Dynamic Bioreactors with Integrated Microfabricated Devices for Mechanobiological Screening

Control of hydrostatic pressure and osmotic stress in 3D cell culture for mechanobiological studies

Hydrostatic pressure (HP) and osmotic stress (OS) play an important role in various biological processes, such as cell proliferation and differentiation. In contrast to canonical mechanical signals transmitted through the anchoring points of the cells with the extracellular matrix, the physical and molecular mechanisms that transduce HP and OS into cellular functions remain elusive. Three-dimensional cell cultures show great promise to replicate physiologically relevant signals in well-defined host bioreactors with the goal of shedding light on hidden aspects of the mechanobiology of HP and OS. This review starts by introducing prevalent mechanisms for the generation of HP and OS signals in biological tissues that are subject to pathophysiological mechanical loading. We then revisit various mechanisms in the mechanotransduction of HP and OS, and describe the current state of the art in bioreactors and biomaterials for the control of the corresponding physical signals.

Engineered models for placental toxicology: Emerging approaches based on tissue decellularization

Recent increases in prescriptions and illegal drug use as well as exposure to environmental contaminants during pregnancy have highlighted the critical importance of placental toxicology in understanding and identifying risks to both mother and fetus. Although advantageous for basic science, current in vitro models often fail to capture the complexity of placental response, likely due to their inability to recreate and monitor aspects of the microenvironment including physical properties, mechanical forces and stiffness, protein composition, cell-cell interactions, soluble and physicochemical factors, and other exogenous cues. Tissue engineering holds great promise in addressing these challenges and provides an avenue to better understand basic biology, effects of toxic compounds and potential therapeutics. The key to success lies in effectively recreating the microenvironment. One strategy to do this would be to recreate individual components and then combine them. However, this becomes challenging due to variables present according to conditions such as tissue location, age, health status and lifestyle. The extracellular matrix (ECM) is known to influence cellular fate by working as a storage of factors. Decellularized ECM (dECM) is a recent tool that allows usage of the original ECM in a refurbished form, providing a relatively reliable representation of the microenvironment. This review focuses on using dECM in modified forms such as whole organs, scaffold sheets, electrospun nanofibers, hydrogels, 3D printing, and combinations as building blocks to recreate aspects of the microenvironment to address general tissue engineering and toxicology challenges, thus illustrating their potential as tools for future placental toxicology studies.

The Synergistic Effect of Cyclic Tensile Force and Periodontal Ligament Cell-Laden Calcium Silicate/Gelatin Methacrylate Auxetic Hydrogel Scaffolds for Bone Regeneration

The development of 3D printing technologies has allowed us to fabricate complex novel scaffolds for bone regeneration. In this study, we reported the incorporation of different concentrations of calcium silicate (CS) powder into fish gelatin methacrylate (FGelMa) for the fabrication of CS/FGelMa auxetic bio-scaffolds using 3D printing technology. Our results showed that CS could be successfully incorporated into FGelMa without influencing the original structural components of FGelMa. Furthermore, it conveyed that CS modifications both the mechanical properties and degradation rates of the scaffolds were improved in accordance with the concentrations of CS upon modifications of CS. In addition, the presence of CS enhanced the adhesion and proliferation of human periodontal ligament cells (hPDLs) cultured in the scaffold. Further osteogenic evaluation also confirmed that CS was able to enhance the osteogenic capabilities via activation of downstream intracellular factors such as pFAK/FAK and pERK/ERK. More interestingly, it was noted that the application of extrinsic biomechanical stimulation to the auxetic scaffolds further enhanced the proliferation and differentiation of hPDLs cells and secretion of osteogenic-related markers when compared to CS/FGelMa hydrogels without tensile stimulation. This prompted us to explore the related mechanism behind this interesting phenomenon. Subsequent studies showed that biomechanical stimulation works via YAP, which is a biomechanical cue. Taken together, our results showed that novel auxetic scaffolds could be fabricated by combining different aspects of science and technology, in order to improve the future chances of clinical applications for bone regeneration.

