User:Samrajaved/sandbox

Tissue Bioengineering

The bioengineering of tissues and organs, sometimes called tissue engineering and at other times regenerative medicine is emerging as a science, as a technology, and as an industry. The goal is the repair, replacement, and/or the regeneration of tissues and organs. Tissue engineering is an emerging biotechnological area, which combines various aspects of medicine, cell and molecular biology, materials science and engineering for the purpose of regenerating, repairing or replacing diseased tissues. The term ‘tissue engineering’ was officially coined by Fung in October 1987 at a National Science Foundation Workshop in Washington. Tissue bioengineering is evolving as a significant potential alternative or complementary solution to these problems, whereby tissue and organ failure is addressed by implanting natural, synthetic or semi synthetic tissue and organ mimics that are either fully functional or that grow into the required functionality. Ultimately these ‘engineered spare parts’ can be put into a patient, either by injection or by implantation of intact tissues or an entire organ. Thus, bioengineering has the potential to revolutionize methods in health care treatment to improve the quality of life for many and in the future it will provide a cost-effective and long-term solution to age related conditions. Furthermore, engineered tissues could reduce the need for organ replacement and could greatly accelerate the development of new drugs that may cure patients, thus eliminating the need for organ transplants.

Scaffolds in Bioengineering
Biomaterials in bioengineering provide instinctive support and biochemical cues to cells in tissue engineering scaffolds. Numerous biomaterials have been designed, and the selection of scaffolds depends upon the specificity of the fabricated biomaterial. Natural bioengineered materials contain fibrin, which stimulate vascular integration and angiogenesis. Collagen, a pervasive component of the extracellular matrix with various integrin-binding motifs. Others include hyaluronic acid, the basement membrane–mimicking Matrigel and alginate. Though, these natural biomaterials are less responsive and less well characterized as compared to synthetic materials to modification and engineering. To improve these limitations, a comprehensive variety of polymeric materials have been advanced for bioengineering applications. US FDA approved such synthetic materials such as poly ethylene glycol, poly lactic-co-glycolic acid based materials and some newer classifications of synthetic polymers that show better  anti-fouling characteristics , modularity responsiveness. These synthetic biomaterials have gel-forming and mechanical properties which can be modified over varied ranges and have characteristically been fabricated to provide a biochemical inert support upon which bioactive motifs can be added.

Cells for Bioengineered Tissues
Cells for tissue bioengineering are derived from donor tissue, which is disassociated into individual cells. These individual cells are either expended or implanted directly in culture, fixed to a support matrix, and after the expansion are embedded into the host. Cells used in bioengineering can be obtained from several sources. It includes cell lines and primary tissues. Source of cells may be autologous allogenic and xenogeneic. Cells obtained from autologous source are easy to isolate and grow in vitro, moreover it comprise the advantage of handling with least risk of adversative host response. Cells from allogenic source provide the advantage of banking preceding to need, however is more prospective to be intricate by the occurrence of disease transmitting viruses. Characteristically, the cells for bioengineering should be non-immunogenic, easy to isolate, highly proliferative and have the tendency to differentiate into different cell types with specified functions.

Bioengineering and Stem Cells
Current and recent strategies for bioengineering depend on autologous source from diseased tissues or organs of the host. Though, in extreme situations such as widespread last-stage organ failure, biopsy may not produce sufficient normal cells for transplantation and expansion. Therefore, stem cells hold significant promise as an alternate source of cells for such circumstances .Embryonic stem cells have great potential because of their significant properties. Embryonic stem cells have the tendency to multiply in an undifferentiated cells, however pluripotent state and the tendency to differentiate into numerous specified cell types. Though, these cells has the maximum potential to differentiate into diverse tissues, growth of human ESC involves demolition of human embryos that rises important human and ethical issues. Autologous stem cells have the advantage in bioengineering and tissue transplantation applications because these cells have the ability to become different type of cell in the body.

Bioreactors
Once cells and tissues are harvested then grown into a suitable scaffold to support the rapid growth and expansion. Furthermore it provides the essential 3D architecture. To grow the cells into the desired tissues or organs, it is important they must be needed similar microenvironment. The microenvironment conditions can fairly be mimicked by the usage of bioreactors. The use of bioreactors facilitates researches with a system capable of regulating environmental factors such as temperature, pH, mechanical forces and surface tension. The practice of these dynamic in cell culture techniques also results in the sterility maintenance and labor reduction. When these bioreactors used in a closed engineering system enables the seeding of cells and their growth, freezing and preservation of the engineered products all in the same container.

