Proliferating cells versus differentiated cells in tissue engineering

Insights into cellular behavior and micromolecular communication in urothelial micrografts

Autologous micrografting is a technique currently applied within skin wound healing, however, the potential use for surgical correction of other organs with epithelial lining, including the urinary bladder, remains largely unexplored. Currently, little is known about the micrograft expansion potential and the micromolecular events that occur in micrografted urothelial cells. In this study, we aimed to evaluate the proliferative potential of different porcine urothelial micrograft sizes in vitro, and, furthermore, to explore how urothelial micrografts communicate and which microcellular events are triggered. We demonstrated that increased tissue fragmentation subsequently potentiated the yield of proliferative cells and the cellular expansion potential, which confirms, that the micrografting principles of skin epithelium also apply to uroepithelium. Furthermore, we targeted the expression of the extracellular signal-regulated kinase (ERK) pathway and demonstrated that ERK activation occurred predominately at the micrograft borders and that ERK inhibition led to decreased urothelial migration and proliferation. Finally, we successfully isolated extracellular vesicles from the micrograft culture medium and evaluated their contents and relevance within various enriched biological processes. Our findings substantiate the potential of applying urothelial micrografting in future tissue-engineering models for reconstructive urological surgery, and, furthermore, highlights certain mechanisms as potential targets for future wound healing treatments.

Photobiomodulation in 3D tissue engineering

SIGNIFICANCE

The method of photobiomodulation (PBM) has been used in medicine for a long time to promote anti-inflammation and pain-resolving processes in different organs and tissues. PBM triggers numerous cellular pathways including stimulation of the mitochondrial respiratory chain, alteration of the cytoskeleton, cell death prevention, increasing proliferative activity, and directing cell differentiation. The most effective wavelengths for PBM are found within the optical window (750 to 1100 nm), in which light can permeate tissues and other water-containing structures to depths of up to a few cm. PBM already finds its applications in the developing fields of tissue engineering and regenerative medicine. However, the diversity of three-dimensional (3D) systems, irradiation sources, and protocols intricate the PBM applications.

AIM

We aim to discuss the PBM and 3D tissue engineered constructs to define the fields of interest for PBM applications in tissue engineering.

APPROACH

First, we provide a brief overview of PBM and the timeline of its development. Then, we discuss the optical properties of 3D cultivation systems and important points of light dosimetry. Finally, we analyze the cellular pathways induced by PBM and outcomes observed in various 3D tissue-engineered constructs: hydrogels, scaffolds, spheroids, cell sheets, bioprinted structures, and organoids.

RESULTS

Our summarized results demonstrate the great potential of PBM in the stimulation of the cell survival and viability in 3D conditions. The strategies to achieve different cell physiology states with particular PBM parameters are outlined.

CONCLUSIONS

PBM has already proved itself as a convenient and effective tool to prevent drastic cellular events in the stress conditions. Because of the poor viability of cells in scaffolds and the convenience of PBM devices, 3D tissue engineering is a perspective field for PBM applications.

Effect of Skeletal Paracrine Signals on the Proliferation of Interzone Cells

OBJECTIVE

Articular cartilage in mammals has limited intrinsic capacity to repair structural defects, a fact that contributes to the chronic and progressive nature of osteoarthritis. In contrast, Mexican axolotl salamanders have demonstrated the remarkable ability to spontaneously and completely repair large joint cartilage lesions, a healing process that involves interzone cells in the intraarticular space. Furthermore, interzone tissue transplanted into skeletal defects in the axolotl salamander demonstrates a multi-differentiation potential. Cellular and molecular mechanisms of this repair process remain unclear. The objective of this study was to examine whether paracrine mitogenic signals are an important variable in the interaction between interzone cells and the skeletal microenvironment.

DESIGN

The paracrine regulation of the proliferation of equine interzone cells was evaluated in an in vitro co-culture system. Cell viability and proliferation were measured in equine fetal interzone cells after exposure to conditioned medium from skeletal and nonskeletal primary cell lines. Steady-state expression was determined for genes encoding 37 putative mitogens secreted by cells that generated the conditioned medium.

RESULTS

All experimental groups of conditioned media elicited a mitogenic response in interzone cells. Fetal anlage chondrocytes (P < 0.0001) and dermal fibroblasts (P < 0.0001) conditioned medium showed a significantly higher mitogenic potential compared with interzone cells. Conditioned medium from bone marrow-derived cells elicited a significantly higher proliferative response relative to that from young adult articular chondrocytes (P < 0.0001) or dermal fibroblasts (P < 0.0001). Sixteen genes had expression patterns consistent with the functional proliferation assays.

CONCLUSIONS

The results indicate a mitogenic effect of skeletal paracrine signals on interzone cells.

The ER protein TLC domain 3B2 and its enzymatic product lactosylceramide enhance chondrocyte maturation

Purpose/Aim of study: We previously cloned Tlcd3b2 (Tram-Lag1-CLN8 domain 3B2, formerly Fam57b2) from bone fracture repair callus tissue of Cyp24a1 knockout mice and showed that it synthesizes lactosylceramide (LacCer) under allosteric control of the vitamin D metabolite, 24,25-dihydroxyvitamin D3 [24,25(OH)2D3]. Tlcd3b2 was mainly detected in chondrocytes and the 24,25(OH)2D3-TLCD3B2-LacCer signaling cascade was shown to be important for optimal bone fracture repair, suggesting a role for TLCD3B2 in chondrocyte differentiation or maturation. We report the subcellular localization of TLCD3B2 and its effect on chondrocyte differentiation. Materials and Methods: Immunofluorescence detection of epitope-tagged mutants was used to assess localization. ATDC5 chondrogenic cells were transfected with Tlcd3b2 expression vectors to examine effects on chondrocyte differentiation. Results and Conclusions: TLCD3B2 localized to the endoplasmic reticulum, with both the N- and C-termini facing the cytosolic compartment. Chondrogenic ATDC5 cells stably overexpressing Tlcd3b2 showed elevated type 2 (Col2a1) and type 10 (Col10a1) collagen gene expression and increased proteoglycan synthesis, and the effect on Col2a1 was enhanced by treatment with 24,25(OH)2D3. LacCer treatment of ATDC5 cells potentiated Col10a1 expression. Our results show that TLCD3B2 is an ER protein and implicate its expression and enzymatic product in chondrocyte maturation.

