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During the development of de novo synthesized cartilage tissue engineered constructs, transport and biophysical properties are expected to change in time and space. Monitoring and control of the evolution of these parameters are of crucial importance to process biohybrid constructs in vitro. The aim of this work was to measure fluid and macromolecular transport and evolution of mechanical properties of tissue-engineered cartilage constructs as a function of culture time and extracellular matrix (ECM) production. It was found, in agreement with other literature reports, that mechanical and fluid transport properties of the constructs correlated well with time of culture and glycosaminoglycan (GAG) content. Further, diffusion coefficients of 2 probes, dextran (500 kDa) and bovine serum albumin (BSA), correlated well with GAG production. Diffusion coefficients (D) were measured with high spatial and temporal resolution by fluorescent recovery after photobleaching (FRAP). Diffusivity steadily decreases with time while it does not vary through the thickness of the specimen. On the basis of these results, an empirical relationship between diffusion coefficient and GAG content was proposed for the 2 probes analyzed. The results of this study provide useful information to optimize and control the tissue culture process in vitro.

An intestine-on-chip has been developed to study intestinal physiology and pathophysiology as well as intestinal transport absorption and toxicity studies in a controlled and human similar environment. Here, we report that dynamic culture of an intestine-on-chip enhances extracellular matrix (ECM) remodeling of the stroma, basement membrane production and speeds up epithelial differentiation. We developed a three-dimensional human intestinal stromal equivalent composed of human intestinal subepithelial myofibroblasts embedded in their own ECM. Then, we cultured human colon carcinoma-derived cells in both static and dynamic conditions in the opportunely designed microfluidic system until the formation of a well-oriented epithelium. This low cost and handy microfluidic device allows to qualitatively and quantitatively detect epithelial polarization and mucus production as well as monitor barrier function and ECM remodeling after nutraceutical treatment.

Cystic fibrosis is characterized by lung dysfunction involving mucus hypersecretion, bacterial infections, and inflammatory response. Inflammation triggers pro-fibrotic signals that compromise lung structure and function. At present, several in vitro cystic fibrosis models have been developed to study epithelial dysfunction but none of these focuses on stromal alterations. Here we show a new cystic fibrosis 3D stromal lung model made up of primary fibroblasts embedded in their own extracellular matrix and investigate its morphological and transcriptomic features. Cystic fibrosis fibroblasts showed a high proliferation rate and produced an abundant and chaotic matrix with increased protein content and elastic modulus. More interesting, they had enhanced pro-fibrotic markers and genes involved in epithelial function and inflammatory response. In conclusion, our study reveals that cystic fibrosis fibroblasts maintain in vitro an activated pro-fibrotic state. This abnormality may play in vivo a role in the modulation of epithelial and inflammatory cell behavior and lung remodeling. We argue that the proposed bioengineered model may provide new insights on epithelial/stromal/inflammatory cells crosstalk in cystic fibrosis, paving the way for novel therapeutic strategies.

Here, we proposed an innovative organotypic cervical tumor model able to investigate the bi-directional crosstalk between epithelium and stroma as well as the key disease features of the epithelial-mesenchymal transition (EMT) process in vitro. By using a modular tissue assembling approach, we developed 3D cervical stromal models composed of primary human cervical fibroblasts (HCFs) or cervical cancer-associated fibroblasts (CCAFs) embedded in their own ECM to produce 3D normal cervical-instructed stroma (NCIS) or 3D cervical cancer-instructed stroma (CCIS), respectively. Then, we demonstrate the role of the tumor microenvironment (TME) in potentiating the intrinsic invasive attitude of cervical cancer derived SiHa cells and increasing their early viral gene expression by comparing the SiHa behavior when cultured on NCIS or CCIS (SiHa-NCIS or SiHa-CCIS). We proved the crucial role of the CCAFs and stromal microenvironment in the mesenchymalization of the cancer epithelial cells by analyzing several EMT markers. We further assessed the expression of the epithelial adhesion molecules, matricellular enzymes, non-collagenous proteins as well as ECM remodeling in terms of collagen fibers texture and assembly. This cervical tumor model, closely recapitulating key cervical carcinogenesis features, may provide efficient and relevant support to current approaches characterizing cancer progression and develop new anticancer therapy targeting stroma rather than cancer cells.

