Mesenchymal stem cells have contributed to the continuous progress of tissue engineering and regenerative medicine. Among different mesenchymal stem origins, the ones derived from adipose tissue possess many advantages including the ease of tissue harvesting, self-renewal potential and rapid population doubling time. Adipose derived stem cells (ADSC) have multipotent ability and they can differentiate into different cell linages: osteoblastic among others. In vitro bone models represent a much needed tool to carry out an initial safety assessment in the study of novel bone regenerative therapies1,2. We hypothesized that 3D bone-on-a-chip models containing ADSC could closely recreate the physiological bone microenvironment. Thus, they might become an intermedium step between the traditional 2D-in vitro and the in vivo experiments to speed up the screening of different therapeutic molecules while saving resources.
In this work we differentiated ADSC during 7 and 14 days and they were used to fabricate in vitro bone models. Undifferentiated ADSC were also assayed as negative control. Those pre-differentiated and undifferentiated cells were embedded in a 3D collagen matrix placed in a microfluidic chip. Microfluidic devices were fabricated out of PDMS as described previously3 and the hydrogel was composed of rat tail collagen Type-I. Cells were seeded at a final concentration of 1.106 ADSC/ml.
Biochemical assays and staining procedures were conducted to study cell type and morphology after 3, 7, 14, 21 days of culture. Osteogenic markers such as Alkaline phosphatase (ALP) activity, calcium mineralization, changes on cell morphology and expression of specific proteins (bone sialoprotein 2 (BSP-2), Dentin matrix acidic phosphoprotein-1 (DMP-1) and osteocalcein (OCN)) were evaluated inside the devices to determine their differentiation potential and the evolution of the culture. To the best of our knowledge, this is the first time a 3D-in vitro bone model from adipose-derived stem cells has been developed.
RESULTS AND CONCLUSIONS
ALP activity, specific protein release and culture morphology evolution show the stem cells osteogenic transition and prove that mature bone cells are obtained at the end of the culture. Thus, fully osteogenic differentiation has been successfully achieved inside the microfluidic device. Collagen hydrogel embedding bone cell niches is able to replicate bone tissue environment in vitro. This fact offers a powerful tool to study, inside a thoroughly controlled atmosphere, bone cell responses against different stimuli.
The use of SAI and SCT (IACS-Universidad de Zaragoza), Spanish Ministry of Economy and Competitiveness through Projects DPI2017-84780-C2-1-R and PID2020-113819RB-I00 and the Government of Aragon in the form of grant awarded to PAD (Grant No.2018-22).
1. Brown, C. et al. Mesenchymal stem cells: Cell therapy and regeneration potential. J. Tissue Eng. Regen. Med. 13, 1738–1755 (2019).
2. Antebi, B., Pelled, G. & Gazit, D. Stem cell therapy for osteoporosis. Curr. Osteoporos. Rep. 12, 41–47 (2014).
3. Del Amo, C., Borau, C., Movilla, N., Asín, J. & García-Aznar, J. M. Quantifying 3D chemotaxis in microfluidic-based chips with step gradients of collagen hydrogel concentrations. Integr. Biol. (United Kingdom) 9, 339–349 (2017).