The corrosion resistance and biomineralization of the DCPD-PCL coating on the surface of the additively manufactured NiTi alloy

Selective laser melting (SLM)-manufactured shape memory Nickel-Titanium (NiTi) alloy has great potential to use as an implant because it can achieve sophisticated structures and possess excellent mechanical properties. However, poor corrosion performance, biological inertness, and toxic Ni ions release limit its wide application. This study reports a multifunctional composite coating which composed of polycaprolactone (PCL) and dicalcium phosphate dihydrate (DCPD) by dipping method and electrodeposition to improve biomineralization and corrosion resistance of SLM-NiTi alloy. The results revealed that PCL coating successfully sealed the pores and cracks of DCPD coating and significantly improved the corrosion resistance of the coating (the corrosion current density decreased from 2.6 x 10-7 to 1.4 x 10-8 A/cm2) and the binding force was also improved (from 2397 to 2910 mN). In long-term immersion tests, the composite coating exhibited good biomineralization properties which promoted the deposition of Ca and P in simulated body fluids to form hydroxyapatite (HA). Moreover, the in vitro cell experiment showed that the composite coating was beneficial to cell adhesion and proliferation. Therefore, the DCPD-PCL-coated SLM-NiTi alloy has enormous potential as a medical implant in clinical applications.