Mechanobiology in Tendon, Ligament, and Skeletal Muscle Tissue Engineering

Unveiling Mechanobiology: A Compact Device for Uniaxial Mechanical Stimulation on Nanofiber Substrates and Its Impact on Cellular Behavior and Nanoparticle Distribution

Biotechnology and its allied sectors, such as tissue culture, regenerative medicine, and personalized medicine, primarily rely upon extensive studies on cellular behavior and their molecular pathways for generating essential knowledge and innovative strategies for human survival. Most such studies are performed on flat, adherent, plastic-based surfaces and use nanofiber and hydrogel-like soft matrices from the past few decades. However, such static culture conditions cannot mimic the immediate cellular microenvironment, where they perceive or generate a myriad of different mechanical forces that substantially affect their downstream molecular pathways. Including such mechanical forces, still limited to specialized laboratories, using a few commercially available or noncommercial technologies are gathering increasing attention worldwide. However, large-scale consideration and adaptation by developing nations have yet to be achieved due to the lack of a cost-effective, reliable, and accessible solution. Moreover, investigations on cellular response upon uniaxial mechanical stretch cycles under more in vivo mimetic conditions are yet to be studied comprehensively. In order to tackle these obstacles, we have prepared a compact, 3D-printed device using a microcontroller, batteries, sensors, and a stepper motor assembly that operates wirelessly and provides cyclic mechanical attrition to any thin substrate. We have fabricated water-stable and stretchable nanofiber substrates with different fiber orientations by using the electrospinning technique to investigate the impact of mechanical stretch cycles on the morphology and orientation of C2C12 myoblast-like cells. Additionally, we have examined the uptake and distribution properties of BSA-epirubicin nanoparticles within cells under mechanical stimulation, which could act as fluorescently active drug-delivery agents for future therapeutic applications. Consequently, our research offers a comprehensive analysis of cellular behavior when cells are subjected to uniaxial stretching on various nanofiber mat architectures. Furthermore, we present a cost-effective alternative solution that addresses the long-standing requirement for a compact, user-friendly, and tunable device, enabling more insightful outcomes in mechanobiology.

Intermittent Cyclic Stretch of Engineered Ligaments Drives Hierarchical Collagen Fiber Maturation in a Dose- and Organizational-Dependent Manner

Hierarchical collagen fibers are the primary source of strength in tendons and ligaments, however these fibers do not regenerate after injury or with repair, resulting in limited treatment options. We previously developed a culture system that guides ACL fibroblasts to produce native-sized fibers and fascicles by 6 weeks. These constructs are promising ligament replacements, but further maturation is needed. Mechanical cues are critical for development in vivo and in engineered tissues; however, the effect on larger fiber and fascicle formation is largely unknown. Our objective was to investigate whether intermittent cyclic stretch, mimicking rapid muscle activity, drives further maturation in our system to create stronger engineered replacements and to explore whether cyclic loading has differential effects on cells at different degrees of collagen organization to better inform engineered tissue maturation protocols. Constructs were loaded with an established intermittent cyclic loading regime at 5 or 10% strain for up to 6 weeks and compared to static controls. Cyclic loading drove cells to increase hierarchical collagen organization, collagen crimp, and tissue mechanics, ultimately producing constructs that matched or exceeded immature ACL properties. Further, the effect of loading on cells varied depending on degree of organization. Specifically, 10% load drove early improvements in mechanics and composition, while 5% load was more beneficial later in culture, suggesting a cellular threshold response and a shift in mechanotransduction. This study provides new insight into how cyclic loading affects cell-driven hierarchical fiber formation and maturation, which will help to develop better rehabilitation protocols and engineer stronger replacements.

