Biomedical Engineering Reference
In-Depth Information
tive elastin, a protein found in muscle, ligaments, and cartilage [295]. In
another study, Kisiday et al. investigated the effect of KLD-12 peptide hy-
drogel scaffolds on cartilage tissue engineering [286]. Both young and adult
bovine chondrocytes seeded within these hydrogels were found to retain their
characteristic phenotype and produced abundant glycosaminoglycans and
type II collagen [286].
Self-assembly mediated in-situ gelation has also been utilized to create
matrices with nanometer dimensions resembling the native ECM compo-
nents [288, 296-299]. For example, Stupp and coworkers used supramolecu-
lar self-assembly to create nanofiber hydrogel scaffolds in situ by designing
a peptide-amphiphile with a suitable balance of hydrophilic and hydropho-
bic groups [296-298]. In another study, the same group has developed in situ
self-assembled nanofibrillar structures by utilizing electrostatic interactions
between two oppositely charged peptide amphiphiles [299]. This method can
also be applied to incorporate various bio-interactive ligands which promote
cell adhesion into a single nanofiber by exploiting electrostatic interactions
between peptides containing different amino acid sequences [288, 299].
Shape Memory Polymers
Another up-and-coming class of materials that could have a number of po-
tential applications in minimally invasive surgical procedures involves shape
memory polymers [127, 128, 300-303]. These materials have a huge poten-
tial application for many biomedical applications because of their unique
properties, although, strictly speaking, they have not yet been applied to tis-
sue engineering. Biomedical applications of shape memory materials hinge
on the basic idea that these materials change their shape in response to
certain external stimuli (such as temperature, pH, and light) from a com-
pressed state, which can be administered through a noninvasive manner, to
a bulky one, which can then fill the defect site. This application was moti-
vated by metallic alloys such as NiTi (nitinol), which are known to exhibit
shape memory (through martensitic structural transformation) and are well
known for their applications in biomedical fields, e.g. surgical devices and
implants [304]. However, polymer-based shape memory materials offer more
advantages over such metal alloys, naturally due to their superior biocompat-
ibility and biodegradability.
Polymers where reversible shape memory is induced by a change in tem-
perature are known as thermo-responsive shape memory polymers. For ex-
ample, a hydrogel formed by acrylic acid and stearyl acrylate shows signifi-
cant temperature dependent mechanical properties [128]. Below 50 C, this
hydrogel behaves like a tough polymer whereas above 50 C it behaves like
a soft material. This transition allows one to process the hydrogels above
50 C, where they are easily malleable, into the desired shape, which can be
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