Skull injuries caused by trauma, pathologies, such as tumour, or birth defects require the reconstruction of complex craniofacial prostheses and the choice of suitable biomaterials is currently the main challenge for a successful implant repair. Indeed, different classes of mono-materials, such as polymer, ceramics and light metals, are used for craniofacial prosthesis. But a quite big discrepancy between the mechanical properties and the weight of the implant and the bone that has to be replaced still exists[1]-[3]. Since, mono-materials alone cannot solve this problem in an optimal way, the design of innovative hybrid systems, composed of two metallic sheets and a polymer core, can represent an interesting alternative for the fabrication of skull prosthesis thanks to their tunable mechanical properties and high formability[4],[5].
Metal/polymer sandwich systems are well known in the automotive industry because of their high mechanical properties and lightweight. They deal with the combination of steel and a polyolefin (PP-PE) foil, stuck together with an epoxy resin using a roll-bonding technique. Recently we have substituted the steel with the titanium (Ti) in order to: to (i) decrease the weight; (ii) reach mechanical properties close to those of the bone; (iii) increase the biocompatibility and (iv) maintain a good forming behaviour[5].
The main drawback of this system for biological application is the presence of the toxic epoxy resin, commonly used to stick the polymer onto the metal surface.
Our idea consists in replace the epoxy resin with a chemical functionalization of the Ti surfaces in order to covalently bond the polymer chains and the metal.
In particular the poly(methyl methacrylate) (PMMA) chains have been grown on the Ti surface using a “grafting from” method coupled with a Controlled Radical Polymerization (CRP) reaction. First of all, the Ti surfaces have been physically and chemically activated in order to remove the native oxide layer which passives the surface. Then, the organic polymerization initiator molecules are grafted through covalent bonds on the activated Ti surface. Finally, the polymer chains are grown starting from the initiator using a CRP of the methyl methacrylate monomer.
Moreover, in order to validate our approach the Ti/PMMA interfaces have been accurately characterized. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) have been employed to study the morphology of the Ti modified surfaces. Instead, their chemical composition has been investigated by surface spectroscopies (such as X-ray photoelectron spectroscopy (XPS), Energy-dispersive X-ray spectroscopy (EDX) and Infrared Fourier Transform Spectroscopy).
Overall, our goal is to prove that PMMA chains can be covalently bonded to Ti foils up to 10x10 mm² by grafting and CRP reaction without delaminate and demonstrate their biocompatibility.
References:
[1] Lethaus B, Safi Y, Laak-Poort M, Kloss-Brandstatter A, Banki F, Robbenmenke C, Steinseifer U, Kessler P. Journal of neurotrauma (2012), 29(6), 1077-83.
[2] Origitano TC, Izquierdo R Scannicchio LB, Skull base surgery (1995), 5(2), 109-16.
[3] Isaza Saldarriaga JF, Correa Vélez S, MD Cumplido Posada A, IE Balmore Bedoya Henao and ME Andrés Torres Valencia C. American J. of Engineering and Applied Sciences (2011) 4 (1): 169-174
[4] Sokolova O, Carradò A, Palkowski H. Composite Structures (2011) 94, 1: 1-7.
[5] Carradò A, Faerber J, Niemeyer S, Ziegmann G, Palkowski H. Composite Structures (2011);93(2):715-21.