internal restoring stresses in the network chains of the remaining network, due to
rubber-like elasticity, also persist and produce changes in the microstructure. The
molecular details of the microstructure recovery are not yet fully known, but the
global microstructure of the gel eventually recovers.
The supramolecular nature of SAHs allows the hydrogel to be dissolved by
solvating the hydrophobic bonds with a suitable solvent, such as isopropanol or a
mixed solvent of water and isopropanol or DMSO. The resulting solutions may be
electrospun into micro- or nanofiber mats that may be used as scaffolds for tissue
engineering or injected through a capillary (syringe) into a non-solvent medium to
form a hydrogel in situ during a medical procedure. Alternatively, the hydrophobic
bonds can be sufficiently weakened by either raising the temperature above the T g of
the nanodomains, 45
C, or by applying a sufficient stress to the hydrogel, so that the
hydrogel itself can be extruded through a capillary.
The SAHs have potential uses in many of the biomedical applications that have
been discussed elsewhere for physical hydrogels, in general [110, 111]. However,
their two-phase microstructure provides an extra degree of freedom in the development of controllable drug release media using these hydrogels. The antifreeze and
shape memory characteristics of the SAHs, which may have a number of biomedical
implications, are also advantageous consequences of the microphase-separated
microstructure.
A serious deficiency of the SAHs discussed in this chapter is that the fluoro(meth)
acrylate monomers that were used are no longer commercially available, and
although they were commonly use in commercial products (e.g., in Scotchgard, a
former product of the 3 M company) when the work on SAHs was begun in the late
1990s, they are today considered to be a persistent organic pollutant (POP). As such,
these hydrogels cannot and should not be further developed. Research on similar
microphase-separated amphiphilic hydrogels where a hydrocarbon-based hydrophobic monomer replaces the fluoro(meth)acrylate monomers, however, is currently
underway. Early results indicate that similar mechanical properties as described here
for the fluorocarbon SAHs are possible, as well as controlled drug release, antifreeze,
and shape memory properties.
Acknowledgments This review was derived from the research and journal papers of the following
MS and PhD students and postdoctoral research associates from the University of Connecticut and
the University of Akron: Sung-Su Bae, Kaushik Chakrabarty, Debashis Debnath, Jinkun Hao, Xing
Lu, Matthew Mullarney, Siamak Shams Es-Haghi, Jun Tian, Chao Wang, Fei Wang, Clinton
Wiener, and Yiming Yang. We also acknowledge the contributions to this research by Prof. Thomas
A. P. Seery (University of Connecticut); Prof. Colleen Pugh (University of Akron (now, Wichita
State University); Dr. Masatumi Fukuto and Dr. Ruipeng Li (Brookhaven National Laboratory,
Upton, NY); Dr. Christopher White, Dr. Yun Liu, and Dr. Derek Ho (National Institute of Standards
and Technology, Gaithersburg, MD); and Prof. Kenneth Shull and Kazi Sadman (Northwestern
University). The nanostructure characterization of these hydrogels was enabled by user facilities for
SAXS [Complex Materials Scattering (CMS/11-BM) beamline, operated by the National Synchrotron Light Source II and the Center for Functional Nanomaterials, which are US Department of
Energy (DOE) Office of Science User Facilities operated for the DOE Office of Science by
Brookhaven National Laboratory under Contract No. DE-SC0012704] and SANS (Center for
High Resolution Neutron Scattering, a partnership between the National Institute of Standards
and Technology and the National Science Foundation under Agreement No. DMR-1508249).
204
B. D. Vogt and R. A. Weiss
rubber-like elasticity, also persist and produce changes in the microstructure. The
molecular details of the microstructure recovery are not yet fully known, but the
global microstructure of the gel eventually recovers.
The supramolecular nature of SAHs allows the hydrogel to be dissolved by
solvating the hydrophobic bonds with a suitable solvent, such as isopropanol or a
mixed solvent of water and isopropanol or DMSO. The resulting solutions may be
electrospun into micro- or nanofiber mats that may be used as scaffolds for tissue
engineering or injected through a capillary (syringe) into a non-solvent medium to
form a hydrogel in situ during a medical procedure. Alternatively, the hydrophobic
bonds can be sufficiently weakened by either raising the temperature above the T g of
the nanodomains, 45
C, or by applying a sufficient stress to the hydrogel, so that the
hydrogel itself can be extruded through a capillary.
The SAHs have potential uses in many of the biomedical applications that have
been discussed elsewhere for physical hydrogels, in general [110, 111]. However,
their two-phase microstructure provides an extra degree of freedom in the development of controllable drug release media using these hydrogels. The antifreeze and
shape memory characteristics of the SAHs, which may have a number of biomedical
implications, are also advantageous consequences of the microphase-separated
microstructure.
A serious deficiency of the SAHs discussed in this chapter is that the fluoro(meth)
acrylate monomers that were used are no longer commercially available, and
although they were commonly use in commercial products (e.g., in Scotchgard, a
former product of the 3 M company) when the work on SAHs was begun in the late
1990s, they are today considered to be a persistent organic pollutant (POP). As such,
these hydrogels cannot and should not be further developed. Research on similar
microphase-separated amphiphilic hydrogels where a hydrocarbon-based hydrophobic monomer replaces the fluoro(meth)acrylate monomers, however, is currently
underway. Early results indicate that similar mechanical properties as described here
for the fluorocarbon SAHs are possible, as well as controlled drug release, antifreeze,
and shape memory properties.
Acknowledgments This review was derived from the research and journal papers of the following
MS and PhD students and postdoctoral research associates from the University of Connecticut and
the University of Akron: Sung-Su Bae, Kaushik Chakrabarty, Debashis Debnath, Jinkun Hao, Xing
Lu, Matthew Mullarney, Siamak Shams Es-Haghi, Jun Tian, Chao Wang, Fei Wang, Clinton
Wiener, and Yiming Yang. We also acknowledge the contributions to this research by Prof. Thomas
A. P. Seery (University of Connecticut); Prof. Colleen Pugh (University of Akron (now, Wichita
State University); Dr. Masatumi Fukuto and Dr. Ruipeng Li (Brookhaven National Laboratory,
Upton, NY); Dr. Christopher White, Dr. Yun Liu, and Dr. Derek Ho (National Institute of Standards
and Technology, Gaithersburg, MD); and Prof. Kenneth Shull and Kazi Sadman (Northwestern
University). The nanostructure characterization of these hydrogels was enabled by user facilities for
SAXS [Complex Materials Scattering (CMS/11-BM) beamline, operated by the National Synchrotron Light Source II and the Center for Functional Nanomaterials, which are US Department of
Energy (DOE) Office of Science User Facilities operated for the DOE Office of Science by
Brookhaven National Laboratory under Contract No. DE-SC0012704] and SANS (Center for
High Resolution Neutron Scattering, a partnership between the National Institute of Standards
and Technology and the National Science Foundation under Agreement No. DMR-1508249).
204
B. D. Vogt and R. A. Weiss