Fabrication of functional three-dimensional tissues by stacking cell sheets in vitro. Nat Protoc. 2012;7:850-858. [PMID: 22481530 DOI: 10.1038/nprot.2012.027]

Cell sheet technology-driven re-epithelialization and neovascularization of skin wounds

Skin regeneration remains a challenge, requiring a well-orchestrated interplay of cell-cell and cell-matrix signalling. Cell sheet (CS) engineering, which has the major advantage of allowing the retrieval of the intact cell layers along with their naturally organized extracellular matrix (ECM), has been poorly explored for the purpose of creating skin substitutes and skin regeneration. This work proposes the use of CS technology to engineer cellular constructs based on human keratinocytes (hKC), key players in wound re-epithelialization, dermal fibroblasts (hDFb), responsible for ECM remodelling, and dermal microvascular endothelial cells (hDMEC), part of the dermal vascular network and modulators of angiogenesis. Homotypic and heterotypic three-dimensional (3-D) CS-based constructs were developed simultaneously to target wound re-vascularization and re-epithelialization. After implantation of the constructs in murine full-thickness wounds, human cells were engrafted into the host wound bed and were present in the neotissue formed up to 14 days post-implantation. Different outcomes were obtained by varying the composition and organization of the 3-D constructs. Both hKC and hDMEC significantly contributed to re-epithelialization by promoting rapid wound closure and early epithelial coverage. Moreover, a significant increase in the density of vessels at day 7 and the incorporation of hDMEC in the neoformed vasculature confirmed its role over neotissue vacularization. As a whole, the obtained results confirmed that the proposed 3-D CS-based constructs provided the necessary cell machinery, when in a specific microenvironment, guiding both re-vascularization and re-epithelialization. Although dependent on the nature of the constructs, the results obtained sustain the hypothesis that different CS-based constructs lead to improved skin healing.

Cell sheet engineering for regenerative medicine: current challenges and strategies

Substantial progress made in the areas of stem cell research and regenerative medicine has provided a number of innovative methods to repair or regenerate defective tissues and organs. Although previous studies regarding regenerative medicine, especially those involving induced pluripotent stem cells, have been actively promoted in the past decade, there remain some challenges that need to be addressed in order to enable clinical applications. Designed for use in clinical applications, cell sheet engineering has been developed as a unique, scaffold-free method of cell processing utilizing temperature-responsive cell culture vessels. Clinical studies using cell sheets have shown positive outcomes and will be translated into clinical practice in the near future. However, several challenges stand in the way of the industrialization of cell sheet products and the widespread acceptance of regenerative medicine based on cell sheet engineering. This review describes current strategies geared towards the realization of the regenerative medicine approach.

In vitro pre-vascularisation of tissue-engineered constructs A co-culture perspective

In vitro pre-vascularization is one of the main vascularization strategies in the tissue engineering field. Culturing cells within a tissue-engineered construct (TEC) prior to implantation provides researchers with a greater degree of control over the fate of the cells. However, balancing the diverse range of different cell culture parameters in vitro is seldom easy and in most cases, especially in highly vascularized tissues, more than one cell type will reside within the cell culture system. Culturing multiple cell types in the same construct presents its own unique challenges and pitfalls. The following review examines endothelial-driven vascularization and evaluates the direct and indirect role other cell types have in vessel and capillary formation. The article then analyses the different parameters researchers can modulate in a co-culture system in order to design optimal tissue-engineered constructs to match desired clinical applications.

Thermoresponsive nanofabricated substratum for the engineering of three-dimensional tissues with layer-by-layer architectural control

Current tissue engineering methods lack the ability to properly recreate scaffold-free, cell-dense tissues with physiological structures. Recent studies have shown that the use of nanoscale cues allows for precise control over large-area 2D tissue structures without restricting cell growth or cell density. In this study, we developed a simple and versatile platform combining a thermoresponsive nanofabricated substratum (TNFS) incorporating nanotopographical cues and the gel casting method for the fabrication of scaffold-free 3D tissues. Our TNFS allows for the structural control of aligned cell monolayers which can be spontaneously detached via a change in culture temperature. Utilizing our gel casting method, viable, aligned cell sheets can be transferred without loss of anisotropy or stacked with control over individual layer orientations. Transferred cell sheets and individual cell layers within multilayered tissues robustly retain structural anisotropy, allowing for the fabrication of scaffold-free, 3D tissues with hierarchical control of overall tissue structure.

Macromolecular crowding meets tissue engineering by self-assembly: a paradigm shift in regenerative medicine

MMC, the addition of inert polydispersed macromolecules in the culture media, effectively emulates the dense in vivo extracellular space, resulting in amplified deposition of ECM in vitro and subsequent production of cohesive, ECM-rich living substitutes.

