Bioprinted living tissue constructs with layer-specific, growth factor-loaded microspheres for improved enthesis healing of a rotator cuff

Substantial challenges remain in constructing the native tendon-to-bone interface for rotator cuff heal-ing owing to the enthesis tissues' highly organized structural and compositional gradients. Herein, we propose to bioprint living tissue constructs with layer-specific growth factors (GFs) to promote enthesis regeneration by guiding the zonal differentiation of the loaded stem cells in situ . The sustained release of tenogenic, chondrogenic, and osteogenic GFs was achieved via microsphere-based delivery carriers em-bedded in the bioprinted constructs. Compared to the basal construct without GFs, the layer-specific tis-sue analogs realized region-specific differentiation of stem cells in vitro . More importantly, bioprinted living tissue constructs with layer-specific GFs rapidly enhanced the enthesis regeneration in a rabbit ro-tator cuff tear model in terms of biomechanical restoration, collagen deposition, and alignment, showing gradient interface of fibrocartilage structures with aligned collagen fibrils and an ultimate load failure of 154.3 +/- 9.5 N resembling those of native enthesis tissues in 12 weeks. This exploration provides a feasi-ble strategy to engineer living tissue constructions with region-specific differentiation potentials for the functional repair of gradient enthesis tissues.Statement of significancePrevious studies that employed acellular layer-specific scaffolds or stem cells for the reconstruction of the rotator cuff faced challenges due to their insufficient capability to rebuild the anisotropic compositional and structural gradients of native enthesis tissues. This manuscript proposed a living tissue construct with layer-specific, GFs-loaded mu S, which can direct in situ and region-specific differentiation of the em-bedded stem cells to tenogenic, chondrogenic, and osteogenic lineages for functional regeneration of the enthesis tissues. This bioprinted living tissue construct with the unique capability to reduce fibrovascular scar tissue formation and simultaneously facilitate enthesis tissue remodeling might provide a promising strategy to repair complex and gradient tissues in the future.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.