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.

Automated summary

Extrusion bioprinted constructs with different fiber architectures were fabricated to study their effects on encapsulated human mesenchymal stem cells' tissue-specific matrix deposition and integration. The gradient fiber (G-Fib) architecture showed increased chondral integration over time, while the segmented fiber (S-Fib) architecture was associated with significant mineralization. Both architectures demonstrated similar cartilage integration as re-inserted tissue controls. The study highlights the importance of considering spatial architecture in the engineering of multi-phasic tissue environments.