Tensile Mechanical Properties of Three-Dimensional Type I Collagen Extracellular Matrices With Varied Microstructure

TLDR

The design of scaffold micro‑structure and mechanics is critical for biomaterials that emulate the extracellular matrix and support tissue repair. This study aimed to prepare 3‑D type I collagen matrices and investigate their structural‑mechanical relationships. Collagen concentration (0.3–3 mg mL⁻¹) and pH (6–9) were varied during polymerization, and confocal reflection microscopy quantified fibril diameter, length, and organization. Higher collagen concentration and pH increased fibril density, length, and linear modulus/failure stress, while diameter remained constant with concentration and decreased with pH; all matrices shared a similar stress‑strain profile and exhibited strain‑rate dependence.

Abstract

Abstract The importance and priority of specific micro-structural and mechanical design parameters must be established to effectively engineer scaffolds (biomaterials) that mimic the extracellular matrix (ECM) environment of cells and have clinical applications as tissue substitutes. In this study, three-dimensional (3-D) matrices were prepared from type I collagen, the predominant compositional and structural component of connective tissue ECMs, and structural-mechanical relationships were studied. Polymerization conditions, including collagen concentration (0.3–3 mg/mL) and pH (6–9), were varied to obtain matrices of collagen fibrils with different microstructures. Confocal reflection microscopy was used to assess specific micro-structural features (e.g., diameter and length) and organization of component fibrils in 3-D. Microstructural analyses revealed that changes in collagen concentration affected fibril density while maintaining a relatively constant fibril diameter. On the other hand, both fibril length and diameter were affected by the pH of the polymerization reaction. Mechanically, all matrices exhibited a similar stress-strain curve with identifiable “toe,” “linear,” and “failure” regions. However, the linear modulus and failure stress increased with collagen concentration and were correlated with an increase in fibril density. Additionally, both the linear modulus and failure stress showed an increase with pH, which was related to an increased fibril length and a decreased fibril diameter. The tensile mechanical properties of the collagen matrices also showed strain rate dependence. Such fundamental information regarding the 3-D microstructural-mechanical properties of the ECM and its component molecules are important to our overall understanding of cell-ECM interactions (e.g., mechanotransduction) and the development of novel strategies for tissue repair and replacement.