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.

In VivoCellular Infiltration and Remodeling in a Decellularized Ovine Osteochondral Allograft

“…44 In addition, decellularization of cartilage by SDS, as performed in this work, has also been shown to affect the mechanical properties of the tissue. 8,11,13,14 This is consistent with what is seen in the work performed herein. Interestingly, empty defect samples were found to have the lowest friction coefficient, but all treatment groups had similar surface roughness.…”

“…[8][9][10] As a result, researchers have used the potential of tissue decellularization as a source of healthy cartilage tissue potentially useful for driving repair. 6,7 The use of the native cartilage structure is additionally in clinical use, although without the use of decellularization.…”

Densification of Type I Collagen Matrices as a Model for Cardiac Fibrosis

“…At each depth level, a linear regression was performed to relate image intensity to collagen concentration. Collagen concentration of compressed samples was determined at each depth using this linear relationship similar to that previously described …”

“…However, collagen‐based tissue engineered matrices have been historically plagued by poor mechanical strength due to solubility limitations. Plastic compression of collagen substrates has been shown as a means to push past these natural limitations and significantly increase mechanical properties . Additionally, recent collagen extraction developments have yielded collagen materials that more closely mimic the cross‐linking behavior seen in vivo .…”

“…Plastic compression of collagen substrates has been shown as a means to push past these natural limitations and significantly increase mechanical properties . Additionally, recent collagen extraction developments have yielded collagen materials that more closely mimic the cross‐linking behavior seen in vivo . Such a combination of collagen formulation and plastic compression allows for the development and tunability of matrices that more closely emulate the native state of the tissue.…”