Geometry-Driven Cell Organization Determines Tissue Growths in Scaffold Pores: Consequences for Fibronectin Organization

Abstract

To heal tissue defects, cells have to bridge gaps and generate new extracellular matrix (ECM). Macroporous scaffolds are frequently used to support the process of defect filling and thus foster tissue regeneration. Such biomaterials contain micro-voids (pores) that the cells fill with their own ECM over time. There is only limited knowledge on how pore geometry influences cell organization and matrix production, even though it is highly relevant for scaffold design. This study hypothesized that 1) a simple geometric description predicts cellular organization during pore filling at the cell level and that 2) pore closure results in a reorganization of ECM. Scaffolds with a broad distribution of pore sizes (macroporous starPEG-heparin cryogel) were used as a model system and seeded with primary fibroblasts. The strategies of cells to fill pores could be explained by a simple geometrical model considering cells as tensioned chords. The model matched qualitatively as well as quantitatively by means of cell number vs. open cross-sectional area for all pore sizes. The correlation between ECM location and cell position was higher when the pores were not filled with tissue (Pearson’s coefficient ρ = 0.45±0.01) and reduced once the pores were closed (ρ = 0.26±0.04) indicating a reorganization of the cell/ECM network. Scaffold pore size directed the time required for pore closure and furthermore impacted the organization of the fibronectin matrix. Understanding how cells fill micro-voids will help to design biomaterial scaffolds that support the endogenous healing process and thus allow a fast filling of tissue defects.

Availability of extracellular matrix biopolymers and differentiation state of human mesenchymal stem cells determine tissue-like growth in vitro

“…Supplemented, soluble ECM biopolymers may also bind to integrin receptors without being integrated within matrix assemblies, thus resulting in shielding of the receptor as another potential reason for less effective matrix remodeling. Our findings seem furthermore in line with results reported by Joly et al [47] which showed that tissue growth in a 3D space requires spreading of cells in combination with formation and remodeling of ECM fibers.…”

Gradual conversion of cellular stress patterns into pre-stressed matrix architecture during in vitro tissue growth

“…Cells adopt an elongated chord-like appearance, as we reported earlier [44], owing to the balance of contractile actomyosin forces and substrate geometry [34,55]. Moreover, the change of cellular behaviour around pore closure compares with that described in a study showing the relevance of the geometrical model in smaller pores [56] ( figure 1f ). Also, the continuous actin band forming parallel to the tissue-medium interface is reminiscent of the actin ring observed in other contexts of tissue growth, such as wound healing [57].…”

Glycosaminoglycan‐Based Biohybrid Hydrogels: A Sweet and Smart Choice for Multifunctional Biomaterials

“…[65] Accordingly, the macroporous hydrogel provides heterogeneous physical structure signals to the cells, a cue with a tremendous impact on cell growth (e.g., void filling) independent of the initial pore size. [66] …”