The effect of multi-material architecture on the ex vivo osteochondral integration of bioprinted constructs

Extrusion bioprinted constructs for osteochondral tissue engineering were fabricated to study the effect of multi-material architecture on encapsulated human mesenchymal stem cells' tissue-specific matrix de-position and integration into an ex vivo porcine osteochondral explant model. Two extrusion fiber archi-tecture groups with differing transition regions and degrees of bone-and cartilage-like bioink mixing were employed. The gradient fiber (G-Fib) architecture group showed an increase in chondral integration over time, 18.5 +/- 0.7 kPa on Day 21 compared to 9.6 +/- 1.6 kPa on Day 1 for the required peak push-out force, and the segmented fiber (S-Fib) architecture group did not, which corresponded to the increase in sulfated glycosaminoglycan deposition noted only in the G-Fib group and the staining for cellularity and tissue-specific matrix deposition at the fiber-defect boundary. Conversely, the S-Fib architecture was as-sociated with significant mineralization over time, but the G-Fib architecture was not. Notably, both fiber groups also had similar chondral integration as a re-inserted osteochondral tissue control. While archi-tecture did dictate differences in the cells' responses to their environment, architecture was not shown to distinguish a statistically significant difference in tissue integration via fiber push-out testing within a given time point or explant region. Use of this three-week osteochondral model demonstrates that these bioink formulations support the fabrication of cell-laden constructs that integrate into explanted tissue as capably as natural tissue and encapsulate osteochondral matrix-producing cells, and it also highlights the important role that spatial architecture plays in the engineering of multi-phasic tissue environments.Statement of significance Here, an ex vivo model was used to interrogate fundamental questions about the effect of multi-material scaffold architectural choices on osteochondral tissue integration. Cell-encapsulating constructs resem-bling stratified osteochondral tissue were 3D printed with architecture consisting of either gradient tran-sitions or segmented transitions between the bone-like and cartilage-like bioink regions. The printed con-structs were assessed alongside re-inserted natural tissue plugs via mechanical tissue integration push-out testing, biochemical assays, and histology. Differences in osteochondral matrix deposition were ob-served based on architecture, and both printed groups demonstrated cartilage integration similar to the native tissue plug group. As 3D printing becomes commonplace within biomaterials and tissue engineer-ing, this work illustrates critical 3D co-culture interactions and demonstrates the importance of consider-ing architecture when interpreting the results of studies utilizing spatially complex, multi-material scaf-folds.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.