Significance: Pathologic fibrosis is associated with altered collagen microarchitecture, but the functional impact of these changes on myofibroblast differentiation remains poorly understood. We experimentally and computationally analyzed the effect of collagen microstructure on matrix mechanics and determined its functional consequences on adipose-derived stem cells (ASCs), a cell type contributing to obesity- and cancer-associated fibrosis. Our findings highlight that collagen networks with thicker fibers and larger pores exhibit higher shear moduli than their similarly concentrated counterparts with thinner fibers and smaller pores. These differences promoted ASC mechanosignaling and consequential differentiation into α-smooth muscle actin-positive, contractile, and proangiogenic myofibroblasts. Insights from this work will advance the design of biomaterials for tissue engineering applications as well as antifibrotic therapies.

Distinct anti-inflammatory macrophage (M2) subtypes, namely M2a and M2c, are reported to modulate the tissue repair process tightly and chronologically by modulating fibroblast differentiation state and functions. To establish a well-defined three-dimensional (3D) cell culture model to mimic the tissue repair process, we utilized THP-1 human monocytic cells and a 3D collagen matrix as a biomimetic tissue model. THP-1 cells were differentiated into macrophages, and activated using IL-4/IL-13 (M_IL-4/IL-13) and IL-10 (M_IL-10). Both activated macrophages were characterized by both their cell surface marker expression and cytokine secretion profile. Our cell characterization suggested that M_IL-4/IL-13 and M_IL-10 demonstrate M2a- and M2c-like subtypes, respectively. To mimic the initial and resolution phases during the tissue repair, both activated macrophages were co-cultured with fibroblasts and myofibroblasts. We showed that M_IL-4/IL-13 were able to promote matrix synthesis and remodeling by induction of myofibroblast differentiation via transforming growth factor beta-1 (TGF-β1). On the contrary, M_IL-10 demonstrated the ability to resolve the tissue repair process by dedifferentiation of myofibroblast via IL-10 secretion. Overall, our study demonstrated the importance and the exact roles of M2a and M2c-like macrophage subtypes in coordinating tissue repair in a biomimetic model. The established model can be applied for high-throughput platforms for improving tissue healing and anti-fibrotic drugs testing, as well as other biomedical studies.

The extracellular matrix (ECM) establishes the basis for the cell's microenvironment providing structural and mechanical support to cells and tissues, and regulating multiple cell functions including gene expression, cell cycle, apoptosis, morphogenesis, and migration. Tumor development can be considered as a process where the cells are subjected to mutations. However, changes in the microenvironment of tumor cells can strongly impact the growth, invasion and survival of tumor cells. This specialized microenvironment is known to have an abundance of inflammatory cells and activated fibroblasts both expressing ECM components and growth factors that support the survival and proliferation of tumor cells in a paracrine fashion. Growing evidence points towards a key role of the ECM in the modulation of tumor progression and metastasis, even influencing therapeutic pharmacosensitivity. Accordingly, to better understand the mechanisms of tumor cell behavior, e.g. proliferation, invasion and survival, in dependence on microenvironmental cues as well as the cell–microenvironment interaction, it is necessary to engineer well-defined 3D matrices to closely mimic in vivo like microenvironments in a controlled in vitro setting. In that way the full repertoire of high-resolution, in-depth analytical technologies available for in vitro settings can be applied to reveal the underlying molecular mechanisms in an in vivo like ECM microenvironment. This review provides an overview of the current bioengineering techniques of defined biomimetic 3D models with a focus on naturally derived biopolymer components for the investigation of tumor cell behavior in vitro.

Collagen alignment is one of the key microarchitectural signatures of many pathological conditions, including scarring and fibrosis. Investigating how collagen alignment modulates cellular functions will pave the way for understanding tissue scarring and regeneration and new therapeutic strategies. However, current approaches for the fabrication of three‐dimensional (3D) aligned collagen matrices are low‐throughput and require special devices. To overcome these limitations, a simple approach to reconstitute homogeneous 3D collagen matrices with adjustable degree of fibril alignment using 3D printed inclined surfaces is developed. By characterizing the mechanical properties of reconstituted matrices, it is found that the elastic modulus of collagen matrices is enhanced with an increase in the alignment degree. The reconstituted matrices are used to study fibroblast behavior to reveal the progression of scar formation where a gradual enhancement of collagen alignment can be observed. It is found that matrices with aligned fibrils trigger fibroblast differentiation into myofibroblasts via cell contractility, while collagen stiffening through a crosslinker does not. The results suggest the impact of collagen fibril organization on the regulation of fibroblast differentiation. Overall, this approach to reconstitute 3D collagen matrices with fibril alignment opens opportunities for biomimetic pathological‐relevant tissue in vitro, which can be applied for other biomedical research.