We present in situ studies on the self-assembly and dynamic evolution of collagen gels from semidilute solutions in a microfluidic device.Collagen fibrils not only reinforce the mechanical properties of bone and tissues,but they also influence cellular motility and morphology.We access the initial steps of the hierarchical self-assembly of collagen fibrils and networks by using hydrodynamic focusing to form oriented fibers.The accurate description of the conditions within the microchannel requires a numerical expression for the pH in the device as well as a modified mathematical description of the viscosity,which increases nearly 300-fold as collagen fibrils form around neutral pH.Finite element modeling profiles overlay impressively with cross-polarized microscopy images of the birefringent fibrils in the channel.Real-time X-ray microdiffraction measurements in flow indicate an enhanced supramolecular packing having a unit spacing commensurate with that of a pentameric collagen subunit.These results have significant implications for the field of biomedicine,wherein new aligned,cellularly active,and mechanically strengthened materials continue to be in demand.However,this work is also remarkable from a more fundamental,biophysical point of view because the underlying concepts may be generalized to a large pool of systems.
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