Injectable tissue engineering using biodegradable polymeric microparticles

Abstract

Injectable cell therapy would provide a patient friendly procedure for treatment of degenerated or wounded tissue. Biodegradable injectable porous microspheres were fabricated to use as dual-purpose microcarriers for cell culture and injectable scaffold for tissue regeneration. Gas foaming in a water-in-oil-in-water (W/O/W) double emulsion was performed for fabricating the well-interconnected porous microcarriers using poly(lactic-co-glycolic acid) (PLGA). The gas foaming conditions were finely tuned to control the structural and morphological characteristics. Porous microcarriers with a mean size of ~ $175\mum$ and an average pore diameter of ~ $29\mum$ were produced for cell cultivation and injectable delivery. To promote cell seeding, amine functionalized porous microcarriers were prepared by blending amine functionalized PLGA with unreacted PLGA. To assess the porous microcarriers for chondrocyte cultivation, bovine articular chondrocytes were seeded and cultured in vitro in spinner flasks for 4 weeks. Visualization and biochemical analyses of the microcarrier-cell constructs were performed to demonstrate cell proliferation and phenotypic expression. Quantification of DNA, glycosaminoglycan, and collagen content showed that greatly enhanced cell proliferation and expression of cartilage-specific phenotype were observed for cultures in the order of amine functionalized porous microcarriers, porous microcarriers, nonporous microcarriers, and monolayer culture. Cellular aggregates were prepared using biodegradable porous microspheres for injectable reconstruction of soft tissues $\it{in vivo}$. Biodegradable porous microspheres with sizes of ~ $50\mum$ were prepared by a porogen leaching-phase separation process in an oil-in-water single emulsion method using poly(D,L-lactide-co-glycolide) (PLGA). 3T3 L1 mouse preadipocyte cells were transformed into cellular aggregates by suspension cultivation in a spinner flask using the porous microspheres as effectiv...