Biomimetic Culture System Research Articles

Active Osteoblasts or Quiescent Bone Lining Cells? Preosteoblasts Fate Orchestrated by Curvature and Stiffness of an In Vitro 2.5D Biomimetic Culture System.

Biomimetic cell culture systems are required to provide more physiologically relevant microenvironments for bone cells. Here, a simple 2.5D culture platform is proposed, combining adjustable stiffness and surface features that mimic bone topography by using sandpaper grits as master molds with two stiffness formulations of polydimethylsiloxane (PDMS). The subsequent replicas perfectly conform the grits and reproduce the corresponding negative relief with cavities separated by convex edges. Biomimicry is also provided by an extracellular matrix (ECM)-like thin film coating, using the layer-by-layer (LbL) method. The topographical features, alternating concave, and convex structures drive preosteoblasts organization and morphology. Strikingly, curvature orchestrates the commitment of preosteoblasts, with i) maturation to active osteoblasts able to produce a dense collagenous matrix that ultimately mineralizes in the cavities, and ii) edges hosting quiescent cells that synthetize a very thin immature collagen layer with no mineralization. In summary, the present in vitro culture system model offers a cell-instructive 2.5D microenvironment that controls preosteoblasts fate, leading to two coexisting subpopulations: mature osteoblasts and bone lining cells (BLC). This promising culture system opens new avenues to advanced tissue-engineered modeling and can be applied to precellularized bone biomaterials.

068 Bovine Oviductal Organoids: 3-D biomimetic culture system to study the maternal cellular and extracellular response to thermal stress

068 Bovine Oviductal Organoids: 3-D biomimetic culture system to study the maternal cellular and extracellular response to thermal stress

C-Kit M541L variant is related to ineffective hemopoiesis predisposing to clonal evolution in 3D in vitro biomimetic co-culture model of bone marrow niche

Hematopoietic stem cell (HSC) maintenance in vitro is challenging because stem cell survival relies on cell-to-cell contacts and paracrine signals from bone marrow (BM) microenvironment. Indeed, HSCs easily differentiate in conventional culture systems, and in vitro study of stem cell biology, leukemogenesis, and evolutionary trajectories is limited. 3D-culture systems can mimic tissue architecture and microenvironment thus preserving HSC phenotype. In this study, we developed a calcium alginate hydrogel-based 3D co-culture system of BM mononuclear cells (BMMCs) and BM-derived mesenchymal stem cells (BM-MSCs) to study hemopoiesis in health and disease, such as biological roles of c-Kit M541L somatic mutation of unknown significance. BMMCs and peripheral blood stem cells were obtained from an acute myeloid leukemia patient who experienced graft failure and his haploidentical donor, and from a healthy donor. Cells embedded in alginate scaffolds were cultured for up to 21 days, and flow cytometry immunophenotyping was performed at baseline and every seven days. Our results showed suitability of our 3D culture system in preserving HSC vitality and phenotype throughout the culture period, and also in maintaining composition and vitality of total BMMCs. Moreover, 3D in vitro culture results suggested that M541L c-Kit somatic mutation could be a loss-of-function alteration by reducing HSC maintenance ability thus quickly promoting differentiation, as documented by in vivo graft failure and in vitro absence of long-term culture stability. In conclusions, our 3D BM-like biomimetic culture system allowed long-term stemness maintenance, making it a valid and effective tool for in vitro study of physiological and pathological hemopoiesis.

Biophysics Role and Biomimetic Culture Systems of ECM Stiffness in Cancer EMT.

Oncological diseases have become the second leading cause of death from noncommunicable diseases worldwide and a major threat to human health. With the continuous progress in cancer research, the mechanical cues from the tumor microenvironment environment (TME) have been found to play an irreplaceable role in the progression of many cancers. As the main extracellular mechanical signal carrier, extracellular matrix (ECM) stiffness may influence cancer progression through biomechanical transduction to modify downstream gene expression, promote epithelial‐mesenchymal transition (EMT), and regulate the stemness of cancer cells. EMT is an important mechanism that induces cancer cell metastasis and is closely influenced by ECM stiffness, either independently or in conjunction with other molecules. In this review, the unique role of ECM stiffness in EMT in different kinds of cancers is first summarized. By continually examining the significance of ECM stiffness in cancer progression, a biomimetic culture system based on 3D manufacturing and novel material technologies is developed to mimic ECM stiffness. The authors then look back on the novel development of the ECM stiffness biomimetic culture systems and finally provide new insights into ECM stiffness in cancer progression which can broaden the fields’ horizons with a view toward developing new cancer diagnosis methods and therapies.