Sustained delivery of vascular endothelial growth factor from mesoporous calcium-deficient hydroxyapatite microparticles promotes in vitro angiogenesis and osteogenesis

Promoting the growth of blood vessels within engineered tissues remains one of the main challenge in bone tissue engineering. One way to improve angiogenesis is the use of vascular endothelial growth factor (VEGF) as it holds the ability to increase the formation of a vascular network. In the present study, collagen scaffolds with VEGF-releasing hydroxyapatite particles were fabricated, in order to engineer a material both capable of presenting an osteoconductive surface and delivering an angiogenic growth factor in a localized and sustained manner, in order to enhance osteogenesis as well as angiogenesis. To this end, we developed microparticles and characterize their size, chemical properties and Ca/P ratio to validate the formation of hydroxyapatite. We then evaluated the osteogenic potential of HAp when cultured with mesenchymal stem cells and compare it to commercially available hydroxyapatite (SBp). Finally, we characterized the encapsulation and release of VEGF in the HAp and assess the angiogenic potential of the VEGF-HAp when cultured with endothelial cells. We demonstrated the successful fabrication of calcium deficient hydroxyapatite microparticles (CDHAp), with biological properties closer to the bone than stoichiometric, commercially available hydroxyapatite. This CDHAp exhibited a well-defined 3D network of crystalline nanoplates forming mesoporous and hollow structures. The high specific area created by those structures enabled the loading of VEGF with high efficiency when compared to the loading efficiency of SBp. Furthermore, their biological performances were evaluated in vitro. Our results indicate that VEGF-CDHAp can be used to improve both osteogenesis and angiogenesis in vitro.

Inhibition of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) stimulates osteoblastogenesis by potentiating bone morphogenetic protein 2 (BMP2) responses

The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) is a pleiotropic enzyme involved in DNA repair, cell cycle control, and transcription regulation. A potential role for DNA-PKcs in the regulation of osteoblastogenesis remains to be established. We show that pharmacological inhibition of DNA-PKcs kinase activity or gene silencing of Prkdc (encoding DNA-PKcs) in murine osteoblastic MC3T3-E1 cells and human adipose-derived mesenchymal stromal cells markedly enhanced osteogenesis and the expression of osteoblast differentiation marker genes. Inhibition of DNA-PKcs inhibited cell cycle progression and increased osteogenesis by significantly enhancing the bone morphogenetic protein 2 response in osteoblasts and other mesenchymal cell types. Importantly, in vivo pharmacological inhibition of the kinase enhanced bone biomechanical properties. Bones from osteoblast-specific conditional Prkdc-knockout mice exhibited a similar phenotype of increased stiffness. In conclusion, DNA-PKcs negatively regulates osteoblast differentiation, and therefore DNA-PKcs inhibitors may have therapeutic potential for bone regeneration and metabolic bone diseases.

Fibroblast feeder layer supports adipogenic differentiation of human adipose stromal/progenitor cells

Adipose stromal/progenitor cells (ASCs) can differentiate into adipocytes in the course of adipogenesis. This process is governed by systemic factors and signals of the adipose stem cell niche. ASCs isolated from fat tissues and amplified in vitro provide an essential and reliable model system to study adipogenesis. However, current cell culture models routinely grow ASCs on plastic surfaces largely missing niche parameters. In the present communication, we employed human foreskin fibroblasts (HFFs) monolayers as feeder cells for ASCs, which were isolated from human subcutaneous white adipose tissue and amplified in vitro. We found that PPARγ2 and several adipocyte markers were significantly higher expressed in differentiated ASCs growing on feeder layers relative to plastic dishes. Moreover, a significant higher number of adipocytes was generated from ASCs cultured on feeder layer and these adipocytes contained larger fat droplets. Insulin strongly stimulated glucose uptake into adipocytes produced on feeder layer suggesting that these cells show characteristic metabolic features of fat cells.  Finally, we show that the HFF feeder layer allows adipogenic differentiation of low-density-seeded ASCs. In conclusion, we demonstrate that the HFF feeder layer increases adipocyte differentiation of ASCs and allows differentiation of low density seeded progenitor cells  into functional adipocytes.

Injectable, redox-polymerized carboxymethylcellulose hydrogels promote nucleus pulposus-like extracellular matrix elaboration by human MSCs in a cell density-dependent manner

Low back pain is a major cause for disability and is closely linked to intervertebral disc degeneration. Mechanical and biological dysfunction of the nucleus pulposus in the disc has been found to initiate intradiscal degenerative processes. Replacing or enriching the diseased nucleus pulposus with an injectable, stem cell-laden biomaterial that mimics its material properties can provide a minimally invasive strategy for biological and structural repair of the tissue. In this study, injectable, in situ-gelling carboxymethylcellulose hydrogels were developed for nucleus pulposus tissue engineering using encapsulated human marrow-derived mesenchymal stromal cells (hMSCs). With the goal of obtaining robust extracellular matrix deposition and faster construct maturation, two cell-seeding densities, 20 × 10⁶ cells/ml and 40 × 10⁶ cells/ml, were examined. The constructs were fabricated using a redox initiation system to yield covalently crosslinked, cell-seeded hydrogels via radical polymerization. Chondrogenic culture of the hydrogels over 35 days exhibited high cell viability along with deposition of proteoglycan and collagen-rich extracellular matrix, and mechanical and swelling properties similar to native human nucleus pulposus. Further, the matrix production and distribution in the carboxymethylcellulose hydrogels was found to be strongly influenced by hMSC-seeding density, with the lower cell-seeding density yielding a more favorable nucleus pulposus-specific matrix phenotype, while the rate of construct maturation was less dependent on the cell-seeding density. These findings are the first to demonstrate the utility of redox-polymerized carboxymethylcellulose hydrogels as hMSC carriers for potential minimally invasive treatment strategies for nucleus pulposus replacement.

