Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

Gurmessa, Bekele; Fitzpatrick, Robert; Falzone, Tobias T.; Robertson‐Anderson, Rae M.

doi:10.1021/acs.macromol.5b02802

Cited by 26 publications

(76 citation statements)

References 59 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As described above, elastic and viscous systems should display starkly different relaxation behaviors following strain, with purely elastic systems exhibiting no relaxation and viscous systems exhibiting immediate and complete force relaxation. Viscoelastic systems display behavior in between these two extremes, with viscoelastic biopolymer networks exhibiting both exponential and power-law relaxation over varying timescales 2,27,[36][37][38]63 . To characterize the relaxation dynamics of the composites, we measure the time-dependent force F(t) exerted on the bead by each composite for 15 s following the strain (Figs.…”

Section: Relaxation Dynamicsmentioning

confidence: 99%

“…To determine the macromolecular mechanisms underlying the observed relaxation behavior, we evaluate fits of the force curves to a range of exponential and power-law functions that have been previously used to fit relaxation data for entangled and crosslinked biopolymer networks 27,[36][37][38]48 . We find that the force relaxations for all composites can be well fit to a sum of three exponential decays with well-separated time constants (Fig.…”

Section: As Shown Inmentioning

confidence: 99%

“…Despite the relevance of actin-microtubule composites to biology, physics, and engineering, most in vitro studies to date have focused on single-component networks of either actin or microtubules 4,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] . In response to strain, entangled actin networks have been reported to exhibit varying degrees of stiffening, softening, and yielding depending on the actin concentration and the scale of the strain 36,38,39 . Crosslinked actin networks exhibit enhanced stiffness and prolonged, more pronounced elasticity compared to entangled solutions 35,37,43,44 .…”

Section: Introductionmentioning

confidence: 99%

“…The optical trap used in all microrheology measurements, which has been previously described and validated 27,36,37,68 , was formed by a IX71 fluorescence microscope (Olympus) outfitted with a 1064 nm Nd:YAG fiber laser (Manlight) and focused with a 60x 1.4 NA objective (Olympus). A position-sensing detector (Pacific Silicon Sensor) measured the deflection of the trapping laser, which is proportional to the force acting on the trapped microsphere.…”

mentioning

confidence: 99%

See 3 more Smart Citations

Varying crosslinking motifs drive the mesoscale mechanics of actin-microtubule composites

Ricketts

Francis

Farhadi

et al. 2019

Preprint

Self Cite

View full text Add to dashboard Cite

The cytoskeleton dynamically tunes its mechanical properties by altering the interactions between semiflexible actin filaments, rigid microtubules, and crosslinking proteins. Here, we use optical tweezers microrheology and confocal microscopy to characterize how varying crosslinking motifs impact the microscopic and mesoscale mechanics and mobility of actin-microtubule composites. We show that, upon subtle changes in the crosslinking pattern, composites separate into two distinct classes of force responseprimarily elastic versus more viscous behavior. For example, a composite in which actin and microtubules are crosslinked to each other is markedly more elastic than one in which both filaments are crosslinked but cannot link together. Notably, this distinction only emerges at mesoscopic scales in response to nonlinear forcing, whereas varying crosslinking motifs have little impact on the microscale mechanics and steadystate mobility of composites. Our unexpected scale-dependent results not only inform the physics underlying key cytoskeleton processes and structures, but, more generally, provide valuable perspective to materials engineering endeavors focused on polymer composites.

show abstract

Section: Relaxation Dynamicsmentioning

confidence: 99%

Section: As Shown Inmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Varying crosslinking motifs drive the mesoscale mechanics of actin-microtubule composites

Ricketts

Francis

Farhadi

et al. 2019

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…The timescale for this process, often termed disengagement, is on the order of minutes to hours for actin and microtubules (9)(10)(11). Entangled actin can also partially relax via faster mechanisms such as bending fluctuations (12)(13)(14). The degree of filament entanglement and density in networks of actin and microtubules can be characterized by their respective mesh sizes, ξ A = 0.3/c A 1/2 and ξ M = 0.89/c T 1/2 , where c A and c T are the corresponding protein concentrations in units of mg/ml and the resulting mesh sizes are in units of microns (15)(16)(17).…”

Section: Introductionmentioning

confidence: 99%

Co-entangled actin-microtubule composites exhibit tunable stiffening and power-law stress relaxation

Ricketts¹,

Ross

Robertson‐Anderson³

2018

Preprint

Self Cite

View full text Add to dashboard Cite

We use optical tweezers microrheology and fluorescence microscopy to characterize the nonlinear mesoscale mechanics and mobility of in vitro co-entangled actin-microtubule composites. We create a suite of randomly-oriented, well-mixed networks of actin and microtubules by co-polymerizing varying ratios of actin and tubulin in situ. To perturb each composite far from equilibrium, we use optical tweezers to displace an embedded microsphere a distance greater than the lengths of the filaments at a speed much faster than their intrinsic relaxation rates. We simultaneously measure the resistive force the filaments exert and the subsequent force relaxation. We find that the presence of a large fraction of microtubules (>0.7) is needed to substantially increase the resistive force, which is accompanied by large heterogeneities in force response. Actin minimizes these heterogeneities by reducing the mesh size of the composites and supporting microtubules against buckling. Composites also undergo a sharp transition from stress-softening to stiffening when the fraction of microtubules (φ T ) exceeds 0.5, by microtubules suppressing actin bending fluctuations. The induced force following strain relaxes via two time-dependent power-law decays. The first decay phase, with scaling exponents that increase proportionally with the fraction of actin, signifies actin bending fluctuations. Alternatively, the second phase, with a φ Tindependent scaling exponent of ~0.4, is indicative of filaments reptating out of deformed entanglement constraints. Corresponding mobility measurements of steady-state actin and microtubules show that both filaments are more mobile in equimolar composites (φ T =0.5) compared to networks of primarily actin or microtubules. This non-monotonic dependence of mobility on φ T , which further demonstrates the important role mesh size plays in composites, highlights the surprising emergent properties that can arise in composites.

show abstract

Experimental Methods

2017

Nonlinear Polymer Rheology

View full text Add to dashboard Cite

Entanglement Density Tunes Microscale Nonlinear Response of Entangled Actin

Cited by 26 publications

References 59 publications

Varying crosslinking motifs drive the mesoscale mechanics of actin-microtubule composites

Varying crosslinking motifs drive the mesoscale mechanics of actin-microtubule composites

Co-entangled actin-microtubule composites exhibit tunable stiffening and power-law stress relaxation

Experimental Methods

Contact Info

Product

Resources

About