Matrix Hyaluronic Acid and Hypoxia Influence a CD133+ Subset of Patient-Derived Glioblastoma Cells.

Glioblastoma (GBM) displays diffusive invasion throughout the brain microenvironment, which is partially responsible for its short median survival rate (<15 months). Stem-like subpopulations (GBM stem-like cells, GSCs) are believed to play a central role in therapeutic resistance and poor patient prognosis. Given the extensive tissue remodeling and processes such as vessel co-option and regression that occur in the tumor microenvironment, it is essential to understand the role of metabolic constraint such as hypoxia on GBM cell populations. This work describes the use of a multidimensional gelatin hydrogel to culture patient-derived GBM cells, to evaluate the influence of hypoxia and the inclusion brain-mimetic hyaluronic acid on the relative activity of GSCs versus overall GBM cells. Notably, CD133+ GBM cell fraction is crucial for robust formation of tumor spheroids in multidimensional cultures. In addition, while the relative size of the CD133+ GBM subpopulation increased in response to both hypoxia and matrix-bound hyaluronan, we did not observe cell subtype-specific changes in invasion signaling pathway activation. Taken together, this study highlights the potential of biomimetic culture systems for resolving changes in the population dynamics and behavior of subsets of GBM specimens for the future development of precision medicine applications. Impact Statement This study describes a gelatin hydrogel platform to investigate the role of extracellular hyaluronic acid and hypoxia on the behavior of a CD133+ subset of cells within patient-derived glioblastoma (GBM) specimens. We report that the relative expansion of the CD133+ GBM stem cell-like population is strongly responsive to extracellular cues, highlighting the significance of biomimetic hydrogel models of the tumor microenvironment to investigate invasion and therapeutic response.

Heart slice culture system reliably demonstrates clinical drug-related cardiotoxicity

The limited availability of human heart tissue and its complex cell composition are major limiting factors for the reliable testing of drug efficacy and toxicity. Recently, we developed functional human and pig heart slice biomimetic culture systems that preserve the viability and functionality of 300 μm heart slices for up to 6 days. Here, we tested the reliability of this culture system for testing the cardiotoxicity of anti-cancer drugs. We tested three anti-cancer drugs (doxorubicin, trastuzumab, and sunitinib) with known different mechanisms of cardiotoxicity at three concentrations and assessed the effect of these drugs on heart slice viability, structure, function and gene expression. Slices incubated with any of these drugs for 48 h showed diminished in viability as well as loss of cardiomyocyte structure and function. Mechanistically, RNA sequencing of doxorubicin-treated tissues demonstrated a significant downregulation of cardiac genes and upregulation of oxidative stress responses. Trastuzumab treatment downregulated cardiac muscle contraction-related genes consistent with its clinically known effect on cardiomyocytes. Interestingly, sunitinib treatment resulted in significant downregulation of angiogenesis-related genes, in line with its mechanism of action. Similar to hiPS-derived-cardiomyocytes, heart slices recapitulated the expected toxicity of doxorubicin and trastuzumab, however, slices were superior in detecting sunitinib cardiotoxicity and mechanism in the clinically relevant concentration range of 0.1–1 μM. These results indicate that heart slice culture models have the potential to become a reliable platform for testing and elucidating mechanisms of drug cardiotoxicity.

Tissue engineered vessel from a biodegradable electrospun scaffold stimulated with mechanical stretch

