Graphene-reinforced collagen hydrogels with through-thickness porosity

Abstract

Collagen, an extracellular protein abundant in animal tissues, is an excellent candidate for tissue engineering and other biomedical applications. Superporous hydrogels for gastric retention drug delivery systems and ice-templated materials, which have distinct advantages in cell interations, are some examples. Although it has been one of the most preferred biomaterials for in vivo medical applications, its difficult processing and poor mechanical properties have been the barriers to its use. The poor mechanical properties of collagen led previous researchers to use reinforcing particles for strengthening purpose. Hydroxyapatite nanoparticles have been the primary choice for researchers interested in bone tissue engineering. Silica nanoparticles and carbon nanotubes have also been employed, and carbon nanotubes functionalized with carboxyl groups were able to dramatically improve the mechanical properties. With advances in preparation techniques and the understanding of graphene, experimental and theoretical studies of graphene composite scaffolds have been increasingly explored. So far, no systematic experimental study of graphene/collagen combination has been reported to the best of our knowledge, and only several theoretical predictions that surface ripples or charged functional groups are critical for mechanical strengthening in graphene/collagen composites have recently been reported. This study demonstrates the successful reinforcement effects of reduced graphene oxide (rGO, Figure S1, Supporting Information) in superporous collagen hydrogels with a pore morphology engineered by directional cooling crystallization of water. The resulting composite hydrogels can be used as strong, biocompatible hydrogels for tissue engineering, drug delivery systems, and sensors. Furthermore, the directional cylindrical pores are expected to have the ability to guide cells, and the incorporation of rGO is expected to provide electrical conductivity.