Photo-crosslinked alginate hydrogels support enhanced matrix accumulation by nucleus pulposus cells in vivo.
OBJECTIVE
Intervertebral disc (IVD) degeneration is a major health concern in the United States. Replacement of the nucleus pulposus (NP) with injectable biomaterials represents a potential treatment strategy for IVD degeneration. The objective of this study was to characterize the extracellular matrix (ECM) assembly and functional properties of NP cell-encapsulated, photo-crosslinked alginate hydrogels in comparison to ionically crosslinked alginate constructs.


METHODS
Methacrylated alginate was synthesized by esterification of hydroxyl groups with methacrylic anhydride. Bovine NP cells were encapsulated in alginate hydrogels by ionic crosslinking using CaCl(2) or through photo-crosslinking upon exposure to long-wave UV light in the presence of a photoinitiator. The hydrogels were evaluated in vitro by gross and histological analysis and in vivo using a murine subcutaneous pouch model. In vivo samples were analyzed for gene expression, ECM localization and accumulation, and equilibrium mechanical properties.


RESULTS
Ionically crosslinked hydrogels exhibited inferior proteoglycan accumulation in vitro and were unable to maintain structural integrity in vivo. In further studies, photo-crosslinked alginate hydrogels were implanted for up to 8 weeks to examine NP tissue formation. Photo-crosslinked hydrogels displayed temporal increases in gene expression and assembly of type II collagen and proteoglycans. Additionally, hydrogels remained intact over the duration of the study and the equilibrium Young's modulus increased from 1.24+/-0.09 kPa to 4.31+/-1.39 kPa, indicating the formation of functional matrix with properties comparable to those of the native NP.


CONCLUSIONS
These findings support the use of photo-crosslinked alginate hydrogels as biomaterial scaffolds for NP replacement.
Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd Street, Philadelphia, PA 19104-6321, USA. aic@seas.upenn.edu
A I
AI
Chou
S O
SO
Akintoye
S B
SB
Nicoll
D000464:Alginates / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D024043:Collagen Type II / Q000235:genetics / Q000378:metabolism*; D005260:Female; D020100:Hydrogels / Q000737:chemistry*; D007403:Intervertebral Disc / Q000166:cytology*; D008422:Materials Testing; D051379:Mice; D023421:Models, Animal; D055668:Photochemical Processes; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*
D000464:Alginates; D024043:Collagen Type II; D020100:Hydrogels; D011509:Proteoglycans