Significant increase in Young׳s modulus of ATDC5 cells during chondrogenic differentiation induced by PAMPS/PDMAAm double-network gel: Comparison with induction by insulin

A double-network (DN) gel, which was composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N′-dimethyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. The present study investigated the biomechanical and biological responses of chondrogenic progenitor ATDC5 cells cultured on the DN gel. ATDC5 cells were cultured on a polystyrene surface without insulin (Culture 1) and with insulin (Culture 2), and on the DN gel without insulin (Culture 3). The cultured cells were evaluated using micropipette aspiration for cell Young?s modulus and qPCR for gene expression of chondrogenic and actin organization markers on days 3, 7 and 14. On day 3, the cells in Culture 3 formed nodules, in which the cells exhibited an actin cortical layer inside them, and gene expression of type-II collagen, aggrecan, and SOX9 was significantly higher in Culture 3 than Cultures 1 and 2 (p<0.05). Young?s modulus in Culture 3 was significantly higher than that in Culture 1 throughout the testing period (p<0.05) and that in Culture 2 on day 14 (p<0.01). There was continuous expression of actin organization markers in Culture 3. This study highlights that the cells on the DN gel increased the modulus and mRNA expression of chondrogenic markers at an earlier time point with a greater magnitude compared to those on the polystyrene surface with insulin. This study also demonstrates a possible strong interrelation among alteration of cell mechanical properties, changes in actin organization and the induction of chondrogenic differentiation.     

Preparation of single or double-network chitosan/poly(vinyl alcohol) gel films through selectively cross-linking method

A selectively cross-linking method, which is based on the “di–diol” interaction between poly(vinyl alcohol) and borate and the strong electrostatic interaction between chitosan and tripolyphosphate, was developed. Chitosan/poly(vinyl alcohol) films cross-linked separately with borate, tripolyphosphate and borate/tripolyphosphate were then prepared in terms of this method. Water vapor permeation, mechanical strength, surface morphology and molecular interactions of the films were studied by water permeation test, texture test, atomic force microscopy and ATR-FTIR spectroscopy. With the introduction of cross-linking structure, there is a large improvement in elastic modulus from 271 ± 14.2 to 551 ± 14.7 MPa and a large decrease in water vapor permeability from (5.41 ± 0.21) × 10⁻⁷ g/m h Pa to (3.12 ± 0.24) × 10⁻⁷ g/m h Pa of chitosan/poly(vinyl alcohol) films. The surface morphology of the cross-linked films exhibits a nanoparticle aggregation structure. The size and aggregation behavior of these nanoparticles are strongly related to the type of cross-linker. Furthermore, ATR-FTIR results indicate that strong interaction between polymer matrix and cross-linker exists in our system. This work provides a simple and efficient way to prepare chitosan/poly(vinyl alcohol) films with controllable network structure.