Biomedical Engineering Reference
In-Depth Information
cells for enhanced function via pattern recognition receptor (PRR) engagement. (C) The acute inflammatory response is
dominated by the action of PMNs. PMNs secrete proteolytic enzymes and reactive oxygen species (ROS), corroding the bio‐
material surface. Interleukin (IL)-8 released from PMNs enhances PMN influx and priming. In the transition from acute to
chronic inflammation, PMNs stop secreting IL-8 in favor of cytokines promoting immigration and activation of monocytes
and macrophages. (D) Macrophages are the driving force of chronic inflammation. Constant release of inflammatory me‐
diators like tumor-nekrose-faktor alpha (TNFα), IL-6, and monocyte chemotactic protein (MCP)-1 results in permanent acti‐
vation of macrophages. Fusion-inducing stimuli like IL-4 and IL-13 promote the fusion of macrophages to foreign body
giant cells (FBGCs,) which form a highly degradative environment on the biomaterial surface. Furthermore, FBGC promote
extracellular matrix (ECM) remodeling and fibroblast activation resulting in excessive fibrosis and biomaterial encapsula‐
tion. (E) Macrophage-derived cytokines and pattern recognition receptor engagement activate dendritic cells (DCs) on the
biomaterial surface. Depending on the nature of the stimulus, DCs mature to either immunogenic or tolerogenic subtypes,
amplifying or suppressing the inflammatory response [5].
Compared with autografts which come from the same bodies and are only available in limit‐
ed amounts, allografts are more readily available and accompany with less risk and postop‐
erative morbidity. The healing times is therefore shorter and less painful for a patient with
no second surgical site is required (as there is when an autograft is utilised). Currently, the
use of allograft tissues is increasingly popular all over the world, with widespread orthopae‐
dic surgeons and debilitating musculoskeletal conditions. Nearly one tissue/organ donor
can save or improve the lives of up to 60 people. Especially, Musculoskeletal Transplant
Foundation, the world's largest tissue bank, provides allograft tissue and biologic solutions
for ligament reconstruction [8]. Meanwhile bone and soft tissue allografts from the Steri‐
Graft™ line has been in existence for over 13 years and has helped doctors and their patients
with over one hundred thousand successful transplantations. Before transplantation, a
blood sample from the donor is normally tested in case any infected diseases, such as hu‐
man immunodeficiency virus (HIV), Hepatitis, and Syphilis [9].
Specially, decellularized tissue/organ matrices derived from allografts have been used since
the 1940s to support tissue repair and replacement. Their popularity has grown sharply dur‐
ing the last decade with the advent of tissue engineering [10]. At present, decellularized tis‐
sues/organs have been successfully used in a variety of tissue/organ regenerative medicines.
The efficiency of cell removal from a tissue/organ is dependent on the origin of the tissue/
organ and the specific physical, chemical, and enzymatic methods that are used. Each of
these treatments affects the biochemical composition, tissue ultrastructure, and mechanical
behavior of the remaining extracellular matrix (ECM) scaffold, which in turn, affect the host
response to the material [11].
3. Collagen and gelatin
Collagen is one of the most prevalent proteins in the connective tissue of animals and consti‐
tutes approximately 25% of total body protein in vertebrates. It therefore is an important bi‐
omaterial in medical, dental, and pharmacological fields. After the immunogens in the
collagen molecules are dislodged, collagen has excellent biocompatibilities either
in vitro
or
in vivo
. Collagen is capable of being cross-linked into solid or lattice-like gels. Resorbable
forms of collagen have been used to dress oral, skin or some of the other soft tissue wounds,
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