Applications of Bioengineered Tissues
Bioengineering in Orthopedics

Bioengineering is an evolving substitute for improving current treatments for bone diseases and for skeletal restoration. Besides others, bioengineering of cartilage, ligament has been the primary focus of tissue bioengineers. Bioengineering may be an approach to overcome the limitations of current therapies. Skin is the largest organ of body and the first defense system of body against infectious organisms. As it prevents the body from dehydration, holds widespread capillary systems and sweat glands and retains body temperature. Although skin cells can repair and regenerate themselves, the regeneration ability is very limited in the situation of deep burns. Bioengineered skin products were the first products and approved by FDA for clinical use. Bioengineered scaffolds for skin include polylactic acid, polyglycolic acid and their co-polymers.

Cardiovascular Bioengineering

Cardiac diseases always remain a major cause of mortality in the world. Effective treatment has been inadequate in many circumstances by the deprived potential of synthetic materials used for tissue engineering. Existing surgical treatments for damaged vessels less than six nanometer in diameter comprises bypass surgeries with autologous veins or arteries .Cardiovascular bioengineering is concentrating on the improvement of heart valves, blood vessels and myocardium. Bioengineering approaches may also be utilized to advance the function of the natural tissues, for example congestive heart failure. Therefore, bioengineering of cardiovascular tissues will surely be significant to the improvement of a central heart diseases. Existing researches on bioengineered blood vessels and tissues will one day graft an ideal blood vessel alternative.

Dental Bioengineering

Periodontal problems is one of the most common diseases of humans and dental caries continue one of the most prevailing childhood and young adult diseases. Present treatment modalities comprise bridges, dentures or implants. Recent developments in bioengineering and stem cell biology are principal to the advance of cutting edge techniques to dentistry, both in the replacement and repair of teeth. Through dental bioengineering, the hopes are to restore dent alveolar tissues containing periodontal ligament, alveolar bone, enamel and dentin  and possibly to grow entire new teeth.

Corneal Bioengineering

Transplantation of cornea is the common method for treating corneal diseases. Furthermore, corneal transplantation signifies the most effective transplants due to the comparative remoteness of the avascular cornea to the immune system cells and corneal grafts involve only native immune suppression. Bioengineering of the cornea appears as a challenging domain to the researchers’ globally as it can help as a new way of treatment for corneal disease.

Bioengineering in the Genitourinary Tract

Bioengineering can also play a significant role for relieving the disorders and problems related to the genitourinary tract. Although genitourinary tract is subject to both inborn abnormalities and acquired diseases, such as trauma, cancer, inflammation, infection and other disorders. All these might principal to organ damage/failure or damage of tissue and subsequent reconstruction. These complications have motivated the involvement of bioengineers to discover a solution to the constantly increasing diseases of the genitourinary tract. The attainment of using bioengineering approaches for numerous reconstruction drives depends on the capability to use donor tissue proficiently and to facilitate the precise conditions for differentiation, growth and long-term survival. Currently numerous bioengineering approaches have been applied clinically such as the usage of cells as bulking agents to treatment the incontinence and vesicoureteral reflux, bladder reconstruction and urethral replacement. Therefore, urologic engineered tissues may have extensive clinical prospects in the future.

Blood Vessels Bioengineering

Vascular transplants have extensive applications to treat the cardiovascular disease (CVD), comprising infrainguinal artery occlusive diseases and myocardial infarction. Current clinical demonstrations have revealed a great potential for the use of bioengineered blood vessels as a treatment possibility for numerous vascular diseases. Extensive clinical use of bioengineered blood vessels for the treatment of vascular diseases might attain approval subsequent multicenter efficacy and safety trials that use off the shelf products which would further reduce engineering costs and might be mass-produced. Though great improvements have been made over the last decades, numerous bioengineered blood vessels prototypes continue at the preclinical phase in rat, mouse , ovine  , rabbit ,  porcine  and canine models.