Stacked stem cell sheets enhance cell-matrix interactions

Cell sheet engineering has enabled the production of confluent cell sheets stacked together for use as a cardiac patch to increase cell survival rate and engraftment after transplantation, thereby providing a promising strategy for high density stem cell delivery for cardiac repair. One key challenge in using cell sheet technology is the difficulty of cell sheet handling due to its weak mechanical properties. A single-layer cell sheet is generally very fragile and tends to break or clump during harvest. Effective transfer and stacking methods are needed to move cell sheet technology into widespread clinical applications. In this study, we developed a simple and effective micropipette based method to aid cell sheet transfer and stacking. The cell viability after transfer was tested and multi-layer stem cell sheets were fabricated using the developed method. Furthermore, we examined the interactions between stacked stem cell sheets and fibrin matrix. Our results have shown that the preserved ECM associated with the detached cell sheet greatly facilitates its adherence to fibrin matrix and enhances the cell sheet-matrix interactions. Accelerated fibrin degradation caused by attached cell sheets was also observed.

ADVANCED TISSUE ENGINEERING STRATEGIES FOR VASCULARIZED PARENCHYMAL CONSTRUCTS

The fabrication of vascularized parenchymal organs to alleviate donor shortage in organ transplantation is the holy grail of tissue engineering. However, conventional tissue-engineering strategies have encountered huge challenges in recapitulating complex structural organization of native organs (e.g., orderly arrangement of multiple cell types and vascular network), which plays an important role in engineering functional vascularized parenchymal constructs in vitro. Recent developments of various advanced tissue-engineering strategies have exhibited great promise in replicating organ-specific architectures into artificial constructs. Here, we review the recent advances in top-down and bottom-up strategies for the fabrication of vascularized parenchymal constructs. We highlight the fabrication of microfluidic scaffolds potential for nutrient transport or vascularization as well as the controlled multicellular arrangement. The advantages as well as the limitations associated with these strategies will be discussed. It is envisioned that the combination of microfluidic concept in top-down strategies and multicellular arrangement concept in bottom-up strategies could potentially generate new insights for the fabrication of vascularized parenchymal organs.

3D reconstitution of nerve-blood vessel networks using skeletal muscle-derived multipotent stem cell sheet pellets

AIM

To cover the large tissue deficits associated with significant loss of function following surgery, a 3D gel-patch-like nerve-vascular reconstitution system was developed using the skeletal muscle-derived multipotent stem cell (Sk-MSC) sheet pellet.

MATERIALS & METHODS

The Sk-MSC sheet pellet was prepared from GFP transgenic mice by the collagenase extraction and 7 days expansion cell culture, and transplanted into a severe muscle damage model with large disruptions to muscle fibers, blood vessels and peripheral nerves.

RESULTS

At 4 weeks after transplantation, engrafted cells contributed to nerve-vascular regeneration associated with cellular differentiation into Schwann cells, perineurial/endoneurial cells, vascular endothelial cells and pericytes. However, skeletal myogenic differentiation was scarcely observed. Paracrine effects regarding donor cells/tissues could also be expected, because of the active expression of neurogenic and vasculogenic factor mRNAs in the sheet pellet.

CONCLUSION

These results indicate that the vigorous skeletal myogenic potential of Sk-MSCs was clearly reduced in the sheet pellet preparation and this method may be a useful adjuvant for nerve-vascular regeneration in various tissue engineering applications.

Fabrication of Cell Patches Using Biodegradable Scaffolds with a Hexagonal Array of Interconnected Pores (SHAIPs)

Cell patches are widely used for healing injuries on the surfaces or interfaces of tissues such as those of epidermis and myocardium. Here we report a novel type of porous scaffolds made of poly(D,L-lactic-co-glycolic acid) for fabricating cell patches. The scaffolds have a single layer of spherical pores arranged in a unique hexagonal pattern and are therefore referred to as "scaffolds with a hexagonal array of interconnected pores (SHAIPs)". SHAIPs contain both uniform pores and interconnecting windows that can facilitate the exchange of biomacromolecules, ensure homogeneous cell seeding, and promote cell migration. As a proof-of-concept demonstration, we have created skeletal muscle patches with a thickness of approximately 150 μm using SHAIPs. The myoblasts seeded in the scaffolds maintained high viability and were able to differentiate into multi-nucleated myotubes. Moreover, neovasculature could efficiently develop into the patches upon subcutaneous implantation in vivo.

Cell sheet technology for cardiac tissue engineering

In this chapter, we describe the methods for the fabrication and transfer/transplantation of 3D tissues by using cell sheet technology for cardiac tissue regeneration. A temperature-responsive culture surface can be fabricated by grafting a temperature-responsive polymer, poly(N-isopropylacrylamide), onto a polystyrene cell culture surface. Cells cultured confluently on such a culture surface can be recovered as an intact cell sheet, and functional three-dimensional (3D) tissues can then be easily fabricated by layering the recovered cell sheets without any scaffolds or complicated manipulation. Cardiac cell sheets, myoblast sheets, mesenchymal stem cell sheets, cardiac progenitor cell sheets, etc., which are prepared from temperature-responsive culture surfaces, can be easily transplanted onto heart tissues of animal models, and those cell sheet constructs enhance the cell transplant efficiency, resulting in the induction of effective therapy.

