Mechanical engineering, as a discipline, imbues a strong appreciation for how forces influence the world around us. The combination of theoretical and practical training yield in students the ability to creatively think about a wide variety of applications for the purposes of novel design. A deep understanding of mechanics can be applied in a wide variety of fields. As a mechanical engineering student, I was stunned and somewhat awed by the fact that mechanical engineers designed wood screws with mathematical governing equations to make sure forces were distributed appropriately for long lasting, secure attachment. The elegance of the math used to describe forces at such a relatively small scale really fascinated me. Moreover, the notion that relatively simple math could be used to describe complex physical interactions in three-dimensional space because Newton’s Law of the Conservation of Energy creates limitless opportunity to continue understanding our world at a deeper level.
One central area of study, probably from the beginning of our species, is that of the mechanics with respect to the human body. The early human researchers discovered things like “I can lift this heavy rock if I bend my legs,” or “using a tree trunk as a lever makes it even easier to move this heavy rock.” From an engineering perspective, the mammalian body presents an impressive set of integrated systems with an astonishing complexity which plays out at length scales spanning meters to angstroms. Billions of cells utilize force internally and respond to tissue level external forces in a carefully balanced dance to achieve homeostasis. Today, thanks to advancements in many scientific disciplines, we can study mechanics in biology with much greater detail and at increasingly smaller length scales (i.e., actin/myosin rather than rock/tree). Chemists and biologists have outlined many biological principles of cell biology, and engineers have contributed technology with increasing ability to measure and/or observe biological events. And here we arrive at my passion as a scientific investigator: Using engineering principles to better understand what governs mechanically influenced biological phenomena in health and disease.
The importance of mechanical forces in the tissue specific biological functions and health of various tissues has steadily become increasingly apparent over the last 30 years. Technological advancements in atomic force microscopyCitation1, in vitro cell substrate modificationsCitation2, fluorescent reporter technologyCitation3, and in situ imaging modalitiesCitation4,Citation5 have all played significant roles in our ability to study mechanobiology. The study of bone mechanobiology is a good practical example of these late advancements. Mathematical models describing how very small tissue level deformations are magnified by cellular anatomy to induce mechanotransduction responses in osteocytesCitation6. In vitro analysis of fluid flow induced activation of bone cells have been reported using both parallel plate flow chambersCitation7, and specialized devices for activation at specific cell anatomical sitesCitation8. Finally, advancements in imaging have provided detailed information about bone cells in situCitation9,Citation10, and in vivoCitation11.
It is an exciting time to be in the field of musculoskeletal biology, as these advancements in bone have been paralleled by advancements in other connective tissues. I am very excited to have been invited to edit this issue of Connective Tissue Research devoted to present-day cutting-edge research on the topic of mechanobiology and grateful to the contributors for sharing their work with us in this format. Work by Bergman et alCitation12 highlights the role of selective estrogen receptor modulators in anabolic bone responses to mechanical loading in a mouse model (REF), providing insights into the impact of estrogen in bone mechanobiology. In an effort to increase the understanding of bone morphogenic protein 2 (BMP-2) in bone repair, Klosterhoff and colleagues have contributed new insights regarding mechanical modulation of BMP-2Citation13. For tendon, we have here a comprehensive review of the role of extracellular matrix properties in tendon mechanotransduction from Chatterjee et alCitation14, as well as exciting new findings showing a connection between tissue stress state and proteoglycan degradation from Egerbacher et alCitation15. Song and colleagues contribute very interesting work highlighting mechanical activation of RhoA and its impact in fibrosis development in the intervertebral disk nucleus pulposusCitation16. Finally, Savadipour et al report a cutting edge engineered cartilage approach used to interrogate the role of channel biology in chondrocyte responses to hydrostatic pressureCitation17.
It is my hope that you enjoy this collection of articles as a representative slice of the field I am so passionate about and take from it an appreciation of the important work being done to deepen our understanding of how mechanical forces impact human biological processes.
Acknowledgments
Sincerest thanks to the editor-in- chief of Connective Tissue Research, Dr. Gary Balian, for the opportunity to guest edit a special edition focused on musculoskeletal mechanobiology. His guidance and mentorship throughout the process have been invaluable. We are lucky to have leaders from the field as contributors here, and I would like to thank all authors who provided scientific and intellectual content. Thank you to the reviewers, whose expertise and thoughtful comments helped to make sure articles of the highest quality were brought to publication. Finally, thanks so much to Elizabeth Lux, for her tireless editorial assistance and the invaluable help in coordinating the review process.
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References
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- Chatterjee M, Muljadi PM, Andarawis-Puri N. The role of the tendon ECM in mechanotransduction: disruption and repair following overuse. Connect Tissue Res. 2021;1–15. doi:https://doi.org/10.1080/03008207.2021.1925663.
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