properties, corrosion resistance, and especially biocompatibility. Recently, silk fibroin (i.e., SF), a natural protein extracted from Bombyx mori silkworms, has been expected to be a coating strategy that protects of magnesium from corrosion for a long time. [10][11][12][13][14] This biological protein was similar to the collagen components in bone with osteogenic activity, which can endow inorganic Mg with osteoinductivity and osteoconductivity functions as a protective organic coating. However, the surface pretreatment process is essential in the application of biodegradable magnesium alloys, aiming to improve the adhesion force (or bonding strength) between organic protein coatings and inorganic magnesium substrates. [15] Thus, strong bonding at the interface can reinforce the anticorrosion performance of the coated structure in an immersed body fluid environment as well as the biocompatibility.Popular surface pretreatment includes chemical conversion, [16,17] microarc oxidation (MAO), [18,19] and intermediate layers, [20,21] which leads to some concerns regarding reliability or biosafety with increasing reports of clinical trials. The chemical conversion method applies alkaline or acid solutions on magnesium surfaces to form magnesium hydroxide [22] or magnesium fluoride, [23] which is simple and inexpensive. A single chemical conversion layer cannot provide long-term protection yet, and the biosafety of fluorine in vivo needs further confirmation. Although MAO is one of the most widely commercialized surface treatment technologies for magnesium, coatings are usually brittle with holes. Some materials such as poly dopamine [24] or 3-amino-propyltriethoxysilane (APTES, reported by our previous work) [25] are considered intermediate layers to generate bonds between outer coatings and magnesium substrates. However, their biodegradable behaviors are not controlled, and the biocompatibility of APTES is not clear. Generally, all the surface pretreatment technologies above provide one or more intermediate layers between coatings and substrates to improve adhesion at the bonding interfaces. [26][27][28][29] Some problems, including chemical residue, surface contamination, interface cracking probability, uncontrollable degradation, and biocompatibility are potential dangers when making use of intermediate layers, which form two or more bonding interfaces. [30][31][32][33] Biodegradable magnesium alloys show superior potential as bone repair implants, which are coated by natural polymers such as biological proteins to reinforce anticorrosion and biocompatibility. Surface pretreatment can facilitate the adhesion force of the organic coating/inorganic metal interface, but potentially causes one or more unfavorable intermediate layers. Herein, hybrid plasma activation is introduced to modify magnesium alloy (MgZnCa), which is directly coated by a natural protein, silk fibroin (i.e., SF), thus achieving a protein/magnesium direct bonding interface. Different plasmas exhibit distinctive physical and chemical performances o...