Ectopic Telomerase Expression Fails to Maintain Chondrogenic Capacity in Three-Dimensional Cultures of Clinically Relevant Cell Types

The poor healing capacity of cartilage and lack of effective treatment for associated disease and trauma makes it a strong candidate for a regenerative medicine approach. Potential therapies tested to date, although effective, have met with a number of intrinsic difficulties possibly related to limited autologous chondrocyte cell yield and quality of cartilage produced. A potential mechanism to bypass limited cell yields and improve quality of differentiation is to immortalize relevant cell types through the ectopic expression of telomerase. Pellet cultures of human chondrocytes (OK3), bone marrow mesenchymal stem cells (BMA13), and embryonic stem cell (H1 line)-derived cells (1C6) and their human telomerase reverse transcriptase (hTERT) transduced counterparts were maintained for 20 days in standard maintenance medium (MM) or transforming growth factor-β3-supplemented prochondrogenic medium (PChM). Pellets were assessed for volume and density by microcomputed tomography. Quantitative gene expression (COL1A2, COL2A1, COL3A1, COL6A3, COL10A1, ACAN, COMP, SOX9); sulfated glycosaminoglycans (sGAGs), and DNA quantification were performed. Histology and immunohistochemistry were used to determine matrix constituent distribution. Pellet culture in PChM resulted in significantly larger pellets with an overall increased density when compared with MM culture. Gene expression analysis revealed similarities in expression patterns between telomerase-transduced and parental cells in both MM and PChM. Of the three parental cell types examined OK3 and BMA13 produced similar amounts of pellet-associated sGAG in PChM (4.62 ± 1.20 and 4.91 ± 1.37 μg, respectively) with lower amounts in 1C6 (2.89 ± 0.52 μg), corresponding to 3.1, 2.3, and 1.6-fold increases from day 0. In comparison, telomerase-transduced cells all had much lower sGAG with OK3H at 2.74 ± 0.11 μg, BMA13H 1.29 ± 0.34 μg, and 1C6H 0.52 ± 0.01 μg corresponding to 1.2, 0.87, and 0.34-fold changes compared with day 0. Histology of day 20 pellets displayed reduced staining overall for collagens and sGAG in telomerase-transduced cells, most notably with alterations in aggrecan and collagen VI; all cells stained positively for collagen II. We conclude that while telomerase transduction may be an effective technique to extend cellular proliferative capacity, it is not sufficient in isolation to sustain a naive chondrogenic phenotype across multiple cell types.

Osseous differentiation of human fat tissue grafts: From tissue engineering to tissue differentiation

Conventional bone tissue engineering approaches require isolation and in vitro propagation of autologous cells, followed by seeding on a variety of scaffolds. Those protracted procedures impede the clinical applications. Here we report the transdifferentiation of human fat tissue fragments retrieved from subcutaneous fat into tissue with bone characteristics in vitro without prior cell isolation and propagation. 3D collagen-I cultures of human fat tissue were cultivated either in growth medium or in osteogenic medium (OM) with or without addition of Bone Morphogenetic Proteins (BMPs) BMP-2, BMP-7 or BMP-9. Ca²⁺ depositions were observed after two weeks of osteogenic induction which visibly increased when either type of BMP was added. mRNA levels of alkaline phosphatase (ALP) and osteocalcin (OCN) increased when cultured in OM alone but addition of BMP-2, BMP-7 or BMP-9 caused significantly higher expression levels of ALP and OCN. Immunofluorescent staining for OCN, osteopontin and sclerostin supported the observed real-time-PCR data. BMP-9 was the most effective osteogenic inducer in this system. Our findings reveal that tissue regeneration can be remarkably simplified by omitting prior cell isolation and propagation, therefore removing significant obstacles on the way to clinical applications of much needed regeneration treatments.

Surface-Functionalized Silk Fibroin Films as a Platform To Guide Neuron-like Differentiation of Human Mesenchymal Stem Cells

Surface interactions at the biomaterial-cellular interface determine the proliferation and differentiation of stem cells. Manipulating such interactions through the surface chemistry of scaffolds renders control over directed stem cell differentiation into the cell lineage of interest. This approach is of central importance for stem cell-based tissue engineering and regenerative therapy applications. In the present study, silk fibroin films (SFFs) decorated with integrin-binding laminin peptide motifs (YIGSR and GYIGSR) were prepared and employed for in vitro adult stem cell-based neural tissue engineering applications. Functionalization of SFFs with short peptides showcased the peptide sequence and nature of functionalization-dependent differentiation of bone marrow-derived human mesenchymal stem cells (hMSCs). Intriguingly, covalently functionalized SFFs with GYIGSR hexapeptide (CL2-SFF) supported hMSC proliferation and maintenance in an undifferentiated pluripotent state and directed the differentiation of hMSCs into neuron-like cells in the presence of a biochemical cue, on-demand. The observed morphological changes were further corroborated by the up-regulation of neuronal-specific marker gene expression (MAP2, TUBB3, NEFL), confirmed through semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis. The enhanced proliferation and on-demand directed differentiation of adult stem cells (hMSCs) by the use of an economically viable short recognition peptide (GYIGSR), as opposed to the integrin recognition protein laminin, establishes the potential of SFFs for neural tissue engineering and regenerative therapy applications.

Effects of corticosteroids and their combinations with hyaluronanon on the biochemical properties of porcine cartilage explants

Background

Intra-articular injection of corticosteroids is used to treat the inflammatory pain of arthritis and osteoarthritis (OA), but our previous study found a deleterious effect of these steroids on chondrocyte cells. Hyaluronic acid (HA) injection has been suggested as a means to counteract negative side effects through replenishment of synovial fluid that can decrease pain in affected joints. To better understand the effects of corticosteroids on these processes, dexamethasone (Dex) and prednisolone (Pred) were administered to porcine cartilage explants at several concentrations with and without HA. We examined corticoid effects by determining sulfate-glycosaminoglycan (s-GAG) and uronic acid (UA) content of the explant media, and safranin-O staining of the cells. Analysis of lactate dehydrogenase (LDH) activity was conducted to assess cell cytotoxicity.

Results

Dex treatment significantly reduced cellular cytotoxicity compared to the other treatment groups, especially with regards to the release of s-GAG, and protects against superficial proteoglycan damage. However, there was no difference between Pred and Dex, with and without HA, in the UA content remaining in porcine cartilage explants.

Conclusions

The data suggest that combinations of Dex and Pred with HA did not have a significant effect on protection or enhancement of the articular cartilage matrix under the current conditions.

The formation of human auricular cartilage from microtic tissue: An in vivo study

OBJECTIVES

This study aimed to isolate, culture-expand and characterize the chondrocytes isolated from microtic cartilage and evaluate its potential as a cell source for ear cartilage reconstruction. Specific attention was to construct the auricular cartilage tissue by using fibrin as scaffold.

STUDY DESIGN

Cell culture experiment with the use of microtic chondrocytes.

DESIGN

Cell culture experiment with the use of microtic chondrocytes.

