Cell seeding via bioprinted hydrogels supports cell migration into porous apatite-wollastonite bioceramic scaffolds for bone tissue engineering

Cell seeding via cell-laden hydrogels offers a rapid way of depositing cells onto a substrate or scaffold. When appropriately formulated, hydrogels provide a dense network of fibres for cellular encapsulation and attachment, creating a protective environment that prevents cells to be washed away by media. However, when incorporating hydrogels into a cell seeding strategy the cellular capacity for migration from a hydrogel network and subsequent biofunctionality must be assessed. Here, we compare cell seeding via a bioprinted hydrogel with conventional manual cell seeding in media. To this end, we use a binder jet 3D printed bioceramic scaffold as a model system for bone tissue engineering and the reactive jet impingement (ReJI) bioprinting system to deliver high cell density cell-laden hydrogels onto the surface of the scaffolds. The bioceramic scaffolds were produced in apatite-wollastonite (AW) glass-ceramic, with a total porosity of ~50 %, with pore size predominantly around 50-200 μm. Bone marrow-derived mesenchymal stromal cells were seeded onto the porous AW substrate both in media and via ReJI bioprinting. Cell seeding in media confirmed the osteoinductive nature and the ability of the scaffold to support cell migration within the porous structure. Cell seeding via ReJI bioprinting demonstrated that the cell-laden hydrogel penetrated the porous AW structure upon hydrogel deposition. Furthermore, cells would then migrate out from the hydrogel network and interact with the bioceramic substrate. Overall, levels of cell migration and mineralisation were significant and comparable for both seeding approaches. However, cell seeding via bioprinted hydrogels may serve as an effective strategy for in situ cell seeding into implants, which is desired in clinical tissue engineering procedures, avoiding the time taken for cell attachment from media, and the requirement to maintain a specific orientation until attachment has occurred.