3D BioPrinted Carbon Nanotubes used to Stimulate Bone Regrowth
Reporter: Irina Robu, PhD
Bone disorders are of significant concern due to increase in the median age of our population and at this present time bone grafts have are used to restore damaged bone. However, synthetic biomaterials are now being used as bone graft substitutes and they are selected for structural restoration based on their biomechanical properties. Lately, scaffolds are engineered to be bioactive to enhance tissue growth. These scaffolds are usually porous, made of biodegradable factors, drugs or stem cells.
The research group led by Dr. Maria Vallet-Regi at Faculty of Pharmacy-Universidad Complutense de Madrid showed that carbon nanotubes to the mix to create 3D electrical network within the bone tissue can stimulate bone cell regrowth. The polymer they used was polycarpolactone (PCL), which is rather easy to 3D print.
According to Mercedes Vila, the Principal Investigator in charge of the project, the carbon nanotubes were added to the bio-printable material mixture to create a three-dimensional electrical conducting network all through the volume of the scaffold, which would allow the application of this stimulation to the scaffold once implanted on the damaged bone site.
“In this sense, electrical stimulation has been explored since the discovery of the presence of electrical potentials in mechanically loaded bones,” Mercedes pointed out. “Certain types of cell behavior, such as adhesion and differentiation, can be affected by the application of electrical stimulation. Thus, the creation of a permanent charge on the material surface, positive or negative, as well as a direct electrical stimulation can promote the attraction of charged ions from the environment to the cells. This would modify their protein adsorption with the subsequent influence on the cells’ metabolic activity. Therefore, the use of electrical stimulation after biomaterial implantation to favor cell adhesion and differentiation and, consequently, induce bone healing seems a smart approach to accelerate the osteointegration process.”
Adding CNTs into the bio-printed polymer and mineral prosthetic bone can stimulate regrowth of the actual bone cells. However, bio-printing CNTs created no extra difficulties, as they are so thin that they can be extruded with ease through any pneumatic syringe. Most of the complications are related to finding the correct viscosity in the combination of CPL and hydroxypatite.
“Finding the right right viscosity to be extruded through the syringe while keeping enough robustness to get the 3D scaffold printed at room temperature, was complicated,” Mercedes admitted. “At the same time as the slurry was prepared in dichloromethane solution for diluting the PCL, achieving the right viscosity while evaporating the solvent was tricky. Moreover, once the PCL and the hydroxyapatite were mixed together, the addition of the CNTs was performed and reaching a proper dispersion took a bit of stirring time.”
Using EnvisionTEC’s 3D bioplotter, the researchers were able to create very complex 3D structures which would enhance the future for tissue replacements as it allows tailored solutions by capturing the anatomical information of the patient’s wound by computed tomography and magnetic resonance, for example, to obtain a personalized and unique implant.
As with many other 3D printing applications, it appears we are only starting to scratch the surface of the possibilities that are ahead for bioprinting.