A Modular Strategy to Engineer Complex Tissues and Organs

Abstract

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. These rings and tubes can be fabricated with tunable wall thicknesses and lumen diameters with promising mechanical properties for airway collapse prevention. Epithelialized cartilage is developed by establishing a spatially defined composite tissue composed of human epithelial cells on the surface of an hMSC‐derived cartilage sheet. Prevascular rings comprised of human umbilical vein endothelial cells and hMSCs are fused with cartilage rings to form prevascular–cartilage composite tubes, which are then coated with human epithelial cells, forming a tri‐tissue construct. When prevascular– cartilage tubes are implanted subcutaneously in mice, the prevascular structures anastomose with host vasculature, demonstrated by their ability to be perfused. This microparticle–cell self‐assembly strategy is promising for engineering complex tissues such as a multi‐tissue composite trachea.

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

“…Recently, we reported a modular, scalable, scaffold-free system for engineering hMSC rings that can be assembled and fused into tubular structures (27)(28)(29). Here, we also employed gelatin microspheres (30) for early TGF-β1 presentation (32), and mineral-coated hydroxyapatite microparticles (31) for sustained BMP-2 presentation (32), the combination of which exerts potent in situ chondrogenic priming effects on early hMSC condensations, consistent with our recent study (28).…”

“…Limitations of this approach include (i) the necessity to pre-culture hMSC condensations for ≥3 weeks in induction medium supplied with morphogens (e.g., transforming growth factor-β1 (TGF-β1)) to stimulate cartilage template formation, and (ii) and the inability to generate tubular tissue constructs. To that end, we have recently reported a modular, scalable, scaffold-free system for engineering hMSC rings that can be assembled and fused into tubular structures (27)(28)(29). The incorporation of TGF-β1-presenting gelatin microspheres for in situ chondrogenic priming (30) and BMP-2-presenting mineral-coated hydroxyapatite microparticles to induce bony remodeling of the cartilaginous template (31) circumvents the need for lengthy pre-differentiation and may enable early in vivo implantation.…”

Selection of the optimum 3D‐printed pore and the surface modification techniques for tissue engineering tracheal scaffold in vivo reconstruction

“…Tissue engineering aims to combine seed cells and scaffolds effectively to repair target tissue defects and reconstruct organs . It is undeniable that the self‐assembly modular bottom up (scaffold‐free) approach used to grow stem cell‐based tubes, with control over tissue size and geometry, is a promising platform to engineer complex organs (e.g., trachea) . But, it generally required the isolation and culture of seed cells in advance, and then incubated in a suitable in vitro or in vivo bioreactor for a period of time.…”

“…1 It is undeniable that the self-assembly modular bottom up (scaffold-free) approach used to grow stem cell-based tubes, with control over tissue size and geometry, is a promising platform to engineer complex organs (e.g., trachea). [20][21][22] But, it generally required the isolation and culture of seed cells in advance, and then incubated in a suitable in vitro or in vivo bioreactor for a period of time. These processes will increase the risk of infection and more expenditure, and for instance, it could not meet the needs of patients with airway defects in an emergency situation.…”

Living cell-only bioink and photocurable supporting medium for printing and generation of engineered tissues with complex geometries

“…printed hMSC constructs were digested in papain buffer (1 mL, pH 6.5)) containing papain (25 μ g m/l, Sigma), l-cysteine (2 × 10 -3 M, Sigma), sodium phosphate (50 × 10 -3 M) and EDTA (2 × 10 -3 M) at 65 °C overnight. GAG content (N=4) was quantified by a dimethylmethylene blue assay 4 and DNA content (N=4) was measured using the PicoGreen assay as described above.…”