Simple, Rapid, and Large-Scale Fabrication of Multi-Branched Hydrogels Based on Viscous Fingering for Cell Culture Applications

Hydrogels are widely used in cell culture applications. For fabricating tissues and organs, it is essential to produce hydrogels with specific structures. For instance, multiple-branched hydrogels are desirable for the development of network architectures that resemble the biological vascular network. However, existing techniques are inefficient and time-consuming for this application. To address this issue, a simple, rapid, and large-scale fabrication method based on viscous fingering is proposed. This approach utilizes only two plates. To produce a thin solution, a high-viscosity solution is introduced into the space between the plates, and one of the plates is peeled off. During this procedure, the solution's high viscosity results in the formation of multi-branched structures. Using this strategy, 180 mm × 200 mm multi-branched Pluronic F-127 hydrogels are successfully fabricated within 1 min. These structures are used as sacrificial layers for the fabrication of polydimethylsiloxane channels for culturing human umbilical vein endothelial cells (HUVECs). Similarly, multi-branched Matrigel and calcium (Ca)-alginate hydrogel structures are fabricated, and HUVECs are successfully cultured inside the hydrogels. Also, the hydrogels are collected from the plate, while maintaining their structures. The proposed fabrication technique will contribute to the development of network architectures such as vascular structures in tissue engineering.

Electrochemical microwell sensor with Fe-N co-doped carbon catalyst to monitor nitric oxide release from endothelial cell spheroids

Endothelial cells have been widely used for vascular biology studies; recent progress in tissue engineering have offered three-dimensional (3D) culture systems for vascular endothelial cells which can be considered as physiologically relevant models. To facilitate the studies, we developed an electrochemical device to detect nitric oxide (NO), a key molecule in the vasculature, for the evaluation of 3D cultured endothelial cells. Using an NO-sensitive catalyst composed of Fe-N co-doped reduced graphene oxide, the real-time monitoring of NO release from the endothelial cell spheroids was demonstrated.

Nanomaterial-based cell sheet technology for regenerative medicine and tissue engineering

Nanomaterial-based cell sheet technology has been reported to be an effective method in regenerative medicine and tissue engineering. Here, we summarized several types of nanomaterials used to harvest cell sheets. Currently, the technology is divided into four categories according to the mechanisms: light-induced cell sheet technology, thermo-responsive cell sheet technology, magnetic-controlled cell sheet technology, and reactive oxygen species (ROS)-induced cell sheet technology. Furthermore, some studies have been conducted to show that nanomaterial-based cell sheets produce satisfying outcomes in the regeneration of bone, skeletal muscle, cardiac tissue, and tendon, as well as angiogenesis and osseointegration. Nevertheless, some shortcomings still exist, such as comprehensive preparation, unclear safety, and cell quality. Thus, future studies should aim to produce more types of nanomaterials to solve this problem.

Ion Conductance-Based Perfusability Assay of Vascular Vessel Models in Microfluidic Devices

We present a novel methodology based on ion conductance to evaluate the perfusability of vascular vessels in microfluidic devices without microscopic imaging. The devices consisted of five channels, with the center channel filled with fibrin/collagen gel containing human umbilical vein endothelial cells (HUVECs). Fibroblasts were cultured in the other channels to improve the vascular network formation. To form vessel structures bridging the center channel, HUVEC monolayers were prepared on both side walls of the gel. During the culture, the HUVECs migrated from the monolayer and connected to the HUVECs in the gel, and vascular vessels formed, resulting in successful perfusion between the channels after culturing for 3-5 d. To evaluate perfusion without microscopic imaging, Ag/AgCl wires were inserted into the channels, and ion currents were obtained to measure the ion conductance between the channels separated by the HUVEC monolayers. As the HUVEC monolayers blocked the ion current flow, the ion currents were low before vessel formation. In contrast, ion currents increased after vessel formation because of creation of ion current paths. Thus, the observed ion currents were correlated with the perfusability of the vessels, indicating that they can be used as indicators of perfusion during vessel formation in microfluidic devices. The developed methodology will be used for drug screening using organs-on-a-chip containing vascular vessels.

