Modulation of biomimetic mineralization of collagen by soluble ectodomain of discoidin domain receptor 2

Extracellular matrix-induced signaling pathways in mesenchymal stem/stromal cells

The extracellular matrix (ECM) is a crucial component of the stem cell microenvironment, or stem-cell niches, and contributes to the regulation of cell behavior and fate. Accumulating evidence indicates that different types of stem cells possess a large variety of molecules responsible for interactions with the ECM, mediating specific epigenetic rearrangements and corresponding changes in transcriptome profile. Signals from the ECM are crucial at all stages of ontogenesis, including embryonic and postnatal development, as well as tissue renewal and repair. The ECM could regulate stem cell transition from a quiescent state to readiness to perceive the signals of differentiation induction (competence) and the transition between different stages of differentiation (commitment). Currently, to unveil the complex networks of cellular signaling from the ECM, multiple approaches including screening methods, the analysis of the cell matrixome, and the creation of predictive networks of protein-protein interactions based on experimental data are used. In this review, we consider the existing evidence regarded the contribution of ECM-induced intracellular signaling pathways into the regulation of stem cell differentiation focusing on mesenchymal stem/stromal cells (MSCs) as well-studied type of postnatal stem cells totally depended on signals from ECM. Furthermore, we propose a system biology-based approach for the prediction of ECM-mediated signal transduction pathways in target cells. Video Abstract.

Embedding Collagen in Multilayers for Enzyme-Assisted Mineralization: A Promising Way to Direct Crystallization in Confinement

The biogenic calcium phosphate (CaP) crystallization is a process that offers elegant materials design strategies to achieve bioactive and biomechanical challenges. Indeed, many biomimetic approaches have been developed for this process in order to produce mineralized structures with controlled crystallinity and shape. Herein, we propose an advanced biomimetic approach for the design of ordered hybrid mineralized nano-objects with highly anisotropic features. For this purpose, we explore the combination of three key concepts in biomineralization that provide a unique environment to control CaP nucleation and growth: (i) self-assembly and self-organization of biomacromolecules, (ii) enzymatic heterogeneous catalysis, and (iii) mineralization in confinement. We use track-etched templates that display a high density of aligned monodisperse pores so that each nanopore may serve as a miniaturized mineralization bioreactor. We enhance the control of the crystallization in these systems by coassembling type I collagen and enzymes within the nanopores, which allows us to tune the main characteristics of the mineralized nano-objects. Indeed, the synergy between the gradual release of one of the mineral ion precursors by the enzyme and the role of the collagen in the regulation of the mineralization allowed to control their morphology, chemical composition, crystal phase, and mechanical stability. Moreover, we provide clear insight into the prominent role of collagen in the mineralization process in confinement. In the absence of collagen, the fraction of crystalline nano-objects increases to the detriment of amorphous ones when increasing the degree of confinement. By contrast, the presence of collagen-based multilayers disturbs the influence of confinement on the mineralization: platelet-like crystalline hydroxyapatite form, independently of the degree of confinement. This suggests that the incorporation of collagen is an efficient way to supplement the lack of confinement while reinforcing mechanical stability to the highly anisotropic materials. From a bioengineering perspective, this biomineralization-inspired approach opens up new horizons for the design of anisotropic mineralized nano-objects that are highly sought after to develop biomaterials or tend to replicate the complex structure of native mineralized extracellular matrices.

In Vitro Mineralization of Collagen

Collagen mineralization is a biological process in many skeletal elements in the animal kingdom. Examples of these collagen-based skeletons are the siliceous spicules of glass sponges or the intrafibrillar hydroxyapatite platelets in vertebrates. The mineralization of collagen in vitro has gained interest for two reasons: understanding the processes behind bone formation and the synthesis of scaffolds for tissue engineering. In this paper, the efforts toward collagen mineralization in vitro are reviewed. First, general introduction toward collagen type I, the main component of the extracellular matrix in animals, is provided, followed by a brief overview of collagenous skeletons. Then, the in vitro mineralization of collagen is critically reviewed. Due to their biological abundance, hydroxyapatite and silica are the focus of this review. To a much lesser extent, also some efforts with other minerals are outlined. Combining all minerals and the suggested mechanisms for each mineral, a general mechanism for the intrafibrillar mineralization of collagen is proposed. This review concludes with an outlook for further improvement of collagen-based tissue engineering scaffolds.