Biomechanical forces have been shown to significantly affect tissue development, morphogenesis, pathogenesis and healing, especially in orthopaedic tissues. Such biological processes are critically related to the differentiation of human mesenchymal stem cells (hMSCs). However, the mechanistic details regarding how mechanical forces direct MSC This article is protected by copyright. All rights reserved. were upregulated in response to the increased magnitudes of compressive strain, whereas osteogenic markers (COL1A1, SPARC, RUNX2) and calcium deposition had noticeable decreases by compressive loading in a magnitude-dependent manner. Dynamic mechanical analysis showed enhanced viscoelastic modulus with respect to the increased dynamic strain peaking at 15%, which coincides with the maximal GAG synthesis. Furthermore, polarization-sensitive optical coherence tomography (PS-OCT) revealed that mechanical loading enhanced the alignment of extracellular matrix to the greatest level by 15% strain as well. Overall, we show that the degree of differentiation of hMSCs towards osteogenic or chondrogenic lineage is inversely related, and it depends on the magnitude of dynamic compressive strain. These results demonstrate that multi-phenotypic differentiation of hMSCs can be controlled by varying the strain regimens, providing a novel strategy to modulate differentiation specification and tissue morphogenesis.
Hydrogels have demonstrated the excellent ability to enhance chondrogenesis of stem cells due to their hydrated fibrous nanostructure providing a cellular environment similar to native cartilage. However, the necessity for multi-step processes, including mixing of hydrogel precursor with cells and subsequent gelation in a mold to form a defined shape, limits their off-the-shelf usage. In this study, we developed a hybrid scaffold by combining a thermosensitive hydrogel with a mechanically stable polymer, which provides a facile means to inoculate cells in a 3D hydrogel with a mold-less, single step cell seeding process. We further showed that the hybrid scaffold enhanced chondrogenesis of mesenchymal stem cells, demonstrating its potential for cartilage tissue engineering.
Within the osteochondral interface, cellular and extracellular
matrix gradients provide a biomechanical and biochemical niche for
homeostatic tissue functions. Postnatal joint loading is critical
for the development of such tissue gradients, leading to the formation
of functional osteochondral tissues composed of superficial, middle,
and deep zones of cartilage, and underlying subchondral bone, in a
depth-dependent manner. In this regard, a novel, variable core–shell
electrospinning strategy was employed to generate spatially controlled
strain gradients within three-dimensional scaffolds under dynamic
compressive loading, enabling the local strain-magnitude dependent,
multiphenotypic stem cell differentiation. Human mesenchymal stem
cells (hMSCs) were cultured in electrospun scaffolds with a linear
or biphasic mechanical gradient, which was computationally engineered
and experimentally validated. The cell/scaffold constructs were subjected
to various magnitudes of dynamic compressive strains in a scaffold
depth-dependent manner at a frequency of 1 Hz for 2 h daily for up
to 42 days in osteogenic media. Spatially upregulated gene expression
of chondrogenic markers (ACAN, COL2A1, PRG4) and glycosaminoglycan deposition was observed
in the areas of greater compressive strains. In contrast, osteogenic
markers (COL1A1, SPARC, RUNX2) and calcium deposition were downregulated in response
to high local compressive strains. Dynamic mechanical analysis showed
the maintenance of the engineered mechanical gradients only under
dynamic culture conditions, confirming the potent role of biomechanical
gradients in developing and maintaining a tissue gradient. These results
demonstrate that multiphenotypic differentiation of hMSCs can be controlled
by regulating local mechanical microenvironments, providing a novel
strategy to recapitulate the gradient structure in osteochondral tissues
for successful regeneration of damaged joints in vivo and facile development of interfacial tissue models in vitro.
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