METHODS

After ear reconstructive surgery at the Universiti Kebangsaan Malaysia Medical Center, chondrocytes were isolated from microtic cartilage. Chondrocytes isolated from the tissue were cultured expanded until passage 4 (P4). Upon confluency at P4, chondrocytes were harvested and tissue engineered constructs were made with human plasma polymerized to fibrin. Constructs formed later is implanted at the dorsal part of nude mice for 8 weeks, followed by post-implantation evaluation with histology staining (Hematoxylin and Eosin (H&E) and Safranin O), immunohistochemistry and RT-PCR for chondrogenic associated genes expression level.

RESULTS

Under gross assessment, the construct after 8 weeks of implantation showed similar physical characteristics that of cartilage. Histological staining showed abundant lacunae cells embedded in extracellular matrix similar to that of native cartilage. Safranin O staining showed positive staining which indicates the presence of proteoglycan-rich matrix. Immunohistochemistry analysis showed the strong positive staining for collagen type II, the specific collagen type in the cartilage. Gene expression quantification showed no significant differences in the expression of chondrogenic gene used which is collagen type I, collagen type II, aggrecan core protein (ACP), elastin and sox9 genes when compared to construct formed from normal auricular tissue.

CONCLUSION

Chondrocytes isolated from microtia cartilage has the potential to be used as an alternative cell source for external ear reconstruction in future clinical application.

Chondrogenic potential of physically treated bovine cartilage matrix derived porous scaffolds on human dermal fibroblast cells

Extracellular matrices have drawn attention in tissue engineering as potential biomaterials for scaffold fabrication because of their bioactive components. Noninvasive techniques of scaffold fabrication and cross-linking treatments are believed to maintain the integrity of bioactive molecules while providing proper architectural and mechanical properties. Cartilage matrix derived scaffolds are designed to support the maintenance of chondrocytes and provide proper signals for differentiation of chondroinducible cells. Chondroinductive potential of bovine articular cartilage matrix derived porous scaffolds on human dermal fibroblasts and the effect of scaffold shrinkage on chondrogenesis were investigated. An increase in sulfated glycosaminoglycans production along with upregulation of chondrogenic genes confirmed that physically treated cartilage matrix derived scaffolds have chondrogenic potential on human dermal fibroblasts.

Development of scaffold-free elastic cartilaginous constructs with structural similarities to auricular cartilage

External ear reconstruction with autologous cartilage still remains one of the most difficult problems in the fields of plastic and reconstructive surgery. As the absence of tissue vascularization limits the ability to stimulate new tissue growth, relatively few surgical approaches are currently available (alloplastic implants or sculpted autologous cartilage grafts) to repair or reconstruct the auricle (or pinna) as a result of traumatic loss or congenital absence (e.g., microtia). Alternatively, tissue engineering can offer the potential to grow autogenous cartilage suitable for implantation. While tissue-engineered auricle cartilage constructs can be created, a substantial number of cells are required to generate sufficient quantities of tissue for reconstruction. Similarly, as routine cell expansion can elicit negative effects on chondrocyte function, we have developed an approach to generate large-sized engineered auricle constructs (≥3 cm(2)) directly from a small population of donor cells (20,000-40,000 cells/construct). Using rabbit donor cells, the developed bioreactor-cultivated constructs adopted structural-like characteristics similar to native auricular cartilage, including the development of distinct cartilaginous and perichondrium-like regions. Both alterations in media composition and seeding density had profound effects on the formation of engineered elastic tissue constructs in terms of cellularity, extracellular matrix accumulation, and tissue structure. Higher seeding densities and media containing sodium bicarbonate produced tissue constructs that were closer to the native tissue in terms of structure and composition. Future studies will be aimed at improving the accumulation of specific tissue constituents and determining the clinical effectiveness of this approach using a reconstructive animal model.

Latent Transforming Growth Factor-beta1 Functionalised Electrospun Scaffolds Promote Human Cartilage Differentiation: Towards an Engineered Cartilage Construct

Background

To overcome the potential drawbacks of a short half-life and dose-related adverse effects of using active transforming growth factor-beta 1 for cartilage engineering, a cell-mediated latent growth factor activation strategy was developed incorporating latent transforming growth factor-β1 (LTGF) into an electrospun poly(L-lactide) scaffold.

Methods

The electrospun scaffold was surface modified with NH₃ plasma and biofunctionalised with LTGF to produce both random and orientated biofunctionalised electrospun scaffolds. Scaffold surface chemical analysis and growth factor bioavailability assays were performed. In vitro biocompatibility and human nasal chondrocyte gene expression with these biofunctionalised electrospun scaffold templates were assessed. In vivo chondrogenic activity and chondrocyte gene expression were evaluated in athymic rats.

Results

Chemical analysis demonstrated that LTGF anchored to the scaffolds was available for enzymatic, chemical and cell activation. The biofunctionalised scaffolds were non-toxic. Gene expression suggested chondrocyte re-differentiation after 14 days in culture. By 6 weeks, the implanted biofunctionalised scaffolds had induced highly passaged chondrocytes to re-express Col2A1 and produce type II collagen.

Conclusions

We have demonstrated a proof of concept for cell-mediated activation of anchored growth factors using a novel biofunctionalised scaffold in cartilage engineering. This presents a platform for development of protein delivery systems and for tissue engineering.

Noninvasive real-time monitoring by alamarBlue(®) during in vitro culture of three-dimensional tissue-engineered bone constructs

Bone tissue engineering (TE) aims to develop reproducible and predictive three-dimensional (3D) TE constructs, defined as cell-seeded scaffolds produced by a controlled in vitro process, to heal or replace damaged and nonfunctional bone. To control and assure the quality of the bone TE constructs, a prerequisite for regulatory authorization, there is a need to develop noninvasive analysis techniques to evaluate TE constructs and to monitor their behavior in real time during in vitro culturing. Most analysis techniques, however, are limited to destructive end-point analyses. This study investigates the use of the nontoxic alamarBlue(®) (AB) reagent, which is an indicator for metabolic cell activity, for monitoring the cellularity of 3D TE constructs in vitro as part of a bioreactor culturing processes. Within the field of TE, bioreactors have a huge potential in the translation of TE concepts to the clinic. Hence, the use of the AB reagent was evaluated not only in static cultures, but also in dynamic cultures in a perfusion bioreactor setup. Hereto, the AB assay was successfully integrated in the bioreactor-driven TE construct culture process in a noninvasive way. The obtained results indicate a linear correlation between the overall metabolic activity and the total DNA content of a scaffold upon seeding as well as during the initial stages of cell proliferation. This makes the AB reagent a powerful tool to follow-up bone TE constructs in real-time during static as well as dynamic 3D cultures. Hence, the AB reagent can be successfully used to monitor and predict cell confluence in a growing 3D TE construct.

