This shows tissue of smooth muscle at 400x magnification.
smooth muscle tissue is made up of individual cells long from 20 mM to 0.5 mm with a central oval nucleus evident. The smooth muscle is under the control of the autonomic nervous system and the endocrine system. The smooth muscle tissue generates two types of contraction, a "rhythmic", where you detect periodic pulses that spread in all the tissue, and a "tonic", which gives the walls visceral a state of partial contraction said "muscle tone" . Generally, in this muscle tissue we find a contraction speed lower than the other tissues, with the ability, however, to maintain it for a long time and with a relatively low energy expenditure. The smooth muscle cells, depending on their function, assume a different spatial location. In the vessels have a circular pattern, so as to create a set of rings that can facilitate the rhythmic movement. In the viscera and in large hollow organs, however, the smooth muscle cells, take, generally, a circular, inner, and one, perpendicular to the first, in longitudinal arrangement, more external. This organization allows a better grip of the viscera and facilitates the movement of the contents of the gut in its path, thanks to the peristaltic movements of the wall. In some hollow organs, such as the urinary bladder and the uterus, the laminae muscle assume a less regular pattern and form a dense network so as to have, in addition to the function of support and typical shrinkage of each muscle tissue, also the task of facilitating the extension in space and therefore to increase the capacity of the containment body itself. This type of muscle tissue is said "flexiform".
A bioreactor is generally defined as a system capable of providing the cells the intake of nutrients and removal of waste products of cell metabolism. Normally bioreactors are used in industry for the cultivation of bacteria, yeasts, fungi, algae, plant cells and animal cells on a large scale, thanks to the advantage of being able to optimize the control of vital parameters with respect to culture performed on the plate. The environment in which they grow the cells is tightly controlled from the point of view of the chemical-physical parameters: thanks to the presence of special sensors can monitor specific parameters of the crop, such as the temperature, the concentration of gases dissolved in the culture medium, the pH, concentration of inorganic ions and carbohydrates. In case be detected alterations of these components, control systems ensure their appropriate correction via the administration of liquid or gas.
The cells can grow in suspension or adherent to a substrate; the homogeneous distribution of the cell suspension through the substrate is ensured by a perfusion system that uses a flow of liquid through the substrate. Even the flow of culture medium within the bioreactor can increase the viability and cellular activity. The use of the bioreactors was thus proposed for the construction of artificial tissues in a three-dimensional system, where also the mechanical stress influence the development and tissue remodeling. In this regard, the bioreactor can be used to generate specific physical stimuli, for example compression and tension, which can stimulate the growth and maturation of the tissues during their development in vitro . Numerous studies have been made for the building of tissues in the bioreactor such as cartilage, tendon and blood vessels, as well, although still at the theoretical level, for the generation of organs such as liver, pancreas and kidney.
The history of the use of artificial tissues as a substitute for compromised tissue is born in the eighties, when they were put in place the conditions to expand the keratinocytes, the cells of the epidermis that is, to reconstruct in the laboratory flaps of tissue to be transplanted into patients who had suffered burns. From a small skin biopsy of the patient are isolated keratinocytes, cultivated in a test tube until the formation of a package that can be transplanted on the surface burned. Other interesting applications have focused on the reconstruction of the corneal epithelium of patients who had undergone thermal or chemical burns to the eye. More recently the interest of scientists turned to the regeneration and repair of skeletal tissues, bone and cartilage, through the use of cells isolated from the bone marrow, respectively, or from a small biopsy of cartilage. In the case of large bone defects, the regenerative ability of the bone is insufficient to ensure the repair of the lesion and the current therapeutic techniques of transplantation of autologous bone or from donor have limitations. Stromal cells derived from bone marrow can in these cases represent a suitable cell type in the regeneration of bone tissue, given their osteogenic potential. There are also numerous studies related to the use of cartilage cells, chondrocytes for the repair of cartilage lesions. The progress achieved by encouraging scientific research have opened new possibilities in the use of tissue engineering for the treatment of diabetes, the regeneration of cardiac muscle tissue when the heart is damaged by a heart attack and the use of endothelial cells for the coating of implants vascular. Even the nerve cells destroyed by degenerative diseases such as Parkinson's disease and Alzheimer's disease could be replaced by the use of cell therapy.
The development of knowledge of cell biology integrated with those of bioengineering has recently opened new perspectives in the field of tissue engineering has established itself, which proposes the use of the cells in the laboratory for the construction of artificial biological tissues to be used as a substitute for damaged ones in result of disease or trauma. This would help solve the problems of reduced availability of organs for transplantation and the risk of graft rejection derived from the donor. The association of cells with biocompatible and biodegradable materials is leading to the production of engineered tissues transplantable. The actors involved in the scenario biotech tissue regeneration are basically three: the cells, signaling molecules and biomaterials .
To ensure the maintenance of the function of the implanted cells using a material or scaffold that acts as a scaffold to guide the three-dimensional organization of the cells in the final construction. The scaffold , synthetic or natural, must be able to support the growth and differentiation of cells, ie it must recreate the more possible the microenvironment characteristic of the fabric that you want to replace. Once transplanted, it will perform the function of guide in tissue growth, before being completely resorbed. For the preparation of the plant to be transplanted, the cells are derived from a fragment of the healthy tissue of the patient to which you want to reconstruct the damaged tissue; follows the combination between the cells and biomaterial appropriate, in the presence or absence of signal molecules necessary for proper cell differentiation. Recently aroused great excitement in the scientific community as a resource in the stem cell regenerative therapy due to their ability to give rise to different cell types depending on how they are stimulated.
The process by which a relatively non-specialized cell becomes a very specialized is called 'differentiation' and affects both the embryo is an individual adult. During embryonic development, many cell types are generated from the fertilized egg cell, to get the range of cells that characterize the adult subject. The route followed by each embryonic cell differentiation is fundamentally dependent on the signals it receives from the environment; the latter, in turn, depend on the position of the cell in the embryo. As a result of the differentiation of different cell types acquire different shapes and express specific proteins: for example, the skeletal muscle cells contain contractile proteins particular, plasma cells are specialized for the production of antibodies, etc.. The differentiation processes continue in the adult body in those tissues that are subject to continuous renewal (eg., Hematopoietic cells).
Each fabric is renewed with its characteristic rhythm, thanks to the presence of stem cells undifferentiated which help keep constant the number of cells in the tissue. Stem cells are defined as undifferentiated cells capable of self-renewal, that is, to produce cells similar to themselves and to generate cells destined to differentiate. They therefore represent a reservoir of cells which the body draws to ensure the renewal of cell tissue death. An example of a stem cell is provided by the hematopoietic stem cells of the bone marrow, capable of giving rise to all cell types of the blood. The adult contains different types of stem cells, which give rise to the cells of the organs in which they are located. Recent studies have however shown that certain adult stem cells have plasticity, ie they are able to differentiate in cell types other than those of the tissue of origin.