Figure 2.

In vitro assessment of the inflammatory environment (A), the one-way signals from macrophages to differentiating stem cells (B), and the two-way signals in a simulated FBR with macrophages at the surface of a cell-laden hydrogel (C, D). In (A), cartilage cells (i.e., chondrocytes) embedded in an agarose hydrogel and cultured continuously with interleukin-1β (IL-1β) led to reduce cartilage extracellular matrix deposition shown by the red staining for sulfated glycosaminoglycans. Reproduced with permission from [26]. In (B), macrophages were conditioned with different activators (i.e., no activator (CM0), lipopolysaccharide (LPS) + interferon gamma (IFN-γ) for a classically activated (inflammatory) macrophage (CM1), or interleukin-4 (IL-4) for an alternatively activated macrophage (CM2). After 24 hours, the medium with activator was removed, and fresh media applied without activator for 24 hours, to create the conditioned medium (CM). The CM was then supplemented with osteogenic factors and applied to bone marrow derived mesenchymal stem cells (MSCs) for seven days. Gene expression of two osteogenic genes, osterix and osteocalcin, are shown. Reproduced from [30]. In (C), macrophages were seeded on top of a fibroblast-laden poly(ethylene glycol) (PEG) hydrogel with RGD and cultured with or without LPS. The cell populations were separated after 24 hours and gene expression analyzed for the macrophage by IL-1β and tumor necrosis factor-α (TNF-α) and for the fibroblast for collagen 1α and IL-1β. The horizontal line represents the corresponding mono-culture. Reproduced with permission from [39]. In (D), macrophages were seeded on top of a MSC-laden poly(ethylene glycol) (PEG) hydrogel with RGD and cultured with or without LPS for 24 hours. Relative expression for the macrophage was assessed by TNF-α and TNF-α protein was measured in the medium. Reproduced with permission from [35].