DLK1(PREF1) is a negative regulator of adipogenesis in CD105⁺/CD90⁺/CD34⁺/CD31⁻/FABP4⁻ adipose-derived stromal cells from subcutaneous abdominal fat pats of adult women

The main physiological function of adipose-derived stromal/progenitor cells (ASC) is to differentiate into adipocytes. ASC are most likely localized at perivascular sites in adipose tissues and retain the capacity to differentiate into multiple cell types. Although cell surface markers for ASC have been described, there is no complete consensus on the antigen expression pattern that will precisely define these cells. DLK1(PREF1) is an established marker for mouse adipocyte progenitors which inhibits adipogenesis. This suggests that DLK1(PREF1) could be a useful marker to characterize human ASC. The DLK1(PREF1) status of human ASC is however unknown. In the present study we isolated ASC from the heterogeneous stromal vascular fraction of subcutaneous abdominal fat pats of adult women. These cells were selected by their plastic adherence and expanded to passage 5. The ASC were characterized as relatively homogenous cell population with the capacity to differentiate in vitro into adipocytes, chondrocytes, and osteoblasts and the immunophenotype CD105⁺/CD90⁺/CD34⁺/CD31⁻/FABP4⁻. The ASC were positive for DLK1(PREF1) which was well expressed in proliferating and density arrested cells but downregulated in the course of adipogenic differentiation. To investigate whether DLK1(PREF1) plays a role in the regulation of adipogenesis in these cells RNAi-mediated knockdown experiments were conducted. Knockdown of DLK1(PREF1) in differentiating ASC resulted in a significant increase of the expression of the adipogenic key regulator PPARγ2 and of the terminal adipogenic differentiation marker FABP4. We conclude that DLK1(PREF1) is well expressed in human ASC and acts as a negative regulator of adipogenesis. Moreover, DLK1(PREF1) could be a functional marker contributing to the characterization of human ASC.

Membranes for biohybrid liver support: the behaviour of C3A hepatoblastoma cells is dependent on the composition of acrylonitrile copolymers

Co-polymers based on acrylonitrile, N-vinylpyrrolidone, aminoethylmethacrylate and sodium methallylsulfonate were used to prepare flat membranes by phase inversion. The surface properties of membranes were characterised by water contact angle measurements, atomic force microscopy and X-ray photoelectron spectroscopy (XPS). Membrane permeability was estimated by porosity measurements with water as test liquid. Human C3A hepatoblastoma cells were plated on these materials. Cell-material interaction was characterised by overall cell morphology, formation of focal adhesion contacts and intercellular junctions. Furthermore, cell proliferation was measured and compared with the functional activity of cells as indicated by 7-ethoxycoumarin-O-deethylation. More hydrophilic materials reduced spreading of cells, formation of focal adhesion and subsequent proliferation while homotypic cell adhesion was facilitated in correlation with stronger expressions of intercellular junctions and improved functional activity. In contrast, membranes with stronger adhesivity enhanced cell proliferation but reduced the functional activity of cells. It was concluded that the co-polymerisation of acrylonitrile with hydrophilic co-monomers, such as N-vinylpyrrolidone, could be used to tailor membrane materials for the application in biohybrid liver support systems.

Optimum combination of insulin-transferrin-selenium and fetal bovine serum for culture of rabbit articular chondrocytes in three-dimensional alginate scaffolds

Fetal bovine serum (FBS) has been reported to affect chondrocyte biosynthesis in monolayer culture. Insulin-Transferrin-Selenium (ITS) was investigated as a partial replacement for FBS during in vitro culture of rabbit articular chondrocytes in three-dimensional alginate scaffold. Chondrocyte-seeded alginate hydrogels were cultured in Dulbecco's modified Eagle's medium plus 10% FBS, 1% ITS plus 2% FBS, 1% ITS plus 4% FBS, or 1% ITS plus 8% FBS. At designed time point, the Chondrocyte-seeded alginate hydrogels were harvested and evaluated with histological staining, immunohistochemistry, and quantitative gene expression analysis. Viable cell density and cell division were also evaluated. Chondrocytes biosynthesis and cell division in 1% ITS with 2% FBS medium were similar to that in medium added with 10% FBS. For a total culture of 3 weeks, phenotypic gene expression in chondrocyte-seeded hydrogels was maintained at high levels in medium with 1% ITS plus 2% FBS, while it was decreased to varying degrees in the other groups. In conclusion, with 1% ITS, medium with 2% FBS could promote chondrocyte biosynthesis and cell division, and prevented cell dedifferentiation in three-dimensional alginate scaffolds.

Molecular and phenotypic modulations of primary and immortalized canine chondrocytes in different culture systems

This study was conducted to determine physiological and functional features of primary and immortalized canine chondrocytes. Chondrocytes were immortalized by introducing the catalytic component of human telomerase namely human telomerase reverse transcriptase (hTERT). Primary chondrocytes lost their characteristic phenotype and growth properties whereas the immortalized cells remained polygonal with rapid growth rate. The expression of chondrocyte-specific markers decreased many-fold whereas that of chondrocyte-non-specific gene increased in primary chondrocytes. The immortalized cells did not express chondrocyte-specific genes in monolayers. Both primary and immortalized cells were encapsulated in alginate microspheres to construct three-dimensional (3D) culture system. As the primary chondrocytes, also the telomerase-transfected cells adopted a chondrocyte-specific gene expression pattern in alginate culture. Thus, the expression of telomerase represents possibility to expand chondrocytes without limitation while maintaining the chondrocyte-specific phenotype in 3D cultures. Use of such cells provides a standardized tool for testing different tissue engineering applications in canine model.

Mechanical and biochemical characterization of cartilage explants in serum-free culture

Allografts of articular cartilage are both used clinically for tissue-transplantation procedures and experimentally as model systems to study the physiological behavior of chondrocytes in their native extracellular matrix. Long-term maintenance of allograft tissue is challenging. Chemical mediators in poorly defined culture media can stimulate cells to quickly degrade their surrounding extracellular matrix. This is particularly true of juvenile cartilage which is generally more responsive to chemical stimuli than mature tissue. By carefully modulating the culture media, however, it may be possible to preserve allograft tissue over the long-term while maintaining its original mechanical and biochemical properties. In this study juvenile bovine cartilage explants (both chondral and osteochondral) were cultured in both chemically defined medium and serum-supplemented medium for up to 6 weeks. The mechanical properties and biochemical content of explants cultured in chemically defined medium were enhanced after 2 weeks in culture and thereafter remained stable with no loss of cell viability. In contrast, the mechanical properties of explants in serum-supplemented medium were degraded by ( approximately 70%) along with a concurrent loss of biochemical content (30-40% GAG). These results suggest that long-term maintenance of allografts can be extended significantly by the use of a chemically defined medium.

