Corneal epithelial stem cell delivery using cell sheet engineering: not lost in transplantation

Enhancement of Lymphangiogenesis by Human Mesenchymal Stem Cell Sheet

Preparation of human mesenchymal stem cell (hMSC) suspension for lymphedema treatment relies on conventional enzymatic digestion methods, which severely disrupts cell-cell and cell-extracellular matrix (ECM) connections, and drastically impairs cell retention and engraftment after transplantation. The objective of the present study is to evaluate the ability of hMSC-secreted ECM to augment lymphangiogenesis by using an in vitro coculturing model of hMSC sheets with lymphatic endothelial cells (LECs) and an in vivo mouse tail lymphedema model. Results demonstrate that the hMSC-secreted ECM augments the formation of lymphatic capillary-like structure by a factor of 1.2-3.6 relative to the hMSC control group, by serving as a prolymphangiogenic growth factor reservoir and facilitating cell regenerative activities. hMSC-derived ECM enhances MMP-2 mediated matrix remodeling, increases the synthesis of collagen IV and laminin, and promotes lymphatic microvessel-like structure formation. The injection of rat MSC sheet fragments into a mouse tail lymphedema model confirms the benefits of the hMSC-derived ECM by stimulating lymphangiogenesis and wound closure.

Therapeutic measures for sulfur mustard-induced ocular injury

The use of sulfur mustard (SM) in global terrorism is still a relevant threat to both civilian population and military personnel. Casualties exposed to SM may present mild, moderate or severe acute ocular lesions followed by a complete ocular resolution, chronic lesions or re-emerged ocular pathologies after a latent period. Current treatment for SM-induced ocular injury is based mainly on the clinical manifestation at the different stages of the injury and includes pharmaceutical and surgical interventions. These therapeutic measures are beneficial but not sufficient, and the ocular injury remains a continuous challenge for medical professionals. This review focuses on treatment experience carried out in humans and studied in animal models, for both SM-induced ocular acute injury and late pathology. In general, therapeutic measures are based on clinical features of the ocular injury or on the involvement of specific factors during the ocular injury that point out towards potential treatments. Anti-inflammatory treatments and limbal stem cell transplantation techniques were developed based on the clinical manifestation of the ocular injury. Optional therapies for impaired corneal innervation and endothelium are suggested for future research. Additionally, studies on potential treatments with anti-matrix metalloproteinase (MMP), anti-vascular endothelial growth factor (VEGF) and anti-IL-6 agents are discussed. Consequently, future studies may reveal the potential of additional pharmacological and biological treatments or advanced cellular and molecular biology methods to serve as novel therapeutic measures and techniques for this complicated ocular injury.

Preseeding of Mesenchymal Stem Cells Increases Integration of an iPSC-Derived CM Sheet into a Cardiac Matrix

Cell sheet technology has demonstrated great promise in delivering a large amount of therapeutic cells for tissue repair, including in the myocardium. However, the lack of host integration remains one of the key challenges in using cell sheets for cardiac repair. Paracrine factors secreted by mesenchymal stem cells (MSCs) have been reported to facilitate tissue repair and regeneration in a variety of ways. It has been demonstrated that paracrine factors from MSCs could enhance scaffold recellularization and vascularization. In this study, we used an in vitro cardiac matrix mimic platform to examine the effects of hMSCs preseeding on the interactions between cell sheets and cardiac matrix. The fabricated human induced pluripotent stem cells-derived cardiomyocyte sheets were attached to a decellularized porcine myocardium slice with or without preseeding of hMSCs. The hMSCs preseeding significantly enhanced the interactions between cardiomyocyte sheets and cardiac matrix in terms of cell migration distance, cell distribution, and mature vascular and cardiomyocyte marker expressions in the matrix. Growth factor and matrix metalloproteinases array analysis suggested that hMSCs- induced vascularization and MMPs regulation are the two possible mechanisms that lead to the improved CMs and cardiac matrix interactions. Further examination of these two mechanisms will enable the development of new approaches to facilitate transplanted cells for tissue repair.

