Microstructural implications of mass transport properties of collagen matrices
Abstract
To effectively develop engineered extracellular matrices for both research and medical applications, the physical properties, mass transport properties, and biological properties of the matrices must be characterized. These properties can be manipulated by controlling polymerization conditions, collagen content, and the monomer (individual collagen molecules) and oligomer (at least two collagen molecules covalently linked together) building blocks incorporated within the matrix (Kreger 2010). In this way, the properties of engineered matrices may be considered design variables (Drury 2003). The Harbin lab at Purdue University has identified strategies for isolation and standardization of monomer and oligomer collagen formulations from tissue. Previous research in the Harbin lab has demonstrated that control of this parameter (monomer/oligomer content) results in dramatic changes to matrix fibril microstructure-mechanical properties and biological responses of cells grown in matrices that are polymerized from these solutions. However, the impact of monomer/oligomer content on mass transport properties has not yet been thoroughly investigated. A falling head permeameter was used to measure the Darcy permeability of collagen matrices prepared with monomer and oligomer formulations at varying concentrations. Permeability decreased significantly as collagen concentration increased for both monomer and oligomer formulations. Monomer/oligomer content was found to also significantly impact permeability, as oligomeric matrices were shown to be significantly less permeable than monomeric matrices. The Carman-Kozeny model was used to estimate the effective pore size of each matrix based on Darcy permeability. Estimated pore sizes ranged from 260–1100 nm over the range of matrices tested. These estimates show that monomer/oligomer significantly impacts the microstructural properties of collagen matrices. Independent image analysis confirmed that pores are smaller in oligomeric matrices. The results of this research clearly demonstrate that differences in the fibril microstructure of collagen matrices that result from varied intermolecular crosslink content can be detected by measurement of mass transport properties. Diffusivity of target particles (10 kDa, 40 kDa, 500 kDa, 2 MDa MW) within monomer and oligomer collagen matrices was measured using a variation of the fluorescence recovery after photobleaching (FRAP) method. Diffusivity of the target particles in PBS ranged from 2.0–10.0 m2/s. Diffusive hindrance increased as collagen concentration and particle size increased, with a maximum 30% decrease in diffusivity observed for large (2 MDa MW) particles in high concentration matrices. Monomer/oligomer content did not significantly impact diffusivity in the matrices tested. The primary endpoint of this study was the quantification of the mass transport properties of monomer and oligomer collagen matrices. These data directly characterize parameters that are critical for the design and use of engineered matrices. In addition to this primary focus, the impact of monomer/oligomer content on the mass transport properties was evaluated. Monomer/oligomer and associated intermolecular cross-link content is of particular interest, as previous research has shown highly divergent mechanical properties based on this parameter (Bailey 2010). Finally, the differences in the mass transport properties of monomeric and oligomeric matrices were used to draw conclusions about the microstructural differences that exist between these two types of matrices.
Degree
M.S.B.M.E.
Advisors
Voytik-Harbin, Purdue University.
Subject Area
Biomedical engineering
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