Tendon cell and tissue culture: Perspectives and recommendations

The wide variety of cell and tissue culture systems used to study and engineer tendons can make it difficult to choose the best approach and "optimal" culture conditions to test a given hypothesis. Therefore, a breakout session was organized at the 2022 ORS Tendon Section Meeting that focused on establishing a set of guidelines for conducting cell and tissue culture studies of tendon. This paper summarizes the outcomes of that discussion and presents recommendations for future studies. In the case of studying tendon cell behavior, cell and tissue culture systems are reductionist models in which the culture conditions should be strictly defined to approximate the in vivo condition as closely as possible. In contrast, for tissue engineering tendon replacements, the culture conditions do not need to replicate native tendon, but the outcome measures for success should be narrowly defined for the specific clinical application. Common recommendations for both applications are that researchers should perform a baseline phenotypic characterization of the cells that are ultimately used for experimentation. For models of tendon cell behavior, culture conditions should be well justified by existing literature and meticulously reported, tissue explant viability should be assessed, and comparisons to in vivo conditions should be made to determine baseline physiological relevance. For tissue engineering applications, the functional/structural/compositional outcome targets should be defined by the specific tendons they seek to replace, with key biologic and material properties prioritized for construct assessment. Lastly, when engineering tendon replacements, researchers should utilize clinically approved cGMP materials to facilitate clinical translation.

Mechanoresponsive regulation of fibroblast-to-myofibroblast transition in three-dimensional tissue analogues: mechanical strain amplitude dependency of fibrosis

The spatiotemporal interaction and constant iterative feedback between fibroblasts, extracellular matrix, and environmental cues are central for investigating the fibroblast-induced musculoskeletal tissue regeneration and fibroblast-to-myofibroblast transition (FMT). In this study, we created a fibroblast-laden 3D tissue analogue to study (1) how mechanical loading exerted on three-dimensional (3D) tissues affected the residing fibroblast phenotype and (2) to identify the ideal mechanical strain amplitude for promoting tissue regeneration without initiating myofibroblast differentiation. We applied uniaxial tensile strain (0, 4, 8, and 12%) to the cell-laden 3D tissue analogues to understand the interrelation between the degree of applied mechanical loading amplitudes and FMT. Our data demonstrated that 4% mechanical strain created an anabolic effect toward tissue regeneration, but higher strain amplitudes over-stimulated the cells and initiated fibrotic tissue formation. Under increased mechanical strain amplitudes, fibroblasts were activated from a homeostatic state to a proto-myofibroblast state which resulted in increased cellularity accompanied by increased expressions of extracellular matrix (ECM) components, activation stressors (TGF-β1 and TGF-βR1), and profibrotic markers. This further transformed fibroblasts into α-smooth muscle actin expressing myofibroblasts. Understanding the interplay between the applied degree of mechanical loading exerted on 3D tissues and residing fibroblast phenotypic response is important to identify specific mechanomodulatory approaches for tissue regeneration and the informed mechanotherapy-guided tissue healing strategies.

Micro/Nanosystems for Magnetic Targeted Delivery of Bioagents

Targeted delivery of pharmaceuticals is promising for efficient disease treatment and reduction in adverse effects. Nano or microstructured magnetic materials with strong magnetic momentum can be noninvasively controlled via magnetic forces within living beings. These magnetic carriers open perspectives in controlling the delivery of different types of bioagents in humans, including small molecules, nucleic acids, and cells. In the present review, we describe different types of magnetic carriers that can serve as drug delivery platforms, and we show different ways to apply them to magnetic targeted delivery of bioagents. We discuss the magnetic guidance of nano/microsystems or labeled cells upon injection into the systemic circulation or in the tissue; we then highlight emergent applications in tissue engineering, and finally, we show how magnetic targeting can integrate with imaging technologies that serve to assist drug delivery.

Cyclic pulsation stress promotes bone formation of tissue engineered laminae through the F-actin/YAP-1/β-Catenin signaling axis

Mechanical loads are fundamental regulators of bone formation and remodeling. However, the molecular regulation of mechanotransduction during vertebral laminae regeneration remains poorly understood. Here, we found that cerebrospinal fluid pulsation (CSFP) stress—cyclic pulsation stress—could promote the osteogenic and angiogenic abilities of rat mesenchymal stromal cells (MSC), thereby promoting tissue-engineered laminae’s bone and blood vessel formation. In the process, F-actin relayed CSFP stress to promote the nuclear translocation of YAP1, which then decreased the degradation and promoted the nuclear translocation of β-Catenin. In turn, the nuclear translocation of β-Catenin promoted the osteogenic differentiation and angiogenic abilities of MSC, thereby promoting tissue-engineered laminae’s bone and blood vessel formation. Thus, we conclude that CSFP promotes the osteogenesis and angiogenesis of tissue-engineered laminae through the F-actin/YAP-1/β-Catenin signaling axis. This study advances our understanding of vertebral laminae regeneration and provides potential therapeutic approaches for spinal degeneration after spinal laminectomy.