Photodynamic Activity of Protoporphyrin IX-Immobilized Cellulose Monolith for Nerve Tissue Regeneration

The development of nerve conduits with a three-dimensional porous structure has attracted great attention as they closely mimic the major features of the natural extracellular matrix of the nerve tissue. As low levels of reactive oxygen species (ROS) function as signaling molecules to promote cell proliferation and growth, this study aimed to fabricate protoporphyrin IX (PpIX)-immobilized cellulose (CEPP) monoliths as a means to both guide and stimulate nerve regeneration. CEPP monoliths can be fabricated via a simple thermally induced phase separation method and surface modification. The improved nerve tissue regeneration of CEPP monoliths was achieved by the activation of mitogen-activated protein kinases, such as extracellular signal-regulated kinases (ERKs). The resulting CEPP monoliths exhibited interconnected microporous structures and uniform morphology. The results of in vitro bioactivity assays demonstrated that the CEPP monoliths with under 0.54 +/- 0.07 mu mol/g PpIX exhibited enhanced photodynamic activity on Schwann cells via the generation of low levels of ROS. This photodynamic activation of the CEPP monoliths is a cell-safe process to stimulate cell proliferation without cytotoxic side effects. In addition, the protein expression of phospho-ERK increased considerably after the laser irradiation on the CEPP monoliths with low content of PpIX. Therefore, the CEPP monoliths have a potential application in nerve tissue regeneration as new nerve conduits.