Limits...
Strain-induced alignment in collagen gels.

Vader D, Kabla A, Weitz D, Mahadevan L - PLoS ONE (2009)

Bottom Line: This alignment is found to be irreversibly imprinted in uncrosslinked collagen networks, suggesting a simple mechanism for tissue organization at the microscale.Plasticity is therefore not required to align fibers.On the contrary, our data show that this effect is part of the fundamental non-linear properties of fibrous biological networks.

View Article: PubMed Central - PubMed

Affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States of America.

ABSTRACT
Collagen is the most abundant extracellular-network-forming protein in animal biology and is important in both natural and artificial tissues, where it serves as a material of great mechanical versatility. This versatility arises from its almost unique ability to remodel under applied loads into anisotropic and inhomogeneous structures. To explore the origins of this property, we develop a set of analysis tools and a novel experimental setup that probes the mechanical response of fibrous networks in a geometry that mimics a typical deformation profile imposed by cells in vivo. We observe strong fiber alignment and densification as a function of applied strain for both uncrosslinked and crosslinked collagenous networks. This alignment is found to be irreversibly imprinted in uncrosslinked collagen networks, suggesting a simple mechanism for tissue organization at the microscale. However, crosslinked networks display similar fiber alignment and the same geometrical properties as uncrosslinked gels, but with full reversibility. Plasticity is therefore not required to align fibers. On the contrary, our data show that this effect is part of the fundamental non-linear properties of fibrous biological networks.

Show MeSH

Related in: MedlinePlus

Comparison of critical strains measured from bulk rheology and 2-point stretching.Comparison of critical strain measured from the PIV method ( such that , see Results) on locally stretched samples with the onset of strain stiffening ( such that , see Results) obtained from rheological measurements.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2691583&req=5

pone-0005902-g006: Comparison of critical strains measured from bulk rheology and 2-point stretching.Comparison of critical strain measured from the PIV method ( such that , see Results) on locally stretched samples with the onset of strain stiffening ( such that , see Results) obtained from rheological measurements.

Mentions: The critical deformation, as defined above from the kinematic behavior in local stretching tests, can be directly compared with the strain associated with the mechanical stiffening measured in rheological experiments (see figure 3). These two quantities, measured independently, show good correlations in their values and trends. For unfixed collagen samples, critical strain values, measured either from rheological meansurements or from the kinematics, range from a few percents at high collagen concentration to 15% at low concentration (see figure 6). The critical strain is therefore very weakly dependant on the concentration, in particular compared with the variation of the elastic modulus at small deformation that varies over more than two orders of magnitude in the same concentration range. GA-fixed samples, whose stiffness is estimated at an order of magnitude higher than their non-fixed counterparts, also show similar values for . Taken together, these results show that the strains above which the gel behavior becomes non-linear as evidenced i) from the elastic modulus for a simple shear geometry and ii) from the Poisson ratio in the local stretching experiments are related with each other and only weakly sensitive to physical scales such as the actual value of the elastic modulus.


Strain-induced alignment in collagen gels.

Vader D, Kabla A, Weitz D, Mahadevan L - PLoS ONE (2009)

Comparison of critical strains measured from bulk rheology and 2-point stretching.Comparison of critical strain measured from the PIV method ( such that , see Results) on locally stretched samples with the onset of strain stiffening ( such that , see Results) obtained from rheological measurements.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2691583&req=5

pone-0005902-g006: Comparison of critical strains measured from bulk rheology and 2-point stretching.Comparison of critical strain measured from the PIV method ( such that , see Results) on locally stretched samples with the onset of strain stiffening ( such that , see Results) obtained from rheological measurements.
Mentions: The critical deformation, as defined above from the kinematic behavior in local stretching tests, can be directly compared with the strain associated with the mechanical stiffening measured in rheological experiments (see figure 3). These two quantities, measured independently, show good correlations in their values and trends. For unfixed collagen samples, critical strain values, measured either from rheological meansurements or from the kinematics, range from a few percents at high collagen concentration to 15% at low concentration (see figure 6). The critical strain is therefore very weakly dependant on the concentration, in particular compared with the variation of the elastic modulus at small deformation that varies over more than two orders of magnitude in the same concentration range. GA-fixed samples, whose stiffness is estimated at an order of magnitude higher than their non-fixed counterparts, also show similar values for . Taken together, these results show that the strains above which the gel behavior becomes non-linear as evidenced i) from the elastic modulus for a simple shear geometry and ii) from the Poisson ratio in the local stretching experiments are related with each other and only weakly sensitive to physical scales such as the actual value of the elastic modulus.

Bottom Line: This alignment is found to be irreversibly imprinted in uncrosslinked collagen networks, suggesting a simple mechanism for tissue organization at the microscale.Plasticity is therefore not required to align fibers.On the contrary, our data show that this effect is part of the fundamental non-linear properties of fibrous biological networks.

View Article: PubMed Central - PubMed

Affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States of America.

ABSTRACT
Collagen is the most abundant extracellular-network-forming protein in animal biology and is important in both natural and artificial tissues, where it serves as a material of great mechanical versatility. This versatility arises from its almost unique ability to remodel under applied loads into anisotropic and inhomogeneous structures. To explore the origins of this property, we develop a set of analysis tools and a novel experimental setup that probes the mechanical response of fibrous networks in a geometry that mimics a typical deformation profile imposed by cells in vivo. We observe strong fiber alignment and densification as a function of applied strain for both uncrosslinked and crosslinked collagenous networks. This alignment is found to be irreversibly imprinted in uncrosslinked collagen networks, suggesting a simple mechanism for tissue organization at the microscale. However, crosslinked networks display similar fiber alignment and the same geometrical properties as uncrosslinked gels, but with full reversibility. Plasticity is therefore not required to align fibers. On the contrary, our data show that this effect is part of the fundamental non-linear properties of fibrous biological networks.

Show MeSH
Related in: MedlinePlus