Membrane-based biomaterials and devices for the development of microtissues

New therapeutic areas especially the development of neo-organs with complex three-dimensional structure may offer new solution to tissue loss or organ failure. Cell trans-plantation is primarily useful for replacing small areas of tissue. Bioartificial homologues are necessary to replace larger tissue areas or whole organs. For the biofabrication of an organ or tissue is required a biomimetic approach that utilizes expandable cells, a cell-affinity bio-material that serves as scaffold and an optimal bioreactor. Micro- and nano-structured mem-brane bioartificial systems consisting of functional cells and polymeric membranes can be used for the reconstruction of tissue analogous because of the high control at molecular level of cell microenvironment. These artificial systems compartmentalize cells in micro and nanostructured complexes providing a wide surface area for the cell adhesion and ensuring a continuous and selective transport of nutrients and metabolites to and from cells. Membrane systems are able to create a biomimetic environment with highly selective and specific physico-chemical, mor-phological and transport properties. Tailor-made membranes designed and operated according to well-defined engineering criteria are able to sustain specific functions, to provide adequate transport of oxygen, nutrients and catabolites throughout the cellular compartment, and to sup-ply appropriate biomechanical stimuli of the developing tissue. Membranes with specific phys-ico-chemical, morphological and transport properties would be able to modulate the adhesion, proliferation and differentiation of cells, which are fundamental processes for tissue regenera-tion by governing the mass transfer of molecules that generate a precisely controlled microen-vironment that mimic the specific features of in vivo environment. Attempt to engineering bi-ological tissues in vitro have been pursued by applying novel concepts of bioreactor design and membranes to enhance the ability to trigger biological signals that promote the morphogenesis of tissue. This approach allows the realization of microtissues inducing self-assembling process of spheroids through the use of membranes with selective permeability, specific surface and mechanical properties. A designed approach has been utilized for the development of a 3D liver system. This approach makes use of primary human sinusoidal endothelial cells, stellate cells and hepatocytes that are seeded sequentially in a hollow fiber membrane bioreactors in order to mimic the layers of cells found in vivo. The organotypic system was maintained functionally active in the HF membrane bioreactor, which ensured a continuous perfusion of cells and the selective mass transfer of molecules to and from cell compartment creating a physiologically relevant microenvironment. A novel membrane bioreactor was created to provide a 3D well-controlled microenvironment for neuronal outgrowth. The bioreactor consisted of poly-L-lactic acid highly aligned microtube array membranes assembled in parallel within a chamber that establish an intraluminal and an extraluminal compartment whose communication occurs through the pores of the membrane walls. The high performing device built up in this study modulated and enhanced neuronal outgrowth, thanks to a synergistic action of the membrane properties and the uniform dynamic bioreactor microenvironment. The membrane bioreactor besides enhancing acquisition of neuronal phenotype guided the neurons into a defined aligned orientation according to the direction of the microtubes. Overall, our bioreactor accomplished two main achievements: it promotes long-term growth and differentiation of neuronal cells, and orients neurite alignment generating a neuronal tissue-like construct.