Surface Curvature Differentially Regulates Stem Cell Migration and Differentiation via Altered Attachment Morphology and Nuclear Deformation

Signals from the microenvironment around a cell are known to influence cell behavior. Material properties, such as biochemical composition and substrate stiffness, are today accepted as significant regulators of stem cell fate. The knowledge of how cell behavior is influenced by 3D geometric cues is, however, strongly limited despite its potential relevance for the understanding of tissue regenerative processes and the design of biomaterials. Here, the role of surface curvature on the migratory and differentiation behavior of human mesenchymal stem cells (hMSCs) has been investigated on 3D surfaces with well-defined geometric features produced by stereolithography. Time lapse microscopy reveals a significant increase of cell migration speed on concave spherical compared to convex spherical structures and flat surfaces resulting from an upward-lift of the cell body due to cytoskeletal forces. On convex surfaces, cytoskeletal forces lead to substantial nuclear deformation, increase lamin-A levels and promote osteogenic differentiation. The findings of this study demonstrate a so far missing link between 3D surface curvature and hMSC behavior. This will not only help to better understand the role of extracellular matrix architecture in health and disease but also give new insights in how 3D geometries can be used as a cell-instructive material parameter in the field of biomaterial-guided tissue regeneration.Peer reviewe

A biomaterial with a channel-like pore architecture induces endochondral healing of bone defects

Biomaterials developed to treat bone defects have classically focused on bone healing via direct, intramembranous ossification. In contrast, most bones in our body develop from a cartilage template via a second pathway called endochondral ossification. The unsolved clinical challenge to regenerate large bone defects has brought endochondral ossification into discussion as an alternative approach for bone healing. However, a biomaterial strategy for the regeneration of large bone defects via endochondral ossification is missing. Here we report on a biomaterial with a channel-like pore architecture to control cell recruitment and tissue patterning in the early phase of healing. In consequence of extracellular matrix alignment, CD146+ progenitor cell accumulation and restrained vascularization, a highly organized endochondral ossification process is induced in rats. Our findings demonstrate that a pure biomaterial approach has the potential to recapitulate a developmental bone growth process for bone healing. This might motivate future strategies for biomaterial-based tissue regeneration

Mesoscale substrate curvature overrules nanoscale contact guidance to direct bone marrow stromal cell migration

The intrinsic architecture of biological tissues and of implanted biomaterials provides cells with large-scale geometrical cues. To understand how cells are able to sense and respond to complex structural environments, a deeper insight into the cellular response to multi-scale and conflicting geometrical cues is needed. In this study, we subjected human bone marrow stromal cells (hBMSCs) to mesoscale cylindrical surfaces (diameter 250–5000 mm) and nanoscale collagen fibrils (diameter 100–200 nm) that were aligned perpendicular to the cylinder axis. On flat surfaces and at low substrate curvatures (cylinder diameter d . 1000 mm), cell alignment and migration were governed by the nanoscale collagen fibrils, consistent with the contact guidance effect. With increasing surface curvature (decreasing cylinder diameter, d, 1000 mm), cells increasingly aligned and migrated along the cylinder axis, i.e. the direction of zero curvature. An increase in phosphorylated myosin light chain levels was observed with increasing substrate curvature, suggesting a link between substrate-induced cell bending and the F-actin–myosin machinery. Taken together, this work demonstrates that geometrical cues of up to 10 cell size can play a dominant role in directing hBMSC alignment and migration and that the effect of nanoscale contact guidance can even be overruled by mesoscale curvature guidance

Mesoscale substrate curvature overrules nanoscale contact guidance to direct bone marrow stromal cell migration

\u3cp\u3eThe intrinsic architecture of biological tissues and of implanted biomaterials provides cells with large-scale geometrical cues. To understand how cells are able to sense and respond to complex structural environments, a deeper insight into the cellular response to multi-scale and conflicting geometrical cues is needed. In this study, we subjected human bone marrow stromal cells (hBMSCs) to mesoscale cylindrical surfaces (diameter 250–5000 mm) and nanoscale collagen fibrils (diameter 100–200 nm) that were aligned perpendicular to the cylinder axis. On flat surfaces and at low substrate curvatures (cylinder diameter d . 1000 mm), cell alignment and migration were governed by the nanoscale collagen fibrils, consistent with the contact guidance effect. With increasing surface curvature (decreasing cylinder diameter, d, 1000 mm), cells increasingly aligned and migrated along the cylinder axis, i.e. the direction of zero curvature. An increase in phosphorylated myosin light chain levels was observed with increasing substrate curvature, suggesting a link between substrate-induced cell bending and the F-actin–myosin machinery. Taken together, this work demonstrates that geometrical cues of up to 10 cell size can play a dominant role in directing hBMSC alignment and migration and that the effect of nanoscale contact guidance can even be overruled by mesoscale curvature guidance.\u3c/p\u3

Collagen Fibrils Mechanically Contribute to Tissue Contraction in an In Vitro Wound Healing Scenario

Wound contraction is an ancient survival mechanism of vertebrates that results from tensile forces supporting wound closure. So far, tissue tension was attributed to cellular forces produced by tissue-resident (myo-) fibroblasts alone. However, difficulties in explaining pathological deviations from a successful healing path motivate the exploration of additional modulatory factors. Here, it is shown in a biomaterial-based in vitro wound healing model that the storage of tensile forces in the extracellular matrix has a significant, so-far neglected contribution to macroscopic tissue tension. In situ monitoring of tissue forces together with second harmonic imaging reveal that the appearance of collagen fibrils correlates with tissue contraction, indicating a mechanical contribution of tensioned collagen fibrils in the contraction process. As the re-establishment of tissue tension is key to successful wound healing, the findings are expected to advance the understanding of tissue healing but also underlying principles of misregulation and impaired functionality in scars and tissue contractures

Supplementary figure 1 from Mesoscale substrate curvature overrules nanoscale contact guidance to direct bone marrow stromal cell migration

Optical profilometry images of a cylindrical surface (d = 500 µm) without (A,B) and with (C,D) the addition of the thin extra PDMS layer

Supplementary figure 3 from Mesoscale substrate curvature overrules nanoscale contact guidance to direct bone marrow stromal cell migration

Calculation of the curvature that a projected linear element (e.g. F-actin fibre, green) would be exposed to on top of a cylindrical surface, depending on its orientation (angle α) relative to the cylinder axis. The bent shape is approximated as an ellipse (intersection of planes with different orientation angles and the cylinder's surface). The curvature of interest is the lowest curvature of the ellipse (at φ=90°)

Supplementary material from "Mesoscale substrate curvature overrules nanoscale contact guidance to direct bone marrow stromal cell migration"

The intrinsic architecture of biological tissues and of implanted biomaterials provides cells with large-scale geometrical cues. To understand how cells are able to sense and respond to complex structural environments, a deeper insight into the cellular response to multi-scale and conflicting geometrical cues is needed. In this study, we subjected human bone marrow stromal cells (hBMSCs) to mesoscale cylindrical surfaces (diameter 250–5000 µm) and nanoscale collagen fibrils (diameter 100–200 nm) that were aligned perpendicular to the cylinder axis. On flat surfaces and at low substrate curvatures (cylinder diameter d > 1000 µm), cell alignment and migration were governed by the nanoscale collagen fibrils, consistent with the contact guidance effect. With increasing surface curvature (decreasing cylinder diameter, d