Magnetic assembly of 3D cell clusters: visualizing the formation of an engineered tissue

OBJECTIVES

Contactless magnetic assembly of cells into 3D clusters has been proposed as a novel means for 3D tissue culture that eliminates the need for artificial scaffolds. However, thus far its efficacy has only been studied by comparing expression levels of generic proteins. Here, it has been evaluated by visualizing the evolution of cell clusters assembled by magnetic forces, to examine their resemblance to in vivo tissues.

MATERIALS AND METHODS

Cells were labeled with magnetic nanoparticles, then assembled into 3D clusters using magnetic force. Scanning electron microscopy was used to image intercellular interactions and morphological features of the clusters.

RESULTS

When cells were held together by magnetic forces for a single day, they formed intercellular contacts through extracellular fibers. These kept the clusters intact once the magnetic forces were removed, thus serving the primary function of scaffolds. The cells self-organized into constructs consistent with the corresponding tissues in vivo. Epithelial cells formed sheets while fibroblasts formed spheroids and exhibited position-dependent morphological heterogeneity. Cells on the periphery of a cluster were flattened while those within were spheroidal, a well-known characteristic of connective tissues in vivo.

CONCLUSIONS

Cells assembled by magnetic forces presented visual features representative of their in vivo states but largely absent in monolayers. This established the efficacy of contactless assembly as a means to fabricate in vitro tissue models.

Liposomes in tissue engineering and regenerative medicine

Liposomes are vesicular structures made of lipids that are formed in aqueous solutions. Structurally, they resemble the lipid membrane of living cells. Therefore, they have been widely investigated, since the 1960s, as models to study the cell membrane, and as carriers for protection and/or delivery of bioactive agents. They have been used in different areas of research including vaccines, imaging, applications in cosmetics and tissue engineering. Tissue engineering is defined as a strategy for promoting the regeneration of tissues for the human body. This strategy may involve the coordinated application of defined cell types with structured biomaterial scaffolds to produce living structures. To create a new tissue, based on this strategy, a controlled stimulation of cultured cells is needed, through a systematic combination of bioactive agents and mechanical signals. In this review, we highlight the potential role of liposomes as a platform for the sustained and local delivery of bioactive agents for tissue engineering and regenerative medicine approaches.

Magnetic force-based cell patterning for evaluation of the effect of stromal fibroblasts on invasive capacity in 3D cultures

Biomimetic cell culture systems that recreate tumor microenvironments are necessary in understanding the progression of cancer cells in cell-to-cell interaction and in cell-to-extracellular matrix interaction. We have developed a three-dimensional spheroid array embedded in collagen for evaluation of the effect of stromal fibroblasts associated with cancer cells. When the breast epithelial cancer cell model MCF10A/myr-Akt1 was magnetically labeled and aligned in the array by an external magnetic force using a pin-holder device and a magnet, a stellate configuration was observed. Changes in MCF10A/myr-Akt1 cell behavior were only slight when normal human dermal fibroblasts (NHDF) cells coexisted in collagen (indirect-interaction array). In contrast, when NHDF were magnetically labeled and patterned together with MCF10A/myr-Akt1 (direct-interaction array), spreading and progression were observed along with NHDF. Cell image analysis indicated that the length and area were statistically significantly increased in the direct-interaction array compared to the MCF10A/myr-Akt1 alone or to the indirect-interaction array. A cell susceptibility assay was undertaken with breast cancer MDA-MB-231 associated with NHDF in the indirect-interaction array. Interestingly, although distinct suppression of cell movement and proliferation was observed with 100 μM of collagenase inhibitor, formation of invadepodia significantly increased with coexistent NHDF. Since cancer progression is influenced by its microenvironment, this magnetic cell-patterning method which clarifies direct and indirect effects of stromal cells on invasion and proliferation, is well suited for evaluation and design of more efficient approaches in cancer prevention and treatment.

Engineering the multifunctional surface on magnetic nanoparticles for targeted biomedical applications: a chemical approach

Research on multifunctional magnetic nanoparticles for biomedicines has experienced rapid growth because of the progressive advancements in nanotechnology and in modern biotechnology. However, the design of multifunctional surfaces on magnetic nanoparticles generally lacks a systematic approach. This article will try to unfold the complex chemistry in constructing a multifunctional surface, and layout a simplified guide for researchers to follow, particularly those from nonchemistry backgrounds. A number of design principles with critical rationales are to be introduced and followed by four main strategies: multifunctionality on a polymer chain, use of block copolymers, cocondensation of alkoxysilanes and of the secondary reaction on groups, with a particular reference to the use of alkoxysilanes. Nanoparticles of higher complexity are expected to be reported in the near future. These advanced systems are likely to be designed from some more logical, strategic mechanisms rather than the 'pick-and-mix' approaches we have seen in the last decade.