A tissue engineered vessel has the potential to provide an alternative small diameter vascular graft for patients with cardiovascular disease in need of surgical revascularization. In this study, a polyglycolic acid (PGA) electrospun scaffold seeded with human dermal fibroblasts was stimulated with circumferential mechanical stretch by a pulsatile perfusion system. The PGA scaffold was fabricated using a custom electrospinning set-up to co-electrospray a sacrificial polyethylene oxide microparticle to increase pore size and bulk porosity. The tissue engineered vessel exposed to circumferential mechanical stretch was compared to an engineered vessel cultured under static conditions without any mechanical stimulation. The histology cross-sections demonstrated a similar thickness of engineered vessels with mechanical stretch and static, but on Masson’s Trichrome stain there was nearly twice the amount of staining for collagen. The collagen content was quantified, and the collagen content was 60% greater in the human tissue engineered vessel exposed to mechanical stretch compared to the static vessel. The total collagen cross-linking was similar, but on a per collagen basis there was significantly more cross-linking in the static vessel over the stretch vessel. The stress-strain curve of the tissue engineered vessel with mechanical stretch demonstrated a statistically significantly greater ultimate tensile strength (UTS) of 1.86 ± 0.14 MPa (n = 6) and elastic modulus (EM) of 7.62 ± 0.39 MPa (n = 6) versus the static engineered vessel UTS of 0.31 ± 0.07 MPa (n = 5) and EM of 1.37 ± 0.21 MPa (n = 5). The primary determinant of the mechanical properties of the tissue engineered vessel correlated to the collagen content with minimal contribution of the collagen cross-linking. Therefore, the versatile properties of an electrospun scaffold are ideal in combination with a biomimetic culture system to generate a tissue engineered vessel composed of extracellular matrix suitable as a vascular graft.

Three-dimensional biomimetic hyaluronic acid hydrogels to investigate glioblastoma stem cell behaviors.

Glioblastoma multiforme (GBM) is the deadliest form of primary brain tumor. GBM tumors are highly heterogeneous, being composed of tumor cells as well as glioblastoma stem cells (GSCs) that contribute to drug resistance and tumor recurrence following treatment. To develop therapeutic strategies, an improved understanding of GSC behavior in their microenvironment is critical. Herein, we have employed three-dimensional (3D) hyaluronic acid (HA) hydrogels that allow the incorporation of brain microenvironmental cues to investigate GSC behavior. U87 cell line and patient-derived D456 cells were cultured as suspension cultures (serum-free) and adherently (in the presence of serum) and were then encapsulated in HA hydrogels. We observed that all the seeded single cells expanded and formed spheres, and the size of the spheres increased with time. Increasing the initial cell seeding density of cells influenced the sphere size distribution. Interestingly, clonal expansion of serum-free grown tumor cells in HA hydrogels was observed. Also, stemness marker expression of serum and/or serum-free grown cells was altered when cultured in HA hydrogels. Finally, we demonstrated that HA hydrogels can support long-term GSC culture (up to 60 days) with retention of stemness markers. Overall, such biomimetic culture systems could further our understanding of the microenvironmental regulation of GSC phenotypes.

Meet the First Authors.

Meet the First Authors.

Abstract 208: Reliable Biomimetic Culture System for Pig and Human Heart Slices

Rationale: Heart failure is the number one killer and drug induced cardiotoxicity is a major cause of market withdrawal. The lack of availability of culture systems for human heart tissue that is functionally and structurally viable for more than 24 hours is a limiting factor in validation of novel heart failure therapies as well as reliable cardiotoxicity testing. Therefore, there is an urgent need to develop a reliable system for culturing human heart tissue for testing drug efficacy and toxicity. Objective: To develop a reliable method to culture pig and human heart slices under full physiological conditions for a period of time sufficient to test therapeutic efficacy and acute drug toxicity. Methods and Results: Here we describe a novel biomimetic culture system that maintains full viability and functionality of human and pig heart slices (300 μm thickness) for 6 days in culture through optimization of the medium and culture conditions with continuous electrical stimulation at 1.2 Hz and oxygenation of the medium. Functional viability of these slices over 6 days was confirmed by assessing their calcium homeostasis, twitch force generation, and response to β-adrenergic stimulation. Temporal transcriptome analysis using RNAseq at day 2, 6, and 10 in culture confirmed overall maintenance of normal gene expression for up to 6 days, while over 500 transcripts were differentially regulated after 10 days. Electron microscopy demonstrated intact mitochondria and Z-disc ultra-structures after 6 days in culture under our optimized conditions. This biomimetic culture system was successful in keeping human heart slices completely viable and functionally and structurally intact for 6 days in culture. We also used this system to demonstrate the effects of a novel gene therapy approach in human heart slices. Conclusions: We have developed and optimized a reliable and easily reproducible culture system for pig and human heart slices as a platform for testing the efficacy of novel heart failure therapeutics as well as reliable testing of cardiotoxicity in a 3D heart model.

Physiological Biomimetic Culture System for Pig and Human Heart Slices.

