Table 1.

Methods to characterize IF mechanical properties in vitro

IF type	method	concentration	time scale	main result
NF / glial IFs (Leterrier & Eyer, 1987)	Falling ball viscometry	1 to 5 mg/ml	Seconds to minutes	NFs form gels by crossbridging divalent ions affect gelation
NF Vimentin (Leterrier et al., 1996)	Oscillatory shear rheometry Parallel plate	3 mg/ml	10 ms to 1000 s	NF networks strain- stiffen G' increases from <100 Pa to >kPa Modified by phosphorylation
Desmin Keratin NF (Kreplak et al., 2005)	AFM	Single filaments	Seconds to hours	IFs withstand stretching to >200% without rupture
NF NF-F-actin (Wagner et al., 2007)	Oscillatory shear rheometry	4 mg/ml	Seconds to minutes	NF gels rupture at high strain but rapidly reform. NF- F-actin composites lose recovery after large strain
Keratin (Leitner et al., 2012)	Single bead thermal fluctuation microrheometry	0.5 mg/ml	0.5 ms to 1 s	G' = 0.5 Pa with 2 mM Mg2+. Divalent ions stabilize networks
Vimentin (Janmey et al., 1991)	Torsion pendulum	0.3 to 10 mg/ml	10 ms to 100 s	Vimentin networks strain stiffen. Gels withstand >80 % strain
Keratin Vimentin (Pawelzyk et al., 2014)	Macroscopic shear rheometry and optical microrheometry	0.1 to 2 mg/ml	50 ms to 10 s	IF have attractive interactions due to hydrophobic and H bonds
Keratin Vimentin (Yamada, Wirtz, & Coulombe, 2003)	Shear rheometry Couette and cone-plate geometries	1 mg/ml	50 ms to 10 s	Apparent G' on order of 1–10 Pa affected by interfacial tensions. Weak frequency dependence
Vimentin (Lin, Broedersz, et al., 2010)	Parallel plate shear rheometry	0.2 to 1 mg/ml	300 ms to 50 s	Elastic response mainly entropic. Divalent ions act as crosslinkers.
Desmin (Schopferer et al., 2009)	1. Oscillatory squeeze flow 2. Cone-plate shear rheometry	1 to 2 mg/ml	1. 50 μs to 1 s 2. 1 s	Strain stiffening but not always initial gelation is altered by disease-causing mutations
Vimentin and NF (Lin, Yao, et al., 2010)	Cone-plate shear rheometry	0.3 to 3 mg/ml	0.03 to 1000 s	Elasticity and strain- stiffening fit by theory for semi- flexible polymer networks
Desmin Vimentin (Schopferer et al., 2009)	1. Oscillatory squeeze flow 2. Cone-plate shear rheometry	0.4 to 2.8 mg/ml	50 μs to 1 s	Desmin (lp≈900 nm) is stiffer than vimentin (lp ≈400 nm) both electrostatics and binding affects network stiffness
Vimentin Vimentin+actin (Esue et al., 2006)	Cone-plate shear rheometry	0.04 to 0.4 mg/ml	1- ms to 5 s	Vimentin C-terminal tail binds F-actin to increase elastic modulus
Vimentin (Guzman et al., 2006)	AFM deflection	Single filaments	seconds	Bending modulus of single IFs between 300 and 400 MPa
Vimentin (Mucke et al., 2004)	EM and AFM imaging	Single filaments	static	Persistence length 1 μm
Keratin (Bousquet et al., 2001)	Cone-plate shear rheometry	0.5 to 1 mg/ml	seconds	K14 C-terminal tail binds filament side to form crosslink
Keratin (Chou & Buehler, 2012)	Molecular dynamics	Single dimer	<20 ns	All atom simulation predicts force- extension of keratin dimer
NF (Janmey et al., 2007)	Parallel plate shear rheometry	2 mg/ml	seconds	Shear deformations generate negative normal stress in NF networks