Biomedical Engineering Reference
In-Depth Information
Fig. 11
Reaction scheme of hydrogel-tissue integration using ALD-CS-MA primer. The
aldehyde groups react with amines in the cartilage tissue while methacrylate groups react
with the polymerizing PEGDA precursor
oratory, we have exploited the ability of collagen chains located in the ECM to
integrate covalently with the hydrogel implant via photopolymerization [321].
This technology, known as tissue-initiated photopolymerization, generates
reactive tyrosyl radicals on the cartilage collagen backbone with the help of
an oxidizing agent. The tyrosyl radicals on the cartilage, upon exposure to UV
light, react with the oligomers (which also react amongst themselves to create
a hydrogel) to create a well-integrated hydrogel-cartilage system, as shown in
the schematic illustration (Fig. 10) [321].
As an alternative strategy, Wang et al. created a CS-based tissue adhe-
sive to achieve covalent bond-mediated integration between the hydrogels
and the host tissue. Here, CS is multi-functionalized with both methacrylate
and aldehyde groups. The aldehyde groups react with collagen segments lo-
cated within the host tissue whereas the methacrylate groups form covalent
bonds between the adhesive and the PEGDA-cell solution during photopoly-
merization, which subsequently undergoes in situ gelation as shown in Fig. 11
(Wang and Elisseeff, 2005, personal communication). Our in vivo studies on
the rabbit knee joint demonstrate the viability of this technique. In addition
to anchoring the implant within the defect site initially, the strategy also
enhances the integration of the engineered tissue with the native tissue at
a molecular level by allowing migration of cells between the interface, and
thereby regenerating tissue across the interface.
9
Concluding Remarks
This review outlined the progress over the past few decades in tissue en-
gineering strategies that use hydrogels to treat musculoskeletal tissue loss.
Significant advancements have been made in the design and development
of hydrogel scaffolds which incorporate many of the required biochemical
and biophysical cues for tissue development. Novel methods have been de-
