Towards systems tissue engineering: Elucidating the dynamics, spatial coordination, and individual cells driving emergent behaviors

Bridging systems biology and tissue engineering: Unleashing the full potential of complex 3D in vitro tissue models of disease

Rapid advances in tissue engineering have resulted in more complex and physiologically relevant 3D in vitro tissue models with applications in fundamental biology and therapeutic development. However, the complexity provided by these models is often not leveraged fully due to the reductionist methods used to analyze them. Computational and mathematical models developed in the field of systems biology can address this issue. Yet, traditional systems biology has been mostly applied to simpler in vitro models with little physiological relevance and limited cellular complexity. Therefore, integrating these two inherently interdisciplinary fields can result in new insights and move both disciplines forward. In this review, we provide a systematic overview of how systems biology has been integrated with 3D in vitro tissue models and discuss key application areas where the synergies between both fields have led to important advances with potential translational impact. We then outline key directions for future research and discuss a framework for further integration between fields.

Assembled/Disassembled Modular Scaffolds for Multicellular Tissue Engineering

The behavior of tissue resident cells can be influenced by the spatial arrangement of cellular interactions. Therefore, it is of significance to precisely control the spatial organization of various cells within multicellular constructs. It remains challenging to construct a versatile multicellular scaffold with ordered spatial organization of multiple cell types. Herein, a modular multicellular tissue engineering scaffold with ordered spatial distribution of different cell types is constructed by assembling varying cell-laden modules. Interestingly, the modular scaffolds can be disassembled into individual modules to evaluate the specific contribution of each cell type in the system. Through assembling cell-laden modules, the macrophage-mesenchymal stem cell (MSC), endothelial cell-MSC, and chondrocyte-MSC co-culture models are successfully established. The in vitro results indicate that the intercellular cross-talk can promote the proliferation and differentiation of each cell type in the system. Moreover, MSCs in the modular scaffolds may regulate the behavior of chondrocytes through the nuclear factor of activated T-Cells (NFAT) signaling pathway. Furthermore, the modular scaffolds loaded with co-cultured chondrocyte-MSC exhibit enhanced regeneration ability of osteochondral tissue, compared with other groups. Overall, this work offers a promising strategy to construct a multicellular tissue engineering scaffold for the systematic investigation of intercellular cross-talk and complex tissue engineering.

Cells-Micropatterning Biomaterials for Immune Activation and Bone Regeneration

Natural tissues are composed of ordered architectural organizations of multiple tissue cells. The spatial distribution of cells is crucial for directing cellular behavior and maintaining tissue homeostasis and function. Herein, an artificial bone bioceramic scaffold with star-, Tai Chi-, or interlacing-shaped multicellular patterns is constructed. The "cross-talk" between mesenchymal stem cells (MSCs) and macrophages can be effectively manipulated by altering the spatial distribution of two kinds of cells in the scaffolds, thus achieving controllable modulation of the scaffold-mediated osteo-immune responses. Compared with other multicellular patterns, the Tai Chi pattern with a 2:1 ratio of MSCs to macrophages is more effective in activating anti-inflammatory M2 macrophages, improving MSCs osteogenic differentiation, and accelerating new bone formation in vivo. In brief, the Tai Chi pattern generates a more favorable osteo-immune environment for bone regeneration, exhibiting enhanced immunomodulation and osteogenesis, which may be associated with the activation of BMP-Smad, Oncostatin M (OSM), and Wnt/β-catenin signaling pathways in MSCs mediated by macrophage-derived paracrine signaling mediators. The study suggests that the manipulation of cell distribution to improve tissue formation is a feasible approach that can offer new insights for the design of tissue-engineered bone substitutes with multicellular interactions.

Organ-on-a-Chip systems for new drugs development

Research on alternatives to the use of animal models and cell cultures has led to the creation of organ-on-a-chip systems, in which organs and their physiological reactions to the presence of external stimuli are simulated. These systems could even replace the use of human beings as subjects for the study of drugs in clinical phases and have an impact on personalized therapies. Organ-on-a-chip technology present higher potential than traditional cell cultures for an appropriate prediction of functional impairments, appearance of adverse effects, the pharmacokinetic and toxicological profile and the efficacy of a drug. This potential is given by the possibility of placing different cell lines in a three-dimensional-arranged polymer piece and simulating and controlling specific conditions. Thus, the normal functioning of an organ, tissue, barrier, or physiological phenomenon can be simulated, as well as the interrelation between different systems. Furthermore, this alternative allows the study of physiological and pathophysiological processes. Its design combines different disciplines such as materials engineering, cell cultures, microfluidics and physiology, among others. This work presents the main considerations of OoC systems, the materials, methods and cell lines used for their design, and the conditions required for their proper functioning. Examples of applications and main challenges for the development of more robust systems are shown. This non-systematic review is intended to be a reference framework that facilitates research focused on the development of new OoC systems, as well as their use as alternatives in pharmacological, pharmacokinetic and toxicological studies.

A Numerical Study of Fluid Flow in the Porous Structure of Biological Scaffolds

Tissue engineering (TE) is one of the promising areas that aims to address the global problem of organ and tissue shortages. The successful development of TE, particularly in bone tissue engineering, consists of the use of modern methods that allow the creation of scaffolds, the physicochemical, mechanical, and structural parameters of which will allow achieving the desired clinical results. The vast possibilities of the rapidly developing technology of three-dimensional (3D) printing, which allows the creation of individual scaffolds with high precision, has led to various developments in bone tissue TE. In this work, for the successful use of three-dimensional printing in TE to ensure the diffusion of nutrients during cell cultivation throughout the entire structure of the scaffold, a model of a rotating scaffold is proposed, and the movement of the diffusion flow of nutrient fluid is calculated based on Darcy’s law, which regulates the flow of fluids through porous media. The conducted studies of the rate of diffusion flow of nutrients based on glucose in the porous structure of scaffolds with a 10% content of calcium hydroxyapatite demonstrated the promise of using a model of a rotating composite scaffold in TE of bone tissue. The results show that at a scaffold rotation speed of 12 rpm, the diffusion flow rate of nutrients in the composite scaffolds porous structure is practically not affected by their geometric shape.