Intestine-Liver-on-chip systems can be useful to predict oral drug administration and first-pass metabolism in vitro in order to partly replace the animal model. While organ-on-chip technology can count on sophisticated micro-physiological devices, the engineered organs still remain artificial surrogates of the native counterparts. Here, we used a bottom-up tissue engineering strategy to build-up physiologically functional 3D Human Intestine Model (3D-HIM) as well as 3D Liver-microtissues (HepG2-μTPs) in vitro and designed a microfluidic Intestine-Liver-On-Chip (InLiver-OC) to emulate first-pass mechanism occurring in vivo. Our results highlight the ethanol-induced 3D-HIM hyper-permeability and stromal injury, the intestinal prevention on the liver injury, as well as the synergic contribution of the two 3D tissue models on the release of metabolic enzymes after high amount of ethanol administration.

Transdermal drug delivery represents an appealing alternative to conventional drug administration systems. In fact, due to their high patient compliance, the development of dissolvable and biodegradable polymer microneedles has recently attracted great attention. Although stamp-based procedures guarantee high tip resolution and reproducibility, they have long processing times, low levels of system engineering, are a source of possible contaminants, and thermo-sensitive drugs cannot be used in conjunction with them. In this work, a novel stamp-based microneedle fabrication method is proposed. It provides a rapid room-temperature production of multi-compartmental biodegradable polymeric microneedles for controlled intradermal drug release. Solvent casting was carried out for only a few minutes and produced a short dissolvable tip made of polyvinylpyrrolidone (PVP). The rest of the stamp was then filled with degradable poly(lactide-co-glycolide) (PLGA) microparticles (μPs) quickly compacted with a vapor-assisted plasticization. The outcome was an array of microneedles with tunable release. The ability of the resulting microneedles to indent was assessed using pig cadaver skin. Controlled intradermal delivery was demonstrated by loading both the tip and the body of the microneedles with model therapeutics; POXA1b laccase from Pleurotus ostreatus is a commercial enzyme used for the whitening of skin spots. The action and indentation of the enzyme-loaded microneedle action were assessed in an in vitro skin model and this highlighted their ability to control the kinetic release of the encapsulated compound.

The intestine is a highly heterogeneous hollow organ with biological, mechanical and chemical differences between lumen and wall. A functional human intestine model able to recreate the in vivo dynamic nature as well as the native tissue morphology is demanded for disease research and ​drug discovery. Here, we present a system, which combines an engineered three-dimensional (3D) tubular-shaped intestine model (3D In-tube) with a custom-made microbioreactor to impart the key aspects of the in vivo microenvironment of the human intestine, mimicking the rhythmic peristaltic movement. We adapted a previously established bottom-up tissue engineering approach, to produce the 3D tubular-shaped lamina propria and designed a glass microbioreactor to induce the air–liquid interface ​condition and peristaltic-like motion. Our results demonstrate the production of a villi-like protrusion and a correct spatial differentiation of the intestinal epithelial cells in enterocyte-like as well as mucus-producing-like cells on the lumen side of the 3D In-tube. This dynamic platform offers a proof-of-concept model of the human intestine. Keywords: 3D engineered tubular-shaped intestine model, Air--liquid interface, Peristaltic-like motion, Extracellular matrix, Microbioreactor

