Modulation of macrophage phenotype through controlled release of interleukin-4 from gelatine coatings on titanium surfaces.

Pro-inflammatory phenotype (M1) macrophages initiate angiogenesis, while their prolonged activation can induce chronic inflammation. Anti-inflammatory phenotype (M2) macrophages promote vessel maturation and tissue regeneration. Biomaterials which can promote M2 polarisation after appropriate inflammation should enhance angiogenesis and wound healing. Herein, Interleukin-4 (IL-4), an anti-inflammatory cytokine, was adsorbed onto a titanium surface. Then, a genipin cross-linked gelatine hydrogel was coated onto the surface to delay IL-4 release. The cross-linking degree of the hydrogel was modulated by the different amount of genipin to control release of IL-4. When 0.7 wt% (weight %) genipin was used as a cross-linker, the sample (GG07-I) released less IL-4 within the first several days, followed by a sustained release time to 14 d. Meanwhile, the release rate of IL-4 in GG07-I reached a peak between 3 d and 7 d. In culture with macrophages in vitro, GG07-I and GG07 exhibited good cytocompatibility. The phenotypical switch of macrophages stimulated by the samples was determined by FACS, ELISA and PCR. Macrophages cultured with GG07-I, GG07 and PT were firstly activated to the M1 phenotype by interferon-gamma (IFN-γ). Then, due to the release of IL-4 in 5 to 7 d, GG07-I enhanced CD206, increased the secretion and gene expression of M2 marker, such as interleukin-10 (IL-10), arginase-1 (ARG-1) and platelet derived growth factor-BB (PDGF- BB). GG07-I prompted the switch from M1 to M2 phenotype. Those appropriate secretion of cytokines would benefit both vascularisation and osseointegration. Thus, the biomaterial directing inflammatory reaction has good prospects for clinical treatments.