Preclinical testing of cardiotoxicity and efficacy of novel heart failure therapies faces a major limitation: the lack of an in situ culture system that emulates the complexity of human heart tissue and maintains viability and functionality for a prolonged time. To develop a reliable, easily reproducible, medium-throughput method to culture pig and human heart slices under physiological conditions for a prolonged period of time. Here, we describe a novel, medium-throughput biomimetic culture system that maintains viability and functionality of human and pig heart slices (300 µm thickness) for 6 days in culture. We optimized the medium and culture conditions with continuous electrical stimulation at 1.2 Hz and oxygenation of the medium. Functional viability of these slices over 6 days was confirmed by assessing their calcium homeostasis, twitch force generation, and response to β-adrenergic stimulation. Temporal transcriptome analysis using RNAseq at day 2, 6, and 10 in culture confirmed overall maintenance of normal gene expression for up to 6 days, while over 500 transcripts were differentially regulated after 10 days. Electron microscopy demonstrated intact mitochondria and Z-disc ultra-structures after 6 days in culture under our optimized conditions. This biomimetic culture system was successful in keeping human heart slices completely viable and functionally and structurally intact for 6 days in culture. We also used this system to demonstrate the effects of a novel gene therapy approach in human heart slices. Furthermore, this culture system enabled the assessment of contraction and relaxation kinetics on isolated single myofibrils from heart slices after culture. We have developed and optimized a reliable medium-throughput culture system for pig and human heart slices as a platform for testing the efficacy of novel heart failure therapeutics and reliable testing of cardiotoxicity in a 3-dimensional heart model.

Enhanced osteogenic differentiation of mesenchymal stem cells in ankylosing spondylitis: a study based on a three-dimensional biomimetic environment

The mechanism of pathological osteogenesis in Ankylosing spondylitis (AS) is largely unknown. Our previous studies demonstrated that the imbalance between BMP-2 and Noggin secretion induces abnormal osteogenic differentiation of marrow-derived mesenchymal stem cells (MSCs) from AS patients in a two-dimensional culture environment. In this study, HA/β-TCP scaffolds were further used as a three-dimensional (3D) biomimetic culture system to mimic the bone microenvironment in vivo to determine the abnormal osteogenic differentiation of AS-MSCs. We demonstrated that when cultured in HA/β-TCP scaffolds, AS-MSCs had a stronger osteogenic differentiation capacity than that of MSCs from healthy donors (HD-MSCs) in vitro and in vivo. This dysfunction resulted from BMP2 overexpression in AS-MSCs, which excessively activated the Smad1/5/8 and ERK signalling pathways and finally led to enhanced osteogenic differentiation. Both the signalling pathway inhibitors and siRNAs inhibiting BMP2 expression could rectify the enhanced osteogenic differentiation of AS-MSCs. Furthermore, BMP2 expression in ossifying entheses was significantly higher in AS patients. In summary, our study demonstrated that AS-MSCs possess enhanced osteogenic differentiation in HA/β-TCP scaffolds as a 3D biomimetic microenvironment because of BMP2 overexpression, but not Noggin. These results provide insights into the mechanism of pathological osteogenesis, which can aid in the development of niche-targeting medications for AS.

Apoptotic effect of atorvastatin in glioblastoma spheroids tumor cultured in fibrin gel.

Glioblastoma multiform (GBM) is one of the most common and highly aggressive primary brain tumors that thought to be of glial cells origin. The new available therapy for glioblastoma is based on better understanding of molecular malignant progression in this tumor. It is better to identify key molecular targets stimulating signaling pathways that lead to initiation of apoptosis for treatment of glioblastoma. Tumorigenesis broadly is controlled by tumor microenvironment and design of best biomimetic culture systems dependency on these conditions allow for in vitro and in vivo tumor modeling for studies of cancer cells behavior to drugs. We engineered three-dimensional (3D) human tumor models using U87 glioma cells in fibrin gel that mimic microenvironmental feature of glioblastoma in vivo. In this study, atorvastatin was used as a kind of statins for induction of apoptosis, and inhibition of migration and invasion in glioma cells. To reach for these aims, 3D model of glioma in fibrin gel was used with different concentrations of atorvastatin (1, 5, 10μM) to assay apoptotic genes expression by real time PCR and Tunel assay. After 24 and 48h exposing with different concentrations of atorvastatin, cell migration and invasion of tumor cells were investigated. The results showed atorvastatin induced apoptosis of glioma spheroids dose- dependently. The most likely mechanisms are the induction of apoptosis by caspase-8- caspase-3 signaling pathway. The invasion and migration of U87 spheroid cells decreased after 48h especially with 10μM concentration of atorvastatin. Finally these results suggest that this biomimetic model with fibrin may provide a vastly applicable 3D culture system to study the effect of anti-cancer drugs such as atrovastatin on tumor malignancy in vitro and in vivo and atorvastatin could be used as anticancer agent for glioblastoma treatment.

