Biomedical Engineering Reference
In-Depth Information
Osteocytes are star-shaped cells with less organelles than osteoblasts. Osteocytes
are osteoblasts embedded in bone ECM. The main role of osteocytes is mechano-
transduction, osteoid calcification, and regulation of calcium blood levels [
12
-
14
].
Osteoclasts are multinuclear cells formed by the fusion of several mononuclear
hematopoietic precursors. These cells and osteoblasts have crucial roles in bone
remodeling, which is a complex process where old bone is continuously and gradually
digested by osteoclasts and replaced by new bone secreted by osteoblasts [
12
-
14
].
7.2.2 Repair
Bone is a tissue capable of repairing its defects. Most bone lesions can heal
spontaneously or with minimal intervention. At the fracture site, a series of events
happens to promote the repair process. Upon damage, inflammation occurs followed
by migration, proliferation, and differentiation of mesenchymal cells to the damaged
site [
15
,
16
]. In some disorders, including osteogenesis imperfecta (OI), Paget
disease, hyperparathyroidism, osteomyelitis, and osteoporosis, the repair process
does not work properly. These diseases, along with large bone defects resulting from
trauma and tumor resection, are problematic conditions in the orthopedic field.
7.2.3 Current Therapy
Among the different methods of bone repair, autograft is the gold standard for bone
defect reconstruction [
17
]. In this treatment, bone is obtained from another site within
the patient's body, such as the iliac crest and then transplanted into the defective site.
An autograft does not trigger the host immune response. Nevertheless, due to the
limited availability of autografts, in addition to the necessity for extensive surgery,
pain, and possibility of infection and paresthesia, a better treatment is needed [
18
-
20
].
Although the use of the allogenic graft for repairs does not have some of the
limitations of the autologous graft, such as pain and quantity; however, this method
triggers the host immune response. Furthermore, the irradiation and freeze-drying
processes used during allograft preparation may remove the cells and damage
allograft osteoconductivity, hence decreasing their regenerative capacity [
21
].
Xenografts, on the other hand, may be considered as an alternative. However, some
disadvantages limit their application, including the possibility of viral transmission,
toxicity, and immunogenicity associated with these types of transplantable materials
[
22
,
23
]. Another option is to use metal implants such as titanium, stainless steel, and
cobalt chromium, all of which are biocompatible, processable, strong, and relatively
inexpensive. In contrast to biodegradable materials, metal implants are not as easily
degradable. However, they may release toxic ions which lead to an inflammatory
response or infection at the transplant site. Furthermore, to remove these implants an
additional operation is required [
24
,
25
]. Therefore, finding an appropriate substitute
for lost bone tissue is of utmost importance in orthopedic and maxillofacial surgeries.