Despite the well-known role of chronic human papillomavirus (HPV) infections in causing tumors (i.e., all cervical cancers and other human malignancies from the mucosal squamous epithelia, including anogenital and oropharyngeal cavity), its persistence is not sufficient for cancer development. Other co-factors contribute to the carcinogenesis process. Recently, the critical role of the underlying stroma during the HPV life cycle and HPV-induced disease have been investigated. The tumor stroma is a key component of the tumor microenvironment (TME), which is a specialized entity. The TME is dynamic, interactive, and constantly changing—able to trigger, support, and drive tumor initiation, progression, and metastasis. In previous years, in vitro organotypic raft cultures and in vivo genetically engineered mouse models have provided researchers with important information on the interactions between HPVs and the epithelium. Further development for an in-depth understanding of the interaction between HPV-infected tissue and the surrounding microenvironment is strongly required. In this review, we critically describe the HPV-related cancers modeled in vitro from the simplified ‘raft culture’ to complex three-dimensional (3D) organotypic models, focusing on HPV-associated cervical cancer disease platforms. In addition, we review the latest knowledge in the field of in vitro culture systems of HPV-associated malignancies of other mucosal squamous epithelia (anogenital and oropharynx), as well as rare cutaneous non-melanoma associated cancer.

The use of 3D cancer models will have both ethical and economic impact in drug screening and development, to promote the reduction of the animals employed in preclinical studies. Nevertheless, to be effective, such cancer surrogates must preserve the physiological relevance of the in vivo models in order to provide realistic information on drugs’ efficacy. To figure out the role of the architecture and composition of 3D cancer models on their tumor-mimicking capability, here we studied the efficacy of doxorubicin (DOX), a well-known anticancer molecule in two different 3D cancer models: our 3D breast cancer microtissue (3D-μTP) versus the golden standard represented by spheroid model (sph). Both models were obtained by using cancer associated fibroblast (CAF) and breast cancer cells (MCF-7) as cellular component. Unlike spheroid model, 3D-μTP was engineered in order to induce the production of endogenous extracellular matrix by CAF. 3D-μTP have been compared to spheroid in mono- (MCF-7 alone) and co-culture (MCF-7/CAF), after the treatment with DOX in order to study cytotoxicity effect, diffusional transport and expression of proteins related to cancer progression. Compared to the spheroid model, 3D-μTP showed higher diffusion coefficient of DOX and lower cell viability. Also, the expression of some tumoral biomarkers related to cell junctions were different in the two models. Statements of Significance Cancer biology has made progress in unraveling the mechanism of cancer progression, anyway the most of the results are still obtained by 2D cell cultures or animal models, that do not faithfully copycat the tumor microenvironment. The lack of correlation between preclinical models and in vivo organisms negatively influences the clinical efficacy of chemotherapeutic drugs. Consequently, even if a huge amount of new drugs has been developed in the last decades, still people are dying because of cancer. Pharmaceutical companies are interested in 3D tumor model as valid alternative in drug screening in preclinical studies. However, a 3D tumor model that completely mimics tumor heterogeneity is still far to achieve. In our work we compare 3D human breast cancer microtissues and spheroids in terms of response to doxorubicin and drug diffusion. We believe that our results are interesting because they highlight the potential role of the proposed tumor model in the attempts to improve efficacy tests.

Therapeutic approaches based on nanomedicine have garnered great attention in cancer research. In vitro biological models that better mimic in vivo conditions are crucial tools to more accurately predict their therapeutic efficacy in vivo. In this work, a new 3D breast cancer microtissue has been developed to recapitulate the complexity of the tumor microenvironment and to test its efficacy as screening platform for drug delivery systems. The proposed 3D cancer model presents human breast adenocarcinoma cells and cancer-associated fibroblasts embedded in their own ECM, thus showing several features of an in vivo tumor, such as overexpression of metallo-proteinases (MMPs). After demonstrating at molecular and protein level the MMP2 overexpression in such tumor microtissues, we used them to test a recently validated formulation of endogenous MMP2-responsive nanoparticles (NP). The presence of the MMP2-sensitive linker allows doxorubicin release from NP only upon specific enzymatic cleavage of the peptide. The same NP without the MMP-sensitive linker and healthy breast microtissues were also produced to demonstrate NP specificity and selectivity. Cell viability after NP treatment confirmed that controlled drug delivery is achieved only in 3D tumor microtissues suggesting that the validation of therapeutic strategies in such 3D tumor model could predict human response. Statement of Significance A major issue of modern cancer research is the development of accurate and predictive experimental models of human tumors consistent with tumor microenvironment and applicable as screening platforms for novel therapeutic strategies. In this work, we developed and validated a new 3D microtissue model of human breast tumor as a testing platform of anti-cancer drug delivery systems. To this aim, biodegradable nanoparticles responsive to physiological changes specifically occurring in tumor microenvironment were used. Our findings clearly demonstrate that the breast tumor microtissue well recapitulates in vivo physiological features of tumor tissue and elicits a specific response to microenvironmentally-responsive nanoparticles compared to healthy tissue. We believe this study is of particular interest for cancer research and paves the way to exploit tumor microtissues for several testing purposes.

