title: Mechanisms and Microenvironment Investigation of Cellularized High Density Gradient Collagen Matrices via Densification.
abstract: Biological tissues and biomaterials are often defined by unique spatial gradients in physical properties that impart specialized function over hierarchical scales. The structure and organization of these materials forms continuous transitional gradients and discrete local microenvironments between adjacent (or within) tissues, and across matrix-cell boundaries, which can be difficult to replicate with common scaffold systems. Here, we studied the matrix densification of collagen leading to gradients in density, mechanical properties, and fibril morphology. High-density regions formed via a fluid pore pressure and flow-driven mechanism, with increased relative fibril density (10×), mechanical properties (20×, to 94.40±18.74kPa), and maximum fibril thickness (1.9×, to >1μm) compared to low-density regions, while maintaining porosity and fluid/mass transport to support viability of encapsulated cells. Similar to the organization of the articular cartilage zonal structure, we found that high-density collagen regions induced cell and nuclear alignment of primary chondrocytes. Chondrocyte gene expression was maintained in collagen matrices, and no phenotypic changes were observed as a result of densification. Densification of collagen matrices provides a unique, tunable platform for the creation of gradient systems to study complex cell-matrix interactions. These methods are easily generalized to compression and boundary condition modalities useful to mimic a broad range of tissues.
authors.affiliation: Department of Biomedical Engineering, Purdue University, West Lafayette, IN, USA.
authors.forename: Tyler
authors.initials: T
authors.lastname: Novak
authors.affiliation: Department of Biomedical Engineering, Purdue University, West Lafayette, IN, USA; Department of Mechanical Engineering, University of Colorado, Boulder, CO, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Seelbinder
authors.affiliation: Department of Biomedical Engineering, Purdue University, West Lafayette, IN, USA.
authors.forename: Celina M
authors.initials: CM
authors.lastname: Twitchell
authors.affiliation: Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
authors.forename: Corrinus C
authors.initials: CC
authors.lastname: van Donkelaar
authors.affiliation: Department of Biomedical Engineering, Purdue University, West Lafayette, IN, USA; Department of Basic Medical Sciences, Purdue University, West Lafayette, IN, USA.
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Voytik-Harbin
authors.affiliation: Department of Biomedical Engineering, Purdue University, West Lafayette, IN, USA; Department of Mechanical Engineering, University of Colorado, Boulder, CO, USA.
authors.forename: Corey P
authors.initials: CP
authors.lastname: Neu
keywords: 3D microenvironment; chondrocyte phenotype and dedifferentiation; molecular crowding; physical gradient scaffold; plastic compression