Towards an intraoperative engineering of osteogenic and vasculogenic grafts from the stromal vascular fraction of human adipose tissue

Grafts generated by cultivation of progenitor cells from the stromal vascular fraction of human adipose tissue have been proven to have osteogenic and vasculogenic properties in vivo. However, in vitro manufacture of such implants is challenged by complex, impractical and expensive processes, and requires implantation in a separate surgery. This study investigates the feasibility of an intraoperative approach to engineer cell-based bone grafts with tissue harvest, cell isolation, cell seeding onto a scaffold and subsequent implantation within a few hours. Freshly isolated adipose tissue cells from a total of 11 donors, containing variable fractions of mesenchymal and endothelial progenitors, were embedded at different densities in a fibrin hydrogel, which was wrapped around bone substitute materials based on beta-tricalcium phosphate (ChronOS), hydroxyapatite (Engipore), or acellular xenograft (Bio-Oss). The resulting constructs, generated within 3 hours from biopsy harvest, were immediately implanted ectopically in nude mice and analysed after eight weeks. All explants contained blood vessels formed by human endothelial cells, functionally connected to the recipient's vasculature. Human origin cells were also found within osteoid structures, positively immunostained for bone sialoprotein and osteocalcin. However, even with the highest loaded cell densities, no frank bone tissue was detected, independently of the material used. These results provide a proof-of-principle that an intraoperative engineering of autologous cell-based vasculogenic bone substitutes is feasible, but highlight that - in the absence of in vitro commitment--additional cues (e.g., low dose of osteogenic factors or orthotopic environmental conditions) are likely needed to support complete osteoblastic cell differentiation and bone tissue generation.

Engineering of osteoinductive grafts by isolation and expansion of ovine bone marrow stromal cells directly on 3D ceramic scaffolds

In this work, we investigated whether osteoinductive constructs can be generated by isolation and expansion of sheep bone marrow stromal cells (BMSC) directly within three-dimensional (3D) ceramic scaffolds, bypassing the typical phase of monolayer (2D) expansion prior to scaffold loading. Nucleated cells from sheep bone marrow aspirate were seeded into 3D ceramic scaffolds either by static loading or under perfusion flow and maintained in culture for up to 14 days. The resulting constructs were exposed to enzymatic treatment to assess the number and lineage of extracted cells, or implanted subcutaneously in nude mice to test their capacity to induce bone formation. As a control, BMSC expanded in monolayer for 14 days were also seeded into the scaffolds and implanted. BMSC could be isolated and expanded directly in the 3D ceramic scaffolds, although they proliferated slower than in 2D. Upon ectopic implantation, the resulting constructs formed a higher amount of bone tissue than constructs loaded with the same number of 2D-expanded cells. Constructs cultivated for 14 days generated significantly more bone tissue than those cultured for 3 days. No differences in bone formation were found between samples seeded by static loading or under perfusion. In conclusion, the culture of bone marrow nucleated cells directly on 3D ceramic scaffolds represents a promising approach to expand BMSC and streamline the engineering of osteoinductive grafts.