We fabricated three-dimensional microtissues with the aim to replicate in vitro the composition and the functionalities of the tumor microenvironment. By arranging either normal fibroblasts (NF) or cancer-activated fibroblasts (CAF) in two different three dimensional (3D) configurations, two kinds of micromodules were produced: spheroids and microtissues. Spheroids were obtained by means of the traditional cell aggregation technique resulting in a 3D model characterized by high cell density and low amount of extracellular proteins. The microtissues were obtained by culturing cells into porous gelatin microscaffolds. In this latter configuration, cells assembled an intricate network of collagen, fibronectin and hyaluronic acid. We investigated the biophysical properties of both 3D models in terms of cell growth, metabolic activity, texture and composition of the extracellular matrix (via histological analysis and multiphoton imaging) and cell mechanical properties (via Particle Tracking Microrheology). In the spheroid models such biophysical properties remained unchanged regardless to the cell type used. In contrast, normal-microtissues and cancer-activated-microtissues displayed marked differences. CAF-microtissues possessed higher proliferation rate, superior contraction capability, different micro-rheological properties and an extracellular matrix richer in collagen fibronectin and hyaluronic acid. At last, multiphoton investigation revealed differences in the collagen network architecture. Taken together, these results suggested that despite to cell spheroids, microtissues better recapitulate the important differences existing in vivo between normal and cancer-activated stroma representing a more suitable system to mimic in vitro the stromal element of the tumor tissues. Statement of Significance This work concerns the engineering of tumor tissue in vitro. Tumor models serve as biological equivalent to study pathologic progression and to screen or validate the drugs efficacy. Tumor tissue is composed by malignant cells surviving in a microenvironment, or stroma. Stroma plays a pivotal role in cancer progression. Current in vitro models, i.e. spheroids, can’t replicate the phenomena related to the tumor stroma remodeling. For this reason, to better replicate the tumor physiology in vitro that include functional and morphological changes, a novel 3D cancer model is proposed.

Many of the existing three-dimensional (3D) cancer models in vitro fail to represent the entire complex tumor microenvironment composed of cells and extra cellular matrix (ECM) and do not allow a reliable study of the tumoral features and progression. In this paper we reported a strategy to produce 3D in vitro microtissues of pancreatic ductal adenocarcinoma (PDAC) for studying the desmoplastic reaction activated by the stroma–cancer crosstalk. Human PDAC microtissues were obtained by co-culturing pancreatic cancer cells (PT45) and normal or cancer-associated fibroblasts within biodegradable microcarriers in a spinner flask bioreactor. Morphological and histological analyses highlighted that the presence of fibroblasts resulted in the deposition of a stromal matrix rich in collagen leading to the formation of tumor microtissues composed of a heterotypic cell population embedded in their own ECM. We analyzed the modulation of expression of ECM genes and proteins and found that when fibroblasts were co-cultured with PT45, they acquired a myofibroblast phenotype and expressed the desmoplastic reaction markers. This PDAC microtissue, closely recapitulating key PDAC microenvironment characteristics, provides a valuable tool to elucidate the complex stroma–cancer interrelationship and could be used in a future perspective as a testing platform for anticancer drugs in tissue-on-chip technology. Statement of Significance Tumor microenvironment is extremely complex and its organization is due to the interaction between different kind of cells and the extracellular matrix. Tissue engineering could give the answer to the increasing need of 3D culture model that better recapitulate the tumor features at cellular and extracellular level. We aimed in this work at developing a microtissue tumor model by mean of seeding together cancer cells and fibroblasts on gelatin microsphere in order to monitor the crosstalk between the two cell populations and the endogenous extracellular matrix deposition. Results are of particular interest because of the need of heterotypic cancer model that can replicate the complexity of the tumor microenvironment and could be used as drug screening platform.

