The Influence of Substrate Elasticity and Shear Rate on Human Blood Platelet Contraction

Time Resolved Data Acquisition, Microfluidic Designs and Algorithms

by Jana Hanke
Doctoral thesis
Date of Examination:2018-04-20
Date of issue:2018-09-12
Advisor:Prof. Dr. Sarah Köster
Referee:Prof. Dr. Sarah Köster
Referee:Prof. Dr. Claudia Steinem
Persistent Address: http://dx.doi.org/10.53846/goediss-7053

 

 

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Abstract

English

Human blood platelets are small, anucleate cell fragments that are important for the life-saving process of haemostasis, i.e. the process of wound healing. Upon injury, blood platelets adhere to the exposed extra-cellular matrix and further spread and contract to close the wound. This process must work reliably in a multitude of different environments, including different stiffnesses of the surrounding tissue as well as various shear rates stemming from the blood flow. Employing the technique of time-resolved Traction Force Microscopy in combination with a specifically tailored differential Particle Image Velocimetry method and a self-developed microfluidic system, it is found that platelets exhibit very dynamic as well as comparably high forces taking their small size into account. The experimental results show that platelets are not mechanosensitive within the studied stiffness or shear rate ranges. This was seen both in the spatial as well as in the temporal force development. By modelling the contractile behaviour of the cells according to the data taken on various substrate stiffnesses it was concluded that due to their small size, platelets are only mechanosenstive to substrates of at least one order of magnitude softer than used here. The only adaptation to their environment that was observed was the angle of orientation between the contraction and the flow direction. Here, the orientation changed from 45° to 90° with increasing shear rate. From the experimentally indicated correlation between the force-transmitting network and the observed spatial force patterns, using numerical simulation, the orientation of platelets under flow may be governed by the active reduction of the stress exerted on the integrins which connect the cells to the underlying substrate. In conclusion, platelets, due to their unique structure, are mechanoinsensitive to a multitude of different environments, indicating an 'all-or-nothing' response to wounds at such sites.
Keywords: human blood platelet; time-resolved Traction Force Microscopy; differential Particle Image Velocimetry; microfluidics; fluorescence microscopy; biophysics; single cells; mechanosensitivity
 
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