Bone tissue engineering in a rotating bioreactor using a microcarrier matrix system

A novel approach was utilized to grow in vitro mineralized bone tissue usin g lighter-than-water, polymeric scaffolds in a high aspect ratio rotating b ioreactor. We have adapted polymer microencapsulation methods for the forma tion of hollow, lighter-than-water microcarriers of degradable poly(lactic- co-glycolic acid). Scaffolds were fabricated by sintering together lighter- than-water microcarriers from 500 to 860 mum in diameter to create a fully interconnected, three-dimensional network with an average pore size of 187 mum and aggregate density of 0.65 g/mL. Motion in the rotating bioreactor w as characterized by numerical simulation and by direct measurement using an in situ particle tracking system. Scaffold constructs established a near c ircular trajectory in the fluid medium with a terminal velocity of 98 mm/s while avoiding collision with the bioreactor wall. Preliminary cell culture studies on these scaffolds show that osteoblast-like cells readily attache d to microcarrier scaffolds using controlled seeding conditions with an ave rage cell density of 6.5 x 10(4) cells/cm(2). The maximum shear stress impa rted to attached cells was estimated to be 3.9 dynes/cm(2). In addition, ce lls cultured in vitro on these lighter-than-water scaffolds retained their osteoblastic phenotype and showed significant increases in alkaline phospha tase expression and alizarin red staining by day 7 as compared with statica lly cultured controls. (C) 2001 John Wiley & Sons, Inc.