Tissue-on-chip (TOC) systems aim at replicating complex biological dynamics in vitro with the potential either to improve the understanding of human biology or to develop more accurate therapeutic strategies. To replicate faithfully the intricate interrelationships between cells and their surrounding microenvironment, the three-dimensional (3D) tissue model must possess a responsive extracellular matrix (ECM). ECM remodeling plays a pivotal role in guiding cells and tissues functions and such aspect is somewhat denied during in vitro studies. For this purpose, we fabricated a micro-perfusion bioreactor capable to sustain the viability of 3D engineered tissue models recapitulating the process of the native ECM deposition and assembly. Engineered human dermis micro-tissue precursors (HD-mu TP) were used as building blocks to generate a final tissue. HD-mu TP were loaded in the perfusion space of the micro-perfusion bioreactor and, under the superimposition of different fluid dynamic regimes and biochemical stimulation, they synthesized new collagen proteins that were, then, assembled in the perfusion space forming a continuum of cells embedded in their own ECM. The micro-perfusion bioreactor was fabricated to allow the on-line monitoring of the oxygen consumption and the assembly of the newly formed collagen network via real time acquisition of the second harmonic generation (SHG) signal. The possibility to detect the collagen reorganization due to both fluid dynamic and biochemical stimulation, let us to define the optimal perfusion configuration in order to obtain a TOC system based on an endogenous and responsive ECM.

The in vitro fabrication of an endogenous cardiac muscle would have a high impact for both in vitro studies concerning cardiac tissue physiology and pathology, as well as in vivo application to potentially repair infarcted myocardium. To reach this aim, we engineered a new class of cardiac tissue precursor (CTP), specifically conceived in order to promote the synthesis and the assembly of a cardiac extracellular matrix (ECM). The CTPs were obtained by culturing a mixed cardiac cell population, composed of myocyte and non-myocyte cells, into porous gelatin microspheres in a dynamic bioreactor. By engineering the culture conditions, the CTP developed both beating properties and an endogenous immature cardiac ECM. By following a bottom-up approach, a macrotissue was fabricated by molding and packing the engineered tissue precursor in a maturation chamber. During the macrotissue formation, the tissue precursors acted as cardiac tissue depots by promoting the formation of an endogenous and interconnected cardiac network embedding the cells and the microbeads. The myocytes cell fraction pulled on ECM network and induced its compaction against the internal posts represented by the initial porous microbeads. This reciprocal interplay induced ECM consolidation without the use of external biophysical stimuli by leading to the formation of a beating and endogenous macrotissue. We have thus engineered a new class of cardiac micromodules and show its potential for the fabrication of endogenous cardiac tissue models useful for in vitro studies that involve the cardiac tissue remodeling.

In this work, a new model of breast cancer is proposed featuring both epithelial and stromal tissues arranged on a microfluidic chip. The main task of the work is the in vitro replication of the stromal activation during tumor epithelial invasion. The activation of tumor stroma and its morphological/compositional changes play a key role in tumor progression. Despite emerging evidences, to date the activation of tumor stroma in vitro has not been achieved yet. The tumor-on-chip proposed in this work is built in order to replicate the features of its native counterpart: multicellularity (tumor epithelial cell and stromal cell); 3D engineered stroma compartment composed of cell-assembled extracellular matrix (ECM); reliable 3D tumor architecture. During tumor epithelial invasion the stroma displayed an activation process at both cellular and ECM level. Similarly of what repeated in vivo, ECM remodeling is found in terms of hyaluronic acid and fibronectin overexpression in the stroma compartment. Furthermore, the cell-assembled ECM featuring the stromal tissue, allowed on-line monitoring of collagen remodeling during stroma activation process via real time multiphoton microscopy. Also, trafficking of macromolecules within the stromal compartment has been monitored in real time.

