Biology subjects

Lee, Y. B.

Publications and source records attributed to Lee, Y. B..

4 recordsLinked to original sources

bioRxiv2024

In situ cell condensation-based cartilage tissue engineering via immediately implantable high-density stem cell core and rapidly degradable shell microgels

Formation of chondromimetic human mesenchymal stem cells (hMSCs) condensations typically required in vitro culture in defined environments. In addition, extended in vitro culture in differentiation media over several weeks is usually necessary prior to implantation, which is costly, time consuming and delays clinical treatment. Here, this study reports on immediately implantable core/shell microgels with a high-density hMSC-laden core and rapidly degradable hydrogel shell. The hMSCs in the core formed cell condensates within 12 hours and the oxidized and methacrylated alginate (OMA) hydrogel shells were completely degraded within 3 days, enabling spontaneous and precipitous fusion of adjacent condensed aggregates. By delivering transforming growth factor-{beta}1 (TGF-{beta}1) within the core, the fused condensates were chondrogenically differentiated and formed cartilage microtissues. Importantly, these hMSC-laden core/shell microgels, fabricated without any in vitro culture, were subcutaneously implanted into mice and shown to form cartilage tissue via cellular condensations in the core after 3 weeks. This innovative approach to form cell condensations in situ without in vitro culture that can fuse together with each other and with host tissue and be matured into new tissue with incorporated bioactive signals, allows for immediate implantation and may be a platform strategy for cartilage regeneration and other tissue engineering applications.

bioengineering↗

bioRxiv2021

Stem cell-laden hydrogel bioink for generation of high resolution and fidelity engineered tissues with complex geometries

Recently, 3D bioprinting has been explored as a promising technology for biomedical applications with the potential to create complex structures with precise features. Cell encapsulated hydrogels composed of materials such as gelatin, collagen, hyaluronic acid, alginate and polyethylene glycol have been widely used as bioinks for 3D bioprinting. However, since most hydrogel-based bioinks may not allow rapid stabilization immediately after 3D bioprinting, achieving high resolution and fidelity to the intended architecture is a common challenge in 3D bioprinting of hydrogels. In this study, we have utilized shear-thinning and self-healing ionically crosslinked oxidized and methacrylated alginates (OMAs) as a bioink, which can be rapidly gelled by its self-healing property after bioprinting and further stabilized via secondary crosslinking. It was successfully demonstrated that stem cell-laden calcium-crosslinked OMA hydrogels can be bioprinted into complicated 3D tissue structures with both high resolution and fidelity. Additional photocrosslinking enables long-term culture of 3D bioprinted constructs for formation of functional tissue by differentiation of encapsulated human mesenchymal stem cells.

bioengineering↗

bioRxiv2019

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

Scaffold-free engineering of three-dimensional (3D) tissue has focused on building sophisticated structures to achieve functional constructs. Although the development of advanced manufacturing techniques such as 3D printing has brought remarkable capabilities to the field of tissue engineering, technology to create and culture individual cell only-based high-resolution tissues, without an intervening biomaterial scaffold to maintain construct shape and architecture, has been unachievable to date. In this report, we introduce a cell printing platform which addresses the aforementioned challenge and permits 3D printing and long-term culture of a living cell-only bioink lacking a biomaterial carrier for functional tissue formation. A biodegradable and photocrosslinkable microgel supporting bath serves initially as a fluid, allowing free movement of the printing nozzle for high-resolution cell extrusion, while also presenting solid-like properties to sustain the structure of the printed constructs. The printed human stem cells, which are the only component of the bioink, couple together via transmembrane adhesion proteins and differentiate down tissue-specific lineages while being cultured in a further photocrosslinked supporting bath to form bone and cartilage tissue with precisely controlled structure. Collectively, this system, which is applicable to general 3D printing strategies, is paradigm shifting for printing of scaffold-free individual cells, cellular condensations and organoids, and may have far reaching impact in the fields of regenerative medicine, drug screening, and developmental biology.

bioengineering↗

bioRxiv2019

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 and is directed by local morphogen signals and mechanical cues. Here, we aimed to mimic these developmental conditions for regeneration of large bone defects. We hypothesized that engineered human mesenchymal stem cell (hMSC) condensations with in situ presentation of transforming growth factor-{beta}1 (TGF-{beta}1) and/or bone morphogenetic protein-2 (BMP-2) from encapsulated microparticles would promote endochondral regeneration of critical-sized rat femoral bone defects in a manner dependent on the in vivo mechanical environment. Mesenchymal condensations induced bone formation dependent on morphogen presentation, with dual BMP-2 + TGF-{beta}1 fully restoring mechanical bone function by week 12. In vivo ambulatory mechanical loading, initiated at week 4 by delayed unlocking of compliant fixation plates, significantly enhanced the bone formation rate in the four weeks after load initiation in the dual morphogen group. In vitro, local presentation of either BMP-2 alone or BMP-2 + TGF-{beta}1 initiated endochondral lineage commitment of mesenchymal condensations, inducing both chondrogenic and osteogenic gene expression through SMAD3 and SMAD5 signaling. In vivo, however, endochondral cartilage formation was evident only in the BMP-2 + TGF-{beta}1 group and was enhanced by mechanical loading. The degree of bone formation was comparable to BMP-2 soaked on collagen but without the ectopic bone formation that limits the clinical efficacy of BMP-2/collagen. In contrast, mechanical loading had no effect on autograft-mediated repair. Together, this study demonstrates a biomimetic template for recapitulating developmental morphogenic and mechanical cues in vivo for tissue engineering. One Sentence SummaryMimicking aspects of the cellular, biochemical, and mechanical environment during early limb development, chondrogenically-primed human mesenchymal stem cell condensations promoted functional healing of critical-sized femoral defects via endochondral ossification, and healing rate and extent was a function of the in vivo mechanical environment.

bioengineering↗