2.4.2 Osteocytes
Osteocytes are mature cells derived from the osteoblasts implanted in mineralized
bone matrix. They have a minor contribution to new bone formation compared to
osteoblasts. Osteocytes are arranged around the central lumen of an osteon and
between lamellae (Fig. 1). Osteocytes have an interconnecting three-dimensional
(3D) network. They are linked with adjacent osteocytes through small channels
called canaliculi. Osteocytes are responsive to physiological stress and strain
signals in bone tissue and also help to balance osteoblastic and osteoclastic activity
to deposit new bone and to dissolve old bone, respectively. Additionally, they act as
transporting agents of minerals between bone and blood.
2.4.3 Osteoclasts
Osteoclasts are the large cells (up to 100 μm in diameter) that are found at the
surface of bone mineral next to the resorbing bone. Osteoclasts are primarily
responsible for bone resorption (“clast” means to break; osteoclasts break down
bone). Osteoclasts have multiple nuclei, up to 100 per cell. To dissolve the minerals
and collagen from the mature bone, they use acids or enzymes. The dissolved
minerals then re-enter the bloodstream and are carried to different parts of the body.
Bone-lining cells are responsible for regulating the transportation of bone tissue
minerals. They are found along the surface of the mature bone. Osteoclasts can be
activated by some exclusive proteins. All these types of cells are together responsible for building the bone matrix with hierarchical self-assembly, maintenance, and
remodeling and these processes must be in equilibrium to ensure healthy bone
tissue. Importantly, the extent of bone remodeling that occurs at an implant surface
will determine the fate of the prosthetic device. For example, loosening and failure
of the implant may result from either (1) little or no remodeling in the bone
surrounding an implant, which may lead to malnourished juxtaposed bone, or (2)
too much remodeling in the bone surrounding an implant, which may lead to
excessive bone resorption, or osteolysis.
2.5 Current Scenario of Bone Grafting
Bone is the second-most transplanted tissue in humans. Bone grafting is a
surgical process that repairs or replaces the defective bones with healthy bones
with the help of bone graft materials taken either from the patient’s own body or
from synthetic sources without damaging living tissues. The bone grafting
technique is a widely applied and universally accepted technique in several
types of surgery, such as orthopedic surgery, plastic surgery, oral and maxillofacial surgery, and dental surgery. Along with filling defective gaps by bone
Hydroxyapatite-Packed Chitosan-PMMA Nanocomposite: A Promising Material for. . .
143
Osteocytes are mature cells derived from the osteoblasts implanted in mineralized
bone matrix. They have a minor contribution to new bone formation compared to
osteoblasts. Osteocytes are arranged around the central lumen of an osteon and
between lamellae (Fig. 1). Osteocytes have an interconnecting three-dimensional
(3D) network. They are linked with adjacent osteocytes through small channels
called canaliculi. Osteocytes are responsive to physiological stress and strain
signals in bone tissue and also help to balance osteoblastic and osteoclastic activity
to deposit new bone and to dissolve old bone, respectively. Additionally, they act as
transporting agents of minerals between bone and blood.
2.4.3 Osteoclasts
Osteoclasts are the large cells (up to 100 μm in diameter) that are found at the
surface of bone mineral next to the resorbing bone. Osteoclasts are primarily
responsible for bone resorption (“clast” means to break; osteoclasts break down
bone). Osteoclasts have multiple nuclei, up to 100 per cell. To dissolve the minerals
and collagen from the mature bone, they use acids or enzymes. The dissolved
minerals then re-enter the bloodstream and are carried to different parts of the body.
Bone-lining cells are responsible for regulating the transportation of bone tissue
minerals. They are found along the surface of the mature bone. Osteoclasts can be
activated by some exclusive proteins. All these types of cells are together responsible for building the bone matrix with hierarchical self-assembly, maintenance, and
remodeling and these processes must be in equilibrium to ensure healthy bone
tissue. Importantly, the extent of bone remodeling that occurs at an implant surface
will determine the fate of the prosthetic device. For example, loosening and failure
of the implant may result from either (1) little or no remodeling in the bone
surrounding an implant, which may lead to malnourished juxtaposed bone, or (2)
too much remodeling in the bone surrounding an implant, which may lead to
excessive bone resorption, or osteolysis.
2.5 Current Scenario of Bone Grafting
Bone is the second-most transplanted tissue in humans. Bone grafting is a
surgical process that repairs or replaces the defective bones with healthy bones
with the help of bone graft materials taken either from the patient’s own body or
from synthetic sources without damaging living tissues. The bone grafting
technique is a widely applied and universally accepted technique in several
types of surgery, such as orthopedic surgery, plastic surgery, oral and maxillofacial surgery, and dental surgery. Along with filling defective gaps by bone
Hydroxyapatite-Packed Chitosan-PMMA Nanocomposite: A Promising Material for. . .
143