Bioengineering Approaches for Corneal Regenerative Medicine

BACKGROUND

Since the cornea is responsible for transmitting and focusing light into the eye, injury or pathology affecting any layer of the cornea can cause a detrimental effect on visual acuity. Aging is also a reason for corneal degeneration. Depending on the level of the injury, conservative therapies and donor tissue transplantation are the most common treatments for corneal diseases. Not only is there a lack of donor tissue and risk of infection/rejection, but the inherent ability of corneal cells and layers to regenerate has led to research in regenerative approaches and treatments.

METHODS

In this review, we first discussed the anatomy of the cornea and the required properties for reconstructing layers of the cornea. Regenerative approaches are divided into two main categories; using direct cell/growth factor delivery or using scaffold-based cell delivery. It is expected delivered cells migrate and integrate into the host tissue and restore its structure and function to restore vision. Growth factor delivery also has shown promising results for corneal surface regeneration. Scaffold-based approaches are categorized based on the type of scaffold, since it has a significant impact on the efficiency of regeneration, into the hydrogel and non-hydrogel based scaffolds. Various types of cells, biomaterials, and techniques are well covered.

RESULTS

The most important characteristics to be considered for biomaterials in corneal regeneration are suitable mechanical properties, biocompatibility, biodegradability, and transparency. Moreover, a curved shape structure and spatial arrangement of the fibrils have been shown to mimic the corneal extracellular matrix for cells and enhance cell differentiation.

CONCLUSION

Tissue engineering and regenerative medicine approaches showed to have promising outcomes for corneal regeneration. However, besides proper mechanical and optical properties, other factors such as appropriate sterilization method, storage, shelf life and etc. should be taken into account in order to develop an engineered cornea for clinical trials.

Tissue engineering of retina through high resolution 3-dimensional inkjet bioprinting

The mammalian retina contains multiple cellular layers, each carrying out a specific task. Such a controlled organization should be considered as a crucial factor for designing retinal therapies. The maintenance of retinal layered complexity through the use of scaffold-free techniques has recently emerged as a promising approach for clinical ocular tissue engineering. In an attempt to fabricate such layered retinal model, we are proposing herein a unique inkjet bioprinting system applied to the deposition of a photoreceptor cells (PRs) layer on top of a bioprinted retinal pigment epithelium (RPE), in a precise arrangement and without any carrier material. The results showed that, after bioprinting, both RPE and PRs were well positioned in a layered structure and expressed their structural markers, which was further demonstrated by ZO1, MITF, rhodopsin, opsin B, opsin R/G and PNA immunostaining, three days after bioprinting. We also showed that considerable amounts of human vascular endothelial growth factors (hVEGF) were released from the RPE printed layer, which confirmed the formation of a functional RPE monolayer after bioprinting. Microstructures of bioprinted cells as well as phagocytosis of photoreceptor outer segments by apical RPE microvilli were finally established through transmission electron microscopy (TEM) imaging. In summary, using this carrier-free bioprinting method, it was possible to develop a reasonable in vitro retina model for studying some sight-threatening diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP).

Evaluation of Mesenchymal Stem Cell Sheets Overexpressing BMP-7 in Canine Critical-Sized Bone Defects

The aim of this study was to investigate the in vitro osteogenic capacity of bone morphogenetic protein 7 (BMP-7) overexpressing adipose-derived (Ad-) mesenchymal stem cells (MSCs) sheets (BMP-7-CS). In addition, BMP-7-CS were transplanted into critical-sized bone defects and osteogenesis was assessed. BMP-7 gene expressing lentivirus particles were transduced into Ad-MSCs. BMP-7, at the mRNA and protein level, was up-regulated in BMP-7-MSCs compared to expression in Ad-MSCs. Osteogenic and vascular-related gene expressions were up-regulated in BMP-7-CS compared to Ad-MSCs and Ad-MSC sheets. In a segmental bone-defect model, newly formed bone and neovascularization were enhanced with BMP-7-CS, or with a combination of BMP-7-CS and demineralized bone matrix (DBM), compared to those in control groups. These results demonstrate that lentiviral-mediated gene transfer of BMP-7 into Ad-MSCs allows for stable BMP-7 production. BMP-7-CS displayed higher osteogenic capacity than Ad-MSCs and Ad-MSC sheets. In addition, BMP-7-CS combined with demineralized bone matrix (DBM) stimulated new bone and blood vessel formation in a canine critical-sized bone defect. The BMP-7-CS not only provides BMP-7 producing MSCs but also produce osteogenic and vascular trophic factors. Thus, BMP-7-CS and DBM have therapeutic potential for the treatment of critical-sized bone defects and could be used to further enhance clinical outcomes during bone-defect treatment.