Exploring innovation in stem cell and regenerative medicine in Japan: the power of the consortium-based approach

This article describes a recent trend in Japanese research, development and commercialization toward the application of stem cell technologies. Japan is the world's third largest economy and has a significant national presence in the pharmaceutical and biotechnology businesses; as such, stem cell R&D is abundant in the country. As indicated by the second largest share of patent applications worldwide, Japan had been expected to assert significant added value in the commercialization and industrial application of stem cell technologies; however, difficulties have impeded clinical development in this area, particularly the very small number of clinical trials and approved products for regenerative medicine or cell therapy. To address this 'Japan paradox', this report provides an overview of approaches for the commercialization of stem cell technologies in areas such as drug discovery, cell therapy and regenerative medicine, by discussing representative case examples of listed firms.

Smart hydrogels as functional biomimetic systems

This review discusses the principles underlying stimuli-responsive behavior of hydrogels and how these properties contribute to their biomimetic functions and applications.

Surface design of antibody-immobilized thermoresponsive cell culture dishes for recovering intact cells by low-temperature treatment

Antibody-immobilized thermoresponsive poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) [poly(IPAAm-co-CIPAAm)]-grafted cell culture surfaces were designed to enhance both the initial adhesion of weakly adhering cells and the ability of cells to detach in response to low temperature through the regulation of affinity binding between immobilized antibodies and antigens on the cellular surface. Ty-82 cells and neonatal normal human dermal fibroblasts (NHDFs), which express CD90 on the cell surface, adhered to anti-CD90 antibody-immobilized thermoresponsive surfaces at 37°C, a condition at which the grafted thermoresponsive polymer chains shrank. Adherent Ty-82 cells were detached from the surfaces by lowering the temperature to 20°C and applying external forces, such as pipetting, whereas cultured NHDF sheets spontaneously detached themselves from the surface in response to reduced temperature alone. When the temperature was decreased to 20°C, the swelling of grafted thermoresponsive polymer chains weakened the affinity binding between immobilized antibody and antigen on the cells due to the increasing steric hindrance of the polymer chains around the antigen-recognition site of the immobilized antibodies. No contamination was detected on cells harvested from covalently immobilized antibodies on the culture surfaces by low-temperature treatment, whereas a carryover of the antibody and avidin from the avidin-biotin binding surface was observed. Furthermore, the initial adhesion of adipose tissue-derived cells, which adhere weakly to PIPAAm-grafted surfaces, was enhanced on the antibody-immobilized thermoresponsive surfaces.

Switchable substrates for analyzing and engineering cellular functions

Cellular activity is highly dependent on the extracellular environment, which is composed of surrounding cells and extracellular matrices. This focus review summarizes recent advances in chemically and physically engineered switchable substrates designed to control such cellular microenvironments by application of an external stimulus. Special attention is given to their molecular design, switching strategies, and representative examples for bioanalytical and biomedical applications.

Engineered skeletal muscle tissue for soft robotics: fabrication strategies, current applications, and future challenges

Skeletal muscle is a scalable actuator system used throughout nature from the millimeter to meter length scales and over a wide range of frequencies and force regimes. This adaptability has spurred interest in using engineered skeletal muscle to power soft robotics devices and in biotechnology and medical applications. However, the challenges to doing this are similar to those facing the tissue engineering and regenerative medicine fields; specifically, how do we translate our understanding of myogenesis in vivo to the engineering of muscle constructs in vitro to achieve functional integration with devices. To do this researchers are developing a number of ways to engineer the cellular microenvironment to guide skeletal muscle tissue formation. This includes understanding the role of substrate stiffness and the mechanical environment, engineering the spatial organization of biochemical and physical cues to guide muscle alignment, and developing bioreactors for mechanical and electrical conditioning. Examples of engineered skeletal muscle that can potentially be used in soft robotics include 2D cantilever-based skeletal muscle actuators and 3D skeletal muscle tissues engineered using scaffolds or directed self-organization. Integration into devices has led to basic muscle-powered devices such as grippers and pumps as well as more sophisticated muscle-powered soft robots that walk and swim. Looking forward, current, and future challenges include identifying the best source of muscle precursor cells to expand and differentiate into myotubes, replacing cardiomyocytes with skeletal muscle tissue as the bio-actuator of choice for soft robots, and vascularization and innervation to enable control and nourishment of larger muscle tissue constructs.

Chondrocyte differentiation of human endometrial gland-derived MSCs in layered cell sheets

Recently, regenerative medicine using engineered three-dimensional (3D) tissues has been focused. In the fields of cell therapy and regenerative medicine, mesenchymal stem cells (MSCs) are attractive autologous cell sources. While, in bioengineered tissues, a 3D environment may affect the differentiation of the stem cells, little is known regarding the effect of 3D environment on cellular differentiation. In this study, MSC differentiation in in vitro 3D tissue models was assessed by human endometrial gland-derived MSCs (hEMSCs) and cell sheet technology. hEMSC sheets were layered into cell-dense 3D tissues and were cultured on porous membranes. The tissue sections revealed that chondrocyte-like cells were found within the multilayered cell sheets even at 24 h after layering. Immunostainings of chondrospecific markers were positive within those cell sheet constructs. In addition, sulfated glycosaminoglycan accumulation within the tissues increased in proportion to the numbers of layered cell sheets. The findings suggested that a high cell density and hypoxic environment in 3D tissues by layering cell sheets might accelerate a rapid differentiation of hEMSCs into chondrocytes without the help of chondro-differentiation reagents. These tissue models using cell sheets would give new insights to stem cell differentiation in 3D environment and contribute to the future application of stem cells to cartilage regenerative therapy.

