Biomedical Engineering Reference
In-Depth Information
a desired cell function, and degrade as the tissue repair proceeds. Regenera-
tion of skin using a porous hydrogel scaffold containing glycosaminoglycan
(GAG) and collagen is an example where the implanted scaffold stimulates
the self repair ability of our bodies to regenerate the lost tissue [38-40], and
this material received FDA approval in 1996 [41]. This product commercially
known as
Integra
(by Integra life science and Johnson & Johnson) is used
for skin burn treatments. In another study, Ono et al. have used a combi-
nation of polymers and growth factors to accelerate the healing process in
bio-interactive wound dressings [42].
Guided tissue engineering with the aid of acellular biomaterials has also
been explored for bone regeneration. One of the polymeric materials that has
been widely used to promote osteogenesis and periodontal regeneration is ex-
panded poly(tetrafluroethylene) membrane (e-PTFE or Gore-Tex) which has
a useful microporous structure and is biocompatible [43, 44]. The drawback
of this material is that it is bio-inert and nondegradable. Bio-degradable poly-
mers that have been used for guided regeneration of bone include polylactide,
polyglycolide, and their copolymers, biomimetic peptide hydrogels, collagen-
based matrices, and poly(propylene fumerate) [44-48]. Acellular porcine
small intestinal submucosa (SIS) has been extensively studied as a xenogenic
scaffold for tissue repair and it is a bio-resorbable material [49]. This material
recently gained FDA approval for skin repair, soft tissue support, and rotator
cuff repair [49, 50]. The success of SIS as a scaffold navigator for regenera-
tion is attributed to the presence of ECM proteins, and other growth factors
such as fibroblast growth factor (FGF-2) and transforming growth factor
β
(TGF-
β
) [51].
2.2
Cell Therapies
Cell therapy, serendipitously discovered by Paul Niehans in 1931, involves
the transplantation of allograft and autograft cells to repair dysfunctional
tissues. Since then, procedures attempting to utilize allograft as well as au-
tograft cells that are capable of producing biotherapeutic substances have
been exploited to treat diabetes, liver failure, and neural disorders such as
Alzheimer's diseases, Parkinson's disease, spinal cord injuries, etc. [52-55].
However, such an approach needs to be reconsidered for transplantation of
allograft and xenograft cells owing to their vulnerability to immunorejec-
tion. In order to circumvent immunorejection, allograft and xenograft cells
are often encapsulated within a permeable polymer membrane. The main
role of the polymer membrane is to prevent the entrance of high molecu-
lar weight immuno-responsive agents into the implant site. The encapsulated
cells are then expected to produce the required biotherapeutic substance
which will treat the disease (see Fig. 1). The permeable membrane also allows
the exchange of nutrients, oxygen and biotherapeutic substances between