Angiogenesis and lymphangiogenesis in corneal transplantation-A review

Corneal transplantation has been proven effective for returning the gift of sight to those affected by corneal disorders such as opacity, injury, and infections that are a leading cause of blindness. Immune privilege plays an important role in the success of corneal transplantation procedures; however, immune rejection reactions do occur, and they, in conjunction with a shortage of corneal donor tissue, continue to pose major challenges. Corneal immune privilege is important to the success of corneal transplantation and closely related to the avascular nature of the cornea. Corneal avascularity may be disrupted by the processes of angiogenesis and lymphangiogenesis, and for this reason, these phenomena have been a focus of research in recent years. Through this research, therapies addressing certain rejection reactions related to angiogenesis have been developed and implemented. Corneal donor tissue shortages also have been addressed by the development of new materials to replace the human donor cornea. These advancements, along with other improvements in the corneal transplantation procedure, have contributed to an improved success rate for corneal transplantation. We summarize recent developments and improvements in corneal transplantation, including the current understanding of angiogenesis mechanisms, the anti-angiogenic and anti-lymphangiogenic factors identified to date, and the new materials being used. Additionally, we discuss future directions for research in corneal transplantation.

Culturing bone marrow cells with dexamethasone and ascorbic acid improves osteogenic cell sheet structure

Objectives

To assess the structure and extracellular matrix molecule expression of osteogenic cell sheets created via culture in medium with both dexamethasone (Dex) and ascorbic acid phosphate (AscP) compared either Dex or AscP alone.

Methods

Osteogenic cell sheets were prepared by culturing rat bone marrow stromal cells in a minimal essential medium (MEM), MEM with AscP, MEM with Dex, and MEM with Dex and AscP (Dex/AscP). The cell number and messenger (m)RNA expression were assessed in vitro, and the appearance of the cell sheets was observed after mechanical retrieval using a scraper. β-tricalcium phosphate (β-TCP) was then wrapped with the cell sheets from the four different groups and subcutaneously implanted into rats.

Results

After mechanical retrieval, the osteogenic cell sheets from the MEM, MEM with AscP, and MEM with Dex groups appeared to be fragmented or incomplete structures. The cell sheets cultured with Dex/AscP remained intact after mechanical retrieval, without any identifiable tears. Culture with Dex/AscP increased the mRNA and protein expression of extracellular matrix proteins and cell number compared with those of the other three groups. More bridging bone formation was observed after transplantation of the β-TCP scaffold wrapped with cell sheets cultured with Dex/AscP, than in the other groups.

Conclusions

These results suggest that culture with Dex/AscP improves the mechanical integrity of the osteogenic cell sheets, allowing retrieval of the confluent cells in a single cell sheet structure. This method may be beneficial when applied in cases of difficult tissue reconstruction, such as nonunion, bone defects, and osteonecrosis.

Cite this article: M. Akahane, T. Shimizu, T. Kira, T. Onishi, Y. Uchihara, T. Imamura, Y. Tanaka. Culturing bone marrow cells with dexamethasone and ascorbic acid improves osteogenic cell sheet structure. Bone Joint Res 2016;5:569–576. DOI: 10.1302/2046-3758.511.BJR-2016-0013.R1.

