Scaffold-free human mesenchymal stem cell construct geometry regulates long bone regeneration.

Biomimetic bone tissue engineering strategies partially recapitulate development. We recently showed functional restoration of femoral defects using scaffold-free human mesenchymal stem cell (hMSC) condensates featuring localized morphogen presentation with delayed in vivo mechanical loading. Possible effects of construct geometry on healing outcome remain unclear.

Combinatorial morphogenetic and mechanical cues to mimic bone development for defect repair.

Endochondral ossification during long bone development and natural fracture healing initiates by mesenchymal cell condensation, directed by local morphogen signals and mechanical cues. Here, we aimed to mimic development for regeneration of large bone defects. We hypothesized that engineered human mesenchymal condensations presenting transforming growth factor-β1 (TGF-β1) and/or bone morphogenetic protein-2 (BMP-2) from encapsulated microparticles promotes endochondral defect regeneration contingent on in vivo mechanical cues.

Gelatin microspheres releasing transforming growth factor drive in vitro chondrogenesis of human periosteum derived cells in micromass culture.

For cartilage tissue engineering, several in vitro culture methodologies have displayed potential for the chondrogenic differentiation of mesenchymal stem cells (MSCs). Micromasses, cell aggregates or pellets, and cell sheets are all structures with high cell density that provides for abundant cell-cell interactions, which have been demonstrated to be important for chondrogenesis. Recently, these culture systems have been improved via the incorporation of growth factor releasing components such as degradable microspheres within the structures, further enhancing chondrogenesis.

A Modular Strategy to Engineer Complex Tissues and Organs.

Currently, there are no synthetic or biologic materials suitable for long-term treatment of large tracheal defects. A successful tracheal replacement must (1) have radial rigidity to prevent airway collapse during respiration, (2) contain an immunoprotective respiratory epithelium, and (3) integrate with the host vasculature to support epithelium viability. Herein, biopolymer microspheres are used to deliver chondrogenic growth factors to human mesenchymal stem cells (hMSCs) seeded in a custom mold that self-assemble into cartilage rings, which can be fused into tubes.

High-density human mesenchymal stem cell rings with spatiotemporally-controlled morphogen presentation as building blocks for engineering bone diaphyseal tissue.

Emerging biomimetic tissue engineering strategies aim to partially recapitulate fundamental events that transpire during embryonic skeletal development; namely, cellular self-organization and targeted morphogenetic pathway activation. Here, we describe self-assembled, scaffold-free human mesenchymal stem cell (hMSC) rings featuring microparticle-mediated presentation of transforming growth factor-β1 (TGF-β1) and bone morphogenetic protein-2 (BMP-2). We tested the hypothesis that spatiotemporally-controlled dual presentation of TGF-β1 and BMP-2 is superior in modulating endochondral ossification of high-density cellular constructs compared to single morphogen delivery.