Preparation and characteristics of a binderless carbon nanotube monolith and its biocompatibility

A carbon nanotube (CNT) monolith without any binders was obtained by spark plasma sintering (SPS) treatment at 1100 °C under 40 MPa pressure. Transmission electron microscope results confirmed that this material maintained the nanosized tube microstructure of raw CNT powder after SPS treatment. The density and mechanical properties of this material were similar to cancellous bone. The material was implanted in subcutaneous tissue and femurs of rats and tissue samples were analyzed by histopathology at 1 and 4 weeks after surgery. Although some foreign body giant cells were seen around the CNTs, no severe inflammatory response such as necrosis was observed, and CNT implants were surrounded by newly formed bone in the femur. The study provides the first in vivo testing evidence that pure bulk carbon nanotubes are not a strongly inflammatory substance and have no toxicity for bone regeneration. Our study is the first successful experiment to consolidate CNTs without binders, and may provide an effective method for CNT monolith synthesis, as well as demonstrating that a binderless carbon nanotube material with a strength matching that of bone could be a candidate bone substitute material and a bone tissue engineering scaffold material.