The effect of tendon stem/progenitor cell (TSC) sheet on the early tendon healing in a rat Achilles tendon injury model

Tissue-engineering approaches have a great potential to improve the treatment of tendon injuries that affect millions of people. The present study tested the hypothesis that introduction of a tendon derived stem/progenitor cell (TSC) sheet accelerates tendon healing and tendon regeneration in a rat model. TSC sheets were produced on temperature-responsive culture dishes. Then, they were grafted on unwounded Achilles tendons and at sites of a 3mm of Achilles tendon defect. At 2 and 4weeks after implantation tendons were examined by histology, immunohistochemistry, transmission electron microscopy (TEM) and mechanical testing. The results showed that the implanted TSC sheet remained stably attached on the tendon surface at 4 weeks after implantation. Moreover, in the tendon defect model, tendon defect area where TSC sheet was implanted was well regenerated and had better organized collagen fibers with elongated spindle shaped cells, compared to relatively disorganized collagen fibers and round shaped cells in the control group. TEM observations revealed longitudinally aligned collagen fibers and thick collagen fibrils in the TSC sheet implanted group. Finally, at 4weeks mechanical property of the TSC sheet implanted tendon had better ultimate load than the control. In conclusion, this study demonstrates the feasibility of implanting TSC sheets on tendons in vivo. Introduction of the cell sheets into a tendon defect significantly improved histological properties and collagen content at both 2 and 4 weeks after implantation, indicating that TSC sheets may effectively promote tendon remodeling in the early stages of tendon healing.

STATEMENT OF SIGNIFICANCE

Tendon injury is a highly prevalent clinical problem that debilitates millions of people worldwide in both occupational and athletic settings. It also costs billions of healthcare dollars in treatment every year. In this study, we showed the feasibility of using tendon derived stem cell sheet to deliver biologically active tenogenic-constructs and promote tendon regeneration. This work has the potential to impact the orthopaedic surgery and sports medicine fields in the treatment of tendon injury.

Comparison of the canine corneal epithelial cell sheets cultivated from limbal stem cells on canine amniotic membrane, atelocollagen gel, and temperature-responsive culture dish

OBJECTIVE

The current study compared canine corneal epithelial cell sheets cultivated from limbal stem cells on amniotic membrane, atelocollagen gel, and temperature-responsive culture dish.

PROCEDURES

We collected limbal epithelial cells from the intact eyes of beagles and cultivated the cells on denuded canine amniotic membranes, temperature-responsive cell culture labware, and collagen gel with 3T3 feeder cells. Immunofluorescence staining for Ki-67 was used to analyze the capacity of cell proliferation in the sheets. Immunofluorescence staining was also performed for the corneal epithelium-specific marker cytokeratin 3 and putative stem cell markers ABCG2 and p63. Reverse-transcription polymerase chain reaction (RT-PCR) was performed to detect ABCG2 and p63.

RESULTS

The growth rates of the cultivated cells, or the times it took them to reach confluency, were different for the three scaffolds. The cultivated sheet on the temperature-responsive dish consisted of 2-3 layers, while those on the collagen gel and on the amniotic membrane consisted of 5-8 layers. The basal layer cells grown on all three scaffolds expressed putative stem cell markers. In real-time RT-PCR analysis, the highest level of p63 was observed in the sheets grown on collagen gel.

CONCLUSIONS

In this study, the cells cultured on the collagen gel demonstrated a capacity for cell proliferation, and the expressions of stem cells in the sheets suggested that collagen gel is the most suitable carrier for clinical use.

Cultivation and characterization of limbal epithelial stem cells on contact lenses with a feeder layer: toward the treatment of limbal stem cell deficiency

PURPOSE

Limbal epithelial sheets are used to promote corneal surface reconstruction after the detection of limbal epithelial stem cell deficiency. The aim of this study was to evaluate a novel combination of limbal stem cells (LSCs) maintained on contact lenses (CLs) in the presence of a 3T3 feeder cell layer regarding preservation of stem cell phenotype and the potential use for future in vivo transplantation.

