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Bone is a highly specialized support tissue, which is characterized by its rigidity and hardness. The major functions of bone are providing structural support for the body, provide protection of vital organs and provide an environment for marrow. Bone is the only tissue that undergoes continuous remodeling throughout life and is one of the few organs that retains the potential for regeneration in adult life. (1, 2) Bone regeneration is required to achieve fracture healing and bone loss or bone tumors. Bone loss may be due to aging, periodontal resorption, osteoporosis, arthroplasty and accidents.
The apparent decrease in bone mass is the major cause for bone fractures and bone loss (3). The relationship studies between the age and bone loss in various bones are explained in the fallowing tabular column 1. It is clear that decrease in bone mineral density in bones is the ultimate cause of bone loss which further leads to fractures and associated complications.
Tissue Engineering (TE), as a potential medical treatment holds promises of eliminating re-operations by using biological substitutes and solves the problems of implant rejection, transmission of diseases associated with xenografts, allografls and shortage in organ donation . With increase in the aged population and the need to extend average individual health span, tissue engineering with biomaterials have an increasingly important role in the development of new generation medical devices and drug delivery systems (5). Bone tissue engineering a multidisciplinary science applying the principles of biology and engineering in developing viable substitutes that restore and maintain the function of human bone tissues.
Implants in Tissue Engineering:
One of the principle methods in tissue engineering involves growing the relevant cell(s) in vitro into the required three-dimensional (3D) organ or tissue. But cells lack the ability to grow in favored 3D orientations and thus define the anatomical shape of the tissue. Instead, they randomly migrate to form a two-dimensional (2D) layer of cells. However, 3D tissues are required and this is achieved by seeding the cells onto porous matrices, known as scaffolds, to which the cells attach and colonize (6). The scaffold therefore is a very important component for tissue engineering. Major issues in designing tissue engineering scaffolds are use of appropriate matrix materials for scaffolds. Pore characteristics, mechanical strength, osteoconductivity & osteoinductivity are mandatory requirements for a scaffold [7, 13]. Many different materials (natural, synthetic, biodegradable and permanent) have been investigated. Most of these materials have been known in the medical field before the advent of tissue engineering as a research topic, being already employed as bioresorbable sutures.
Figure 1: (A) Porous titanium scaffold with 59.1% porosity. (B) Porous titanium scaffolds with 200, 300, and 400 Î¼m pore sizes.
The new generation biomaterials include alloys of Titanium (Ti), polymers and bioceramic implants. Since cells are inherently sensitive to their surroundings, the performance of biomaterials strongly depends on their initial interaction with a biological environment (5). Thus, the surface properties of biomaterials are associated with cell adhesion and subsequent various cell behaviors such as proliferation, migration, differentiation and apoptosis. In the field of bone tissue engineering, hard tissues like bone and cartilage were substituted with "hydroxyapatite (HAp)" and "Tricalcium phosphate ceramics (TCP)", because all natural hard tissues are primarily composed of hydroxyapatite (HAp). In consequence, the nanoscale topography of calcium phosphate ceramics determines the cellular performance of mesenchymal stem cells and osteoblast cells. Osteoblast proliferation was reported to be enhanced on HAp.
Figure 2: Pressed Green & Sintered Hydroxyapatite. Figure 3: Hydroxyapatite Foam
Figure 4: Pressed Sintered Tricalcium Phosphate.
Stem Cells in Tissue Engineering:
Stem cell progenitor cells act as a repair system in side the body, which replenish and maintain the normal turnover of specialized cells in regenerative medicine. Based on there potentiality stem cells are classified mainly in to two multipotent stem cell types, they are Mesenchymal Stem Cells (MSC's) giving rise to connective tissue have enormous therapeutic potential to differentiate into multiple cell types including osteocytes, adipocytes, chondrocytes and cardiomyocytes and Hematopoietic Stem Cells (HSC's) for blood regeneration [8,9]. Stem cells can now be grown and transformed into specialized cells with characteristics consistent with cells of various tissues such as blood, bone tissue, etc.
Although the bone marrow serves as the primary reservoir for MSCs, aspirating bone marrow from the patient is an invasive procedure and in addition, it has been demonstrated that the number and the differentiating potential of bone marrow MSCs decreases with age . Therefore search for alternative sources of MSCs has aquired greater significance. MSCs presence has been reported in a variety of other tissues including amniotic fluid, cord blood, peripheral blood, fallopian tube, etc .
Fig.1: Stem cell differentiation Fig.2: MSC's confluent culture
Cord Blood Stem Cells:
More recently UCB has been examined for the presence of cells capable of differentiating into cell types of all three embryonic layers (ecto, endo and meso-derm). MSCs from Human Umbilical Cord Blood (UCB) show higher multipotentiality than adult marrow-derived MSCs. Other most important advantages of using cord blood as a source of stem cells are its non-invasive procurement and its vast abundance; thousands of babies are born each day (12). Until recently, umbilical cord blood was discarded after birth, along with the placenta. Now, in several countries around the world, cord blood is collected and banked in public banks for medical purpose.
Figure: Umbilical cord blood collection
MSC's shown to regenerate functional bone tissue when delivered to the site of musculoskeletal defects in experimental animals. We can also enhance the Invitro osteogesis by using novel osteoblast differentiation promoting compound like BMPs (Bone Morphogenic Proteins) & TGF (Transforming Growth Factors) (13).
Origin of the Proposal:
Although several major progresses have been introduced in the field of bone regenerative medicine during the years, current therapies, such as bone grafts still have many limitations. Moreover, and in spite of the fact that material science technology has resulted in clear improvements in the field of bone substitution medicine, no adequate bone substitute has been developed and hence large bone defects/injuries still represent a major challenge for orthopedic and reconstructive surgeons. It is in this context that TE has been emerging as a valid approach to the current therapies for bone regeneration/substitution. The proposal gives an exhaustive overview on components needed for making bone tissue engineering a successful therapy.
Definition of the Problem:
One of the main lessons tissue engineers have learned from their experiences over the last 15 years is that the simple placing of biological components in contact with a given material is not sufficient. It is rather the specific approach used when combining the two which is critical. The basic idea underlying classical tissue engineering has been that the seeding of living cells onto a biocompatible and eventually biodegradable scaffold followed by the culturing of this system in a bioreactor would lead to the initial cell population expanding into a tissue.
1. Process Optimization for MSC's Differentiation and Maintenance from the
Umbilical Cord Blood (UCB) mononuclear cells.
2. Implant Selection & Design for In-vitro Osteogenic Differentiation Studies.
3. Testing the in- vivo Efficiency\ of the Implants (cell seeded) on Small
Animal Cell Culture facilities, Assistance from Material Science Department for implant design, animal house (small animal) for in vivo studies.
Previous experience in the field: 1 year (On bench, official and Purchases)
Paper presentation in Asian Bioceramic Conference (ABC-2008) at IIT madras Rajyalakshmi, Sarika Mishra, M. Naveen Kumar and Balasubramanian. ." Adhesion Patterns of Haematopoietic Stem Cells on Porous Titanium and Bioceramic Scaffolds- an in-vitro study.