Elastic fiber-mediated hierarchical bundling of collagen fibers in subcutaneous fascia

PURPOSE: We aimed to clarify the localization and hierarchical structural roles of elastic fibers in subcutaneous fascia and to determine their contribution to the mechanical properties of this tissue. MATERIALS AND METHODS: Enzymatic digestion, calcein labeling, immunostaining of collagen and fibrillin-rich microfibrillar structures, scanning electron microscopy, immunogold SEM, and TOF-SIMS were performed to analyze the hierarchical fiber architecture of loose and dense regions of chicken subcutaneous fascia. RESULTS: Both loose and dense regions exhibited hierarchical collagen fiber bundles associated with elastic fiber. In loose fascia, these structures were predominantly localized along the surface of flattened collagen bundles, whereas in dense fascia they were detected both on the surface and within the bundles, consistent with repeated hierarchical organization. Under the present experimental conditions, elastase treatment reproducibly altered bundle architecture and increased passive expansion behavior. CONCLUSIONS: These findings support a hierarchical organization of subcutaneous fascia in which fibrillin-rich microfibrillar structures are repeatedly arranged in association with collagen fiber bundles across multiple scales. Together, our results suggest a spatial model of fascial architecture that provides a structural basis for future functional investigations of fascial mechanics.