Reality Check for Nanomaterial‐Mediated Therapy with 3D Biomimetic Culture Systems

The recent progresses in tissue engineering and nanomaterial‐based therapeutics/theranostics have led to the ever increasing utilization of 3D in vitro experimental models as the bona fide culture systems to evaluate the therapeutic/theranostic effects of nanomedicine. Compared to the use of conventional 2D culture platforms, 3D biomimetic cultures offer unmatched advantages as relevant physiological and pathological elements can be incorporated to allow better characterization of the engineered bio‐nanomaterials in the targeted tissue‐specific microenvironment. In this Feature Article, the current state‐of‐the‐art 3D in vitro models that have been developed for the evaluation of biosafety and efficacy of nano‐ therapeutics/theranostics targeting the colon, blood–brain barrier (BBB), lungs, skin tumor models to bridge the nanomedicine bench to pre‐clinical ravine are reviewed. Furthermore, the critical physicochemical parameters of the bio‐nanomaterials that govern its transport and biodistribution in a complex 3D microenvironment will be highlighted. The major challenges and future prospects of evaluating nanomedicine in the third dimension will also be discussed.

Abstract 19693: Modeling Adaptive Growth -- Biomimetic Culture of Neonatal Aortic Root Explants

Background: Heart valve disease afflicts individuals of all ages, but current treatments, involving replacement with non-viable prosthetics, are particularly suboptimal for young patients. To design “growing” valve replacements, postnatal growth mechanisms must be elucidated; models of adaptive growth are lacking, thereby hindering these investigations. We hypothesized that physiologic mechanical loading with growth factor stimulation would enable the adaptive growth of aortic root explants in vitro. To this end, we designed a biomimetic perfusion bioreactor that permits the concomitant delivery of these factors. Methods and Results: We constructed a chamber for culturing neonatal rat hearts under pulsatile flow conditions. Parameters were adjusted to mimic native physiology using ultrasound assessment of cusp motion and invasive measurement of left ventricular and aortic pressures. Culture medium was designed by quantification of key growth factor (IGF-1, TGF-β 2 , VEGF, EGF, BMP-2 and FGF-2) concentrations within age-matched serum via ELISA. Explants were cultured for five days. Controls were explanted from age- and size-matched pups. Dynamically-cultured samples exhibited similar proliferation rates at early time points when compared to those of valve cusps in vivo as assessed by EdU incorporation (10.5% vs. 14.9%, p=0.35). After five days of dynamic culture, native proliferation rates were achieved only with concomitant growth factor administration (13.3% control; 13.1% dynamic+GF; 3.1% dynamic alone). There was no evidence of proliferation in statically-cultured controls. Conclusions: We describe a novel biomimetic culture system that permits the modeling of adaptive growth in aortic root explants. Our results demonstrate recapitulation of in vivo cell proliferation rates in dynamically-cultured hearts and suggest a role for mechanical and humoral stimulation in mediating aortic valve growth. This system enables the elucidation and manipulation of the mechanisms driving postnatal heart valve growth, thereby informing the design of the ideal pediatric valve graft with adaptive growth potential.

