A hydrogel/particle composite with gradient in oxygen releasing microparticle for oxygenation of the...

At the cartilage-to-bone interface, the residing cells are different with respects to metabolic requirements. Fabrication of a scaffold affording different metabolic needs of these cells can be taken account of a promoting step for regeneration of cartilage- to-bone interface. In the present study, a scaffold with a depth-dependent gradient of oxygen releasing microparticles was developed. To this end, oxygen releasing microparticles were fabricated from polylactic acid (PLA) and calcium peroxide and then dispersed in hydrogel precursor of functionalized pectin and fibroin. The microparticles were loaded in a hydrogel precursor solution in a gradient manner using a gradient mixing chamber. The mixing chamber was composed of two compartments filled with hydrogel precursors with different microparticle contents (10 and 30% w/w) and an interfacial mixing port. The velocity of microparticle loaded solution inside the gradient chamber was modeled using momentum balance Navier-Stokes equations. Moreover, spatial and temporal variations of microparticle concentration in the gradient chamber were modeled using mass transfer Navier-Stokes equations. Chemical, morphological and structural variations across the composite thickness were evaluated using microscopy and spectroscopy analyses. The model proposed by Navier-Stokes equation corroborated that the flow velocity was different in various domains of the mixing chamber and in the vicinity of the mixing port the velocity was substantially higher than the bulk flow. Moreover, the velocity profile showed gradual velocity changes from bulk to the mixing port. The model represented for microparticle concentration proved that microparticle content of precursor solution varied both spatially and temporally. As time goes by, the microparticle concentration gradually increased from about 10% w/w and approached to about 30% w/w at the end of the process. SEM micrographs from the cross-section of composite corroborated that microparticle density gradually increased from the lower to the upper surface. Spectroscopy confirmed that the oxygen releasing component, i.e. calcium peroxide, increased across the said direction. Oxygen measurement from successive sections of composite revealed that the amount of produced oxygen increased from the lowermost to the uppermost section. In conclusion, the hydrogel/particle composite with a gradient in oxygen releasing component can be a promising scaffold to satisfy the different metabolic needs of cells at the cartilage- to-bone interface. STATEMENT OF SIGNIFICANCE: Numerous tissue engineering scaffolds have been so far fabricated to recapitulate the gradient nature of cartilage- to-bone interface. Chemical, mechanical, structural and even electrical gradients of cartilage- to-bone interface have been tried to imitate by those scaffolds. However, scaffold with a gradient in metabolic features has not been developed yet. At the cartilage-to-bone interface, the residing cells are different with respects to metabolic requirements. Therefore, fabrication of a scaffold affording different metabolic needs of these cells can be taken account of a promoting step for regeneration of cartilage- to-bone interface. In the present study, a scaffold with a depth-dependent gradient of oxygen releasing microparticles was developed using a gradient making chamber. In addition to mathematical modeling of flow velocity and microparticle concentration in gradient making device, the depth-dependent changes in morphology, chemistry and structure of hydrogel/particle composite were experimentally evaluated.