Novel surface patterning approaches for tissue engineering and their effect on cell behavior

Methods for the creation of specially designed surfaces for use in the preparation of tailor-made tissue constructs with the ultimate aim of tissue engineering are reviewed here. Fundamental aspects of cell adhesion, proliferation and differentiation and the parameters involved in these processes are discussed. A survey of recent micro- and nano-technological methods for creating physical and chemical cues on tissue engineering carriers is presented. This overview is supported with data from the literature on various applications of different cells on materials with widely differing chemistries and physical properties. Interactions between different cell types and micro- and nano-fabricated substrates are summarized.

Human Amniotic Membrane as a Delivery Matrix for Articular Cartilage Repair

The purpose of this study is to evaluate the feasibility of human amniotic membrane (HAM) as a chondrocyte carrier by assessing cell proliferation and maintenance of phenotype in vitro and cartilage regeneration in vivo. Intact HAM was treated with 0.1% trypsin-ethylenediaminetetraacetic acid (EDTA) for 15 min and the epithelial cells removed to make a denuded HAM. Rabbit articular chondrocytes were then seeded on three different HAM substrates: the epithelial side of intact HAM (IHE), basement side of denuded HAM (DHB), and stromal side of denuded HAM (DHS). These cell-substrate specimens were cultured for up to 4 weeks, and cell proliferation rate and phenotypic stability were examined at weeks 1 and 4. While chondrocytes grew in monolayer fashion on the surface of IHE and DHB substrates, the cells seeded in DHS penetrated and spread into the whole thickness of the stromal layer. The proliferating activity of chondrocytes in DHB was continuously up-regulated. A similar proliferating activity was observed in DHS in the first week, which remained stable for up to 4 weeks. The expression of type II collagen gradually increased with time in the DHS group, while it gradually decreased in the DHB group or was not detected at all in the IHE group. These results suggested that denuded HAM was able to support chondrocyte proliferation and maintenance of phenotype in vitro, seemingly more favorable when DHS was used. Based on this data, the DHS with chondrocytes was used to cover rabbit osteochondral defect with the stromal side facing in. The defect area was successfully regenerated with hyaline cartilage in the Safranin-O stain and International Cartilage Repair Society (ICRS) scoring after 8 weeks of implantation. In conclusion, our findings suggest that denuded HAM could be one of the ideal cell carrier matrices for cartilage regeneration.

Scaffold-free, engineered porcine cartilage construct for cartilage defect repair--in vitro and in vivo study

This study introduces an implantable scaffold-free (SF) cartilage tissue construct that is composed of chondrocytes and their self-produced extracellular matrix (ECM). Chondrocytes were isolated from the articular cartilages from knees of domestic pigs (2-week old) and monolayer-cultured for 3-4 days in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum and 50 microg/mL of ascorbic acid. Briefly treated with 0.25% trypsin-ethylenediaminetetraacetic acid (EDTA), an intact chondrocytes/ECM membrane, as a cell sheet was released from the plate bottom and subsequently centrifuged into a pellet-type construct. Each was grown in vitro for up to 5 weeks and subjected to various assays at different time points (1, 7, 14, 21, and 35 days). For in vivo implantation, full-thickness defects (n = 4) were manually created on the femoro-patellar groove of the left porcine knee and 1-week-cultured SF construct was implanted as an allograft for a month. One defect (#1) was an empty control and the remaining three received different recipes; construct only (#2) or 0.25% trypsin/EDTA-treated first and then construct and collagen gel (#3) or construct and collagen gel (#4). While the total cell numbers significantly increased by 2 weeks and then remained stable, cell viability stayed in the mid-70% range through the entire culture period. Biochemical assay found continuous glycosaminoglycan (GAG) accumulation. Histology exhibited that cell distribution was even in the construct and GAG intensity became stronger and uniform with time. Real-time reverse transcription polymerase chain reaction (RT-PCR) results showed that phenotypic stability peaked at 2 weeks, which was arable to that of freshly isolated chondrocytes. Upon analysis of the retrieved implants, some promising results were witnessed in the defects (#3) retaining not only their intact mass but also chondrocytic morphology with lacuna formation.

Human bone marrow stromal cells: In vitro expansion and differentiation for bone engineering

Stromal cells from marrow hold a great promise for bone regeneration. Even if they are already being exploited in many clinical settings, the biological basis for the source and maintenance of their proliferation/differentiation potential after in vitro isolation and expansion needs further investigation. Most studies on osteogenic differentiation of marrow stromal cells (MSC) have been performed using bone marrow from the iliac crest. In this study, MSC were derived from spare femoral bone marrow obtained during hip replacement surgery from 20 adult donors. After in vitro isolation the cells were grown in osteogenic medium, and their proliferation and differentiation analysed during in vitro expansion. We found that MSC isolated from the femur of adult patients consistently maintain an osteogenic potential. Using biochemical signals, these cells turn to fully differentiated osteoblasts with a predictable set of molecular and phenotypic events of in vitro bone deposition. When seeded on polycaprolactone-based scaffold or surfaces, the proliferation and mineralization of femur-derived MSC were modulated by the surface chemistry/topography. Despite remarkable differences between individual colony-forming ability, alkaline phosphatase production, and mineralization ability, these cells are a potential source for bone engineering, either by direct autologous reimplantation or by ex vivo expansion and reimplantation combined to a proper scaffold.

Tissue engineering of tooth crown, root, and periodontium

Tissue engineering of teeth requires the coordinated formation of correctly shaped crowns, roots, and periodontal ligament. Previous studies have shown that the dental mesenchyme controls crown morphogenesis and epithelial histogenesis during tooth development in vivo, but little is known about the inductive potential of dissociated mesenchymal cells used in ex vivo cultures. A 2-step method is described in which, by using different types of reassociations between epithelial and mesenchymal tissues and/or cells from mouse embryos, reassociations were cultured in vitro before in vivo implantation. In vitro, the reassociated tissues developed and resulted in tooth-like structures that exhibited normal epithelial histogenesis and allowed the functional differentiation of odontoblasts and ameloblasts. After implantation, the reassociations formed roots and periodontal ligament, the latter connected to developing bone. The shape of the crown, initially suspected to depend on the integrity of the mesenchyme, could be modulated by adjusting the number of dissociated mesenchymal cells reassociated with the epithelial compartment. Based on these results, we propose a refined strategy for tooth tissue engineering that may help to eventually generate morphologically defined teeth.

