Monolithic microfluidic platform for exerting gradients of compression on cell-laden hydrogels, and application to a model of the articular cartilage

•Monolithic device with a vertical membrane for mechanical stimulation of tissues.•Actuation unit with 3 individual chambers to apply negative and/or positive pressure.•Real-time tissue imaging at the single cell level: monitoring cell deformation.•Application of healthy and hyper-physiological compressions to a cartilage model.•Possible generation of combinations of compression and bulk shear. Movement is essential to our quality of life, and regulates cell behavior via mechanical stimulation. Here, we report a monolithic microfluidic platform, in which engineered tissues composed of cells in a hydrogel are exposed to gradients of mechanical compression. Mechanical stimulation is applied through the deflection of a thin polydimethylsiloxane (PDMS) vertical membrane. The device design and all actuation parameters were optimized in this work to produce physiologically relevant compression on a cartilage model (strain of 5–12 %), as well as gradients of compression ranging from healthy to hyper-physiological conditions in the same device, as evidenced by the measured gradients in cell deformation. While this work focuses on mechanical compression of engineered tissues, we also demonstrated that our platform allowed creating more sophisticated multi-modal stimulation patterns. As the membrane is actuated by three independently addressed yet connected pressurized chambers, a variety of programmable deflection patterns and various cell stimulation modalities can easily be created by tuning the pressure applied in the different chambers (positive vs. negative, and amplitude). Advantageously, the fabrication of this monolithic platform is straightforward, with a single-step process. Moreover, the vertical membrane configuration allows for real-time imaging of cells encapsulated in the hydrogel matrix. The herein reported platform is highly versatile and of great interest to model other types of tissues, which also experience complex mechanical actuation patterns in vivo.