Tissue Engineering Bone

The State of the Art of Tissue Engineering вЂ" Bone

Content

1. IntroductionвЂ¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦.вЂ¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦3

2. Bone Grafts and Bone Graft SubstitutesвЂ¦Ð²Ð‚¦.вЂ¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦4

3. Bone BiologyвЂ¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦..4

4. Tissue engineeringвЂ¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦..5

пЃ¶ 4.1. Ideal Scaffold

пЃ¶ 4.2. Growth factors

пЃ¶ 4.3. Stem cells

5. Future remarks/ConclusionвЂ¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦7

6. AppendixвЂ¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦Ð²Ð‚¦..8

1. Introductions

In the U.S. and E.U alone, bone fractures results in more than 2.4 million surgical procedures a year. Currently, bone grafting procedures are used in the healing and the repairing of bone defects. Autologous bone grafting, although effective as a clinical gold standard for bone repair, is gravely challenged by the availability of enough donor tissue supply and problems associated with donor site morbidity. Efforts to deal with these problems and restrictions have led to development of new biomaterials and other therapies, among which is tissue engineering holds immense potential.

The approaches to tissue engineering are illustrated in (Fig 1). The main idea is to make replacement tissues; two approaches can be used, depending on the target tissues.

In approach A, a small number of cells can be harvested from the patient using a biopsy, and then are cultured in vitro. The cells can be cultivated within a three dimensional scaffold in the presence of suitable growth and differentiation factors, an with the right conditions, the signals secrete several matrix materials to create a living tissue that can be used as replacement tissue that can be replaced back into the target site of the tissue. The scaffold should be biodegradable to avoid certain risks that can take place with any foreign material in the human body.

Approach B, on the other hand, acquires scaffold materials loaded with or without suitable growth and differentiation factors to be implanted into the target site; the scaffold materials will guide growth in situ with the help of suitable growth and differentiation factors secreted by the host or by the release of loaded factors .

In essence, three elements are central in tissue engineering:

I. Stem or precursor cells;

II. An appropriate scaffold and;

III. Growth factors.

The developments and limitations of each of these areas will be addressed in turn and their impact within bone tissue engineering.

2. Bone Grafts and Bone Graft Substitutes

At the moment the preferred option for bone repair is the use of autografts. With a success rate of between 80%-90%, autografts are considered as the gold standard of bone grafts. The high rate of success can be attributed to the make-up of autografts; tissue harvested for an injury from a remote site of the patient. The process of harvesting the tissue can lead to complications independent of the initial injury since the tissue harvest can result in infections, and possibly mechanical weakening of the donor site. These complications are jointly known as donor-site morbidity and are seen in nearly a fifth of all procedures. There are also constraints on the amount of tissue that can be harvested from the site, presenting limitations in supply of harvested tissue.

Allograft, bone taken from somebody else’s body, could be an alternative. However, the rate of graft incorporation is lower than with the autograft. Allograft bone introduces the likelihood of immune rejection and even the chance of an infection in the recipient’s body after the transplantation.

Hence it is clearly seen that an adequate bone replacement is yet to be found and it is at the same time urgently needed for full recovery of the patients. A possible way around this problem may be in tissue engineering, which is discussed below. But firstly an understanding to bone biology is very important and vital step tissue engineering.

3. Brief insight into bone biology

Bone tissue in the adult skeleton at a macroscopic level consists of two types of tissues: trabecular (around 20% of the total skeleton) and cortical bone (around 80% of the total skeleton). Bone together with cartilage, make up the human skeletal system. Bone is a dynamic, highly vascular, constantly changing, specialised type of mineralised connective tissue