Mechanical properties of bacterial cellulose and interactions with smooth muscle cells

Tissue engineered blood vessels (TEBV) represent an attractive approach for overcoming reconstructive problems associated with vascular diseases by providing small calibre vascular grafts. The aim of this study has been to evaluate a novel biomaterial, bacterial cellulose (BC), as a potential scaffold for TEBV. The morphology of the BC pellicle grown in static culture was investigated with SEM. Mechanical properties of BC were measured in Krebs solution and compared with the properties of porcine carotid arteries and ePTFE grafts. Attachment, proliferation and ingrowth of human smooth muscle cells (SMC) on the BC were analysed in vitro. The BC pellicle had an asymmetric structure composed of a fine network of nanofibrils similar to a collagen network. The shape of the stress-strain response of BC is reminiscent of the stress-strain response of the carotid artery, most probably due to the similarity in architecture of the nanofibrill networks. SMC adhered to and proliferated on the BC pellicle; an ingrowth of up to 40 microm was seen after 2 weeks of culture. BC exhibit attractive properties for use in future TEBV.

Long-term maintenance of human articular cartilage in culture for biomaterial testing

Cartilage is a tissue that derives its unique mechanical and biological properties from the combination of relatively few cells and a large amount of a complex extracellular matrix. Furthermore, cartilage tissue is comparatively slow to respond to changes or harmful influences. To date, the optimal generation and long-term maintenance of cultured human articular cartilage for in vitro testing of biomaterials, poses an experimental difficulty. Experiments using cultured isolated chondrocytes in combination with scaffolds often fail to yield results comparable to the in-vivo situation. Consequently, our aim was to develop a culture method that allows in vitro maintenance of human hyaline cartilage explants in an optimal quality over an extended period of time. Such a culture could, for example, be used to determine the long-term effect of a new scaffold on intact cartilage, as an in vitro model for repair processes and to investigate biomaterial integration. In this study we compared conventional static cultures with and without serum supplementation to a serum-free perfusion culture for the ability to maintain human articular cartilage explants in a morphologically intact and differentiated state over an extended period of time of up to 56 days. Results were evaluated and compared by morphological, histochemical and immunohistochemical methods. The experiments showed that short-term maintenance of cartilage in a differentiated state for up to 14 days is possible under all culture conditions tested. However, best long-term culture results for up to 56 days were obtained with perfusion culture under serum-free conditions. Such a perfusion culture system can be used to perform biocompatabilty tests in vitro by long-term coculture of biomaterial and intact human articular cartilage.

Influence of oxygen on the proliferation and metabolism of adipose derived adult stem cells

Articular cartilage is an avascular connective tissue that exhibits little intrinsic capacity for repair. Articular cartilage exists in a reduced oxygen ( approximately 5%) environment in vivo; therefore, oxygen tension may be an important factor that regulates the metabolism of chondrocyte progenitors. A number of recent studies have developed tissue engineering approaches for promoting cartilage repair using undifferentiated progenitor cells seeded on biomaterial scaffolds, but little is known about how oxygen might influence these engineered tissues. Human adipose-derived adult stem (hADAS) cells isolated from the stroma of subcutaneous fat were suspended in alginate beads and cultured in control or chondrogenic media in either low oxygen (5%) or atmospheric oxygen tension (20%) for up to 14 days. Under chondrogenic conditions, low oxygen tension significantly inhibited the proliferation of hADAS cells, but induced a two-fold increase in the rate of protein synthesis and a three-fold increase in total collagen synthesis. Low oxygen tension also increased glycosaminoglycan synthesis at certain timepoints. Immunohistochemical analysis showed significant production of cartilage-associated matrix molecules, including collagen type II and chondroitin-4-sulfate. These findings suggest oxygen tension may play an important role in regulating the proliferation and metabolism of hADAS cells as they undergo chondrogenesis, and the exogenous control of oxygen tension may provide a means of increasing the overall accumulation of matrix macromolecules in tissue-engineered cartilage.

Induction of proliferation and differentiation of cultured urothelial cells on acellular biomaterials

OBJECTIVE

To determine the optimum conditions for the proliferation of urothelial cells, leading to the confluent coverage of large surfaces of biocompatible membranes, and for their terminal differentiation.

MATERIALS AND METHODS

Porcine and human urothelial cells were cultured on different matrices under different growth conditions. Proliferative activity and the viability of cells were evaluated using fluorescent markers for nuclei and cytoplasm. Growth and differentiation were assessed by histological, histochemical and immunohistochemical methods.

RESULTS

Under fibroblastic induction and supplementation of 5% fetal calf serum (FCS), urothelial cells showed more proliferation than in other conditions tested. Terminal differentiation of superficial cells was achieved by lowering the concentration of FCS to 1% at the air-liquid interface.

CONCLUSIONS

The mitogenic effects of the extracellular matrix content of biological membranes and fibroblastic inductive factors are synergistic with each other, and can compensate for a low FCS concentration and the absence of other additives. Lowering the FCS concentration to 1% inhibits the proliferation of urothelial cells and permits their terminal differentiation.

[Tissue engineering of the urinary bladder]

In tissue engineering of the urinary bladder with autologous cell transplantation, high differentiation of the cells cultivated in vitro on biocompatible membranes is essential for the functionality of the tissue constructs after implantation. The terminal differentiation of superficial urothelial cells has a key role because of the barrier function of these cells against urine. The aim of this study was to determine optimized conditions for the creation of terminally differentiated urothelium to cover large membrane surfaces. This can bring us closer to the goal of using functioning tissue constructs in clinical trials.

Effects of enamel matrix derivative on proliferation and differentiation of primary osteoblasts

OBJECTIVE

The aim of this study was to investigate the effects of enamel matrix derivative (EMD) on proliferation, protein synthesis, and mineralization in primary mouse osteoblasts.

STUDY DESIGN

Osteoblasts were obtained from mouse calvaria by enzymatic digestion and grown in monolayer together with EMD (2-100 microg/ml). Metabolic activity and cell proliferation were determined by tetrazolium salt assay (MTT) and by 5-bromo-2'-deoxyuridine (BrdU) incorporation. For differentiation studies, a 3-dimensional organoid culture system was used. Osteoblastic differentiation was estimated by alkaline phosphatase (ALP) activity and calcium content. Collagen synthesis was assessed by [(3)H]-proline incorporation. Morphologic observations were made by electron microscopy.

