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Mechanics and contraction dynamics of single platelets and implications for clot stiffening


Platelets interact with fibrin polymers to form blood clots at sites of vascular injury1,2,3. Bulk studies have shown clots to be active materials, with platelet contraction driving the retraction and stiffening of clots4. However, neither the dynamics of single-platelet contraction nor the strength and elasticity of individual platelets, both of which are important for understanding clot material properties, have been directly measured. Here we use atomic force microscopy to measure the mechanics and dynamics of single platelets. We find that platelets contract nearly instantaneously when activated by contact with fibrinogen and complete contraction within 15 min. Individual platelets can generate an average maximum contractile force of 29 nN and form adhesions stronger than 70 nN. Our measurements show that when exposed to stiffer microenvironments, platelets generated higher stall forces, which indicates that platelets may be able to contract heterogeneous clots more uniformly. The high elasticity of individual platelets, measured to be 10 kPa after contraction, combined with their high contractile forces, indicates that clots may be stiffened through direct reinforcement by platelets as well as by strain stiffening of fibrin under tension due to platelet contraction. These results show how the mechanosensitivity and mechanics of single cells can be used to dynamically alter the material properties of physiologic systems.

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Figure 1: Measuring the contraction of single platelets with AFM.
Figure 2: Stiffness dependence and timescale of platelet contraction.
Figure 3: Elasticity and adhesion measurement for contracted platelets.
Figure 4: Proposed effects of platelets on clot retraction and mechanics.


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We thank S. Parekh, G. Venugopalan, G. Stephens, P. Andre, D. Phillips, X. Zhao and the Fletcher Lab for their advice and useful discussions. Financial support for this work was provided by an NSF GRFP for O.C., NIH grant K08-HL093360, a UCSF REAC award, and a Biomedical Research Fellowship from The Hartwell Foundation for W.A.L., and an NSF CAREER Award and NIH R01 grants to D.A.F.

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W.A.L., O.C., A.C., K.D.W., J.H. and D.A.F. conceived and designed the experiments; W.A.L., O.C., T-D.L. and A.K. carried out the experiments; W.A.L., O.C. and D.A.F. analysed and interpreted the data; and W.A.L., O.C., D.A.F., A.C., K.D.W. and J.H. wrote the manuscript.

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Correspondence to Daniel A. Fletcher.

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The authors declare no competing financial interests.

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Lam, W., Chaudhuri, O., Crow, A. et al. Mechanics and contraction dynamics of single platelets and implications for clot stiffening. Nature Mater 10, 61–66 (2011).

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