Determination of the elastic shear modulus of cultured human red blood cells

Mesenchymal Stem Cell Deformability and Implications for Microvascular Sequestration

Mesenchymal stem cells (MSCs) have received considerable attention in regenerative medicine, particularly in light of prospects for targeted delivery by intra-arterial injection. However, little is known about the mechanics of MSC sequestration in the microvasculature and the yield pressure (P_Y), above which MSCs will pass through microvessels of a given diameter. The objectives of the current study were to delineate the dependency of P_Y on cell size and the heterogeneity of cell mechanical properties and diameters (D_CELL) of cultured MSCs. To this end the transient filtration test was employed to elucidate the mean filtration pressure (〈P_Y〉) for an ensemble of pores of a given size (D_PORE) similar to in vivo microvessels. Cultured MSCs had a log-normal distribution of cell diameters (D_CELL) with a mean of 15.8 ± 0.73 SD μm. MSC clearance from track-etched polycarbonate filters was studied for pore diameters of 7.3-15.4 μm. The pressure required to clear cells from filters with 30-85 × 10³ pores rose exponentially with the ratio λ = D_CELL/D_PORE for 1.1 ≤ λ ≤ 2.2. The clearance of cells from each filter was characterized by a log-normal distribution in P_Y, with a mean filtration pressure of 0.02 ≤ 〈P_Y〉 ≤ 6.7 cmH₂O. For λ ≤ 1.56, the yield pressure (P_Y) was well represented by the cortical shell model of a cell with a viscous interior encapsulated by a shell under cortical tension τ₀ = 0.99 ± 0.42 SD dyn/cm. For λ > 1.56, the 〈P_Y〉 characteristic of the cell population rose exponentially with λ. Analysis of the mean filtration pressure (〈P_Y〉) of each sample suggested that the larger diameter cells that skewed the distribution of D_CELL contributed to about 20% of the mean filtration pressure. Further, if all cells had the same deformability (i.e., P_Y as a function of λ) as the average cell population, then 〈P_Y〉 would have risen an order of magnitude above the average from fivefold at λ = 1.56 to 200-fold at λ = 2.1. Comparison of 〈P_Y〉 to published microvascular pressures suggested that 〈P_Y〉 may exceed microvessel pressure drops for λ exceeding 2.1, and rise 14-fold above capillary pressure drop at λ = 3 leading to 100% sequestration. However, due to the large variance of in vivo microvascular pressures entrapment of MSCs may be mitigated. Thus it is suggested that selecting fractions of the MSC population according to cell deformability may permit optimization of entrapment at sites targeted for tissue regeneration.

Mechanical properties of cells and ageing

Mechanical properties are fundamental properties of the cells and tissues of living organisms. The mechanical properties of a single cell as a biocomposite are determined by the interdependent combination of cellular components mechanical properties. Quantitative estimate of the cell mechanical properties depends on a cell state, method of measurement, and used theoretical model. Predominant tendency for the majority of cells with ageing is an increase of cell stiffness and a decrease of cell ability to undergo reversible large deformations. The mechanical signal transduction in old cells becomes less effective than that in young cells, and with ageing, the cells lose the ability of the rapid functional rearrangements of cellular skeleton. The article reviews the theoretical and experimental facts touching the age-related changes of the mechanical properties of cellular components and cells in the certain systems of an organism (the blood, the vascular system, the musculoskeletal system, the lens, and the epithelium). In fact, the cell mechanical parameters (including elastic modulii) can be useful as specific markers of cell ageing.