title: Remodeling by fibroblasts alters the rate-dependent mechanical properties of collagen.
abstract: The ways that fibroblasts remodel their environment are central to wound healing, development of musculoskeletal tissues, and progression of pathologies such as fibrosis. However, the changes that fibroblasts make to the material around them and the mechanical consequences of these changes have proven difficult to quantify, especially in realistic, viscoelastic three-dimensional culture environments, leaving a critical need for quantitative data. Here, we observed the mechanisms and quantified the mechanical effects of fibroblast remodeling in engineered tissue constructs (ETCs) comprised of reconstituted rat tail (type I) collagen and human fibroblast cells. To study the effects of remodeling on tissue mechanics, stress-relaxation tests were performed on ETCs cultured for 24, 48, and 72h. ETCs were treated with deoxycholate and tested again to assess the ECM response. Viscoelastic relaxation spectra were obtained using the generalized Maxwell model. Cells exhibited viscoelastic damping at two finite time constants over which the ECM showed little damping, approximately 0.2s and 10-30s. Different finite time constants in the range of 1-7000s were attributed to ECM relaxation. Cells remodeled the ECM to produce a relaxation time constant on the order of 7000s, and to merge relaxation finite time constants in the 0.5-2s range into a single time content in the 1s range. Results shed light on hierarchical deformation mechanisms in tissues, and on pathologies related to collagen relaxation such as diastolic dysfunction.
  
  
  
  As fibroblasts proliferate within and remodel a tissue, they change the tissue mechanically. Quantifying these changes is critical for understanding wound healing and the development of pathologies such as cardiac fibrosis. Here, we characterize for the first time the spectrum of viscoelastic (rate-dependent) changes arising from the remodeling of reconstituted collagen by fibroblasts. The method also provides estimates of the viscoelastic spectra of fibroblasts within a three-dimensional culture environment. Results are of particular interest because of the ways that fibroblasts alter the mechanical response of collagen at loading frequencies associated with cardiac contraction in humans.
authors.affiliation: Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis, MO, USA.
authors.forename: Behzad
authors.initials: B
authors.lastname: Babaei
authors.affiliation: Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA; ​Ischemic Disorders Research Center, Golestan University of Medical Sciences, Gorgan, Iran​​
authors.forename: Ali
authors.initials: A
authors.lastname: Davarian
authors.affiliation: Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis, MO, USA; Department of Physics, National Taiwan University, Taipei, Taiwan.
authors.forename: Sheng-Lin
authors.initials: SL
authors.lastname: Lee
authors.affiliation: Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA.
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Pryse
authors.affiliation: Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA.
authors.forename: William B
authors.initials: WB
authors.lastname: McConnaughey
authors.affiliation: Department of Biochemistry & Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA.
authors.forename: Elliot L
authors.initials: EL
authors.lastname: Elson
authors.affiliation: Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, St. Louis, MO, USA. Electronic address: genin@wustl.edu.
authors.forename: Guy M
authors.initials: GM
authors.lastname: Genin
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D024042:Collagen Type I / Q000737:chemistry*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D051381:Rats; D054457:Tissue Scaffolds / Q000737:chemistry*
chemical_list: D024042:Collagen Type I
keywords: Collagen; Human dermal fibroblasts; Remodeling; Viscoelasticity