3D printed bioresorbable scaffolds for articular cartilage tissue engineering: a comparative study between neat polycaprolactone (PCL) and poly(lactide-b-ethylene glycol) (PLA-PEG) block copolymer

This work identifies and describes different material-scaffold geometry combinations for cartilage tissue engineering (CTE). Previously reported potentially interesting scaffold geometries were tuned and printed using bioresorbable polycaprolactone and poly(lactide-b-ethylene) block copolymer. Medical grades of both polymers were 3D printed with fused filament fabrication technology within an ISO 7 classified cleanroom. Resulting scaffolds were then optically, mechanically and biologically tested. Results indicated that a few material-scaffold geometry combinations present potential for excellent cell viability as well as for an enhance of the chondrogenic properties of the cells, hence suggesting their suitability for CTE applications.

Integration of clinical perspective into biomimetic bioreactor design for orthopedics

The challenges to accommodate multiple tissue formation metrics in conventional bioreactors have resulted in an increased interest to explore novel bioreactor designs. Bioreactors allow researchers to isolate variables in controlled environments to quantify cell response. While current bioreactor designs can effectively provide either mechanical, electrical, or chemical stimuli to the controlled environment, these systems lack the ability to combine all these stimuli simultaneously to better recapitulate the physiological environment. Introducing a dynamic and systematic combination of biomimetic stimuli bioreactor systems could tremendously enhance its clinical relevance in research. Thus, cues from different tissue responses should be studied collectively and included in the design of a biomimetic bioreactor platform. This review begins by providing a summary on the progression of bioreactors from simple to complex designs, focusing on the major advances in bioreactor technology and the approaches employed to better simulate in vivo conditions. The current state of bioreactors in terms of their clinical relevance is also analyzed. Finally, this review provides a comprehensive overview of individual biophysical stimuli and their role in establishing a biomimetic microenvironment for tissue engineering. To date, the most advanced bioreactor designs only incorporate one or two stimuli. Thus, the cell response measured is likely unrelated to the actual clinical performance. Integrating clinically relevant stimuli in bioreactor designs to study cell response can further advance the understanding of physical phenomenon naturally occurring in the body. In the future, the clinically informed biomimetic bioreactor could yield more efficiently translatable results for improved patient care.

Engineered microenvironment for the study of myofibroblast mechanobiology

Myofibroblasts are mechanosensitive cells and a variety of their behaviours including differentiation, migration, force production and biosynthesis are regulated by the surrounding microenvironment. Engineered cell culture models have been developed to examine the effect of microenvironmental factors such as the substrate stiffness, the topography and strain of the extracellular matrix (ECM) and the shear stress on myofibroblast biology. These engineered models provide well-mimicked, pathophysiologically relevant experimental conditions that are superior to those enabled by the conventional two-dimensional (2D) culture models. In this perspective, we will review the recent advances in the development of engineered cell culture models for myofibroblasts and outline the findings on the myofibroblast mechanobiology under various microenvironmental conditions. These studies have demonstrated the power and utility of the engineered models for the study of microenvironment-regulated cellular behaviours. The findings derived using these models contribute to a greater understanding of how myofibroblast behaviour is regulated in tissue repair and pathological scar formation.

Recent Advances in Biomaterial-Based High-Throughput Platforms

High-throughput systems allow screening and analysis of large number of samples simultaneously under same conditions. Over recent years, high-throughput systems have found applications in fields other than drug discovery like bioprocess industries, pollutant detection, material microarrays, etc. With the introduction of materials in such HT platforms, the screening system has been enabled for solid phases apart from conventional solution phase. The use of biomaterials has further facilitated cell-based assays in such platforms. Here, the authors have focused on the recent developments in biomaterial-based platforms including the fabricationusing contact and non-contact methods and utilization of such platforms for discovery of novel biomaterials exploiting interaction of biological entities with surface and bulk properties. Finally, the authors have elaborated on the application of the biomaterial-based high-throughput platforms in tissue engineering and regenerative medicine, cancer and stem cell studies. The studies show encouraging applications of biomaterial microarrays. However, success in clinical applicability still seems to be a far off task majorly due to absence of robust characterization and analysis techniques. Extensive focus is required for developing personalized medicine, analytical tools and storage/shelf-life of cell laden microarrays.