Shaping the Cell and the Future: Recent Advancements in Biophysical Aspects Relevant to Regenerative Medicine

Journal of Functional Morphology and Kinesiology Review Shaping the Cell and the Future: Recent Advancements in Biophysical Aspects Relevant to Regenerative Medicine Melanie L. Hart 1 , Jasmin C. Lauer 1 , Mischa Selig 1 , Martha Hanak 1 , Brandan Walters 2 and Bernd Rolauffs 1, * 1 2 * G.E.R.N. Tissue Replacement, Regeneration & Neogenesis, Department of Orthopedics and Trauma Surgery, Medical Center—Albert-Ludwigs-University of Freiburg, Faculty of Medicine, Albert-Ludwigs-University of Freiburg, Hugstetter Straße 55, 79106 Freiburg, Germany; (M.L.H.); (J.C.L.); (M.S.); (M.H.) Department of Biomedical Engineering, University of Michigan, Michigan, MI 48109, USA; Correspondence: ; Tel.: +49-761-270-26101 Received: 14 November 2017; Accepted: 13 December 2017; Published: 22 December 2017 Abstract: In a worldwide effort to generate clinically useful therapeutic or preventive interventions, harnessing biophysical stimuli for directing cell fate is a powerful strategy. With the vision to control cell function through engineering cell shape, better understanding, measuring, and controlling cell shape for ultimately utilizing cell shape-instructive materials is an emerging “hot” topic in regenerative medicine. This review highlights how quantitation of cellular morphology is useful not only for understanding the effects of different microenvironmental or biophysical stimuli on cells, but also how it could be used as a predictive marker of biological responses, e.g., by predicting future mesenchymal stromal cell differentiation. We introduce how high throughput image analysis, combined with computational tools, are increasingly being used to efficiently and accurately recognize cells. Moreover, we discuss how a panel of quantitative shape descriptors may be useful for measuring specific aspects of cellular and nuclear morphology in cell culture and tissues. This review focuses on the mechano-biological principle(s) through which biophysical cues can affect cellular shape, and recent insights on how specific cellular “baseline shapes” can intentionally be engineered, using biophysical cues. Hence, this review hopes to reveal how measuring and controlling cellular shape may aid in future regenerative medicine applications. Keywords: cell morphology; cell shape; biophysical cues; tissue engineering; cell imaging; quantitative analysis; engineering cell morphology; predicting phenotypic outcomes; morphological signatures; morphological fingerprints; mesenchymal stromal cells 1. Is Shaping the Cell Also Shaping Regenerative Medicine? Worldwide, regenerative medicine works toward improving practical methods and experimental strategies to generate clinically useful therapeutic or preventive interventions. In this view, mesenchymal stromal cells (MSCs) are recognized as adult, self-renewing, and multipotent stem cells with substantial potential for therapeutic use [1,2] that were forecasted to significantly improve disease outcomes and patient lives [3]. In this review, we chose the term “mesenchymal stromal cells” over “mesenchymal stem cells” to describe a heterogeneous population of cells that can be differentiated in vitro into a range of lineages, and whose self-renewal and subsequent in vivo differentiation remains to be proven [4]. Publication titles such as the “rise of mechano-transduction” [5], “mechano-transduction: use the force” [6], and “mechano-transduction: may the force be with you” [7] J. Funct. Morphol. Kinesiol. 2018, 3, 2; doi:10.3390/jfmk3010002 www.mdpi.com/journal/jfmk J. Funct. Morphol. Kinesiol. 2018, 3, 2 2 of 16 illustrate that besides biochemical and genetic factors, biophysical cues may be equally important in controlling cell fate [8], and that harnessing biophysical stimuli is a modern, powerful approach to steering cell function in regenerative medicine. Developmental biology demonstrates that cell shape follows function. Classic examples are skeletal myogenic cells, which exhibit an elongated cylindrical morphology. This morphology aligns multi-nucleated myofibers parallel to the direction of muscle tissue tension and contraction. In the context of biophysically steering cell fate, cellular shape has only recently emerged as potential determinant, because cellular shape influences tissue structure and function [9,10] and determines the lineage of differentiation [11]. Additionally, the physical shape of cells is a fundamental signal for proliferation [12], a potent regulator of cell growth and physiology, and is adapted for specific functions [13]. Thus, in a way, actively shaping cellular morphology by biophysical means contributes to shaping the future of regenerative medicine. As this invited review was given the task to summarize topic-related advancements presented in the Tissue Engineering and Regenerative Medicine International Society (TERMIS) European Chapter Meeting 2017, this review focuses on cellular morphology as a novel assessment of biological responses and discusses broadly how biophysical cues affect cellular shape, how cellular shape can be measured quantitatively, and introduces the computational tools and approaches necessary for this task. Finally, this review will discuss means of controlling cellular shape, its effects on functional phenotype, and impact it will have on regenerative medicine applications. 2. Cell Morphology as a Novel Tool to Assess Biological Responses in Tissue Engineering As this review is in included in the TERMIS special issue: selected papers from TERMIS European Chapter Meeting 2017 on “Biomechanics, Morphology and Imaging”, we are highlighting some selected studies that were presented at this meeting that demonstrated the importance of measuring cell morphological features and their implications on tissue engineering. Topics ranged from the effect of exposure to normogravity (or earth gravity force) vs. simulated hypergravity conditions using the large diameter centrifuge (LDC) from the European Space Research and Technology Centre (ESTEC, ESA, The Netherlands) [14] to how different degrees of compressive stiffness in 3D-printed scaffolds containing mesenchymal stromal cells (MSCs) affected cell function and morphology [15]. According to the former group [14], microgravity-induced alterations, found during spaceflight, but more importantly, during bed rest, were comparable to tissue degeneration caused by disuse and ageing. In this study, human tendon-derived cells were exposed to normogravity (earth gravity force) vs. hypergravity. After 16 h, the different g-levels led to cell and cytoskeleton morphology changes (an increase in cell area, actin stress fiber formation and intracellular anisotropy) that correlated with tenogenic differentiation markers, highlighting the importance of measuring cell shape and suggesting that exposure of musculoskeletal tissues to hypergravity may simulate loading and rescue the phenotype of degenerated tendon cells after exposure to near-weightless (...truncated)