METHODS

Limbal epithelial cells were isolated from rabbit cornea and cultured with 3T3 cells on CLs. The preservation of LSC phenotype was determined using p63α and ABCG2 immunostaining, whereas epithelial differentiation was evaluated using CK3 and CK19. The colony-forming assay was used to determine the percentage of LSCs in cultures. Finally, CLs seeded with PKH26-labeled LSCs were transferred to rabbit eyes after performing a surgical keratectomy, and the transition and phenotype of labeled cells on the corneal surface were evaluated in whole-mount corneas.

RESULTS

Proliferation of individual limbal cells was observed on CLs with a 3T3 feeder cell layer, showing holoclone formation and retention of viable stem or progenitor cell phenotype. Finally, a higher transition of cultivated cells after a dual sequential CL transplantation to the ocular surface was observed, showing the preservation of the LSC phenotype in the corneal surface.

CONCLUSIONS

Limbal cells cultivated on a CL carrier overlaying a 3T3 feeder layer are mitotically active and retain the LSC phenotype. This novel technique of using CLs as a carrier offers an easily manipulable and nonimmunogenic method for transferring LSCs for ocular surface reconstruction in patients with limbal epithelial stem cell deficiency.

Cell sheet injection as a technique of osteogenic supply

We previously reported a new cell transplantation method utilizing injections of mesenchymal stem cell (MSC) sheets that have osteogenic potential. After subcutaneous transplantation without any scaffold, the sheet demonstrated in vivo bone formation. In the present study, we transplanted such sheets by injection into implanted ceramics and assessed whether the injectable MSC sheets could stimulate osteogenic integration of the ceramics. To fabricate MSC sheets, bone marrow cells cultured from femur shafts of 7-week-old rats were subcultured in regular 10-cm dishes containing dexamethasone and ascorbic acid phosphate until confluent. Each cell sheet was then lifted using a scraper. Porous β-tricalcium phosphate (β-TCP) disks (5 mm Φ×2 mm) were transplanted subcutaneously into the backs of the rats. Immediately following implantation, the sheets were injected around the disks via a 16G needle (immediate group). Cell sheets were also injected into the remaining implanted disks 1 week after disk implantation (1-wk group). Four weeks following sheet injection, radiography and histology revealed calcification and bone tissue around the harvested disks of the immediate group (eight disks exhibited bone formation/eight implanted disks), whereas calcification and bone tissue were observed in 50% of the samples in the 1-wk group (four disks exhibited bone formation/eight implanted disks). The present study indicates that injected cell sheets can supply osteogenic potential to implanted ceramics. Owing to the usage of a needle for cell sheet transplantation, such an injection method can be applied as a minimally invasive technique of osteogenic supply to implanted ceramics.

A non-destructive culturing and cell sorting method for cardiomyocytes and neurons using a double alginate layer

A non-destructive method of collecting cultured cells after identifying their in situ functional characteristics is proposed. In this method, cells are cultivated on an alginate layer in a culture dish and released by spot application of a calcium chelate buffer that locally melts the alginate layer and enables the collection of cultured cells at the single-cell level. Primary hippocampal neurons, beating human embryonic stem (hES) cell-derived cardiomyocytes, and beating hES cell-derived cardiomyocyte clusters cultivated on an alginate layer were successfully released and collected with a micropipette. The collected cells were recultured while maintaining their physiological function, including beating, and elongated neurites. These results suggest that the proposed method may eventually facilitate the transplantation of ES- or iPS-derived cardiomyocytes and neurons differentiated in culture.

