Hybrid, combination, and replant materials - Orthopaedic Biomaterials in Research and Practice - page 251

1997. It uses a patient's own cells to repair cartilage injuries in the knee
and is implanted in a surgical procedure called autologous chondrocyte
implantation. Autologous cultured chondrocytes are derived from in
vitro expansion of chondrocytes harvested from the patient's normal,
femoral articular cartilage. The source of chondrocytes are biopsies
from a lesser-weight bearing area, which are isolated, expanded through
cell culture, and implanted into articular cartilage defects beneath an
autologous periosteal flap. Prior to final packaging, cell viability is
assessed to be at least 80%. The implanted cells can form new hyaline-
like cartilage, with properties similar to normal cartilage, which may
reduce pain and improve knee function. It has been reported that the
most common complications include arthrofibrosis/joint adhesions, graft
overgrowth, chondromalacia or chondrosis, cartilage injury, graft com-
plication, meniscal lesion, and graft delamination.
Blood vessels
Autologous blood vessels, such as the internal mammary vein and the
saphenous vein, have been used for grafting bypass procedures. However,
because of vascular disease, amputation, age, or limited allograft sup-
plies, patients may not possess appropriate vessels for grafting purposes.
Therefore, there has been interest in developing engineered blood vessel
substitutes that can meet the mechanical, biological, and hemocompat-
ibility demands of the vascular system. Some of the key characteristics
for tissue-engineered biohybrid vessels include elasticity and compli-
ance, as well as exhibiting a luminal surface that can prevent thrombus
formation and leakage to mimic the function of the endothelial lining in
native vessels.
Engineered vessels using expanded polytetrafluoroethylene (ePTFE)
have been used clinically for almost three decades. These possess the
benefit of low thrombogenicity potential, scaffold porosity, and high
strength. However, they are relatively noncompliant, leading to a stiff-
ness mismatch with the native vessel, which could lead to intimal hyper-
plasia, activation of coagulation and complement cascades, thrombus
formation from turbulent flow, and graft malfunction. Synthetic mol-
ecules and extracellular matrix materials have been added to the ePTFE
constructs to limit their thrombogenicity. These promote endothelial cell
adhesion and decrease turbulence. A key issue continues to be provision
of appropriate wall porosity to enable healing without excessive loss of
non-cellular vessel contents.
As an alternative to synthetic scaffolds, natural materials have also
been used to construct composite scaffolds. For example, collagen and
fibrin scaffolds have been found to have improved mechanical properties
over scaffolds that have been constructed using solely the pure compo-
nent. Although biologically based composite scaffolds have improved
properties, questions still persist over their relative strength compared to
synthetic scaffolds. Engineered constructs also often require weeks of