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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.

We have previously reported that the thyroid-targeted expression of the RET/PTC3 oncogene (Tg-RET/PTC3) in transgenic mice induces follicular hyperplasia with papillary architecture, resulting in a modest increase of the thyroid gland volume, followed by the appearance of papillary carcinomas in approximately 1-year-old animals. In order to analyze the genetic alterations that may cooperate with RET/PTC3 in the development or progression of thyroid tumors, we interbred Tg-RET/PTC3 mice with Tg-E7 transgenic mice, which express the E7 oncogene of the human papilloma virus 16 in thyroid cells. Tg-E7 mice develop large colloid goiters with small papillae and well-differentiated thyroid carcinomas in older animals. Here we show that thyroid lesions in Tg-RET/PTC3-Tg-E7 double transgenics were morphologically different from those occurring in Tg-RET/PTC3 mice, while they were virtually indistinguishable from those occurring in Tg-E7 mice. In addition, the coexpression of RET/PTC3 and E7 oncogenes neither enhanced the malignant phenotype nor reduced the latency period of thyroid lesions with respect to parental transgenic lines. We conclude that the coexpression of RET/PTC3 and E7 lacks any cooperative effect in the neoplastic transformation of thyroid cells and that the E7-induced thyroid phenotype is dominant with respect to the RET/PTC3 one.

The aim of this work was to analyse the hindrance effect of the naturally derived bioactive polymer hyaluronic acid (HA) considered responsible for the interstitium transport regulation. The diffusion coefficient measurements of several macromolecular probes, different for nature and dimension have been performed within HA water solution and HA collagenous gels in order to study the role of HA on the control of macromolecular transport. HA matrices showed less diffusional hindrance then HA water solutions. Moreover, the HA, interpenetrating with the collagen fibres, selectively affected the transport, depending on the HA concentration. These preliminary studies indicate that the biopolymer HA can be employed to design novel biopolymer interpenetrating gels suitable as molecular sieves for membrane permeation and controlled drug delivery.

The fate of any tissue engineering implant relies upon an adequate oxygen and nutrients supply throughout the cellular construct and, hence, by the ability of the scaffold to induce and guide vascular ingrowth. However, implant vascularization is usually an uncontrolled process that takes several weeks. In this work, we assessed the feasibility of controlling vascular sprout rate and direction within three-dimensional collagen–hyaluronic acid semi-interpenetrated networks by modulating the spatial distribution of the matricellular cues. Results indicated that increasing amount of hyaluronic acid (HA) within the matrix led to a progressive inhibition of sprouting. In HA-rich matrices, the sprout number and the propagation rate showed a 2.7- and 4-fold reduction, respectively, compared to collagen matrices. Furthermore, by creating HA gradients within the collagen network, we were able to direct and enhance the sprouting rate. This study provides an experimental platform for controlling vascularization of engineered tissues. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2007

The use of embryonic stem (ES) cells as unlimited cell source in tissue engineering has ignited the hope of regenerating any kind of tissue in vitro. However, the role of the material in control and guidance of their development and commitment into complex and viable three-dimensional (3D) tissues is still poorly understood. In this work, we investigate the role of material composition and structure on promoting ES cells growth and differentiation, by culturing mouse ES cell-derived embryoid bodies (EBs) in various semi-interpenetrating polymer networks (SIPNs), made of collagen, fibronectin (FN) and laminin (LM). We show that both composition and strength of the supportive matrix play an important role in EBs development. High collagen concentrations inhibit EBs cavitation and hence the following EBs differentiation, by inhibiting apoptosis. The presence of FN in 3D collagen constructs strongly stimulates endothelial cell differentiation and vascularization. Conversely, LM increases the ability of ES cells to differentiate into beating cardiomyocytes. Our data suggest that matrix composition has an important role in EBs development and that it is possible to influence stem cell differentiation toward preferential pattern, by modulating the physical and biochemical properties of the scaffold.