Carrier-free epithelial cell sheets prepared by enzymatic degradation of collagen gel

Limbal stem-cell deficiency by ocular trauma or disease causes corneal opacification and vision loss. Conventional tissue engineering using biodegradable scaffolds has met with limited success. In this study, we developed a novel method for preparing carrier-free epithelial cell sheets, which have potential for use in repairing defects of the ocular surface. Stratified corneal epithelial cell sheets were prepared in culture dishes coated with biodegradable type I collagen. Haematoxylin and eosin staining, electron microscopy and immunohistochemistry were performed to characterize the cell sheets. Then, carrier-free epithelial sheets were successfully engineered using specific collagenase to degrade the collagen gel. Cell sheets of four to six cell layers after culture for 14 days were similar to natural rabbit corneal epithelia, as shown by pathological examination. Microvillus, tight cell-cell junctions and desmosome junctions were observed via electron microscopy. K3 and basement membrane components, such as type IV collagen and laminin, were expressed in the cells sheets and integrin β1 was maintained in basal cells. This novel method of using collagenase to degrade collagen gel is both simple and effective in preparing intact carrier-free epithelial cell sheets. Such sheets have great potential for application during in vivo corneal regeneration.

Scaffold-free cell sheet injection results in bone formation

We previously reported a new cell transplantation method in which mesenchymal stem cells (MSCs) were cultured as cell sheets. The cultured MSC sheets showed high alkaline phosphatase (ALP) activities and osteocalcin (OC) contents. In the present study, we transplanted such sheets by injection to assess whether the injectable MSC sheets could form bone tissue at subcutaneous sites. At 4 weeks after the subcutaneous injection, the injected areas showed hard mass formation. Each mass consisted of newly formed bone, as evaluated by radiographic, histological and gene expression analyses as well as three-dimensional computed tomography (3D-CT). Histological analyses revealed extracellular bone matrix together with osteocytes and active osteoblasts. Real-time PCR analyses showed high ALP and OC mRNA expressions. We also injected the cell sheets into dead bone to determine whether the lost osteogenic potential could be rescued, and histological analyses revealed that the injected cell sheets supplied osteogenic potential to the dead bone. The present study clearly indicates that osteogenic MSC sheets can be transplanted via injection through a needle and that bone formation results in the injected areas. Owing to its usage of a needle for fabrication of in vivo bone tissue, this injection method can be applied as a minimally invasive approach for hard tissue reconstruction.

Cell culture platform with mechanical conditioning and nondamaging cellular detachment

Cells implanted after injury may remodel undesirably with improper mechanical stimulation from surrounding tissue. Proper conditioning of tissue engineered constructs before implantation can lead to suitable tissue architectures, along with an extracellular matrix (ECM) environment that more closely mimics native tissue. Additionally, cell implantation without bulky polymeric scaffolding is often desirable. Previous researchers have created devices capable of applying mechanical forces to cells (e.g., stretch) but cellular removal from these devices, such as by trypsin, often results in irreversible damage. Conversely, devices are available that can detach intact cells, but these are inelastic, nonstretchable substrates. We have created a cell culture platform that allows for mechanical conditioning and then subsequent nondamaging detachment of those cells. We have modified silicone culture surfaces, to incorporate thermally responsive polymers of N-isopropylacrylamide (NIPAAm) to create an elastic substrate that can also change surface properties with temperature change. A copolymer of NIPAAm and 10percent w/w acrylic acid (AAc) was conjugated to an amine-bonded silicone surface through carbodiimide chemistry. Cells were able to attach to the resulting surfaces at 37 degreeC and showed detachment by rounded morphology at 25degreeC. Following mechanical stretching, cells were still able to spontaneously detach from these modified silicone surfaces with temperature change.

Cell sheet engineering: a unique nanotechnology for scaffold-free tissue reconstruction with clinical applications in regenerative medicine

Cell sheet technology (CST) is based on the use of thermoresponsive polymers, poly(N-isopropylacrylamide) (PIPAAm). The surface of PIPAAms is formulated in such a way as to make its typical thickness <100 nm. In this review, we first focus on how the methods of PIPAAm-grafted surface preparations and functionalization are important to be able to harvest a functional cell sheet, to be further transplanted. Then, we present aspects of tissue mimics and three-dimensional reconstruction of a tissue in vitro. Finally, we give an overview of clinical applications and clinically relevant animal experimentations of the technology, such as cardiomyopathy, visual acuity, periodonty, oesophageal ulcerations and type 1 diabetes.

