Coupling of Metals and Biominerals: Characterizing the Interface between Ferromagnetic Shape-Memory Alloys and Hydroxyapatite

Abstract

Durable, mechanically robust osseointegration of metal implants poses one of the largest challenges in contemporary orthopedics. The application of biomimetic hydroxyapatite (HAp) coatings as mediators for enhanced mechanical coupling to natural bone constitutes a promising approach. Motivated by recent advances in the field of smart metals that might open the venue for alternate therapeutic concepts, we explore their mechanical coupling to sputter-deposited HAp layers in a combined experimental-theoretical study. While experimental delamination tests and comprehensive structural characterization, including high-resolution transmission electron microscopy, are utilized to establish structure-property relationships, density functional theory based total energy calculations unravel the underlying physics and chemistry of bonding and confirm the experimental findings. Experiments and modeling indicate that sputter-deposited HAp coatings are strongly adherent to the exemplary ferromagnetic shape-memory alloys, Ni-Mn-Ga and Fe-Pd, with delamination stresses and interface bonding strength exceeding the physiological scales by orders of magnitude.

Properties and Mechanism of Hydroxyapatite Coating Prepared by Electrodeposition on a Braid for Biodegradable Bone Scaffolds

“…The ball-and-stick model diagram shows that the calcium ion and the phosphate group are located at upper and lower planes of hexagonal prism, and the hydroxyl group lies on the left and right sides of the prism portion. The hydrogen bond between the hydroxyl groups forms the connection to the HA unit cell, while the calcium phosphate group connects with the HA upper- and lower-unit cells [43,44].…”

Hydroxylapatite and Related Minerals in Bone and Dental Tissues: Structural, Spectroscopic and Mechanical Properties from a Computational Perspective

“…One of the first works in this sense was proposed by Allenstein and co-workers, who performed a combined experimental/theoretical study of the structural and adhesion properties of hydroxylapatite coating on two ferromagnetic shape-memory alloys, Ni−Mn−Ga and Fe−Pd. The authors considered experimental delamination tests on sputter-deposited thin films of OHAp, and performed DFT simulations on simplified models of OHAp/alloy interfaces using the PWSCF code, PBE functional, and plane-wave basis sets [ 172 ]. The authors measured for the OHAp/Ni–Mn–Ga system a delamination work of 1.6 J m −2 , with failure occurring at the composite interface, and a theoretical adhesion of −1.9 J m −2 .…”

Structure of A–C Type Intervariant Interface in Nonmodulated Martensite in a Ni–Mn–Ga Alloy

“…[1][2][3] The MFIS is achieved in a martensitic state. The modulated (M) martensite exhibits large MFIS (up to 10%), 4 whereas the non-modulated (NM) martensite exhibits very small MFIS in many cases.…”

“…[6][7] Thus the microstructure of twinned martensite and the structure of intervariant interface play a crucial role in MFIS. In the Ni-Mn-Ga alloys there are four mutually twin-related martensitic variants within a plate group, commonly designated as A, B, 3 C and D, and these four variants can be categorized into three types of variant pairs: namely A-B, A-C and A-D types ( Figure S1). 8 For a modulated structure (e.g.…”

“…The Ni–Mn–Ga ferromagnetic shape memory alloys (FSMAs) can generate large magnetic-field-induced-strains (MFIS) with many potential applications for sensors and actuators in the medical, aerospace, and marine industries. − The MFIS is achieved in a martensitic state. The modulated (M) martensite exhibits large MFIS (up to 10%), whereas the nonmodulated (NM) martensite exhibits very small MFIS in many cases .…”