RESULTS

EMD treatments increased metabolic cell activity and BrdU incorporation. In the organoid cultures, ALP activity and calcium accumulation were enhanced by EMD treatment, but [(3)H]-proline incorporation was not. Morphologically, an increased deposition of mineralized nodules was found.

CONCLUSIONS

EMD treatment enhanced cellular activities of primary osteoblasts and might support the regeneration of periodontal bony defects.

Effects of transforming growth factor beta1 and dexamethasone on the growth and chondrogenic differentiation of adipose-derived stromal cells

The effects of soluble mediators and medium supplements commonly used to induce chondrogenic differentiation in different cell culture systems were investigated to define their dose-response profiles and potentially synergistic effects on the chondrogenic differentiation of adipose-derived adult stromal (ADAS) cells. Human ADAS cells were suspended within alginate beads and cultured in basal medium with insulin, transferrin, and selenious acid (ITS+) or fetal bovine serum (FBS) and treated with different doses and combinations of TGF-beta1 (0, 1, and 10 ng/mL) and dexamethasone (0, 10, and 100 nM). Cell growth and chondrogenic differentiation were assessed by measuring DNA content, protein and proteoglycan synthesis rates, and proteoglycan accumulation. The combination of ITS+ and TGF-beta1 significantly increased cell proliferation. Protein synthesis rates were increased by TGF-beta1 and dexamethasone in the presence of ITS+ or FBS. While TGF-beta1 significantly increased proteoglycan synthesis and accumulation by 1.5- to 2-fold in the presence of FBS, such effects were suppressed by dexamethasone. In summary, the combination of TGF-beta1 and ITS+ stimulated cell growth and synthesis of proteins and proteoglycans by human ADAS cells. The addition of dexamethasone appeared to amplify protein synthesis but had suppressive effects on proteoglycan synthesis and accumulation.

Engineering of Multilayered Urinary Tissue in Vitro

Regeneration of the urinary conduit, using engineered autologous material, could have many clinical implications. The urinary system is composed of a three-layered wall consisting of different cell types. In this study we investigated the possibility to coculture these components in vitro into a continuous sheet for total autologous regeneration. To address this issue, human urothelial cells, fibroblasts, and smooth muscle cells were isolated separately and expanded in vitro. Cells were then cocultured by seeding them in layers in a "sandwich model." After coculturing the material was investigated histologically and with immunoassays. The different cells could be cocultured after being isolated and expanded separately in vitro. The cells formed a continuous sheet that could be enzymatically detached and that sustained mechanical handling. The morphology of different cell layers and the reaction to immunostaining indicated their preserved individual phenotype. In conclusion, we showed that human urothelial cells, fibroblasts, and smooth muscle cells can be expanded in vitro and cocultured to form a continuous cellular sheet consisting of three distinct layers of different types of cells. This could provide the surgeon with autologous tissue for urogenital reconstructive purposes.

Biological response of chondrocytes cultured in three‐dimensional nanofibrous poly(ϵ‐caprolactone) scaffolds

Nanofibrous materials, by virtue of their morphological similarities to natural extracellular matrix, have been considered as candidate scaffolds for cell delivery in tissue-engineering applications. In this study, we have evaluated a novel, three-dimensional, nanofibrous poly(epsilon-caprolactone) (PCL) scaffold composed of electrospun nanofibers for its ability to maintain chondrocytes in a mature functional state. Fetal bovine chondrocytes (FBCs), maintained in vitro between passages 2 to 6, were seeded onto three-dimensional biodegradable PCL nanofibrous scaffolds or as monolayers on standard tissue culture polystyrene (TCPS) as a control substrate. Gene expression analysis by reverse transcription-polymerase chain reaction showed that chondrocytes seeded on the nanofibrous scaffold and maintained in serum-free medium supplemented with ITS+, ascorbate, and dexamethasone continuously maintained their chondrocytic phenotype by expressing cartilage-specific extracellular matrix genes, including collagen types II and IX, aggrecan, and cartilage oligomeric matrix protein. Specifically, expression of the collagen type IIB splice variant transcript, which is indicative of the mature chondrocyte phenotype, was up-regulated. FBCs exhibited either a spindle or round shape on the nanofibrous scaffolds, in contrast to a flat, well-spread morphology seen in monolayer cultures on TCPS. Organized actin stress fibers were only observed in the cytoplasm of cells cultured on TCPS. Histologically, nanofibrous cultures maintained in the supplemented serum-free medium produced more sulfated proteoglycan-rich, cartilaginous matrix than monolayer cultures. In addition to promoting phenotypic differentiation, the nanofibrous scaffold also supported cellular proliferation as evidenced by a 21-fold increase in cell growth over 21 days when the cultures were maintained in serum-containing medium. These results indicate that the biological activities of FBCs are crucially dependent on the architecture of the extracellular scaffolds as well as the composition of the culture medium, and that nanofibrous PCL acts as a biologically preferred scaffold/substrate for proliferation and maintenance of the chondrocytic phenotype. We propose that the PCL nanofibrous structure may be a suitable candidate scaffold for cartilage tissue engineering.

IN SITU COLLAGEN GELATION: A NEW METHOD FOR CONSTRUCTING LARGE TISSUE IN ROTARY CULTURE VESSELS

In situ collagen gelation is a method that combines a static three-dimensional culture technique with rotating bioreactors. This method was designed for large dense tissue engineering ex vivo. To challenge the current limitations on size, we combined the static collagen gel embedding method with high-aspect ratio rotating bioreactors. Rat calvarial cells in gelated collagens were cultured in rotating vessels with 5 mM beta-glycerophosphate-containing medium for 1, 2, or 3 wk and then analyzed for cell morphology, cell distribution, and viability, as well as for contraction of the collagen gel. The size of collagen gels with rat calvarial cells averaged 2.8 cm in diameter x 0.25 cm in thickness at the end of 3 wk. Scanning electron microscopy and laser scanning confocal microscopy of collagen gels revealed a homogeneous distribution of living cells. Despite the barrier effects from induced calcification, in collagen gels, cell metabolic activity (alkaline phosphatase assay and 3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2H-tetrazolium bromide assay) increased over the 3 wk, and cell viability (trypan blue exclusion and flow cytometry analysis) remained at about 90% at the end of 3 wk. Based on our results, we determined that in situ collagen gelation provides a feasible method for engineering large dense tissue ex vivo.