A hydrogel/particle composite with a gradient of oxygen releasing microparticle for concurrent osteogenic and chondrogenic differentiation in a single scaffold.

In the present study, a hydrogel/particle scaffold with a gradient of the oxygen releasing microparticles was developed. Hydrogel component was composed of the oxidized pectin and silk fibroin, whereas the microparticles were constituted from polylactic acid (PLA) and calcium peroxide (CPO). A controlled mixing of the suspensions with different content of the PLA/CPO microparticles conferred a gradient of microparticles in scaffold thickness in a manner that the microparticle content increased with moving from lower to upper face of the composite. Measurement of the scaffold mechanical properties corroborated that with moving from lower to upper face, the compressive modulus increased by 78 %. The measurement of the oxygen and calcium release from the successive sections of the composite revealed that the gradient of microparticle concentration resulted in the gradient of the released oxygen and calcium. MTT analysis proved that the gradient oxygen releasing composite did not induce any toxic effect on human adipose-derived mesenchymal stem cells (hAd-MSCs). Moreover, the cell culture on successive sections of the gradient composite confirmed that oxygen releasing composite substantially improved the cell viability and density comparing the pristine hydrogel and the non-oxygen releasing counterpart. The increase in microparticle content conferred a positive impact on the number of viable cells. The study of osteogenic (ALP, OCN and OPN) and chondrogenic (SOX9, AGG and COL ⅠⅠ) gene expression proved that the gradient composite parts with high microparticle content promoted osteogenesis, whereas the parts with low microparticle content encouraged chondrogenesis of mesenchymal stem cells.