Optical coherence microscopy of living cells and bioengineered tissue dynamics in high-resolution cross-section

Thickness-wise growth technique for human articular chondrocytes to fabricate three-dimensional cartilage grafts

INTRODUCTION

Cutting the cost of manufacturing is important for extending the use of tissue-engineered therapeutic products. The present study aimed to develop a simple method for fabrication of cartilaginous tissues for regenerative therapy, utilizing the phenomenon where human articular chondrocytes grow thickness-wise and spontaneously form three-dimensionally thick tissues.

METHODS

Normal human articular chondrocytes (NHACs) were cultured with varying concentrations of transforming growth factor beta 1 (TGF-β1) and/or fibroblast growth factor-2 (FGF-2) to optimize the culture condition for thickness-wise growth of chondrocytes. Next, the tissues grown in the optimal condition were subjected to re-differentiation culture in attached and detached states to assess differentiation capacity by evaluating secreted factors, histological analysis, and a gene expression assay.

RESULTS

NHACs grew thickness-wise efficiently in the presence of 1 ng/mL TGF-β1 and 10 ng/mL FGF-2. After two weeks of culture, NHACs grew with 11-fold higher thickness and 16-fold higher cell number compared to cells which were neither treated with TGF-β1 nor with FGF-2. These thickness-wise-grown chondrocytes could be re-differentiated by a differentiation medium according to the increase in melanoma inhibitory activity (MIA) and positive safranin-O staining. Interestingly, the cartilaginous gene expression was considerably different between the attached and detached conditions even in the same culture medium, indicating the necessity of detachment and shrinkage to achieve further differentiation.

CONCLUSIONS

Spontaneous thickness-wise growth might provide a simple tissue-engineering method for manufacturing cartilaginous 3D tissues.

Contractile force measurement of human induced pluripotent stem cell-derived cardiac cell sheet-tissue

We have developed our original tissue engineering technology “cell sheet engineering” utilizing temperature-responsive culture dishes. The cells are confluently grown on a temperature-responsive culture dish and can be harvested as a cell sheet by lowering temperature without enzymatic digestion. Cell sheets are high-cell-density tissues similar to actual living tissues, maintaining their structure and function. Based on this “cell sheet engineering”, we are trying to create functional cardiac tissues from human induced pluripotent stem cells, for regenerative therapy and in vitro drug testing. Toward this purpose, it is necessary to evaluate the contractility of engineered cardiac cell sheets. Therefore, in the present study, we developed a contractile force measurement system and evaluated the contractility of human iPSC-derived cardiac cell sheet-tissues. By attaching the cardiac cell sheets on fibrin gel sheets, we created dynamically beating cardiac cell sheet-tissues. They were mounted to the force measurement system and the contractile force was measured stably and clearly. The absolute values of contractile force were around 1 mN, and the mean force value per cross-sectional area was 3.3 mN/mm². These values are equivalent to or larger than many previously reported values, indicating the functionality of our engineered cardiac cell sheets. We also confirmed that both the contractile force and beating rate were significantly increased by the administration of adrenaline, which are the physiologically relevant responses for cardiac tissues. In conclusion, the force measurement system developed in the present study is valuable for the evaluation of engineered cardiac cell sheet-tissues, and for in vitro drug testing as well.