Relationship between the Porous Structure Hierarchy and the Physical and Mechanical Properties of Calcium Phosphate Drug
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RELATIONSHIP BETWEEN THE POROUS STRUCTURE HIERARCHY AND THE PHYSICAL AND MECHANICAL PROPERTIES OF CALCIUM PHOSPHATE DRUG CARRIERS E. G. Komarova,1 M. B. Sedelnikova,1 E. A. Kazantseva,1,2 P. V. Uvarkin,1 and Yu. P. Sharkeev1
UDC 621.794.61
A relationship between the structural-morphological and physical-mechanical properties of macro-porous calcium phosphate (CaP) coatings on the surface of titanium implants is studied. The produced CaP coatings can be used as carriers for target drug delivery in biomedical applications. The regularities of the formation of bulk (thickness of 15–130 µm) and rough (Ra = 1.7–8.5 µm) CaP coatings deposited by the micro-arc oxidation (MAO) method are studied. The coatings have a hierarchical porous structure and a uniform distribution of the structural elements (spheres and pores) over the surface. Correlations between the value of the applied voltage and structural-morphological and physical-mechanical characteristics of the CaP coatings have been established. The value of the coating adhesion strength has been determined with tensile tests. Both cohesive and mixed adhesive-cohesive pull-off of the MAO coating from the substrate have been identified. Keywords: micro-arc oxidation, calcium phosphate coating, spheroidal structural element, porosity, adhesion strength.
INTRODUCTION A promising direction in biomedical materials science is the development of calcium phosphate (CaP) materials with regulated porous structure as drug carriers (antibacterial, anticancer, etc.) [1]. The success in the development of such systems as matrices for controlled and targeted drug delivery is in many respects determined by their characteristics, such as biocompatibility, mechanical strength, adsorption properties, specific composition and structure preventing uncontrolled release of the drug as well as by the well studied methods of obtaining porous structures with morphology changing in a wide range [2, 3]. Nowadays the CaP materials are being developed in different forms, such as powders, granules, bulk materials, coatings on metals, and separate components of composite materials representing fragmented or continuous matrices [4]. Among other methods of formation of porous CaP coatings, the method of micro-arc oxidation (MAO), also known as plasma electrolytic oxidation (PEO), is distinguished by high adaptability to manufacture, ecological compatibility, productivity, and low energy consumption. This method can be used to form CaP biocoatings with a wide range of physical and chemical properties, high corrosion resistance, strong adhesion to the substrate, various degrees of crystallinity, thickness, roughness, and porosity on the surface of valve metals (Ti, Zr, Nb, Mg, etc.) [5, 6]. As a rule, the problem of increasing the porosity and pore sizes of the MAO coatings is solved by fabricating new compositions of electrolytes and new power supplies as well as by optimization of the main electrophysical parameters of the process, in particular, of the applied electric voltage [5, 7]. However, the i
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