Cell migration is fundamental to various physiological processes, including metastasis, wound healing and tissue development. The complex processes involved in cell migration; polymerization, adhesion, and retraction, are mediated by highly orchestrated structure-function interactions that occur within the actin cytoskeletal structure. Thus understanding how migrating cells regulate the global dynamics of their cytoskeletal components, which result from rather localized protein-protein interactions, is fundamental to elucidating the mechanisms of cell motility. The objective of this review is to explore the mechanical regulation of actin network dynamics in migrating cells, and to discuss its regulatory role in cell migration. Specifically, we examine the various mechanical forces involved in cell migration, and how they couple with biomechanical factors to spatiotemporally regulate the dynamics of the actin cytoskeleton during cell motility. Two aspects of actin network dynamics are addressed, namely, network turnover by polymerization and depolymerization, and network flow resulting from actomyosin activity. We begin by highlighting the fundamental features of actin network dynamics in migrating cells. We then examine the coupling relationship between actin network flow and traction forces, as well as the mechanism underlying the regulation of traction forces by actin network flow. Finally, we integrate the various motility processes into a mechanical pathway in order to elucidate the importance of mechanical regulation of actin network dynamics to cell migration.

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Attempts to interface human-made systems with neural systems are commonly based on direct electrical stimulation or exogenous drug delivery. Few techniques have attempted to mimic neurons' own combination of electronic and chemical signaling with endogenous substances. We demonstrate below the organic electronic ion pump (OEIP), a technology which aims to accomplish just that: electronically controlled delivery of ions, neurotransmitters and other bio-substances. Based on electrophoretic migration through an organic electronic system, delivery is diffusive and non-convective, that is, without fluid flow. Various experiments involving OEIP technology are reviewed, culminating in its use, in an encapsulated form, to modulate sensory function in a living animal. As a first step towards an “artificial neuron”, this technology has significant potential for both neural system interfacing and in the treatment of various neurological disorders.

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Cell functions are known to be regulated not only by the biochemical or physiological conditions of extracellular milieu but also by the mechanical conditions of substrate surface or extracellular matrix. The detailed understandings for the cellular responses induced by such mechanical field or mechanical stimuli, and its application for systematic design of mechanical field of cell culture substrate are expected to establish solid basis for constructing high-functional cell manipulation materials. Especially, cell manipulation by the elastic substrates has recently drawn a strong attention in relation to the stem cell manipulation technologies. In this mini-review, to address the mechanical design of elastic interface for cell manipulation, we will focus on the mechanics of cell adhesion and the cell motility manipulation as the dynamical control of adhesion mechanics. The potential application of the systematic design of micromechanical environment of elastic substrate for cell functional regulation is discussed.

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In this paper, we report an in vitro study on the biocompatibility of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) films for the implantable artificial cochlea. The implantable artificial cochlea comprises a piezoelectric membrane made of P(VDF-TrFE), platinum (Pt) thin film electrodes, and a silicon substrate which are designed to stimulate neurons in a cochlea and fabricated by microelectromechanical systems (MEMS) and thin film technologies. The biocompatibility of P(VDF-TrFE) film is evaluated by culturing cerebral cortical neurons from rats on it. The fibronectin from human plasma and the collagen from the calf skin are used as the cell adhesion factors. Since neurons extend dendrites and axons from the somata, it is found that the neurons are successfully cultured on the surface of P(VDF-TrFE) films modified both by the fibronectin and by the collagen. Furthermore, it is also found that the neurons are also successfully cultured over the Pt electrode on the P(VDF-TrFE) of the implantable artificial cochlea modified by the fibronectin. Consequently, the biocompatibility and the applicability of the MEMS fabricated P(VDF-TrFE) films and the implantable artificial cochlea are confirmed.

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Living muscle tissue seems to have an efficient potential as an actuator. We propose to utilize a tissue engineered skeletal muscle (TESM) as a bio-actuator by connecting to the object through artificial anchors. We designed a rod-shaped TESM with artificial anchors and fabricated it by culturing myoblasts in collagen gel for several days. The contractile ability and controllability of the TESM were confirmed by stimulating electrically. The contractions were evoked forcibly and synchronously by electrical pulses under 4.5 Hz. The electrical pulses at 8 Hz kept the contractile state. As potential anchor materials, silicone sponge and nonwoven nylon mesh were examined. The anchors made of nonwoven nylon mesh held a rod-shaped TESM for more than 3 weeks successfully, while the anchors made of silicone sponge held it for only 2-4 days and the TESM broke down at the connecting area. The mechanical endurance between the TESM and the nylon anchors was examined using our original stretching device. No damage was observed from the repeated mechanical loading at 0.5 Hz with 5 % stretch rate for 10 days. We concluded that the TESM has good potential for utilization as a bio-actuator and its abilities can be exploited by connecting it to an object through artificial anchors.