Ex vivo cultivation of corneal limbal epithelial cells in a thermoreversible polymer (Mebiol Gel) and their transplantation in rabbits: an animal model

We evaluated the efficacy of autologous expanded corneal epithelial cell transplants derived from harvested limbal biopsy cultured on a thermoreversible polymer (Mebiol Gel) for the management of unilateral limbal stem cell deficiency (LSCD). Corneal limbal biopsies from 12 rabbits were cultured on a thermoreversible polymer Mebiol Gel at 37 degrees C. Cells were harvested from the dishes after 3 weeks by reducing temperature to 4 degrees C. Autologous transplantation was undertaken to reconstruct the experimentally induced limbal stem cell deficiency in the rabbit eyes. The corneas of both eyes of all rabbits were harvested later for molecular studies. Reparative surgery was a total success in seven rabbits, partial success in two, and failure in three eyes. Histology of the seven successful eyes showed the successful growth of the corneal epithelium. Immunohistochemistry and reverse transcriptase polymerase chain reaction showed the cornea phenotype and stem cell-associated markers in the limbus of the seven successful eyes, indicating the homing of these cells into limbus. In the three failure cases and in the two control rabbit eyes, used in the study, histology showed presence of goblet cells and vascularization in the stroma with abortive formation of corneal epithelium. Our results suggest that transplantation of autologous limbal epithelial cells grown in thermoreversible polymer Mebiol Gel may restore a nearly normal ocular epithelial surface in eyes with unilateral LSCD.

Sequential development of intercellular junctions in bioengineered human corneas

We have carried out a sequential study of intercellular junction formation and differentiation on human corneal substitutes consisting of an artificial corneal stroma and a corneal epithelium, developed by tissue engineering. To generate these artificial human corneas, we developed a corneal stroma substitute, using fibrin and agarose scaffolds with human keratocytes immersed within, then cultured the human corneal epithelium on top. Electron microscopy and immunofluorescence analyses revealed that artificial corneas with one or two epithelial cell layers did not show any formation of intercellular junctions. In contrast, several types of cell-cell junction, especially desmosomes, were found in multilayered mature corneal substitutes. Concomitantly, the expression of genes encoding for plakoglobin 3 (PKG3), desmoglein 3 (DSG3) and desmoplakin (DSP), zonula occludens 1 (ZO-1) and 2 (ZO-2) and connexin 37 (Cx37) was higher in multilayered artificial corneas than in immature artificial corneas, as shown by both microarray and immunofluorescence. Although expression of ZO-1, ZO-2 and Cx37 proteins was homogeneous, PKG3, DSG3 and DSP expression was restricted to the most apical cell layers in artificial corneas submerged in culture medium at all times, whereas expression was higher in intermediate cell layers, similar to normal human control corneas, when corneal substitutes are submitted to air-liquid culture techniques. These results suggest that cultured corneal substitutes submitted to air-liquid culture technique tend to form a well-developed epithelium that is very similar to the epithelium of human native corneas, suggesting that these artificial corneas could eventually be used for clinical or in vitro purposes.

A fully automated approach to quantitatively determine thickness of tissue-engineered cell sheets

Sheet-based tissue engineering is an innovative field that has provided the scientific community with new tissue-engineered products such as skin, cornea, heart valves, and vascular grafts. As this area of tissue engineering progresses toward clinical implementation, quality control becomes more and more important. Imaging methods advertise themselves because of their high resolution and good tissue-fluid contrast. We present and compare two methods, one based on a custom-designed automatized large-area confocal scanner that uses backscattered light for image formation, and one based on optical coherence tomography (OCT). In both modalities, additional image processing is used to extract sheet thickness and density information and to create a quantitative tissue thickness map in a fully automated fashion. In test objects (glass of known thickness and scattering samples) and engineered tissue sheets with artificially introduced defects we found high agreement between the two methods in the measurement of thickness and the visual representation of the defects. Both the OCT and the confocal scanner were able to provide high-detail images visually consistent to those obtained with brightfield microscopy. Both OCT and large-area confocal scanning in combination with specialized image processing algorithms promise to provide information on tissue homogeneity, density, and the presence of potential defects in tissue sheets in an unsupervised fashion and thus help establish new quality control methods in sheet-based tissue engineering.

