Biomedical Engineering Reference
In-Depth Information
synthetic scaffolds for an engineered tissue are regarded as a kind of ECM. However,
ECM in native tissues possesses complex compositions and a dynamic nature, which
bring multiple biological functions such as cell adhesion, migration, proliferation,
and differentiation. Ideal scaffolds should therefore mimic the features of the native
ECM of the target tissue. Nevertheless, the complexity of ECM makes it difficult to
mimic exactly the structure and functions of native ECM in synthetic scaffolds.
14
Therefore, the focus in tissue engineering is how to manipulate the process to
integrate the key components of TE, trying to replicate the natural structure of tissue
and mimic the functions of native ECM, at least partially. There are many
technologies developed to achieve these aims. Although these techniques have
succeeded in making biomimetic scaffolds, they have their own limitations. This
chapter reviews the bone TE strategies involved in preparation of scaffolds and
briefly discusses the drawbacks and advantages of these strategies.
6.2 CLINIC NEEDS IN BONE REGENERATION FIELDS
Every year, there are roughly 1 million bone grafting procedures in the United States
and EuropeanUnion.
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These include indications arising fromresection of primary and
metastatic tumors, bone loss after skeletal trauma, failed fracture healing, spinal
arthrodesis, and trabecular voids. In addition, more than 20million people in theUnited
States are totally edentulous.
16
About half a million children worldwide are born
annually with congenital craniofacial deformities, such as cleft palate and hyper-
telorism.
17
Current treatments in clinic are based on autologous and allogeneic bone
grafts.
18-22
Autografts have been the gold standard of bone replacement for many years
because they provide the patient's own osteogenic cells, ECM, and essential osteoin-
ductive factors needed for bone healing and regeneration.
21,23
Because an autograft is
harvested from the patient's own body, there is a limited supply and morbidity of the
harvest site, and the additional trauma is a concern. Although autograft is highly
efficient for bone repair, the outcome for large bone defects is less predictable.
Allografts could be used as an alternative for treating bone defects. However, allografts
could introduce the possibilities of immune system rejection, pathogen disease
transmission from donor to recipient, and infections after the transplantation.
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Therefore, biomaterials for bone defects, as an alternative to those two bone
grafts, have been extensively studied to meet the increasing clinical demand.
Currently, all kinds of biomaterials, including metals, ceramics, and polymers,
have been studied for bone regeneration. However, none of these biomaterials,
by themselves, can currently be used for full recovery of the patient. Metals exhibit
poor integration with the tissue at the implantation site because of a lack of
degradability, although they provide mechanical support at the site of the defect.
Ceramics, because of their low tensile strength and brittleness, have limited
application in loading-bearing sites. Polymers have been extensively used in drug
delivery systems but have limitations in bone tissue engineering because of their low
compressive strength and acid degradation products. It is clear that an adequate bone
graft is yet to be found.
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