Tissue engineering of the corneal endothelium: a review of carrier materials

Functional impairment of the human corneal endothelium can lead to corneal blindness. In order to meet the high demand for transplants with an appropriate human corneal endothelial cell density as a prerequisite for corneal function, several tissue engineering techniques have been developed to generate transplantable endothelial cell sheets. These approaches range from the use of natural membranes, biological polymers and biosynthetic material compositions, to completely synthetic materials as matrices for corneal endothelial cell sheet generation. This review gives an overview about currently used materials for the generation of transplantable corneal endothelial cell sheets with a special focus on thermo-responsive polymer coatings.

3D in vitro tissue models and their potential for drug screening

INTRODUCTION

The development of one standard, simplified in vitro three-dimensional tissue model suitable to biological and pathological investigation and drug-discovery may not yet be feasible, but standardized models for individual tissues or organs are a possibility. Tissue bioengineering, while concerned with finding methods of restoring functionality in disease, is developing technology that can be miniaturized for high throughput screening (HTS) of putative drugs. Through collaboration between biologists, physicists and engineers, cell-based assays are expanding into the realm of tissue analysis. Accordingly, three-dimensional (3D) micro-organoid systems will play an increasing role in drug testing and therapeutics over the next decade. Nevertheless, important hurdles remain before these models are fully developed for HTS.

AREAS COVERED

We highlight advances in the field of tissue bioengineering aimed at enhancing the success of drug candidates through pre-clinical optimization. We discuss models that are most amenable to high throughput screening with emphasis on detection platforms and data modeling.

EXPERT OPINION

Modeling 3D tissues to mimic in-vivo architecture remains a major challenge. As technology advances to provide novel methods of HTS analysis, so do potential pitfalls associated with such models and methods. We remain hopeful that integration of biofabrication with HTS will significantly reduce attrition rates in drug development.

Characterization of squamous cell carcinoma in an organotypic culture via subsurface non-linear optical molecular imaging

Tristetraprolin (TTP) is an RNA-binding protein which downregulates multiple cytokines that mediate progression of head and neck squamous cell carcinoma (HNSCC). We previously showed that HNSCC cells with shRNA-mediated knockdown of TTP are more invasive than controls. In this study, we use control and TTP-deficient cells to present a novel subsurface non-linear optical molecular imaging method using a three-dimensional (3D) organotypic construct, and compare the live cell imaging data to histology of fixed tissue specimens. This manuscript describes how to prepare and image the novel organotypic system that closely mimics HNSCC in a clinical setting. The oral cancer equivalent (OCE) system allows HNSCC cells to stratify and invade beyond the basement membrane into underlying connective tissue prepared from decellularized human dermal tissue. The OCE model was inspired by tissue engineering strategies to prepare autologous transplants from human keratinocytes. Advantages of this method over previously used in vitro cancer models include the simulation of the basement membrane and complex connective tissue in the construct, in addition to the ability to track the 3D movement of live invading cells and quantify matrix destruction over time. The OCE model and novel live cell imaging strategy may be applied to study other types of 3D tissue constructs.

Advanced nanobiomaterial strategies for the development of organized tissue engineering constructs

Nanobiomaterials, a field at the interface of biomaterials and nanotechnologies, when applied to tissue engineering applications, are usually perceived to resemble the cell microenvironment components or as a material strategy to instruct cells and alter cell behaviors. Therefore, they provide a clear understanding of the relationship between nanotechnologies and resulting cellular responses. This review will cover recent advances in nanobiomaterial research for applications in tissue engineering. In particular, recent developments in nanofibrous scaffolds, nanobiomaterial composites, hydrogel systems, laser-fabricated nanostructures and cell-based bioprinting methods to produce scaffolds with nanofeatures for tissue engineering are discussed. As in native niches of cells, where nanofeatures are constantly interacting and influencing cellular behavior, new generations of scaffolds will need to have these features to enable more desirable engineered tissues. Moving forward, tissue engineering will also have to address the issues of complexity and organization in tissues and organs.

The effect of electrically charged polyion complex nanoparticle-coated surfaces on adipose-derived stromal progenitor cell behaviour

Surface characteristics of biomaterials such as wettability, rigidity, roughness, and electrical charge affect the fate of transplanted cells such as progenitor cells or stem cells for use in regenerative medicine. Of these, the effects of surface electrical charges on cellular behaviour such as adhesion, proliferation, and differentiation are not well understood. We prepared precisely charged culture surfaces ranging from -28 mV to +21 mV, simply by surface deposition of polyion complex nanoparticles prepared by mixing a positively charged thermoresponsive homopolymer, poly(N,N-dimethylaminoethyl methacrylate), with negatively charged plasmid DNA at various charge ratios. Drastic morphological changes of adipose-derived vascular progenitor cells were generated on the positively charged surface of organized forms at +19 mV. Capillary-like networks or single aggregates of these cells were selectively created depending on cell seeding density. Our findings offer new insights that may aid develop stem cell-processing techniques for use in regenerative medicine.