Osteogenic matrix sheet-cell transplantation using osteoblastic cell sheet resulted in bone formation without scaffold at an ectopic site

We previously reported that in vivo bone formation could be observed in composites of porous hydroxyapatite (HA) scaffolds and cultured mesenchymal stem cells (MSCs). In the present study, we developed a new method for transplantation of cultured MSCs without the necessity of using a scaffold to form bone tissue. MSCs were culture-expanded and lifted as cell sheet structures. These cell sheets, designated osteogenic matrix sheets, showed positive alkaline phosphatase (ALP) staining, high ALP activities and high osteocalcin (OC) contents, indicating their osteogenic potential. We transplanted these sheets into subcutaneous sites in rats to assess whether they possessed in vivo bone-forming capability. The transplanted sheets showed mineralized matrix together with osteocytes and an active osteoblast lining, indicating new bone formation, at 6 weeks after transplantation. HA scaffolds were also wrapped with the sheets to make HA/sheet composites and implanted into subcutaneous sites in rats. Histological sections of the composites revealed bone formation in the HA pores at 4 weeks after implantation. Our present results indicate that MSCs can be cultured as sheet structures, and the resulting sheets themselves or HA-sheet composites represent osteogenic implants that can be used for hard tissue reconstruction.

The development of a tissue-engineered cornea: biomaterials and culture methods

The field of corneal tissue engineering has made many strides in recent years. The challenges of engineering a biocompatible, mechanically stable, and optically transparent tissue are significant. To overcome these challenges, researchers have adopted two basic approaches: cell-based strategies for manipulating cells to create their own extracellular matrix, and scaffold-based strategies for providing strong and transparent matrices upon which to grow cells. Both strategies have met with some degree of success. In addition, recent advances have been made in innervating a tissue-engineered construct. Future work will need to focus on further improving mechanical stability of engineered constructs as well as improving the host response to implantation.

Influence of keratocytes and retinal pigment epithelial cells on the mechanical properties of polyester-based tissue engineering micropatterned films

In this paper the mechanical properties of micropatterned polyester films prepared to serve as tissue engineering scaffolds of cornea were examined. Films were prepared by solvent casting of blends of poly(l-lactide-co-d,l-lactide) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid), on a micropatterned silicon template. They were seeded with keratocytes or retinal pigment epithelial cells and subjected to tensile testing to assess the contribution of cells and the deposited extra-cellular matrix (ECM) to the mechanical properties of the scaffold. In all the tests, the films used were wet and the cells were not fixed. Cell-free scaffolds showed a gradual deterioration in strength upon incubation in the cell culture medium at 37 degrees C; the deterioration rate was highest in the first week and decreased significantly over the second and third weeks. The ultimate strength of the cell-free scaffolds decreased from 0.99 to 0.42N/mm after 21 days of incubation. Cell seeded scaffolds showed a more complicated mechanical strength profile. Their response was found to depend both on the extent of surface coverage and on the cell type. The results were examined after dividing the data into two groups of lower and higher stiffness. For keratocyte seeded scaffolds, the strength of the high stiffness groups continued to increase as the incubation period increased while the lower stiffness groups did not show a distinct change. For the keratocyte seeded scaffolds, tensile strength increased from 0.65N/mm on Day 7 to 0.73N/mm on Day 21. On the other hand, the scaffolds seeded with retinal pigment epithelial cells showed a gradual deterioration over time in both the higher and lower stiffness groups. For epithelial cell seeded scaffolds this was 0.98N/mm on Day 7 and decreased to 0.77N/mm on Day 21 still an improvement over the unseeded scaffolds. This most probably was a result of a lower rate of ECM secretion in comparison to keratocytes and the newly secreted ECM could not compensate for the influence of scaffold degradation on the mechanical properties. It could, therefore, be concluded that cell seeding plays a positive role in strengthening a tissue engineered construct, and cell type has a significant influence on the extent of this improvement.