The type of tissue produced by periosteal explants can be tuned by combining mechanical stimulation and soluble factors. TGF-β1 stimulated a chondrocyte phenotype and sliding indentation stimulated collagen synthesis. Such a combination may be valuable for improvement of the quality of tissue-engineered cartilage.

AimsMonocytes play a significant role in the development of atherosclerosis. During the process of inflammation, circulating monocytes become activated in the blood stream. The consequent interactions of the activated monocytes with the blood flow and endothelial cells result in reorganization of cytoskeletal proteins, in particular of the microfilament structure, and concomitant changes in cell shape and mechanical behavior. Here we investigate the full elastic behavior of activated monocytes in relation to their cytoskeletal structure to obtain a better understanding of cell behavior during the progression of inflammatory diseases such as atherosclerosis.Methods and ResultsThe recently developed Capillary Micromechanics technique, based on exposing a cell to a pressure difference in a tapered glass microcapillary, was used to measure the deformation of activated and non-activated monocytic cells. Monitoring the elastic response of individual cells up to large deformations allowed us to obtain both the compressive and the shear modulus of a cell from a single experiment. Activation by inflammatory chemokines affected the cytoskeletal organization and increased the elastic compressive modulus of monocytes with 73–340%, while their resistance to shape deformation decreased, as indicated by a 25–88% drop in the cell’s shear modulus. This decrease in deformability is particularly pronounced at high strains, such as those that occur during diapedesis through the vascular wall.ConclusionOverall, monocytic cells become less compressible but more deformable upon activation. This change in mechanical response under different modes of deformation could be important in understanding the interplay between the mechanics and function of these cells. In addition, our data are of direct relevance for computational modeling and analysis of the distinct monocytic behavior in the circulation and the extravascular space. Lastly, an understanding of the changes of monocyte mechanical properties will be important in the development of diagnostic tools and therapies concentrating on circulating cells.

We introduce a simple micro-fluidic device containing an actuated flexible membrane, which allows the viscoelastic characterization of cells in small volumes of suspension by loading them in compression and observing the cell deformation in time. From this experiment, we can determine the characteristic time constant of recovery of the cell. To validate the device, two cell types known to have different cytoskeletal structures, 3T3 fibroblasts and HL60 cells, are tested. They show a substantially different response in the device and can be clearly distinguished on the basis of the measured characteristic recovery time constant. Also, the effect of breaking down the actin network, a main mechanical component of the cytoskeleton, by a treatment with Cytochalasin D, results in a substantial increase of the measured characteristic recovery time constant. Experimental variations in loading force, loading time, and surface treatment of the device also influence the measured characteristic recovery time constant significantly. The device can therefore be used to distinguish between cells with different mechanical structure in a quantitative way, and makes it possible to study changes in the mechanical response due to cell treatments, changes in the cell’s micro-environment, and mechanical loading conditions.

We introduce a microfluidic device for chemical manipulation and mechanical investigation of circulating cells. The device consists of two crossing microfluidic channels separated by a porous membrane. A chemical compound is flown through the upper Bstimulus channel^, which diffuses through the membrane into the lower Bcell analysis channel^, in which cells are mechanically deformed in two sequential narrow constrictions, one before and one after crossing the stimulus channel. Thus, this system permits to measure cell deformability before and after chemical cues are delivered to the cells within one single chip. The validity of the device was tested with monocytic cells stimulated with an actindisrupting agent (Cytochalasin-D). Furthermore, as proof of principle of the device application, the effect of an antiinflammatory drug (Pentoxifylline) was tested on monocytic cells activated with Lipopolysaccharides and on monocytes from patients affected by atherosclerosis. The results show that the system can detect differences in cell mechanical deformation after chemical cues are delivered to the cells through the porous membrane. Diffusion of Cytochalasin-D resulted in a considerable decrease in entry time in the narrow constriction and an evident increase in the velocity within the constriction. Pentoxifylline showed to decrease the entry time but not to affect the transit time within the constriction for monocytic cells. Monocytes from patients affected by atherosclerosis were difficult to test in the device due to increased adhesion to the walls of the microfluidic channel. Overall, this analysis shows that the device has potential applications as a cellular assay for analyzing cell-drug interaction.

High prevalence of osteoarthritis and poor intrinsic healing capacity of articular cartilage create a demand for cell-based strategies for cartilage repair. It is possible to tissue engineer cartilage with almost native proteoglycan content, but collagen reaches only 15% to 35% of the native content. Also its natural arcade-like structural organization is not reproduced. These drawbacks contribute to its insufficient load-bearing properties. It is generally believed that the application of mechanical loading during culturing will improve the mechanical properties. However, a suitable mechanical loading regime has not yet been established.