ECH) is presented. The mechanical response of these hydrogels was evaluated by uniaxial tensile tests; in addition, their structural properties such as average molecular weight between cross-link points (Mcrl), mesh size (DN), and volume fraction (v(s)) were determined. This was done using the equivalent polymer network theory in combination with the obtained results from tensile and swelling tests. The films showed Young's modulus values of 11 ± 2 MPa and 9 ± 1 MPa for none irradiated and ultraviolet (UV) irradiated hydrogels, respectively. The cell viability was assessed using Calcein AM and Ethidium homodimer-1 assay and environmental scanning electron microscopy. The 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan thiazolyl blue formazan (MTT Formazan assay) results did not show cytotoxic effects; this was in good agreement with nuclear magnetic resonance and fourier transform infrared spectroscopies; their results did not show traces of ECH. This indicated that after the crosslinking process, there was no free ECH; furthermore, any possibility of ECH release in the construct during cell culture was discarded. The CS-PVA-ECH hybrid hydrogel allowed cell growth and extracellular matrix formation and showed adequate mechanical, structural, and biological properties for potential use in tissue engineering applications.

Genetic variation among four Mexican populations (Huichol, Purepecha, Tarahumara, and Mestizo) revealed by two VNTRs and four STRs.

Allele distributions of two polymorphisms with variable number of tandem repeats (VNTR), D1S80 and APOB, and four polymorphisms with short tandem repeats (STR), VWA, TH01, CSF1PO, and HPRTB, were analyzed in three Mexican ethnic groups: Huichol, Purepecha, and Tarahumara. Genotype distribution was in agreement with Hardy-Weinberg expectations for each locus and ethnic group. Heterozygosity (H), power of discrimination, and probability of exclusion were estimated. The three groups presented some distinctive genetic features: (1) a diminished genetic diversity (H = 66.8% to 73.4%) and mean number of alleles by locus (5.8 to 6.3) in comparison with Mexican mestizos (H = 78.3%, 10.5 alleles/locus), and (2) uneven allele distributions as evidenced by "distinctive alleles" with high frequencies, especially in the Tarahumara and the Huichol. Genetic relatedness analysis included data from a previously typed mestizo population, the largest and most widely distributed population in Mexico. Allele distribution differentiation was observed among all four groups, except between mestizo and Purepecha (p > 0.05), which was interpreted as indicating a larger Spanish component in the Purepecha as a result of gene flow effects. Although intrapopulation inbreeding (FIS) was not significant, heterozygote deficiency in the total population (FIT) and divergence among populations (FST) were significant (p < 0.05). Genetic distances displayed a closer relationship among mestizos, Purepechas, and Huichols in relation to Tarahumaras. Correlation between the observed genetic features and the geographic isolation level points to genetic drift as the main cause of differentiation among these Mexican populations.