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A technique to attach muscle cells to artificial micro mechanical systems was studied using dog body hair and rat primary skeletal muscle. Muscle-powered cantilever for microtweezers were fabricated which consisted of a single strand of hair for the skeleton and differentiated myotubes for the actuator. The three-dimensional mechanical part of the microtweezers was fabricated using a focused ion beam-induced ion milling technique. The micro hair skeleton was used as a scaffold for the muscular cells and the mechanical structure. Electrical stimulation induced related contraction of the myotubes and displacement of the muscle-powered cantilever of the microtweezers, although the displacement was not yet enough for useful microtools.

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Tissue-engineered grafts using a scaffold can be used in treating periodontal disease; however, previous scaffolds for the cultivations of the periodontal ligament cells have been structurally incompatible with the morphological requirements of human periodontal tissue. Here, we describe a self-organized honeycomb-patterned film (honeycomb film) that acted as an appropriate scaffold for periodontal tissue regeneration. The honeycomb films were prepared from biodegradable poly(ε-caprolactone) with highly regular three-dimensional micropatterned surface topography by casting a polymer solution of water-immiscible solvent under humid conditions. To evaluate its performance in activating the proliferation and organizing of cells, we have demonstrated specific behaviors of the cultured periodontal ligament cells on the self-organized honeycomb structures in vitro. Fibroblast-like cells derived from the periodontal ligament of extracted human molar teeth were cultivated on three types of honeycomb films with 5-, 10-, and 15-µm pore sizes for 4 h to 42 d. Morphological observation of the cultured tissues at 4—72 h revealed that the pseudopodiums of cell bodies were attached to the pillars in the honeycomb structure. A certain number of cells shifted their cell bodies into the honeycomb structural lumen through the oscula of 10- and 15-µm pores. After 28 and 42 d, the cells were observed to have formed multiple layers; further, each cell had penetrated through the 10- and 15-µm pores in the honeycomb film. The morphological examination of the honeycomb film along with the pillar structures revealed that the scaffold was clusteringly arrayed with interconnected structures, remarkably enhanced proliferation, and extension of the cultured cells. We consider that the film can be applied in periodontal therapy for use as a scaffold for periodontal tissue regeneration.

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Cellular traction forces were measured by using a microfabricated substrate, particularly exploring how cytoskeletal structures such as actin filaments and microtubules contribute to traction forces. Smooth muscle cells isolated from bovine aortas were cultured and transfected with fluorescence proteins to visualize cell microstructures and then plated on a micropatterned elastomer substrate with arrays of micropillars. Cell spreading on the substrates produced deflection of micropillars which was used for estimation of cellular traction forces, and was closely associated with organization of stress fibers of actin filaments. Traction forces varied considerably among cells, showing the order of several 10 nN. After disruption of microtubules with nocodazole, traction forces significantly increased and there was no detectable change in formation of stress fibers. To inhibit the ROCK pathway, a signaling pathway of myosin light chain phosphorylation, possibly being induced by disruption of microtubules, significantly depressed the increase in traction forces after the disruption of microtubules. This result indicates that microtubules disassembly may regulate the actomyosin-based contractile system mainly through the ROCK pathway. The present study suggests that formation of stress fibers are mainly involved in cellular traction forces and a contribution of microtubules should include not only a force balance but also rather a modulator of the actomyosin contractile system in actin stress fibers.

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Stem cell research is today an active and promising field of research. To learn more about the biology of stem cells, technical improvements are needed such as tools to study stem cells in order to characterize them further and to gain insights to the molecular regulations of their maintenance, differentiation and identification. Common procedure when studying stem cells is to coat the surface where the stem cells are to be cultured with organic materials like matri-gel, poly-L-lysine and fibronectin. The resulting coating is usually relatively fragile and it is difficult to know if the coating is evenly distributed. In addition, these forms of coatings cannot be sterilized and re-used, but must be added as an initial, time-consuming step in the daily protocol. A microwell chip with hundreds of 500 nl wells has recently been shown to be a useful tool for stem cell culturing. This platform is here modified to facilitate and improve the coating conditions for adherent cell culture. A robust and highly porous film of TiO₂ is deposited in the wells prior cell seeding. TiO₂ is known to be biocompatible and provides a surface that is even and well characterized, simple to produce and re-usable. Furthermore it enables the microwell chips to be stored pre-coated for longer periods of time before use. We investigated the growth of rat mesenchymal stem cells on nanoporous titania films and found that they proliferated much faster than on conventional coatings. The combination of the robust TiO₂ coating of the microwell chip enables thousands of individually separated single, or clones of, stem cells to be studied simultaneously and opens up the possibility for more user-friendly cell culturing.

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