Three-dimensional cell culture array using magnetic force-based cell patterning for analysis of invasive capacity of BALB/3T3/v-src

A three-dimensional (3D) cell culture system has been fabricated using a magnetic force based cell patterning method, demonstrating a facile approach for the analysis of invasive capacity of BALB/3T3/v-src using an magnetic force and magnetite nanoparticles. The 3D cell patterning was performed using an external magnetic force and a pin holder, which enables the assembly of the magnetically labeled cells on the collagen gel-coated surface as array-like cell patterns, resulting in the development of a 3D in vitro culture model. The cells embedded in type I collagen showed a compacted, spheroid like configuration at each spot, and distinct, accelerated cell growth was observed in cancer model cells compared with the control cells. The developed 3D cell culture array was applied to the susceptibility assay of the GM6001 matrix metalloproteinase (MMP) inhibitor, a collagenase inhibitor; a distinct suppression of cell proliferation was observed, while little change was observed in 2D. The developed 3D cell culture array system is useful to assess the effects of pharmacologic and/or microenvironmental influences on tumor cell invasion.

Fabrication of complex three-dimensional tissue architectures using a magnetic force-based cell patterning technique

We describe the fabrication of three-dimensional tissue constructs using a magnetic force-based tissue engineering technique, in which cellular organization is controlled by magnetic force. Target cells were labeled with magnetite cationic liposomes (MCLs) so that the MCL-labeled cells could be manipulated by applying a magnetic field. Line patterning of human umbilical vein endothelial cells (HUVECs) labeled with MCLs was successfully created on monolayer cells or skin tissues using a magnetic concentrator device. Multilayered cell sheets were also inducible on a culture surface by accumulating MCL-labeled cells under a uniform magnetic force. Based on these results, we attempted to construct a complex multilayered myoblast C2C12 cell sheet. Here, patterned HUVECs were embedded by alternating the processes of magnetic accumulation of C2C12 cells for cell layer formation and magnetic patterning of HUVECs on the cell layers. This technique may be applicable for the fabrication of complex tissue architectures required in tissue engineering.

Application of magnetic force-based cell patterning for controlling cell-cell interactions in angiogenesis

To investigate the effects of cell-cell interactions on cellular function, the microenvironment surrounding cells should be precisely controlled. Here, we describe a cell patterning technique, which utilizes magnetic force and magnetite nanoparticles. This method was used to develop cell culture arrays for investigation of cell behaviors in angiogenesis. Pin holder devices that contain more than 6,000 pillars on the surface are used for fabricating the cell culture arrays by setting it on a magnet. The magnetically labeled cells were arranged by magnetic distribution. When the human umbilical vein endothelial cells are arranged at 250 microm intervals (5.9 cells/spot), the cells spread toward other cell cluster on adjacent spots in 4.5 h, and formed cord-like structures in 8.5 h. It was shown that cell-cell interactions were successfully investigated using magnetic cell arrangement.

Plasmid DNA transfection using magnetite cationic liposomes for construction of multilayered gene-engineered cell sheet

Modification of cellular functions by overexpression of genes is being increasingly practiced for tissue engineering. In the present study, we investigated whether transfection efficiency could be enhanced by magnetofection that involves the use of plasmid DNA (pDNA)/magnetite cationic liposomes (MCLs) complexes (pDNA/MCL) and magnetic force. The transfection efficiencies of the magnetofection technique by pDNA/MCL in fibroblasts and keratinocytes using reporter genes were 36- and 10-fold higher, respectively, than those of a lipofection technique by cationic liposomes. Moreover, in vitro construction of three-dimensional (3D) tissues is an important challenge. We recently proposed a novel technique termed "magnetic force-based tissue engineering" (Mag-TE) to produce 3D tissues. Since the fibroblasts after magnetofection incorporated both magnetite nanoparticles and pDNA, we investigated whether multilayered heterotypic cell sheets expressing transgene could be fabricated by Mag-TE. First, the fibroblasts were seeded onto an ultra-low attachment culture plate. When a magnet was placed under the plate, the cells accumulated at the bottom of the culture plate. After 24 h of culture, the transgene-expressing cells formed a multilayered cell sheet-like structure. These results indicated that MCLs are a potent biomanipulation tool for both gene transfer and 3D tissue construction, suggesting that these techniques are useful for tissue engineering.

