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@ARTICLE{Ji:1007668,
      author       = {Ji, Fengting and Bansal, Manik and Wang, Bingrui and Hua,
                      Yi and Islam, Mohammad R. and Matuschke, Felix and Axer,
                      Markus and Sigal, Ian A.},
      title        = {{A} direct fiber approach to model sclera collagen
                      architecture and biomechanics},
      journal      = {Experimental eye research},
      volume       = {232},
      issn         = {0014-4835},
      address      = {London},
      publisher    = {Academic Press},
      reportid     = {FZJ-2023-02151},
      pages        = {109510 -},
      year         = {2023},
      abstract     = {Sclera collagen fiber microstructure and mechanical
                      behavior are central to eye physiology and pathology. They
                      are also complex, and are therefore often studied using
                      modeling. Most models of sclera, however, have been built
                      within a conventional continuum framework. In this
                      framework, collagen fibers are incorporated as statistical
                      distributions of fiber characteristics such as the
                      orientation of a family of fibers. The conventional
                      continuum approach, while proven successful for describing
                      the macroscale behavior of the sclera, does not account for
                      the sclera fibers are long, interwoven and interact with one
                      another. Hence, by not considering these potentially crucial
                      characteristics, the conventional approach has only a
                      limited ability to capture and describe sclera structure and
                      mechanics at smaller, fiber-level, scales. Recent advances
                      in the tools for characterizing sclera microarchitecture and
                      mechanics bring to the forefront the need to develop more
                      advanced modeling techniques that can incorporate and take
                      advantage of the newly available highly detailed
                      information. Our goal was to create a new computational
                      modeling approach that can represent the sclera fibrous
                      microstructure more accurately than with the conventional
                      continuum approach, while still capturing its macroscale
                      behavior. In this manuscript we introduce the new modeling
                      approach, that we call direct fiber modeling, in which the
                      collagen architecture is built explicitly by long,
                      continuous, interwoven fibers. The fibers are embedded in a
                      continuum matrix representing the non-fibrous tissue
                      components. We demonstrate the approach by doing direct
                      fiber modeling of a rectangular patch of posterior sclera.
                      The model integrated fiber orientations obtained by
                      polarized light microscopy from coronal and sagittal
                      cryosections of pig and sheep. The fibers were modeled using
                      a Mooney-Rivlin model, and the matrix using a Neo-Hookean
                      model. The fiber parameters were determined by inversely
                      matching experimental equi-biaxial tensile data from the
                      literature. After reconstruction, the direct fiber model
                      orientations agreed well with the microscopy data both in
                      the coronal plane (adjusted R2 = 0.8234) and in the sagittal
                      plane (adjusted R2 = 0.8495) of the sclera. With the
                      estimated fiber properties (C10 = 5746.9 MPa; C01 = -5002.6
                      MPa, matrix shear modulus 200 kPa), the model's
                      stress-strain curves simultaneously fit the experimental
                      data in radial and circumferential directions (adjusted R2's
                      0.9971 and 0.9508, respectively). The estimated fiber
                      elastic modulus at $2.16\%$ strain was 5.45 GPa, in
                      reasonable agreement with the literature. During stretch,
                      the model exhibited stresses and strains at sub-fiber level,
                      with interactions among individual fibers which are not
                      accounted for by the conventional continuum methods. Our
                      results demonstrate that direct fiber models can
                      simultaneously describe the macroscale mechanics and
                      microarchitecture of the sclera, and therefore that the
                      approach can provide unique insight into tissue behavior
                      questions inaccessible with continuum approaches.},
      cin          = {INM-1},
      ddc          = {610},
      cid          = {I:(DE-Juel1)INM-1-20090406},
      pnm          = {5251 - Multilevel Brain Organization and Variability
                      (POF4-525)},
      pid          = {G:(DE-HGF)POF4-5251},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {37207867},
      UT           = {WOS:001009422800001},
      doi          = {10.1016/j.exer.2023.109510},
      url          = {https://juser.fz-juelich.de/record/1007668},
}