Introduction: Mg alloys have been used as degradable implants in the clinic since 1878 for their good biocompatibility. Magnesium ions play an important role in the body through its anti-inflammatory properties and by acting as Ca2+ antagonist[1]. Among several magnesium compounds it has been demonstrated that Mg(OH)2 is very effective in temporarily enhancing osteoblast activity and in decreasing the density of osteoclasts peri-implant bone remodeling due to a realease of Mg2+ and a local increasing of pH[2]. This paper represents the first example in literature of sputter deposition of magnesium and its compounds on external surface of 3D porous Poly(caprolactone), PCL scaffolds to improve their biocompatibility.
Materials and Methods: PCL scaffolds 5mm thick, 10 mm diameter were fabricated with the solvent-casting particulate-leaching technique, as explained in detail elsewhere[3]. Scaffolds of 150-300 mm pore size and 97±3 % apparent mean porosity were obtained. Mg containing coatings have been produced by means of RF (13.56 MHz) sputtering of a MgO target (MgO 99.9%, Goodfellow US). Discharges fed with H2, H2O, Ar and mixture of them (20sccm tot. flow) at 6.7-10.7 Pa and 50W were carried out. Materials were characterized by means of dynamic water contact angle (WCA, CAM200 KSV instrument) XPS (Theta Probe Thermo VG Scientific), FE-SEM (Zeiss SUPRA 40), and FT-IR (vertex70V Bruker spectrometer). The release of Magnesium was assessed after 36 hours of immersion in double distilled water at 25°C of the samples by ICP-MS (PerkinElmer Nexion 300X). Saos2 osteoblast-like cells (ICLC) were grown in DMEM medium supplemented with 10% FBS.
Results: Plasma deposited coatings show thickness lower than 10nm. XPS analysis shows that the coatings penetrate 1mm inside the scaffold. When the H2/Ar ratio in the gas fed increases an increase of the amount of sputtered magnesium in the coatings is present (max %Mg: 20%). A best fitting of XPS Mg2p high resolution spectra shows the presence of both Mg(OH)2 (together with elemental Mg), and of MgO. The content of Mg(OH)2/MgO ratio increases (i.e. from 0.5 to 2) with H2 in the gas feed . All tested materials are hydrophilic (static WCA<60°) except the native one (WCA: 120±4°). The amount of total released magnesium in water ranges from 120ppb to 320 ppb after 36 hours of double distilled water rinsing. A hydrocarbon barrier coating was successfully used to control the release of magnesium during time[4]. By increasing the total magnesium content in the coating (i.e. magnesium released) in vitro cell adhesion and proliferation are promoted. A cell ingrowth was obtained depending on the investigated experimental conditions.
Discussion: The increasing of elemental magnesium and magnesium hydroxide in the coatings when the hydrogen in the gas feed increses is due to the reducing effect of hydrogen. A good correlation between released magnesium and cell spreading has been reported thus demonstrating the active role of magnesium at the cell/material interface.
Conclusions: Chemically different plasma sputtered coatings from a MgO target were successfully deposited on PCL porous scaffolds. The plasma deposited Mg-containing surfaces have shown an interesting attitude to support such cell behavior, thus making them good candidate surfaces for TE scaffolds for bone regeneration.
RINOVATIS (MIUR; PON 02_00563_3448479, Dhitech); LIPP (Regione Puglia; Laboratorio di ricerca Industriale Pugliese dei Plasmi, Rete di Laboratorio 51),; RIGENERA (Regione Puglia; “Partenariati”, n° P9Y0834); SISTEMA (MIUR; PONa3_00369, Univ. Bari),
References:
[1] J. H. F. de Baaij, J. G. J. Hoenderop, R. J. M. Bindels; Physiol Rev 95: 1–46, 2015
[2] C. Janning, E. Willbold, C. Vogt, J. Nellesen, A. Meyer-Lindenberg, H. Windhagen, F. Thorey, F. Witte; Acta Biomaterialia 6, 1861-1868, 2010
[3] E. Sardella, E. R. Fisher, J. C. Shearer, M. Garzia Trulli, R. Gristina, P. Favia, Plasma Proc. Polym. DOI: 10.1002/ppap.201400201, 2015
[4] Patent WO2013021409-A1: E. Sardella, P. Favia et al. 2013