Abstract
After several years of research and development, it has been reported that magnesium alloys can be used as degradable metals in some medical device applications. Over the years, fluoride coatings have received increasing research attention for improving the corrosion resistance of magnesium. In this paper, different methods for preparing fluoride coatings and the characteristics of these coatings are reported for the first time. The influence of the preparation conditions of fluoride coatings, including the magnesium substrate, voltage, and electrolyte, on the coatings is discussed. Various properties of magnesium fluoride coatings are also summarized, with an emphasis on corrosion resistance, mechanical properties, and biocompatibility. We screened experiments and papers that planned the application of magnesium fluoride coatings in living organisms. We have selected the literature with the aim of enhancing the performance of in vivo implants for reading and further detailed classification. The authors searched PubMed, SCOPUS, Web of Science, and other databases for 688 relevant papers published between 2005 and 2021, citing 105 of them. The selected time range is the last 16 years. Furthermore, this paper systematically discusses future prospects and challenges related to the application of magnesium fluoride coatings to medical products.
Highlights
With the rapid increase in the number of tissue injury repair procedures, metals have been widely used for the replacement and regeneration of injured tissues owing to their high mechanical properties [1]. eir common applications include scaffolds [2, 3], bone plates [4, 5], bone nails [6], wound closing devices [7], artificial joint prostheses [8], and guided tissue/bone regeneration membranes [9]
As a biodegradable metal, magnesium is preferred as a biologically essential trace element, with an elastic modulus similar to bone in fracture healing, eliminating the need for a secondary surgical removal [13]. e ideal clinical biodegradable metals must be perfectly suited for the injured tissue reconstruction in a biologically nontoxic precondition, providing absolute mechanical protection in the early stages and gradually degrading at an acceptable rate as the tissue heals [7]
Fluoride coatings have received more attention in recent years, for methods such as immersion fluorination, microarc fluorination [32], and ultrasonic immersion fluorination [24] based on the composite fluoride coatings derived from the abovementioned methods, such as hydroxyapatite/magnesium fluoride composite coatings [33], fluoride-treated and sol-gel film composite coatings [34], and composite coatings with fluoride as a pretreatment, an electrolyte, or additives [35–41]; these composite and multilayer coatings are not discussed in detail in this paper because there are no strict standards for their conceptual classification
Summary
With the rapid increase in the number of tissue injury repair procedures, metals have been widely used for the replacement and regeneration of injured tissues owing to their high mechanical properties [1]. eir common applications include scaffolds [2, 3], bone plates [4, 5], bone nails [6], wound closing devices [7], artificial joint prostheses [8], and guided tissue/bone regeneration membranes [9]. Nonbiodegradable metals used in traditional metal implants include stainless steel, titanium, and cobalt-chromium alloys [7, 10] Despite their excellent biocompatibility and mechanical properties, they can cause inflammatory reactions because of the release of toxic ions, which often require secondary surgical removal [11, 12]. E ideal magnesium alloy coating has properties such as corrosion resistance, degradability, and biocompatibility for clinical applications [17]. Tightly bonded to the substrate and insoluble in water, is formed via chemical reactions between fluorine and magnesium by the specific methods listed above. 2. Growth of Fluorinated Coatings e fabrication of a dense, homogeneous, and biocompatible fluorinated coating on the surface of magnesium alloys by chemical transformation is a widely used treatment to enhance the corrosion resistance of magnesium alloys [29, 30], that is, HF acid immersion treatment. Fluoride coatings have received more attention in recent years, for methods such as immersion fluorination, microarc fluorination [32], and ultrasonic immersion fluorination [24] based on the composite fluoride coatings derived from the abovementioned methods, such as hydroxyapatite/magnesium fluoride composite coatings [33], fluoride-treated and sol-gel film composite coatings [34], and composite coatings with fluoride as a pretreatment, an electrolyte, or additives [35–41]; these composite and multilayer coatings are not discussed in detail in this paper because there are no strict standards for their conceptual classification
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