Design and Fabrication of Changeable Cell Culture Mold

Although the fabrication of engineered organs as replacements for damaged organs has been widely studied over the past decade, practical fabrication is very difficult because the engineered organ usually has a very complex structure and cannot be fabricated simply by using a fixed scaffold. Special attention has therefore been paid to methods of making engineered organs by assembling composite parts. Since structures of these individual parts are very different, fabrication using fixed scaffolds requires a lot of effort and time. The concept of a changeable scaffold offered by “changeable cell culture (C3) mold” is proposed in this paper as a means to simplify the fabrication of these parts. Using a thin PDMS membrane as an actuator layer enables various scaffold structures to be formed and altered, in turn enabling the fabrication of many different tissue structures.C3mold consists of a 3 × 3 microactuator array with a diameter of 500 µm and spacing of 650 µm. Plant oil is used as the working fluid enabling deformation of the actuator layer. Various micropatterned gel sheets are fabricated, in order to demonstrate the possibility of usingC3molds in future tissue fabrication.

Measuring Mechanical Properties of Cell Sheets by a Tensile Test Using a Self-Attachable Fixture

In this paper, we present a tensile test system and a new self-attachable fixture for measuring mechanical properties of cell sheets. Previously when measuring the mechanical properties of cell sheets, the sheets would be damaged because they dried out. With our system, the tensile test can be carried out while the cell sheets are in the culture medium, so there is no damage by drying. Previously, it has also been difficult to attach a cell sheet in the tensile test system owing to the structure of the conventional fixture, and there has been no tensile test system which had a measurement range that covered the tension force range of the cell sheets. Therefore, we have addressed these problems by developing a self-attachable fixture and a tensile test system. To confirm suitability of the fixture and test system, we measured mechanical properties of two different kinds of cultured cell sheets, C2C12 (cells mouse myoblast cells) and NIH-3T3 (3T3) cells (mouse fibroblast cells), and of the same kinds of sheets treated with cytochalasin-D. We confirmed differences in mechanical properties for each kind of cell sheet. This indicates that our new fixture and test system are applicable for measurement of mechanical properties of cell sheets without damage of the sheets by drying.

Tuning of cell-biomaterial anchorage for tissue regeneration

Which mechanisms mediate cell attachment to biomaterials? What role does the surface charge or wettability play on cell-material anchorage? What are the currently investigated strategies to modify cell-matrix adherence spatiotemporally? Considering the development of scaffolds made of biocompatible materials to temporarily replace the structure and/or function of the extracellular matrix, focus is given to the analysis of the specific (i.e., cell adhesive peptide sequences) and unspecific (i.e., surface charge, wettability) mechanisms mediating cell-matrix interactions. Furthermore, because natural tissue regeneration is characterized by the dynamic attachment/detachment of different cell populations, the design of advanced scaffolds for tissue engineering, based in the spatiotemporal tuning of cell-matrix anchorage is discussed.

Initiated chemical vapor deposition of thermoresponsive poly(N-vinylcaprolactam) thin films for cell sheet engineering

Poly(N-vinylcaprolactam) (PNVCL) is a thermoresponsive polymer known to be nontoxic, water soluble and biocompatible. Here, PNVCL homopolymer was successfully synthesized for the first time by use of a one-step vapor-phase process, termed initiated chemical vapor deposition (iCVD). Fourier transform infrared spectroscopy results showed that radical polymerization took place from N-vinylcaprolactam monomers without damaging the functional caprolactam ring. A sharp lower critical solution temperature transition was observed at 31°C from the iCVD poly(N-vinylcaprolactam) (PNVCL) film. The thermoresponsive PNVCL surface exhibited a hydrophilic/hydrophobic alteration with external temperature change, which enabled the thermally modulated attachment and detachment of cells. The conformal coverage of PNVCL film on various substrates with complex topography, including fabrics and nanopatterns, was successfully demonstrated, which can further be utilized to fabricate cell sheets with aligned cell morphology. The advantage of this system is that cells cultured on such thermoresponsive surfaces could be recovered as an intact cell sheet by simply lowering the temperature, eliminating the need for conventional enzymatic treatments.