Tissue-engineered constructs can be fabricated by the assembly of smaller building blocks in order to mimic much of the native biology that is often made from repeating functional units. Our aim was to realize a three-dimensional (3-D) tissue-like construct in vitro by inducing the assembly of functional micrometric tissue precursors (microTPs). MicroTPs were obtained by dynamic cell seeding of bovine fibroblasts on porous gelatine microcarriers using a spinner flask bioreactor. During the dynamic seeding, cells adhered, proliferated and synthesized a thin layer of extracellular matrix (ECM) in and around the macroporous beads, generating the microTPs. The analysis showed that the ECM produced was rich in type I collagen. The cells and ECM layer around the microTPs allowed their biological sintering via cell-cell and cell-matrix interaction after only a few days of dynamic seeding. The assembling ability of microTPs was exploited by placing them in a maturation chamber. After 1 week of culture disc-shaped constructs (1cm in diameter, 1mm in thickness) of completely assembled microTPs were collected. The biohybrid obtained presented both a homogeneous and compact aspect. Moreover, histological and immunohistochemical analyses revealed an abundant ECM, rich in type I collagen, interconnecting the microTPs. The results obtained in this survey pave the way to realizing a 3-D dermal tissue equivalent by means of a bottom-up tissue engineering approach.

Three-dimensional (3D) cell cultures have recently garnered great attention because they promote levels of cells differentiation and tissue organisation not possible in conventional two-dimensional (2D) culture systems. Cancer development is a complex process regulated by interactions between epithelial cells, activated stromal cells, and soluble and insoluble components of the extracellular matrix (ECM). As a consequence, in the field of cancer biology a 3D tumour model that accurately recreates the in vivo tumour phenotype would be a valuable tool for studying tumour biology and would allow better pre-clinical evaluation of anticancer drug candidates. Here, we review the 3D tumour models currently available and the more advanced techniques from the tissue-engineering field used to create a more clinically accurate ex vivo tumour model. Moreover, we highlight the drastic differences in drug responses between 3D and 2D models and give a glance to the emerging multi-organ microdevices that can mimic in vivo tissue-tissue interactions.

Tissue engineering aims at creating biological tissues to improve or restore the function of diseased or damaged tissues. To enhance the performance of engineered tissues, it is required to recapitulate in vitro not only the composition but also the structural organization of native tissues. To this end, tissue engineering techniques are beginning to focus on generating micron-sized tissue modules having specific microarchitectural features that can be used alone as living filler in the damaged areas or serve as building blocks to engineer large biological tissues by a bottom-up approach. This work discusses the shortcomings related to traditional ???top-down??? strategies and the promises of emerging ??????bottom-up??? approaches in creating engineered biological tissues. We first present an overview of the current tissue-building techniques and their applications, with an analysis of the potentiality and shortcomings of different approaches. We then propose and discuss a novel method for the biofabrication of connective-like micro tissues and how this technique can be translated to cardiac muscle fabrication.

In this study we realized a three-dimensional human dermis equivalent (3D-HDE) and, by exploiting multi-photon microscopy (MPM) we validated its use as an in vitro model to study collagen network re-arrangement under simulated solar exposure. The realization of 3D-HDE has been pursed by means of a bottom-up tissue engineering strategy that comprises firstly the fabrication of micron sized tissue building blocks and then their assembly in a 3D tissue construct. The building blocks injected in a maturation chamber, and cultured under optimized culture condition, were able to fuse due to the establishment of cell-cell and cell-extra cellular matrix (ECM) interactions that induced a biological sintering process resulting in 3D-HDE production. The final 3D tissue was made-up by fibroblasts embedded in their own ECM rich in endogenous collagen type I, resembling the composition and the architecture of native human dermis. Second Harmonic Generation (SHG) and Two-Photon Excited Fluorescence (TPEF) imaging have been exploited to assess modification in collagen assembly before and after UV irradiation. Textural features and SHG to TPFE ratio of the endogenous ECM within 3D-HDE have been shown to vary after UVA irradiation, proving the hypothesis that the 3DHDE realized can be used as biological platform in vitro to study ECM modifications induced by photo-damage.

