gms | German Medical Science

Objectives: Mechanotransduction as translation of mechanical stimulation into biochemical signals can be influenced by cyclic compression, shear stress and fluid-flow and affects the differentiation of mesenchymal progenitor cells such as bone marrow-derived stromal cells (MSCs). Influencing the differentiation process at the cellular level can lead to the formation of new bone substance at the macroscopic level. In turn, the formation of bone substance is able to improve the healing process after a fracture or prevent diseases caused by decreased bone mass such as osteopenia. Disruption of mechanical stimulus transmission can also lead to chronic diseases of the skeleton, such as osteoporosis. For being able to analyse mechanotransduction, it is necessary to have a useful platform to exert mechanical strain. In this study, we established flexible polyurethane (PU) scaffolds to apply mechanical forces. Additionally, the use of a 3D system in a bioreactor offers the advantage of being closer to the situation in vivo.

Methods: The suitability of a 3D PU scaffold was analyzed by studying the growth behavior and applying various mechanical stimuli such as fluid-flow and repeated compression. Human MSCs were obtained from bone marrow and were seeded onto the scaffolds, cultured, and subjected to mechanical stress. We analyzed three different flow rates from 2.5 to 5 ml/min and scaffold compression with a frequency of 1 Hz and 10% of the scaffold height. In addition, we analyzed the application of both stimuli with a flow rate of 2.5 ml/min and a compression of 10 % of the scaffold height with a frequency of 1 Hz. The cells were harvested at three different time points: 15 min, 4 h and 24 h the expression of mechanoresponsive markers over time was evaluated at the mRNA level.

Results and conclusion: After the 7-day cultivation of the cells, they were well distributed over the PU foam scaffolds. By measuring the total amount of protein, the number of cells remaining in the scaffolds after stimulation was obtained. Neither fluid-flow nor cyclic compression flushed the cells out of the scaffold and we assume that all cells harvested from the scaffolds were affected by the applied mechanical forces. The first results of qPCR analysis showed significant upregulation of the mechanoresponsive genes FOS and PTGS2 compared with the untreated scaffold controls, regardless of whether fluid-flow or cyclic compression was applied.

In general, we established a flexible 3D polyurethan cell culture platform for mechanical stimulation of bone-derived cells that can be used to study mechanotransduction under physiological or pathological conditions via the supplementation of growth factors, chemicals or cell culture supernatants. The cellular response can be validated via testing cell vitality, proliferation and differentiation capability.