A 3D in vitro co-culture model for evaluating biomaterial-mediated modulation of foreign-body responses

The immune response after implantation of a biomaterial may shorten the functional life of the implant, depending on the degree of the response. In this study, we used a polyacrylamide-alginate (PAAm-Alg) hydrogel, which has been previously characterized as a biocompatible material and shown to enhance regeneration of cartilage in vivo, along with a graphite-enhanced hydrogel (PAAm-Alg-G) as a non-biocompatible counterpart, to evaluate macrophage attachment and polarization to pro- or anti-inflammatory phenotypes. The performance of each biomaterial in the presence of fibroblasts and chondrocytes was validated by an in vitro model which demonstrated modulation of the foreign-body response. A blend of 5% gelatin methacryloyl and 0.1% methacrylated hyaluronic acid was optimized to mimic the extracellular matrix (ECM) and support cell viability, proliferation, migration, and functionality at an initial concentration of 3.25 x 10(5) cells/mL. The PAAm-Alg-G hydrogel localized in the simulated ECM showed cytotoxic and genotoxic effects for both fibroblasts and chondrocytes, while exhibiting a proliferative effect on macrophages with elevated immune response. The M1/M2 ratio was 0.73 for PAAm-Alg hydrogel but 2.64 for PAAm-Alg-G, leading to significant M1 dominance (p < 0.0001), as expected, on day 13. Moreover, loading PAAm-Alg hydrogel with transforming growth factor beta-3 (TGF-beta 3) resulted in a slightly more balanced M1/M2 ratio of 0.87 (p > 0.05). The interleukin-6 (IL-6) concentration secreted in the presence of PAAm-Alg hydrogel (4.58 pg/mL) significantly decreased (p < 0.0001) on day 13, while the increase (p < 0.0001) in interleukin-10 (IL-10) concentration (120.73 pg/mL) confirmed the switch from a pro-inflammatory to an anti-inflammatory response. Predicting immune responses by developing a simplistic yet powerful three-dimensional in vitro model provides advantages in preparing for clinical use of biomaterials. [GRAPHICS] .