On the symmetry of siblings: automated single-cell tracking to quantify the behavior of hematopoietic stem cells in a biomimetic setup

The interplay between hematopoietic stem and progenitor cells (HSPC) and their local microenvironment is a key mechanism for the organization of hematopoiesis. To quantitatively study this process, a time-resolved analysis of cellular dynamics at the single-cell level is an essential prerequisite. One way to generate sufficient amounts of appropriate data is automatic single-cell tracking using time-lapse video microscopy. We describe and apply newly developed computational algorithms that allow for an automated generation of high-content data of single-cell characteristics at high temporal and spatial resolution, together with the reconstruction and statistical evaluation of complete genealogical histories. This methodology has been applied to the particular example of purified primary human HSPCs in bioengineered culture conditions. The combination of genealogical information and dynamic profiles of cellular properties identified a marked symmetry between sibling HSPCs regarding cell cycle time, but also migration speed and growth kinetics. Furthermore, we demonstrate that this symmetry of HSPC siblings can be altered by exogenous cues of the local biomimetic microenvironment. Using the example of HSPC growth in biomimetic culture systems, we show that our approach provides a valuable tool for the quantitative analysis of dynamic single-cell features under defined invitro conditions, allowing for integration of functional and genealogical data. The efficiency and accuracy of our approach pave the way for new and intriguing insights into the organizational principles of developmental patterns and the respective influence of exogenous cues not limited to the study of primary HSPCs.

Engineering Biomimetic Culture Systems: Impact On Human Bone Marrow-Derived Stem Cells.

Abstract 3628Poster Board III-564The bone marrow (BM) harbours haematopoietic stem/progenitor cells (HSCs) in anatomically distinct sites (niches) where HSCs are subjected to regulatory cues such as cytokines, cell-cell contacts and extra-cellular matrix (ECM) all of which control stem cell fate. In particular mesenchymal stromal cells (MSCs) are an integral part of the bone marrow and are known to be key regulators of the HSC niche. We have previously shown that bio-artificial scaffolds can have a significant impact on the in vitro behaviour of MSCs. Here, we are therefore focussing on the role of (native) ECM within the MSC-HSC microenvironment by building on our previous findings and published data (Seib et al.,Tissue Eng Part A., 2009 in press). Thus the aim of the current study is (a) to identify niche-specific ECM components and (b) the use of such ECMs for in vitro culture of BM-derived stem cells. To mimic the natural ECM composition of the BM, different ECM types were generated from BM-derived cells using (a) Dexter cultures, (b) standard MSC cultures, (c) MSCs subjected to osteogenic differentiation. After 10 days of culture those MSC-derived ECMs were decellularised using 0.5% Triton-X and 20mM NH4OH leaving only the ECM behind (verified by scanning electron microscopy). Those ECMs were used as a substrate for a second culture of MSCs, which were analysed for their proliferation and differentiation potential. Cell-free ECM from standard MSC cultures improved MSC proliferation compared to cells grown on regular tissue culture plastic (TCP) over the period of 8 days. Most notably, all cell-free ECM preparations lead to a significant difference in the cytoskeletal arrangement of MSCs during the first 2 days of culture compared to TCP controls. Cultivation of MSCs on native ECM provided a guiding structure for those cells to grow into, and helped to maintain an elongated cell shape compared to substantial cell spreading on TCP (roundness 0.2 versus 0.5 and cell area of 2.2 versus 8.2mm2, respectively, p<0.001, n=60. A factor of 1 was set to equate to a perfect circle). Next, we investigate if native ECM could either directly improve HSC cultures or maximise MSC feeder characteristics. For the latter set of studies MSCs were initially cultured for 7 days on cell-free ECM (from standard MSC cultures) and subsequently co-cultured with human peripheral blood CD34+ HSCs in serum free medium supplemented with cytokines (Tpo, Flt3, and SCF at 10ng/ml). Following a 14 day culture period up to 3.5-fold more CD34+ cells were present in ECM co-cultures compared to TCP co-cultures that was accompanied with an overall expansion of CD45+ cells of 109-fold versus 35-fold, respectively. Our data suggest that ECM preparations derived from MSCs might be useful to accomplish better expansion of HSCs under defined culture conditions. In addition, this system permits the identification of bimolecular key components that can be utilized in the future design of simple and robust carrier systems for improved HSC maintenance in vitro. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Maintenance and Expansion of Hematopoietic Stem/Progenitor Cells in a Biomimetic Hematopoietic Cells Niche.