Rapid fabricating technique for multi-layered human hepatic cell sheets by forceful contraction of the fibroblast monolayer

Cell sheet engineering is attracting attention from investigators in various fields, from basic research scientists to clinicians focused on regenerative medicine. However, hepatocytes have a limited proliferation potential in vitro, and it generally takes a several days to form a sheet morphology and multi-layered sheets. We herein report our rapid and efficient technique for generating multi-layered human hepatic cell (HepaRG® cell) sheets using pre-cultured fibroblast monolayers derived from human skin (TIG-118 cells) as a feeder layer on a temperature-responsive culture dish. Multi-layered TIG-118/HepaRG cell sheets with a thick morphology were harvested on day 4 of culturing HepaRG cells by forceful contraction of the TIG-118 cells, and the resulting sheet could be easily handled. In addition, the human albumin and alpha 1-antitrypsin synthesis activities of TIG-118/HepaRG cells were approximately 1.2 and 1.3 times higher than those of HepaRG cells, respectively. Therefore, this technique is considered to be a promising modality for rapidly fabricating multi-layered human hepatocyte sheets from cells with limited proliferation potential, and the engineered cell sheet could be used for cell transplantation with highly specific functions.

Functional cell-laden alginate scaffolds consisting of core/shell struts for tissue regeneration

We report an innovative cell-dispensing process using a three-axis robot system coupled with a micro-core/shell nozzle and an aerosol cross-linking process to achieve controlled mechanical properties and high cell viability of porous cell-laden alginate scaffolds. The scaffolds were fabricated into layer-by-layer struts, which were used to design the pore structure. The struts consisted of a core/shell region; a low weight fraction of alginate and cells (MC3T3-E1) was injected in the shell region to efficiently exchange nutrients and metabolic wastes, while a high weight fraction of alginate without cells was deposited in the core region to improve the mechanical properties of the cell-laden scaffold. After 10 days of cell culture, the cell viability (95%) in the shell region improved significantly compared to 70% for the cells homogeneously distributed in the struts, and the mechanical properties were enhanced from 1.4 to 15.7 kPa. Stained nuclei and F-actin images showed that the laden cells proliferated well on the functional hydrogel scaffold after 20 days of cell culture, indicating that the cells concentrated in the shell region of the struts survived and increased their metabolic functions during several incubation periods compared to the standard cell-laden scaffold. This innovative cell-dispensing technique represents a promising fabrication tool for obtaining bottom-up scaffolds for various tissue regenerations.

Engineered nanomembranes for directing cellular organization toward flexible biodevices

Controlling the cellular microenvironment can be used to direct the cellular organization, thereby improving the function of synthetic tissues in biosensing, biorobotics, and regenerative medicine. In this study, we were inspired by the microstructure and biological properties of the extracellular matrix to develop freestanding ultrathin polymeric films (referred as "nanomembranes") that were flexible, cell adhesive, and had a morphologically tailorable surface. The resulting nanomembranes were exploited as flexible substrates on which cell-adhesive micropatterns were generated to align C2C12 skeletal myoblasts and embedded fibril carbon nanotubes enhanced the cellular elongation and differentiation. Functional nanomembranes with tunable morphology and mechanical properties hold great promise in studying cell-substrate interactions and in fabricating biomimetic constructs toward flexible biodevices.

The use of anisotropic cell sheets to control orientation during the self-organization of 3D muscle tissue

In some parts of native tissues, the orientation of cells and/or extracellular matrixes is well organized. We know that because anisotropy produces important tissue functions, an appropriate anisotropy needs to be designed to biomimetically construct complex tissue. Here, we show the unique features of anisotropic myoblast sheets for organizing the three-dimensional (3D) orientation of myoblasts and myotubes. Utilizing a micropatterned thermoresponsive surface, human skeletal muscle myoblasts were aligned on the surface, and manipulated as a single anisotropic cell sheet by reducing the culture temperature. Consequently, layering of anisotropic myoblast sheets using gelatin gel allowed 3D myotube constructs to be built up with the desired anisotropy. We also discovered a surprising myoblast behavior. An anisotropic cell sheet placed on top of other cell sheets in fabricating thick tissue was able to change the cell orientation in several layered cell sheets underneath. This self-organization is believed to provide the uniqueness required in designing 3D cell orientation architecture for reconstructed muscle tissue.

Dynamic substrate based on photocleavable poly(ethylene glycol): zeta potential determines the capability of geometrical cell confinement

Dynamic substrates whose cell adhesiveness changes in response to an external stimulus are useful not only for patterning cells in various geometries but also for inducing cell migration or arraying heterotypic cells. The requirements for such applications are high switching efficiency in cell adhesiveness and long-term persistence of the created cellular patterns. In this study, we prepared a dynamic substrate bearing photocleavable poly(ethylene glycol) (PEG) and examined the effect of the surface PEG density and the charge of cationic base materials on the above-mentioned key requirements. An amino-terminated substrate with a certain amino group density and charge was functionalized with photocleavable PEG5K, with and without subsequent backfilling of photocleavable PEG2K. The PEG chains made the surface non-cell-adhesive, but subsequent near-UV irradiation of the substrate induced photocleavage of the PEG, eventually making the surface cell-adhesive. The substrates were analyzed by atomic force microscopy, contact angle measurements, ellipsometry, and zeta potential measurements, complemented with protein adsorption observations. Although the density of amino group in the base material affected both the grafting efficiency of the backfilling PEG and the electrokinetic potential mainly in the positive range, the latter mainly determined the protein- and cell-repelling abilities of the substrates. Furthermore, varying the surface compositions had almost no effect on the switching efficiency in the early stage of the culture, but it became more significant after culturing cells for a longer time; the cells fouled the nonirradiated PEGylated regions earlier on the surfaces with higher positive zeta potentials. These results indicate that the zeta potential is an essential factor in the long-term persistence of cellular patterns on photoactivatable substrates. This study not only provides a recipe for the development of a dynamic substrate with an adequate time frame but also clarifies how the interfacial nanoarchitectures, composed of the nanometer-scale PEG brushes and charged base materials, affect the biocompatibility.

