Page 167 - Physico-Chemical Niche Conditions for Bone Cells

interesting to also investigate the effect of a longer PFF treatment time (> 2 min) on live bone cell behavior.
In vivo, many cell types are subjected to mechanical factors, e.g. stiffness of ECM, tensile stress, external pressure, and shear stress [27]. Cell functions are affected by these mechanical factors through the interaction of cell receptors, such as integrins [27]. Cells respond to mechanical factors and continuously maintain homeostasis in their environmental surroundings via cell structures, including cell body, nucleus, and organelles [27]. The cytoskeleton, as a primary load-bearing element, responds to mechanical factors, and strongly connects with mitochondria. This suggests a possible role of mitochondria as mechanosensors as well [27]. In chapter 5 we found that the mitochondrial network structure was affected by PFF. The movements of mitochondria and F-actin in cells treated by PFF followed a different direction from the top view. This suggested that PFF changed the mitochondrial network structure and dynamics in bone cells without mitochondria being connected to actin filaments. Mitochondria actually interact with actin filaments in many cell types, e.g. plant cells, fungi, budding yeast, and neurons [28]. However, little is known about the interaction between mitochondria and actin filaments in bone cells. In this chapter, we observed the phenomenon of a lack of interaction between mitochondria and actin filaments in bone cells. Currently we do not have an explanation of the mechanism behind the mechanical loading-induced mitochondrial movement and changes in structure. It is possible that the mitochondrial structure and dynamics are affected by mechanical loading via the cyclic AMP signaling cascade or changes in Ca2+ concentration [24,29]. Future studies are needed to unravel this mechanism.
Cell behavior and function are not only affected by physical factors (e.g. surface topography, electric charges, wettability, free energy, matrix stiffness and mechanical loading) [30–32], but also by (bio)chemical factors (e.g. hormones, growth factors, cytokines, collagen, enzymes, ions, minerals and ECM proteins) [33]. Engineering artificial ECM is of great importance for further studies and increased understanding of the mechanisms of bone tissue regeneration, based on a biomimetic ECM microenvironment using proteins and growth factors [34]. Natural ECM contains proteins (e.g. laminin, fibronectin, and vitronectin) and peptides (e.g. RGD) to control cell behavior [35,36]. RGD immobilized onto substrate surface increases cell adhesion and osteogenic differentiation. Cell adhesion plays an important role in guiding osteogenic lineage commitment [37,38]. In chapter 6 we investigated osteoblast adhesion, morphology, focal adhesions, proliferation, and osteogenic potential on glass substrate coated by RGD-functionalized supported lipid bilayers (SLBs), in comparison with cells on PLL and unfunctionalized SLB-coated glass substrates. In this study, RGD- functionalized SLBs on glass substrate increased osteogenic potential of osteoblasts, suggesting that RGD-functionalized SLB coating as (bio)chemical cue might be useful for
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