Self-crosslinked fibrous collagen/chitosan blends: Processing, properties evaluation and monitoring of degradation by bi-fluorescence imaging.

Porous collagen/chitosan scaffolds with different Collagen:Chitosan (Coll:Ch) ratios were prepared by freeze-drying followed by self-crosslinking via dehydrothermal treatment (DHT) and characterized as biomaterials for tissue engineering. Cy7 and Cy5.5 fluorochromes were covalently grafted to collagen and chitosan, respectively. Thus, it was possible, using optical fluorescence imaging of the two fluorochromes, to simultaneously track their in vivo biodegradation, in a blend scaffold form. The fluorescence signal evolution, due to the bioresorption, corroborated with histological analysis. In vitro cytocompatibility of Coll:Ch blend scaffolds were evaluated with standardized tests. In addition, the scaffolds showed a highly interconnected porous structure. Extent of crosslinking was analyzed by convergent analysis using thermogravimetry, Fourier Transform Infrared Spectroscopy and PBS uptake. The variations observed with these techniques indicate strong interactions between collagen and chitosan (covalent and hydrogen bonds) promoted by the DHT. The mechanical properties were characterized to elucidate the impact of the different processing steps in the sample preparation (DHT, neutralization and sterilization by ß-irradiation) and showed a robust processing scheme with low impact of Coll:Ch composition ratio.

Scaffold vascularization: a challenge for three-dimensional tissue engineering.

The prevalent challenge facing tissue engineering today is the lack of adequate vascularization to support the growth, function, and viability of tissue substitutes that require blood vessel supply. Researchers rely on the increasing knowledge of angiogenic and vasculogenic processes to stimulate vascular network formation within three-dimensional tissue constructs. These processes are mainly endothelial cell-regulated, although in the context of tissue engineering, specific interactions with scaffold materials, growth factors and other cell types may require in vitro vascularization schemes to be altered accordingly. To better mimic the complete in vivo environment, increasing attention is given to the integration of co-cultures and mechanical conditioning in bioreactors. Such approaches show great promise for the enhancement of the functionality and clinical applicability of tissue engineering constructs. This paper reviews some scaffold materials used in tissue engineering and the effect of their properties on the vascularization process. Also, it specifically addresses the pivotal role of biomaterials vascularization in tissue engineering applications, along with the effect of angiogenic factors and adhesive molecules on angiogenesis. Assays and markers of angiogenesis are also outlined. One section highlights the need for bioreactor cultures and mechanical conditioning in controlling endothelial cell responses. Finally, we conclude with a brief section on the effects of oxygen concentration and hypoxia over microvessel formation.