Simple suspension culture system of human iPS cells maintaining their pluripotency for cardiac cell sheet engineering

In this study, a simple three-dimensional (3D) suspension culture method for the expansion and cardiac differentiation of human induced pluripotent stem cells (hiPSCs) is reported. The culture methods were easily adapted from two-dimensional (2D) to 3D culture without any additional manipulations. When hiPSCs were directly applied to 3D culture from 2D in a single-cell suspension, only a few aggregated cells were observed. However, after 3 days, culture of the small hiPSC aggregates in a spinner flask at the optimal agitation rate created aggregates which were capable of cell passages from the single-cell suspension. Cell numbers increased to approximately 10-fold after 12 days of culture. The undifferentiated state of expanded hiPSCs was confirmed by flow cytometry, immunocytochemistry and quantitative RT-PCR, and the hiPSCs differentiated into three germ layers. When the hiPSCs were subsequently cultured in a flask using cardiac differentiation medium, expression of cardiac cell-specific genes and beating cardiomyocytes were observed. Furthermore, the culture of hiPSCs on Matrigel-coated dishes with serum-free medium containing activin A, BMP4 and FGF-2 enabled it to generate robust spontaneous beating cardiomyocytes and these cells expressed several cardiac cell-related genes, including HCN4, MLC-2a and MLC-2v. This suggests that the expanded hiPSCs might maintain the potential to differentiate into several types of cardiomyocytes, including pacemakers. Moreover, when cardiac cell sheets were fabricated using differentiated cardiomyocytes, they beat spontaneously and synchronously, indicating electrically communicative tissue. This simple culture system might enable the generation of sufficient amounts of beating cardiomyocytes for use in cardiac regenerative medicine and tissue engineering.

Emerging in vitro models for safety screening of high-volume production nanomaterials under environmentally relevant exposure conditions

The rising production of nanomaterial-based consumer products has raised safety concerns. Testing these with animal and other direct models is neither ethically nor economically viable, nor quick enough. This review aims to discuss the strength of in vitro testing, including the use of 2D and 3D cultures, stem cells, and tissue constructs, etc., which would give fast and repeatable answers of a highly specific nature, while remaining relevant to in vivo outcomes. These results can then be combined and the overall toxicity predicted with relative accuracy. Such in vitro models can screen potentially toxic nanomaterials which, if required, can undergo further stringent studies in animals. The cyto- and phototoxicity of some high-volume production nanomaterials, using in vitro models, is also reviewed.

Self-organization and the self-assembling process in tissue engineering

In recent years, the tissue engineering paradigm has shifted to include a new and growing subfield of scaffoldless techniques that generate self-organizing and self-assembling tissues. This review aims to cogently describe this relatively new research area, with special focus on applications toward clinical use and research models. Particular emphasis is placed on providing clear definitions of self-organization and the self-assembling process, as delineated from other scaffoldless techniques in tissue engineering and regenerative medicine. Significantly, during formation, self-organizing and self-assembling tissues display biological processes similar to those that occur in vivo. These processes help lead to the recapitulation of native tissue morphological structure and organization. Notably, functional properties of these engineered tissues, some of which are already in clinical trials, also approach native tissue values. This review endeavors to provide a cohesive summary of work in this field and to highlight the potential of self-organization and the self-assembling process for providing cogent solutions to currently intractable problems in tissue engineering.

Rapid Fabrication of Living Tissue Models by Collagen Plastic Compression: Understanding Three-Dimensional Cell Matrix Repair In Vitro

OBJECTIVE

To produce biomimetic collagen scaffolds for tissue modeling and as tissue-engineered implants.

APPROACH

Control of collagen fibril material parameters in collagen hydrogel scaffolds by using plastic compression (PC), resulting in direct control of cell proliferation, cell migration, and cell-cell interaction.

RESULTS

We were able to control the density of collagen in such scaffolds from between 0.2% and 30%, and controllably layer the fibrils in the Z-plane. Cell migration was observed in gels where a gradient of collagen density was present. In these gels, cells preferentially migrated toward the collagen-dense areas. Cell proliferation rates were measurably higher in dense collagen gels.

INNOVATION

The use of PC to control material properties of collagen hydrogels results in collagen scaffolds that are biomimetic. These collagen gels reproduce the relevant matrix-mechanical environment in which behavior is more representative of that found in vivo.

CONCLUSION

The material properties of native collagen type I gels can be engineered to match those found in tissues in vivo to elicit more biomimetic cell behavior.

