Numerical Simulation of Real-Time Deformability Cytometry To Extract Cell Mechanical Properties

The measurement of cell stiffness is an important part of biological research with diverse applications in biology, biotechnology and medicine. Real-time deformability cytometry (RT-DC) is a new method to probe cell stiffness at high throughput by flushing cells through a microfluidic channel where cell deformation provides an indicator for cell stiffness (Otto et al. Real-time deformability cytometry: on-the-fly cell 725 mechanical phenotyping. Nat. Methods 2015, 12, 199-202). Here, we propose a full numerical model for single cells in a flow channel to quantitatively relate cell deformation to mechanical parameters. Thereby the cell is modeled as a viscoelastic material surrounded by a thin shell cortex, subject to bending stiffness and cortical surface tension. For small deformations our results show good agreement with a previously developed analytical model that neglects the influence of cell deformation on the fluid flow (Mietke et al. Extracting Cell Stiffness from Real-Time Deformability Cytometry: 728 Theory and Experiment. Biophys. J. 2015, 109, 2023-2036). Including linear elasticity as well as neo-Hookean hyperelasticity, our model is valid in a wide range of cell deformations and allows to extract cell stiffness for largely deformed cells. We introduce a new measure for cell deformation that is capable to distinguish between deformation effects stemming from cell cortex and cell bulk elasticity. Finally, we demonstrate the potential of the method to simultaneously quantify multiple mechanical cell parameters by RT-DC.

[Effect of smoking on the long-term course of ulcerative colitis]

OBJECTIVE

To evaluate the effects of smoking on the long term clinical course in patients with ulcerative colitis.

METHODS

The medical charts of 556 patients with ulcerative colitis were reviewed retrospectively. Patients were classified as smokers (n = 85) or nonsmokers (n = 471) according to their smoking status during the course of the disease. Extent of colonic lesions, complications, medical requirements, and actuarial rate of colectomy were compared in smokers and nonsmokers.

RESULTS

Mean follow-up (+/- SD) was longer in smokers than in nonsmokers (116 +/- 107 mo, vs 87 +/- 94 mo.). Less smokers than nonsmokers required oral steroids (52 vs 63%, P = 0.05). No difference between the groups was observed regarding the use of salicylates, the need for intravenous steroids, for immunosuppressive drugs, for colectomy, and the occurrence of complications. The actuarial rate of colectomy was less in smokers than in nonsmokers (32 +/- 12% and 42 +/- 6% at 10 years respectively. P = 0.04). Initial and cumulative extent of the disease process did not differ between the groups. However, in the subgroup of patients with limited disease at onset, development of pancolitis was less frequent in smokers than in nonsmokers (14 and 26%, respectively, P = 0.04).

CONCLUSION

The lesser need for oral steroids and the lower actuarial rate of colectomy in smokers suggest that ulcerative colitis in smokers is characterized by a less severe clinical presentation and a better long term prognosis than in nonsmokers.