title: Thermoresponsive, in situ cross-linkable hydrogels based on N-isopropylacrylamide: fabrication, characterization and mesenchymal stem cell encapsulation.
abstract: Hydrogels that solidify in response to a dual, physical and chemical, mechanism upon temperature increase were fabricated and characterized. The hydrogels were based on N-isopropylacrylamide, which renders them thermoresponsive, and contained covalently cross-linkable moieties in the macromers. The effects of the macromer end group, acrylate or methacrylate, and the fabrication conditions on the degradative and swelling properties of the hydrogels were investigated. The hydrogels exhibited higher swelling below their lower critical solution temperature (LCST). When immersed in cell culture medium at physiological temperature, which was above their LCST, hydrogels showed constant swelling and no degradation over 8 weeks, with the methacrylated hydrogels showing greater swelling than their acrylated analogs. In addition, hydrogels immersed in cell culture medium under the same conditions showed lower swelling compared with phosphate-buffered saline. The interplay between chemical cross-linking and thermally induced phase separation affected the swelling characteristics of the hydrogels in different media. Mesenchymal stem cells encapsulated in the hydrogels in vitro were viable over 3 weeks and markers of osteogenic differentiation were detected when the cells were cultured with osteogenic supplements. Hydrogel mineralization in the absence of cells was observed in cell culture medium with the addition of fetal bovine serum and β-glycerol phosphate. The results suggest that these hydrogels may be suitable as carriers for cell delivery in tissue engineering.
authors.affiliation: Department of Bioengineering, Rice University, Houston, TX 77251-1892, USA.
authors.forename: Leda
authors.initials: L
authors.lastname: Klouda
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Perkins
authors.forename: Brendan M
authors.initials: BM
authors.lastname: Watson
authors.forename: Michael C
authors.initials: MC
authors.lastname: Hacker
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Bryant
authors.forename: Robert M
authors.initials: RM
authors.lastname: Raphael
authors.forename: F Kurtis
authors.initials: FK
authors.lastname: Kasper
authors.forename: Antonios G
authors.initials: AG
authors.lastname: Mikos
mesh_terms: D000178:Acrylamides / Q000737:chemistry* / Q000494:pharmacology; D000818:Animals; D002021:Buffers; D002118:Calcium / Q000032:analysis; D002417:Cattle; D002474:Cell-Free System / Q000187:drug effects; D002478:Cells, Cultured; D018914:Cells, Immobilized / Q000166:cytology / Q000187:drug effects; D003432:Cross-Linking Reagents / Q000737:chemistry* / Q000494:pharmacology; D003470:Culture Media / Q000494:pharmacology; D020100:Hydrogels / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D008297:Male; D008422:Materials Testing / Q000379:methods*; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects*; D008856:Microscopy, Fluorescence; D008903:Minerals / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects; D051381:Rats; D011916:Rats, Inbred F344; D013696:Temperature
chemical_list: D000178:Acrylamides; D002021:Buffers; D003432:Cross-Linking Reagents; D003470:Culture Media; D020100:Hydrogels; D008903:Minerals; C067295:N-isopropylacrylamide; D002118:Calcium