title: Assembly of collagen matrices as a phase transition revealed by structural and rheologic studies.
abstract: We have studied the structural and viscoelastic properties of assembling networks of the extracellular matrix protein type-I collagen by means of phase contrast microscopy and rotating disk rheometry. The initial stage of the assembly is a nucleation process of collagen monomers associating to randomly distributed branched clusters with extensions of several microns. Eventually a sol-gel transition takes place, which is due to the interconnection of these clusters. We analyzed this transition in terms of percolation theory. The viscoelastic parameters (storage modulus G' and loss modulus G") were measured as a function of time for five different frequencies ranging from omega = 0.2 rad/s to 6.9 rad/s. We found that at the gel point both G' and G" obey a scaling law, with the critical exponent Delta = 0.7 and a critical loss angle being independent of frequency as predicted by percolation theory. Gelation of collagen thus represents a second order phase transition.
authors.affiliation: Department of Physics and Biology, University of Missouri, Columbia, Missouri 65211, USA. forgacsg@missouri.edu
authors.forename: Gabor
authors.initials: G
authors.lastname: Forgacs
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Newman
authors.forename: Bernhard
authors.initials: B
authors.lastname: Hinner
authors.forename: Christian W
authors.initials: CW
authors.lastname: Maier
authors.forename: Erich
authors.initials: E
authors.lastname: Sackmann
mesh_terms: D000818:Animals; D024042:Collagen Type I / Q000737:chemistry* / Q000648:ultrastructure*; D004548:Elasticity; D005109:Extracellular Matrix / Q000737:chemistry*; D005782:Gels / Q000737:chemistry; D046911:Macromolecular Substances; D008858:Microscopy, Phase-Contrast; D018715:Microscopy, Video / Q000379:methods; D009038:Motion; D051381:Rats; D012212:Rheology / Q000379:methods*; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical; D013696:Temperature; D014783:Viscosity
chemical_list: D024042:Collagen Type I; D005782:Gels; D046911:Macromolecular Substances