Objective: To identify possible sonographic prenatal parameters and postnatal parameters in order to obtain more bankable cord blood units (CBUs) containing a high number of primitive progenitor cells, allowing CBUs to be used as a source of haematopoietic progenitors for clinical transplantation. Study design: Prospective study undertaken in the Department of Gynaecology, Obstetrics and Reproductive Science, Second University of Naples, Italy. In total, 219 unrelated CBU donors were enrolled. Ultrasound parameters (biparietal diameter, head circumference, abdominal circumference, femur length, estimation of fetal weight, umbilical artery pulsatility index), collected at hospital admission, together with birth weight and placental weight, were correlated with bankable CBU parameters (CBU volume, total nucleated cell count, CD34+ cell count). Results: Femur length and abdominal circumference correlated positively with bankable CBUs. Receiver operating curve analysis showed that these parameters can identify bankable CBUs. Conclusions: This is the first prospective study to show the relationship between ultrasonographic fetal parameters at term and the possibility of obtaining high-quality CBUs. As such, cord blood banking could be improved worldwide by performing low-cost ultrasonographic scans. (C) 2013 Elsevier Ireland Ltd. All rights reserved.

Tissue engineering creates biological tissues that aim to improve the function of diseased or damaged tissues. In this chapter, we examine the promise and shortcomings of “top-down” and “bottom-up” approaches for creating engineered biological tissues. In top-down approaches, the cells are expected to populate the scaffold and create the appropriate extracellular matrix and microarchitecture often with the aid of a bioreactor that furnish the set of stimuli required for an optimal cellular viability. Specifically, we survey the role of cell material interaction on oxygen metabolism in three-dimensional (3D) in vitro cultures as well as the time and space evolution of the transport and biophysical properties during the development of de novo synthesized tissue-engineered constructs. We show how to monitor and control the evolution of these parameters that is of crucial importance to process biohybrid constructs in vitro as well as to elaborate reliable mathematical model to forecast tissue growth under specific culture conditions. Furthermore, novel strategies such as bottom-up approaches to build tissue constructs in vitro are examined. In this fashion, tissue building blocks with specific microarchitectural features are used as modular units to engineer biological tissues from the bottom up. In particular, the attention will be focused on the use of cell seeded microbeads as functional building blocks to realize 3D complex tissue. Finally, a challenge will be the potential integration of bottom-up techniques with more traditional top-down approaches to create more complex tissues than are currently achievable using either technique alone by optimizing the advantages of each technique.

Bottom-up approach is an appealing strategy to build complex three-dimensional (3D) viable tissues in vitro starting from microtissue precursors (μTP). In this work we biofabricated a thick dermal-like tissue by sequentially combining two steps: a μTPs production and assembly followed by tissue maturation in a purpose-built bioreactor. The μTPs were produced by first seeding bovine primary fibroblasts on gelatine microparticles and then cultivating them in stirring conditions until a thick layer of ∼80μm of de novo synthesized extracellular matrix uniformly covered the microparticle surface. The μTPs were then loaded into a cylindrical chamber (2mm in depth and 35mm in diameter) and let to maturate and assemble into a 3D viable biohybrid tissue under specific fluid flow conditions. Several combinations of perfusion and/or tangential fluid flow were applied and their effect on the tissue formation and maturation was assessed. Results show that structural composition and mechanical features of the final 3D bioengineered tissue are strongly affected by the hydrodynamic environment and demonstrate that by optimizing culture conditions a 3D viable tissue with properties similar to that of native derma could be produced. © 2011 Mary Ann Liebert, Inc.