Microdevices for nanomedicine

This review surveys selected methods of manufacture and applications of microdevices-miniaturized functional devices capable of handling cell and tissue cultures or producing particles-and discusses their potential relevance to nanomedicine. Many characteristics of microdevices such as miniaturization, increased throughput, and the ability to mimic organ-specific microenvironments are promising for the rapid, low-cost evaluation of the efficacy and toxicity of nanomaterials. Their potential to accurately reproduce the physiological environments that occur in vivo could reduce dependence on animal models in pharmacological testing. Technologies in microfabrications and microfluidics are widely applicable for nanomaterial synthesis and for the development of diagnostic devices. Although the use of microdevices in nanomedicine is still in its infancy, these technologies show promise for enhancing fundamental and applied research in nanomedicine.

Emerging applications of superhydrophilic-superhydrophobic micropatterns

Water on superhydrophilic surfaces spreads or is absorbed very quickly, and exhibits water contact angles close to zero. We encounter superhydrophilic materials in our daily life (e.g., paper, sponges, textiles) and they are also ubiquitous in nature (e.g., plant and tree leaves, Nepenthes pitcher plant). On the other hand, water on completely non-wettable, superhydrophobic surfaces forms spherical droplets and rolls off the surface easily. One of the most well-known examples of a superhydrophobic surface is the lotus leaf. Creating novel superhydrophobic surfaces has led to exciting new properties such as complete water repellency, self-cleaning, separation of oil and water, and antibiofouling. However, combining these two extreme states of superhydrophilicity and superhydrophobicity on the same surface in precise two-dimensional micropatterns opens exciting new functionalities and possibilities in a wide variety of applications from cell, droplet, and hydrogel microarrays for screening to surface tension confined microchannels for separation and diagnostic devices. In this Progress Report, we briefly describe the methods for fabricating superhydrophilic-superhydrophobic patterns and highlight some of the newer and emerging applications of these patterned substrates that are currently being explored. We also give an outlook on current and future applications that would benefit from using such superhydrophilic-superhydrophobic micropatterns.

Biomaterial applications in cardiovascular tissue repair and regeneration

Cardiovascular disease physically damages the heart, resulting in loss of cardiac function. Medications can help alleviate symptoms, but it is more beneficial to treat the root cause by repairing injured tissues, which gives patients better outcomes. Besides heart transplants, cardiac surgeons use a variety of methods for repairing different areas of the heart such as the ventricular septal wall and valves. A multitude of biomaterials are used in the repair and replacement of impaired heart tissues. These biomaterials fall into two main categories: synthetic and natural. Synthetic materials used in cardiovascular applications include polymers and metals. Natural materials are derived from biological sources such as human donor or harvested animal tissues. A new class of composite materials has emerged to take advantage of the benefits of the strengths and minimize the weaknesses of both synthetic and natural materials. This article reviews the current and prospective applications of biomaterials in cardiovascular therapies.

Hormone supplying renal cell sheet in vivo produced by tissue engineering technology

Regenerative medicine is a new medical field and is expected to have a profoundly positive effect in curing difficult-to-treat diseases. Cell sheet fabrication is an important tissue engineering technology used in regenerative medicine. This study investigated the creation of a hormone-releasing tissue using cell sheet technology, which could be utilized in future therapy for chronic renal disease. Renal cell sheets were fabricated on a temperature-responsive cell culture surface with primary renal cells from adult porcine kidney. These sheets contained various kinds of renal cells that showed cyst-like formation. An important renal function is the synthesis of 1,25-dihydroxyvitamin D3, and this was confirmed in the cell sheets in vitro. Erythropoietin (EPO) production is another important renal function. This ability was also observed in the renal cell sheets in vitro, and then again after transplantation in a nude rat. In particular, the relative expression of EPO mRNA increased more under cell sheet culture conditions compared with exponential cell growth conditions. Histological analysis of the implanted renal cell sheets showed them to be Dolichos biflorus agglutinin-positive and to have regenerated renal tubular-like morphology. These results indicated that both functional and morphological regenerative renal tissues were fabricated by cell sheet technology. This study introduces a hormone-supplying treatment for renal dysfunctional diseases using engineered renal tissues. Moreover, since our renal cell sheets developed renal tubular-like structures in vivo, it holds promise for fabricating artificially engineered true renal tissue in the future.

Hydrogels in Healthcare: From Static to Dynamic Material Microenvironments

Advances in hydrogel design have revolutionized the way biomaterials are applied to address biomedical needs. Hydrogels were introduced in medicine over 50 years ago and have evolved from static, bioinert materials to dynamic, bioactive microenvironments, which can be used to direct specific biological responses such as cellular ingrowth in wound healing or on-demand delivery of therapeutics. Two general classes of mechanisms, those defined by the user and those dictated by the endogenous cells and tissues, can control dynamic hydrogel microenvironments. These highly tunable materials have provided bioengineers and biological scientists with new ways to not only treat patients in the clinic but to study the fundamental cellular responses to engineered microenvironments as well. Here, we provide a brief history of hydrogels in medicine and follow with a discussion of the synthesis and implementation of dynamic hydrogel microenvironments for healthcare-related applications.