title: Synthesis and characterization of injectable, thermally and chemically gelable, amphiphilic poly(N-isopropylacrylamide)-based macromers.
abstract: In this study, we synthesized and characterized a series of macromers based on poly( N-isopropylacrylamide) that undergo thermally induced physical gelation and, following chemical modification, can be chemically cross-linked. Macromers with number average molecular weights typically ranging from 2000-3500 Da were synthesized via free radical polymerization from, in addition to N-isopropylacrylamide, pentaerythritol diacrylate monostearate, a bifunctional monomer containing a long hydrophobic chain, acrylamide, a hydrophilic monomer, and hydroxyethyl acrylate, a hydrophilic monomer used to provide hydroxyl groups for further chemical modification. Results indicated that the hydrophobic-hydrophilic balance achieved by varying the relative concentrations of comonomers used during synthesis was an important parameter in controlling the transition temperature of the macromers in solution and stability of the resultant gels. Storage moduli of the macromers increased over 4 orders of magnitude once gelation occurred above the transition temperature. Furthermore, chemical cross-linking of these macromers resulted in gels with increased stability compared to uncross-linked controls. These results demonstrate the feasibility of synthesizing poly( N-isopropylacrylamide)-based macromers that undergo tandem gelation and establish key criteria relating to the transition temperature and stability of these materials. The data suggest that these materials may be attractive substrates for tissue engineering and cellular delivery applications as the combination of mechanistically independent gelation techniques used in tandem may offer superior materials with regard to gelation kinetics and stability.
authors.affiliation: Department of Bioengineering, Rice University, MS-142, Post Office Box 1892, Houston, Texas 77251-1892, USA.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Hacker
authors.forename: Leda
authors.initials: L
authors.lastname: Klouda
authors.forename: Brandy B
authors.initials: BB
authors.lastname: Ma
authors.forename: James D
authors.initials: JD
authors.lastname: Kretlow
authors.forename: Antonios G
authors.initials: AG
authors.lastname: Mikos
mesh_terms: D000178:Acrylamides / Q000138:chemical synthesis* / Q000737:chemistry*; D000179:Acrylates / Q000737:chemistry; D000180:Acrylic Resins; D001672:Biocompatible Materials / Q000138:chemical synthesis; D002152:Calorimetry, Differential Scanning; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents / Q000737:chemistry; D004355:Drug Stability; D020100:Hydrogels / Q000138:chemical synthesis* / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007267:Injections; D009682:Magnetic Resonance Spectroscopy; D008689:Methacrylates / Q000138:chemical synthesis; D008970:Molecular Weight; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry*; D011409:Propylene Glycols / Q000737:chemistry; D012212:Rheology; D013229:Stearic Acids / Q000737:chemistry; D044366:Transition Temperature
chemical_list: D000178:Acrylamides; D000179:Acrylates; D000180:Acrylic Resins; D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D020100:Hydrogels; D008689:Methacrylates; D011108:Polymers; D011409:Propylene Glycols; D013229:Stearic Acids; C052970:poly-N-isopropylacrylamide; C008783:pentaerythritol