Cell culture arrays using magnetic force-based cell patterning for dynamic single cell analysis

In order to understand the behavior of individual cells, single cell analyses have attracted attention since most cell-based assays provide data with values averaged across a large number of cells. Techniques for the manipulation and analysis of single cells are crucial for understanding the behavior of individual cells. In the present study, we have developed single cell culture arrays using magnetic force and a pin holder, which enables the allocation of the magnetically labeled cells on arrays, and have analyzed their dynamics. The pin holder was made from magnetic soft iron and contained more than 6000 pillars on its surface. The pin holder was placed on a magnet to concentrate the magnetic flux density above the pillars. NIH/3T3 fibroblasts that were labeled with magnetite cationic liposomes (MCLs) were seeded into a culture dish, and the dish was placed over the pin holder with the magnet. The magnetically labeled cells were guided on the surface where the pillars were positioned and allocated on the arrays with a high resolution. Single-cell patterning was achieved by adjusting the number of cells seeded, and the target cell was collected by a micromanipulator after removing the pin holder with the magnet. Furthermore, change in the morphology of magnetically patterned cells was analyzed by microscopic observation, and cell spreading on the array was observed with time duration. Magnetic force-based cell patterning on cell culture arrays would be a suitable technique for the analysis of cell behavior in studies of cell-cell variation and cell-cell interactions.

Effective cell-seeding technique using magnetite nanoparticles and magnetic force onto decellularized blood vessels for vascular tissue engineering

Increasing attention has been given to vascular tissue engineering in recent years. Although cell seeding onto tubular scaffolds is the first step for constructing three-dimensional vascular grafts, the tubular geometry of the grafts hinders the efficient delivery of cells onto the scaffold. To overcome these limitations, we present here a novel cell-seeding technique using magnetic force and magnetite nanoparticles, termed Mag-seeding. NIH/3T3 fibroblasts (3T3s) were labeled magnetically using our original magnetite cationic liposomes (MCLs), which have a positive surface charge, to improve adsorption onto cell surface. In this study, porcine decellularized common carotid artery (dCCA) was used as one of the most promising scaffolds, because dCCA consists of a mixture of structural and functional proteins that constitute the extracellular matrix. When a cylindrical magnet was inserted into the lumen of dCCA and the dCCA was immersed into a suspension of magnetically labeled 3T3s, almost all the 3T3s attached onto the dCCA, whereas a low cell-seeding efficiency was achieved without using a magnet. When the magnetite uptake rate per cell increased, cell-seeding efficiency by Mag-seeding was enhanced. Furthermore, to construct a vascular graft for humans, the porcine dCCA, which was reseeded with two human cells (smooth muscle cells and dermal fibroblasts), was successfully constructed by Mag-seeding. These results indicate that Mag-seeding can be used for vascular tissue engineering.

Cell patterning using magnetite nanoparticles and magnetic force

Technologies for fabricating functional tissue architectures by patterning cells precisely are highly desirable for tissue engineering. Although several cell patterning methods such as microcontact printing and lithography have been developed, these methods require specialized surfaces to be used as substrates, the fabrication of which is time consuming. In the present study, we demonstrated a simple and rapid cell patterning technique, using magnetite nanoparticles and magnetic force, which enables us to allocate cells on arbitrary surfaces. Magnetite cationic liposomes (MCLs) developed in our previous study were used to magnetically label the target cells. When steel plates placed on a magnet were positioned under a cell culture surface, the magnetically labeled cells lined on the surface where the steel plate was positioned. Patterned lines of single cells were achieved by adjusting the number of cells seeded, and complex cell patterns (curved, parallel, or crossing patterns) were successfully fabricated. Since cell patterning using magnetic force may not limit the property of culture surfaces, human umbilical vein endothelial cells (HUVECs) were patterned on Matrigel, thereby forming patterned capillaries. These results suggest that the novel cell patterning methodology, which uses MCLs, is a promising approach for tissue engineering and studying cell-cell interactions in vitro.