title: Photo-cross-linked PLA-PEO-PLA hydrogels from self-assembled physical networks: mechanical properties and influence of assumed constitutive relationships.
abstract: Poly(lactide)-block-poly(ethylene oxide)-block-poly(lactide) (PLA-PEO-PLA) triblock copolymers are known to form physical hydrogels in water as a result of the polymer's amphiphilicity. Their mechanical properties, biocompatibility, and biodegradability have made them attractive for use as soft tissue scaffolds. However, the network junction points are not covalently cross-linked, and in a highly aqueous environment these hydrogels adsorb more water, transform from gel to sol, and lose the designed mechanical properties. In this article, a hydrogel was formed by the use of a novel two-step approach. In the first step, the end-functionalized PLA-PEO-PLA triblock was self-assembled into a physical hydrogel through hydrophobic micelle network junctions, and in the second step, this self-assembled physical network structure was locked into place by photo-cross-linking the terminal acrylate groups. In contrast with physical hydrogels, the photo-cross-linked gels remained intact in phosphate-buffered solution at body temperature. The swelling, degradation, and mechanical properties were characterized, and they demonstrated an extended degradation time (approximately 65 days), an exponential decrease in modulus with degradation time, and a tunable shear modulus (1.6-133 kPa). We also discuss the various constitutive relationships (Hookean, neo-Hookean, and Mooney-Rivlin) that can be used to describe the stress-strain behavior of these hydrogels. The chosen model and assumptions used for data fitting influenced the obtained modulus values by as much as a factor of 3.5, which demonstrates the importance of clearly stating one's data fitting parameters so that accurate comparisons can be made within the literature.
authors.affiliation: Department of Polymer Science & Engineering, University of Massachusetts, 120 Governors Drive, Amherst, Massachusetts 01003, USA.
authors.forename: Naomi
authors.initials: N
authors.lastname: Sanabria-DeLong
authors.forename: Alfred J
authors.initials: AJ
authors.lastname: Crosby
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Tew
mesh_terms: D000179:Acrylates / Q000737:chemistry; D001672:Biocompatible Materials / Q000737:chemistry; D001673:Biodegradation, Environmental; D019245:Compressive Strength; D003432:Cross-Linking Reagents / Q000737:chemistry / Q000494:pharmacology*; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry; D008027:Light; D008968:Molecular Conformation; D011091:Polyesters / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D000179:Acrylates; D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D020100:Hydrogels; D011091:Polyesters; D011108:Polymers; C507889:polylactide-polyethylene glycol-polylactide; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D011092:Polyethylene Glycols; C036658:acrylic acid