Substrate stiffness directs the phenotype and polarization state of cord blood derived macrophages

Cord blood (CB) mononuclear cell populations have demonstrated significant promise in biomaterials-based regenerative therapies; however, the contributions of monocyte and macrophage subpopulations towards proper tissue healing and regeneration are not well understood, and the phenotypic responses of macrophage to microenvironmental cues have not been well-studied. In this work, we evaluated the effects of cytokine stimulation and altered substrate stiffness. Macrophage derived from CB CD14⁺ monocytes adopted distinct inflammatory (M1) and anti-inflammatory (M2a and M2c) phenotypes in response to cytokine stimulation (M1: lipopolysaccharide (LPS) and interferon (IFN-γ); M2a: interleukin (IL)-4 and IL-13; M2c: IL-10) as determined through expression of relevant cell surface markers and growth factors. Cytokine-induced macrophage readily altered their phenotypes upon sequential administration of different cytokine cocktails. The impact of substrate stiffness on macrophage phenotype was evaluated by seeding CB-derived macrophage on 3wt%, 6wt%, and 14wt% poly(ethylene glycol)-based hydrogels, which exhibited swollen shear moduli of 0.1, 3.4, and 10.3 kPa, respectively. Surface marker expression and cytokine production varied depending on modulus, with anti-inflammatory phenotypes increasing with elevated substrate stiffness. Integration of specific hydrogel moduli and cytokine cocktail treatments resulted in the differential regulation of macrophage phenotypic biomarkers. These data suggest that CB-derived macrophages exhibit predictable behaviors that can be directed and finely tuned by combinatorial modulation of substrate physical properties and cytokine profiles.