Stoichiometry, crystallinity, and nano-scale surface morphology of the graded calcium phosphate-based bio-ceramic interl
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Stoichiometry, crystallinity, and nano-scale surface morphology of the graded calcium phosphate-based bio-ceramic interlayer on Ti-Al-V J. D. Long, K. Ostrikov, and S. Xu Advanced Materials and Nanostructures Laboratory, Natural Sciences, Nanyang Technological University, 637616 Singapore V. Ligatchev School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore ABSTRACT A plasma-assisted concurrent Rf sputtering technique for fabrication of biocompatible, functionally graded CaP-based interlayer on Ti-6Al-4V orthopedic alloy is reported. Each layer in the coating is designed to meet a specific functionality. The adherent to the metal layer features elevated content of Ti and supports excellent ceramic-metal interfacial stability. The middle layer features nanocrystalline structure and mimics natural bone apatites. The technique allows one to reproduce Ca/P ratios intrinsic to major natural calcium phosphates. Surface morphology of the outer, a few to few tens of nanometers thick, layer, has been tailored to fit the requirements for the bio-molecule/protein attachment factors. Various material and surface characterization techniques confirm that the optimal surface morphology of the outer layer is achieved for the process conditions yielding nanocrystalline structure of the middle layer. Preliminary cell culturing tests confirm the link between the tailored nano-scale surface morphology, parameters of the middle nanostructured layer, and overall biocompatibility of the coating. INTRODUCTION Calcium phosphate-based bio-ceramics have recently attracted a great deal of interest as functional surface coatings in dental and orthopedic implants because of excellent bio-activity, bio-compatibility, chemical and mechanical properties [1-5]. In particular, hydroxyapatite (HA, Ca10(PO4)6(OH)2, Ca/P=1.67) coatings reveal inspiring clinical advantages in promoting efficient implant fixation and implant-to-bone adhesion shortly after the implantation, as well as faster bone remodeling due to enhanced bi-directional growth and formation of a bonding interlayer between bone and implant [1]. Furthermore, calcium phosphates with apatite-like structure are the major constituents of the bone mineral phase, are compatible with various soft and muscular tissue types, and can efficiently sustain protein attachment and growth [1]. Clinical applications of CaP-based bio-ceramics for improved fixation between bone and implant pose a number of challenges for tailoring the coating quality specifications. The key quality factors include stoichiometry, crystallinity, microstructure, metal-implant interfacial stability and several others [6]. In addition, a successful technique for fabrication of a viable biocompatible
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coating would intrinsically imply a certain degree of replication of biological apatites, featuring nano-crystalline structures in bone and dentin materials. Above all, surface morphology with nano-scale features and excellent island uniformity, a
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