This paper investigates the direct-write inkjet method for depositing multi-layer coatings of biodegradable polymers on magnesium alloy surface. Immersion studies were conducted on Poly(lactic-co-glycolic) acid (PLGA), polycaprolactone (PCL), and poly-ester urethane urea (PEUU) coatings to determine the corrosion behavior of different samples based on their varying degradation properties. Using the inductively coupled plasma spectroscopy, a reduction in magnesium ion concentration was observed from the polymer-coated samples indicative of the lower corrosion rates as compared to the uncoated Mg substrate. Findings also showed correlation between the release of the magnesium ions and the health of fully differentiated normal human bronchial epithelial (NHBE) cells via evaluation of key biomarkers of inflammation and toxicity, cyclooxygenase-2 (COX-2) and lactate dehydrogenase (LDH), respectively. The induction of COX-2 gene expression was proportional to the increase in magnesium exposure. In addition, the release of higher magnesium content from uncoated and PCL polymer coated samples resulted in lower LDH activity based on the favorable response of the NHBE cells. PEUU and PLGA polymer coatings provided good barrier layer corrosion protection. This research evaluates candidate polymer coatings as a source for therapeutic agents and barrier layer to control the corrosion of magnesium alloys for tracheal applications.

In recent years, much progress has been made on the development of biodegradable magnesium alloys as “smart” implants in cardiovascular and orthopedic applications. Mg-based alloys as biodegradable implants have outstanding advantages over Fe-based and Zn-based ones. However, the extensive applications of Mg-based alloys are still inhibited mainly by their high degradation rates and consequent loss in mechanical integrity. Consequently, extensive studies have been conducted to develop Mg-based alloys with superior mechanical and corrosion performance. This review focuses on the following topics: (i) the design criteria of biodegradable materials; (ii) alloy development strategy; (iii) in vitro performances of currently developed Mg-based alloys; and (iv) in vivo performances of currently developed Mg-based implants, especially Mg-based alloys under clinical trials.

The global orthopedic device market is expected to grow by 9% annually, which will equate to US$50 billion by 2015, necessitating innovation in medical devices that improve the quality of life. The first step in the creation of a foundation of knowledge and technology to improve these implant devices is through the creation of new materials with the capabilities of biodegradation and bioabsorption without a toxicity effect that will pass through Food and Drug Administration regulatory procedures. Magnesium and its alloys have gained attention as biomedical implant materials based on biocompatibility and biodegradability. The objective of this study is to investigate the cytocompatibility effects of adding zinc to a magnesium–calcium system through in-direct cell culture assays utilizing MC3T3-E1 preosteoblast mouse cells. Cell culture assays indicate that there is a level of cytotoxicity that develops from adding zinc to a magnesium–calcium system, but descriptive evidence suggests that solution heat treatment may reduce these cytotoxic effects.

Some of the most important characteristics of a medical implant biomaterial are its corrosion resistance, cytotoxicity, mechanical property, and overall biological performance. Optimizing these characteristics is therefore vital to the success of creating effective medical biomaterials. It is well known that heat treatment processes affect the microstructure of metallic alloys which consequently can have favorable influences on the mechanical properties. The determination of the effects of heat treatment on the corrosion resistance of metallic alloys is another aspect that must be examined. That is the goal of this investigation. The corrosion characteristics of two MgZnCa alloy systems (MgZnCa-31 and MgZnCa-32) were studied to determine the correlation between T4 and T6 heat treatment and the corrosion rate on the alloys. The alloys were produced by melting and casting at 730°C and then heat treated. The corrosion performances of the alloys were examined by both immersion and electrochemical analysis, which were conduct in 0.9% NaCl physiological saline solution. In terms of the effects of the T4 heat treatment, the corrosion rate of the MgZnCa-31 decreases as the time period of the heat treatment increases, whereas the MgZnCa-32 alloys have an opposite effect meaning that the corrosion rate increases as the time period of the heat treatment increases. There was no significant change in corrosion with the introduction of T6 heat treatment to both alloy systems.

In the present study, Mg-8at.%Zn-1at.%Ca alloys were fabricated via T4 and T6 solid solution treatment technique for biomedical applications. The alloys were prepared at three different temperatures: 400 °C, 465 °C and 530°C followed by water or liquid nitrogen quenching. The microstructure of Mg-Zn-Ca alloys was characterized using X-ray diffraction (XRD) analysis, optical and electron microscopes, and energy dispersive spectroscopy, respectively. The examination of mechanical properties was conducted on micro hardness tester. The following differences can be concluded from the results: In water quenched samples, the following three phases were identified from XRD pattern: α -Mg matrix, binary Mg2Zn3 and ternary Ca2Mg6Zn3, the secondary phases are more agglomerated. At higher solution treatment temperature, the secondary phases became more dissolved to the Mg-matrix which creates better homogenized material. Higher treatment temperatures cause grains to grow and to a limited extent, samples quenched in liquid nitrogen have smaller grains than those quenched in water. The sample heat treated at the temperature of 465°C reaches a minimum hardness. While in liquid nitrogen quenched samples, the alloys consisted of four phases: α -Mg matrix, binary Mg2Zn3 and MgZn2 and ternary Ca2Mg6Zn3, the secondary phases are more distributed in a network form, at higher magnification, there are some secondary phases precipitated in rod/needle shape in the samples, the hardness of the samples decreases with the temperature increases.

Mg–10Zn–1Ca, Mg–20Zn–1Ca and Mg–6Zn–1Ca alloys were processed from powders in an argon filled glove box. The solidification rate was varied. Fast solicitation resulted in very small grain size and continuous 3D network distribution of the secondary phase in grain boundary. The alloy processed from fast solidification had better corrosion resistance than those solidified at low cooling rates. It may be because of the increased Zn and Ca in magnesium grains when the alloy was quickly cooled down from its molten state. Liquid nitrogen quenching at the end of solution treatment also created better distribution of network shaped secondary phase than water quenched alloys. Moderate temperature in solution treatment is preferred because it did not cause too much grain growth but increased microhardness of the treated alloys. Alloy with lower Zn amount had better corrosion resistance in PBS solution in this study.

Porous magnesium (Mg) alloys were processed by solid state sintering from mixture of elemental metal powders and pore-filling materials, such as, carbamide (urea). The porosity of the Mg alloy was controlled by selecting different particle size and volume fraction of the pore-filling material, as well as the sintering condition, which were arranged by a factorial experimental design. The effects of their porosity and porous structure were analyzed and the mechanical strength was evaluated with compression tests.