Biomedical Engineering Reference
In-Depth Information
indicated its ability to withstand unconfined compression while concurrently
expressing water during loading [
109
]. Following load removal, EGC hydrogels
exhibited the capacity to immediately re-establish their pre-compression water
content and recover their initial height and shape (Fig.
3
)[
109
]. We define these
combined characteristics as a shape-memory sponge effect, which to the best of our
knowledge has yet to be reported in the literature. The unconfined equilibrium
compressive modulus of ECG hydrogels is similar to that of the human NP, and
long-term cell culture studies utilizing porcine NP cells indicate that the material is
cytocompatible [
109
]. Although others have attempted to develop biomaterials
composed of these elements, their formulations were predominantly composed of
collagen and the material applications was not specifically tailored for NP regener-
ation [
110
]. Thus, our results demonstrate the formation of a novel biopolymeric
material for NP replacement that has physical characteristics similar to the native
NP and may allow for adaptation to a patients' anatomy following minimally
invasive surgical introduction.
8.2.3 Tissue-Based Scaffolds
In our research laboratory, we have also considered an alternative approach to
generation of a scaffold for TE of the human NP. The use of ECM-based scaffolds
derived from the decellularization of healthy xenogenic or allogenic tissues has
become increasingly popular [
111
]. It is believed that scaffold development
utilizing such techniques may prove advantageous because biologically appropriate
scaffolds with an ECM microarchitecture tailored towards specific tissues are
formed from the outset by the resident host tissue cells themselves. Recent literature
indicates that this approach is suitable for the regeneration of numerous tissues
including heart valves, vascular grafts, and corneal tissue [
107
,
108
,
112
]. In
considering this, we hypothesized that an ideal scaffold for TE of the NP could
be generated via the utilization of decellularized xenogenic NP. Theoretical
advantages to our approach include the formation of a natural biopolymeric scaf-
fold whose components, including whole aggrecan molecules and minor collagens,
may be maintained in relevant ratios while innate ECM molecule interactions
are preserved, thus yielding a close match to the native tissue microarchitecture.
Using a combination of chemical and physical methodologies to successfully
decellularize porcine NP, we were able to create a scaffold (Fig.
4
) that closely
approximates the chemical, physical, and mechanical nature of the human NP
[
113
]. Our acellular porcine nucleus pulposus (APNP) scaffolds contain many of
the major and minor ECM components found in the human NP including aggrecan
and collagen types II, IX, and XI [
113
]. Quantification of the APNP GAGs and
hydroxyproline content revealed a 21:1 ratio of these components, respectively.
This closely approximates the 27:1 ratio found in the healthy human NP [
23
,
113
].
Porcine cell remnants including DNA and the antigenic epitope alpha-Gal are
absent within this material. The unconfined compressive material properties of
the APNP approach values reported by others for the human NP [
113
-
115
].
