Biomedical Engineering Reference
In-Depth Information
ing, and clinical research. The primary purpose of regenerative medicine is
to assist the body in regenerating diseased or damaged tissues and organs.
Developments in regenerative medicine involving gene and protein ther-
apy, advanced biomaterials, and tissue engineering have evolved to render
new opportunities to treat and cure many diseases which were irremedia-
ble decades ago. Such therapies range from recombinant human proteins that
effectively treat certain metabolic deficiencies to specialized ceramics and
polymers that serve as orthopedic implants in various joint replacements and
bone grafts. These developments in medicinal technology have extended the
longevity of human beings by several decades over their past generations. Ex-
cellent reviews on these subjects may be found elsewhere [1-6]. The focus of
this review is to evaluate the role of one particular subset of biomaterials in
regenerative medicine, namely, the impact of hydrogels on musculoskeletal
tissue engineering.
Recent years have witnessed an exponential growth in the field of tissue en-
gineering as documented by Lysaght and Reyes [7]. The overarching principle
of tissue engineering is to create “off-the-shelf” tissues and organs to poten-
tially replace those compromised by trauma, injury, disease, or aging. Current
therapies for damaged tissue restoration using artificial implants have several
shortcomings such as suboptimal long-term outcomes, long-term presence of
implants within the body, invasive surgical procedure and associated mor-
bidity, risk of infection, structural failure, and implant rejection [8-11]. In
addition, the materials from which these implants are constructed do not
integrate well with the host tissue and have a limited lifetime [10]. Other
strategies involving the use of allografts and autografts also suffer from var-
ious drawbacks such as lack of donor tissue availability, donor site morbidity,
increased susceptibility to disease transmission and immunorejection [11-
13]. Table 1 lists the number of surgical procedures that have been carried out
in USA alone per year to rectify tissue and/or organ damage [14]. As of May
15, 2005, approximately 88 475 patients in USA are waiting for organ trans-
plant whereas only 4367 patients have received transplants this year by April
29, 2005 [15]. This striking gap between donor supply and demand wors-
ens year by year, and is predicted to widen even further with the aging of
the baby-boomer generation. In fact, it is predicted that in USA alone, one
person out of every five approaching the age of 65 will need some form of
temporary or permanent organ replacement therapy at least once in their
life time [16]. According to the Business Communications Company, Inc., the
USA market for regenerative medicine products for bone and joint implants
has been projected to approach 1.4 billion by 2007 [17]. However, there are
still a number of challenges, both scientific and translational (manufactur-
ing and regulatory), that must be overcome before widespread application of
these technologies can be achieved.
The musculoskeletal system includes bone, cartilage, and spine which
are exciting tissue engineering targets as the need for their replacement is