As main hematopoietic organ, bone marrow have three dimensional microenvironment for hematopoietic stem/progenitor cells grow in, so call “hematopoietic cells niche”, which are composed by stromal cells and extracelluar matrix. The interactions of cell to cell and cell to matrix between stem/progenitor cells with hematopoietic niche are facilitated by its three dimensional conformation. The biology behaviors of hematopoietic stem cells are mediate by many signal transductions between stem/progenitor cells with their corresponding microenvironment. Now there are strong evidence from animal model study suggests that osteoblasts might play an essential role in creation of a hematopoietic stem cell niche and thereby regulation of stem cell maintenance, proliferation, and maturation. In light of the structure-function relationship of bone marrow topography, we conceived a biomimetic culture system (3D culture system) with bio-derived bone as framework, composited with human marrow mesenchymal stem cells, and induced the cells into osteoblasts to simulate the effects of hematopoietic osteobalst niche. CD 34+ cells or mononuclear cells separated from umbilical cord blood were cultured for 2∼5 weeks in the 3D culture system and also in a conventional 2D culture system as control without additional cytokine supplement. Based on our results, higher expression of extracelluar matrix and N-cadherin were observed in 3D culture system compared to 2D system. At 2 weeks culture, 3D culture system showed higher number of CD34+ cells and CD34+/CD38- cells when compared with the input (P<0.05), the increased cells were predominant CD34+/CD38-cells. Although CD34+ cells were decreased at 5 weeks culture; nevertheless, CD34+/CD38- cells were still maintained at high level. We also observed that imbedding MNCs with a higher percentage of CD34+/CD38-cells cultured in 3D system (P<0.05), which may represent a down regulation of CD38 phenotype during culture. The function of cultured cells was evaluated in colony forming unit (CFU) assay and long term culture initial cell (LTC-IC) assay. 3D system produced higher expansion of CFU progenitors than 2D system (7.13–8.89 times vs. 1.22–1.31times) after 2 weeks culture. Of note, the colony distribution of 3D system manifested higher percentage of BFU-E and CFU-GEMM, while 2D system showed mainly CFU-GM. LTC-IC represents the primitive progenitor, 3D system showed a 6.2 times increment over input after 2 weeks culture. Furthermore, it was competent to maintain the immaturation of hematopoietic progenitor cells (HPCs) over 5 weeks. This study demonstrated that our 3D culture system constructed with the bio-derived bone composited with induced osteoblast is capable to allow maintenance and expansion of primitive hematopoietic progenitor cells in vitro. It may open a new avenue to study HSCs/HPCs behaviors and to achieve sustained primitive progenitor cell expansion.

Engineering tumors with 3D scaffolds

Microenvironmental conditions control tumorigenesis and biomimetic culture systems that allow for in vitro and in vivo tumor modeling may greatly aid studies of cancer cells' dependency on these conditions. We engineered three-dimensional (3D) human tumor models using carcinoma cells in polymeric scaffolds that recreated microenvironmental characteristics representative of tumors in vivo. Strikingly, the angiogenic characteristics of tumor cells were dramatically altered upon 3D culture within this system, and corresponded much more closely to tumors formed in vivo. Cells in this model were also less sensitive to chemotherapy and yielded tumors with enhanced malignant potential. We assessed the broad relevance of these findings with 3D culture of other tumor cell lines in this same model, comparison with standard 3D Matrigel culture and in vivo experiments. This new biomimetic model may provide a broadly applicable 3D culture system to study the effect of microenvironmental conditions on tumor malignancy in vitro and in vivo.

Cardiac tissue engineering

We hypothesized that clinically sized (1-5 mm thick),compact cardiac constructs containing physiologically high density of viable cells (?108 cells/cm3) can be engineered in vitro by using biomimetic culture systems capable of providing oxygen transport and electrical stimulation, designed to mimic those in native heart. This hypothesis was tested by culturing rat heart cells on polymer scaffolds, either with perfusion of culture medium (physiologic interstitial velocity, supplementation of per fluorocarbons), or with electrical stimulation (continuous application of biphasic pulses, 2 ms, 5 V, 1 Hz). Tissue constructs cultured without perfusion or electrical stimulation served as controls. Medium perfusion and addition of per fluorocarbons resulted in compact, thick constructs containing physiologic density of viable, electromechanically coupled cells, in contrast to control constructs which had only a?100 ?m thick peripheral region with functionally connected cells. Electrical stimulation of cultured constructs resulted in markedly improved contractile properties, increased amounts of cardiac proteins, and remarkably well developed ultrastructure (similar to that of native heart) as compared to non-stimulated controls. We discuss here the state of the art of cardiac tissue engineering, in light of the biomimetic approach that reproduces in vitro some of the conditions present during normal tissue development.